Lack of emergence of cytomegalovirus UL97 mutations conferring ganciclovir (GCV) resistance following preemptive GCV therapy in allogeneic stem cell transplant recipients

American Society for Transplantation and Cellular Therapy Series: #4 - Cytomegalovirus treatment and management of resistant or refractory infections after hematopoietic cell transplantation

The Practice Guidelines Committee of the American Society of Transplantation and Cellular Therapy (ASTCT) partnered with its Transpl. Infect. Dis. Special Interest Group (TID-SIG) to update its 2009 compendium-style infectious disease guidelines for hematopoietic cell transplantation (HCT). A new approach was employed with the goal of better serving clinical providers by publishing each standalone topic in the infectious diseases series as a concise format of frequently asked questions (FAQ), tables, and figures. Adult and pediatric infectious diseases and HCT content experts developed and answered FAQs. Topics were finalized with harmonized recommendations that were made by assigning an A through E strength of recommendation paired with a level of supporting evidence graded I through III. The fourth topic in the series focuses on the management and treatment of cytomegalovirus (CMV) resistant and refractory infections. The diagnosis, definitions of resistant and refractory CMV, risk factors, virological genotypes and treatment algorithms are reviewed.

How I treat CMV reactivation after allogeneic hematopoietic stem cell transplantation

Cytomegalovirus (CMV) reactivation remains one of the most common and life-threatening infectious complications following allogeneic hematopoietic stem cell transplantation, despite novel diagnostic technologies, several novel prophylactic agents, and further improvements in preemptive therapy and treatment of established CMV disease. Treatment decisions for CMV reactivation are becoming increasingly difficult and must take into account whether the patient has received antiviral prophylaxis, the patient's individual risk profile for CMV disease, CMV-specific T-cell reconstitution, CMV viral load, and the potential drug resistance detected at the time of initiation of antiviral therapy. Thus, we increasingly use personalized treatment strategies for the recipient of an allograft with CMV reactivation based on prior use of anti-CMV prophylaxis, viral load, the assessment of CMV-specific T-cell immunity, and the molecular assessment of resistance to antiviral drugs.

Comparison of different cytomegalovirus diseases following haploidentical hematopoietic stem cell transplantation

Cytomegalovirus (CMV) can cause end-organ diseases including pneumonia, gastroenteritis, retinitis, and encephalitis in hematopoietic stem cell transplantation recipients. Potential differences among different CMV diseases remain uncertain. This study aimed to compare the clinical characteristics, risk factors, and mortality among different CMV diseases. A retrospective nested case-control study was performed based on a cohort of 3862 patients who underwent haploidentical hematopoietic stem cell transplantation at a single-center. CMV diseases occurred in 113 (2.92%) of 3862 haplo-HSCT recipients, including probable CMV pneumonia (CMVP, n = 34), proven CMV gastroenteritis (CMVG, n = 34), CMV retinitis (CMVR, n = 31), probable CMV encephalitis (CMVE, n = 7), and disseminated CMV disease (Di-CMVD, n = 7). Most (91.2%) cases of CMVG developed within 100 days, while most (90.3%) cases of CMVR were late onset. Refractory CMV infection and CMV viral load at different levels were associated with an increased risk of CMVP, CMVG, and CMVR. Compared with patients without CMV diseases, significantly higher non-relapse mortality at 1 year after transplantation was observed in patients with CMVP and CMVR, rather than CMVG. Patients with CMVP, Di-CMVD, and CMVE had higher overall mortality after diagnosis than that of patients with CMVG and CMVR (61.7%, 57.1%, 40.0% vs 27.7%, 18.6%, P = 0.001). In conclusion, the onset time, viral dynamics, and mortality differ among different CMV diseases. The mortality of CMV diseases remains high, especially for CMVP, Di-CMVD, and CMVE.

