Ebook Transplant infections (3rd edition): Part 2

(BQ) Part 2 book Transplant infections presents the following contents: Viral infections, fungal infections, infection control, immune reconstitution strategies for prevention and treatment of infections, hot topics.

Cytomegalovirus Infection after

Stem Cell Transplantation

MORGAN HAKKI, MICHAEL J BOECKH, PER LJUNGMAN

311

SECTION V■Viral Infections

VIRUS STRUCTURE AND REPLICATION

Human cytomegalovirus (HCMV) is a member of the beta

( ) subfamily of the herpesviridae, along with human

her-pesvirus (HHV)-6 and HHV-7 The CMV virion is composed

of a double-stranded DNA genome encased in an icosahedral

capsid Surrounding the capsid is a region known as the

tegu-ment (or matrix) and an outermost lipid membrane containing

viral glycoproteins, which mediate viral binding to and entry

into the host cell

The genome contains approximately 230 thousand basepairs of DNA that encode approximately 200 proteins, and is

organized into long and short unique segments that are

flanked by inverted repeats (1,2) CMV genes are named based

on their position within each segment of the genome For

ex-ample, UL97 is the 97th open reading frame (ORF) in the

unique long segment Some genes also have names based on

historical usage or homologies to genes of other herpesviruses;

UL55, for example, is also known as glycoprotein B

CMV grows in a limited number of cell lines in the ratory, such as diploid human fibroblasts, endothelial cells,

labo-and macrophages During human infection, however, CMV

has been found in a wide range of cells, including endothelial

cells, epithelial cells, blood cells including neutrophils, and

smooth muscle cells (3) The presence of CMV in these cells

may be due to active replication within the cell, phagocytosis

of CMV proteins, or abortive (incomplete) replication, and

likely contributes to dissemination and transmission

The ability to persist in a latent state in which evidence ofviral replication is undetectable but replication-competent

virus is present is a hallmark of herpesviruses In the case of

CMV, little is known about the site or mechanisms of latency

Since CMV can be transmitted from seropositive blood donors,

a blood component is likely to be one site of latency Several

studies support the idea that cells of the granulocyte–monocyte

lineage harbor latent CMV (4–6) Transplantation of solid

or-gans clearly can transmit CMV, so it is possible that cells other

than those mentioned above can harbor and transmit latent

CMV However, whether the latently infected cell type in these

organs is transitory blood cells, macrophages, or permanent

cells is not yet clear

INTERACTION OF CMV WITH THE HOST IMMUNE SYSTEM Adaptive Immunity

The importance of a competent immune system in controllingCMV replication is manifested by the clear association of im-munosuppression with CMV disease The role of humoral im-munity in controlling CMV replication is not clear Antibodies

to multiple different CMV proteins, primarily glycoproteins B(gB) and H (gH), develop during infection (7–9) Althoughantibodies to gB and gH can neutralize the virus in cell cul-ture, they do not appear to prevent primary infection in adults,but rather may function to limit disease severity (10,11).Paramount in controlling CMV replication is T-cell medi-ated cellular immunity CMV provokes a robust CD8 cyto-toxic T lymphocyte (CTL) response, and the proportion ofcirculating CD8 T-cells in healthy individuals that are specificfor CMV antigens ranges from 10% to 40%, depending on theage of the person (12–17) Numerous CMV proteins are targeted

by the CD8 T-cell response, the most immunodominant onesbeing the gene products of UL123 (IE-1), UL122 (IE-2), andUL83 (pp65) (14,17–23) Lack of CMV-specific CD8 CTL re-sponses predispose to CMV infection, whereas reconstitution ofCMV-specific CD8 CTL responses after hematopoietic celltransplantation (HCT) correlates with protection from CMVand improved outcome of CMV disease (24–28)

After HCT, detectable CMV-specific CD4 responsesare associated with protection from CMV disease (24,29–31).The lack of CMV-specific CD4 cells is associated with lateCMV disease and death in patients who have undergone HCT(32) CMV-specific CD4 cells likely function at least in part

by helping to maintain robust CMV-specific CD8 cell sponses (28,33)

re-Innate Immunity

Innate immunity also functions to control CMV replication.CMV triggers cellular inflammatory cytokine productionupon binding to the target cell, mediated in part by the inter-action of gB and gH with toll-like receptor (TLR) 2 (34–36).Polymorphisms in TLR2 have been associated with CMV

infection after liver transplantation (37) In mouse studies,

TLR3 and TLR9 proved to be important components in limiting

murine cytomegalovirus (MCMV) replication (38,39)

Natural killer (NK) cells represent another arm of the

in-nate immune response and have been shown to limit MCMV

replication in mice (25,40–44) In humans, NK cell responses

increase during CMV infection after renal transplantation,

and a deficiency in NK cells is associated with severe CMV

infection (among other herpesviruses) (45,46) The genotype of

the donor activating killer immunoglobulin-like receptor (aKIR),

which regulates NK cell function, has recently been

demon-strated to influence the development of CMV infection after

allo-geneic HCT (47–49) The mechanisms behind these associations

are not fully understood and these findings require validation in

independent cohorts

Finally, polymorphisms in chemokine receptor 5 (CCR5)

and interleukin (IL)-10 have been associated with CMV

dis-ease, whereas polymorphisms in monocyte chemoattractant

protein 1 (MCP-1) are associated with reactivation after

allo-geneic HCT (50) Much more work needs to be done to

deter-mine the role(s) of these components of innate immunity in

regulating CMV replication in humans

Immune Evasion

An array of CMV genes has been found to function in immune

evasion For example, CMV has genes that inhibit apoptosis (51),

major histocompatibility complex (MHC)-I-restricted antigen

presentation (52), and interferon-mediated pathways (53–56)

CMV also encodes several homologues of cellular proteins,

in-cluding MHC class-I molecules, CCRs, IL-10, TNF receptors,

and CXC-1 homologues, that function to evade the host immune

response (57–61)

DIAGNOSTIC METHODS

The serologic determination of IgG and IgM has an important

role in determining a patient’s risk for CMV infection after

transplantation (see “Risk Factors” section) or during

im-munosuppressive therapy, but is not useful in the diagnosis of

CMV infection or disease

Growth of CMV in tissue culture takes several weeks,

limit-ing its clinical usefulness as a diagnostic tool Culture-proven

viremia is highly predictive of CMV disease, but is of limited

util-ity for screening since this finding frequently coincides with the

onset of symptomatic disease (62–64)

The shell-vial technique, in which monoclonal antibodies

are used to detect CMV immediate-early proteins in cultured

cells, can be performed within 18 to 24 h after inoculation This

assay is not sensitive enough to use for routine blood monitoring

(63), but is highly useful on bronchoalveolar lavage (BAL) fluid

in the diagnosis of CMV pneumonia (65)

The detection of the CMV pp65 tegument tein in peripheral blood leukocytes offers a rapid, sensitive, andspecific method of diagnosing CMV viremia In this assay, pe-ripheral leukocytes are spread on a glass slide, stained with afluorescent antibody directed against pp65, and the number ofpositive cells is reported per number of total leukocytes on theslide, thereby providing a rough quantitative assessment of thecirculating viral load In the transplant setting, a positive CMVpp65 assay has been shown to predict the development of inva-sive disease (66,67) Since this assay relies on the detection ofpp65 in circulating leukocytes, it may not be reliable in pa-tients with profound leukopenia The predictive value of thisassay has not been validated when performed on other bodyfluids such as BAL fluid

phosphopro-Quantitative polymerase chain reaction (qPCR) relies onthe amplification and quantitative measurement of CMVDNA PCR is the most sensitive method for detecting CMV(68), whereas at the same time maintaining high specificity Inaddition, it is very rapid, with results usually available within

24 h qPCR provides a direct quantitative measurement ofCMV viral load, which is an accurate predictor of CMV dis-ease after transplantation (32,69–72) qPCR testing has becomethe standard method for detecting CMV in blood (eitherwhole blood or plasma) and spinal fluid at many, if not most,institutions Although PCR has been used on BAL fluid (73),viral-load cut-offs have not been defined And even thoughthe sensitivity and negative predictive values are very high, thespecificity and positive predictive values are not known.The detection of CMV mRNA by nucleic acid sequence-based amplification (NASBA) on blood samples has proven to

be as useful as DNA PCR or p65 antigenemia for guiding emptive therapy after HCT (74,75) However, this method hasnot been as widely adopted as the pp65 antigenemia- or PCR-based assays

pre-The presence of characteristic CMV “owl’s eye” nuclearinclusions in histopathology specimens is useful in the diagno-sis of invasive CMV disease This method has relatively lowsensitivity, but can be enhanced by use of immunohistochemi-cal techniques to identify CMV antigens even when classic in-clusions may not be evident

of CMV) (76,77)

International definitions of CMV disease, broadly defined

as the presence of symptoms and signs compatible with CMV

CMV reactivation, delayed lymphocyte engraftment, andGVHD (86).

Other manifestations, including hepatitis, encephalitis,and infection of the bone marrow resulting in myelosuppres-sion, are all rare with current preventative strategies

RISK FACTORS Allogeneic HCT Recipients

In the setting of allogeneic HCT, the most important riskfactor is the serological status of the donor and recipient.CMV-seronegative patients who receive stem cells from aCMV-seronegative donor (D/R) have a very low risk ofprimary infection Primary infection can still occur if CMV

is transmitted in transfused blood products or is acquired viasexual contact or through contact with another individualwith primary CMV infection

Approximately 30% of seronegative recipients who ceive stem cells from a seropositive donor (D/R) will de-velop primary CMV infection due to transmission of latentCMV via the allograft Although the risk of CMV disease islow due to pre-emptive treatment of CMV infection, mortalitydue to bacterial and fungal infections in these patients ishigher than in similarly matched D/R transplants (18.3%

re-vs 9.7%, respectively) (89) The reason for this is not entirelyclear, one hypothesis being that CMV infection after HCT hasadditional immunomodulating effects (indirect effects) thatincrease a patient’s susceptibility to infection with other, unre-lated organisms

Without prophylaxis, approximately 80% of seropositive patients will experience CMV infection after allo-geneic HCT Again, current preventative strategies haveresulted in a substantial decrease in the incidence of CMV dis-ease, which had historically occurred in 20% to 35% of thesepatients (90) Although a CMV-seropositive recipient is athigher risk for transplant-related mortality (TRM) than aseronegative recipient (91,92), the impact of donor serostatuswhen the recipient in seropositive remains controversial Somestudies have reported a beneficial effect of having seropositivedonor with regards to a reduction in relapse- or nonrelapse-related mortality (NRM), whereas other studies have found nosuch benefit (93–104) A large CIBMTR study is presently under-way to reconcile these controversial findings However, althoughthe effects on NRM and overall survival are controversial, thisserological combination has been reported as a risk factor fordelayed CMV-specific immune reconstitution (105–108), CMVreactivation (106,109), late CMV recurrence (110), and CMV dis-ease (72,106,111)

CMV-Other risk factors for CMV infection after allogeneic HCTinclude the use of steroids at doses greater than 1 mg/kg bodyweight/day, T-cell depletion, acute and chronic GVHD, and theuse of mismatched or unrelated donors (69,72,111–115)

end-organ involvement along with the detection of CMV

using a validated method in the appropriate clinical specimen,

have been published (78) Fever is a common manifestation,

but may be absent in patients receiving high-dose

immuno-suppression Almost any organ can be involved in CMV

dis-ease and therefore CMV infection has protean manifestations

Pneumonia is the most important clinical manifestation

of CMV disease due to its high associated mortality Patients

who have undergone autologous or allogeneic HCT have

mortality rates of 60% to 90% (79–81) This unacceptably high

mortality rate has not changed much in the past 20 years,

indi-cating that much more work needs to be done in order to

opti-mize the management of these patients

CMV pneumonia often manifests with fever, tive cough, hypoxia, and interstitial infiltrates on radiography

nonproduc-Rarely, nodules may be observed on radiography The onset of

symptoms can occur over 1 to 2 weeks, often times with rapid

progression to respiratory failure and the requirement for

mechanical ventilation The diagnosis of CMV pneumonia is

established by detection of CMV by shell-vial culture, or

his-tology in BAL or lung biopsy specimens in the presence of

compatible clinical signs and symptoms Pulmonary shedding

of CMV is common, but CMV detection in BAL from

asymp-tomatic patients who underwent routine BAL screening at

day 35 after HCT was predictive of subsequent CMV

pneu-monia in approximately two thirds of cases (82) Therefore,

the presence of CMV in a BAL specimen in the absence of

clinical evidence of CMV disease must be interpreted with

caution We do not recommend PCR testing on BAL fluid

since there is little data correlating CMV DNA detection by

PCR in BAL fluid with CMV pneumonia However, due to

the high negative predictive value afforded by its high

sensi-tivity, a negative PCR result can be used to rule out the

diag-nosis of CMV pneumonia (73)

CMV can affect any part of the gastrointestinal tract fromthe esophagus to the colon Esophagitis typically results in

odynophagia, whereas abdominal pain and hematochezia

occur with colitis Ulcers extending deep into the submucosal

layers are seen on endoscopy, and visual differentiation of

these lesions from other processes that may affect the

gastroin-testinal tract in these populations, such as graft-versus-host

(GVHD) disease, is often difficult The diagnosis of

gastroin-testinal disease relies on detection of CMV in biopsy specimens

by culture and/or histology Given the relative lack of

sensitiv-ity of each method, both methods should be used on biopsy

specimens to diagnose CMV disease Notably, gastrointestinal

disease can occur in the absence of CMV detection in the blood

(83,84)

Retinitis is relatively uncommon after HCT (85–88)

Decreased visual acuity or blurred vision are typical

present-ing symptoms, and approximately 60% of patients will have

involvement of both eyes (86) Most cases present later than

day 100 after transplantation and are associated with prior

Whether the source of stem cells (peripheral blood vs bone

mar-row) has a significant impact on the development of CMV

infec-tion and disease is not clear, as several studies have yielded

conflicting results (111,115–117) Interestingly, the use of

sirolimus for GVHD prophylaxis appears to protect against

CMV infection, possibly due to the inhibition of cellular

signal-ing pathways that are co-opted by CMV dursignal-ing infection for

synthesis of viral proteins (111,118)

Late CMV Infection after Allogeneic HCT

Whereas CMV was typically seen by 100 days after allogeneic

HCT (119), in the current era of pre-emptive ganciclovir

ther-apy, it has become a significant problem after day 100 following

allogeneic HCT (32,110,120) In the absence of specific

preven-tative measures, 15% to 30% of allogeneic HCT patients will

experience late CMV infection and 6% to 18% will

conse-quently develop the disease (32,69,110,121–123) Late CMV

in-fection is strongly associated with NRM (110) Several factors

predict the development of late CMV infection (Table 22.1)

(24,30,32,110,112) Measures such as prolonged courses of

ther-apy and continued weekly surveillance (Table 22.1) are

war-ranted in these patients in order to reduce the risk of late CMV

disease (32,123,124)

Nonmyeloablative HCT

The use of matched, related nonmyeloablative conditioning

regimens generally results in a less CMV infection and disease

early after HCT compared to standard myeloablative

regi-mens (113,124) However, by 1 year after HCT, the risk of

CMV infection and disease is equal among nonmyeloablative

and myeloablative groups (124,125) Conditioning regimens

that include T-cell depletion show no reduction in CMV after

nonmyeloablative transplantation compared to myeloablative

regimens (126), and matched, unrelated nonmyeloablative

transplantation carries the same risk of CMV infection anddisease as does myeloablative transplantation (124)

