Characterization of cytotoxic function of CMV-pp65-specific CD8+ T-lymphocytes identified by HLA tetramers in recipients and donors of stem-cell transplants

Features of the TCR repertoire associate with patients' clinical and molecular characteristics in acute myeloid leukemia

Background

Allogeneic hematopoietic stem cell transplant remains the most effective strategy for patients with high-risk acute myeloid leukemia (AML). Leukemia-specific neoantigens presented by the major histocompatibility complexes (MHCs) are recognized by the T cell receptors (TCR) triggering the graft-versus-leukemia effect. A unique TCR signature is generated by a complex V(D)J rearrangement process to form TCR capable of binding to the peptide-MHC. The generated TCR repertoire undergoes dynamic changes with disease progression and treatment.

Method

Here we applied two different computational tools (TRUST4 and MIXCR) to extract the TCR sequences from RNA-seq data from The Cancer Genome Atlas (TCGA) and examine the association between features of the TCR repertoire in adult patients with AML and their clinical and molecular characteristics.

Results

We found that only ~30% of identified TCR CDR3s were shared by the two computational tools. Yet, patterns of TCR associations with patients' clinical and molecular characteristics based on data obtained from either tool were similar. The numbers of unique TCR clones were highly correlated with patients' white blood cell counts, bone marrow blast percentage, and peripheral blood blast percentage. Multivariable regressions of TCRA and TCRB median normalized number of unique clones with mutational status of AML patients using TRUST4 showed significant association of TCRA or TCRB with WT1 mutations, WBC count, %BM blast, and sex (adjusted in TCRB model). We observed a correlation between TCRA/B number of unique clones and the expression of T cells inhibitory signal genes (TIGIT, LAG3, CTLA-4) and foxp3, but not IL2RA, CD69 and TNFRSF9 suggestive of exhausted T cell phenotypes in AML.

Conclusion

Benchmarking of computational tools is needed to increase the accuracy of the identified clones. The utilization of RNA-seq data enables identification of highly abundant TCRs and correlating these clones with patients' clinical and molecular characteristics. This study further supports the value of high-resolution TCR-Seq analyses to characterize the TCR repertoire in patients.

Immunologic monitoring of cytomegalovirus (CMV) enzyme-linked immune absorbent spot (ELISPOT) for controlling clinically significant CMV infection in pediatric allogeneic hematopoietic stem cell transplant recipients

The dynamics of recovery of cytomegalovirus (CMV)-specific cell-mediated immunity (CMI) and its impact on controlling clinically significant CMV infections following hematopoietic stem cell transplant (HSCT) are rarely reported in pediatric HSCT recipients. In this study, dynamics of recovery of CMV-specific CMI and its clinical significance in controlling CMV viremia and clinically significant CMV infections were assessed in pediatric allogeneic HSCT recipients. All subjects underwent CMV pp65- and IE1-specific enzyme-linked immune absorbent spot (ELISPOT) assays just before transplantation and then monthly until the detection of CMV-specific CMI with ≥ 5 spot-forming cells (SFC) / 2.0 × 105 cells. Clinically significant CMV infections were defined as CMV diseases, prolonged CMV infections, recurrent CMV infections or late onset CMV infections. Among 52 recipients, 88.5% of recipients recovered CMV-specific CMI with ≥ 5 SFC/ 2.0 × 105 cells at a median of 34 days (interquartile range [IQR]: 29-95 days) following HSCT, 55.8% at 30 days following HSCT, and 73.1% at 90 days following HSCT. The presence of CMV-specific CMI before HSCT was the significant factors for the reconstitution of CMV specific CMI after HSCT (adjusted odds ratio [aOR] = 13.33; 95% confidence interval [CI] = 1.21-142.86). After HSCT, 30 recipients experienced CMV viremia, of which 20 were clinically significant CMV infections. The full recovery of CMV-specific CMI with ≥ 50 SFC / 2.0 × 105 cells after HSCT was the protective factor for the development of clinically significant CMV infections (aOR = 0.13; 95% CI = 0.22-0.71). In the haploidentical HSCT recipients, 82.1% recovered CMV-specific CMI at a median of 65 days after HSCT (IQR: 34-118 days) with a tendency to recover their CMV-specific CMI later than did those from non-haploidentical donors (65 days vs. 30 days; P = 0.001). Clinically significant CMV infections tended to occur more frequently in the haploidentical HSCT recipients compared to those with matched donor HSCT (46.4% vs. 29.2%; P = 0.205). The full recovery of CMV-specific CMI with ≥ 50 SFC/2.0 × 105 cells after HSCT also lowered the risk of development of clinically significant CMV infections (aOR = 0.08; 95% CI = 0.01-0.90). However, transplantation from haploidentical donors was a significant risk factor hampering recovery of CMV-specific CMI (aOR = 0.08; 95% CI = 0.01-0.86) and full recovery of CMV-specific CMI (aOR = 0.05; 95% CI = 0.01-0.50). Pre-transplant CMV-specific CMI influenced the recovery of CMV-specific CMI, and the full recovery of CMV-specific CMI could be a surrogate marker for preventing clinically significant CMV infections in pediatric HSCT recipients. Immunologic monitoring using ELISPOT assay before and after HSCT helps in identifying patients with a high risk of CMV infection and in controlling CMV infection.