Global estimate of phenotypic and genotypic ganciclovir resistance in cytomegalovirus infections among HIV and organ transplant patients; A systematic review and meta-analysis

Human cytomegalovirus (CMV), an opportunistic pathogen belonging to Herpesviridae family, is considered as one of the major causes of morbidity and mortality among wide variety of patients, particularly in transplant recipients and HIV positive patients. As this virus can be resistant to treatment, frequency of CMV in patients who receive organ transplantation and people suffering from AIDS was studied between 1980 and 2019. Medline (via PubMed), Embase, Web of Science, and the Iranian Database were reviewed, and Comprehensive Meta-Analysis (V2.0, Biostat) software analyzed all data. Finally, we used Cochran's Q-statistic to encounter heterogeneity between different studies. Meta-analyses indicated, GCV resistance was 14.1% (95% CI 11.2-17.7); however, in patients suffering from AIDS and organ transplantation were 19.5% (95% CI 14.7-25.4) and 11.4% (95% CI 8.1-15.8), respectively. There were increasing rates in the prevalence of GCV resistance in CMV among transplant recipients, and HIV positive patients. Therefore, evaluation of these refractory infections is beneficial.

Cytomegalovirus retinitis in children and adolescents with acute leukemia following allogeneic hematopoietic stem cell transplantation

Cytomegalovirus retinitis (CMVR) may occur after allogeneic hematopoietic stem cell transplantation (HSCT). However, little is known about its incidence, strategies for ophthalmic surveillance, and timely implementation of adequate antiviral treatment in pediatric allogeneic HSCT recipients. We provide a retrospective analysis of the epidemiology and clinical features of CMVR in pediatric allogeneic HSCT patients transplanted at our center over a 16-year period. Two patients of this cohort with leukemia are presented. Our analysis is supplemented by a systematic review on pediatric patients with leukemia and CMVR in the setting of allogeneic HSCT. The overall incidence of CMVR in our cohort was 1% (4/338) and 14.2% (3/21) in leukemic patients. In published cases, CMVR occurred at a median of 143 days after transplantation, and, in the majority of patients, was preceded by CMV detection in blood by a median of 93 days. Continued immune suppression following engraftment likely triggers CMVR. Preemptive treatment with ganciclovir as standard is usually successful. Foscarnet is used in case of resistance to ganciclovir or drug-induced granulocytopenia. Overall, CMVR after HSCT in pediatric leukemic patients is rare, but a potentially higher vulnerability of this population for involvement of the eye warrants a standardized ophthalmological examination plan.

Infectious complications after hematopoietic stem cell transplantation: current status and future perspectives in Korea

Hematopoietic stem cell transplantation (HSCT) is a treatment for hematologic malignancies, immune deficiencies, or genetic diseases, ect. Recently, the number of HSCTs performed in Korea has increased and the outcomes have improved. However, infectious complications account for most of the morbidity and mortality after HSCT. Post-HSCT infectious complications are usually classified according to the time after HSCT: pre-engraftment, immediate post-engraftment, and late post-engraftment period. In addition, the types and risk factors of infectious complications differ according to the stem cell source, donor type, conditioning intensity, region, prophylaxis strategy, and comorbidities, such as graft-versushost disease and invasive fungal infection. In this review, we summarize infectious complications after HSCT, focusing on the Korean perspectives.

How I treat resistant cytomegalovirus infection in hematopoietic cell transplantation recipients

Cytomegalovirus (CMV) infection is a significant complication in hematopoietic cell transplantation (HCT) recipients. Four antiviral drugs are used for preventing or treating CMV: ganciclovir, valganciclovir, foscarnet, and cidofovir. With prolonged and repeated use of these drugs, CMV can become resistant to standard therapy, resulting in increased morbidity and mortality, especially in HCT recipients. Antiviral drug resistance should be suspected when CMV viremia (DNAemia or antigenemia) fails to improve or continue to increase after 2 weeks of appropriately dosed and delivered antiviral therapy. CMV resistance is diagnosed by detecting specific genetic mutations. UL97 mutations confer resistance to ganciclovir and valganciclovir, and a UL54 mutation confers multidrug resistance. Risk factors for resistance include prolonged or previous anti-CMV drug exposure or inadequate dosing, absorption, or bioavailability. Host risk factors include type of HCT and degree of immunosuppression. Depending on the genotyping results, multiple strategies can be adopted to treat resistant CMV infections, albeit no randomized clinical trials exist so far, after reducing immunosuppression (if possible): ganciclovir dose escalation, ganciclovir and foscarnet combination, and adjunct therapy such as CMV-specific cytotoxic T-lymphocyte infusions. Novel therapies such as maribavir, brincidofovir, and letermovir should be further studied for treatment of resistant CMV.