Autologous HCT and Umbilical Cord Blood Transplantation

After autologous transplantation, approximately 40% ofseropositive patients will have detectable CMV infection(79,127) Although CMV disease is rare after autologous trans-plantation (116,128–130), the outcome of CMV pneumonia issimilar to that after allogeneic HCT (79,131,132) Risk factorsfor CMV disease after autologous transplantation includeCD34 selection, high-dose corticosteroids, and the use oftotal-body irradiation or fludarabine as a part of the condition-ing regimen (116) Therefore, although CMV is not typicallyconsidered a significant pathogen after autologous HCT, cer-tain patients who are at high risk for CMV in this setting meritroutine surveillance and pre-emptive therapy

Umbilical cord blood transplantation (CBT) is a techniquethat is now utilized when a suitable donor for bone marrow orperipheral blood stem cell transplantation is not available (133).Since most infants are born without CMV infection, the trans-planted allograft is almost always CMV-negative AmongCMV-seropositive recipients who do not receive antiviral pro-phylaxis, the rate of CMV infection after CBT is 40% to 80%,with one study reporting 100% (134–138) When patients re-ceive prophylaxis with high-dose valacyclovir after CBT, itdoes not appear that CBT entails a significantly greater risk ofCMV infection and disease than does peripheral blood stemcell or bone marrow transplantation (115)

Impact of Novel Immunosuppressive Agents

The increasing use of immunomodulating monoclonal bodies in the setting of HCT and hematological malignanciesposes a new risk for CMV infection (139) Alemtuzumab is an

Risk Factors, Surveillance Strategies, and Treatment

• Risk factors -CMV infection or disease before day 100, or use of prophylaxis (ganciclovir, valganciclovir, foscarnet, and cidofovir), PLUS any one of

• Lack of CMV-specific T-cell immune reconstitution

• Acute or chronic GVHD requiring systemic immunosuppression

• Lymphopenia

• Mismatched/unrelated transplant

• Surveillance -Weekly PCR screening until

• Immunosuppression tapered ( 0.5 mg/kg/day prednisone, no further anti-T-cell therapy), and

• Three consecutive negative assays

• Pre-emptive therapy -IV ganciclovir or oral valganciclovir (if oral absorption is reliable) induction until viral load declines (at least 1 week) or foscarnet in the setting of neutropenia

-Maintenance therapy until viremia is cleared

anti-CD52 monoclonal antibody that results in CD4 and

CD8 lymphopenia that can last for up to 9 months after

ad-ministration CMV infection typically occurs during the

pe-riod of maximal immunosuppression, which is 3 to 6 weeks

after alemtuzumab therapy (140,141) Patients who received

alemtuzumab as a part of the conditioning regimen or for

GVHD prophylaxis during HCT experienced a higher rate of

CMV infection compared to matched controls not receiving

alemtuzumab (142,143)

PREVENTION OF CYTOMEGALOVIRUS INFECTION AND DISEASE

Pre- and Posttransplant Risk Reduction

CMV serological status of the recipient and donor should be

assessed as early as possible prior to HCT, as this is the most

important predictor of subsequent CMV infection For the

seronegative recipient, the main goal is to prevent primary

CMV infection Therefore, recipients who are CMV

seronega-tive before allogeneic HCT should ideally receive a graft from

a negative donor Weighing the factor of donor

CMV-serostatus compared to other relevant donor factors, such as

human leukocyte antigen (HLA)-match, is difficult No data

exist indicating whether study HLA-matching is more

impor-tant compared to CMV-serostatus in affecting a good outcome

for the patient Given the choice, an antigen-matched donor

for HLA-A, B, or DR would most likely be preferred to a

CMV-negative donor For lesser degrees of mismatch

(allele-mismatches or (allele-mismatches on HLA-C, DQ, or DP), the

CMV-serostatus of donor should be considered a factor even if

the match was poorer Compared to other donor factors such

as age or blood group, a CMV-seronegative donor would have

preference

The transfusion of blood products represents a significantsource for CMV transmission in D−/R− patients (144) To re-

duce this risk, blood products from CMV seronegative donors

or leukocyte-reduced, filtered blood products should be used

in this setting (145–147) It is not clear which strategy is the

most effective (148,149), and no controlled study has

investi-gated whether there is an extra benefit from the use of both

methods

Immunoprophylaxis

Intravenous immune globulin (IVIG) is not reliably effective

as prophylaxis against primary CMV infection One study

demonstrated a reduction in the rate of CMV infection but not

disease with the use of CMV-specific immunoglobulin (150),

whereas another study was unable to confirm protection from

infection using anti-CMV hyperimmune globulin (151)

Similarly negative results were observed using a CMV-specific

monoclonal antibody (152) Likewise, the effect of munoglobulin on reducing CMV infection in seropositive pa-tients is modest, and no survival benefit among those receivingimmunoglobulin has been reported in any study or meta-analysis (153–158) Therefore, the prophylactic use of immuneglobulin is not recommended

im-Antiviral Prophylaxis and Pre-Emptive Therapy

The prophylactic or pre-emptive use of antiviral agents afterHCT has markedly reduced the incidence of early CMV diseaseand has improved survival among certain high-risk populations(63,112,159) Prophylaxis denotes the routine administration ofantivirals to all at-risk patients regardless of the presence of ac-tive CMV infection Pre-emptive therapy, on the other hand,withholds antiviral therapy until CMV infection is detected, butprior to the development of CMV disease

Both prophylaxis and pre-emptive therapy have their efits and drawbacks Since prophylaxis involves the treatment

ben-of all at-risk patients, close monitoring is not required whenganciclovir or foscarnet are used, making this the easier strat-egy conceptually and useful in situations where rapid, sensitiveCMV diagnostic methods are not available Additionally, pro-phylaxis may prevent the indirect effects associated with CMVinfection However, since not all at-risk patients will experi-ence CMV infection, prophylaxis strategies result in some pa-tients receiving the drug unnecessarily, thereby exposing thepatient to potential drug-related toxicities without discernablebenefit This is not an issue with pre-emptive treatment, since

by definition all patients who receive treatment will have tive CMV infection

ac-The success of the pre-emptive treatment strategy islargely dependent on the early detection of viremia This, inturn, depends on access to rapid, sensitive CMV surveillancemethods and on strict adherence to a surveillance-testingschedule By allowing a limited amount of viral replication,pre-emptive therapy may stimulate immune responses andthereby promote CMV-specific immune reconstitution (24).Since both strategies are equally effective in preventing CMVdisease (159), most transplant centers have moved towardpre-emptive strategies as pp65 antigenemia and DNA PCR-based diagnostics techniques have become readily available(160–162)

More recently, there has been great interest in utilizingmethods to determine CMV-specific immune reconstitutionafter HCT as an additional means to stratify risk of CMV in-fection and disease (immune monitoring) and further tailorsurveillance and pre-emptive therapy strategies The types ofassays used, their strengths and limitations, and their predic-tive value in terms of CMV infection and disease after trans-plantation have been extensively reviewed elsewhere (12,163).The utility of measuring T-cell responses as a guide for with-holding therapy was evaluated in a small pilot study involving

HCT recipients more than 100 days after transplant (105).

Although promising, the use of immune monitoring in this

fashion requires validation in larger, randomized trials before

it can be recommended

Antiviral Agents

Several antiviral drugs that demonstrate activity against CMV

are available once the decision is made to employ either

pro-phylaxis or pre-emptive treatment (Table 22.2) High-dose

acyclovir reduces the risk for CMV infection and possibly

dis-ease (164,165) Valacyclovir is the valin-ester prodrug of

acy-clovir and is better absorbed, thereby attaining higher serum

concentrations than acyclovir High-dose valacyclovir is more

effective than acyclovir in reducing CMV infection and the

need for pre-emptive therapy with ganciclovir after HCT,

al-though the impact of this on survival after HCT is not clear

(166) Routine monitoring for CMV infection is still required

if valacyclovir or acyclovir prophylaxis is used

Ganciclovir is a nucleoside analogue of guanosine thatacts as a competitive inhibitor of deoxyguanosine triphos-phate incorporation into viral DNA A CMV gene, UL97,encodes a phosphotransferase that converts ganciclovir toganciclovir monophosphate Cellular enzymes then convertganciclovir monophosphate to the active triphosphate form.Ganciclovir is currently the first-line agent for CMV prophy-laxis and pre-emptive treatment barring contraindications.Intravenous ganciclovir has been demonstrated to reduce therisk of CMV infection and disease compared to placebo, butdid not improve overall survival (159,167–169) Neutropeniaoccurs in up to 30% of HCT recipients during ganciclovirtherapy (170), thereby placing the patient at risk of invasivebacterial and fungal infections (159,167,170) Neutropeniaoften responds to dose reduction and support with granulo-cyte-colony stimulating factor, but occasionally discontinua-tion of ganciclovir is required, in which case foscarnet istypically the second-line agent of choice Measurement ofganciclovir concentrations can be helpful to guide therapy

CMV Disease after HCT

Dose Based on Reason for Use

Treatment of

reactions (IV), PO: 800 mg q.i.d.

nephrotoxicity, ( 40 kg) or 600 headache, and nausea mg/m 2 q.i.d ( 40 kg) Valacyclovir Gastrointestinal upset, 2 g t.i.d to q.i.d ( 40 kg) Not recommended Not recommended

neutropenia, and TTP/HUSa

thrombocytopenia, b.i.d., maintenance: b.i.d., maintenance: mg/kg b.i.d.,

5 mg/kg/day

900 mg/kg/day ( 40 kg)

3–5 mg/kg/week  2–3 doses 3–5 mg/kg/week

for 3 doses maintenance not established maintenance

3–5 mg/kg/every other week

b.i.d or t.i.d.

aCausality remains to be determined.

bTypically observed with the concomitant use of nephrotoxic immunosuppressive agents.

c

and reduce the risk for toxicity especially in the situation of

pre-existing renal impairment

Valganciclovir is the orally available prodrug of clovir and achieves serum concentrations at least equivalent to

ganci-intravenous ganciclovir (171–173) The results of several

un-controlled studies suggest that valganciclovir is comparable to

intravenous ganciclovir in terms of efficacy and safety when

used as pre-emptive therapy after allogeneic HCT (171,

174–176) As of the writing of this chapter, no data comparing

valganciclovir to intravenous ganciclovir in the setting of a

randomized, controlled trial have been published Preliminary

data from a randomized trial have been presented indicating

little or no difference in efficacy or toxicity compared to

intra-venous ganciclovir (177) Until more data are available,

cau-tion should be exercised when choosing valganciclovir as

pre-emptive therapy

Foscarnet is a pyrophosphate analogue that binds directly

to and competitively inhibits the CMV DNA polymerase

Foscarnet is generally considered to be as effective as

ganci-clovir for pre-emptive therapy after allogeneic transplantation

(178) However, three uncontrolled studies have documented

cases of breakthrough CMV disease during foscarnet therapy

(179–181) These findings, combined with commonly

encoun-tered toxicities of foscarnet, have led to the use of foscarnet as a

second-line agent when ganciclovir is contraindicated or not

tolerated

Cidofovir is a cytosine nucleotide analogue that does notrequire phosphorylation by viral enzymes for antiviral activity

Cellular enzymes convert cidofovir to cidofovir triphosphate,

which then inhibits the CMV DNA polymerase The long

half-life of cidofovir allows a once-per-week dosing schedule

However, the major toxicity with cidofovir—acute renal

tu-bular necrosis—limits its utility after HCT, and it should

therefore be considered third-line therapy after ganciclovir

and foscarnet (182)

Monitoring for CMV Infection and Initiation of

Pre-Emptive Therapy

qPCR assays for CMV DNA are increasingly used for

surveil-lance because they offer two advantages First, they are more

sensitive than pp65 antigenemia, thereby prompting treatment

initiation in cases of CMV disease that have been missed with

the pp65 antigenemia assay (159) Additionally, the quantitative

nature of the assay may enable the development of

institution-specific viral load thresholds for beginning treatment,

thereby avoiding unnecessary treatment of patients who are

at low risk of progression to disease It has been reported that

the initial viral load as well as the viral load kinetics are

im-portant as risk factors for CMV disease (183) Currently,

there are no validated universal viral load thresholds, and

such thresholds would be difficult to establish due to

differ-ences in assay performance and testing material (whole blood

vs plasma) (184)

With the exception of those receiving ganciclovir laxis, all patients who have undergone allogeneic HCT, re-gardless of pretransplant donor and recipient serostatus,should be monitored on a weekly basis for CMV infectionusing pp65 antigenemia, DNA PCR, or mRNA NASBA.Although CMV infection is rare in D/Rpatients, routinemonitoring was effective in identifying CMV infection andpreventing disease in a large cohort (185) Monitoring is gener-ally performed until day 100 after engraftment or longer in pa-tients at risk for late CMV disease (Table 22.1) The idealduration and frequency of CMV monitoring in the later trans-plantation periods have not been determined (123,124).Routine monitoring of autograft recipients is not recom-mended, with the exception being high-risk patients as de-scribed above (161,162,186)

prophy-A general approach to prophylaxis and pre-emptivetherapy is presented in Table 22.3 If a pre-emptive strategy isused, the initial detection of CMV in peripheral blood afterallogeneic HCT should prompt the initiation of antiviraltherapy and a thorough evaluation of the patient in order toassess for signs and symptoms concerning for CMV disease(186) Various durations of pre-emptive antiviral treatmenthave been explored Initial studies administered gancicloviruntil day 100 after engraftment, which ultimately entailedapproximately 6 to 8 weeks of therapy in the average recipi-ent Studies from the mid-1990s using short courses (2 to 3week) of ganciclovir based on negative PCR assays at the end

of therapy were generally effective; however, resumption ofpre-emptive therapy was necessary in approximately 30% ofpatients (63,178,188) Most centers now continue antiviraltreatment until the designated viral marker is negative andthe patient has received at least 2 weeks of antiviral therapy

If less sensitive markers than DNA PCR, such as the pp65antigenemia assay, are used, then pre-emptive therapyshould be continued until two negative assays are obtained(178) If a patient is still viremic by PCR or pp65 antigenemiaassay after 2 weeks of therapy, treatment should be extended

at maintenance dosing until clearance is achieved It has beenshown that a low rate of viral load decrease is a risk factor forlater-occurring CMV disease (72)

SPECIAL POPULATIONS

Patients with CMV infection occurring prior to planned geneic HCT have a very high risk of death after transplanta-tion (189) After transplantation, a patient with documentedpretransplant CMV infection should either be monitored forCMV very closely (i.e., twice weekly), or be given prophylaxiswith ganciclovir or foscarnet

allo-The optimal approach to CMV after CBT is not clear.One study described successful pre-emptive treatment withganciclovir (138), whereas another combined high-dosevalacyclovir prophylaxis with continued monitoring and

aIncludes use of total body irradiation (TBI) in conditioning, r

bMust be combined with active surveillance for CMV infection. Modified fr

pre-emptive therapy (115) Due to initial experience in Seattle

suggesting a high rate of infection and disease early

posttrans-plant, the latter approach, coupled with ganciclovir

prophy-laxis for the week prior to transplant and continued CMV

surveillance posttransplant, has been adopted

Antiviral Resistance

Drug resistance is relatively uncommon after HCT but can

occur with all drugs used for the treatment and prophylaxis of

CMV Risk factors for drug resistance include prolonged

(months) antiviral therapy, intermittent low-level viral

repli-cation in the presence of drug due to profound

immunosup-pression or suboptimal drug levels, and lack of prior immunity

to CMV (190) Drug resistance should be suspected in patients

that are on an appropriate dosage of an antiviral drug and who

have increasing quantitative viral loads for more than 2 weeks

After start of antiviral therapy in treatment-nạve patients, an

increase in the viral load will occur in approximately one third

of patients and is likely due to the underlying

immunosup-pression, not true drug resistance (67) If a patient has received

ganciclovir before transplantation or if viral load increases

occur in the late setting where most patients are not antiviral

drug nạve anymore, drug resistance should be suspected

An approach to the patient with suspected drug-resistantCMV is presented in Figure 22.1 Since ganciclovir is used as a

first-line agent in most cases of CMV infection, resistance to

this antiviral is the most commonly encountered problem.Resistance is most often due to mutations in the UL97 gene,and less often to mutations in the UL54-encoded DNA poly-merase UL97 mutations that confer resistance have been de-scribed and genotypic assays are available for diagnosticanalysis in reference laboratories (191) Phenotypic testing can

be performed, but this type of assay is time-consuming and istherefore not as helpful as rapid genotypic testing in guidingpatient management However, since different UL97 muta-tions confer varying degrees of ganciclovir resistance, somecases of genotypically defined ganciclovir-resistant CMV maystill respond to ganciclovir therapy (192) and therefore caremust be taken in interpreting genotype results