Cytomegalovirus infection is associated with AML relapse after allo-HSCT: a meta-analysis of observational studies

Cytomegalovirus (CMV) infection and primary disease relapse remain challenging problems after allogeneic hematopoietic stem cell transplantation (allo-HSCT). We sought to assess the association between CMV infection and disease relapse after transplantation. PubMed, EMBASE, the Cochrane Library, SCI, and Chinese Biomedicine Databases were searched up to July 1, 2018, for all studies that investigate pre-transplant CMV serostatus, CMV replication, and primary disease relapse in allo-HSCT patients with hematologic malignancies. Meta-analysis of 24 eligible cohort studies showed a significantly lower relapse risk after allo-HSCT in patients with CMV replication in acute myeloid leukemia (AML) (HR = 0.64, 95% CI, 0.50-0.83; P < 0.001) subgroup. However, CMV replication was associated with increased non-relapse mortality (NRM) in AML patients (HR = 1.64, 95% CI, 1.46-1.85; P < 0.001), but not associated with overall survival (OS) or graft-versus-host disease for AML patients (P > 0.05). There was no association between pre-transplant CMV serostatus and disease relapse, although D-/R- was associated with better OS in acute leukemia patients (HR = 0.89, 95% CI, 0.83-0.96; P = 0.003). In AML patients, CMV replication may be a protective predictor against disease relapse, although the potential benefit of CMV replication is offset by increased NRM.

Going beyond serology for stratifying the risk of CMV infection in transplant recipients

Knowledge of donor and recipient (D/R) cytomegalovirus (CMV) serostatus is critical for risk stratification of CMV infection and disease in transplant recipients, particularly in the solid organ transplantation (SOT) setting. Despite its broad availability and the success of it use, the risk stratification based on the D/R serostatus is not free of limitations since there are a nondepreciable number of patients that are not accurately categorized by this approach. In fact, up to 20% of seropositive SOT recipients, classically considered at intermediate risk, develop episodes of CMV infection and disease after transplantation. Here, we provide an overview of additional donor and recipient factors that may have utility in identifying patients at risk for post-transplant CMV infection. Specifically, we summarize our current understanding regarding the potential use of use CMV-specific T-cell-mediated immunity, neutralizing antibodies and host genetics that may influence the risk of CMV infection and disease. We provide an overview of the benefits and limitations associated with using these immunological factors in risk stratification and propose specific variables that could be analyzed at the pretransplant evaluation to improve the identification of patients with increased individual susceptibility.

CMV-specific immune reconstitution following allogeneic stem cell transplantation

Cytomegalovirus (CMV) remains a major contributor to morbidity and mortality following allogeneic haemopoietic stem cell transplant (HSCT) despite widespread use of viraemia monitoring and pre-emptive antiviral therapy. Uncontrolled viral replication occurs primarily in the first 100 d post transplant but this high risk period can extend to many months if immune recovery is delayed. The re-establishment of a functional population of cellular effectors is essential for control of virus replication and depends on recipient and donor serostatus, the stem cell source, degree of HLA matching and post-transplant factors such as CMV antigen exposure, presence of GVHD and ongoing use of immune suppression. A number of immune monitoring assays exist but have not yet become widely accessible for routine clinical use. Vaccination, adoptive transfer of CMV specific T cells and a number of graft engineering processes are being evaluated to enhance of CMV specific immune recovery post HSCT.

Viraemia, immunogenicity, and survival outcomes of cytomegalovirus chimeric epitope vaccine supplemented with PF03512676 (CMVPepVax) in allogeneic haemopoietic stem-cell transplantation: randomised phase 1b trial

BACKGROUND

Patients seropositive for cytomegalovirus (CMV) and undergoing allogeneic haemopoietic stem-cell transplantation (HCT) are at risk for CMV reactivation. Stimulating viral immunity by vaccination might achieve CMV viraemia control without the need for antiviral agents. CMVPepVax is a chimeric peptide composed of a cytotoxic CD8 T-cell epitope from CMV pp65 and a tetanus T-helper epitope. It is formulated with the adjuvant PF03512676, a Toll-like receptor 9 agonist, which augments cellular immunity. We aimed to assess safety, immunogenicity, and possible clinical benefit of the CMVPepVax vaccine in patients undergoing HCT.

