Ebook Transplant infections (3rd edition): Part 1

(BQ) Part 1 book Transplant infections presents the following contents: Introduction to transplant infections, risks and epidemiology of infections after transplantation, specific sites of infection, bacterial infections.

Transplant Infections

Transplant Infections

E D I T O R S RALEIGH A BOWDEN, MD

Clinical Associate Professor of PediatricsUniversity of Washington School of MedicineSeattle, Washington

PER LJUNGMAN, MD, PhD

Professor of HematologyKarolinska University Hospital andKarolinska Institutet

Stockholm, Sweden

DAVID R SNYDMAN, MD, FACP

Professor of Medicine Tufts University School of MedicineChief, Division of Geographic Medicine and Infectious Diseases

Tufts Medical Center Boston, Massachusetts

T H I R D E D I T I O N

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Third Edition

Copyright © 2010 by LIPPINCOTT WILLIAMS & WILKINS, a WOLTERS KLUWER business

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by the above-mentioned copyright.

9 8 7 6 5 4 3 2 1

Library of Congress Cataloging-in-Publication Data

Transplant infections / editors, Raleigh A Bowden, Per Ljungman, David R Snydman.—3rd ed.

p ; cm.

Includes bibliographical references and index.

ISBN 978-1-58255-820-2 (alk paper)

1 Communicable diseases 2 Transplantation of organs, tissues, etc.—Complications 3 Nosocomial infections.

I Bowden, Raleigh A II Ljungman, Per III Snydman, David R

[DNLM: 1 Transplants—adverse effects 2 Bacterial Infections—etiology 3 Mycoses—etiology 4 Virus Diseases— etiology WO 660 T691 2010]

RC112.T73 2010

617.9'5—dc22

2010001262 DISCLAIMER

Care has been taken to confirm the accuracy of the information presented and to describe generally cepted practices However, the authors, editors, and publisher are not responsible for errors or omissions or for any consequences from application of the information in this book and make no warranty, expressed or implied, with re- spect to the currency, completeness, or accuracy of the contents of the publication Application of the information in a particular situation remains the professional responsibility of the practitioner.

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10 9 8 7 6 5 4 3 2 1

Transplantation infectious disease has emerged as an important

clinical subspecialty in response to a growing need for clinical

ex-pertise in the management of patients with various forms of

im-mune compromise The field is evolving rapidly In the past,

with fairly standardized immunosuppressive regimens, clinical

expertise in the care of immunocompromised patients required

an understanding of the common pathogens causing infection at

various times after transplantation and an understanding of the

common toxicities and interactions of immunosuppressive

med-ications and antimicrobial agents Some of these concepts have

now reached the level of “transplant gospel.” Thus, the equation

of infectious risk after transplantation is determined by the

rela-tionship between two factors: the individual’s epidemiologic

ex-posures and a conceptual measure of all those factors

contribut-ing to an individual’s infectious risk—“the net state of

immunosuppression.” In the absence of assays that measure an

individual’s absolute risk for infection, allograft rejection, or

graft-vs.-host disease, any determination of the net state of

im-munosuppression is imprecise and is largely based on the

clini-cian’s bedside skills and experience In practice, the lack of such

assays predicts that most patients will suffer excessive or

inade-quate immunosuppression at some points during their

posttrans-plant course provoking infection and/or rejection or GvHD

As with most good “rules” in medicine, exceptions to therules have become common Presentations of infection have

been altered as transplantation has been applied to a broader

range of clinical conditions, immunosuppressive regimens

have become more diverse, and prophylactic antimicrobial

regimens have been deployed How do we proceed? Some

components of the “risk equation” have changed little While

different factors control the risk for infection in the earliest

(weeks) periods following either transplant surgery (technical

issues) or hematopoietic transplantation (neutropenia), the full

impact of immunosuppression on adaptive immunity has not

yet been achieved Thus, in both groups, colonization by

noso-comial flora and mechanical or technical challenges dominate

risk including postoperative fluid collections, vascular

catheters and surgical drains, tissue ischemia, drug side effects,

underlying immune deficits (e.g., diabetes), organ

dysfunc-tion, metabolic derangements, and antimicrobial exposures

Following the earliest posttransplant time period, tions into the pathogenesis of infection are beginning to unravel

investiga-some of the underpinnings of host susceptibility via advances in

microbiology, molecular biology, and immunology While the

equation of risk for infection balancing epidemiology and the

“net state of immune suppression” remain valuable, at the basic

science level, “susceptibility” to infection is now recognized to be

a function of both the “virulence” of the organism and of host

de-fenses, including both innate and adaptive immunity The

deter-minants of virulence of a particular organism are the genetic,

biochemical, and structural characteristics that contribute to the

production of disease Susceptibility can be explained with ence to the presence or absence of specific receptors forpathogens, the cells and proteins determining protective immu-nity, and the coordination of the host’s response to infection Therelationship between the host and the pathogen is dynamic.Thus, some of the alterations in susceptibility previously ascribed

refer-to “indirect effects” of the pathogen (e.g., for cyrefer-tomegalovirus)can now be explained as virally mediated effects on processes in-cluding antigen presentation, cellular maturation and mobiliza-tion, and cytokine profiles Much of the impact of these infec-tions appears to be at the interface of the innate immune system(monocytes, macrophages, dendritic cells, and NK cells) and theadaptive immune system (lymphocytes and antibodies) Othereffects are the result of alterations in cell-surface (e.g., toll-like)receptors and on the milieu of other inflammatory mediators—both locally and systemically In an admittedly anthropomorphicdescription of these effects, the virus (and other pathogens) hasaltered the host to avoid detection and destruction and to pro-mote successful parasitism and persistence As host and pathogen

“respond” during the course of infection (and are modified byantimicrobial therapy or immunosuppression), each modifies theactivities and functions of the other and a dynamic relationshipdevelops The outcome of such a relationship depends on the vir-ulence of the pathogen and the relative degree of resistance orsusceptibility of the host, due largely to host defense mechanismsand to a more trivial degree, by antimicrobial therapies.Investigations into immune mechanisms are beginning toprovide assays that measure an individual’s pathogen-specificimmune function (T-cell subsets, HLA-restricted lymphocytesorting using tetramers, antigen-specific interferon-γ release as-says) as a suggestion of pathogen-specific infectious risk Thisapproach may be of particular relevance in the future in regard

to development of vaccines for use in immunocompromisedhosts and in the assessment of immune reconstitution followingchemotherapy and hematopoietic stem cell transplantation.The “equation of risk” has been further altered by a num-ber of additional factors Outbreaks of epidemic infections (WestNile virus, H1N1 “swine” influenza, SARS) have disproportion-ately affected transplant recipients The epidemiology of infec-tion has also been changed by the expanded population of pa-tients undergoing immunosuppression for transplantation,notably in terms of parasitic, mycobacterial, and other endemicinfections Thus, Chagas disease and leishmaniasis are routinelyconsidered in the differential diagnosis of infection in the appro-priate setting Donor-derived infections have been recognized inboth hematopoietic and solid organ transplant recipients Untilrecently, careful medical histories coupled with serologic andculture-based screening of organ donors and recipients, and rou-tine antimicrobial prophylaxis for surgery have successfully pre-vented the transmission of most infections with grafts With theemergence of antimicrobial-resistant organisms in hospitals and

Foreword

in the community, routine surgical prophylaxis for

transplanta-tion surgery may fail to prevent transmission of common

organ-isms including methicillin-resistant Staphylococcus aureus,

van-comycin-resistant Enterococcus species, and azole-resistant yeasts.

Highly sensitive molecular diagnostic assays have also allowed

the identification of a series of uncommon viral infections

(lym-phocytic choriomeningitis virus [LCMV], West Nile virus, rabies

virus, HIV) with allografts These infections appear to be

ampli-fied in the setting of immunosuppression Despite technological

advances, deficiencies in the available screening assays are notable

in that both false-positive assays (causing discarding of potentially

usable organs) and false-negative assays (the inability to identify

LCMV in a deceased donors transmitting LCMV to multiple

re-cipients) have been recognized Sensitive and specific diagnostic

assays remain unavailable for some pathogens of interest and

those that are available require careful validation and

standardi-zation Improved molecular assays and antigen detection-based

diagnostics may help to prevent graft-derived transmissions in

the future

Routine use of antimicrobial prophylaxis has also altered

the presentation of infection following transplantation In

part, this manifests as a “shift-to-the-right” (late infections)

due to common pathogens such as cytomegalovirus (CMV) in

solid organ recipients Increasingly, this is reflected in the

emergence of antimicrobial-resistant pathogens The impact

of routine prophylaxis is difficult to measure—it is uncertain

that there is a clear mortality benefit of these strategies Sicker

patients arrive at transplantation having survived multiple

in-fections, organ failure, or malignancies that would have been

fatal in the past These individuals may become “Petri dishes”

for organisms for which effective therapies are lacking The

need for new antimicrobial agents is increasing at a time when

the pipeline for new agents appears to be contracting

The net state of immunosuppression has also shifted The

duration of neutropenia following HSCT and with

nonmye-loablative transplantation is shorter than that after traditional

bone marrow transplantation The duration of neutropenia

has also been reduced with the introduction of

chemothera-peutic agents targeting specific cellular sites (enzymes,

protea-somes) rather than acting on rapidly dividing cancer cells

Among solid organ transplants, the recent introduction of

ex-perimental protocols that use combinations of HSCT with

renal transplantation to induce immunologic tolerance carries

the promise of immunosuppression-free lifetimes for patients

A series of innovations will impact future clinical practice

The adoption of quantitative molecular and protein-based

mi-crobiologic assays in routine clinical practice has enhanced

diag-nosis and serves as a basis for the deployment of antiviral agents

and modulation of exogenous immune suppression In many

ways, given currently available science, these assays may be the

best measure of an individual’s immune function relative to their

own pathogens Potent “biologic agents” in transplantation

in-cluding antibody-based therapies to deplete lymphocytes (and

other cells) have the capacity to reduce both graft rejection and

graft-vs.-host disease in place of commonly used agents

includ-ing corticosteroids and the calcineurin inhibitors The

short-term gain in short-terms of infectious risk and renal dysfunction from

currently available agents must be balanced against longer termsusceptibly to infections with organisms including mycobacteria,fungi, and viruses Among the side effects of these therapies may

be an increased risk for virally mediated malignancies (includingPTLD) and BK (nephropathy) and JC polyomavirus-associatedinfections (i.e., progressive multifocal leukoencephalopathy,PML) The full impact of the biologic agents remains to be de-termined High throughput sequencing and genome-wide asso-ciation studies are beginning to determine the basis of both ge-netic susceptibility to infection and responses to antimicrobialtherapies (e.g., hepatitis C virus and interferon) These observa-tions will allow the application of specific drugs to the popula-tions in which they are most useful and least toxic (pharmacoge-nomics) The introduction of clinical xenotransplantation (i.e.,pig-to-human transplantation) may introduce a series of novelpathogens into the epidemiologic equation in the near future.The evolution of the immunosuppression used in organand hematopoietic stem cell transplantation has reduced the in-cidence of acute graft rejection and graft-vs.-host disease whileincreasing the longer term risks for infection and virally medi-ated malignancies With introduction of each new immunosup-pressive agent, a new series of effects on the presentation andepidemiology of infection have been recognized in the trans-plant recipient In the absence of assays that measure “infectiousrisk,” transplant infectious disease remains as much a clinical artform as a science In the future, improved assays for microbio-logic and immunologic monitoring will allow individualization

of prophylactic strategies for transplant recipients and reducethe risk of infection in this highly susceptible population

As a reflection of the challenges posed by a rapidly changingfield, the editors and contributors of this text have identified boththe advances and the gaps in our knowledge in transplant infec-tious diseases The unique risk factors and epidemiology for in-fection have been characterized for each of the major transplantpopulations Important shifts in the epidemiology that have beenidentified include those due to donor-derived pathogens and theintroduction of transplantation into geographically diverse pop-ulations The clinical utility of the text is enhanced by discussions

of common and important presentations of infection includinginfections of the lungs, skin, central nervous system, and gas-trointestinal tract Individual pathogens and therapies are ad-dressed in detail Vaccination for the immunocompromised hostand innovative therapies entering clinical practice are clearlypresented and assessed, including adoptive immunotherapy Ineach case, clinically important management issues are identifiedincluding infection control, immunosuppressive adjustments,and prophylactic and therapeutic antimicrobials The authorshave, in addition, identified important controversies and trendsfor each topic so as to clue the reader into areas in which change

is ongoing In sum, this volume is an important addition to thecurrently available literature in transplantation for infectious dis-ease and transplantation specialists, for both expert and novicealike The availability of this information in a single volume willserve one group particularly well—our patients

Jay A Fishman, MD Boston, Massachusetts, USA

The success of both the first edition of Transplant Infections,

published in 1998, and the second edition, published in 2003,

as a reference work to bring together information directed at

the management of the infectious complications occurring

specifically in immunocompromised individuals undergoing

transplantation has led to the creation of this third edition No

other text focuses solely on exogenously immunosuppressed

transplant patients, and no text combines solid organ and

hematopoietic stem cell transplantation (historically referred

to as bone marrow transplantation) Many texts focus on

im-munocompromised patients, but the field of transplant

infec-tious diseases has evolved over the past 20 years as a field unto

itself, with conferences devoted solely to this specialty, and

guidelines, both national and international, being developed

for the management of such patients In addition, peer

re-viewed journals now exist which publish information on this

specialized area, and training programs devoted to the

subspe-cialty of transplant infectious diseases within the field of

infec-tious disease are being developed

The field of transplant infectious diseases has continued togrow and expand since the second edition was published in

2003 We have expanded the third edition to include a greater

emphasis on surgical complications for each type of organ

trans-planted In addition, there are new chapters on organ donor

screening, drug interactions after transplantation, and new

im-munosuppressive agents Chapters differentiating differences

between solid organ and hematopoietic stem cell

transplanta-tion have been expanded, as have chapters discussing fungal

in-fections, as more data accumulate for improved diagnosis and

treatment and many new antifungal agents are developed

There is a new section in the cardiac transplant chapter on

ventricular assist device infections, a problem the transplant

in-fectious disease specialist must wrestle with often in patients

awaiting cardiac transplantation We have also expanded somechapters on viral infections, such as the polyomaviruses andadenovirus since recognition of the importance of thesepathogens has grown A chapter on rare viral infections hasbeen updated as well Transplant tourism as a topic has alsobeen added to a section on transplant travel medicine and vac-cines A number of new authors have been added and chaptershave been substantially revised or completely rewritten.This edition remains a globally inclusive product of lead-ing authors and investigators from around the world.Perspectives from Argentina, Brazil, Chile, New Zealand,Western Europe (Italy, Spain, Sweden, Germany, France, andSwitzerland), Austria, the United States, Canada, and Israelhave been synthesized in this edition

We continue to believe that much can be learned ing an appreciation of both the similarities and the differences

regard-in the pattern of regard-infections and the resultregard-ing morbidity andmortality in various transplant settings Our goal with thistextbook is to provide background and knowledge for allpractitioners who work with transplant patients, in order toimprove both the care and outcomes of transplant recipientsand to provide a framework for education of physicians, andtransplant coordinators, and trainees in the field As success inthe field continues to grow we hope that this text would pro-vide some small incremental knowledge base that would ad-vance the field and make transplantation safer for all whoneed this lifesaving intervention We thank all the contribu-tors for their effort, and trust the reader will find this a valu-able reference text as they care for transplant recipients