High rate of cytomegalovirus drug resistance among patients receiving preemptive antiviral treatment after haploidentical stem cell transplantation

We examined the rate, clinical impact, and risk factors of cytomegalovirus (CMV) drug resistance in 561 patients who underwent 616 hematopoietic stem cell transplantations (HSCTs) over 5 years. Drug resistance was exclusively identified in haploidentical (haplo)-HSCT recipients receiving preemptive therapy, among whom the rate was 14.5%. Resistance appeared after prolonged treatment (median, 70 days), was associated with higher preceding viral load (P < .001), and was the strongest predictor for disease by multivariate analysis. The high rate of drug resistance as interlinked with severe disease in haplo-HSCT recipients suggests the potential advantage of prophylactic over preemptive treatment in high-risk patients and highlights the need for better-tolerable anti-CMV drugs.

Failure of pre-emptive treatment of cytomegalovirus infections and antiviral resistance in stem cell transplant recipients

BACKGROUND

Treatment of cytomegalovirus (CMV) infections after stem cell transplantation (SCT) does not always lead to a rapid viral response. The causes of treatment failure may be either viral resistance or immunological failure to control viral replication. This study investigated the response to pre-emptive treatment in CMV infections in order to define risk factors for treatment failure, including the role of antiviral resistance.

METHODS

Adult recipients of allogeneic T-cell depleted SCT were studied retrospectively (n=92). CMV infections were treated with (val)ganciclovir according to a CMV DNA-load-based pre-emptive strategy. Treatment failure was defined as a CMV DNA load of 1,000 copies/ml or more after at least 2 weeks of treatment. Resistance was analysed by nucleotide sequence analysis of the UL97 and UL54 genes in the first CMV DNA-positive sample and in samples during treatment failure.

RESULTS

Treatment failure occurred in 26 of the 47 pre-emptively treated patients (55%) and in 39 of 86 (45%) treatment episodes. The risk of treatment failure was increased during first treatment episodes (P=0.01) and during the use of immunosuppressive medication (P=0.02). Antiviral resistance was found in only 1 patient (4%) with treatment failure.

CONCLUSIONS

A slow response to pre-emptive antiviral treatment occurred frequently in CMV infections in SCT recipients. Antiviral resistance was observed but played a minor role in treatment failure.

The genetic basis of human cytomegalovirus resistance and current trends in antiviral resistance analysis

Infections due to resistant human cytomegalovirus (CMV) are an emerging problem, particularly in immunocompromised hosts. When managing such patients, clinicians should be aware of the possibility of developing CMV antiviral resistance, especially while on prolonged therapy or if severe immunosuppression is present. CMV resistance to current antiviral agents is mediated by alterations in either the UL97 kinase or DNA polymerase, encoded by the UL97 and UL54 genes, respectively. UL97 mutations are capable of conferring resistance to ganciclovir, while UL54 mutations can impart resistance to ganciclovir, cidofovir, and foscarnet. If treatment failure is suspected to be due to antiviral resistance, CMV resistance analysis should be obtained. Phenotypic resistance assays performed on clinical isolates measure antiviral susceptibilities directly, but are laborious and time-consuming. Therefore, genotypic resistance analysis has become the more common means of diagnosing CMV resistance. Mutations in UL97 or UL54 may be clinically associated with resistance, but their effect on antiviral susceptibility must be confirmed by marker transfer techniques such as recombinant phenotyping.

Paradoxical rising cytomegalovirus antigenemia during preemptive ganciclovir therapy in hematopoietic stem cell transplant recipients: incidence, risk factors, and clinical outcomes

Preemptive ganciclovir (GCV) therapy is adopted increasingly in hematopoietic stem cell transplant (HCT) recipients, but occasional cases of increasing cytomegalovirus (CMV) antigenemia levels occur during preemptive GCV therapy. This prospective study investigated the incidence, risk factors, and clinical outcomes of paradoxical responses during GCV therapy. Adult patients receiving allogeneic HCTs during a 24-month period were enrolled. Patients were prospectively monitored for CMV antigenemia once a week until 3 months after engraftment. Paradoxical responders were defined as patients exhibiting CMV antigenemia levels elevated from the baseline after the first week of preemptive GCV therapy. Of 252 HCT recipients, 97 (38%) received preemptive GCV therapy due to CMV infection. Of these 97 patients, 23 (24%) were classified as paradoxical responders. Risk factors for paradoxical response were a low white blood cell (WBC) count (P = 0.02) and a prolonged duration of CMV antigenemia (P = 0.04) before preemptive therapy. There were no significant differences in rates of successful viral clearance and secondary episodes of CMV infection between paradoxical responders (87% [20/23] and 26% [6/23]) and nonparadoxical responders (95% [70/74] and 23% [17/74], respectively). However, breakthrough CMV disease during preemptive GCV therapy was significantly more frequent in paradoxical responders (17% [4/23]) than in nonparadoxical responders (3% [2/74], P = 0.03). Paradoxical responses occurred in one-quarter of the HCT recipients receiving preemptive GCV therapy. A low WBC count and a long duration of CMV antigenemia before GCV therapy were associated with paradoxical responses, and breakthrough CMV disease during preemptive GCV therapy occurred more frequently in paradoxical responders.