METHODS

We did a randomised, open-label, phase 1b trial at one transplant centre in the USA. Eligible patients were CMV-seropositive, positive for HLA-A*0201, aged 18-75 years, and undergoing HCT from a matched-related or matched-unrelated donor. Patients were reassessed for eligibility on day 28 after HCT. We randomly allocated patients to either the CMVPepVax vaccine or observation, in blocks stratified by CMV donor serostatus. CMVPepVax was administered subcutaneously on days 28 and 56. The primary outcome was safety, which consisted of secondary graft failure, grade III-IV acute GVHD, non-relapse mortality by day 100, serious adverse events related to the vaccine (judged by the data and safety monitoring committee [DSMC]) grade 3-4 adverse events related to the vaccine (judged by the DSMC) within 2 weeks of vaccination, and development of double-strand (ds) DNA autoantibodies. Statistical analyses included all randomised patients and were done per-protocol. This study is registered with ClinicalTrials.gov, number NCT01588015. This trial is closed to accrual and the final analysis is presented in this report.

FINDINGS

Between Oct 31, 2012, and Nov 5, 2014, 36 eligible patients were allocated to either CMVPepVax (n=18) or observation (n=18), with no adverse effect on HCT (no secondary graft failures in either group) or cases of acute GVHD (seven patients assigned vaccine and six under observation had acute GVHD of grade 2 or less), and no unexpected adverse events. Compared with observation, better relapse-free survival was recorded in patients allocated the vaccine (seven vs one; hazard ratio [HR] 0·12, 95% CI 0·01-0·94; p=0·015). No patients had non-relapse mortality by day 100. One serious adverse event (grade 1 fever) was attributed to CMVPepVax but resolved within 48 h. Four patients assigned the vaccine had a serious adverse event, which was unrelated to the vaccine (grade 3 thrombocytopenia, grade 3 device-related infection, grade 2 nausea, and grade 1 fever), compared with nine patients under observation (grade 4 maculopapular rash, grade 3 nausea, grade 3 infection, grade 3 thrombotic thrombocytopenic purpurea, grade 2 nausea, grade 2 generalised muscle weakness, grade 2 infection, grade 1 fever, and grade 1 fatigue; p=0·16). 54 grade 3-4 adverse events were reported in patients assigned the vaccine compared with 91 in patients who were under observation (p=0·2). No patients had grade III-IV acute GVHD or developed dsDNA autoantibodies.

INTERPRETATION

The results show safety and immunogenicity of the CMVPepVax vaccine. The prospect of substantial clinical benefits warrant testing in a phase 2 trial.

FUNDING

National Cancer Institute.

The immune response to cytomegalovirus in allogeneic hematopoietic stem cell transplant recipients

Approximately, up to 70 % of the human population is infected with cytomegalovirus (CMV) that persists for life in a latent state. In healthy people, CMV reactivation induces the expansion of CMV-specific T cells up to 10 % of the entire T cell repertoire. On the contrary, CMV infection is a major opportunistic viral pathogen that remains a leading cause of morbidity and mortality after allogeneic hematopoietic stem cell transplantation. Due to the delayed CMV-specific immune recovery, the incidence of CMV reactivation during post-transplant period is very high. Several methods are currently available for the monitoring of CMV-specific responses that help in clinical monitoring. In this review, essential aspects in the immune recovery against CMV are discussed to improve the better understanding of the immune system relying on CMV infection and, thereby, helping the avoidance of CMV disease or reactivation following hematopoietic stem cell transplantation with severe consequences for the transplanted patients.

Monitoring of human cytomegalovirus and virus-specific T-cell response in young patients receiving allogeneic hematopoietic stem cell transplantation

In allogeneic hematopoietic stem-cell transplantation (HSCT) recipients, outcome of human cytomegalovirus (HCMV) infection results from balance between viral load/replication and pathogen-specific T-cell response. Using a cut-off of 30,000 HCMV DNA copies/ml blood for pre-emptive therapy and cut-offs of 1 and 3 virus-specific CD4⁺ and CD8⁺ T cells/µl blood for T-cell protection, we conducted in 131 young patients a prospective 3-year study aimed at verifying whether achievement of such immunological cut-offs protects from HCMV disease. In the first three months after transplantation, 55/89 (62%) HCMV-seropositive patients had infection and 36/55 (65%) were treated pre-emptively, whereas only 7/42 (17%) HCMV-seronegative patients developed infection and 3/7 (43%) were treated. After 12 months, 76 HCMV-seropositive and 9 HCMV-seronegative patients (cumulative incidence: 90% and 21%, respectively) displayed protective HCMV-specific immunity. Eighty of these 85 (95%) patients showed spontaneous control of HCMV infection without additional treatment. Five patients after reaching protective T-cell levels needed pre-emptive therapy, because they developed graft-versus-host disease (GvHD). HSCT recipients reconstituting protective levels of HCMV-specific T-cells in the absence of GvHD are no longer at risk for HCMV disease, at least within 3 years after transplantation. The decision to treat HCMV infection in young HSCT recipients may be taken by combining virological and immunological findings.

Monitoring of cytomegalovirus-specific CD8+ T-cell response with major histocompatibility complex pentamers in kidney transplant recipients

INTRODUCTION

Cytomegalovirus (CMV) can reactivate causing serious clinical problems during immunosuppression. CMV-specific CD8(+) T cells play an important role in the control of CMV reactivation. Using pentameric major histocompatibility complex (MHC) peptide complexes, we investigated cellular immune responses to CMV among healthy individuals and kidney transplantation recipients in Korea, which is an endemic area of CMV infection.