Raleigh A Bowden Per Ljungman David R Snydman

v

Preface

Contributors

Tamara Aghamolla

Immunocompromised Host Section

Pediatric Oncology Branch

Clinical Research Center

National Cancer Institute

National Institutes of Health

Cleveland Clinic Lerner College of Medicine

of Case Western Reserve University

Section Head

Transplant Infectious Disease

The Cleveland Clinic

Vaccine and Infectious Disease Institute

Fred Hutchinson Cancer Research Center

Seattle, Washington

Helen W Boucher, M D , F A C P

Assistant Professor of Medicine Tufts University School of Medicine Director

Fellowship Program Division of Geographic Medicine and Infectious Diseases

Tufts Medical Center Boston, Massachusetts

Emilio Bouza, M D , Ph D

Professor Clinical Microbiology University Complutense of Madrid Chief

Clinical Microbiology and Infectious Diseases Hospital General Universitario Gregorio Marañon (HGUGM)

Madrid, Spain

Almudena Burillo, M D , Ph D

Physician Clinical Microbiology and Infectious Diseases Hospital de Mostoles

Madrid, Spain

Professor Department of Medicine University of Alberta Medical Director Renal Transplant Program Walter C Mackenzie Health Science Center Edmonton, Alberta, Canada

Jeffrey T Cooper, M D

Assistant Professor of Surgery Tufts University School of Medicine Attending Surgeon

Tufts Medical Center Boston, Massachusetts

Professor of Hematology Hematology Oncology Université Paris 12 Head

Clinical Hematology Department Henri Mondor University Hospital Créteil, France

Professor of Medicine Medical Oncology University of Washington Medical Center

Member Transplantation Biology Fred Hutchinson Cancer Research Center

Professor Departments of Medicine and Surgery Vanderbilt University School of Medicine

Chief Transplant Infectious Diseases Vanderbilt University Hospital Nashville, Tennessee

Hermann Einsele

Professor Department of Medicine University Würzburg Director

Department of Internal Medicine II University Hospital Würzburg Würzburg, Germany

Pediatric Infectious Diseases

Seattle Children’s Hospital

Transplant Infectious Diseases

Rhode Island Hospital

Providence, Rhode Island

Professor and Chair

Department of Surgery

Dartmouth Medical School

Hanover, New Hampshire

Chair

Department of Surgery

Dartmouth-Hitchcock Medical Center

Lebanon, New Hampshire

Auckland City Hospital

Auckland, New Zealand

National Cancer Institute, National Institutes of Health

Chief Infectious Diseases Consultation Service National Institutes of Health Clinical Research Center

Bethesda, Maryland

PhD Course Clinical Microbiology University Complutense of Madrid Research Fellow

Clinical Microbiology and Infectious Diseases

Hospital General Universitario Gregorio Marañon (HGUGM)

Madrid, Spain

Professor of Dermatology Director of Dermatopathology Mayo Clinic

Birmingham, Alabama

Michael Green, M D , M D H

Professor Pediatrics and Surgery University of Pittsburgh School of Medicine Attending Physician

Division of Infectious Diseases Children’s Hospital of Pittsburgh Pittsburgh, Pennsylvania

Andreas H Groll, M D

Associate Professor Department of Pediatrics Wilhelms University Head

Infectious Disease Research Program Center for Bone Marrow Transplantation and Department of Pediatric

Hematology/Oncology Children’s University Hospital Muenster, Germany

Assistant Professor Division of Infectious Diseases Oregon Health and Science University Portland, Oregon

Professor of Medicine Division of Hematology/Oncology University of Florida College of Medicine Attending Physician

Bone Marrow Transplant/Leukemia Program

Shands at the University of Florida Gainesville, Florida

Hans H Hirsch, M D , M S

Professor Institute for Medical Microbiology Department of Biomedicine University of Basel Senior Physician Infectious Diseases & Hospital Epidemiology

Department of Internal Medicine University Hospital Basel Petersplatz, Basel, Switzerland

Jack W Hsu, M D

Assistant Professor Department of Medicine University of Florida Clinical Assistant Professor Department of Medicine University of Florida Shands Cancer Center

Gainesville, Florida

Professor Department of Surgery University of Pittsburgh Chief of Transplant Starzl Transplant Institute University of Pittsburgh Medical Center Pittsburgh, Pennsylvania

Atul Humar, M D , M SC , F R C P ( C )

Associate Professor of Medicine Transplant Infectious Diseases University of Alberta Director

Transplant Infectious Diseases University of Alberta Hospital Edmonton, Alberta, Canada

Transplant & Immunocompromised Host

Infectious Diseases Service

Northwestern Memorial Hospital

Department of Internal Medicine

University of Michigan Medical School

Chief

Infectious Diseases Section

Veterans Affairs Ann Arbor Healthcare

System

Ann Arbor, Michigan

Assistant Professor

Department of Medicine

Harvard Medical School

Clinical Director

Transplant Infectious Disease and

Compromised Host Program

Infectious Diseases Division

Massachusetts General Hospital

Assistant Professor of Medicine

Transplant Infectious Diseases

University of Alberta

Staff Physician

Transplant Infectious Diseases

University of Alberta Hospital

Edmonton, Alberta, Canada

Professor of Medicine Department of Medicine Mayo Medical School Chair

Division of Infectious Diseases Department of Medicine Mayo Clinic Arizona Phoenix, Arizona

PHARM D

Assistant Professor Department of Medicine Tufts University School of Medicine Senior Clinical Pharmacy Specialist Pharmacy

Tufts Medical Center Boston, Massachusetts

Ingi Lee, M D , M S C E

Instructor Department of Medicine University of Pennsylvania School of Medicine

Division of Infectious Diseases Department of Medicine Hospital of the University of Pennsylvania Philadelphia, Pennsylvania

Ajit P Limaye, M D

Associate Professor Department of Medicine University of Washington Director

Solid-Organ Transplant Infectious Disease University of Washington Medical Center Seattle, Washington

Per Ljungman, M D , Ph D

Professor of Hematology Karolinska Institutet Director

Department of Hematology Karolinska University Hospital Stockholm Stockholm, Sweden

Anna Locasciulli, M D

Associated Professor Pediatric Hematology University of Medicine Director

Pediatric Hematology San Camillo Hospital Rome, Italy

Professor of Medicine and Deputy Chairman

Department of Medicine Tufts University School of Medicine Chairman

Department of Medicine Baystate Medical Center Springfield, Massachusetts

Mitchell R Lunn, B S

Department of Medicine Stanford University School of Medicine Stanford, California

Virology Laboratory São Paulo Institute of Tropical Medicine University of São Paulo

São Paulo, Brazil

Kieren A Marr, M D

Professor of Medicine Department of Medicine Johns Hopkins University Director

Transplant and Oncology Infectious Disease

Department of Medicine Johns Hopkins University Baltimore, Maryland

St Anna Children’s Hospital Stem Cell Transplant Unit Children´s Cancer Research Institute Vienna, Austria

Lisa M McDevitt, PHARM D ,

B C P S

Assistant Professor

Department of Surgery

Tufts University School of Medicine

Senior Clinical Specialist

Head and Member

Gastroenterology, Hospital Section

Fred Hutchinson Cancer Research

Children’s Hospital of Pittsburgh of

University of Pittsburgh Medical

Associate Professor of Medicine

Division of Infectious Diseases and

Chief Clinical Microbiology and Infectious Diseases Hospital General Universitario Gregorio Marañón (HGUGM)

Madrid, Spain

Tue Ngo, M D , M D H

Infectious Diseases Fellow Division of Infectious Diseases Vanderbilt University School of Medicine Nashville, Tennessee

Albert Pahissa, M D , Ph D

Chair Professor Infectious Diseases Medicine Universitat Autònoma de Barcelona Chief

Servei Malalties Infeccioses Vall d’Hebron

Bellaterra, Barcelona, Spain

Peter G Pappas, M D , F A C P

Professor of Medicine Medicine and Infectious Diseases University of Alabama at Birmingham Birmingham, Alabama

Maria Beatrice Pinazzi, M D

Full-time Assistant Pediatric Hematology and Bone Marrow Transplant Unit

San Camillo Hospital Rome, Italy

Jutta K Preiksaitis, M D

Professor of Medicine Department of Medicine University of Alberta Edmonton, Alberta, Canada

Marcelo Radisic, M D

Attending Physician Transplant Infectious Diseases Instituto De Nefrología Buenos Aires, Argentina

Associate Professor of Medicine Department of Medicine Mayo Clinic College of Medicine Consultant Staff

Division of Infectious Diseases Mayo Clinic

Rochester, Minnesota

Jorge D Reyes, M D

Professor Department of Surgery University of Washington Chief

Division of Transplant Surgery University of Washington Medical Center

Seattle, Washington

Research Associate Transplantation Biology Program Fred Hutchinson Cancer Research Center Acting Instructor

Medical Oncology University of Washington Medical Center

Seattle, Washington

Jason Rhee, M D

Transplant Research Fellow Department of Surgery Tufts Medical Center Boston, Massachusetts

Stanely R Riddell, M D

Professor of Medicine Fred Hutchinson Cancer Research Center Seattle, Washington

Antonio Román, M D , Ph D

Senior Consultant Pneumology Department Vall d’Hebron

Barcelona, Spain

Assistant Professor of Medicine State University of New York at Buffalo Head of Infectious Disease

Roswell Park Cancer Institute Buffalo, New York

Maria Teresa Seville, M D

Instructor Division of Infectious Diseases Mayo Clinic

Chair Infection Prevention and Control Mayo Clinic Hospital

Phoenix, Arizona

Nina Singh, M D

Associate Professor of Medicine University of Pittsburgh Pittsburgh, Pennsylvania

David R Snydman, M D , F A C P

Professor of Medicine

Tufts University School of Medicine

Chief, Division of Geographic Medicine

and Infectious Diseases

Gastroenterology, Hospital Section

Fred Hutchinson Cancer Research Center

Seattle, Washington

William J Steinbach, M D

Associate Professor

Departments of Pediatrics and Molecular

Genetics & Microbiology

Adjunct Professor of Medicine University of Maryland School of Medicine Senior Investigator

Chief, Immunocompromised Host Section National Cancer Institute

Baltimore, Maryland

Daniel J Weisdorf, M D

Professor & Director Adult Blood and Marrow Transplant Program

Department of Medicine University of Minnesota Minneapolis, Minnesota

Associate Professor of Medicine University of Washington Associate Medical Director Employee Health Center University of Washington Medical Center Medical Director

Healthcare Epidemiology and Infection Control

University of Washington Medical Center/Seattle Cancer Care Alliance (inpatients)

Seattle, Washington

Professor Department of Medicine University of Florida Director of Bone Marrow Transplant Program

Department of Medicine University of Florida Shands Cancer Center

Gainesville, Florida

Associate Professor Department of Medicine University of Minnesota Director of the Program in Transplant Infectious Disease

Department of Medicine University of Minnesota Medical Center Minneapolis, Minnesota

Foreword iii

Preface v

Contributors vi

Section I

Introduction to Transplant Infections

1 Introduction to Hematopoietic Cell

Transplantation 1 Andrew R Rezvani and H Joachim Deeg

2 Introduction to Solid Organ

Transplantation 13 Barry D Kahan

3 Immunosuppressive Agents 26

Jason Rhee, Nora Al-Mana, Jeffery T Cooper and Richard Freeman

4 Common Drug Interactions Encountered in

Treating Transplant-Related Infections 41 Helen W Boucher, Kenneth R Lawrence

and Lisa M McDevitt

Section II

Risks and Epidemiology of Infections

after Transplantation

5 Risks and Epidemiology of Infections

after Allogeneic Hematopoietic Stem Cell Transplantation 53 Juan Gea-Banacloche

6 Risks and Epidemiology of Infections

after Solid Organ Transplantation 67 Ingi Lee and Emily A Blumberg

7 Donor-Derived Infections: Incidence,

Prevention and Management 77 Michael G Ison

8 Transplant Infections in Developing

Countries 90 Clarisse M Machado

9 Risks and Epidemiology of Infections

after Heart Transplantation 104 David DeNofrio and David R Snydman

10 Risks and Epidemiology of Infections

after Lung or Heart–Lung Transplantation 114 Joan Gavaldà, Antonio Román and Albert Pahissa

11 Infections in Kidney Transplant Recipients 138

Deepali Kumar and Atul Humar

12 Risks and Epidemiology of Infections

after Pancreas or Kidney–Pancreas Transplantation 150 Atul Humar and Abhinav Humar

13 Risks and Epidemiology of Infections after Liver Transplantation 162 Shimon Kusne and David C Mulligan

14 Risks and Epidemiology of Infections after Intestinal Transplantation 179 Jorge D Reyes and Michael Green

Section III

Specific Sites of Infection

15 Pneumonia after Hematopoietic Stem Cell or Solid Organ Transplantation 187 Catherine Cordonnier and Isabel Cunningham

16 Skin Infections after Hematopoietic Stem Cell or Solid Organ Transplantation 203 Mazen S Daoud, Lawrence E Gibson and W P Daniel Su

17 Central Nervous System Infections after Hematopoietic Stem Cell or Solid Organ Transplantation 214 Diana Averbuch and Dan Engelhard

18 Gastrointestinal Infections after Solid Organ

or Hematopoietic Cell Transplantation 236 George B McDonald and Gideon Steinbach

Section IV

Bacterial Infections

19 Gram-Positive and Gram-Negative Infections after Hematopoietic Stem Cell or Solid Organ Transplantation 257 Dan Engelhard

20 Typical and Atypical Mycobacterium

Infections after Hematopoietic Stem Cell or Solid Organ Transplantation 282 Jo-Anne H Young and Daniel J Weisdorf

21 Other Bacterial Infections after Hematopoietic Stem Cell or Solid Organ Transplantation 295

J Stephen Dummer and Tue Ngo

Section V

Viral Infections

22 Cytomegalovirus Infection after Stem Cell Transplantation 311 Morgan Hakki, Michael J Boeckh and Per Ljungman

23 Cytomegalovirus Infection after Solid Organ Transplantation 328 Raymund R Razonable and Ajit P Limaye

Contents

xi

24 Epstein–Barr Virus Infection and

Lymphoproliferative Disorders after Transplantation 362 Jutta K Preiksaitis and Sandra M Cockfield

25 Herpes Simplex and Varicella-Zoster

Virus Infection after Hematopoietic Stem Cell or Solid Organ Transplantation 391 John W Gnann, Jr

26 Infections with Human Herpesvirus–6, –7,

and –8 after Hematopoietic Stem Cell

or Solid Organ Transplantation 411 Nina Singh

27 Community-Acquired Respiratory

Viruses after Hematopoietic Stem Cell

or Solid Organ Transplantation 421 Janet A Englund and Estella Whimbey

28 Adenovirus Infection in Allogeneic

Stem Cell Transplantation 447 Susanne Matthes-Martin

29 Adenovirus Infection in Solid Organ

Transplantation 459 Michael Green, Michael G Ison and Marian G Michaels

30 Polyoma and Papilloma Virus Infections

after Hematopoietic Cell or Solid Organ Transplantation 465 Hans H Hirsch

31 Hepatic Infections after Solid Organ

Transplantation 483

Ed Gane

32 Hepatitis B and C in Hematopoietic

Stem Cell Transplant 498 Anna Locasciulli, Barbara Montante and Maria Beatrice Pinazzi

Section VI

Fungal Infections

33 Yeast Infections after Hematopoietic

Stem Cell Transplantation 507 Tamara Aghamolla, Brahm H Segal and Thomas J Walsh

34 Yeast Infections after Solid Organ

Transplantation 525 Peter G Pappas

35 Mold Infections after Hematopoietic

Stem Cell Transplantation 537 William J Steinbach and Kieren A Marr

36 Aspergillus and Other Mold Infections

after Solid Organ Transplant 554 Patricia Muñoz, Maddalena Giannella, Almudena Burillo

and Emilio Bouza

37 Infections Caused by Uncommon

Fungi in Patients Undergoing Hematopoietic Stem Cell or Solid Organ Transplantation 586 John W Hiemenz, Andreas H Groll and Thomas J Walsh