If ganciclovir resistance is documented or suspected, carnet is generally the second-line agent of choice Unlike gan-ciclovir, foscarnet activity is not dependent on phosphorylation

fos-by the UL97 gene product; thus, CMV that has acquired ciclovir resistance due to UL97 mutations will still be suscepti-ble to foscarnet (193) Studies evaluating the utility ofcombination therapy of foscarnet and ganciclovir for ganci-clovir-resistant CMV disease have been inconclusive andtherefore this strategy is not routinely recommended (194).Resistance to foscarnet can occur and is due to mutations inUL54 Interestingly, cross-resistance between foscarnet andganciclovir does not occur, as mutations in UL54 conferringresistance to foscarnet occur in regions distinct from those con-ferring ganciclovir resistance (195)

gan-Suspicion of ganciclovir (GCV) or valganciclovir (VGCV)resistance:

Rising viral load after two weeks of ongoing GCV or VGCV therapy Prior GCV or VGCV exposure

Symptomatic disease after or during extended GCV or VGCV therapy

Leflunomide Artesunate

UL54 genotyping

Pending UL54 genotyping results:

If high-risk patient, symptomatic disease,

or rapidly increasing viral load, switch to foscamet

If stable viral load and clinically silent infection, continue GCV or VGCV at current dose or consider higher-dose GCV therapy

FIGURE 22.1 Approach to the patient with suspected ganciclovir–valganciclovir-resistant CMV.

Since cidofovir is not phosphorylated by the CMV UL97

gene product, it is active against ganciclovir-resistant UL97

mu-tants However, certain UL54 mutations can confer causes

cross-resistance between ganciclovir and cidofovir (193,195) Therefore,

additional genotype testing of UL54 is indicated to evaluate for

potential cross-resistance conferring mutations There is limited

experience with cidofovir for treatment of ganciclovir-resistant

CMV, and its toxicity profile precludes its routine use as

second-line treatment for ganciclovir-resistant CMV

Drugs presently under evaluation, such as maribavir, may

also provide therapeutic options in the future Maribavir

in-hibits the CMV UL97 kinase and is active and against wild-type

and ganciclovir-resistant CMV strains (196) Other drugs with

possible anti-CMV activity include the arthritis drug

lefluno-mide and the antimalaria compound artesunate (197–199)

None of these are approved by European or American

regula-tory authorities for the treatment of CMV Another potentially

useful approach is to use the immunosuppressive drug sirolimus

as adjunct therapy since it may impair CMV replication by

reg-ulating cellular signaling pathways, and has in fact been shown

to reduce the risk of CMV reactivation after HCT and renal

transplantation (111,118)

Vaccination

Given the costs and toxicities associated with antiviral therapy, a

vaccine to prevent CMV infection would be of substantial

bene-fit Indeed, the Institute of Medicine has given the development

of a CMV vaccine the highest priority (200) Thus far, most

vac-cine candidates have yielded mixed results (201) Recently, a

phase I trial of a bivalent vaccine containing plasmids encoding

gB and pp65 showed promising results in CMV-seronegative

vaccine recipients, but not CMV-seropositive recipients, which

is a limitation common to many CMV vaccine candidates (202)

Since it is the seropositive transplant patient who is at greatest

risk for CMV infection, more work is required to provide

pro-tective immunity in these patients after HCT

Management of CMV Disease

As mentioned earlier, the diagnosis of CMV disease requires

documenting the presence of CMV in the appropriate

diagnos-tic specimen, coupled with symptoms and signs consistent with

CMV For gastrointestinal disease, standard therapy generally

entails induction treatment with an intravenous antiviral, most

often ganciclovir, for 3 to 4 weeks followed by several weeks of

maintenance Shorter courses of induction therapy (2 weeks)

are not as effective (203) There is no role for concomitant

IVIG in the treatment of gastrointestinal disease (204)

Recurrence of gastrointestinal disease may occur in

approxi-mately 30% of patients in the setting of continued

immuno-suppression and such patients may benefit from secondary

prophylaxis with maintenance antivirals until

immunosup-pression has been reduced Foscarnet can be used as an

alternative if neutropenia is present Valganciclovir as nance treatment for gastrointestinal disease has not been wellstudied but may be reasonable if symptoms are improved, sys-temic viremia is suppressed, and there are no factors thatwould impair the absorption of an orally administered med-ication, such as severe gastrointestinal GVHD

mainte-Several studies established the current standard of care forCMV pneumonia, which is treated with ganciclovir (or foscar-net as an alternative agent) in combination with IVIG(205–208) These studies showed improved survival rates com-pared to historical outcome results There does not appear to be

a specific advantage of CMV-specific immune globulin Ig) compared to pooled immunoglobulin (206) However, inspecific clinical situations, such as volume overload, CMV-Igmay be preferred Several studies have raised doubt regardingthe beneficial effect of concomitant IVIG (209,210) However,although the use of IVIG remains a controversial topic, it is stillconsidered as standard of care at many centers until more dataregarding its utility are available

(CMV-CMV retinitis is typically treated with systemic clovir, foscarnet, or cidofovir, with or without intraocular gan-ciclovir injections or implants (86,211–213) Fomivirsen is anantisense RNA molecule that targets mRNA encoded byCMV and is approved as second-line therapy for CMV retini-tis in patients with AIDS (214)

ganci-Other manifestations of CMV disease, such as hepatitisand encephalitis, are uncommon and are typically managedwith intravenous ganciclovir The duration of therapy forthese manifestations has not been well established and should

be tailored to the individual patient

Adoptive Immunotherapy

HCMV-specific T-cells can be generated via several differentmechanisms in attempts to passively restore cellular immu-nity after transplantation (12) Several groups have reported abeneficial impact of adoptive immunotherapy on HCMVviral loads in patients who had undergone HCT (215).Despite these seemingly promising results, scientific ques-tions remain unanswered (such as the optimal cell type anddose for infusion) and technical hurdles persist (availability ofclinical grade reagents) that preclude adoptive immunother-apy from becoming a routine clinical procedure at the currenttime This topic is discussed in more detail in chapter 46

CONCLUSIONS AND FUTURE DIRECTIONS

Although much progress has been made in the prevention ofCMV disease after HCT over the past decade, several issuesremain Increasing the specificity of pre-emptive therapy bycombining detection of viremia with monitoring of CMV-specific T-cell immunity merits evaluation in a randomized

trial CMV pneumonia still carries a poor prognosis that has not

changed in 20 years Therefore, other strategies, such as

combi-nation antiviral therapy, should be studied in this setting in

order to improve outcome Additionally, the benefit provided

by IVIG in the treatment of CMV pneumonia needs to be

de-termined New treatment and vaccination options for CMV

are urgently needed because the currently available drugs have

major limitations, such as toxicity and resistance Novel drugs

such as lipid cidofovir (216), a novel nonnucleoside inhibitor

(217), as well as leflunomide and artesunate, deserve a

system-atic evaluation Vaccination may also play an increasing role in

the future prevention of CMV infection and disease

ACKNOWLEDGMENTS

Per Ljungman had support from Karolinska Institutet

Research Funds and the Swedish Children’s Cancer Fund

Michael Boeckh had support from the National Institute of

Health (NIH CA 18029)

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RAYMUND R RAZONABLE, AJIT P LIMAYE

328

EPIDEMIOLOGY AND PATHOGENESIS

Cytomegalovirus (CMV) is the major pathogen that affects the

outcome of solid organ transplantation (1) Not only is CMV a

common infection among all solid organ transplant

popula-tions, but also its clinical impact translates into significant

morbidity and mortality (1) CMV is a ubiquitous -herpesvirus

that infects most humans (2) The prevalence rate of CMV

seropositivity in the United States is estimated to be 60% among

individuals who are at least 6 years old (2) The seroprevalence

rate increases directly with age, so that 90% of adults who are at

least 80 years old are CMV seropositive (2) Primary infection

with CMV is acquired through contact with infected body

flu-ids such as saliva, urine, or genital secretions from

CMV-infected individuals (3) The vast majority of primary CMV

infections occur during childhood through early adulthood

(3) Clinically, primary CMV infection in immunocompetent

individuals is manifested either as an asymptomatic illness in

the majority of individuals or occasionally as a benign

infec-tious mononucleosis-like syndrome characterized by fever and

lymphadenopathy (3)

The immune response to CMV is initiated upon the

recog-nition of CMV virions and antigens by pathogen-recogrecog-nition

receptors, such as the Toll-like receptors, which are expressed

on macrophages, dendritic cells, and other innate immune cells

(4–6) The outcome of this interaction between CMV and

in-nate immune cells is the secretion of interferon-, tumor

necro-sis factor (TNF)-, interleukins, and other cytokines involved

in the control of the earliest stages of viral infection (4–6) In

addition, innate immune activation leads to the upregulation of

costimulatory molecules that direct the development,

matura-tion, and proliferation of lymphocytes responsible for

CMV-specific cell-mediated and humoral immunity (4–8) However,

CMV has developed immune evasion mechanisms so that

CMV-specific cellular and humoral immune responses do not

completely eliminate the virus Instead, CMV infection

univer-sally leads to lifelong latency, with intermittent periods of

reac-tivation and low-level persistence (9–11)

Cells that allow for CMV latency and/or viral persistence

are widely distributed in the human body, including the

he-matopoietic progenitor cells (12), peripheral blood mononuclear

cells (3,13), polymorphonuclear leukocytes (14), and phages (15) CMV also infects and may persist in fibroblasts,smooth muscle cells, and endothelial cells (16) The wide distri-bution of CMV-infected cells in the various tissues and organs,such as the bone marrow, liver, kidney, lungs, and gastrointesti-nal tract (17–20), allows for the efficient transmission of CMV

macro-to susceptible hosts during organ and tissue transplantation

Mechanisms of Acquiring Cytomegalovirus Infection after Solid Organ Transplantation

The three major mechanisms of acquiring CMV infection aftersolid organ transplantation are (i) primary infection, (ii) reacti-vation infection, and (iii) superinfection

Primary Cytomegalovirus Infection (CMV D /R)

Primary CMV infection occurs when a CMV-seronegative tient (CMV R) receives an allograft from a CMV seropositivedonor (CMV D) This CMV D/R serologic mismatch isestimated to occur in 15% to 25% of all solid organ transplanta-tion (1) In the absence of antiviral prophylaxis, a CMV D/Rserologic mismatch will almost always result in the transmission

pa-of CMV to the susceptible transplant recipient, where it cancause clinically severe primary CMV disease Less commonly,primary CMV infection may occur in a CMV R transplant re-cipient when CMV is transmitted through transfusion of bloodproducts from CMV seropositive donors or through naturaltransmission routes in the community (21,22); these latter twomechanisms account for the occurrence of CMV infection anddisease in CMV D/R solid organ transplant recipients

Reactivation Infection (CMV D /R)

Reactivation infection occurs when endogenous latent CMV in

a CMV seropositive (CMV R) transplant recipient vates during the periods of impaired immunity after solidorgan transplantation Because patients have preexisting CMV-specific cell-mediated and humoral immunity, the degree ofCMV reactivation and replication in CMV R patients is rela-tively lower when compared to the primary CMV infection inCMV D/R patients and hence a relatively lower risk ofdeveloping symptomatic CMV disease (23,24)

reacti-Superinfection (CMV D /R)

Superinfection (also known as reinfection) occurs when a

CMV R transplant recipient is infected with an exogenous

CMV strain from a CMV seropositive donor (or other

ex-ogenous source), and subsequently, either the donor

allograft-transmitted exogenous CMV or recipient-derived endogenous

CMV, or both, reactivate to cause clinical disease after solid

organ transplantation (25) In the majority of cases,

donor-derived CMV is the predominant virus that reactivates in

CMV D/R patients (25–27), suggesting a potentially

in-complete degree of cross-protection against other viral strains

Mechanisms of Cytomegalovirus Reactivation

after Solid Organ Transplantation

Table 23.1 lists some of the risk factors associated with CMV

infection and disease after solid organ transplantation (1)

Central to many of these factors is the secretion of various

proinflammatory cytokines and catecholamines (28–30),

most notably TNF-, which has been implicated in many

studies as a potent transactivator of CMV reactivation (31)

In vitro, TNF- stimulated the activity of CMV

immedi-ate-early (CMV-IE) enhancer/promoter region in a human

monocytic cell line (32,33) Stimulation of the TNF-1

receptor results in the activation of protein kinase C and

nu-clear factor-kappa B (NF-B), which undergoes nuclear

translocation and binds within the CMV-IE

enhancer/pro-moter region (28,34,35), triggering a cascade of events that

lead to CMV reactivation (36) Likewise, catecholamines

re-leased during periods of stress, whether physiologic or in

response to medical illness, could stimulate CMV-IE enhancer/

promoter activity (34,35) through the cyclic adenosine

mono-phosphate (cAMP) pathway Collectively, inflammation,stress, and other factors that influence cAMP and NF-B sig-naling pathways contribute to the reactivation of CMV fromlatency after solid organ transplantation Indeed, clinicalconditions characterized by high levels of TNF-, such asbacterial sepsis and allograft rejection, have been signifi-cantly associated with CMV infection in the transplant andnontransplant settings (37–40)

Risk Factors for Cytomegalovirus Infection after Solid Organ Transplantation

Without antiviral therapy, up to 55% of solid organ transplantrecipients with CMV reactivation will progress to developCMV disease (41–43) The rates of CMV disease vary according

to the type of organ transplantation (Table 23.2) (1) In general,the occurrence of CMV disease after solid organ transplantation

is influenced by many interrelated factors that are categorizedinto (i) those that favor disease progression (e.g., delayed im-mune recovery, immunosuppressive drugs, viral load, viralcoinfections) and (ii) those that control viral replication (e.g.,CMV-specific immunity, antiviral therapy) (Table 23.1)

Cytomegalovirus D /R Serologic Mismatch

A CMV D/R serologic mismatch is considered as the mostimportant variable that predicts CMV disease after solid organtransplantation It is therefore imperative that CMV im-munoglobulin G screening is performed on all transplant donorsand potential transplant candidates so as to allow for risk stratifi-cation and guide the intensity of CMV prevention strategy aftertransplantation (44) Historical data suggest that up to 70% of allCMV D/R solid organ transplant recipients, which lack

Factors that Influence

Factors that Influence Progression to CMV Disease

Allogeneic stimulation Lack of preexisting CMV-specific immunity Preexisting CMV-specific

Mycophenolate mofetil ( 2 g/d) High-dose methylprednisolone

Critical illness Surgical procedure Bacterial and fungal sepsis Abbreviations: CMV, cytomegalovirus; OKT3, muromonab-CD3; ATG, antithymocyte globulin; ALG, antilymphocyte globulin; D /R, donor positive/recipient negative; R, recipient positive.