MATERIALS AND METHODS

Analysis of CMV-specific T cells was performed on 28 healthy individuals and 40 recipients who bore human leukocyte antigen (HLA)-A2 or -A24. CMV pp65 pentamer-binding cells incubated with various monoclonal antibodies were measured by four-color flow cytometry.

RESULTS

Detectable levels of pentamer(+) CD8(+) T cells were present in 109/139 samples (78.4%) that stained with the A*02NLV-pentamer, while 15/67 samples (22.4%) stained with the A*24QYD-pentamer (P < .01). Among patients with HLA-A2, 22/24 (91.7%) samples showing positive CMV antigenemia revealed detectable pentamer(+) CD8(+) T cells, while 87/115 (75.7%) displaying negative CMV antigenemia had detectable pentamer(+) CD8(+) T cells (P = .04). There was no significant difference in percentages of pentamer(+) CD8(+) T cells between patients who did versus who did not experience episodes of CMV infection. The subpopulation of CMV-specific CD8(+) T cells in transplantation recipients was evaluated using phenotypic markers; memory cells comprised the majority of the CMV-specific CD8(+) T-cell population.

CONCLUSION

The A*02NLV-pentamer complex was useful to monitor CMV-specific T cells. However, MHC pentamer-based techniques did not provide a clear distinction between patients who are or are not at risk for CMV infection.

Ex vivo monitoring of human cytomegalovirus-specific CD8(+) T-Cell responses using the QuantiFERON-CMV assay in allogeneic hematopoietic stem cell transplant recipients attending an Irish hospital

Reconstitution of human cytomegalovirus (HCMV) T-cell immunity is crucial in hematopoietic stem cell transplant (HSCT) recipients. The QuantiFERON-CMV assay for cellular HCMV-specific immunity was evaluated in allogeneic HSCT recipients (n = 43) and patients with hematological malignancies (n = 29) attending a tertiary-care Irish hospital. An intracellular cytokine (ICC) assay correlated with the QuantiFERON-CMV assay. Although there was agreement between HCMV seropositivity and QuantiFERON-CMV assay, six HCMV seropositive immunosuppressed patients with hematological malignancy had negative QuantiFERON-CMV results. The 43 HSCT recipients were classified as high risk (D(-)/R(+)) (n = 18), intermediate risk (D(+)/R(+) and D(+)/R(-)) (n = 17), and low risk (D(-)/R(-)) (n = 8). During episodes of HCMV DNAemia no evidence of HCMV-specific immunity was found using the QuantiFERON-CMV assay. Furthermore, the recovery of HCMV-specific CD8(+) T-cell responses in high-risk seropositive recipients of matched unrelated donors was severely delayed, a mean of 200 (SD = 117) days compared to 58 (SD = 23) days for sibling donors (P < or = 0.028). In addition, three patients with late HCMV infection (infection >100 days post-transplant) had delayed reconstitution of HCMV-specific CD8(+) T cells. Interestingly, two recipients (R(+)/D(-)) developed rapid immune reconstitution by days 15 and 36 post-HSCT, suggesting HCMV-specific T-cell lymphopoiesis of recipient origin. Levels of CD8(+) T-cell immunity in HCMV seropositive HSCT recipients were lowest following HSCT. A high number (33%) of indeterminate results was observed immediately after transplantation. Patients with indeterminate QuantiFERON-CMV results had low levels of HCMV-specific CD8(+) T cells. J. Med. Virol. 82:433-440, 2010. (c) 2010 Wiley-Liss, Inc.

Manifestations of human cytomegalovirus infection: proposed mechanisms of acute and chronic disease

Infections with human cytomegalovirus (HCMV) are a major cause of morbidity and mortality in humans with acquired or developmental deficits in innate and adaptive immunity. In the normal immunocompetent host, symptoms rarely accompany acute infections, although prolonged virus shedding is frequent. Virus persistence is established in all infected individuals and appears to be maintained by both a chronic productive infections as well as latency with restricted viral gene expression. The contributions of the each of these mechanisms to the persistence of this virus in the individual is unknown but frequent virus shedding into the saliva and genitourinary tract likely accounts for the near universal incidence of infection in most populations in the world. The pathogenesis of disease associated with acute HCMV infection is most readily attributable to lytic virus replication and end organ damage either secondary to virus replication and cell death or from host immunological responses that target virus-infected cells. Antiviral agents limit the severity of disease associated with acute HCMV infections, suggesting a requirement for virus replication in clinical syndromes associated with acute infection. End organ disease secondary to unchecked virus replication can be observed in infants infected in utero, allograft recipients receiving potent immunosuppressive agents, and patients with HIV infections that exhibit a loss of adaptive immune function. In contrast, diseases associated with chronic or persistent infections appear in normal individuals and in the allografts of the transplant recipient. The manifestations of these infections appear related to chronic inflammation, but it is unclear if poorly controlled virus replication is necessary for the different phenotypic expressions of disease that are reported in these patients. Although the relationship between HCMV infection and chronic allograft rejection is well known, the mechanisms that account for the role of this virus in graft loss are not well understood. However, the capacity of this virus to persist in the midst of intense inflammation suggests that its persistence could serve as a trigger for the induction of host-vs-graft responses or alternatively host responses to HCMV could contribute to the inflammatory milieu characteristic of chronic allograft rejection.