38 Endemic Mycoses after Hematopoietic Stem Cell or Solid Organ Transplantation 607 Carol A Kauffman

Section VII

Other Infections

39 Toxoplasmosis Following Hematopoietic Stem Cell Transplantation 617 Rodrigo Martino

40 Toxoplasmosis after Solid Organ Transplantation 624 Jose G Montoya and Mitchell R Lunn

41 Parasites after Hematopoietic Stem Cell or Solid Organ Transplantation 632 Roberta Lattes and Marcelo Radisic

Section VIII

Infection Control

42 Infection Control Issues after Hematopoietic Stem Cell Transplantation 653 Robin K Avery and David L Longworth

43 Infection Control Issues after Solid Organ Transplantation 667 Maria Teresa Seville, Sharon Krystofiak and Shimon Kusne

46 Adoptive Immunotherapy with Herpesvirus-specific T Cells after Transplantation 724 Hermann Einsele, Max S Topp, Stanley R Riddell

Section X

Hot Topics

47 Emerging and Rare Viral Infections

in Transplantation 745 Staci A Fischer

48 Travel Medicine, Vaccines and Transplant Tourism 756 Camille Nelson Kotton

Index 768

The lymphohematopoietic system is the only organ system in

mammals that has the capacity for complete self-renewal

Therefore, donation of lymphohematopoietic stem cells does not

result in a permanent loss for the donor Reports on the

therapeu-tic use of bone marrow to treat anemia associated with parasitherapeu-tic

infections date back a century (1,2), but not until the observations

on irradiation effects in Hiroshima and Nagasaki and the ensuing

systematic research into hematopoietic cell transplantation (HCT)

in animal models were the principles of HCT established (1,3,4)

In 1957, the first clinical transplant attempts of the modernera were undertaken (1,5,6) As predicted from animal studies,

patients who underwent transplantation from allogeneic donors

(i.e., individuals who were not genetically identical) developed

graft-versus-host disease (GVHD) (4) Patients transplanted

from syngeneic (monozygotic twin) donors generally did not

develop GVHD, but many of them died from progressive

leukemia, apparently because of a lack of the allogeneic

graft-versus-leukemia (GVL) effect which had been described by Barnes

and Loutit (7) in murine models These studies immediately

estab-lished that allogeneic HCT functioned as immunotherapy

Beginning in the late 1950s and early 1960s, Dausset et al

characterized the first histocompatibility antigens in humans

(8) Epstein et al were the first to show the relevance of those

histocompatibility antigens for the development of GVHD in

an outbred species (9) Initially, the only source of hematopoietic

stem cells (HSC) in clinical use was bone marrow However,

cells harvested from peripheral blood, either after recovery

from chemotherapy or after the administration of

hematopoi-etic growth factors such as granulocyte-colony stimulating

fac-tor (G-CSF), were shown to result in accelerated hematopoietic

recovery after autologous transplantation These cells, as well as

cord blood cells, are now being used with increasing frequency

in allogeneic transplantation (10,11)

RATIONALE AND INDICATIONS FOR HEMATOPOIETIC CELL TRANSPLANTATION

Current indications for HCT are summarized in Table 1.1 The

majority of HCT is performed to treat malignant diseases

Myelosuppression is the most frequent dose-limiting toxicity of

the chemoradiotherapy used to treat malignancies Infusion ofHSC—autologous or allogeneic—as a “rescue” procedure al-lows the dose escalation of cytotoxic therapy, such that toxicity

in the next most sensitive organs (intestinal tract, liver, or lungs)becomes dose-limiting This strategy, often referred to as high-dose therapy with stem cell rescue, has been used extensively inthe past However, progressive dose intensification, althoughpossibly effective in disease eradication, has resulted in minimal,

if any, improvement in survival because of an increase intherapy-related toxicity and mortality These observations, com-bined with an increasing appreciation of the central role of im-munologic graft-versus-tumor (GVT) reactions in the success of

SECTION I■Introduction to Transplant Infections

TABLE 1.1 Categories of Disease Treated with

Hematopoietic Cell Transplantation

Malignant

Hematologic malignancies

Acute leukemias Chronic leukemias Myelodysplastic syndromes Myeloproliferative syndromes Non-Hodgkin lymphoma Hodgkin lymphoma Plasma cell dyscrasia (e.g., multiple myeloma)

Selected solid tumors

Renal cell carcinoma Ewing sarcoma Neuroblastoma Breast, colon, ovarian, and pancreatic cancer (investigational)

Nonmalignant

Acquired

Aplastic anemia and red cell aplasias Paroxysmal nocturnal hemoglobinuria Autoimmune disorders (e.g., multiple sclerosis, lupus erythematosus, systemic sclerosis, rheumatoid arthritis)

Osteopetrosis

allogeneic HCT, have led to new concepts of transplant

condi-tioning (see “Modalities for Transplant Condicondi-tioning”) (12)

“Replacement” therapy in patients with congenital or

ac-quired disorders of marrow function, immunodeficiencies, or

storage diseases represents a second indication for HCT

Patients with autoimmune diseases (e.g., rheumatoid arthritis

or systemic sclerosis) can also be considered part of this

cate-gory (13) In contrast to the benefit from GVT alloreactivity in

the malignant setting, patients with these nonmalignant

disor-ders are not thought to derive any benefit from alloreactivity

beyond its “graft-facilitating” effect

Finally, HSC (or their more mature progeny) may be

effec-tive vehicles for gene therapy (14) and for immunotherapy

Objectives of gene therapy include the replacement of defective

or missing enzymes (e.g., adenosine deaminase,

glucocerebrosi-dase) or of the defective gene (15,16) Experience with the use of

allogeneic cells, often T lymphocytes, as immunologic bullets is

more extensive Donor lymphocyte infusion (DLI) for

reinduc-tion of remission in patients with chronic myelogenous leukemia

(CML) who have relapsed after HCT has been remarkably

suc-cessful, leading to broader application of this approach A

modi-fication of this strategy is the use of genetically modified donor

lymphocytes expressing a “suicide gene,” which may be activated

to abrogate the adverse effects of DLI, particularly GVHD (17)

The principle of immunotherapy is also exploited in

reduced-intensity conditioning (RIC), also referred to as

non-myeloablative or “mini” transplants (both terms, however, are

misleading, as the end result is intended to be “ablation” of the

disease, and a mini-transplant is still a full transplant, albeit with

a lower-intensity conditioning regimen) In this approach, the

intensity of the conditioning regimen has been reduced with the

objective of preventing early mortality, and donor antihost

reac-tivity has been enhanced to eliminate host cells (Fig 1.1) (18)

SOURCES OF HEMATOPOIETIC STEM CELLS AND DONOR SELECTION

HSC can be obtained from a variety of donors and cellularcompartments, including the bone marrow, peripheral blood,cord blood, and the fetal liver The choice of stem cell source isdependent upon several factors Although autologous marrow

or peripheral blood stem cells (PBSC) are theoretically able for every patient (feasibility has been reported even forpatients with severe aplastic anemia), these would not be use-ful without genetic manipulation for genetically determineddisorders, and would be suboptimal for malignant disorders,because of the concern of contamination with malignant cellsand the lack of an allogeneic antitumor effect An HLA-haploidentical donor (e.g., parent, sibling, child) is availablefor most patients, and, while clearly investigational at thistime, early results show surprisingly low rates of GVHD andgraft rejection (19)

avail-Generally, each sibling has a 25% chance of sharing theHLA genotype of a patient Phenotypically matched donorscan be identified among family members in about 1% of pa-tients, and somewhat less than 1% of patients will have a syn-geneic (identical twin) donor The lack of an HLA-identicalrelated donor in more than 70% of patients has led to the de-velopment of (a) large data banks of volunteer unrelateddonors; (b) research into alternative allograft sources such asHLA-haploidentical family members and umbilical cordblood, as indicated earlier; and (c) techniques to “purge” autol-ogous cells of tumor contamination

Supported by the efforts of the National Marrow DonorProgram in the United States, the Anthony Nolan Appeal inthe United Kingdom, and other groups internationally, morethan 10 million volunteer donors have been typed for HLA-Aand HLA-B, and a rapidly increasing number also for HLA-C,HLA-DR (DRB1), and HLA-DQ antigens (20) The proba-bility of finding a suitably HLA-matched donor for a whitepatient in North America is about 70% to 80% This probabil-ity is lower for other ethnic groups, in part because of lowerrepresentation in the data bank and in part because of greaterpolymorphism of the HLA genes (21)

Cord blood cells, generally not matched for all HLA gens of the patient, are being used with increasing frequency(22), while fetal liver cells have been used only very rarely inrecent years

anti-Autologous marrow or PBSC can be purged of nating malignant cells by chemical means or by antibodiesthat recognize tumor cells However, slow engraftment andresidual tumor cells that resist the purging regimen limit the usefulness of this approach A complementary approach isaimed at purifying stem cells using specific antibodies

contami-to positively select cells bearing CD34, which is the closestthat the research community has come to characterizinghuman HSC

FIGURE 1.1 Commonly used conditioning regimens for

hematopoietic cell transplantation, stratified by intensity, toxicity,

and relative reliance on immunological graft-versus-tumor

effects Abbreviations: GVT, graft-versus-tumor; CY,

cyclophos-phamide; TBI, total body irradiation; Gy, gray; FLU, fludarabine;

BU, busulfan; ATG, antithymocyte globulin; araC, cytarabine.

TRANSPLANT PROCEDURE

Transplant Conditioning

Rationale for Conditioning

1 To eradicate (ablate) the patient’s disease, or at least to

re-duce the number of malignant or abnormal cells to below

detectable levels (this applies to allogeneic, syngeneic, and

autologous donors)

2 To suppress the patient’s immunity and to prevent rejection

of donor cells (this applies to allogeneic, but not to

auto-logous, HCT) Immunosuppression is also needed in

pre-paration for some syngeneic transplants, apparently to

eliminate autoimmune reactivity which may interfere with

sustained hematopoietic reconstitution

The notion that conditioning is necessary to “generatespace” in the transplant recipient has essentially been aban-

doned Recent data show that donor cells, given in sufficient

numbers, create their own space and proceed to repopulate the

recipient’s marrow (23)

Exceptions to the conditioning requirement exist in dren with severe combined immunodeficiency (SCID), be-

chil-cause of the nature of the underlying disease, which does not

allow them to reject transplanted donor cells, and in patients

in whom even partial donor engraftment can completely

cor-rect the genetic defect (24)

Modalities for Transplant Conditioning

Modalities used to prepare patients for HCT have been

re-viewed extensively elsewhere (25,26); commonly used

regi-mens are listed in Figure 1.1 In principle, conditioning for

HCT may include the following approaches:

1 Irradiation is in the form of total body irradiation (TBI),

total lymphoid irradiation (27), or modifications thereof

Many conventional TBI regimens deliver 1200 to 1400 cGy

over 3 to 6 days In addition, bone-seeking isotopes (e.g.,

holmium) and isotopes (e.g., 131I, 92Y) conjugated to

mono-clonal antibodies (MAbs) directed at lymphoid or myeloid

antigens (e.g., anti-CD20, CD45) are in use (28) TBI may

also be a component of RIC regimens, usually at lower

doses of 2 Gy (29)

2 Chemotherapy (e.g., cyclophosphamide, 120 to 200 mg/kg

over 2 to 4 days) is included in many conventional regimens

Busulfan (available in oral and intravenous formulations) at

16 mg/kg (or lower doses), targeted to predetermined plasma

levels, is often used in combination with cyclophosphamide

Other agents, including etoposide, melphalan, thiotepa,

cy-tarabine, and more recently treosulfan (30), may be used

ei-ther alone or in combination (with or without irradiation)

3 Biologic reagents (e.g., antithymocyte globulin (ATG)) or

MAbs directed at T-cell antigens or adhesion molecules

sup-press recipient immunity Others are directed at antigens

expressed on the recipient’s malignant cells; in addition, tokines or cytokine antagonists are being investigated Anti-T-cell therapy predisposes the individual to viral infections,

cy-in particular cytomegalovirus (CMV) and the development

of Epstein–Barr virus (EBV)-related lymphoproliferativedisorders (PTLD) after transplantation (31)

4 T-cell therapy is based on the observation that broad T phocyte depletion of donor marrow resulted in graft fail-ure This has led to protocols of selective T-cell add-back toensure engraftment The observation that DLI was effec-tive in inducing remission in a proportion of patients whohad experienced relapse after HCT renewed the interest inexploiting T-cell therapy for the treatment of leukemia.Other indications for T-cell therapy are viral infectionssuch as CMV (32) or EBV, especially with the development

lym-of PTLD in the latter (33)

Other procedures involve plasmapheresis of the ent’s blood to remove isoagglutinins directed against thedonor’s ABO blood group or the removal of plasma from thedonor marrow to remove the isoagglutinins directed at recipi-ent cells Alternatively, the donor red blood cells with whichrecipient antibodies may react can be removed, thus minimiz-ing transfusion reactions Due to the procedure by which theyare obtained, these additional manipulations are generally notrequired with PBSC

recipi-Marrow Harvest

The marrow donor receives general or regional (e.g., epidural,spinal) anesthesia, and, under sterile conditions, multiple aspi-rates of marrow are obtained from both posterior iliac crests(34) Additional potential aspiration sites are the anterior iliaccrests and the sternum Approximately 10 to 15 mL/kg ofdonor weight is collected If no ABO incompatibility existsand if the marrow is not to be subjected to any in vitro purgingprocedure, the resulting cell suspension is infused intra-venously without manipulation

Alternative Stem Cell Sources

HSC circulate at low concentrations in blood (35) Their quency increases dramatically during the recovery phase fol-lowing cytotoxic therapy, and after the administration ofrecombinant hematopoietic growth factors such as G-CSFwhich dislodge cells from the marrow Peak blood concentra-tions of CD34cells are typically reached on day 4 to 5 afterinitiating G-CSF A single leukapheresis may be sufficient toharvest the number of HSC required for a transplant For au-tologous procedures, the goal is to collect at least 2 to 5 

fre-106 CD34 cells/kg recipient weight; for allogeneic plants, the goal is 5 to 8  106CD34cells/kg, although theoptimum dose has not been determined (36)

trans-Umbilical cord blood represents a segment of the eral circulation of the fetus and is easily accessible (37) Also,

periph-cord blood cells are less immunocompetent than adult cells,

and might therefore carry a lower risk of inducing GVHD

than adult cells The concentration of HSC in umbilical cord

blood is high, but the small volume that is usually available

(80–150 mL) initially limited the use of these cells to children

and smaller adults In larger adults, approaches have included

the use of two cord blood units to ensure adequate cell dose

and engraftment (11), as well as ex vivo expansion of

hematopoietic precursors in umbilical cord blood units for

in-fusion together with an unmanipulated cord blood unit (38)

Purging

Several rationales exist for purging collected donor cells or

fractionating them into subpopulations In the autologous

set-ting, the goal is to eliminate contaminating tumor cells, either

by negative selection (removal of tumor cells with antibodies

or physicochemical means) or by positive selection

(purifica-tion of CD34cells from the graft) Conversely, one may want

to retain certain populations (e.g., CD4cells) with potential

for later uses such as posttransplant DLI

Hematopoietic Stem Cell Infusion:

