T cell recognition patterns of immunodominant cytomegalovirus antigens in primary and persistent infection

The influence of HLA A, B, C, DR alleles and HLA haplotypes on cytomegalovirus-specific cell mediated immunity in seropositive Korean kidney transplant candidates

We evaluated the effect of specific HLA alleles and haplotypes on cytomegalovirus (CMV)-specific cell mediated immunity (CMI) in kidney transplant (KT) candidates. CMV-specific ELISPOT against pp65 and IE-1 antigens (hereafter referred to as pp65 and IE-1, respectively) was performed in 229 seropositive KT candidates. We analyzed the results related to 44 selected HLA alleles (9 HLA-A, 15 HLA-B, 9 HLA-C, and 11 HLA-DR) and 13 HLA haplotypes commonly found in study participants. The pp65 and IE-1 results in 229 seropositive candidates were 227.5 (114.5-471.5) and 41.0 (8.8-185.8) (median [interquartile range]) spots/2 × 105 PBMCs, respectively. The pp65 and IE-1 results showed significant differences between candidates with different HLA alleles (A*02 vs. A*26 [p = 0.016], A*24 vs. A*30 [p = 0.031], B*07 vs. B*46 [p = 0.005], B*54 vs. B*35 [p = 0.041], B*54 vs. B*44 [p = 0.018], B*54 vs. B*51 [p = 0.025], and C*06 vs. C*14 [p = 0.034]). HLA-A*02 and B*54 were associated with increased pp65 and IE-1 results, respectively (p = 0.005 and p < 0.001, respectively). In contrast, the HLA-A*26 and B*46 alleles were associated with a decreased pp65 response, whereas the A*30 allele was associated with a decreased IE-1 response (p < 0.05). The pp65 results correlated with the HLA-A allele frequencies (R = 0.7546, p = 0.019) and the IE-1 results correlated with the HLA-C allele frequencies of the study participants (R = 0.7882, p = 0.012). Among 13 haplotypes, HLA-A*30 ~ B*13 ~ C*06 ~ DRB1*07 showed decreased CMV-CMIs compared to the other HLA haplotypes, probably due to a combination of HLA alleles associated with lower CMV-CMIs. Our results demonstrated that CMV-specific CMIs may be influenced by the HLA allele as well as the HLA haplotype. To better predict CMV reactivation, it is important to estimate risk in the context of HLA allele and haplotype information.

Impact of cytomegalovirus immunodominant HLA-I donor-recipient matching on the incidence and features of virus DNAemia and virus-specific T-cell immune reconstitution in unmanipulated haploidentical hematopoietic stem cell transplantation

BACKGROUND

We investigated whether donor-recipient mismatch involving one or more cytomegalovirus (CMV) immunodominant (ID) human leukocyte antigen (HLA)-I alleles may impact on the degree of CMV pp65/immediate-early 1 (IE-1) T-cell reconstitution and the incidence of CMV DNAemia in patients undergoing unmanipulated haploidentical hematopoietic stem cell transplantation with high-dose posttransplant cyclophosphamide (PT/Cy-haplo).

METHODS

Multicenter observational study including 106 consecutive adult PT/Cy-haplo patients (34 CMV ID HLA-I matched and 72 mismatched). A real-time PCR was used for plasma CMV DNA load monitoring. Enumeration of CMV-specific (pp65/IE-1) interferon (IFN)-γ-producing T cells from several patients was performed by flow cytometry by days +30, +60, +90 and +180 after transplantation.

RESULTS

The cumulative incidence of CMV DNAemia, clinically significant CMV DNAemia episodes (cs-CMVi), and recurrent CMV DNAemia was comparable across CMV ID HLA-I matched and mismatched patients (71.8% vs. 80.9%, p = .95; 40.7% vs. 44.2%, p = .85; 16.4% vs. 28.1%; p = .43, respectively). The percentage of patients exhibiting detectable CMV-specific IFN-γ-producing T-cell responses (either CD8⁺ or CD4⁺ ) was similar across groups; nevertheless, significantly higher CMV-specific CD8⁺ T-cell counts were enumerated in the CMV ID HLA-I matched compared to mismatched patients by day +60 (p = .04) and +180 (p = .016) after transplantation.

CONCLUSION

CMV ID HLA-I matching may impact on the magnitude of CMV-pp65/IE-1-specific CD8⁺ T-cell reconstitution; yet, this effect seemed not to have an impact on the incidence of initial, recurrent CMV DNAemia, or cs-CMVi.