Programmed death-1 expression in liver transplant recipients as a prognostic indicator of cytomegalovirus disease

Immunological parameters that distinguish solid-organ transplant (SOT) recipients at risk for life-threatening cytomegalovirus (CMV) disease are being actively pursued to aid posttransplant management. A candidate marker is programmed death (PD)-1 receptor, whose overexpression has been associated with disease progression during persistent viral infections. To determine whether levels of this negative regulator of T cell activity are altered in SOT recipients with symptoms of CMV disease, a comparative PD-1 expression analysis was done in healthy, CMV-positive individuals and in liver transplant recipients. PD-1 levels were measured among the total population of CD8(+) and CD8(+) T cells binding to CMV-specific major histocompatibility complex class I tetramers. Minimal PD-1 expression was found in the healthy, CMV-positive cohort, and symptomatic SOT recipients had significantly higher PD-1 levels. PD-1 up-regulation was significantly associated with incipient and overt CMV disease and with viremia. Our findings suggest that PD-1 could be developed as a prognostic tool to predict CMV disease and guide therapeutic interventions.

Comparison of vaccine strategies against congenital CMV infection in the guinea pig model

Vaccines are urgently needed to protect newborns against the devastating sequelae of congenital cytomegalovirus infection. Evaluation of candidate vaccines in the guinea pig model of congenital infection can shed light on potentially useful strategies for humans, since guinea pig CMV (GPCMV) is transmitted to the fetus transplacentally, causing infection and disease in utero. A number of vaccine strategies have been evaluated in this model, including DNA vaccines, live attenuated vaccines, and recombinant glycoprotein vaccines. Induction of virus-neutralizing antibody appears to play a key role in protection of the fetus. Recently, a vectored vaccine based on the GPCMV homolog of the UL83 (pp65) protein has also been shown to be effective when used as a preconceptual vaccine in this model, suggesting that strategies designed to elicit T-cell responses may be of value in protection of the fetus.

Functional analysis of cytomegalovirus-specific T lymphocytes compared to tetramer assay in patients undergoing hematopoietic stem cell transplantation

In order to evaluate whether we could predict reactivation of CMV by monitoring the number of CMV-specific cytotoxic T-lymphocytes (CTL), tetramer analysis was performed in 37 patients who underwent hematopoietic stem cell transplantation (HSCT). The results disclosed that the mean number of CMV-specific CTL at day 30 did not differ among patients who developed CMV antigenemia (22/microl) and those who did not (12/microl). Serial tetramer analysis showed that 21% of the patients had >10/microl CMV-specific CTL at the first detection of CMV antigenemia and 67% of the patients had more than 10/microl CMV-specific CTL at the onset of CMV disease. Intracellular staining upon stimulation by CMV lysates and peptide in patients with CMV colitis revealed that both IFN-gamma producing CD4+ and CD8+ lymphocytes were suppressed at the onset of CMV colitis (1.6 and 8/microl), which increased with recovery of the disease (19 and 47/microl). These data suggest that it is difficult to predict CMV reactivation solely by the number of CMV-specific CTL. We suggest that additional functional analysis by intracellular cytokine assay may be useful for immunomonitoring against CMV.

BY55/CD160 cannot be considered a cytotoxic marker in cytomegalovirus-specific human CD8(+) T cells

CD160/BY55 is a glucosyl-phosphatidylinositol (GPI)-anchored cell membrane receptor that is expressed primarily in natural killer (NK) cells. Its presence in CD8(+) T lymphocytes is considered to be a marker of cytotoxic activity, although there are few data in this regard. In the present work, we analysed the expression of CD160 in subpopulations of cytomegalovirus (CMV)-specific CD8(+) T cells. Subpopulations were defined by CD28 and CD57 expression and exhibited varying degrees of differentiation and cytotoxic potential, as evaluated by the expression of perforin, interferon (IFN)-gamma and interleukin (IL)-7Ralpha/CD127. We included subjects with different intensities of anti-viral immune response. Results showed that the terminally differentiated CD28(-) CD57(+) subset displaying the highest level of perforin expressed CD160 at a level similar to that of memory CD28(+) CD57(-)perforin(-) cells. A comparison of the expression of perforin in CD160(+) cells versus CD160(-) cells showed that expression was significantly higher in the absence of CD160. Interestingly, the CMV-specific CD8(+) T cell subset from a patient with ongoing CMV reactivation did not begin to express CD160 until day +92 of the follow-up period. Taken together, our data show that CD160 cannot be considered a cytotoxic marker in CMV-specific CD8(+) T cells.