The Actual Transplant

Donor cells are infused intravenously via an indwelling

cen-tral line, often a Hickman catheter Directed by surface

mole-cules which interact with receptors on endothelial cells, HSC

home to the marrow cavity The actual infusion of stem cells is

generally uneventful, though it can occasionally cause

tran-sient mild hypotension or hypersensitivity reactions

CARE AFTER TRANSPLANTATION

Complications of HCT, including infections, are related to

sev-eral factors: the underlying disease, the preparative regimen,

and the interactions of donor cells with recipient tissue (GVHD

with immunosuppression and end-organ damage) All patients

experience at least transient pancytopenia, although this may be

mild with RIC regimens Patients undergoing high-dose

condi-tioning generally develop severe pancytopenia, including

neu-tropenia, within days after completion of conditioning This

period may last 2 to 4 weeks with marrow allografts, 10 to

12 days with mobilized PBSC grafts, or 4 to 6 weeks with

umbilical cord blood grafts The period of neutropenia ends

with engraftment of the donor cells, clinically defined by stable

increases in the white blood cell count Cytopenias are less

pronounced after RIC, and the pattern of engraftment may be

less apparent in the peripheral white blood cell count

Engraftment in these patients is generally documented by

demonstrating donor chimerism by cytogenetic or molecular

means in peripheral blood leukocytes and bone marrow

Most patients prepared with high-dose regimens require

transfusion support with platelets, red blood cells, or both

Transfusion requirements are substantially reduced in patientsprepared with RIC regimens, because the nadir of cells often

is in a range in which no transfusions are required (39).Erythropoietin administration after HCT accelerates reticulo-cyte recovery and moderately reduces red blood cell transfu-sion requirements in patients undergoing allogeneic (thoughnot autologous) HCT (34)

Quantitative and functional deficiencies of granulocytesand T-lymphocytes for various periods after HCT are respon-sible for most of the infectious complications seen after HCT(Fig 1.2) Although all patients receive prophylactic antimi-crobials, granulocyte transfusions are not routinely given.Laminar air flow (LAF) rooms and gastrointestinal deconta-mination may reduce the frequency of infections and the du-ration of febrile episodes, but neither is used routinely because

of the high cost of LAF and the availability of effective spectrum antibiotics (40)

broad-The most widely used modality of GVHD prophylaxis isthe in vivo administration of immunosuppressive agents, such

as methotrexate, cyclosporine (CSP), glucocorticoids, tacrolimus(FK506), mycophenolate mofetil (MMF), sirolimus and others,either alone or in combination (41) At many institutions, thecurrent standard is a combination of a calcineurin inhibitorwith methotrexate or MMF, but several other combinations areused Due to the nonselectivity of these agents, recipients arebroadly immunosuppressed and thus susceptible to infections

In vitro T-lymphocyte depletion of donor marrow may obviatethe need for immunosuppressive treatment after HCT; how-ever, the elimination of mature T-cells is associated with a risk

of rejection, delayed immunologic reconstitution, an increasedrisk of PTLD, and, for some disorders, disease recurrence.Both immunodeficiency and therapeutic immunosuppressionpredispose the patient to infections Whether the selective re-moval of naive T-cells will lead to successful transplants with-out GVHD remains under investigation

Years posttransplant

20 40 60 80 100 120

FIGURE 1.2 Approximate trends in immune cell counts after

myeloablative hematopoietic cell transplantation With the use

of reduced-intensity conditioning, nadirs are higher and occur later These recovery rates may be influenced by clinical vari- ables such as graft-versus-host disease, stem cell source, and patient age (Adapted from Storek J Immunological reconsti- tution after hematopoietic cell transplantation—its relation to

the contents of the graft (Review) Expert Opin Biol Ther.

2008;8:583–597.)

HEMATOLOGIC RECOVERY

A high-risk period for infections in patients conditioned with

high-dose regimens exists early after transplantation, when

gran-ulocytopenia develops due to the decline in endogenous marrow

function while donor cells are not yet proliferating If the donor

marrow is T-cell depleted, the recovery may be even more

pro-tracted If the granulocyte count at day 21 after transplantation

is less than 200 cells/L, patients are generally given G-CSF or

granulocyte-macrophage colony-stimulating factor After PBSC

transplants, engraftment (defined by 500 granulocytes/L)

occurs as early as day 9 or 10, thus clearly shortening the

length of granulocytopenia Rather slower recovery (over several

weeks) may be seen with cord blood transplants (42)

One advantage of RIC regimens is the slow decline of tient cells, so that donor cells begin to recover before patient

pa-cells reach their nadir Consequently, several groups have

re-ported lower rates of early infection after RIC conditioning as

compared with high-dose conditioning (43,44)

IMMUNOLOGIC RECOVERY

All components of the innate and adaptive immune systems

are deficient after HCT Cell-mediated immunity,

chemo-taxis, and neutrophil function are severely impaired even after

autologous transplants The development of GVHD

substan-tially impairs immune reconstitution, through a combination

of direct graft-versus-host toxicity to the thymus resulting in

altered T-cell selection and use of immunosuppressive

thera-pies to treat GVHD Thus, optimal immune reconstitution

can only occur in the absence of GVHD (45)

Uncomplicated Recovery

Shortly after HCT, damaged epithelial barriers facilitate the

penetration of pathogenic bacterial or fungal organisms

Mucosal surfaces begin to heal within a week or two of

comple-tion of high-dose condicomple-tioning, helped by the recovery of

granu-locytes and their scavenging function, even though phagocytosis

and superoxide production may still be impaired After the

transplant, the volume and immunoglobulin content of saliva

also improve with time Even with uncomplicated recovery,

T- and B-cell-mediated immune responses against viral,

bac-terial, fungal, and other organisms are broadly suppressed;

nat-ural killer (NK) cells recover more quickly To some extent, the

pattern of immune recovery is dependent on the immunity of

the donor from whom the transplanted cells originated The

pattern of immunocompetence is also influenced by the

recipi-ent’s prior antigen exposure, whether to the pathogen itself or in

the form of a vaccine Much of the literature on immune

recon-stitution after allogeneic HCT describes patients who were

prepared with high-dose conditioning While the use of RIC

regimens has increased rapidly in recent years, there are fewerdata available on immune recovery in this setting, and the im-pact of RIC on immune reconstitution remains somewhat un-clear Preliminary studies suggest that the tempo of immunerecovery may be faster after RIC (46), but late immune functionmay be similar to that seen after high-dose conditioning (47)

B cells tend to persist (50) Nonetheless, some antibodies of hostorigin (e.g., isoagglutinins) that are derived from long-livedplasma cells may be detectable for months or even years afterHCT Persistently low B-cell counts after HCT may predict

a high risk of infection (51) In the era of targeted therapy,treatment with B-cell-directed monoclonal antibodies such

as rituximab prior to HCT may also impair B-cell tion, though relatively little is known about the long-termimplications (52)

reconstitu-During recovery, fewer B cells express CD25 and CD62L;more express CD9c, CD38, IgM, and IgD; and the antigendensity is increased (as in neonatal B cells) CD5cells may ormay not be increased Immunoglobulin gene usage appears to

be restricted shortly after HCT and to be skewed toward theV-segments that are frequently used in neonatal B cells (e.g.,VH6) Concordantly, the antibody repertoire is restricted (53).IgG and IgA production may be abnormal for 1 to 2 yearsafter HCT Serum isotype levels after grafting recover in thesame sequence as they evolve in neonates (i.e., IgM, IgG1, andIgG3 recover early, but IgG2, IgG4, and IgA may not followuntil much later) (54) Many of the early antibodies are autoan-tibodies, or else have irrelevant specificities (55) Antibodieswith relevant specificities recover only if the antigen is en-countered, and they recover more quickly if both patient anddonor are immune (56) At 3 months after HCT, total IgG lev-els in recipients of allogeneic PBSC tend to be lower than those

in marrow recipients Antibodies to polysaccharide antigenstend to recover later than those directed at proteins B-cellcounts and IgM levels may recover more quickly after RIC ascompared to high-dose conditioned patients, though IgArecovery is delayed in both groups (46) In addition to quanti-tative deficits in B-cell number and immunoglobulin levels,the B-cell pool early after HCT is marked by qualitativefunctional impairment Isotype switching is deficient in theabsence of effective T-cell help Additionally, B cells fromtransplant recipients have a decreased capacity for somatic

hypermutation independent of T-cell help, suggesting an

intrinsic or environmental defect (57) Thus, B-cell deficits

after HCT are comprised of at least three factors: low B-cell

numbers, decreased T-cell help, and intrinsic defects such as

impaired somatic hypermutation (54)

Antibody responses to vaccination are almost universally

lower than are those of normal controls, and repeated boosters

are required (58) Responses are better in younger individuals

and in those with T-cell-replete grafts; this may be related to

CD4 recovery, which is faster in younger individuals The

pol-icy has been to delay revaccination until 1 to 2 years after HCT

to minimize the risk of potential side effects and to increase

the probability of antibody responses

T Cells

CD4Cells

The number of CD4cells is low for 1 to 3 months after

high-dose conditioning, and rises slowly toward normal over several

years This rise is faster in children than in adults (58) The

kinetics are similar following both autologous and allogeneic

transplants Early in the process, most cells are memory T cells;

naive T cells follow quite gradually, particularly in older

patients This might be related to diminished thymic function,

although the thymus appears to play some role in T-cell

reconsti-tution even in older patients (59) After PBSC transplantations,

both naive and memory CD4T cells are more abundant than

after marrow transplantations Early after HCT, most CD4

T cells are derived from transplanted mature T cells and T-cell

precursors; later, they are stem-cell-derived, at least in pediatric

patients CD4 T-cell reconstitution may occur more rapidly

after RIC as compared to high-dose conditioning (46)

CD4T cells generally express CD11a, CD29, CD45RO,

and HLA-DR and less CD28, CD45RA, and CD62L,

consis-tent with the prominence of memory cells (58) Responses to

polyclonal stimuli are low Proliferative responses to

fre-quently encountered antigens (e.g., Candida species) tend to

normalize over 1 to 5 years, whereas responses to unlikely

antigens (e.g., tetanus) remain subnormal Responses to

neoantigens (e.g., dinitrochlorobenzene) and recall antigens

(e.g., mumps) are abnormally low for 2 to 3 years after HCT

CD8Cells

CD8 T cells are low for 2 to 3 months after HCT;

subse-quently, they rise quickly, resulting in an inversion of the

typi-cal CD4:CD8 ratio (58) These CD8cells are largely memory

cells expressing CD11a, CD11b, CD29, CD57, HLA-DR, and

CD45RO but little CD28, CD45RA, and CD62L The

pres-ence of a CD11bCD57CD28phenotype suggests anergic

or suppressive CD8 cells CD8 cells appear to be derived

from transplanted T cells and stem cells

CMV-specific or EBV-specific CD8cells can be

trans-ferred successfully to a recipient, and they may persist for at

least 18 months (60,61) Even established and refractory CMVinfections can be treated effectively by the infusion of ex-panded CMV-specific CD8 donor cells (62) The logisticaldifficulty of generating CMV-specific cells for clinical use hasbeen a barrier to the wide application of this approach.However, several groups have reported progress in developingsimpler and more scalable means of producing virus-specificdonor T cells for infusion (63,64)

The role of immunoregulatory CD4CD25 T cells(Treg) in clinical transplantation remains to be fully estab-lished (65)

to settle in tissue in the early posttransplantation period The reconstitution of dendritic cells (DC), their matura-tion, and the development of DC1 and DC2 have been incom-pletely characterized DC precursors in the blood recoverwithin 6 months, and DC reconstitution appears to be a clini-cally important event Low numbers of DC at 1 month afterreduced-intensity HCT have been associated with an in-creased risk of mortality and disease relapse; CD16 DCcounts at 3 months were also strongly prognostic (67) A sepa-rate investigation found that low numbers of plasmacytoid

DC at 3 months after HCT were associated with higher risks

of infection and death (68) Langerhans cell levels are low inthe early posttransplantation period, but return to normal by

6 months Follicular DC are reconstituted rather slowly,which may contribute to the delayed return to function of thegerminal centers and memory B cells (58)

Natural Killer Cells

NK cells recover rapidly after HCT With the recognition ofthe killer inhibitory receptor, renewed interest in these cellshas been seen because of their possible function in engraftmentand the prevention of relapse (69) Robust NK-cell reconstitu-tion after allogeneic HCT has been associated with reducedrelapse and improved survival (70)

GRAFT-VERSUS-HOST DISEASE AND GRAFT-VERSUS-LEUKEMIA EFFECT

Acute and chronic GVHD occur in 10% to 50% and 20% to50%, respectively, of patients after HLA-identical siblingHCT, and in 50% to 90% and 30% to 70%, respectively, ofpatients who undergo transplantation from alternative donors

(71,72) Without prophylaxis, virtually all recipients of

allo-geneic transplants develop GVHD (73) Acute GVHD is the

strongest risk factor for the development of chronic GVHD

(74,75) Acute GVHD may occur within days (e.g., among

nonidentical recipients) or by 3 to 5 weeks after

HLA-identical transplantation following high-dose conditioning

The main target organs are the immune system, skin, liver,

and intestinal tract Only the skin, liver, and intestinal tract are

generally considered in GVHD grading systems (76)

Importantly, after RIC, classic manifestations of acute GVHD

may develop several months after HCT and may overlap

con-siderably with those of chronic GVHD (77) Features of

chronic GVHD may be present as early as 50 to 60 days after

HCT Therefore, recently developed NIH consensus criteria

distinguish acute from chronic GVHD on the basis of

pathol-ogy and biolpathol-ogy, rather than time of onset (78)

HCT is unique in that donor/host tolerance frequentlydevelops over time, to the point that maintenance immuno-

suppression can often be discontinued In patients without

GVHD, all immunosuppressive medication is generally

stopped by 6 months to 1 year after HCT Even chronic

GVHD is not necessarily a lifelong condition; many patients

with chronic GVHD develop tolerance and resolution of

GVHD over time, and are ultimately able to discontinue

im-munosuppressive treatment (79,80)

The immunopathophysiology of GVHD is complex

The initial damage to host tissue is induced by the

transplant-conditioning regimen (81) The subsequent development of

acute GVHD requires antigen presentation; Shlomchik et al

showed that host DC play a pivotal role in this process (82)

Interactions of major histocompatibility complex (MHC)

antigens (with bound peptides derived from minor

histocom-patibility antigens) and T-cell receptors lead to activation, clonal

expansion, and differentiation of donor T cells Accessory T-cell

surface molecules, such as CD4 or CD8, also contribute to the

immunologic synapsis between T cells and antigen-presenting

cells The effector phase leads to host-cell destruction via

in-flammatory signals, cytolytic effects, and programmed cell

death (apoptosis) Inflammatory cytokines, which are primarily

released from the gut, allow the transfer of endotoxins and

lipopolysaccharides (LPS) into the circulation, triggering

macrophage activation The result is the further production of

cytokines, such as tumor necrosis factor  (TNF) and

inter-leukin 1 (IL-1) (83), leading to target cell death and the

expres-sion of costimulatory molecules, such as CD80, CD86, and

MHC class II antigens, on DC; T-cell stimulation; and the

re-lease of T helper-1 (Th1) cytokines (IL-2, interferon- (IFN-))

Recent experiments also emphasize the role of other tokines, particularly TNF, IL-15, and IL-18 (84) In mouse

cy-models, TNF is a central mediator of GVHD that works

predominantly in the intestinal tract Anti-TNF antibodies

prevent or ameliorate GVHD in mice (85) In humans,

anti-TNF therapy appears active in treating established acute

GVHD (86), but ineffective as GVHD prophylaxis (87).However, the actions of different cytokines and effector cells(e.g., large granular lymphocytes) and regulatory cells are stillincompletely understood The role of regulatory T cells with aCD25CD4phenotype, which is functionally reminiscent ofthe classic “suppressor T cell,” is currently being defined (65),

as is the role of Th17 cells (88,89)

Elevated serum levels of soluble Fas ligand (FasL) havebeen observed in some patients with GVHD (90), thoughFas-mediated apoptosis may also be involved in the control ofalloreactive T cells (91) Perforin-mediated cytotoxicity alsoplays a role in both GVHD and GVL effects (92,93) However,even T cells from mice doubly deficient in both FasL and per-forin can cause GVHD after mismatched-donor HCT (94)