Disease after Solid Organ Transplantation

CMV-specific cellular and humoral immunity, will develop

pri-mary CMV disease if they do not receive any CMV prevention

strategy (Table 23.2) (1) The absence of preexisting

CMV-spe-cific immunity in CMV D/R solid organ transplant

recipi-ents allows for a very rapid CMV replication dynamics, with an

estimated CMV doubling rate of 1 day (23,24) Clinically, this

translates to a high rate of clinical CMV disease In contrast, the

presence of preexisting immunity in CMV R solid organ

transplant recipients dampens CMV replication dynamics

(23,24) This lower degree of CMV replication

dynamics could explain the relatively lower incidence and

po-tentially lesser severity of CMV disease in CMV R transplant

patients when compared to CMV D/R patients (23,24,45,46)

Defects in Cytomegalovirus-Specific

T-Cell Immunity

Optimal functioning of CMV-specific T cells is essential for

adequate control of CMV infection (45–48) Expectedly,

CMV-specific CD4 and CD8 T lymphocytes are absent at

the time of organ transplantation in CMV D/R patients,

thereby predisposing these patients to a high rate of CMV

dis-ease (47,49,50) On the contrary, CMV-specific CD4 and

CD8 T lymphocytes are present among CMV R solid

organ transplant recipients, although the use of

lymphocyte-depleting immunosuppressive drugs such as OKT3 or

thy-moglobulin decreases the absolute levels, percentages, and

function of these cells to a level that results in incomplete

pro-tection and hence increased predisposition to CMV

reactiva-tion, replicareactiva-tion, and clinical disease (47,48,50,51) In this regard,

the severity of immunosuppression induced by

lymphocyte-depleting drugs is a major factor that determines who

devel-ops CMV viremia and clinical disease Several studies have

been conducted to estimate the threshold of CD4 and

CD8 T cells that confer protection or risk, but this level hasnot been precisely defined (47,48,50,51)

Defects in Innate Immunity

Since CMV is initially recognized by cells of the innate mune system, through pathogen-recognition receptors, defi-ciencies in cells and molecules of innate immunity have beenimplicated as factors that increase the risk of CMV infectionand disease after solid organ transplantation (52–57) Amongthese are deficiencies in various Toll-like receptors, mannose-binding lectin, mannose-associated serine protease-2, and acti-vating and inhibitory killer cell immunoglobulin-likereceptors, all of which have been reported to be associatedwith a higher incidence of CMV disease after solid organtransplantation (52–57)

of CMV-specific, cell-mediated, and humoral immune sponses and lead to uncontrolled CMV replication and disease(40,58) Among the drugs that are most commonly associatedwith CMV disease are OKT3, antilymphocyte globulin(ALG), antithymocyte globulin (ATG), and alemtuzumab(59–69) Administration of certain lymphocyte-depleting anti-bodies is often complicated by a cytokine release syndrome,characterized by high fevers and rigors Theoretically, cy-tokine (TNF-) release syndrome could induce CMV reacti-vation, which in the presence of global suppression of T-cellfunction could lead to uncontrolled CMV replication and

Abbreviations: CMV, cytomegalovirus; D /R, donor positive/recipient negative; R, recipient positive.

aThe estimated incidence after small bowel transplantation is 22% of all patients, including all donor and recipient CMV serostatus.

bAntiviral prophylaxis is given for a duration of 3 months unless otherwise indicated.

cIndicates 6 months of prophylaxis after lung transplantation.

dCMV disease in patients, who received prophylaxis, generally occurs after the completion of antiviral prophylaxis (delayed-onset CMV disease).

clinical disease (59) Several studies have also implicated high

doses of steroids and mycophenolate mofetil in the

develop-ment of CMV disease (59–69) In addition to the individual

effects and risks associated with specific immunosuppressive

drugs, the overall combined net state of drug

immunosuppres-sion is likely playing a major role in the predisposition to

de-velop CMV disease after solid organ transplantation

Allograft Rejection

Acute rejection is a well-defined major risk factor for CMV

disease after solid organ transplantation (40,58,70,71)

Proin-flammatory cytokines, such as TNF-, released during an

episode of allograft rejection serve as potent transactivators of

CMV from a state of latency to one of active replication In one

study, acute rejection increased the risk of CMV disease by

sixfold in a cohort of CMV D/R liver and renal transplant

recipients (40) In another study, CMV disease occurred in

three-quarters of patients during the month following an

episode of acute rejection (72) Conversely, CMV is implicated

as a major risk factor for the occurrence of acute and chronic

allograft rejection after solid organ transplantation, thereby

establishing a bidirectional relationship between CMV and

re-jection (58) Indeed, antiviral prophylaxis with ganciclovir or

valacyclovir has been associated not only with a reduction in

CMV disease but also with reduction in acute rejection (73,74)

Type of Organ Transplant

The predisposition to develop CMV disease varies depending

on the type of organ transplant Lung, small intestinal, and

pancreas transplant recipients generally have the highest risk,

whereas liver and heart transplant have intermediate risk, and

kidney transplant have the lowest risk for CMV disease

(1,44,75) Although this may be due to the intensity of

im-munosuppression, it has been postulated that the amount of

CMV harbored in the transplanted allograft may contribute to

the increased predisposition of lung and small intestinal

trans-plant recipients to develop CMV disease (1,75)

Viral Interactions

Observational studies demonstrate that liver and kidney

trans-plant recipients with human herpesvirus (HHV)-6 and HHV-7

infections were more likely to develop CMV disease after

transplantation (70,76–79) The underlying mechanisms for

this association is not clearly defined, although it has been

postulated that HHV-6 and HHV-7 have

immunomodulat-ing properties (80–87) that could enhance immune

dysfunc-tion, thereby predisposing to a higher incidence of CMV

disease (76,77,79,88) Alternatively, the reactivation of multiple

viruses including HHV-6 and HHV-7 may only serve as an

in-dicator of a more impaired net state of immune dysfunction,

and hence the reported clinical associations between these

virus infections may be coincidental and not causal

Viral Load and Genotype

Peak viral load and antigenemia levels have been shown to beindependent predictors of CMV disease after solid organtransplantation (23,24,89–92) In one study, the risk of CMVdisease is increased 8-fold in patients with detectable viralload, and 50-fold in patients with viral load greater than 2860copies per 10 (6) peripheral blood mononuclear cells (92).Additionally, genetic variability of viral strains (i.e., the viralgenotype) may influence the pathogenesis of CMV disease(93), and this could potentially account for the higher rate ofCMV disease among CMV D/R compared to CMV

D/R patients Studies in CMV R solid organ transplantrecipients demonstrate that the majority of reactivated CMVstrains originated from donor instead of the recipient (25–27)

Bacterial and Fungal Infections

Invasive bacterial and fungal infections have been associatedwith a higher incidence of CMV disease after solid organtransplantation (39,94) The proinflammatory condition asso-ciated with invasive bacterial and fungal infections wouldfavor for the reactivation of CMV from latency, and this couldlead to clinical disease Conversely, CMV disease per se in-creases the risk of opportunistic bacterial and fungal infectionsafter solid organ transplantation, possibly as a result of CMV-induced immunomodulation (94–96) or as a marker of anoverimmunosuppressed state

Other Factors

Other factors that have been significantly associated with CMVdisease after solid organ transplantation are (i) a higher Charlsoncomorbidity index (39), (ii) a low creatinine clearance (97), (iii) anABO blood group A (97), and (iv) female gender (97) The mech-anisms underlying the significant associations between these clin-ical factors and CMV infection and disease remain undefined

CLINICAL SYNDROMES

In solid organ transplant recipients in whom no specific CMVprevention strategy is used, the onset of CMV infection occursduring the first 3 months after transplantation, when the degree

of pharmacologic immunosuppression is most intense (59,98,99).However, this traditional onset has been delayed, particularlyamong CMV D/R solid organ transplant recipients who arereceiving anti-CMV prophylaxis, so that, in these patients, CMVdisease now occurs most commonly during the first 3 monthsafter completion of anti-CMV prophylaxis (39,74,100–104).CMV infection in solid organ transplant recipients ex-hibits a wide spectrum of clinical manifestations, ranging fromasymptomatic infection to severe and occasionally lethal CMVdisease (105) Based on the clinical manifestations, CMV infec-tion is generally classified either as an asymptomatic infection(termed subclinical CMV infection) or symptomatic infection

(termed CMV disease) CMV disease, which is characterized

by the presence of clinical signs and symptoms, can be further

classified into an infection with organ involvement (termed

tissue-invasive CMV disease) and without organ involvement

(termed CMV syndrome) (Table 23.3) (44,106,107)

The clinical impact of CMV extends beyond these “direct”

syndromes to a myriad of indirect effects, such as the influence

of CMV on acute rejection, chronic rejection, chronic allograft

failure, allograft dysfunction, patient and allograft survival,

lymphomas and other malignancies, and increased

predisposi-tion to other opportunistic infecpredisposi-tions (Table 23.3) (1,107–109)

Collectively, these direct and indirect effects of CMV

con-tribute significantly to increased resource utilization and

over-all cost of solid organ transplantation (110–112)

Direct Cytomegalovirus Effects

The direct effects of CMV in solid organ transplantation result

from the reactivation of the virus in latently infected cells

(cluding the allograft), its dissemination in the blood, and its

in-vasion and replication in target organs (such as the transplanted

allograft and other organs, most commonly the gastrointestinal

tract) These events produce a characteristic febrile illness, often

accompanied by bone marrow suppression, and various

end-organ invasive diseases such as pneumonitis, gastritis, enteritis,

colitis, encephalitis, hepatitis, and retinitis, among others (Table

23.3) The diagnosis of CMV disease is confirmed by

demon-strating the virus in the blood, other body fluids, or tissue

speci-mens (107) Table 23.4 lists the various laboratory methods used

for the diagnosis of CMV infection and disease after solid organ

transplantation (113) Most laboratories utilize CMV nucleic acid

detection assay (such as polymerase chain reaction [PCR]) or

CMV pp65 antigenemia to confirm the clinical suspicion of

CMV infection and disease (113) The slow turn-around timeand poor sensitivity of virus cultures have limited their clinicalutility in the real-time diagnosis of CMV disease after trans-plantation (113) CMV serology is not particularly useful for thediagnosis of CMV disease after transplantation, since immuno-suppressive therapy delays the generation of immunoglobulinresponse in many transplant recipients (113)

Cytomegalovirus Syndrome

CMV syndrome is the term for clinical disease in the absence oftissue or end-organ involvement (107) CMV syndrome ac-counts for approximately 60% of all cases of CMV disease occurring after solid organ transplantation (39,100,102,107).Clinically, CMV syndrome is manifested as fever with consti-tutional symptoms, such as malaise, weakness, myalgia, andarthralgia (107) Many cases of CMV syndrome are accompa-nied by myelosuppression, most commonly with leukopeniaand thrombocytopenia (107) In all cases of CMV syndrome,CMV DNA or antigenemia is detected in the blood (107) Insome cases, coinfections with HHV-6 and HHV-7 may bedemonstrated (114–118) However, the role of these other her-pesviruses in the clinical symptomatology of CMV syndromehas not been conclusively demonstrated (118) Nonetheless, theterm “viral syndrome” has been suggested to account for thepresence of viral coinfections (107)

End-Organ (Tissue-Invasive) Cytomegalovirus Disease

Approximately 40% of CMV disease cases after solid organtransplantation are manifested clinically as tissue-invasivedisease and are characterized by signs and symptoms of end-organ dysfunction (1,39,74,100–102,119) The clinical diagnosis

Tissue-invasive CMV disease Chronic rejection and allograft failure Increased resource utilization

Othersa

Other viruses (HHV-6, HHV-7) Mortality

New-onset diabetes Mortality

Abbreviations: CMV, cytomegalovirus; PTLD, posttransplant lymphoproliferative diseases; HHV, human herpesvirus.

aAny organ system may be affected by cytomegalovirus.

of tissue-invasive CMV disease is confirmed by the

demonstra-tion of CMV in tissue specimens by viral culture, histopathology

(i.e., inclusion bodies), immunohistochemistry, or in situ DNA

hybridization (107) In most cases of tissue-invasive disease,

CMV is demonstrated in the peripheral blood by PCR or pp65

antigenemia However, a small number of cases may present as

a compartmentalized CMV disease with no detectable virus in

the blood (1); in these cases, a tissue specimen is needed to

con-firm the diagnosis of tissue-invasive disease (1)

The most common tissue-invasive form is gastrointestinalCMV disease, which can involve any part of the gastrointesti-

nal tract and manifests clinically as mucositis, diarrhea, and

hemorrhagic ulcerative disease (1,39,74,100–102,119) The

most severe forms of tissue-invasive CMV disease are

pneu-monia and central nervous system disease (e.g., encephalitis)

In some cases, multiple organ systems may be involved, such

as concomitant CMV colitis and hepatitis Very rarely, CMV

may involve the retina to cause retinochoroiditis that can lead

to permanent blindness if not detected and treated early and

aggressively (75) Virtually any organ system can be affected by

CMV, and some of the less common sites of tissue involvement

are the gallbladder and biliary tree, epididymis, skin, and

endometrium (120–125) Congenital CMV has also been reported

to occur in the offspring of female transplant recipients (126)

It is not uncommon for CMV disease to involve the planted allograft, especially among CMV D/R patients Thisclinical observation is not unexpected since the virus in CMVD/R solid organ transplant recipients is present initially only

trans-in the transplanted allograft Accordtrans-ingly, CMV is expected toreactivate initially in the transplanted organ and cause graft dys-function and allograft tissue-invasive CMV disease prior to itssystemic dissemination CMV reactivation in the transplantedallograft could potentially explain the vulnerability of the trans-planted allograft to develop end-organ CMV disease (127–131).Hence, compared to other organ transplant recipients, CMVhepatitis occurs relatively more frequently among liver trans-plant recipients (132), CMV pancreatitis among pancreas trans-plant recipients (127), and CMV pneumonitis among lung andheart–lung transplant recipients (128–130) Although CMV myo-carditis is rare, it is also typically observed among heart transplantrecipients (131) Because many of the clinical manifestations oftissue-invasive CMV disease are difficult to differentiate from al-lograft rejection, performing tissue biopsy for definitive diagno-sis is imperative to guide appropriate therapy

The clinical manifestations of tissue-invasive CMV diseasedepend on the involved organ and the severity of involvement

In addition to fever, CMV hepatitis typically manifests as vated serum levels of gamma-glutamyl transferase, alkaline

Solid Organ Transplantation

Virus isolate may be used for phenotypic drug susceptibility

(IgG, IgM) Not used for real-time Majority of patients are

diagnosis of acute disease IgG seropositive after transplantation

Antigenemia Slide method pp65 antigen Rapid diagnosis of CMV More sensitive than

Guide for preemptive Lacks standardization therapy (e.g., 10 positive Operator-dependent cells per 2 10 5 cells) (subjective interpretation) Guide for duration of Requires immediate

Nucleic acid COBAS Amplicor Viral nucleic acid Rapid diagnosis of CMV Qualitative assay does detection and CMV Monitor (DNA or RNA) infection and disease not distinguish latency amplification LightCycler assay detection Guide for antiviral therapy from active replication