Impact on the cytomegalovirus (CMV) viral load by CMV-specific T-cell immunity in recipients of allogeneic stem cell transplantation

Patients experience cytomegalovirus (CMV) reactivation after stem cell transplantation (SCT) and need repeated courses of pre-emptive therapy. Analysis of CMV-specific immunity might help to assess the need for antiviral therapy. Forty-eight patients were studied during the first 3 months after SCT. Peripheral blood lymphocytes were stimulated by CMV antigen, and interferon (INF)-gamma production by CD3+ and CD4+ T cells was analysed. Results were correlated to transplant factors and CMV disease. Patients with INF-gamma production by CD3+ cells at 4 weeks after SCT had lower peak viral loads than patients with no such production (P=0.03). There was a similar tendency as regards CD4+ cells (P=0.09). Patients who underwent reduced-intensity conditioning (RIC) more frequently had CD3+ (48%) and CD4+ immunity (56%) 4 weeks after SCT compared with patients who received myeloablative conditioning (CD3+ 25%; CD4+ 35%). There was no effect of stem cell source, donor type or acute graft-versus-host disease. Three of 48 patients developed CMV disease and none of them had detectable INF-gamma production. CMV-specific T-cell response is associated with a lower rate of CMV replication. RIC results in improved T-cell reconstitution. Recovery of CMV-specific immunity might be delayed in patients with CMV disease. These observations suggest that detection of CMV-specific T-cells is useful in assessing the immunity against CMV.

Progress toward an elusive goal: current status of cytomegalovirus vaccines

Although infection with human cytomegalovirus (CMV) is ubiquitous and generally asymptomatic in most individuals, certain patient populations are at high risk for CMV-associated disease. These include HIV-infected individuals with AIDS, transplant patients, and newborn infants with congenital CMV infection. Immunity to CMV infection, both in the transplant setting and among women of childbearing age, plays a vital role in the control of CMV-induced injury and disease. Although immunity induced by CMV infection is not completely protective against reinfection, there is nevertheless a sound basis on which to believe that vaccination could help control CMV disease in high-risk patient populations. Evidence from several animal models of CMV infection indicates that a variety of vaccine strategies are capable of inducing immune responses sufficient to protect against CMV-associated illness following viral challenge. Vaccination has also proven effective in improving pregnancy outcomes following CMV challenge of pregnant guinea pigs, providing a 'proof-of-principle' relevant to human clinical trials of CMV vaccines. Although there are no licensed vaccines currently available for human CMV, progress toward this goal has been made, as evidenced by ongoing clinical trial testing of a number of immunization strategies. CMV vaccines currently in various stages of preclinical and clinical testing include: protein subunit vaccines; DNA vaccines; vectored vaccines using viral vectors, such as attenuated pox- and alphaviruses; peptide vaccines; and live attenuated vaccines. This review summarizes some of the obstacles that must be overcome in development of a CMV vaccine, and provides an overview of the current state of preclinical and clinical trial evaluation of vaccines for this important public health problem.

Prospective simultaneous quantification of human cytomegalovirus-specific CD4+ and CD8+ T-cell reconstitution in young recipients of allogeneic hematopoietic stem cell transplants

We investigated immune reconstitution against human cytomegalovirus (HCMV) in 57 hematopoietic stem cell transplant (HSCT) recipients, aged 1 to 24 years, through a novel method combining T-cell stimulation by HCMV-infected autologous dendritic cells with simultaneous cytometric quantification of HCMV-specific, IFNgamma-producing CD4(+) and CD8(+) T cells. Lymphoproliferative response (LPR) to HCMV antigens was also determined. Patients were stratified into 2 groups according to HCMV serostatus, comprising 39 HCMV-seropositive (R(+)) and 18 HCMV-seronegative (R(-)) patients who received a transplant from a sero-positive donor. Recovery of both HCMV-specific CD4(+) and CD8(+) T-cell immunity occurred in all 39 R(+) patients within 6 months and in 6 (33%) of 18 R(-) patients within 12 months. In R(+) patients, the median numbers of HCMV-specific CD8(+) and CD4(+)T cells were significantly higher than those of healthy controls, starting from days +60 and +180, respectively. In (R-) patients, the median numbers of HCMV-specific T cells were consistently lower than in R(+) patients. LPR was delayed compared with reconstitution of IFNgamma-producing T cells. Patients with delayed specific immune reconstitution experienced recurrent episodes of HCMV infection. HCMV seropositivity of young HSCT recipients is the major factor responsible for HCMV-specific immune reconstitution, irrespective of donor serostatus, and measurement of HCMV-specific T cells appears useful for correct management of HCMV infection.