Stem Cell Source

The kinetics of GVHD depend upon the source of stem cells.PBSC mobilized by means of chemotherapy or G-CSF havebeen used extensively for allogeneic and autologous stem cellrescue, and they are associated with rapid hematopoietic recon-stitution (95) Furthermore, G-CSF may polarize donor cellstoward Th2 cells and promote regulatory T-cell function, fa-voring the development of tolerance (96) Several clinical stud-ies suggest that the incidence of acute GVHD is comparablebetween marrow and PBSC recipients; the incidence of chronicGVHD appears to be increased with PBSC (97) However, ameta-analysis of five randomized controlled trials and 11 co-hort studies suggests that both acute and chronic GVHD aremore common with the use of PBSC as opposed to marrow(98) However, the higher incidence of GVHD with PBSC maynot be associated with a significant increase in mortality Infact, the results of several trials suggest that, particularly in pa-tients with “high-risk” disease, survival is improved in PBSCrecipients, perhaps due to a more vigorous GVT effect or tomore rapid immune reconstitution (95,99) Bone marrow allo-grafts are often preferred in nonmalignant disease, whereGVT effects are unnecessary and minimization of GVHD isthe overriding goal

Studies directed at the mechanisms involved in the effects

of PBSC show an increased production of IL-10, decreasedlevels of TNF in monocytes from G-CSF-mobilized PBSC,and reduced expression of costimulatory molecules and MHCclass II antigens Thus, a tolerogenic effect related to mono-cytes may be present, possibly juxtaposed with a countereffectdue to increased numbers of T cells

Chronic GVHD has prominent features of autoreactivity(100), and T lymphocytes with abnormal cytokine profiles(e.g., secretion of IL-4 and IFN) may be present Thymicdamage, inflicted by the conditioning regimen as well as bypreceding acute GVHD, leads to the failure of intrathymic se-lection and an escape of autoreactive cells to the periphery(101) A similar mechanism appears to be responsible for

syngeneic or autologous GVHD Recently, the role of B cells

in chronic GVHD has been the subject of increased attention,

based on reports indicating that the anti-CD20 monoclonal

antibody rituximab could produce remissions of chronic

GVHD (102) Some groups have posited that autoantibodies

produced by autoreactive B-cell clones contribute directly to

chronic GVHD (103) Alternately, B cells may contribute

indi-rectly, by influencing effector and regulatory T-cell

compart-ments, as they do in other autoimmune diseases (104,105)

As stated previously, the immune system is a major target

organ of GVHD Immunodeficiency is a key feature of

GVHD that is amplified by the immunosuppressive therapies

used to treat GVHD, thereby rendering patients highly

suscep-tible to infections The risk is further accentuated by damage to

various barrier structures, particularly the skin and intestinal

tract All aspects of immune recovery after HCT are impaired

or delayed in patients with GVHD; in patients with chronic

GVHD, immunoincompetence may extend over years

GVHD prophylaxis methods are summarized in Table 1.2

Combination regimens of methotrexate and a calcineurin

in-hibitor are the most effective regimens after high-dose

condi-tioning (106) The addition of prednisone to methotrexate and

CSP has been shown to increase or to decrease the incidence of

acute GVHD, depending on the timing of prednisone

adminis-tration (107,108) Some trials of FK506 (tacrolimus) combined

with methotrexate have shown an incidence of GVHD lower

than that observed with CSP; however, disease-free survival

was not improved (109) Other trials have suggested that

tacrolimus may be superior to CSP only in the unrelated-donor

setting (110) Some groups have explored the use of sirolimus in

addition to or in place of methotrexate (111) Various

prophylac-tic regimens have been employed after RIC HCT, including

combinations of MMF with CSP (29), sirolimus (112), and

T-cell depletion

T-cell depletion of donor marrow, which is clearly

effec-tive in reducing the incidence of GVHD, has increased the

probability of graft failure, posttransplant infection, and lapse of leukemia (113,114) Graft failure problems have beenovercome in part by the in vivo administration of a Campath-1Hmonoclonal antibody or of polyclonal ATG (115–117).Alternatively, additional DLI may be given preemptively ortherapeutically after HCT to reduce the risk of disease recur-rence and graft failure Some preliminary studies have suggestedthat depleting specific donor T-cell subsets (e.g., CD8T cells)from the DLI product may render this approach more effective(118,119) The use of Tregis currently being studied (120).GVHD is an important risk factor for long-term survivalpartly because it is associated with a high risk of early andlate, potentially lethal, infections If GVHD develops despiteprophylaxis, aggressive therapy is required SuccessfulGVHD therapy does not appear to interfere with the GVLeffect (121)

The probability of graft failure increases with increasingdegree of HLA-nonidentity, particularly for MHC class Iantigens (122) Several host-cell types, particularly CD8 Tlymphocytes and NK cells, participate in the rejection of donorcells Donor T cells counteract this host response, thereby facili-tating engraftment and preventing rejection As a consequence,T-cell-depleted marrow is more susceptible to rejection as de-scribed earlier Graft failure is associated with an increased risk

of infections due to prolonged neutropenia Patients withgraft failure after high-dose conditioning generally will nothave spontaneous autologous hematopoietic recovery, and re-quire salvage with a second HCT if clinically feasible (123) Incontrast, RIC regimens generally allow recovery of hosthematopoiesis if the donor graft is rejected

DELAYED COMPLICATIONS

By 2 years after HCT, about 80% of patients have returned topretransplant activities However, some patients develop de-layed or chronic complications (Table 1.3) These complica-tions are related to elements of the conditioning regimen (mostimportantly, irradiation), side effects of HCT (e.g., chronicGVHD, immunodeficiency), or combinations thereof (124).Life-threatening complications include infections, pulmonary

Modalities of Graft-versus-Host Disease Prevention

Selection of histocompatible donors

T-cell depletion

Ex vivo

Negative selection and removal of T cells Positive selection and purification of hematopoietic stem cells

dysfunction, autoimmune disease, musculoskeletal problems,

and secondary malignancies

SUMMARY

HCT offers effective and potentially curative therapy for

many life-threatening diseases Side effects include acute

tox-icity to multiple organs, the development of GVHD and

immunoincompetence, and secondary effects related to

im-munosuppressive therapy The result is a high susceptibility

to infections, which are a major cause of mortality after

HCT Both GVHD and its therapy are important

predispos-ing factors; thus, reducpredispos-ing the incidence and severity of

GVHD is an important component of efforts to reduce

post-transplant infections Transplant-conditioning regimens

have been modified to reduce early toxicity and to permit

transplantation of older patients RIC may allow faster

im-mune recovery and better infection control; however, its

availability has also expanded the availability of HCT to

higher-risk patient populations New antibiotics and

meth-ods of cellular therapy have also enhanced the ability to

eradicate infections

ACKNOWLEDGMENTS

This work was supported by grants number CA18105,

CA87948, and HL36444 from the National Institutes of

Health (Bethesda, Maryland) We thank Bonnie Larson and

Helen Crawford for assistance with the manuscript

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HISTORY OF TRANSPLANTATION

Mythology

For more than three millennia, organ replacement has been

the medicine of mythology The literature of several cultures

alludes to organ transplantation both as a symbol of renewal

and as a cure for disease An Indian legend from the

12th century BC recounts the powers of Shiva, the Hindu god

who xenotransplanted an elephant head onto his child to create

Ganesha, the god of wisdom and vanquisher of obstacles (1)

Eight centuries later, Pien Ch’iao (born 430 BC) exchanged the

hearts of two patients afflicted with an unbalanced

equilib-rium of energies; he administered powerful herbs after the

transplantation to promote acceptance of the hearts (2)

The classic Leggenda Aurea of Jacopo da Varagine (3) describes

the “miracle of the black leg” in which the limb of a deceased

Ethiopian gladiator was retrieved by the saints Cosmas and

Damian and was transplanted to the gangrenous leg of a

Roman sacristan Today, after decades of laboratory

experi-ments and clinical trials, kidney, liver, pancreas, lung, heart,

and small bowel transplantations are considered routine

During the past millennium, transplant technology has been

successfully transferred from the realm of mythology to the

arena of fact

Surgical Advances

The modern era of transplant surgery began in the 1900s, in

part because of the discovery of new techniques for vascular

anastomosis In 1902, Ullmann (4) of Vienna performed the

first successful experimental transplantation in dogs, and,

within 8 years, he reported that he had performed more than

100 technically successful canine kidney transplantations

In Lyon, Jaboulay and his assistant Carrel devised the modern

techniques of vascular suture (5) By 1933, the first human

kidney transplantation had been performed, albeit

unsuccess-fully, by the Ukrainian surgeon Voronoy His five subsequent

attempts also failed (6,7); consequently, the interest in organ

Immunobiology of Alloresponsiveness

Medawar’s (19) seminal experiments on the immunologic basis

of graft rejection led to recognition of the necessity of munosuppression for successful organ transplantation Thethree pivotal experiments were the following: first, the secondset phenomenon, namely, a repeat graft is rejected faster thanthe first one Second, the systemic nature of the response—nomatter where the second graft is placed, it is rejected fasterthan the first Third, the response is donor specific—challengegrafts from an unrelated donor are rejected in first set fashion.The acquired immune response toward allografts hasbeen shown to include two arms—T and B cells—mediatingcellular and humoral immunity, respectively However, theyare not totally independent: the B-cell response depends uponT-cell activation Circulating small T lymphocytes become ac-tivated via an antigenic stimulus (signal 1) delivered either di-rectly by interstitial donor cells bearing foreign markers orindirectly by host antigen-presenting cells (APCs) that displayprocessed alloantigen fragments thereby interacting with re-cipient CD4T lymphocytes This interaction is strengthened

im-by a series of coreceptors, including the binding of intercellularadhesion molecule-1 to lymphocyte function antigen 1 and oflymphocyte function antigen 3 to CD2 Signal 1 is amplified by

the costimulation signal 2, which was originally described to be

delivered by CD80/CD86 APC markers binding to CD28 on

the T-cell surface A host of other costimulatory or actually

in-hibitory (CTLA-4) markers have been recently identified to

participate in these interactions The activation engendered by

signals 1 and 2 causes lymphocytes to progress from the G0to

the G1phase with ensuing transcriptional upregulation of

cy-tokine mRNAs Secretion of interleukin (IL)-2 and IL-15

trig-ger T-cell progression to the S phase; interferon (IFN)-

stimulates APCs; and IL-4, IL-5, and IL-7 promote B-cell

de-velopment In addition to specific alloantigen, these cytokines

provide crucial signals to drive adaptive immunity as signal 3

IL-2 is a critical cytokine in the evolution of the immune

response It binds to a heterotrimeric receptor complex,

in-cluding , , and  chains The  chain is expressed upon

activation by signals 1 and 2 In contrast,  chains are

constitu-tively and exclusively present in every lymphoid cytokine

re-ceptor Downstream signaling from the  chain activates Janus

kinase 3, which phosphorylates signal transmission and

trans-duction molecule (Stat) 5, the molecule that dimerizes to form

a transcription factor promoting cell maturation Cytotoxic

actions are mediated both by direct contact between the

lym-phocyte and the target and via the humoral mediator products

granzyme B and perforin

In contrast to direct activation of B cells by a variety of

micro-organisms, humoral immunity toward allografts

re-quires the participation of T cells B-cell cytokines,

particu-larly B-cell-activating factor (BAFF), act as second signals

together with the alloantigen primary signal to select

clono-typic elements to proliferate, differentiate, mature, and secrete

antibody However, it is now recognized that these processes

are controlled by control mechanisms; exploitation of these

negative regulatory vectors de novo could mitigate rejection

leading to graft acceptance

The activated T and B cells recruit elements of

nonspe-cific host resistance in a dialogue that eventually destroys the

transplanted tissue The classical nonspecific elements that

participate in the response—polymorphonuclear leukocytes,

monocytes, and macrophages—are complemented by the

newly described vector, natural killer (NK) T cells In

non-transplanted hosts, cell-mediated immunity controls infections

caused by intracellular micro-organisms While neutralization

of virus can be achieved by humoral antibody, destruction of an

infected cell requires a cell-mediated response Despite an

in-tact antibody response to a micro-organism, elimination of the

pathogen by nonspecific host defenses may be impaired due to

collateral effects of age, original disease, and

immunosuppres-sive agents, such as steroids Thus, it is important to define

im-munosuppressive efficacy of an agent as the concentration of

drug that inhibits elements of nonspecific resistance versus that

necessary to inhibit specific resistance The greater this ratio,

the more useful the drug for clinical immunosuppression:

for example, if the ratio for cyclosporine is high, the ratio for

azathioprine (AZA) or mycophenolic acid is low and the ratiofor steroids is actually inverted due to their greater anti-inflammatory effects on nonspecific resistance

CLINICAL IMMUNOSUPPRESSIVE AGENTS

History

Initially, radiation and chemicals were used as pressive agents seeking to either disrupt cell division or to killlymphoid mediators of rejection The pharmacologic era began

immunosup-in 1914, when Murphy (20) documented the immunosup-inhibitory effects

of the simple organic compounds benzene and toluene on hostresistance In 1952, Baker et al (21) noted that the combination

of nitrogen mustard, cortisone, and splenectomy prolonged thesurvival of canine allografts Among the 12 kidney transplantpatients that Murray et al (22) treated with total body irradia-tion in 1960, only one was a long-term survivor Hamburger

et al (23) obtained similar disappointing results with total bodyirradiation Table 2.1 summarizes the sites of action of the var-ious immunosuppressive agents described below

Antiproliferative Agents

Schwartz and Dameshek (24) initiated the modern era ofpharmacologic immunosuppression by documenting that theantiproliferative drug 6-mercaptopurine (6-MP) dampenedantibody production and prolonged skin allograft survival byvirtue of blocking the initial immune response of clonal ex-pansion Thereafter, Calne et al (25) introduced the imidazolederivative of 6-MP, AZA, which displays more consistent oralbioavailability than the parent compound The combination ofsteroids with antiproliferative agents became a standard regi-men after reports by Starzl et al (26) and Goodwin et al (27).However, 75% of patients treated with this regimen displayedacute rejection and/or infectious episodes because the in-hibitory effects of the combination were only slightly greateragainst adaptive (specific) resistance than those versus innate(nonspecific) resistance, limiting immunosuppressive efficacy.More selective inhibitors than AZA are the antagonists ofinosine monophosphate dehydrogenase that thus disrupt denovo purine nucleoside (guanosine) synthesis: mycophenolatemofetil (MMF; Cellcept, Roche, Basel, Switzerland) (28,29),mycophenolate sodium (MPS; Myfortic, Novartis, Basel,Switzerland) (30), and mizorbine (MZB) In contrast, clinicalexperience has suggested that brequinar (BQR; DuPont-Merck, Wilmington, DE) (31), or leflunamide (Astellas,Osaka, Japan) (32), antagonists of dihydro-orotate dehydroge-nase, offered little therapeutic advantage over inhibitors ofpurine nucleoside synthesis and were more toxic due to therelatively miniscule size of the pyrimidine pool