Hematopoietic stem cell donor vaccination with cytomegalovirus triplex augments frequencies of functional and durable cytomegalovirus-specific T cells in the recipient: A novel strategy to limit antiviral prophylaxis

To enhance protective cytomegalovirus (CMV)-specific T cells in immunosuppressed recipients of an allogeneic hematopoietic cell transplant (HCT), we evaluated post-HCT impact of vaccinating healthy HCT donors with Triplex. Triplex is a viral vectored recombinant vaccine expressing three immunodominant CMV antigens. The vector is modified vaccinia Ankara (MVA), an attenuated, non-replicating poxvirus derived from the vaccinia virus strain Ankara. It demonstrated tolerability and immunogenicity in healthy adults and HCT recipients, in whom it also reduced CMV reactivation. Here, we report feasibility, safety, and immunological outcomes of a pilot phase 1 trial (NCT03560752 at ClinicalTrials.gov) including 17 CMV-seropositive recipients who received an HCT from a matched related donor (MRD) vaccinated with 5.1 × 108 pfu/ml of Triplex before cell harvest (median 15, range 11-28 days). Donor and recipient pairs who committed to participation in the trial resulted in exceptional adherence to the protocol. Triplex was well-tolerated with limited adverse events in donors and recipients, who all engrafted with full donor chimerism. On day 28 post-HCT, levels of functional vaccinia- and CMV-specific CD137+ CD8+ T cells were significantly higher (p < .0001 and p = .0174, respectively) in recipients of Triplex vaccinated MRD than unvaccinated MRD (control cohort). Predominantly, central and effector memory CMV-specific T-cell responses continued to steadily expand through 1-year follow-up. CMV viremia requiring antivirals developed in three recipients (18%). In summary, this novel approach represents a promising strategy applicable to different HCT settings for limiting the use of antiviral prophylaxis, which can impair and delay CMV-specific immunity, leading to CMV reactivation requiring treatment.

Viral T-cell epitopes - Identification, characterization and clinical application

T-cell immunity, mediated by CD4⁺ and CD8⁺ T cells, represents a cornerstone in the control of viral infections. Virus-derived T-cell epitopes are represented by human leukocyte antigen (HLA)-presented viral peptides on the surface of virus-infected cells. They are the prerequisite for the recognition of infected cells by T cells. Knowledge of viral T-cell epitopes provides on the one hand a diagnostic tool to decipher protective T-cell immune responses in the human population and on the other hand various prophylactic and therapeutic options including vaccination approaches and the transfer of virus-specific T cells. Such approaches have already been proven to be effective against various viral infections, particularly in immunocompromised patients lacking sufficient humoral, antibody-based immune response. This review provides an overview on the state of the art as well as current studies regarding the identification and characterization of viral T-cell epitopes and approaches of clinical application. In the first chapter in silico prediction tools and direct, mass spectrometry-based identification of viral T-cell epitopes is compared. The second chapter provides an overview of commonly used assays for further characterization of T-cell responses and phenotypes. The final chapter presents an overview of clinical application of viral T-cell epitopes with a focus on human immunodeficiency virus (HIV), human cytomegalovirus (HCMV) and severe acute respiratory syndrome coronavirus type 2 (SARS-CoV-2), being representatives of relevant viruses.

Functional studies of HLA and its role in SARS-CoV-2: Stimulating T cell response and vaccine development

In the biological immune process, the major histocompatibility complex (MHC) plays an indispensable role in the expression of HLA molecules in the human body when viral infection activates the T-cell response to remove the virus. Since the first case of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection in 2019, how to address and prevent SARS-CoV-2 has become a common problem facing all mankind. The T-cell immune response activated by MHC peptides is a way to construct a defense line and reduce the transmission and harm of the virus. Presentation of SARS-CoV-2 antigen is associated with different types of HLA phenotypes, and different HLA phenotypes induce different immune responses. The prediction of SARS-CoV-2 mutation information and the design of vaccines based on HLAs can effectively activate autoimmunity and cope with virus mutations, which can provide some references for the prevention and treatment of SARS-CoV-2.