Cytomegalovirus immune reconstitution occurs in recipients of allogeneic hematopoietic cell transplants irrespective of detectable cytomegalovirus infection

The question of when immune reconstitution of cytomegalovirus (CMV)-specific CD8 T cells occurs after hematopoietic cell transplantation and, more specifically, to which CMV targets this immunity is likely to be directed remains poorly understood. The dependence of immune reconstitution on CMV reactivation is even less clear. To better understand these events, 44 CMV-seropositive HLA-A*0201 subjects were followed up at approximately days 40, 90, 120, 150, 180, and 360 after hematopoietic cell transplantation for CMV immunity as measured by 2 types of assays: (1) an HLA-A*0201 tetramer-binding assay for both CMV pp65 (pp65) and immediate-early 1 (IE-1) or (2) intracellular cytokine interferon gamma responses induced by pp65 or IE-1-derived peptides. To verify the reliability of IE-1-specific assays relative to the pp65-based assays, a pilot study first compared the development of IE-1-specific immunity in a subgroup by using multiple HLA-A*0201-restricted peptides, and then these recipients were followed up for 1 year for immunologic function and for CMV infection. The IE-1-specific response occurred to each of the 3 HLA-A*0201-restricted peptides studied (IE-1-256, -297, and -316), and there was no predominant IE peptide response. However, the immunodominant HLA-A*0201-restricted pp65 peptide was recognized significantly more frequently than these IE-1 peptides. When this was compared with the occurrence of CMV infection, the overall immune reactivity, as measured by the mean or median number of CD8+ T cells reactive to either pp65 or IE-1 peptides by intracellular cytokine or tetramer binding assay, was not significantly different in those with and without CMV infection. For patients who demonstrated reconstituted immunity to CMV at 1 year, all were reconstituted by 6 months, and the timing of the first observed immune reactivity to either of the pp65 or the IE peptides was not different in those with and without detectable CMV infection.

Assessment of cellular immunity to human cytomegalovirus in recipients of allogeneic stem cell transplants

Effective reconstitution of cellular immunity following hematopoietic stem cell transplantation (HCT) is thought to be important for protection from the morbidity caused by cytomegalovirus (CMV) reactivation and disease. This review critically discusses current methods for assessment of CMV-specific cellular immune responses, with emphasis on flow cytometry-based methodologies such as MHC-I and MHC-II tetramer staining and intracellular cytokine assays. The advantages and weaknesses of these assays are considered in comparison to traditional immunologic techniques. Application of these newer methodologies has provided insight into the dynamics of the levels of CMV-specific CD4(+) and CD8(+) T-lymphocytes following HCT, and into the sources and diversity of these cells. Data from preliminary clinical studies suggest that CMV-specific CD8(+) T-lymphocyte levels greater than 1 x 10(7)/L of peripheral blood may correlate with protection from CMV disease. Studies on the functional phenotypes of CMV-specific CD8(+) T-lymphocytes such as cytokine production, degranulation, and cytotoxicity have indicated that these cells are heterogeneous with regard to these properties. Future research will focus on establishing whether any of these immunologic assays will serve as a correlate of protection and inform as to which patients are at high risk for CMV reactivation and disease. Identification of an informative assay may allow its incorporation into standard clinical practice for monitoring HCT patients.

DNA and low titer, helper-free, recombinant AAV prime-boost vaccination for cytomegalovirus induces an immune response to CMV-pp65 and CMV-IE1 in transgenic HLA A*0201 mice

A prime-boost immunization regimen allowed the use of low titer, helper-free rAAV-pp65mII and rAAV-IE1 virus to elicit specific humoral and cellular responses to two important cytomegalovirus (CMV) antigens: the immediate-early 1 (IE-1) and pp65 proteins. Simultaneous immunization of both CMV proteins, using DNA vaccine priming followed by rAAV boost, induced antibody (Ab) response, CD8 lymphocytes with cytotoxic function, and detectible binding of the cognate peptide epitopes for human HLA A*0201 restriction using tetramer technology.

Reconstitution of HLA-A*2402-restricted cytomegalovirus-specific T-cells following stem cell transplantation

Cytomegalovirus (CMV)-specific immune reconstitution early after stem cell transplantation (SCT) was evaluated prospectively by detecting CD8+ T-cells, which recognize the peptide QYDPVAALF in the context of HLA-A*2402. Fifteen allogeneic SCT recipients were included in the study. All recipients and donors were seropositive for CMV and had the HLA-A*2402 allele. CMV-specific T-cells were detected as early as 1 month after transplantation, and their numbers increased to peak levels 2 to 5 months after transplantation. The numbers of CMV-specific T-cells in patients who developed grade II to IV acute graft-versus-host disease (GVHD) and received corticosteroids for acute GVHD were low in the early period after allogeneic SCT. There was a trend toward earlier reconstitution of CMV-specific CD8+ T-cells in allogeneic peripheral blood SCT (PBSCT) patients than in allogeneic bone marrow transplantation patients. The contribution of T-cells in the graft to the recovery of CMV-specific immune responses was also suggested by the finding that the reconstitution of CMV-specific CD8+ T-cells was delayed in CD34-selected autologous PBSCT compared with unpurged autologous PBSCT. The reconstitution of CMV-specific CD8+ T-cells was delayed in patients with CMV disease or recurrent CMV reactivation. These observations suggest that the detection of CMV-specific T-cells with an HLA-peptide tetramer is useful to assess immune reconstitution against CMV and to identify patients at risk for CMV disease or recurrent CMV reactivation after SCT.