Mass spectrometry-based comparative sequencing to detect ganciclovir resistance in the UL97 gene of human cytomegalovirus

BACKGROUND

Persistent infections with herpesviruses such as human cytomegalovirus (HCMV) frequently occur after solid organ or stem cell transplantation, and are due to either failure of the host to immunologically control the virus or emerging resistance of the virus to the antiviral drug(s) used. Antiviral therapy can be guided by viral drug susceptibility testing based on screening for known resistance-inducing mutations in the viral genome. Mass spectrometry-based comparative sequence analysis (MSCSA) might be advantageous for this purpose because of its suitability for semi-automation.

OBJECTIVES

The applicability of MSCSA to detect sequence polymorphisms and drug resistance-inducing mutations in the HCMV genome was investigated.

STUDY DESIGN

We analyzed the 3' part of the HCMV UL97 gene, which encodes the kinase that is activated by the commonly used anti-HCMV drug ganciclovir. Sequences obtained by MSCSA of material from HCMV-infected patients (43 samples) and the HCMV type strain were compared to conventional cycle sequencing results.

RESULTS

In 94.1% of all samples the results obtained by MSCSA of the UL97 gene were identical to those from conventional cycle sequencing. The threshold to detect mutant sequences in a mixture with wild-type material was 20% using either technique. Furthermore, MSCSA was successfully applied to study the development of drug resistance in a patient who developed encephalitis due to ganciclovir-resistant HCMV.

CONCLUSIONS

MSCSA was found to be equally accurate compared to conventional cycle sequencing in the analysis of UL97 of HCMV.

Antiviral drug resistance of human cytomegalovirus

The study of human cytomegalovirus (HCMV) antiviral drug resistance has enhanced knowledge of the virological targets and the mechanisms of antiviral activity. The currently approved drugs, ganciclovir (GCV), foscarnet (FOS), and cidofovir (CDV), target the viral DNA polymerase. GCV anabolism also requires phosphorylation by the virus-encoded UL97 kinase. GCV resistance mutations have been identified in both genes, while FOS and CDV mutations occur only in the DNA polymerase gene. Confirmation of resistance mutations requires phenotypic analysis; however, phenotypic assays are too time-consuming for diagnostic purposes. Genotypic assays based on sequencing provide more rapid results but are dependent on prior validation by phenotypic methods. Reports from many laboratories have produced an evolving list of confirmed resistance mutations, although differences in interpretation have led to some confusion. Recombinant phenotyping methods performed in a few research laboratories have resolved some of the conflicting results. Treatment options for drug-resistant HCMV infections are complex and have not been subjected to controlled clinical trials, although consensus guidelines have been proposed. This review summarizes the virological and clinical data pertaining to HCMV antiviral drug resistance.

The search for new therapies for human cytomegalovirus infections

Ganciclovir (GCV), the therapy of choice for human cytomegalovirus (CMV) infections and foscarnet, a drug used to treat GCV-resistant CMV infections was approved more than twenty years ago. Although cidofovir and a prodrug of GCV have since been added to the armamentarium, a highly effective drug without significant toxicities has yet to be approved. Such a therapeutic agent is required for treatment of immunocompromised hosts and infants, which bear the greatest burden of disease. The modest antiviral activity of existing drugs is insufficient to completely suppress viral replication, which results in the selection of drug-resistant variants that remain pathogenic, continue to replicate, and contribute to disease. Sustained efforts, largely in the biotech industry and academia, have identified highly active lead compounds that have progressed into clinical studies with varying levels of success. A few of these compounds inhibit new molecular targets, remain effective against isolates that have developed resistance to existing therapies, and promise to augment existing therapies. Some of the more promising drugs will be discussed with an emphasis on those progressing to clinical studies. Their antiviral activity both in vitro and in vivo, spectrum of antiviral activity, and mechanism of action will be reviewed to provide an update on the progress of potential new therapies for CMV infections.