Nanomaterials in tuberculosis DNA vaccine delivery: historical perspective and current landscape

Vaccinations, especially DNA vaccines that promote host immunity, are the most effective interventions for tuberculosis (TB) control. However, the vaccine delivery system exhibits a significant impact on the protective effects of the vaccine. Recently, effective nanomaterial-based delivery systems (including nanoparticles, nanogold, nanoliposomes, virus-like particles, and virus carriers) have been developed for DNA vaccines to control TB. This review highlights the historical development of various nanomaterial-based delivery systems for TB DNA vaccines, along with the emerging technologies. Nanomaterial-based vaccine delivery systems could enhance the efficacy of TB vaccination; therefore, this summary could guide nanomaterial selection for optimal and safe vaccine delivery, facilitating the design and development of highly effective TB vaccines.

Relationship between certain HLA alleles and the risk of cytomegalovirus reactivation following allogeneic hematopoietic stem cell transplantation

INTRODUCTION

Evidence is emerging to support an association between certain HLA alleles and the risk of cytomegalovirus (CMV) reactivation following allogeneic HSCT (allo-HSCT). The primary aim of this study was to identify HLA alleles associated with resistance or susceptibility to CMV reactivation.

METHODS

We studied 586 adults who underwent allo-HSCT for high-risk hematological malignancies. High resolution HLA typing data was available for recipient and donor. HLA Class I and II alleles observed at a frequency of > 5% in our population, were included in the analysis. A CMV viremia level of more than 200 IU/ml on weekly monitoring was considered to be indicative of CMV reactivation.

RESULTS

The median follow-up time in surviving patients was 21 months (range 4-74 months). The cumulative incidence of CMV reactivation at 6 months in the entire cohort was 55% (95% CI 50.8%-59.2%). Mismatched donor, increasing recipient age, occurrence of AGVHD and recipient CMV seropositivity were associated with increased risk of CMV reactivation. HLA B*07:02 (HR 0.59, 95% CI 0.40-0.83) was associated with decreased risk of CMV reactivation. Patients who developed CMV reactivation had a lower incidence of relapse, higher transplant related mortality (TRM) and lower overall survival (OS) compared to those without CMV reactivation. There was an adverse correlation of OS and TRM with increasing numbers of CMV reactivations.

CONCLUSION

We observed that HLA B*07:02 was associated with decreased risk of CMV reactivation. CMV reactivation was associated with lower relapse post-transplant, but this did not translate into a survival benefit due to higher transplant related mortality. This article is protected by copyright. All rights reserved.

Profiling Human CMV-specific T cell responses reveals novel immunogenic ORFs

Despite the prevalence and medical significance of human cytomegalovirus (HCMV) infections, a systematic analysis of the targets of T cell recognition in humans that spans the entire genome and includes recently described potential novel ORFs is not available. Here, we screened a library of epitopes predicted to bind HLA class II that spans over 350 different HCMV ORFs and includes ∼150 previously described and ∼200 recently described potential novel ORFs using an ex vivo IFNγ fluorospot assay. We identified 235 unique HCMV specific epitopes derived from 100 ORFs, some previously described as immunodominant and others that were not previously described to be immunogenic. Of those, 41 belong to the set of recently reported novel ORFs, thus providing evidence that at least some of these are actually expressed in vivo in humans. These data reveal that the breadth of the human T cell response to HCMV is much greater than previously thought. The ORFs and epitopes identified will help elucidate how T cell immunity relates to HCMV pathogenesis and instruct ongoing HCMV vaccine research. Importance To understand the crucial role of adaptive immunity in controlling cytomegalovirus infection and disease, we systematically analyzed the CMV 'ORFeome' to identify new CMV epitopes targeted primarily by CD4 T cells in humans. Our study identified >200 new T cell epitopes derived from both canonical and novel ORFs, highlighting the substantial breadth of anti-CMV T cell response and providing new targets for vaccine design.

Identification of HLA-A2 restricted CD8+ T cell epitopes in SARS-CoV-2 structural proteins

The outbreak of coronavirus disease 2019 (COVID‐19) has now become a pandemic, and the etiologic agent is the severe acute respiratory syndrome‐coronavirus 2 (SARS‐CoV‐2). T cell mediated immune responses play an important role in virus controlling; however, the understanding of the viral protein immunogenicity and the mechanisms of the induced responses are still limited. So, identification of specific epitopes and exploring their immunogenic properties would provide valuable information. In our study, we utilized the Immune Epitope Database and Analysis Resource and NetMHCpan to predict HLA‐A2 restricted CD8⁺ T cell epitopes in structural proteins of SARS‐CoV‐2, and screened out 23 potential epitopes. Among them, 18 peptides showed strong or moderate binding with HLA‐A2 with a T2A2 cell binding model. Next, the mixed peptides induced the increased expression of CD69 and highly expressed levels of IFN‐γ and granzyme B in CD8⁺ T cells, indicating effective activation of specific CD8⁺ T cells. In addition, the peptide‐activated CD8⁺ T cells showed significantly increased killing to the target cells. Furthermore, tetramer staining revealed that the activated CD8⁺ T cells mainly recognized seven epitopes. All together, we identified specific CD8⁺ T cell epitopes in SARS‐CoV‐2 structural proteins, which could induce the production of specific immune competent CD8⁺ T cells. Our work contributes to the understanding of specific immune responses and vaccine development for SARS‐CoV‐2.