Guide for duration antiviral therapy

of antiviral therapy Surrogate marker for

antiviral resistence Abbreviations: ELISA, enzyme-linked immunosorbent assay; CMV, cytomegalovirus.

phosphatase, and aminotransferases, with minimal elevations in

serum bilirubin levels (132) CMV pneumonitis manifests as

fever, dyspnea, and cough, accompanied by hypoxemia and

ra-diographic findings of bilateral interstitial, unilateral lobar, or

nodular pulmonary infiltrates (133) CMV can affect any

seg-ment of the gastrointestinal tract, including the esophagus,

stomach, and small and large intestines (134) Depending on the

segment involved, gastrointestinal CMV disease may manifest

with symptoms such as dysphagia and odynophagia (CMV

esophagitis), nausea, vomiting, delayed gastric emptying, and

abdominal pain (CMV gastritis), gastrointestinal hemorrhage

(CMV gastritis, enteritis, or colitis), and diarrhea (CMV

entero-colitis) (135–137) A high index of suspicion should be

main-tained for CMV colitis in any transplant recipient who presents

with lower gastrointestinal bleeding even at later periods after

transplantation (136) The endoscopic findings of

gastrointesti-nal CMV disease could be nonspecific, such as erythema and

diffuse, shallow erosions, although characteristic ulcerations are

typically observed (136) Histopathologic examination to

demonstrate CMV inclusion bodies in tissue specimens, the use

of in situ hybridization or CMV-specific immunochemical

stains to demonstrate the presence of the virus in biopsy

speci-mens, or the use of viral culture of tissue are necessary to

con-firm the presence of tissue-invasive CMV disease (135) CMV

has also been reported to cause vasculitis that resulted in

is-chemic colitis (138), or thrombosis of the hepatobiliary system

(139,140) CMV retinitis usually presents at a late stage, usually

more than 6 months after solid organ transplantation (75)

Patients with CMV retinitis may be asymptomatic, or they may

experience blurring of vision, scotomata, or decreased visual

acuity (75) Characteristic fundoscopic findings often reveal the

diagnosis of CMV retinitis, although the demonstration of

CMV by PCR or culture of vitreous humor may be necessary in

atypical cases (75) Central nervous system involvement by

CMV occurs very rarely, and it is manifested as change in

men-tal function and confirmed by the demonstration of CMV by

PCR or viral culture of the cerebrospinal fluid (124)

Indirect Cytomegalovirus Effects

In addition to its well-characterized direct effects, CMV is

as-sociated with numerous indirect effects (Table 23.3), which

occur as a result of the ability of the virus to modulate the

im-mune system, either directly or through the upregulation of

cytokines, chemokines, growth factors, and other immune

molecules (109) Some of the indirect effects may be delayed

direct effects of persistent subclinical CMV infection in the

transplanted allograft (e.g., chronic allograft failure) (141)

Increased Opportunistic Infections

CMV causes immunomodulation that could account for the

predisposition to develop bacterial and opportunistic fungal

infections after solid organ transplantation (95,142,143) Some

studies have even shown that the incidence of bacterial and

fungal infections were lower among solid organ transplant cipients who received ganciclovir prophylaxis (96,144,145).The immunomodulatory property of CMV is also postulated

re-to account for the higher risk of Epstein–Barr induced posttransplantation lymphoproliferative diseases(PTLD) among patients with CMV disease (146)

virus(EBV)-Allograft Rejection

CMV has been associated with reduced short- and long-termsurvival and function of liver, kidney, lung, pancreas, andheart allografts (39,147,148) Early-onset acute allograft rejec-tion was found to be significantly higher among CMV-infectedtransplant recipients (149) Prolonged CMV replication hasalso been associated with an increased risk of chronic rejectionafter liver transplantation (150) Although the mechanismsunderlying these clinical associations have not been fully eluci-dated, persistent CMV replication may, even at subclinical lev-els, mediate a persistent T-cell stimulation, either directly orindirectly by increasing the immunogenicity of the trans-planted allograft (i.e., interferon-–mediated upregulation ofmajor histocompatibility complex antigens), hence resulting in

a chronic inflammatory process (151)

Chronic Allograft Failure

The most common cause of long-term allograft loss, chronicallograft failure, has been associated with CMV infection.Among lung transplant recipients, CMV has been signifi-cantly associated with bronchiolitis obliterans syndrome, aform of chronic lung rejection characterized by bronchiolarinflammation and granulation (130) Ganciclovir prophylaxishas been associated with a significant reduction in the incidence

of bronchiolitis obliterans after lung transplantation (152).Among heart transplant recipients, CMV has been implicated

in the pathogenesis of accelerated vasculopathy leading to diac dysfunction (discussed later in the chapter) (152–154) Anassociation between CMV and left ventricular dysfunction hasalso been reported in heart transplant recipients (155) CMVdisease has also been implicated as a factor for the develop-ment of vanishing bile duct syndrome, which is characterized

car-by ductopenia, severe jaundice, and pruritus after liver plantation (156–158) Among kidney transplant recipients,CMV has been significantly associated with tubulointerstitialfibrosis and glomerulopathy, characterized by enlargementand necrosis of endothelial cells and accumulation of mononu-clear cell infiltration and fibrillary material deposition inglomerular capillaries (39,125)

trans-Vasculopathy and Procoagulation

A significant association between CMV and accelerated lopathy has been reported after heart transplantation(153,154,159–161) This clinical association is supported by invitro experimental data showing the ability of CMV to infectendothelial cells, influence smooth muscle cell migration and

vascu-growth in vitro, and induce neointimal proliferation in rat

aor-tic allografts (162) Experimental in vivo data demonstrate that

rat CMV causes endothelial inflammation that results in intimal

thickening in aortic and cardiac allografts, and this effect was

diminished or abolished by ganciclovir (163,164) In addition,

CMV-enhanced allograft vasculopathy may be mediated by a

proliferative effect on the smooth muscle cells and/or

inflamma-tory cells with enhanced production of growth factors

(159,163–166) CMV infection of endothelial cells may also lead

to a procoagulant response that could account for the clinical

as-sociation between CMV and vascular thrombosis (140,167,168)

Anti-CMV drugs together with CMV-hyperimmune globulins

have been suggested to reduce the predisposition to develop

ac-celerated vasculopathy after heart transplantation (153,154)

Viral Interactions

Circumstances after solid organ transplantation predispose not

only the reactivation of CMV but also of other latent viruses,

thus allowing for the potential for microbial interactions

(79,115–117) The potential interactions among reactivated

viruses have been suggested to modify the clinical

presenta-tion of these infecpresenta-tions (79,88,115–117,147,169,170) Examples

of this phenomenon are the proposed interactions among

-herpesviruses, which may be manifested as an increased

inci-dence and severity of CMV disease (79,88), the proposed

associ-ation between CMV and EBV-associated PTLD (146), and the

ability of CMV to accelerate the clinical course of recurrent

hepatitis C virus infection, resulting in allograft failure and

mortality after liver transplantation (169,170)

Mortality

Solid organ transplant recipients who develop CMV disease

have a significantly higher mortality rate when compared to

those who did not develop CMV disease (39,103,171–173)

Causes of death may be directly due to CMV disease or could

result from non-CMV–related causes The use of effective

anti-CMV drugs for prophylaxis has been shown to reduce

all-cause mortality after solid organ transplantation (174–177)

PREVENTION OF CYTOMEGALOVIRUS INFECTION AND DISEASE

Because of the negative impact of CMV on clinical outcomes,

its prevention is considered one of the most important

manage-ment strategies after solid organ transplantation Among the

various anti-CMV prevention strategies, the most common is

the use of antiviral drugs either as antiviral prophylaxis or

pre-emptive therapy Also a common practice is the use of

CMV-seronegative, filtered, or leukocyte-reduced blood products

when blood transfusion is necessary for patient care

CMV-seronegative donor and recipient matching, which would pair a

CMV-seronegative donor and recipient is logistically difficult

Awaiting a CMV-seronegative donor may result in an sarily prolonged waiting time for a patient who needs a life-saving transplant procedure Currently, passive immunizationwith CMV immunoglobulin is less commonly used, partly be-cause of its expense, modest efficacy, and the availability ofmore effective antiviral drug strategies There is no vaccine that

unneces-is available clinically for active immunization against CMV inhumans, although some are in early clinical development

Antiviral Drug Strategies

The two major antiviral drug strategies for the prevention ofCMV disease after solid organ transplantation are (i) antiviralprophylaxis and (ii) preemptive therapy (44,106,178) Antiviralprophylaxis entails the administration of an antiviral drug for afixed duration of time (usually 3 months) to all patients or to

“at-risk” patients after solid organ transplantation (44,106,178)

In contrast, preemptive therapy involves the administration

of antiviral drug only to transplant recipients with evidence ofearly asymptomatic CMV replication (44,106,178) The goal ofpreemptive therapy is to treat early CMV reactivation prior tothe onset of clinical manifestations A variant of preemptivetherapy is targeted prophylaxis, which entails the admin-istration of antiviral drugs during periods highly associatedwith CMV reactivation, such as those times when ATG, ALG,OKT3, and alemtuzumab are administered for the treatment ofacute graft rejection (44,106,178)

There is an ongoing debate whether antiviral prophylaxis

or preemptive therapy is the optimal strategy for preventingCMV disease after solid organ transplantation It is generallybelieved, however, that both strategies are effective for CMVdisease prevention (179–181) Several meta-analyses concludedthat antiviral prophylaxis and preemptive therapy are botheffective in preventing the direct effects of CMV disease(174–177) However, a significant reduction in the incidence ofindirect CMV effects was more evident with antiviral prophy-laxis compared to preemptive therapy (Table 23.5) (174–177).Specifically, a reduction in the all-cause mortality was demon-strated with antiviral prophylaxis but not with preemptivetherapy (1,144,182) In recent head-to-head clinical trials thatdirectly compared the efficacy of both antiviral strategies incohorts of kidney transplant recipients, it appears that both areequally effective in preventing CMV disease (179–181), al-though a reduction in the incidence of acute allograft rejectionand a better long-term survival was observed with antiviralprophylaxis (180), suggesting the potential advantage of an-tiviral prophylaxis over preemptive therapy in reducing theindirect effects of CMV (Table 23.6) The overall cost of bothantiviral strategies appears to be similar, with cost of drug(for antiviral prophylaxis) being counter-balanced by thecost of laboratory monitoring (for preemptive therapy) (181).Table 23.7 summarizes the potential benefits and disadvan-tages of the two antiviral strategies (1) Which of these two

TABLE 23.5 Recently Published Meta-Analyses of Randomized Controlled Trials of Antiviral Prophylaxis and

Preemptive Therapy for the Prevention of Cytomegalovirus Disease after Solid Organ Transplantation

Antiviral prophylaxis

placebo or no 1981 patients 1786 patients 1838 patients No significant effect on

rejection, and graft loss

770 patients 775 patients 502 patients No significant difference in the

risk of CMV disease, CMV infection, and all-cause mortality between antiviral drug combined with IgG compared to antiviral medication alone

Preemptive therapy

Abbreviations: RCT, randomized controlled trial; NA, not assessed; RR, relative risk; 95% CI, 95% confidence intervals; IgG, immunoglobulin G; HSV, herpes simplex virus; VZV, varicellazoster virus; CMV, cytomegalovirus; GCV, ganciclovir; ACV, acyclovir; VACV, valacyclovir.

aData presented as relative risk (95% confidence intervals), number of trials included, and number of patients.

major strategies is more effective in a specific transplant setting

or a specific transplant population is most likely influenced by a

variety of factors, including recipient and donor characteristics,

underlying medical comorbidity, the logistics of frequent CMV

surveillance, the availability of molecular and nonmolecular

methods for CMV detection, and the availability and cost of

antiviral drugs (183,184) Hence, the choice of which antiviral

approach to use after solid organ transplantation is dependent

on institution, organ transplant, and resource

Antiviral Prophylaxis

The antiviral drugs that have been used clinically for the vention of CMV disease after solid organ transplantation arevalganciclovir, oral and intravenous ganciclovir, valacyclovir,and high-dose oral acyclovir (Table 23.8) (74,101,104,185–189).Foscarnet and cidofovir have not been routinely utilized forthe primary prevention of CMV disease after solid organtransplantation because of toxicities (1) Numerous clinical

pre-TABLE 23.6 Selected Clinical Trials Comparing Preemptive Therapy and Antiviral Prophylaxis

in Kidney Transplant Recipients

preemptive therapy vs

antiviral prophylaxis

Monitoring strategy for qPCR WB weekly 16 w qPCR WB weekly 16 w qPCR WB weekly 4 w

Drug for preemptive therapy VGCV 900 mg b.i.d 21 d VGCV 900 mg b.i.d IV GCV 5 mg/kg b.i.d Drug for antiviral prophylaxis VGCV 900 mg q.d 100 d VACV 2 g q.i.d 90 d Oral GCV 1 g t.i.d 90 d Outcomes (preemptive therapy vs antiviral prophylaxis)

CMV infection 59% vs 29% (P 0.004) 92% vs 59% (P 0.001) 51% vs 18% (P 0.001)

Biopsy-proven allograft 8% vs 2% (P 0.36) 36% vs 15% (P 0.034) 28% vs 19% (P ns) rejection at 12 mo

long-term survival (92%

vs 78%; P 0.04) CMV associated with severe impairment in graft function Abbreviations: CMV, cytomegalovirus; D /R, donor positive/recipient negative; GCV, ganciclovir; VGCV, valganciclovir; VACV, valacyclovir; d, days; w, weeks; mo, months; CrCl, creatinine clearance.

Against CMV after Solid Organ Transplantation

Universal prophylaxis ● Prevents reactivation of other herpes ● Prolonged antiviral drug use may lead

viruses (i.e., herpes simplex virus, HHV-6) to the emergence of antiviral drug

● Does not rely on frequent laboratory resistance monitoring for CMV detection ● Prolonged antiviral drug use may

● Reduces incidence of indirect CMV lead to higher incidence of effects (acute rejection, chronic allograft adverse drug effects failure, opportunistic bacterial and viral ● Associated with late-onset infections, posttransplant lymphoproliferative CMV disease

disease, and mortality) Preemptive therapy ● Reduced number of patients exposed to ● Requires a predictive test for early

● Reduced direct drug costs ● Requires patients to comply with

● Reduced duration of antiviral drug use stringent surveillance schedule

● Reduced toxicity related to antiviral drugs ● Requires personnel to actively implement

● Lower risk of antiviral drug resistance the logistics of the CMV surveillance program (although resistance has been observed ● Increased cost of diagnostic surveillance testing with prolonged preemptive therapy) ● May not identify all patients at risk of CMV

disease because of rapid viral replication in CMV

D /R patients

● CMV-selective nature does not prevent reactivation of other herpesviruses

TABLE 23.9 Recommendations for the Prevention of CMV Disease after Solid Organ Transplantation

Kidney, liver, D /R– Universal prophylaxis is preferred over Valganciclovir 900 mg q.d (not

prophylaxis in high-risk kidney recipients IV ganciclovir 5 mg/kg q.d Prophylaxis may be prolonged for patients who Valacyclovir 8 g/d (kidney receive lymphocyte-depleting antibodies for transplant recipients only)

Preemptive therapy may be effective but the high-risk patients (in heart rapid replication dynamics of CMV in CMV transplant patients)

D /R– patients makes preemptive strategy logistically difficult in this population

R  Either antiviral prophylaxis or preemptive therapy Antiviral prophylaxis:

Duration of prophylaxis is 90–100 d (not FDA-approved in liver Preemptive therapy is guided by PCR or transplantation)

Other centers do not provide specific anti-CMV IV ganciclovir 5 mg/kg q.d prevention strategy and opts to clinically Valacyclovir 8 g/d (kidney observed low-risk patients (i.e., D–/R ) transplant recipients only)

Preemptive therapy:

Valganciclovir 900 mg b.i.d.