Characterization of Host Immunity to cytomegalovirus pp150 (UL32)

The basic phosphoprotein 150 (pp150), the product of UL32 (unique long domain 32) gene of human cytomegalovirus (CMV), is an abundant component of the viral tegument and a target of human leukocyte antigen (HLA)-restricted cytotoxic T cells (CTLs) after infection. Identification of minimal cytotoxic epitopes (MCEs) from this CMV protein is of importance for peptide-based vaccines and immunotherapeutic approaches. Several pp150-specific CTL clones were derived from peripheral blood mononuclear cells of healthy CMV-positive donors with autologous fibroblasts infected either with CMV AD169 or with a recombinant vaccinia virus expressing full-length pp150 protein. HLA A*0301- and HLA A*6801-restricted CD8+ pp150 T-cell clones derived from different donors were found to efficiently kill autologous CMV-infected fibroblasts. Fine mapping of each MCE first used a T-cell epitope prediction algorithm. Overlapping peptides within the recognized regions were screened. The analysis identified pp150(792-802) and pp150(945-955) as MCEs for the HLA A*6801 and the HLA A*0301 pp150 clones, respectively. In vitro stimulation by recombinant modified vaccinia Ankara virus expressing full-length pp150 elicited high frequencies of CMV-CTL and interferon gamma production specific for the MCE identified in all subjects. The consistent presence of pp150 T cells in CMV-exposed individuals supports a role for this antigen in shaping the antiviral CTL response and indicates that pp150 could be a pivotal constituent of prophylactic and therapeutic CMV vaccines.

Relative dominance of HLA-B*07 restricted CD8+ T-lymphocyte immune responses to human cytomegalovirus pp65 in persons sharing HLA-A*02 and HLA-B*07 alleles

CD8(+) T-cell responses to three human cytomegalovirus (CMV) pp65 epitopes were studied in panels of healthy seropositive HLA-A*02/HLA-B*07 individuals, and HLA-A*02 donors mismatched for HLA-B*07. The majority of the latter had significant responses to a HLA-A*02-restricted epitope within the CMV pp65 antigen. By contrast, the strongest responses to CMV in the first group were to HLA-B*07-restricted epitopes. Similar immunodominance of HLA-B*07 over HLA-A*02 was found in two immunocompromised HIV-infected HLA-A*02/HLA-B*07 patients, and in the reconstituting immune system of three stem cell transplant recipients. In vitro stimulation of peripheral blood mononuclear cells (PBMC) from two immunocompetent HLA-A*02/HLA-B*07 individuals indicated that cytotoxic T lymphocyte (CTL) precursors specific for both HLA-A*02 and HLA-B*07 restricted epitopes were present and could be expanded by stimulation with the cognate peptides. However, if stimulation was performed by antigen presenting cells infected with recombinant vaccinia expressing full-length native pp65, only HLA-B*07 epitope-specific cells were seen. In one patient the HLA-B*07 dominance was partially broken by using recombinant vaccinia expressing ubiquitinated pp65, suggesting that enhanced protein processing can reveal weaker immune responses. Our results indicate that CMV-specific cellular immune responses restricted by HLA-B*07 dominate those restricted by HLA-A*02 in both immunocompetent and immunocompromised individuals. This may have significant consequences for the design of epitope-specific vaccines.

Cytomegalovirus infection following unrelated cord blood transplantation for adult patients: a single institute experience in Japan

Cytomegalovirus (CMV) infection in 28 adult patients after cord blood transplantation (CBT) from unrelated donors was compared with that after bone marrow transplantation from HLA (human leucocyte antigen)-matched related (R-BMT) and unrelated (U-BMT) donors. Positive CMV antigenaemia was seen in 19 (79%) of 24 CMV-seropositive patients at a median of 42 d (range 29-85 d) after CBT, but in zero of four CMV-seronegative patients. This did not differ significantly from values observed after R-BMT and U-BMT (66%, P = 0.22, and 60%, P = 0.15 respectively). Based on the antigenaemia results, 16 patients (67%) received pre-emptive ganciclovir therapy from a median of 47 d (range 36-67 d) after CBT. This proportion was higher than that observed after R-BMT (28%, P = 0.0048), but did not differ from that after U-BMT (50%, P = 0.21). In addition, the probability of requiring more than two courses of ganciclovir therapy after CBT (21%) was higher than after R-BMT and U-BMT (0%, P = 0.015 and 0.039 respectively). One patient (5%) developed CMV disease after U-BMT, whereas no patients developed CMV disease after CBT or R-BMT. The CMV serostatus, use of a steroid and HLA disparity affected the probability of requiring ganciclovir therapy after CBT (P = 0.024, 0.032 and 0.017 respectively). These results suggest that recovery of CMV-specific immunity after CBT is delayed when compared with BMT.