CMV-Specific Cell-Mediated Immunity in Immunocompetent Adults with Primary CMV Infection: A Case Series and Review of the Literature

Cytomegalovirus-specific cell-mediated immunity (CMV-CMI) in actively infected healthy immunocompetent hosts has been poorly investigated. Conversely, correlates of maternal protective immunity for the fetus after primary infection in pregnancy continue to be studied. The kinetics and magnitude of CMV-specific CMI in immunocompetent primary CMV-infected adults are described. A literature review on CMV-CMI in primarily infected pregnant women and its correlation to the risk of vertical virus transmission is included. Immunological measurements after infection were performed by enzyme-linked ImmunoSPOT assay enumerating IFN-γ secreting CMV-specific T cells, at a single cell level, upon in vitro stimulation with viral antigens. Simultaneously, serological and virological profiles of infected patients were investigated. Patients displayed mild-to-moderate clinical and laboratory profiles for infection, and all showed positive EliSpot results in the early stage of infection (<20 days after onset). The virus-CMI was strong in the majority of patients (58.8%) in which the lowest CMV-DNAemia levels (<300 copies/mL) were detected. Significantly higher viral loads were observed in patients with weak CMV-CMI at the same time-point post-infection (up to 15,104 copies/mL; p < 0.001). T cell response magnitudes to IE-1 and pp65-UL83 peptides were overlapping and stable over time. In these case series, the early presence of CMV-CMI was probably pivotal in controlling viral replication and led to spontaneous viral clearance.

Discordance Between the Predicted Versus the Actually Recognized CD8+ T Cell Epitopes of HCMV pp65 Antigen and Aleatory Epitope Dominance

CD8+ T cell immune monitoring aims at measuring the size and functions of antigen-specific CD8+ T cell populations, thereby providing insights into cell-mediated immunity operational in a test subject. The selection of peptides for ex vivo CD8+ T cell detection is critical because within a complex antigen exists a multitude of potential epitopes that can be presented by HLA class I molecules. Further complicating this task, there is HLA class I polygenism and polymorphism which predisposes CD8+ T cell responses towards individualized epitope recognition profiles. In this study, we compare the actual CD8+ T cell recognition of a well-characterized model antigen, human cytomegalovirus (HCMV) pp65 protein, with its anticipated epitope coverage. Due to the abundance of experimentally defined HLA-A*02:01-restricted pp65 epitopes, and because in silico epitope predictions are most advanced for HLA-A*02:01, we elected to focus on subjects expressing this allele. In each test subject, every possible CD8+ T cell epitope was systematically covered testing 553 individual peptides that walk the sequence of pp65 in steps of single amino acids. Highly individualized CD8+ T cell response profiles with aleatory epitope recognition patterns were observed. No correlation was found between epitopes' ranking on the prediction scale and their actual immune dominance. Collectively, these data suggest that accurate CD8+ T cell immune monitoring may necessitate reliance on agnostic mega peptide pools, or brute force mapping, rather than electing individual peptides as representative epitopes for tetramer and other multimer labeling of surface antigen receptors.

SARS-CoV-2-derived peptides define heterologous and COVID-19-induced T cell recognition

T cell immunity is central for the control of viral infections. To characterize T cell immunity, but also for the development of vaccines, identification of exact viral T cell epitopes is fundamental. Here we identify and characterize multiple dominant and subdominant SARS-CoV-2 HLA class I and HLA-DR peptides as potential T cell epitopes in COVID-19 convalescent and unexposed individuals. SARS-CoV-2-specific peptides enabled detection of post-infectious T cell immunity, even in seronegative convalescent individuals. Cross-reactive SARS-CoV-2 peptides revealed pre-existing T cell responses in 81% of unexposed individuals and validated similarity with common cold coronaviruses, providing a functional basis for heterologous immunity in SARS-CoV-2 infection. Diversity of SARS-CoV-2 T cell responses was associated with mild symptoms of COVID-19, providing evidence that immunity requires recognition of multiple epitopes. Together, the proposed SARS-CoV-2 T cell epitopes enable identification of heterologous and post-infectious T cell immunity and facilitate development of diagnostic, preventive and therapeutic measures for COVID-19.