IV ganciclovir 5 mg/kg q 12 h

although a duration of at least 6 mo to the antiviral regimen

is recommended by many experts

R  Universal prophylaxis is preferred over Valganciclovir 900 mg q.d.

Duration of prophylaxis is 3 mo, although Oral ganciclovir 1 g t.i.d.

a duration of at least 6 mo is recommended by others Intestinal D /R Universal prophylaxis is preferred over IV ganciclovir 5 mg/kg q.d.

Duration of prophylaxis is at least 6 mo; Some centers add CMV-IG to some centers extend the duration beyond the antiviral regimen

6 mo

R  Universal prophylaxis is preferred over IV ganciclovir 5 mg/kg q.d.

Duration of prophylaxis is 3–6 mo after Oral ganciclovir 1 g PO t.i.d transplantation

Abbreviations: CMV, cytomegalovirus; IG, immunoglobulin; D, donor, R, recipient; q.d., once daily; t.i.d., thrice daily; IV, intravenous.

trials have evaluated and demonstrated the efficacy and safety

of antiviral drugs for the prevention of CMV disease after

solid organ transplantation (Table 23.8) (74,101,104,185–189)

In many of these clinical trials, the benefits of antiviral

pro-phylaxis are the reduction in the incidence and severity of

CMV disease and, in some trials, the reduction in the indirect

effects of CMV, such as its impact on other opportunistic

infec-tions (145), bacteremia (96), allograft rejection (152–154), and

patient survival (152–154,174) However, the practice of tiviral prophylaxis is not universally adapted among the dif-ferent transplant populations and programs, as a result of theinherent differences in the risk among solid organ transplantpatient groups, the underlying patient immunity, and thetypes of immunosuppressive regimens, among others Table23.9 lists the recommendations for the prevention of CMV dis-ease after solid organ transplantation (44,106,178,190)

an-Ganciclovir-Based Antiviral Prophylaxis

Ganciclovir has been the most commonly used effective drug

for CMV management after solid organ transplantation A

synthetic analogue of 2

anti-CMV effect through inhibition of CMV DNA

poly-merase (191,192) In order for ganciclovir to exert its

anti-CMV activity, it has to undergo triphosphorylation, a process

that is carried out initially by CMV-encoded UL97 kinase

fol-lowed by human cellular kinases (193) Because of the

neces-sity for CMV-encoded UL97 phosphotransferase for its initial

monophosphorylation, ganciclovir would theoretically become

activated only in the presence of active CMV infection (193)

Upon its activation, ganciclovir triphosphate acts by

competi-tively inhibiting the incorporation of

deoxyguanosinetriphos-phate by CMV DNA polymerase, resulting in the termination

of CMV DNA elongation

The clinical efficacy of ganciclovir for the prevention ofCMV disease after solid organ transplantation is well demon-

strated by multiple clinical trials that compared it with placebo,

acyclovir, or different preparations of immunoglobulins

(194–199) Ganciclovir is available in both intravenous and oral

formulations (193) However, oral ganciclovir is poorly

ab-sorbed in the gastrointestinal tract (200) Valganciclovir, a

valyl-ester prodrug of ganciclovir, circumvents the pharmacokinetic

limitations of oral ganciclovir and provides systemic ganciclovir

levels that are comparable to that achieved with intravenous

ganciclovir (200) Intraocular formulations of ganciclovir are

also available (e.g., ganciclovir implants), although these are

generally used only as adjunctive treatment in the rare cases of

CMV retinitis after solid organ transplantation (75)

com-monly used drug for anti-CMV prophylaxis after solid organ

transplantation (104) A prodrug of ganciclovir, valganciclovir

is a highly recognized substrate of the intestinal peptide

trans-porter PEPT1, which facilitates its rapid and efficient

intes-tinal absorption (193) Following absorption, valganciclovir

undergoes rapid hydrolysis by intestinal and hepatic esterases

into ganciclovir molecules (193) Because of enhanced

intes-tinal absorption, valganciclovir provides serum ganciclovir

concentrations that are comparable to intravenous ganciclovir

(200), thereby circumventing the need for intravenous access

The high ganciclovir levels attained with oral valganciclovir

may theoretically reduce the risk of antiviral resistance when

compared to oral ganciclovir (201)

For antiviral prophylaxis, valganciclovir is administeredorally at a dose of 900 mg once daily in individuals with cre-

atinine clearance 60 mL/min (Table 23.9) (104,193) The

efficacy and safety of valganciclovir for prophylaxis was

demonstrated in an international randomized controlled

mul-ticenter trial, wherein valganciclovir (900 mg once daily for

100 days) was noninferior to standard oral ganciclovir (1 g

three times daily for 100 days) for the prevention of CMV ease in a cohort of 364 CMV D/R kidney, pancreas, liver,and heart transplant recipients (104) The incidences of “end-point committee-defined CMV disease” were 12.1% and15.2% at 6 months and 17.2% and 18.4% at 12 months in thevalganciclovir and oral ganciclovir groups, respectively (104).The incidences of “investigator-treated CMV disease” were30.5% and 28.0% in the valganciclovir and oral ganciclovirgroups, respectively (104) Notably, there was a higher inci-dence of tissue-invasive CMV disease among liver transplantrecipients who received valganciclovir compared to oral ganci-clovir prophylaxis (104), and this observation resulted in thenonapproval by the U.S FDA of valganciclovir for the preven-tion of primary CMV disease after liver transplantation (104).Despite this nonapproval, a recent survey of transplant centers

dis-in North America showed that valganciclovir is still the mostcommon drug used for the prevention of primary CMV dis-ease after liver transplantation (202) The incidence of CMVviremia during prophylaxis was significantly lower, whereasthe incidence of neutropenia was higher among patients whoreceived valganciclovir prophylaxis (104); these findingswere directly correlated with systemic drug levels (203).Several single-center and retrospective analyses have mirroredthese findings by demonstrating the efficacy of valganciclovirprophylaxis after heart, kidney, pancreas, and liver trans-plantation (39,100,102,129,204–206) There have also beensingle-center studies that demonstrated the clinical utility ofvalganciclovir for anti-CMV prophylaxis after lung transplan-tation (129,206) In contrast, clinical data do not yet exist on theuse of valganciclovir in children less than 12 years of age, al-though a liquid formulation of valganciclovir is now availableand this will facilitate clinical studies in the pediatric trans-plant population (207)

The optimal duration of valganciclovir prophylaxis forthe prevention of CMV disease after solid organ transplanta-tion remains undefined, although 3 months of antiviral pro-phylaxis is generally considered as the standard minimumduration for high-risk CMV D/R patients (44,106,178).Longer durations of prophylaxis are being evaluated as ameans to further reduce the incidence of delayed or late-onsetCMV disease, which occur soon after discontinuation of thestandard 3-month antiviral prophylaxis A recently concludedclinical trial indicates further reduction in the incidence ofCMV disease with 200 days compared to the standard 100 days

of valganciclovir prophylaxis in a large cohort of 372 CMV

D/R– kidney transplant recipients (16.1% vs 36.8%), though the degree of protection was incomplete since a num-ber of high-risk patients (16.1%) continued to developlate-onset CMV disease despite 6 months of prophylaxis (208).The optimal duration of anti-CMV prophylaxis after lungtransplantation also remains to be defined, although one con-sensus statement suggested at least 6 months of prophylaxis

al-among high-risk lung transplant recipients (128,129) Table 23.9

lists the recommendations for the prevention of CMV disease

in CMV D/R and CMV R kidney, liver, pancreas, heart,

lung, and intestinal transplant recipients (44,106)

INTRAVENOUS GANCICLOVIR Intravenous ganciclovir was the

agent of choice for CMV prevention during the time when

oral ganciclovir and valganciclovir were not clinically

avail-able Clinical trials have demonstrated the efficacy of

intra-venous ganciclovir for the prevention of CMV disease after

solid organ transplantation (196) However, the outcomes of

many studies were conflicting potentially due to differences in

drug doses, dosing frequency, duration of prophylaxis, and

pa-tient populations (198,209) One trial showed that intravenous

ganciclovir (5 mg/kg three times weekly for 6 weeks) resulted

in a significant reduction in CMV disease in CMV D/R

patients (71% of controls vs 11% of ganciclovir group) (210)

Another study showed that intravenous ganciclovir (5 mg/kg

every 12 h for 2 weeks, then 6 mg/kg/day on weekdays for 2

weeks) resulted in a significant reduction of CMV disease in

CMV R recipients (46% of control vs 9% of ganciclovir

group) (187) In a cohort of CMV D/R kidney

trans-plant recipients, intravenous ganciclovir prophylaxis for 14 to

28 days did not result in the reduction of CMV disease (188),

suggesting that this high-risk patient group does not

signifi-cantly benefit from short-term (i.e., 2 to 4 weeks) intravenous

ganciclovir prophylaxis Thus, a longer duration of antiviral

prophylaxis is suggested in CMV D/R patients (196)

However, the need for vascular access and the concerns for

vascular thrombosis, phlebitis, and catheter-related

infec-tions have limited the prolonged use of intravenous

ganci-clovir for prophylaxis after solid organ transplantation (193)

Accordingly, oral agents have generally replaced intravenous

ganciclovir for prevention of CMV disease after solid organ

transplantation Currently, intravenous ganciclovir remains in

use mainly as short-course “bridge” prophylaxis during the

early period after transplantation, when patients are still

un-able to take oral medications The recommended dose for

in-travenous ganciclovir for prophylaxis is 5 mg/kg/day (dose

adjusted based on renal function)

ORAL GANCICLOVIR Oral ganciclovir was developed in an

effort to circumvent the disadvantages or prolonged

intra-venous ganciclovir use (101) For prophylaxis, oral ganciclovir

is given at a dose of 1 g orally three times daily for 3 months

after solid organ transplantation (44,101) The major

draw-back to oral ganciclovir use is its poor absorption following

oral administration (193,200) Nonetheless, significant

reduc-tions in the incidence of CMV infection and disease were

demonstrated, implying that even low drug levels achieved

may be sufficient to inhibit viral replication (101) In a

prospective, randomized, placebo-controlled trial involving

304 liver transplant recipients, oral ganciclovir (3 g daily for

98 days) reduced the 6-month incidence of CMV infectionfrom 51.5% to 24.5% and CMV disease from 18.9% to 4.8%(101) Significant reduction in the incidence of CMV diseasewas demonstrated even in CMV D/R liver transplant recip-ients (from 44% to 14.8%) and those who received lymphocyte-depleting immunosuppressive drugs (from 32.9% to 4.6%)(101) Prolonging oral ganciclovir prophylaxis to 6 monthsfurther decreased the incidence of CMV disease in kidney re-cipients (211) In a single-center observational study, the inci-dence of CMV disease among patients who received 12 weeks

of oral ganciclovir prophylaxis was 31% compared to only6.5% among transplant patients who received 24 weeks oforal ganciclovir prophylaxis (211)

The suboptimal systemic levels attained following oralganciclovir administration and its prolonged administrationafter solid organ transplantation has been postulated as majorcontributors to the recent emergence of drug-resistant viralstrains, particularly among high-risk CMV D/R solidorgan transplant recipients (201,212–216) In an in vitro study,low ganciclovir levels predisposed to the initial selection oflow-grade UL97 mutations followed thereafter by the accu-mulation of other mutations (217) In the clinical setting, per-sistent CMV replication has been demonstrated despite the use

of oral ganciclovir (40) Although an early study showed thatganciclovir prophylaxis in solid organ transplant recipients didnot select for ganciclovir-resistant CMV isolates (192), subse-quent studies have refuted this observation by demonstratingthat prolonged use of ganciclovir may predispose to the selec-tion of ganciclovir-resistant CMV isolates (215,216) In a study

of lung recipients, 9% of patients developed ganciclovir ance at a median of 4.4 months after lung transplantation afterprolonged ganciclovir therapy (215) Because of these con-cerns, the use of oral ganciclovir has been supplanted in mostcenters by valganciclovir for the prevention of CMV diseaseafter solid organ transplantation (202)

resist-Acyclovir and Valacyclovir

ACYCLOVIR Acyclovir was one of the earliest oral antiviral

drugs used for the prevention of CMV disease after solid organtransplantation (185) In its phosphorylated form, acyclovir acts

as a competitive inhibitor of viral DNA polymerase However,acyclovir possesses little in vitro activity against CMV at clini-cally achievable levels In spite of this limited anti-CMV activity,acyclovir has been used with modest success for the prevention

of CMV infection and disease in solid organ transplantation(Table 23.8) In a prospective, randomized, placebo-controlledtrial of oral acyclovir (dose of 800 to 3200 mg four times daily for

12 weeks), the incidence of CMV infection and disease in ney transplant recipients receiving oral acyclovir was 36% and7.5%, respectively, as compared with 61% and 29%, respectively,among placebo-treated patients (185) However, other studieshave not confirmed the beneficial effects of acyclovir prophy-laxis, especially in liver and thoracic organ transplant recipients

kid-(218,219) Thus, the efficacy of oral acyclovir as an anti-CMV

compound is suboptimal, and, because it is less effective

com-pared to ganciclovir-based regimens, it is not currently

recom-mended as a primary drug for the prevention of CMV disease

after solid organ transplantation

acyclovir that has the advantage of improved bioavailability

following oral administration; thus, its use may result in

en-hanced antiviral efficacy (74) In a prospective, randomized,

placebo-controlled trial involving kidney transplant

recipi-ents, high-dose valacyclovir (2 g orally four times daily for

90 days) reduced the incidence of CMV disease from 45% to

16% in high-risk CMV D/R kidney transplant recipients

and from 6% to 1% in CMV seropositive patients (74) The

sig-nificant benefits with valacyclovir prophylaxis were still

evi-dent 5 years later (220) Reductions in the incidence of herpes

simplex virus infections and allograft rejection were also

ob-served, although the adverse effects of hallucinations and

mental confusion were prominent (74) As with acyclovir, the

potential clinical utility of valacyclovir has not been

demon-strated in recipients of allografts other than kidney (221)

Currently, valacyclovir is indicated only for the prevention of

CMV disease after kidney transplantation (Table 23.9)

Foscarnet and Cidofovir

There have been no randomized, placebo-controlled clinical

studies of foscarnet and cidofovir prophylaxis for the

preven-tion of CMV disease after solid organ transplantapreven-tion Both

drugs exert a mechanism of action that is similar to

ganci-clovir, by inhibiting CMV UL54-encoded DNA polymerase

In contrast to ganciclovir, both drugs do not require

phospho-rylation by CMV UL97 kinase Hence, both foscarnet and

cidofovir have antiviral activity against ganciclovir-resistant

CMV strains with UL97 mutations (222) Although the long

half-life of cidofovir may allow for less frequent dosing (e.g.,

once every 2 weeks), which would make this an attractive

can-didate for CMV prophylaxis, the associated nephrotoxicity

and its need for parenteral administration are major factors

that have limited its use after solid organ transplantation

Likewise, foscarnet is administered parenterally, and,

espe-cially among kidney transplant recipients, the associated risk

of nephrotoxicity has practically prevented its routine use for

anti-CMV prophylaxis after solid organ transplantation (222)