The U.S Food and Drug Administration (FDA) proved MMF for maintenance therapy in renal transplanta-

ap-tion on the basis of findings from multicenter phase 3 trials

(29,33) In combination with cyclosporine A (CsA) and steroid,

MMF was shown to reduce the rate of allograft rejection

episodes to about 30% compared to about 40% using regimens

including AZA However despite this initial benefit, patient

and graft survivals at 1 or 3 years after cadaveric kidney

trans-plantation were not improved, suggesting that MMF affected

neither the occurrence nor the progression of chronic

rejec-tion, in contradistinction to evidence reported in animal

ex-periments The most common adverse effects of MMF,

namely, gastrointestinal complications—diarrhea, esophagitis,

gastritis, and bleeding—have been addressed in many cases by

substitution of MPS, a recently introduced enteric-coated

for-mulation of the active principle (31) In addition to enhanced

recipient susceptibility to invasive forms of cytomegalovirus

(CMV) and to BK virus (BKV) nephropathy, prolonged MMF

therapy has been implicated in augmented rates of lymphoid

malignancies, particularly among children

Therapeutic Antibodies

Seeking to deplete T and B cells as well as monocytes and

leukocytes, antilymphocyte antibodies (Abs) were utilized

ini-tially for rejection reversal and later for induction therapy

Polyclonal Abs raised in horses (equine antihuman thymocyte

globulin, ATGAM; Pharmacia, Kalamazoo, MI) or more

re-cently in rabbits (antithymocyte globulin, ATG; Genzyme,

Boston, MA) (34) opsonize leukocytes and platelets thereby

eliminating them from the circulation In addition to

pro-found inhibition of nonspecific host resistance, polyclonal

antisera produce a broad degree of T-cell inactivation, ing in profound increases in viral infections and lymphoidmalignancies

result-To achieve more selective immunodepression, clonal antibodies (MAbs) have been synthesized by fusion ofsingle rodent B cells which are generating the desired Abswith a plasma cell line These hybridomas produce reagentsselectively directed against a single cell-surface marker.OKT3, a murine immunoglobulin (Ig) G2a MAb directedagainst the epsilon component of the CD3 complex within theT-cell receptor (TCR), was rapidly accepted as an effectivereagent for rejection reversal (35) However, treatment withthis MAb has been beclouded by excessive T-cell depressionand more seriously by the occurrence of cytokine release syn-drome: fever, chills, myalgia, pulmonary edema, and asepticmeningitis Interestingly, this MAb does not deplete lympho-cytes but rather initially stimulates and then modulates themsuch that they cannot transduce a TCR signal

mono-The third generation of biologic agents are chimericmouse–human or fully humanized MAbs, two of which are di-rected against the  chain (CD25) of the IL-2 receptor (IL-2R),namely basiliximab (Simulect; Novartis, East Hanover, NJ) (36)and daclizumab (Zenapax; Roche, Nutley, NJ) (37), respectively.The humanized Abs bear only the murine complementarity-determining regions of rodent Abs engrafted onto a backbone

of human IgG1, an antibody isotype that cannot bind ment The  chain (CD25) of the IL-2R, which is upregulatedupon lymphocyte activation, bears a short polypeptide cytoplas-mic tail that cannot trigger cellular activation Thus, anti-CD25 MAbs do not elicit the cytokine release syndrome.Blockade of IL-2R inhibits the clonal proliferation and differ-entiation of activated T lymphocytes, offering a more selective

comple-TABLE 2.1 Sites of Action of Available Immunosuppressants

T-cell activaton Signal 1: G0 :G1

Lymphoid depletion Polyclonal horse/rabbit antibodies, alemtuzumab

aPhase of the cell cycle.

bInhibitor of kappa kinase.

immunosuppressive modality than polyclonal Abs or OKT3,

which injure both resting and activated T cells Furthermore,

the anti–IL-2R agents display prolonged serum half-lives

rarely evoking the production of neutralizing Abs Several

clinical trials have documented that the addition of anti–IL-2R

MAb to the induction regimen significantly reduces the

inci-dence and severity of acute rejection episodes among kidney,

liver, or heart transplant recipients

The anti-CD52 humanized MAb alemtuzumab, which

destroys a wide array of lymphoid elements (38), is approved

by the FDA for treatment of chronic lymphocytic leukemia

Based on the observation that blockade of signal 2 yields

toler-ance in animal models, a reagent of particular interest is the

humanized CTLA-4–Ig complex (Belatacept; Bristol-Myers

Squibb, New York, NY) that binds to the B7 (CD80/CD86)

complex on activated APCs This reagent is being tested

against cyclosporine as a nonnephrotoxic base of chronic

im-munosuppressive therapy (39)

Following recognition of the seminal role of B lymphocytes

in the development, maturation, and execution of the immune

response, Ab reagents are being developed to target these

vectors One reagent—the anti-CD20 MAb rituximab—is

se-lectively directed against B cells and FDA approved for the

treatment of neoplastic disease It has been applied in “off label”

fashion to transplantation both to reduce presensitization and to

dampen antibody-mediated acute rejection (vide infra)

Calcineurin Inhibitors

The present era of organ transplantation began in 1980 with

the introduction of CsA into immunosuppressive regimens

CsA was the first drug that selectively inhibited specific

adap-tive immunity while sparing nonspecific host resistance CsA,

which was isolated from the fungi imperfecti Tolypocladium

in-flatum Gams, inhibits the maturation of alloreactive T-cell and

B-cell elements by inhibiting lymphokine synthesis (40) The

drug blocks the phosphatase calcineurin, thereby preventing

dephosphorylation of a series of proteins that act as regulators

of DNA transcription, such as the nuclear factor of activated

T cells (NFAT) (41) Because the drug does not directly affect

elements of nonspecific resistance, patients receiving CsA

maintain substantial host defenses in contradistinction to the

actions of purine nucleoside synthesis inhibitors, which may

paralyze the entire immune system However, host innate

re-sponses which depend on activation by T-cell-driven cytokines

are dampened, particularly those seeking to eliminate viral,

fungal, and mycobacterial pathogens

By the mid-1980s, two CsA and prednisone regimens, one

with and one without AZA, became the principal

mainte-nance immunosuppressive protocols (42) However, the initial

oil-based formulation of CsA was not an easy drug to

pre-scribe, due to vast interindividual and intraindividual

differ-ences in absorption, distribution, metabolism, and excretion

(43) Development of the triphasic micellar formulationNeoral has overcome most of the variations leading to a rela-tively consistent absorption peak at 2 h (44)

In 1993, another calcineurin inhibitor (CNI), tacrolimus(TAC), was introduced This macrolide, which is derived

from Streptomyces tsukubaensis, proffers a 50-fold more potent

alternative to CsA (45) Compared with the oil-based originalCsA formulation, a regimen using TAC in combination withsteroid allowed fewer acute rejection episodes (46) Apparentlydue to its apparent greater potency and to the less (albeit stillsubstantial) interindividual and intraindividual pharmacoki-netic differences, most physicians have come to prefer TAC toCsA as the CNI component of immunosuppression The re-cent trials of a once a day formulation of TAC Avagraf arelikely to provide another advantage over the twice daily prescription

Both CsA and TAC exert a pleiotropic array of adverseeffects While CsA produces the cosmetic effects of hirsutismand gingival hyperplasia, TAC leads to alopecia, an enhancedrisk of new-onset type II diabetes mellitus after transplanta-tion (NODAT), which approaches 40% among AfricanAmericans, as well as more severe central nervous system dis-orders, including confusion and coma Furthermore, TACtherapy particularly when combined with MMF is associatedwith increased incidences of CMV and BKV infections, and

of posttransplant lymphoproliferative disease (PTLD) In dition because the targets of both agents, such as NFAT, arewidely distributed among human tissues, CsA and TAC pro-duce renal, hepatic, and peripheral neural toxicities (42,47),which limit the doses that can be prescribed to achieve thefull potential of this drug class Indeed, recent data have doc-umented that prolonged CNI exposure results in chronickidney disease in the majority of transplant recipients (48).Although some CsA analogues (CsA G and SDZ IMM-125) (49,50) have shown little benefit, the use ofIsA(TX)247 (51) has been recently claimed to produce lessnephrotoxicity

ad-Proliferation Signal Inhibitors

The most recent development in immunosuppression isthe introduction of inhibitors of the multifunctional kinasemammalian target of rapamycin (mTOR)—sirolimus andeverolimus (52,53) mTOR catalyzes critical steps both in thecostimulatory pathway during the G0-to-G1transition and inthe transduction cascade that follows reception of cytokine,hormonal, and nutrient signals Thus, proliferation signal in-hibitors (PSIs) block both costimulation (G0-to-G1transition)and the G1phase of T-cell activation (54) As rigorous me-dian effect analyses of preclinical and clinical data haveshown, sirolimus displays synergistic interactions with CsA(55), which are greater than those of agents that either act onthe G-to-G cell cycle transformation (e.g., CsA plus anti-

TCR MAb) or interrupt nonsequential phases of G0-to-G1

and S (e.g., CsA and MMF)

In clinical trials, the sirolimus and CsA combination nificantly reduced the incidence and severity of acute renal al-

sig-lograft rejection episodes (56–58) On the one hand, this

regimen has been associated with a reduced incidence of

ma-lignancies (59,60) On the other hand, it produces a range of

nonimmune toxicities due to the wide distribution of mTOR

Delayed wound healing, hypertriglyceridemia,

thrombocy-topenia, leukopenia, and persistent anemia appear to be the

major sirolimus-related side effects (61) There are much

lower incidences of diarrhea, arthralgia, and drug-induced

pneumonitis In addition, combinations with PSI can

potenti-ate CNI-relpotenti-ated adverse reactions, including renal

dysfunc-tion, hypercholesterolemia, and acne

Because sirolimus does not seem to have nephrotoxic fects (except for the possibility of inhibiting renal tubular cell

ef-regeneration in damaged organs (62)), it has been used to treat

patients deemed to be at risk for delayed graft function, thus

permitting extended periods of freedom from the

administra-tion of a CNI (63), which can be introduced at lower exposures

(64) Sirolimus (SRL) also offers the opportunity for de novo

avoidance (65), minimization, or subsequent withdrawal of

calcineurin inhibitors (CNIs) at 3 months (66) Chronic SRL

therapy may mitigate vasculopathic responses that lead to

long-term graft loss because the drug interferes with smooth

muscle and endothelial cell proliferation (67) Everolimus, the

hydroxyethyl form of sirolimus, is less potent and displays a

shorter half-life due to decreased hydrophobicity (68), but does

not seem to confer any other apparent advantage

Although an array of immunosuppressive drugs are able for use in clinical transplantation (69), present protocols are

avail-often transplant center specific, based on empiric rather than

scientific foundations Moreover, transplant centers tend to use

uniform regimens despite the fact that all patients do not have

equal propensities for rejection, infection, malignancy, or induced toxicities For example, retransplant patients, patientswith high levels of panel reactive antibody (PRA 25%), andblack recipients under the age of 65 years are classified as

drug-“strong immune responders,” for they are at increased risk ofacute rejection episodes and graft loss at 5 years (70)

IMMUNOSUPPRESSIVE REGIMENS

See Table 2.2 for a summary of current immunosuppressiveregimens

Induction Therapy: The First Week

Physicians seek to rapidly establish an adequate level ofimmunosuppression during the immediate posttransplantperiod One principle within this strategy is to produce lym-phopenia Large bolus doses of intravenous steroid (250 to

1000 mg methylprednisolone) drive lymphocytes from the culation into the tissues But the durable effects are achieved

cir-by antilymphocyte Abs Polyclonal antilymphocyte sera(ATGAM or rabbit thymoglobulin) provide rapid T-lympho-cyte depletion that is accompanied by variable, but signifi-cant, effects on granulocytes and platelets OKT3, a murineMAb, offers a greater degree of selectivity against T cells;however, its administration may be associated with the risks of

a severe first-dose cytokine release syndrome and of ing human antimouse Abs However, antilymphocyte anti-body therapy is not only more expensive, but also is associatedwith increased risks of infection and malignancy Increasingly,the course of induction therapy is being shortened from 7–10

develop-to 1–5 doses Whereas anti-IL-2R MAbs are generally scribed for living donor or low-risk recipients, ATG andalemtuzumab are reserved for immunologically high-risk re-cipients or those receiving extended criteria donor (ECD)

pre-TABLE 2.2 Current Immunosuppressive Regimens According

to Posttransplant Phase

Basiliximab  SRL  MMF Weak responder

SRL  pp CNIs  MMF Strong responders

Abbreviations: TAC, tacrolimus; ATG, antithymocyte globulin; MMF, mycophenolate mofetil; CsA, cyclosporine A; SRL, sirolimus;

grafts predicted to experience long periods of impaired

func-tion In addition, the use of high-dose steroids to

antilympho-cyte antibody therapy during the early posttransplantation

period reduces the incidence of adverse reactions to the foreign

proteins and may mitigate vascular injuries during graft

reper-fusion Although little evidence suggested that antilymphocyte

induction protocols were beneficial in the past (71–73), recent

data have documented their utility for most deceased donor

transplants The improved results relate to current use of

or-gans retrieved in settings of advanced age, concomitant

dis-eases, warm ischemia, or other adverse circumstances (34)

These “marginal” organs from ECDs show increased

procliv-ity to experience significant ischemia–reperfusion injury

The induction strategy is based on the belief that full

therapeutic concentrations of a CNI de novo may increase

al-lograft damage; alternatively, a PSI may cause wound healing

complications For grafts likely to function immediately,

namely from living or optimal deceased donors, many

clini-cians initiate CNI therapy either before or immediately after

the transplantation according to a concentration-controlled or

a fixed-dose strategy For high immunologic risk recipients of

grafts from deceased donors with features that raise the

likeli-hood of delayed graft function, physicians may choose among

the three de novo CNI treatment strategies: (i) delayed

intro-duction, (ii) minimization, or (iii) avoidance The combination

of -IL-2R MAbs plus sirolimus and steroid with delayed

(generally within 1 week) introduction of CNIs (when the

graft appears to be recovering) has been associated with an

8% rate of acute rejection episodes among weak immune

re-sponders (70) In contrast, strong responder recipients should

be treated with ATG rather than -IL-2R MAbs Since

sirolimus acts synergistically, it allows an 80% reduction in CsA

exposure without mitigating the benefit of the drug

combina-tion for both types of responders This minimizacombina-tion strategy,

namely reduced CsA exposure together with full doses of

sirolimus de novo, achieves better long-term renal function

than full CNI levels without a penalty in terms of acute

rejec-tion episodes or graft survival One alternative to this regimen,

namely the combination of alemtuzumab, which does not

re-quire steroid coadministration, with 50% reduced doses of

CsA (74) or TAC (75), has not yielded improved long-term

re-sults Since MMF only acts additively with a CNI, suboptimal

amounts of CsA prescribed de novo using an “MMF cover”

are associated with an increased incidence of rejection,

al-though MMF may facilitate subsequent reduction in the CNIs

after 6 months (76)

CNI avoidance has been tested in two settings: On the one

hand, the combination of the anti-IL-2R- reagent

da-clizumab with MMF and steroid was associated with a 50%

incidence of acute rejection episodes among low-risk

recipi-ents (77) On the other hand, low-risk recipirecipi-ents treated with a

CNI-free protocol, including basiliximab plus sirolimus and

MMF as well as steroids showed better renal function at

5 years compared with patients prescribed the same regimen

of an -IL-2R MAb combined with full exposure to CsA plusMMF and steroids (65)

Early Maintenance Therapy: The First 90 Days

The risk of acute rejection is greatest during the first 3 monthsafter transplantation The goal of initial maintenance therapy

is to avert early acute rejection episodes, which unless fully versed appear to increase the risk of eventual graft loss (78).The strategy employed by many physicians, who hope to avoidacute rejection at all costs, prescribes excessive exposure to im-munosuppressants during this period However, this approachmay compromise not only long-term renal function, but alsopatient survival due to drug toxicity

re-CNIs administered alone, in combination with steroids,

or in a triple-drug combination with AZA or MMF have beenthe most widely used agents for organ transplantation Mostprotocols begin with twice daily doses of TAC (4 to 7 mg) orthe oral microemulsion of CsA (4 to 5 mg/kg) The CNI pre-scription is generally adjusted on the basis of measured troughlevels (C0), the whole blood concentration prior to the nextdose Most health care workers consider the therapeutic targetfor TAC trough whole blood concentrations de novo in fulldose regimens to be 10 to 15 ng/mL as measured with an im-munoassay For CsA, the target C0  175–350 ng/mL, asmeasured with a specific MAb-based fluorescence polarizationimmunoassay or by high-performance liquid chromatography

By 3 months after transplantation, most patients receive totaldaily doses of 4 to 7 mg/kg CsA (C0 150–250 ng/mL) or 5 to

7 mg TAC (C0 8–10 ng/mL)