Case report: persistent cytomegalovirus (CMV) infection after haploidentical hematopoietic stem cell transplantation using in vivo alemtuzumab: emergence of resistant CMV due to mutations in the UL97 and UL54 genes

Addition of in vivo alemtuzumab to the conditioning regimen enabled 2- or 3-locus-mismatched hematopoietic stem cell transplantation with an acceptable incidence of graft-versus-host-disease. However, the procedure was associated with a high incidence of cytomegalovirus (CMV) reactivation. Although preemptive therapy with ganciclovir prevented successfully severe CMV diseases and CMV-related mortality, a patient developed persistent positive CMV antigenemia for more than 1 year after transplantation and CMV disease, despite the use of ganciclovir and foscarnet. The in vitro susceptibility assay showed that the clinical isolate was resistant to foscarnet, moderately resistant to ganciclovir, but sensitive to cidofovir. Therefore, cidofovir was administered. CMV antigenemia became negative within 2 weeks and never developed again. Nucleotide sequence of the UL54 and UL97 of the clinical isolate showed 4 amino acid substitutions (V11L, Q578H, S655L, and G874R) in UL54 and 2 mutations (A140V and A594V) in UL97 compared with the Towne and AD169 strains. Ganciclovir resistance was suspected to be caused by both A594V of UL97 and Q578H of UL54, whereas foscarnet resistance was due mainly to Q578H of UL54. In conclusion, the in vitro susceptibility assay as well as nucleotide sequence of clinical isolate is important to choose appropriate antiviral agents for patients who have persistent CMV reactivation after stem cell transplantation.

Development of new cytomegalovirus UL97 and DNA polymerase mutations conferring drug resistance after valganciclovir therapy in allogeneic stem cell recipients

BACKGROUND

We report on two allogeneic stem cell transplant recipients who developed cytomegalovirus disease associated with new viral mutations that conferred antiviral drug resistance.

METHODS

Blood specimens obtained during symptomatic disease were analyzed for mutations in the CMV UL97 and DNA polymerase genes and new mutations were assessed by recombinant phenotyping.

RESULTS

Rising cytomegalovirus (CMV) antigenemia occurred after 4-5 months of preemptive valganciclovir therapy, followed by symptomatic CMV disease including fatal pneumonia in one case. In one case, a new viral UL97 mutation (deletion of codons 601-603) was found which conferred 15-fold increased ganciclovir resistance. In the other case, a known UL97 resistance mutation M460V and a new DNA polymerase (pol) mutation D413A were found. D413A conferred ganciclovir and cidofovir resistance.

CONCLUSIONS

Known and newly discovered drug resistance mutations arising during preemptive therapy may complicate post-transplant CMV disease in stem cell recipients. Improved recombinant phenotyping methods enable the rapid quantitation of the resistance conferred by newly identified UL97 and pol mutations.

Recent advances in the prevention of CMV infection and disease after hematopoietic stem cell transplantation

Cytomegalovirus (CMV) remains an important pathogen in hematopoietic stem cell transplant (HCT) recipients in the current era of antiviral prophylaxis and preemptive therapy, despite the almost complete elimination of CMV disease during the first 3 months after transplantation. Pretransplant CMV serostatus of the donor and/or recipient remains an important risk factor for poor post-transplant outcome, especially in highly immunodeficient patients (e.g. recipients of ex vivo or in vivo T-cell depletion). Prevention of late CMV disease continues to be a challenge in selected high-risk populations, and indirect immunomodulatory effects of CMV (e.g. invasive bacterial and fungal infections) appear to contribute to the poor outcome. The risk of developing antiviral resistance remains low in most patients; however, in a setting of intense immunosuppression (e.g. after transplantation from a haploidentical donor) the incidence may be as high as 8%. Transfusion-transmitted CMV infection can be reduced by the provision of seronegative or leukocyte-depleted blood products; however, a small risk of 1-2% of CMV disease remains. Surveillance and preemptive therapy is effective in preventing transfusion-related CMV disease. The development of new drugs and immunologic strategies (adoptive transfer of CMV-specific T-cells and donor/recipient vaccination strategies) are important goals for the elimination of the negative impact of CMV in the HCT setting.