Late-Onset Cytomegalovirus Disease

One of the major disadvantages of antiviral prophylaxis is

late-onset (also termed delayed-late-onset) CMV disease, which occurs

most commonly among CMV D/R solid organ transplant

recipients (39,44,74,100–102,104) Although antiviral

prophy-laxis protected patients from developing CMV disease during

the time of antiviral prophylaxis, the degree of protection was

diminished as soon as the antiviral drug was discontinued Ineffect, the antiviral prophylaxis has only delayed the onset ofCMV disease in a subset of patients The estimated incidence oflate- or delayed-onset CMV disease varied in different studies,from as low as 8% to as high as 47% of CMV D/R solidorgan transplant recipients (39,44,74,100–102,104,205) Theonset of late- or delayed-onset CMV generally occurs between

130 and 160 days after transplantation among CMV D/R–patients who received 3 months of antiviral prophylaxis (39,44,74,100–102,104,205) Accordingly, the onset of CMV diseasehas been pushed to the first 3 months after the last dose of an-tiviral prophylaxis

The clinical presentation of late- or delayed-onset CMVdisease appears similar to traditional-onset CMV disease, withthe majority of cases presenting as CMV syndrome (estimated60%) and less commonly as tissue-invasive CMV disease(39,44,74,100–102,104,205) The most common organ involved

is the gastrointestinal tract (39,44,74,100–104,173,205) In somecases, however, the clinical presentation may be atypical andthis may be missed due to the difficulties in diagnosis espe-cially among patients residing in communities far from centerswith transplant expertise (223) The severity of the direct clin-ical illness due to CMV appears to be comparatively less thanwhat was observed with early-onset CMV disease, possibly as

a result of the lower degree of immunosuppression at laterposttransplant period Nonetheless, the occurrence of late- ordelayed-onset CMV disease remains significantly associatedwith mortality and poor allograft survival (39,103,173); theseobservations highlight the continued negative impact of CMV

on transplant outcomes, even at a delayed onset

The major risk factor that has been consistently strated in many studies for the occurrence of late- or delayed-onset CMV disease is a CMV D/R– serologic status (39,44,74,100–104,173,205) Other clinical factors that have beenidentified to predispose to the development of late- or delayed-onset CMV disease are acute allograft rejection (40), bacterialand invasive fungal infections (39), low creatinine clearance(97), female gender (97), blood type A (97), high comorbidityindex (39), and overimmunosuppression especially with theuse of mycophenolate mofetil and prednisone (39) The poten-tial utility of viral load monitoring (performed every 2 weeksafter cessation of prophylaxis) and CMV serology (at the end

demon-of antiviral prophylaxis) has not been demonstrated to be ticularly useful in predicting late- or delayed-onset CMV dis-ease (224,225) Studies to assess the potential clinical utility ofCMV-specific T-cell assays in predicting late- or delayed-onsetCMV disease are under way The vast majority of late- or de-layed-onset CMV disease cases remain susceptible to ganci-clovir, although there has been an increasing recognition ofdrug-resistant strains (226) In these cases of ganciclovir-resist-ant CMV, the associated morbidity is high and the clinical dis-ease has resulted in poor allograft and patient survival(226–228)

par-Preemptive Therapy

Preemptive anti-CMV therapy involves the administration of

antiviral agents only to patients with asymptomatic CMV

reac-tivation with the main goal of preventing progression to

symp-tomatic CMV disease (44,106,178) For preemptive therapy to

work optimally, a sensitive laboratory or a clinical indicator is

needed to identify the patients at increased risk of developing

CMV disease (44,113,198,229) In this regard, identifying

patients with evidence of CMV infection prior to the onset

of disease is dependent on laboratory markers (44,113,198,229)

or a clinical event highly associated with CMV reactivation

(59,230); the latter is the basis of targeted prophylaxis (230)

Compared to antiviral prophylaxis, wherein antiviral

drugs are administered to all at-risk patients, the preemptive

therapy approach will provide antiviral drugs only to

pa-tients with evidence of asymptomatic CMV infection (230)

Compared to antiviral prophylaxis, wherein antiviral drugs

are administered for 3 months or longer, the duration of

an-tiviral drug administration is relatively shorter during

pre-emptive therapy, as the duration is guided by CMV surveillance

testing Accordingly, fewer patients will receive an antiviral

drug, and for shorter duration of time, and this has potential

advantages in terms of reducing direct drug costs and the risks

of adverse effects from antiviral medications Moreover,

pre-emptive therapy may be associated theoretically with a lower

risk for the emergence of resistant strains, although

ganci-clovir-resistant CMV has been reported to occur among lung

transplant recipients who received prolonged preemptive

therapy (215)

Intravenous ganciclovir and oral valganciclovir are the

most commonly used antiviral drugs for preemptive anti-CMV

therapy (231) In a randomized comparative trial, both

intra-venous ganciclovir and oral valganciclovir were equally

effec-tive for the preempeffec-tive treatment of CMV infection (231)

Generally, preemptive treatment should be continued until the

virus is no longer detected for at least 2 weeks in the blood

(44,106,178,190) High-dose oral acyclovir, intravenous

acy-clovir, valacyacy-clovir, and immunoglobulin preparations should

not be used for preemptive therapy since they are comparatively

less effective than ganciclovir-based regimens in treating active

CMV replication (44,106,178,190) Oral ganciclovir has been

used successfully for preemptive therapy in many clinical

stud-ies (197,229,232,233), but its poor absorption, the risk of

emer-gence of ganciclovir-resistant CMV in the presence of low

systemic ganciclovir levels, and the availability of more

bioavail-able valganciclovir have limited the use of oral ganciclovir

Because of associated severe toxicities, foscarnet and cidofovir

are not used as first-line agents for preemptive treatment in

solid organ transplant recipients Table 23.10 shows a list of

con-trolled clinical trials of preemptive therapy after solid organ

transplantation (197,199,229)

Because the principle of preemptive therapy requires

iden-tification of patients with CMV reactivation before the onset of

clinical CMV disease, it is essential that a highly predictive nostic assay is available for its optimal implementation (113) Inthis regard, there has been a considerable debate as to the opti-mal method for CMV detection and the frequency of CMV sur-veillance Among the laboratory methods used for the diagnosis

diag-of CMV infection (Table 12.4) (113), those that have been shown

to be effective for guiding preemptive therapy are CMV pp65antigenemia (198,234–237) and nucleic acid detection andamplification assays for CMV DNA or RNA (179,229,233,238–240) Which of these laboratory methods is more effective

in guiding preemptive therapy is dependent on a variety of tors, although both have been demonstrated to be effective Theoptimal frequency of CMV surveillance by CMV PCR or pp65antigenemia has been suggested to be once weekly for thefirst 12 to 14 weeks after solid organ transplantation (44,106,178,190) In contrast, the low sensitivity and slow turn-aroundtime have limited the use of conventional and shell vial culturesystems for preemptive therapy (241,242) In a study that usedvirus cultures in guiding preemptive antiviral therapy amongliver transplant recipients (199), CMV disease developed in 63%

fac-of patients with no prior positive surveillance cultures Thus, it

is recommended that each transplant center has easy access torapid, sensitive, and predictive CMV surveillance assay if pre-emptive therapy is their approach to CMV prevention aftersolid organ transplantation (113)

The rapid replication of CMV in CMV D/R solidorgan transplant patients has led many centers to question thesuccessful implementation of preemptive therapy in this high-risk population (23,24,90) In few studies (229,232,233), manyCMV D/R– solid organ transplant patients were not identifiedsoon enough for the timely initiation of preemptive treatment.Hence, many guidelines have preferred antiviral prophylaxisover preemptive therapy in CMV D/R– solid organ transplantrecipients (44,106,178,190) Other centers, however, have re-ported good experience with preemptive therapy even in thishigh-risk CMV D/R– population (197,198,243)

Polymerase Chain Reaction Assay for Preemptive Therapy

CMV DNA amplification systems are currently the most monly used methods for guiding the initiation of preemptivetherapy of early subclinical CMV reactivation (113) PCR candetect CMV DNA in the sera of 83% of liver transplant recip-ients at a mean of 13 days before the onset of symptomaticCMV infection (244) In a randomized, placebo-controlledtrial of PCR-guided oral ganciclovir preemptive therapy, theincidence of CMV infection and disease was reduced from21% to 3% and 12% to 0%, respectively (229) However, CMVdisease occurred in 25 (15%) of 169 patients prior to or at thetime of CMV PCR positivity, especially among CMV D/R–patients, thus precluding the administration of preemptivetherapy in this high-risk subgroup (92) Accordingly, preemptivetherapy in high-risk (i.e., CMV D/R–) solid organ transplant

com-TABLE 23.10

recipients may require more frequent surveillance testing

(23,90,113) Even then, PCR testing of the blood may not

al-ways detect cases of organ-invasive CMV disease in which

there is transient or lack of CMV viremia (1) Certain types

of compartmentalized CMV diseases, such as

gastrointesti-nal CMV disease or retigastrointesti-nal disease, may not be associated

with preceding or concurrent viremia, and may present

hur-dles to the successful implementation of preemptive antiviral

therapy (1)

The optimal sample for the detection of CMV DNA has

been debated, and current platforms have used various blood

compartments such as plasma, serum, whole blood, or cellular

components (245) One drawback to the use of CMV DNA

PCR assay is the potential uncertainty in distinguishing active

replication from latent infection, particularly with the use of

qualitative PCR assays (246) Use of noncellular samples

(plasma and serum), serial quantification of CMV DNA levels,

and measurement of messenger RNA (mRNA; instead of

DNA) have been suggested approaches to signify active CMV

infection (23,89,91,107,113,224,247–249) The initial virus load

and the rate of virus load increase, which directly implies

in-creasing virus replication, have been independently

corre-lated with the subsequent development of active CMV disease

(23,89) Additionally, several groups have reported that

quan-titative CMV PCR using bronchoalveolar lavage is highly

predictive of CMV pneumonitis in lung and heart–lung

trans-plant recipients (250–252)

The viral load threshold for initiating preemptive

antivi-ral therapy has not been well defined Differences in patient

characteristics, lack of standardization among laboratory

as-says, and the varying analytical performance of diagnostic tests

have made it difficult, if not impossible, to define a specific

clinically significant level of viral replication (113,253,254)

Lacking this widely accepted viral load threshold, it is

impera-tive for individual transplant centers to develop clinically

vali-dated thresholds that will trigger the initiation of preemptive

therapy One guideline suggested, using data generated from

the use of COBAS Amplicor CMV Monitor assay (Roche

Diagnostics, Pleasanton, CA), an optimal viral threshold of

1000 to 5000 copies of CMV DNA per milliliter of plasma for

guiding preemptive therapy in solid organ transplantation

(255); however, this recommendation requires evaluation in a

prospective clinical investigation It is likely that the suggested

threshold may differ between CMV D/R– and R patients,

between lung and nonlung transplant recipients, and between

those who received or did not receive induction therapy with

lymphocyte-depleting agents, among other factors

The duration of antiviral administration during

preemp-tive therapy varies depending on individual clinical practices,

although PCR assays have been useful in defining the optimal

length of preemptive therapy (44,106,178,190) It is generally

recommended to continue preemptive antiviral treatment

until CMV DNAemia is no longer detectable for at least

2 weeks (44,106,178,190) CMV PCR testing is generally ommended on a weekly basis for the duration of preemptiveantiviral treatment and for the entire “high-risk” period (i.e.,

rec-12 to 14 weeks after transplantation) (44) CMV PCR testingwould also provide an indication of the antiviral and clinicalefficacy of the antiviral treatment, with a decline in viral load

as an indication of effective treatment, while nondecline or ing viral load is an indication of antiviral drug resistance orpoor drug bioavailability (215,216,226,256) It is important torecognize, however, that viral load may occasionally tran-siently rise during the first 1 to 2 weeks of preemptive treat-ment, and this does not necessarily suggest antiviral drugresistance (257)

ris-Antigenemia Assay for Preemptive Therapy

Detection of pp65 antigen in peripheral blood leukocytes hasbeen used as a sensitive marker for the presence of activeCMV infection, and a useful laboratory marker for guidingpreemptive therapy (234,258–261) In heart transplant recipi-ents, CMV pp65 antigenemia assay has 83% sensitivity as amarker for subsequent CMV disease, and its detection pre-ceded the onset of CMV disease by 5 days (163) In a study of

72 liver transplant recipients, CMV pp65 antigenemia wasused to successfully guide the administration of intravenous

or oral ganciclovir for the prevention of CMV disease (197).However, other investigators have reported that pp65 anti-genemia did not precede symptoms of CMV disease in up to32% of patients (232,262) These contrasting findings may re-flect the subjectivity of the pp65 antigenemia assay and thepresence of the other factors, such as the rapid replication dy-namics in CMV D/R– solid organ transplant patients, thelack of or transient viremia in some end-organ CMV diseases,and other characteristics such as the use of lymphocyte-depleting agents As with CMV PCR assays, the general rec-ommendation is to perform CMV pp65 antigenemia assay on

a weekly basis during the high-risk period (e.g., during thefirst 12 to 14 weeks after solid organ transplantation) (44,106,178,190) However, a defined cut-off value of a clinically rele-vant level of pp65 antigenemia has not been defined A sug-gested threshold of 10 positive cells per 2 105cells in solidorgan transplant recipients has yet to be validated by prospec-tive clinical trials (255) As with CMV PCR assays, weeklypp65 antigenemia is used to guide the duration of preemptiveantiviral treatment, and a transient rise in the antigenemialevels during the first 2 weeks of antiviral therapy has alsobeen observed in some cases (257)

Antigenemia Versus Polymerase Chain Reaction Assay

Which of the two laboratory methods (pp65 antigenemia ornucleic acid detection) is optimal in guiding preemptive antivi-ral therapy has been debated (197,229,232,234,261,263–265) In

a comparative study, CMV PCR assay performed on peripheral

blood leukocytes was the earliest signal of CMV replication,

followed by PCR performed on plasma and then by pp65

anti-genemia (266) In contrast, another study showed that detection

of CMV mRNA by PCR was inferior to pp65 antigenemia

with respect to the early diagnosis of CMV disease (267)

Findings in another prospective study of liver transplant

recip-ients suggested that both assays were comparable, with a slight

advantage with the use of PCR, in guiding preemptive therapy

(91) The variations in the results of these studies reflect the

nonstandardized methods of CMV detection (254)

“Home-brew” PCR assays are institution-based methods, and results

often are not comparable between centers (113,253) It is not

uncommon to have different reporting systems; hence, a result

of one laboratory may not be reproducible in other centers,

even when using similar assays and protocols (253) This lack of

concordance is likely due to multiple biologic, technical, and

lo-gistical factors Likewise, the use of pp65 antigenemia is

subjec-tive and is dependent on the expertise of laboratory personnel

Moreover, pp65 antigenemia should be performed within 6 to

8 h of blood collection since it is dependent on the stability of

neutrophils in blood specimens (113) This property may limit

its utility among transplant recipients who live distant from

transplant centers Since different transplant centers have

re-ported successes with both methods, it is currently

recom-mended that preemptive therapy be guided by a reliable assay

that has been optimized and clinically validated by the ual transplant centers

individ-Targeted Prophylaxis

Targeted prophylaxis involves the administration of tive” antiviral therapy to selected patients with clinical andepidemiologic characteristics that identify them to be at in-creased risk of CMV infection and disease (Table 23.11)(44,59,92,268–270) This requires an active investigation ofrisk factors, which triggers the administration of an antiviraldrug in a “preemptive” manner The most important identi-fied risk factor is the use of lymphocyte-depleting anti-T-cellreceptor antibodies, either as induction therapy or for treat-ment of allograft rejection (44,59,92)