A major obstacle to monitoring CNI trough levels is thetremendous intrapatient and interpatient pharmacokineticvariability that produces a poor correlation between trough(C0) levels and drug exposure, that is, the estimate derivedfrom measurement of serial concentrations during the dosinginterval—the area under the concentration–time curve (AUC)(43) Thus, C0levels are not a sensitive tool to optimize CNIimmunosuppression

Alternative monitoring strategies have focused on themeasurement of CsA exposure using abbreviated AUC tech-niques, particularly the single concentration at 2 h postdose(C2), which shows the best correlation with the AUC and ap-pears to be a useful strategy to optimize CsA therapy.Current evidence suggests that this approach (albeit cumber-some) predicts exposure and clinical events more accuratelythan does C0 Time-dependent target values have been pro-posed for patients who have undergone liver (1200 ng/mL,tapering to 700 ng/mL) or renal (1700 ng/mL, tapering to 900ng/mL) transplantations Indeed in contradistinction to earlytrials with the original oil-based formulation (79), recentmulticenter clinical trials have demonstrated that regimenswhich include monitoring of C values during CsA

microemulsion therapy yield at least equal outcomes to de

novo TAC therapy (80)

Steroids are valuable (albeit not essential) adjuncts tobasic immunosuppressive protocols Experimental and clinical

data suggest a modest synergism between CNIs and steroids

A popular regimen immediately reduces steroid doses to

30 mg, and to 7.5 mg by 30 days after transplantation The

re-cent trend to avoid or markedly reduce the period of steroid

exposure is popular with patients and physicians, but has not

been shown to affect hypertensive or osteopenic

complica-tions (81) Sirolimus may substitute for the effect of steroid to

block inhibitory factor kappa and thus prevent c-Rel

genera-tion during signal 2

The major concern during this initial 3-month period (inaddition to rejection) is the occurrence of serious infections

which seem to be related primarily to the overall intensity of

the immunosuppression rather than to any single agent per se

Intermediate Maintenance Period

From 90 to 180 days, physicians tend to focus on optimizing

graft function The roles of the major available alternates to

CNIs—sirolimus or MMF—during intermediate-term

main-tenance immunosuppressive therapy remain controversial

Some physicians add these agents in an attempt to further

de-crease or eliminate the CNIs, seeking to reduce drug-induced

nephrotoxicity Furthermore, the combination of a nucleoside

synthesis inhibitor with full CNI exposure tends to increase

the frequency of CMV and BKV infections, malignant

diseases, diarrhea, and bone marrow depression On the one

hand, discontinuation of CNIs with MMF base therapy is

effec-tive for some weak responders (82) On the other hand, among

an array of strong and weak responders, CNI withdrawal with

SRL base therapy (albeit associated with only a slight

insignifi-cant increase in acute rejection episodes) has been shown to

greatly improve kidney transplant function at 5 years (83)

Long-Term Immunosuppressive Therapy

During maintenance treatment two factors are critical:

opti-mizing graft function and miniopti-mizing adverse reactions to

immunosuppressants Recently there has been a shift in the

strategy for long-term maintenance immunosuppressive

regi-mens for renal transplant recipients from CNI administration

to sirolimus monotherapy for weak immunologic risk

recipi-ents, whereas patients with high-risk features require

combi-nations of sirolimus with an antiproliferative agent This

change in therapy was due to the observation of little impact of

CNI-based treatment on the occurrence of chronic rejection;

there were similar 10-year renal graft survivals in the CNI

versus the AZA eras (84) Although this failure may have

re-sulted from an intrinsic resistance of antibody-producing

B cells to CNIs, MMF, or steroids, it has generally been attributed

to the emergence of CNI-induced nephrotoxicity (48).Furthermore, the high variability of chronic CNI exposure(85) as well as the well-documented occurrence of patient non-adherence (86) may predispose recipients to chronic rejection.Calcineurin antagonists promote the production of trans-forming growth factor- (TGF-), a proliferation factor thatleads to interstitial kidney fibrosis and chronic allograft fail-ure In contrast, sirolimus displays antiproliferative effects onendothelial and smooth muscle cells, which are critical ele-ments in the vasculo-obliterative processes characteristic ofgraft failure (67) In addition, sirolimus has been associatedwith a reduced incidence of malignancy among long-termrenal allograft recipients, the emerging major hazard for alltransplant recipients (59,60)

Although the general belief is that the intensity of therapy can be reduced over time—“graft adaptation”—immunosuppression is generally required for continued graftfunction The discontinuation of immunosuppression, evenmany years after transplantation, almost uniformly leads to lateacute rejection episodes or accelerated chronic rejection.Isolated examples of patients displaying acquired transplanta-tion tolerance are under intensive study seeking to discernmarkers of unresponsiveness

Therapy for Acute Rejection Episodes

Rejection remains the most frequent cause of early transplantfailure Because of the significant risks associated with exces-sive immunosuppression, one of the most important issues inthe treatment of rejection is the certainty of the diagnosis.Although some physicians empirically initiate treatment, mostcenters prefer to rely on histopathologic confirmation usingBanff criteria (87)

For mild Banff grade I episodes of acute cellular tion, which are the most common type, corticosteroids con-tinue to be the most cost-effective first line of treatment.Steroid regimens consist of large intravenous doses of methyl-prednisolone, followed by an oral taper over a few weeks tomaintenance doses of prednisone A favorable response totreatment is characterized by a rapid reversal of abnormal lab-oratory tests and of symptoms which tend to occur only in asmall fraction of patients under treatment with modern im-munosuppressive regimens The major risks among the con-stellation of side effects of high-dose steroids includeexacerbating or inducing diabetes mellitus, producing gas-trointestinal irritation or perforation, and triggering psy-choses Steroid regimens reverse approximately 80% of firstacute cellular rejection episodes

rejec-The definition of a steroid-resistant cellular rejection mains ambiguous Usually, after 2 to 5 days of treatment, physi-cians at most centers assess whether the response to steroidtherapy has been unsatisfactory, often confirming any impres-sion of a therapeutic failure by a repeat biopsy When the

re-severity of the infiltration has increased or vascular

compo-nents have appeared, treatment is switched to antilymphocyte

antibody preparations Steroid-resistant rejection may be

re-versed in most cases with either OKT3 or polyclonal

antilym-phocyte sera (88–90) In the past, OKT3 had been the preferred

treatment because it can be administered via a peripheral vein,

whereas polyclonal sera demand central venous delivery

However, the latter preparations are now increasingly

pre-scribed due to their more potent effects and apparent benefit to

confer endothelial protection Immunologic monitoring of

T-cell subsets by fluorescence-activated cell sorter analysis is

used to assess patient responses and to guide dose adjustments

CD3peripheral blood T cells usually fall to less than 10%

after the first few doses of OKT3; with polyclonal reagents, the

absolute CD2T-cell counts should remain between 50/ L

and 150/ L within a few days of administration

Unfortunately, no secure algorithms exist for determining the

proper duration of antilymphocyte therapy On one hand, the

therapeutic effects may be delayed by 7 to 10 days and the

long-term toxic effects by 30 to 60 days On the other hand,

prema-ture discontinuation may presage a “camelback” episode of

repeat rejection which often displays a pernicious intensity

Grafts in patients who experience acute rejection

refrac-tory to steroid and antilymphocyte antibody treatments are

destined to be at increased risk of failure, particularly when

the therapy fails to achieve organ function at levels within 15%

of that prior to the episode Although physicians have used

either TAC or MMF for immunosuppressive salvage with

variable results (91), recent promising data have been reported

with sirolimus rescue treatment for acute cellular rejection

episodes (92) In desperate cases, alemtuzumab has been used

to salvage renal transplants undergoing cell-mediated

im-mune responses refractory to other therapies (93)

Increasingly physicians have recognized a new entity—

acute antibody-mediated rejection (AMR) This immune

reac-tion, which can present without or after a prior bout of cellular

rejection, can be documented to involve humoral antibody by

the presence on a biopsy of deposition of the complement

de-gradation product C4d, of polymorphonuclear leukocytes in

peritubular capillaries, and/or of circulating donor-specific

an-tibody using human leukocyte antigen (HLA)-coated beads in

reactions with recipient serum (94) These episodes are

refrac-tory to modalities that successfully address acute cellular

episodes—steroids or ATG/OKT3 Therapy for this disorder

is based on plasmapheresis to deplete antibody in the

circula-tion, intravenous gammaglobulin (IVIg) to downregulate

anti-body generation, and rituximab to cytolyse B (but not plasma)

cells (95) Salvage rates with these treatments exceed 80%

al-though the intense immunosuppression may predispose to

in-fectious complications Unfortunately, the grafts that have

undergone a bout of AMR are clearly at increased hazard of

chronic vasculopathic reactions for which there is no specific

in-Kidney Transplantation

The overall 1-year and 5-year graft survival rates are 92% and75% for deceased, and 94% and 80% for living donor kidneys,respectively Whereas the major adverse factor for graft sur-vival appears to an acute rejection episode, particularly one that

is not completely reversed during the first 6 months, this ratehas markedly decreased from 75% using AZA–prednisone(Pred) to 40% with CsA–Pred to 30% with CsA–MMF to 25%with TAC–Pred to 10%–15% with TAC–MMF–Pred or SRLlow-dose CNI–Pred The predicted 10-year survival rates ap-pear to be determined by HLA compatibility: for example,79% for HLA-identical sibling transplants, 60% for other liv-ing donor transplants, and 50% for deceased donor transplants.Although many factors influence outcomes, the following arethe key features: HLA matching, ethnicity, transplant center,original recipient disease, initial renal function, and occurrence

of rejection episodes The major cause of long-term graft loss isinterstitial fibrosis/tubular atrophy, which appears to have beenexacerbated by chronic CNI therapy (48) producing vascularobliteration Another important factor is noncompliance to immunosuppressive drug therapy (86)

Recipient morbidity is generally due to adverse reactionsfrom immunosuppressants: dyslipidemia exacerbating cardio-vascular disease, hyperglycemia leading to new onset diabetesmellitus, and persistent or worsened hypertension predis-posing to cerebrovascular accidents as well as myocardial infarction/cardiac failure Posttransplant lymphoproliferativedisease, squamous cell skin cancers, and other malignanciesnow exceed infections as the major cause of recipient death.Because most renal transplant patients have experiencedchronic disease over the course of years on dialysis, rehabilita-tion tends to be poor; save for children who may experiencegrowth and improved social adjustment because they are nolonger tied to the routine of mechanical support

Liver Transplantation

The current 1-year and 5-year graft survivals are 84% and 70%for recipients of deceased versus 75% and 60% for living donor

livers, respectively The lower survival of living donor or split

grafts relates to the use of only a liver lobe in contrast to the

entire liver This smaller mass not only affords less protection

from injury but also entails greater surgical hazard due to the

frequent technical challenges

Early adverse prognostic factors that predispose to primarynonfunction of livers include cardiac death and hepatic steato-

sis Survival is worst for recipients who have undergone

retrans-plantation, who display high scores according to the model

for end-stage liver disease (MELD), for hepatic or malignant

primary diseases, and for ABO incompatible donor/recipient

combinations It is best for patients with metabolic diseases

Interestingly, liver recipients, particularly those with

pre-existent hepatitis C, which is now the major indication for the

procedure, require less immunosuppression than kidney or

cardiac transplant patients Steroids can generally be rapidly

withdrawn and CNI exposure minimized, frequently guided

by drug toxicity profiles The reported rehabilitation rates

after liver transplantation are greater than 80%; most

recipi-ents claim that their quality of life is good to excellent

Thoracic Transplantation

Thoracic organs have shown steady increases in survival rates

over time For most thoracic organs, patient survival rates are

equivalent to graft survival rates The current 1-year and

5-year survival rates for heart transplant recipients are 90%

and 70%, respectively, and, for lung transplants recipients,

85% and 40%, respectively Heart–lung composite graft

survival rates at 1 and 5 years are 56% and 48%, respectively

The donor shortage has been greatest for hearts, since living

donors have been widely utilized for lung grafts

In addition to concerns about the use of organs from donorsover 60 years of age, adverse donor factors for heart or lung

recipients include CMV infections or pre-existent pneumonia,

respectively The long-term survival of cardiac grafts has been

compromised in the past primarily by transplant coronary artery

vasculopathy and for lungs by broncho-obliterative

pulmonopa-thy exacerbated by CMV pneumonitis, gastroesophageal reflux,

and chronic rejection However, de novo malignancy is now

emerging as the major cause of patient loss For these reasons as

well as the occurrence of CNI-induced nephrotoxicity in native

kidneys, centers are increasingly converting patients from

CNI-based to sirolimus regimens

Pancreas Transplantation

The first pancreas transplant was performed in 1966 at the

University of Minnesota by Kelly (96) The current 1-year and

5-year survival rates of 85% and 65% for grafts, and 95% and

85% for patients, respectively, represent major advances over

the past decade Because most diabetic candidates display

concomitant renal failure, simultaneous pancreas–kidney

transplants are the most frequent procedures The combinedgrafts show greater survival rates than pancreas-alone trans-plants, which have been performed for patients who did notneed a kidney or those who had previously received a renalimplant Whereas living donor pancreatic tail transplants areonly performed rarely, the use of a living donor kidney with asimultaneous deceased donor pancreas represents a convenientapproach to overcome the shortage of deceased donor kidneys.Patients with successful grafts are insulin-free; however, ame-lioration of diabetic complications is far from uniform.Enthusiasm for the Edmonton Protocol using sirolimus,TAC, and MMF immunosuppression to facilitate pancreaticislet transplantation (97) has recently dampened due to theneed for multiple engraftments, the limited (

of euglycemia with fewer than 10% successes at 5 years, andthe high degree of recipient anti-HLA sensitization (98).Important issues in islet transplantation relate to optimal isola-tion methods, improved preparation by in vitro culture, andelimination of initial injury due to leukocyte infiltration anddevelopment of a more appropriate immunosuppressive regi-men than TAC or sirolimus, both of which appear to be toxic

to isolated pancreatic  cells

Composite Organ and Tissue Transplantation

The availability of more potent immunosuppression has made

it possible to simultaneously graft multiple organs Beyondsimple dual grafts of liver–kidney, liver–small bowel,heart–kidney, etc., en bloc transplantations of the upper ab-dominal organs, including stomach/duodenum, liver, pan-creas, and kidneys, have been performed in desperatesituations with variable results (99) Translating the legend ofCosmas and Damian to modern times, composite tissue grafts

of the hand, forearm, face, or trachea are being explored withsome sensational results (100)

FUTURE PROSPECTS

Xenografting

Although xenotransplants have been attempted in humans,few have been successful (101) There are major immunologicand ethical obstacles to successful clinical xenografting Themost important mechanism of xenograft rejection are naturalantispecies Abs that bind to the glycoprotein surface markers

on the endothelial cells of the graft, activate the complementcascade, and trigger hyperacute rejection, which cannot becontrolled with current immunosuppressive regimens In ad-dition, complement regulatory proteins, such as CD59 (decayaccelerating factor) and monocyte chemoattractant protein,show strict species specificity Thus, the complement regula-tory proteins on xenogenic endothelial cells do not protect

them from attack by human xenoantibodies and complement.