The influence of mixed HCMV UL97 wildtype and mutant strains on ganciclovir susceptibility in a cell associated plaque reduction assay

BACKGROUND

Ganciclovir (GCV) resistance is an emerging problem following organ transplantation. A restriction fragment length polymorphism (RFLP) assay is a convenient and rapid method to discover known resistance mutations within the UL97 (phosphotransferase) gene for the determination of GCV resistance. Phenotypic resistance testing remains important for the identification of human cytomegalovirus (HCMV) strains possibly harboring novel mutations and also for the determination of foscarnet and cidofovir resistance.

OBJECTIVE

The aim of this work was to evaluate the reliability of a cell-associated plaque reduction assay with respect to an expanded UL97 RFLP assay for use on codons 460, 520, 591, 592, 594, 595 and 603. Furthermore, the influence of mixed viral populations with coexistent wildtype and mutant UL97 sequences on GCV IC(50) values was investigated.

STUDY DESIGN

Twenty-eight clinical HCMV isolates were obtained from six adult patients under clinical and virological suspicion for development of GCV resistance following peripheral blood stem cell transplantation (PBSCT), and from one adult and three pediatric patients with confirmed GCV resistance following PBSCT. All isolates were tested for drug susceptibility and screened for UL97 resistance mutations.

RESULTS

The plaque reduction assay exceeded the GCV cut-off for resistance even when only a small number (5-10%) of the viral population was resistant. The proportion of UL97 mutant and wildtype strains influenced GCV IC(50) values. Genotypically detected GCV resistance always preceded phenotypically detected resistance. Long-term follow-up UL97 resistance screening revealed evidence for transient and compartment-specific UL97 mutations.

CONCLUSION

The stringent and longitudinal use of an expanded HCMV UL97 RFLP assay of specimens from different sites contributes to the rapid and reliable diagnosis of GCV resistance. The influence of the proportion of UL97 mutant and wildtype strains on GCV IC(50) values along with the strong correlation between phenotype and genotype suggests that the cell associated plaque reduction assay is highly reliable.

Prevention of cytomegalovirus disease in recipients of allogeneic stem cell transplants

The main risk factors for cytomegalovirus (CMV) disease in recipients of allogeneic stem cell transplants (SCT) are recipient CMV seropositivity and acute graft-versus-host disease. Currently, two antiviral strategies, prophylactic or preemptive antiviral treatment, are used for prevention of CMV disease. Preemptive treatment is most favorable when short-term (14-day) treatment is applied. Several methods are available for monitoring of CMV reactivation. PCR-based CMV DNA detection assays are the most sensitive methods; however, the clinical benefit of this high sensitivity is unclear. Even more, there is lack of clarity whether PCR tests can better be performed with plasma, whole blood, or peripheral blood leukocyte samples. Recovery of a CMV-specific CD8(+) cytotoxic-T-lymphocyte (CTL) response is necessary for preventing CMV reactivation and disease. Reconstitution of absolute CMV-specific CTL counts to values above 10 x 10(6) to 20 x 10(6) CTLs/liter is associated with protection from CMV disease. In the near future, preemptive therapy might be withheld in patients with CMV reactivation who are shown to have adequate CMV-specific cytotoxic T-cell levels. Antiviral therapy with (val)acyclovir has been studied only as prophylactic treatment for prevention of CMV infection. High-dose oral valacyclovir is more effective than acyclovir when used in addition to preemptive treatment of CMV reactivation with ganciclovir or foscarnet. Three antiviral drugs have been tested for preemptive therapy of CMV reactivation and/or treatment of CMV disease. Although intravenous ganciclovir is considered the drug of choice, foscarnet has similar efficacy and less toxicity, especially hematologic toxicity. Cidofovir has not been tested extensively, but so far the results are disappointing. Oral valganciclovir for preemptive treatment of SCT recipients is currently being studied. In addition to antiviral therapy, adoptive immunotherapy with CMV-specific cytotoxic T cells as prophylactic or preemptive therapy is a very elegant strategy; however, generation of these cells is expensive and time-consuming, and therefore the therapy is not available at every transplantation center. Magnetic selection of CMV-specific CD8(+) T cells from peripheral blood by using HLA class I-peptide tetramers may be very promising, making this strategy more accessible.