“preemp-The principle of this prevention approach is that the sity of antiviral strategy should parallel the intensity of the anti-rejection program Antilymphocyte antibody therapy results insevere immunosuppression and has been identified as one of themost important clinical predisposing factors for CMV disease insolid organ transplant recipients Intravenous ganciclovir ther-apy given during antilymphocyte antibody therapy has beenshown to decrease the incidence of CMV disease (271,272).Currently, valganciclovir is the most commonly used drugfor targeted prophylaxis Intravenous and oral ganciclovir arealternative agents In contrast, immunoglobulins, acyclovir, and

Preparations During Use of Anti-T–Cell Receptor Antibody in Solid Organ Transplant Recipients

Number of Patients (Number

0 and weeks 2 and 4; reduced

250 mg/kg weeks 6 incidence of CMV and 8 vs no prophylaxis complications (272) 64 (0) vs IV GCV 2.5 mg/kg t.i.d Reduction in 14% vs 33% 2% vs 4%

vs no prophylaxis

prophylaxis

5, then q week 3 w with PO ACV 400 mg 5X/d 3 mo vs no prophylaxis

Abbreviations: CMV, cytomegalovirus; D, donor; R, recipient; PO, per orem (orally administered); IV, intravenous; ACV, acyclovir; GCV, ganciclovir; ATG, antithymocyte globulin.

aIf known, the number of patients who were D /R is given in parentheses.

b

valacyclovir are not generally recommended for targeted

pro-phylaxis The exact duration of targeted prophylaxis is not well

defined, although many centers provide antiviral therapy for

1 to 3 months following the use of antilymphocyte antibody

therapy (44,106,178,190)

OTHER CYTOMEGALOVIRUS

PREVENTION APPROACHES

Cytomegalovirus-Seronegative Blood

Products and Protective Matching

Knowledge of the CMV serologic status of the donor and

re-cipient prior to solid organ transplantation is a reliable

predic-tor of identifying which patients will develop CMV disease,

with CMV D/R representing the highest risk (273–275)

The use of protective matching (i.e., transplantation of an

allo-graft from a seronegative donor to a seronegative recipient)

may limit the occurrence of CMV disease in the seronegative

recipient by avoiding the transmission of CMV during solid

organ transplantation (273–275) However, this approach is

impractical because of the scarcity of CMV-seronegative organ

donors Waiting for a CMV-seronegative donor might delay a

life-saving transplant procedure Moreover, the approach does

not guarantee complete protection since natural transmission

of CMV occurs in the community

CMV-seronegative or leuko-reduced blood products are

suggested for CMV D/R transplant recipients who

re-quire blood transfusions during the course of transplant

sur-gery (273–276) Because the majority of blood donors are

CMV seropositive, one limitation is the scarcity of

CMV-seronegative blood products In such a situation, filtered or

leukocyte-poor products, which are associated with a low risk

of CMV transmission, have been suggested (276)

Immunotherapy and Vaccination

In theory, one intervention to prevent or reduce the risk of

pri-mary CMV infection after solid organ transplantation is

im-munization of CMV-seronegative recipients with a CMV

vaccine, in the anticipation of future posttransplant viral

chal-lenge Randomized, placebo-controlled, double-blind trials of

the live-attenuated Towne vaccine in kidney transplant

recipi-ents demonstrated safety and immunogenicity of the vaccine

but it did not demonstrate significant prevention from CMV

infection, although a decrease in the severity of CMV disease

by up to 85% was observed (277–279) Moreover, among the

CMV D/R subgroup, the 1- and 5-year renal allograft

ac-tuarial survival rates were higher in CMV-vaccinated patients

(73% and 62%, respectively) compared to those who received

placebo (40% and 25%, respectively) (280) Since then, there

have been continued efforts to develop an effective CMV

vac-cine (281–284), including peptide-based and subunit vacvac-cines

containing recombinant immunodominant glycoproteins (285).All of these still require rigorous clinical trials, and none is cur-rently near approval for clinical use

Because preexisting CMV-specific immunity ing antibodies and cell-mediated immunity) is associated with

(neutraliz-a lower incidence of CMV dise(neutraliz-ase, (neutraliz-a str(neutraliz-ategy to boost specific immunity after solid organ transplantation may have abeneficial effect in decreasing CMV disease Previous studieshave correlated CMV disease with a lack or diminished CMV-specific T cells (278) Thus, expanding the number and func-tion of virus-specific cytotoxic T lymphocytes could reduce theincidence of CMV disease, although this approach remainsinvestigational

CMV-Despite studies suggesting that humoral response alone isunable to control CMV infection, the administration of unse-lected or CMV immunoglobulins have been used to boost hu-moral CMV immune response in an attempt to prevent CMVdisease after solid organ transplantation (129,286–292) Resultsfrom randomized, controlled trials in kidney transplant recipi-ents indicate that immunoglobulins prevented CMV disease insome but not all trials (129,286–292) Two recent meta-analyseshave demonstrated that the use of immunoglobulin prophy-laxis was associated with reduction in CMV-related death(293,294) However, although one study showed that im-munoglobulins were beneficial in terms of long-term survivaland associated with significant reduction in the incidence ofCMV disease (293), the other study showed no significant re-duction in the risk of CMV disease, CMV infection, and all-cause mortality when compared to placebo or no treatment(294) Although the data are conflicting, some centers haveused unselected or CMV immunoglobulins as adjunctive agentfor the prevention of CMV disease in high-risk transplant pop-ulations such as lung and intestinal transplants, usually in com-bination of antiviral drugs (44,106,178,190) Results of a recentmeta-analysis, however, showed that immunoglobulins had nosignificant added protection when combined with antiviraldrugs (294) In this meta-analysis, there was no difference inthe risk for CMV disease, CMV infection, and all-cause mor-tality between antiviral prophylaxis alone or in combinationwith immunoglobulins (294) The high cost of immunoglobu-lins and the risks associated with parenteral administrationrepresent the main disadvantages of immunoglobulins Further-more, the availability of effective oral antiviral drugs has di-minished the use of immunoglobulins for the prevention ofCMV disease after solid organ transplantation

TREATMENT OF CYTOMEGALOVIRUS DISEASE

CMV disease after solid organ transplantation is a potentiallyfatal illness and should be treated as soon and as aggressively

as possible The antiviral drugs for the treatment of CMV

disease are intravenous ganciclovir and its oral prodrug,

val-ganciclovir, intravenous foscarnet, and intravenous cidofovir

(Table 23.12) (44) All of these drugs inhibit CMV replication by

acting as competitive substrate for the CMV DNA polymerase

In addition to antiviral drug therapy, it is recommended that the

treatment of CMV disease should be complemented by a

reduc-tion in the intensity of drug immunosuppression

Intravenous ganciclovir is considered as the first-line tiviral therapy (44), although valganciclovir has now been

an-demonstrated to be noninferior for treatment of mild to

mod-erate (i.e., nonsevere) CMV disease in selected solid organ

transplant recipients (295) Foscarnet and cidofovir are

gener-ally not recommended as first-line treatment of CMV disease

because of their toxicities Both foscarnet and cidofovir are

re-served for the treatment of ganciclovir-resistant CMV disease

Intravenous Ganciclovir and Valganciclovir

Several clinical trials have demonstrated the efficacy and

safety of intravenous ganciclovir for the treatment of CMV

disease after solid organ transplantation (178,295–298) The

administration of intravenous ganciclovir resulted in a

signifi-cant decline in the CMV DNA levels, which accompanied the

clinical resolution of symptoms (224,245,254,295,296) The

half-life of CMV, which is a measure of the rate of CMV

de-cline, during intravenous ganciclovir therapy ranges from 2.36

days in liver transplant recipients (90) to as long as 5 days in a

heterogenous group of solid organ transplant patients (224,

245) The standard therapeutic dose of ganciclovir is 5 mg/kg

every 12 h, administered intravenously as a 1-h infusion

Because ganciclovir is predominantly excreted by the renalsystem, patients with renal impairment require dose reduc-tions Concentrations of ganciclovir in the blood decrease by50% after 4 h of hemodialysis; thus, ganciclovir must be read-ministered after dialysis (299)

Oral ganciclovir should not be used for treatment of tablished CMV disease (200) because the absorption of ganci-clovir after oral administration is low and the levels achieved

es-in the blood is not sufficient to treat active CMV replication(193,200) In contrast, valganciclovir is characterized by signif-icantly improved bioavailability with serum ganciclovir con-centrations that are 10 times higher than oral ganciclovir andwith levels that approximate those achieved with intravenousganciclovir (193,200) A prospective, randomized, multicentertrial showed that valganciclovir was as safe and effective as in-travenous ganciclovir for the treatment of nonsevere cases ofCMV disease in solid organ transplant recipients (295) Therates of virological decline and clinical resolution by end of apredefined 21-day treatment course and by the end of mainte-nance valganciclovir treatment were similar between thetreatment arms (295) The results of this study may simplifythe current treatment paradigms, as an oral agent is now avail-able for treatment, thereby facilitating outpatient manage-ment The recommended dose of valganciclovir for treatment

of CMV disease is 900 mg twice daily, with dose adjustmentsbased on renal function Valganciclovir is not indicated asfirst-line therapy in severe cases of CMV disease and in patientswhose intestinal absorption is uncertain, such as those withvomiting and diarrhea (193) In these cases, it is recommended

to initiate therapy with intravenous ganciclovir followed by,

Ganciclovir 5 mg/kg IV every 12 h Inhibits CMV DNA Bone marrow First-line drug

absorbed and should not

be used for treatment Valganciclovir 900 mg PO twice Inhibits CMV DNA Bone marrow First-line drug in mild-to-

disease Foscarnet 60 mg/kg IV every Inhibits CMV DNA Electrolyte abnormalities, Second line antiviral drug;

8 h (or 90 mg/kg polymerase nephrotoxicity, anemia, utilized in

Cidofovir 5 mg/kg IV every Inhibits CMV DNA Nephrotoxicity, ocular Rarely used as initial therapy;

thereafter Abbreviation: CMV, cytomegalovirus.

aAll dosing should be adjusted based on renal function The duration of therapy must be tailored as a function of the degree of viral replication, as assessed by CMV DNA PCR or pp65 antigenemia assay, and clinical response (i.e., resolution of symptoms).

when the clinical situation improves, step-down therapy with

treatment doses of valganciclovir

The optimal duration of antiviral therapy remains

un-known Although most patients receive antiviral therapy for 2

to 4 weeks (44), the duration of therapy has been individualized

based on the clinical resolution of symptoms and the clearance

of the virus in the blood CMV PCR or pp65 antigenemia is

generally performed once weekly during treatment to assess

vi-rologic response to antiviral therapy (44,106,178,190) CMV

monitoring should be performed using the same assay, since

viral load values can markedly differ among various tests (106)

Clinical experience suggests that longer durations of treatment

are required in patients with severe end-organ CMV disease,

such as pneumonitis, retinitis, and gastrointestinal CMV

dis-ease (44) Studies on CMV dynamics and kinetics indicate that

the degree of viral replication, as measured by the virus load in

the peripheral blood at the start and end of antiviral therapy,

and the degree of viral decay, influence the duration of therapy

(224,296) Clearance of viremia is a useful guide for the

discon-tinuation of antiviral therapy (224,296) A study of liver

trans-plant recipients demonstrated that a high virus load at the end

of therapy predicted highly the occurrence of clinical and

viro-logic relapse of CMV infection (296) One possible limitation of

viral load as a clinically useful indicator of the duration of

antivi-ral therapy is in cases of “compartmentalized” organ-invasive

diseases, which are characterized by minimal or transient

viremia (e.g., retinitis, some cases of hepatitis and

gastrointesti-nal diseases) (1,75) Maintenance therapy, wherein antiviral

drugs are given at prophylactic doses following an induction

treatment phase, is generally not recommended in solid organ

transplantation, unless the clinical situation indicates persistent

immunocompromise and high risk of relapse; these conditions

may indicate the need for providing additional course of

pro-phylaxis during the period associated with high risk

Recurrent CMV disease occurs in up to 25% to 35% of

solid organ transplant recipients with tissue-invasive CMV

disease (296,298) CMV recurrence has been significantly

cor-related with the incomplete clearance of virus from the blood

at the end of treatment (i.e., the duration of treatment may

have been insufficient) In addition, the immunologic

condi-tion of the host may influence the risk of relapse, and patients

with persistent severe immunocompromise (i.e., CMV-specific

T-cell deficiency) are more likely to have recurrence of CMV

infection and disease after cessation of antiviral therapy Most

cases of recurrent CMV disease respond well to retreatment

with intravenous ganciclovir (296,298); however, a few cases

may be due to ganciclovir-resistant CMV

The adverse effects of intravenous ganciclovir and

val-ganciclovir include leukopenia, neutropenia,

thrombocytope-nia, anemia, eosinophilia, bone marrow hypoplasia, hemolysis,

nausea, diarrhea, renal toxicity, seizures, mental status changes,

fever, rash, and abnormal liver function tests (44,104,193,295)

Thus, the hematologic profile and liver and renal function

should be monitored once weekly while the patient is ing ganciclovir Ganciclovir also has teratogenic and car-cinogenic potential, and gonadal toxicity has been shown inanimal models The long-term safety of ganciclovir intransplant recipients, particularly children, remains to be established (44,104,193,295)

receiv-Foscarnet

Compared with intravenous ganciclovir, there is less ence and clinical data available regarding the use of foscarnetfor the primary treatment of CMV disease in solid organtransplant recipients (178,222,300) Until more clinical data areavailable, foscarnet should be reserved for patients who areintolerant of ganciclovir (such as in cases of severe leukope-nia not responsive to granulocyte colony-stimulating factors)

experi-or fexperi-or those who have failed ganciclovir therapy as a result

of drug resistance Because foscarnet does not require UL97phosphotransferase-mediated chemical modification for antivi-ral activity, it can be used for the treatment of UL97-mutantganciclovir-resistant CMV disease (178,222,300) Foscarnet isadministered intravenously at a dose of 60 mg/kg every 8 h(or 90 mg/kg twice daily); patients with renal insufficiency require dose adjustment The major adverse effects of foscarnetare nephrotoxicity (e.g., acute tubular necrosis, interstitialnephritis, or the precipitation of crystals in the glomerular capil-laries), hemorrhagic cystitis, urethral ulcerations, anemia, hyper-phosphatemia, hypophosphatemia, hypercalcemia, hypocalcemia,hypomagnesemia, nausea, vomiting, and seizures (301) Thehigh incidence of electrolyte disturbances warrant aggressivemonitoring and repletion, as needed

Ganciclovir–Foscarnet Combinations

Small clinical studies have investigated combined antiviral apy with ganciclovir and foscarnet on the basis of in vitro datathat suggest these agents have synergistic antiviral activity (302)

ther-An observational study involving solid organ transplant ents suggests that combined ganciclovir and foscarnet, with eachadministered at half doses, is effective in treating ganciclovir-resistant CMV infection (303) However, a larger trial that eval-uated a mixed group of bone marrow and solid organ trans-plant recipients demonstrated that the adverse events weremore commonly observed among those patients receiving com-bination therapy, even at reduced doses, than among those re-ceiving a single drug (304) Moreover, when half doses are used,the risks associated with lower serum drug concentrations, such

recipi-as fostering drug resistance, must be considered

Cidofovir

Cidofovir, a phosphonomethoxy analogue of cytosine, is usedmuch less commonly than ganciclovir and foscarnet for the

a comparative study, CMV PCR assay performed on peripheral