In an attempt to solve this problem, studies are being

con-ducted with transgenic animals bearing a vascular

endothe-lium that expresses inhibitors of human complement

components Although this maneuver has dampened the

hy-peracute rejection response, acute vascular rejections and

thromboses remain formidable obstacles An alternate

ap-proach seeks to immunoisolate xenogeneic pancreatic islet in

capsules or membranes, although foreign body reactions have

beclouded the long-term outcomes

Induction of Donor-Specific Tolerance

The ultimate goal of transplantation therapy is the induction

of selective tolerance toward donor histocompatibility

anti-gens without the need for continuous immunosuppression

In animal models, special circumstances are associated with

an increased likelihood of tolerance induction, including

ex-posure to donor cells in the neonatal (or prenatal) period,

grafting across weak histocompatibility barriers, or implants

into privileged sites Neonatal tolerance primarily depends

upon a central thymic process of selective depletion of

anti-donor immunoreactive cells (102,103) However, acquisition

of this deletional tolerance status in adults, thereby

produc-ing cellular chimerism, requires abolition of the host

im-mune system by total-body or total-lymphoid irradiation

combined with intense antibody and chemical

pressive maneuvers Only a transient need for

immunosup-pression has been achieved among a small cohort of patients

initially treated for multiple myeloma with bone marrow

transplantation that putatively engendered a tolerant state to

accept a subsequent renal graft from the same donor

(104,105) However, the complexity and cumbersome nature

of these protocols seem to preclude safe, widespread clinical

application

“Prope” (almost) tolerance has been proposed in a

modi-fied deletional approach using either alemtuzumab or ATG in

combination with 50% reduced doses of CsA (74,106) or TAC

(75), respectively However, the 5-year outcomes did not

ap-pear to differ from those patients treated with conventional

therapy Furthermore, antibody-mediated depletion protocols

do not alter the generation of memory-like T cells (106), which

can produce a pernicious form of allograft rejection (107)

A less hazardous approach seeks to cajole mature

lym-phocytes to develop tolerance peripherally by mechanisms of

immunoregulation This postthymic peripheral

unresponsive-ness may be explained by T-cell anergy, immune deviation,

blocking Abs, and/or induction of negative regulatory cells

(105) Anergy emerges when antigenic stimulation fails to

fully generate activation signal 1 This state has been induced

after treatment with agents that block signal 1 coreceptors or

costimulatory molecules, namely, anti-CD4, CTLA-4–Ig, or

MAb directed against the surface markers CD2; intercellular

adhesion molecule-1; or lymphocyte function antigen-1 These models are characterized by deficient cytokine synthesiswith consequent blunting of signal 3 and a failure to develop amature immune response Unfortunately, any stimulation ofthe host immune system, for example, by an infection, canovercome this defect Therefore, only a moderate degree ofimmunosuppression (but not tolerance) was induced by treat-ment of kidney transplant patients with the CTLA-4/IgGconjugate belatacept (39)

Another possible strategy to modulate signal 1 is the ministration of peptides derived from the polymorphic re-gions of donor major histocompatibility complex molecules.Presentation of these peptides via the indirect route might in-duce tolerance by triggering an altered, ineffective signal 1 Asmall, randomized, double-blind, phase 2 clinical trial of treat-ment with human HLA-B27.85-84 peptides failed to show adifference in the incidence of acute rejection episodes whencompared with placebo treatment However, the treatmentdid produce a decrease in the cytotoxic activity of the NK cells

ad-of kidney allograft recipients (108) The clinical relevance ad-ofthis finding remains unclear

Immune deviation is associated with a predominance ofthe T-helper-2 phenotype of CD4T cells with predominantexpression of the cytokines IL-4, IL-5, and IL-10 This state isassociated with emergence of negative regulatory elements(Tregs)—CD4CD25FoxP3T cells—due to expansion of

a naturally occurring pool and/or antigen-induced generation

of putatively donor-specific elements These cells recognizeantigen on APCs by indirect presentation in the afferentphase, shutting down B and T cells via CTLA-4 and the sup-pressive cytokine IL-10 The efferent actions of Tregs areantigen nonspecific and supported by IFN- The infusion ofdonor-specific cells, such as those from the blood or bonemarrow, in combination with CsA, ATG, or particularlysirolimus can induce negative regulatory cells Approachesthat evoke the development of blocking Abs, which preventeither the afferent or efferent phases of rejection, have beenpopularized in animal models but never convincingly demon-strated in man

Gene therapy may proffer another strategy to facilitate ance induction This approach seeks to introduce immunomod-ulatory genes or modify the expression of histocompatibilityantigens (109) However, the utility of gene therapy in humanshas yet to be determined

toler-Unfortunately, clinical trials of tolerance induction mand that the manipulation be performed within the context

de-of a conventional immunosuppressive regimen because thesuccess of the tolerogenic maneuver per se is not assured Thisrequirement for a baseline immunosuppressant may preventlymphocyte differentiation along a tolerogenic pathway; forexample, calcineurin antagonists may blockade, whereassirolimus may facilitate the induction of CD4CD25FoxP3regulatory cells or T-cell apoptosis In addition, because no

assay exists to confirm a tolerant state, extreme caution must

be exercised when baseline immunosuppression is withdrawn

to establish the presence of allo-unresponsiveness

SUMMARY

Organ transplantation has evolved from an experimental

practice to a therapeutic modality Technical advances have

improved the safety of the surgical procedures, and the

major thrust of research efforts has focused on improving

the efficacy and safety of immunosuppressive therapy

Unfortunately, present clinical protocols often include

empir-ically, rather than scientifempir-ically, selected combinations of

im-munosuppressive drugs However, the advent of rigorous

clinical trial designs to test new immunosuppressive regimens

is likely to lead to robust strategies using future agents

Enhanced success of organ transplantation using the

presently available modalities is likely to depend on

develop-ing regimens associated with fewer iatrogenic collateral

toxic-ities and showing better cost–benefit relations Rejection still

represents a major barrier to transplant success—although

the incidence of acute episodes with existing drug

combina-tions is presently low, chronic antigen-dependent and

non-antigen-dependent processes continue to impair long-term

transplant survival The ultimate goal of achieving tolerance,

which is now under investigation in clinical studies, remains

the major challenge for the future

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3 Immunosuppressive AgentsJASON RHEE, NORA AL-MANA, JEFFERY COOPER, RICHARD FREEMAN

26

Transplantation has evolved from highly experimental and

risky procedures to refined, clinically routine treatments for

end-stage organ failure In the earliest days, little was known

about the immunologic barriers to successful transplantation

and there were no specific immunosuppressive treatments to

modulate the highly sophisticated and well-programmed

re-sponse to nonself tissues The first major breakthrough in

al-tering the immune response to transplanted tissue came with

the discovery that pharmacologic agents could suppress the

immune response In 1959, Schwartz and Dameshek,

work-ing at Tufts University, observed that purine analogues such

as 6-mercaptopurine (6-MP) can interfere with DNA and

RNA synthesis to inhibit lymphocyte proliferation in

sponse to an immune challenge, thus demonstrating that

re-versible immunologic unresponsiveness could be purposefully

induced (1) This observation and the subsequent

develop-ment of the orally active precursor of 6-MP, azathioprine

(AZA), ushered in the era of pharmacologic

immunosuppres-sion This achievement overcame a major impediment to

suc-cessful transplantation between genetically different donors

and recipients

Since these initial discoveries, much has been learned

about the immune response to foreign antigens of all types

and about the breadth and depth of both humoral and

cellu-lar effector mechanisms Along the way, researchers have

discovered much more specific targets for interrupting the

cell-mediated responses to transplant organs while, at the

same time, providing much more in-depth understanding of

the consequences of inhibiting this highly conserved line of

self-preservation A full discussion on the allospecific

im-mune response and the diversity of specific targets for

alter-ing the immune response is beyond the scope of this chapter

Subsequent chapters will cover the specific infectious

conse-quences of blocking or suppressing the transplantation

im-mune response This chapter focuses on the various classes

of drugs that have been developed for suppressing the

mune response after transplantation, provides a brief

im-munologic background for understanding the mechanisms

of actions of these drugs, and focuses on the more recent

randomized controlled trials in which these drugs have been

tested clinically

Immunosuppressive drugs are used either as preventativeagents to maintain a steady state of immunosuppression or astreatment for acute rejection (Table 3.1) During acute rejec-tion, usually much more broad and complete inhibition of theimmune response is required to reverse the process Since thereare now multiple immunosuppressive agents whose mecha-nisms of action and toxicity profiles differ, modern immuno-suppressive therapy usually includes several simultaneouslyadministered drugs Consequently, clinical trials testing oneagent against another almost always involve other immuno-suppressant drugs, making complete separation of the clinicaldata difficult The discussion below focuses on the studieswhere the agent in question is being tested against a compara-tor drug, but other drugs used concomitantly in the study arealso mentioned

CORTICOSTEROIDS

The anti-inflammatory properties of corticosteroids have beenknown for more than 50 years The first human leukocyteantigen (HLA)-mismatched transplants received AZA aloneand all failed relatively quickly after transplantation due toprofound marrow suppression and untreatable infections,although researchers noted that rejections could be reversedwith increased doses In 1961, Goodwin et al demonstratedthat addition of corticosteroids to the immunosuppressive reg-imen allowed for reduced, less toxic doses of AZA andachieved longer-term success with nonidentical renal trans-plants (2) This work solidified the concept of using multidrugtherapy to maximize efficacy while reducing individual drugtoxicity Subsequent research has elucidated some of the mech-anisms by which corticosteroids produce an immunosuppres-sive effect Corticosteroids block T-cell–derived andantigen-presenting cell (APC)–derived cytokine expression,including interleukin (IL)-1, IL-2, IL-3, and IL-6 by upregu-lating intracellular kappa B (I-B) I-B is a cytosolic inhibitor

of nuclear factor (NF-B), which is a common transcriptionfactor for many proinflammatory cytokines (3) Since their in-troduction to transplantation in the early 1960s, corticosteroidshave become mainstays of both maintenance and rejection

TABLE 3.1 Immunosuppressive Agents

Usual Adult Maintenance

microemulsion

7–10 days

Daclizumab Monoclonal Induction dose 1 mg/kg No Edema, hypotension, anaphylaxis

antibody every 14 days for a

total of 5 doses

day 4 Sirolimus Cell cycle inhibitor 5–10 mg loading and Yes Hypercholesterolemia, hyperlipidemia,

2 mg daily orally hypertriglyceridemia, deep venous

thrombosis, lymphocele, pancytopenia, thrombotic thrombocytopenic purpura, venous thromboembolism, hepatic artery thrombosis, hepatotoxicity, impaired wound healing

Everolimusd Cell cycle inhibitor 1–3 mg/day Yes Hypercholesterolemia, hyperlipidemia,

hypertriglyceridemia, deep venous thrombosis, lymphocele, pancytopenia, thrombotic thrombocytopenic purpura, venous thromboembolism, hepatic artery thrombosis, hepatotoxicity, impaired wound healing

Abbreviation: ATGAM, antithymocyte globulin.

aSome drugs’ daily doses are divided into two doses per day.

bTherapeutic drug monitoring.

cCalcineurin inhibitor.

dNot approved for use in the United States.

immunosuppression treatment Unfortunately, they also have

a wide side effect profile, including hypertension,

hyper-glycemia, delayed wound healing, osteoporosis, glaucoma,

suppressed growth, hyperlipidemia, increased risk of gastric

ulcers, risk of fungal infections, and suppression of the

hypo-thalamus–pituitary–adrenal axis Thus, many recent trials

have focused on evaluating protocols in which corticosteroids

are reduced or eliminated altogether when used in

combina-tion with newer agents to limit these side effects These trials

will be outlined in later sections of this chapter where the

other agents are described

SIGNAL TRANSDUCTION BLOCKERS

Calcineurin Inhibitors

Cyclosporine (Sandimmune, Neoral, Gengraf)

In 1973, Jean-Francois Borel discovered that cyclosporine A

(CSA), a metabolite of a common soil fungus Tolypocladium

inflatum, has significant immunosuppressive properties (4)

This novel drug was first introduced by Roy Calne in 1979 (5),

and its subsequent approval for clinical use in 1981

revolution-ized transplantation

CSA, a highly lipophilic compound, traverses the cell

membrane and binds to cyclophillin, which is an intracellular

receptor The CSA/cyclophillin complex then binds to

cal-cineurin, an important signal transducer that upregulates

ex-pression of critical T-cell activation factors, such as IL-2, IL-3,

IL-4, granulocyte-macrophage colony-stimulating factor,

interferon-, and tumor necrosis factor (TNF)- (6) IL-2 is

an important stimulant of T-cell responses to HLA class I and

II antigens and it promotes T-cell proliferation Thus, CSA

di-rectly inhibits T-cell responses to foreign tissues CSA is

pri-marily metabolized in the liver via the cytochrome P-450 3A,

4A and therefore is subject to many interactions with other

substances and drugs also metabolized via this system

The introduction of CSA had an immediate impact on

suc-cessful transplantation because it offered a narrower spectrum of

immunosuppressive action compared with the only other

avail-able agents in use at the time, AZA and

cortico-steroid This resulted in dramatic improvements in patient and

graft survival because acute rejection became more controllable

and infectious complications were reduced as a result of the

more precise inhibition of T-cell responses possible with CSA (7)

CSA was originally marketed as Sandimmune This

compound has a very variable absorption profile owing to its

lipophilic characteristics Hence, the amount of fatty foods,

ab-sence or preab-sence of bile, various drugs, and even exposure to

plastic can affect CSA dosing and pharmacokinetics (8) To

address these shortcomings, microemulsion formulations

(Neoral, Gengraf) of CSA were developed These

formula-tions have less variation in absorption and are less affected by

biliary drainage and food (9) The usual initial dose of CSA is

5 to 7 mg/kg/day orally in two divided doses and usuallytapered to 4 to 5 mg/kg/day with time; intravenous dosingshould be one third of the daily oral dose CSA is used primar-ily for prevention of rejection It has not been consistentlyeffective in treating established acute rejection

The most common side effect of CSA is nephrotoxicitydue to renal arteriolar vasoconstriction In the short term, thisvasoconstriction can cause acute renal injury, and in the longterm, it can lead to chronic allograft nephropathy ChronicCSA use has been reported to induce renal dysfunction in 20%

of liver transplant recipients (10) CSA has also been associatedwith increased incidence of hypertension, neurotoxicity in-cluding seizures and peripheral neuropathy, diabetes, hyper-lipidemia, gingival hyperplasia, and hirsutism Neurologicmanifestations ranging from mild tremor and peripheral neu-ropathy to psychoses, hallucinations, seizures, and mutismhave also been reported in 10% to 28% of liver transplant re-cipients treated with CSA (11)

Due to its numerous toxicities, CSA has a narrow peutic window Minimizing toxicity, while still maintainingefficacy given the numerous variations in patient-specific me-tabolism and potential interactions with other medications,necessitates that CSA blood levels be monitored frequently.Different methods are used for blood level concentrationmeasurement, including high-pressure liquid chromatogra-phy and several immunoassays, some of which measure CSAmetabolites as well as the parent compound Consequently, thetherapeutic concentration range varies considerably depend-ing on the type of assay used and the timing of the blood sam-ple relative to the dose of CSA

thera-There has been recent enthusiasm for monitoring CSAblood levels with measurements taken 2 h after a dose (C2) in-stead of 12-h trough monitoring (C0) as C2 levels may be moreaccurate correlates of total CSA exposure (12–14) In a study of

135 renal transplants receiving antibody induction and treatedwith CSA, mycophenolate mofetil (MMF) (see Anti Metobolitesection below), and corticosteroid maintenance immunother-apy, logistic regression analysis revealed that mean C2 was theonly predictor of acute rejection (12) However, in a differentstudy of 160 consecutive renal transplants, C2 monitoring pro-vided no advantage in reducing rejection rates or improvinggraft survival (15) Another study found C0 CSA levels to bemore predictive of acute rejection episodes (16), making it un-clear whether C2 monitoring is of any benefit in CSA-treatedpatients Though the main body of the CSA therapeutic bloodlevel monitoring research is centered on renal transplants, afew studies examining liver (17) and cardiac (18) transplantshave also supported C2 monitoring of CSA levels

The combination of difficult monitoring and toxicitiesobserved with CSA has led transplant programs to investi-gate CSA avoidance or early withdrawal protocols In one ofthe largest such trials, 489 renal transplant recipients wererandomized into three groups: CSA for three monthsfollowed by AZA and corticosteroids; CSA long term; or