Emergence of late cytomegalovirus central nervous system disease in hematopoietic stem cell transplant recipients

Preemptive ganciclovir therapy has reduced the occurrence of early cytomegalovirus (CMV) disease after hematopoietic stem cell (HSC) transplantation. However, late disease is increasingly reported. We describe 2 patients who developed late CMV central nervous system (CNS) disease after haploidentical HSC transplantation. Direct genotypic analysis was used to examine the presence of ganciclovir resistance. One patient had a mixed viral population in the cerebrospinal fluid (CSF), with coexistent wild-type and mutant UL97 sequences. The presence of 2 different strains was confirmed by subclone sequencing of the UL54 gene. One of the strains was different from the concurrent blood strain. The second patient had resistant variant in the lungs. These cases raise concern about the changing natural history of CMV disease in HSC transplantation, with emergence of previously uncommon manifestations following prolonged prophylaxis. Under these circumstances the CNS may be a sanctuary site, where viral persistence and antiviral drug resistance could result from limited drug penetration.

Rapid development of ganciclovir-resistant cytomegalovirus infection in children after allogeneic stem cell transplantation in the early phase of immune cell recovery

As recently reported, children having T cell-depleted peripheral blood stem cell transplantation (PBSCT) might be at increased risk for the development of drug resistance. To investigate if delayed immune recovery was a potential risk factor, the recovery of the CD3(+), CD4(+), CD8(+) and CD19(+) cells was related retrospectively to genotypic detected resistance development in three pediatric patients with ganciclovir (GCV)-resistant human cytomegalovirus (HCMV)-infection out of 79 receiving allogeneic PBSCT. Selected control groups consisted of HCMV-seronegative patients without any infection (A, n = 8), asymptomatic infected patients with viral leuko- and plasmaDNAemia (B, n = 4) and patients with HCMV-disease (pneumonia) (C, n = 3). Patient No. 1 with very early resistance development exhibited a rapid immune recovery with higher T cell counts than in group A. Immune recovery of patient No. 2 was delayed, as also observed in groups B and C. Patient No. 3 showed an immune recovery comparable to group A. Resistance developed before (No. 2) or during (Nos 1 and 3) the recovery of the relevant CD3(+), CD4(+), CD8(+) lymphocytes. GCV-resistance development did not necessarily coincide with delayed immune recovery, but appeared in all three cases in the early phase of immune recovery (range: day +44 to day +95). Therefore, children seem to be at special risk for resistance development in the early phase after transplantation before immune cells have recovered. These results suggest that GCV treatment of an HCMV infection in the early posttransplant phase of children after T cell-depleted PBSCT/BMT should promote more stringent resistance screening.

Resistance of herpesviruses to antiviral drugs: clinical impacts and molecular mechanisms

Nucleoside analogues such as acyclovir and ganciclovir have been the mainstay of therapy for alphaherpesviruses (herpes simplex virus (HSV) and varicella-zoster virus (VZV)) and cytomegalovirus (CMV) infections, respectively. Drug-resistant herpesviruses are found relatively frequently in the clinic, almost exclusively among severely immunocompromised patients receiving prolonged antiviral therapy. For instance, close to 10% of patients with AIDS receiving intravenous ganciclovir for 3 months excrete a drug-resistant CMV isolate in their blood or urine and this percentage increases with cumulative drug exposure. Many studies have reported that at least some of the drug-resistant herpesviruses retain their pathogenicity and can be associated with progressive or relapsing disease. Viral mutations conferring resistance to nucleoside analogues have been found in either the drug activating/phosphorylating genes (HSV or VZV thymidine kinase, CMV UL97 kinase) and/or in conserved regions of the viral DNA polymerase. Currently available second line agents for the treatment of herpesvirus infections--the pyrophosphate analogue foscarnet and the acyclic nucleoside phosphonate derivative cidofovir--also inhibit the viral DNA polymerase but are not dependent on prior viral-specific activation. Hence, viral DNA polymerase mutations may lead to a variety of drug resistance patterns which are not totally predictable at the moment due to insufficient information on specific drug binding sites on the polymerase. Although some CMV and HSV DNA polymerase mutants have been found to replicate less efficiently in cell cultures, further research is needed to correlate viral fitness and clinical outcome.