Slow cytomegalovirus-specific CD4+ and CD8+ T-cell differentiation: 10-year follow-up of primary infection in a small number of immunocompetent hosts

Differentiation of human cytomegalovirus specific T cells is a slow process requiring years. In the acute phase, EM predominate; subsequently, no contraction occurs (memory inflation) and T_EMRA increase, especially among CD8⁺ T cells, while few LTM T cells appear. After some years, LTM stabilizes and predominate among CD4⁺ .

In vivo Downregulation of MHC Class I Molecules by HCMV Occurs During All Phases of Viral Replication but Is Not Always Complete

Based on cell culture data, MHC class I downregulation by HCMV on infected cells has been suggested as a means of immune evasion by this virus. In order to address this issue in vivo, an immunohistochemical analysis of tissue sections from biopsy and autopsy materials of HCMV infected organs was performed. HCMV antigens from the immediate early, early, and late phase of viral replication, and cellular MHC class I molecules were detected simultaneously or in serial sections by immuno-peroxidase and immuno-alkaline phosphatase techniques. Investigated organs included lung, gastrointestinal tract, and placenta. Colocalization of MHC molecules with sites of viral replication as well as MHC expression in individual infected cells were analyzed. To detect immune effector cells at sites of viral replication, leukocytes, CD8+ lymphocytes, and HCMV antigens were stained in serial sections. While strong MHC class I expression was detected in the cells surrounding infected cells, it appeared downregulated in the majority of infected cells themselves, particularly in the late replication phase. Despite significantly reduced MHC class I signals on infected cells, sites of infection were infiltrated by inflammatory cells that consisted predominantly of CD8+ lymphocytes. The extent of inflammatory infiltrates was negatively correlated with the extent of HCMV infected cells. Taken together, our findings indicate that HCMV can downmodulate MHC class I expression in vivo, whereas cytokines originating from infiltrating immune effector cells probably up regulates MHC class I expression in noninfected bystander cells. The presence of cytotoxic lymphocytes in close contact to infected cells may reflect control of viral spread by these cells despite MHC class I downmodulation.

Reverse TCR repertoire evolution toward dominant low-affinity clones during chronic CMV infection

Adaptive evolution is a key feature of T cell immunity. During acute immune responses, T cells harboring high-affinity T cell antigen receptors (TCRs) are preferentially expanded, but whether affinity maturation by clonal selection continues through the course of chronic infections remains unresolved. Here we investigated the evolution of the TCR repertoire and its affinity during the course of infection with cytomegalovirus, which elicits large T cell populations in humans and mice. Using single-cell and bulk TCR sequencing and structural affinity analyses of cytomegalovirus-specific T cells, and through the generation and in vivo monitoring of defined TCR repertoires, we found that the immunodominance of high-affinity T cell clones declined during the chronic infection phase, likely due to cellular senescence. These data showed that under conditions of chronic antigen exposure, low-affinity TCRs preferentially expanded within the TCR repertoire, with implications for immunotherapeutic strategies.

The Presence of a CMV Immunodominant Allele in the Recipient Is Associated With Increased Survival in CMV Positive Patients Undergoing Haploidentical Hematopoietic Stem Cell Transplantation

Specific major histocompatibility (MHC) class I alleles dominate anti-CMV responses in a hierarchal manner. These CMV immunodominant (IMD) alleles are associated with a higher magnitude and frequency of cytotoxic lymphocyte responses as compared to other human leukocyte antigen (HLA) alleles. CMV reactivation has been associated with an increased incidence of graft-vs.-host disease and non-relapse mortality, as well as protection from relapse in HLA-matched HSCT settings. Less is known about the impact of CMV reactivation on these major outcomes after haploidentical (HI) HSCT, an increasingly applied therapeutic option. In HI HSCT, the efficiency of the immune response is decreased due to the immune suppression required to cross the MHC barrier as well as MHC mismatch between presenting and responding cells. We hypothesized that the presence of a CMV IMD allele would increase the efficiency of CMV responses after HI HSCT potentially impacting CMV-related outcomes. In this retrospective, multivariable review of 216 HI HSCT patients, we found that CMV+ recipients possessing at least 1 of 5 identified CMV IMD alleles had a lower hazard of death (HR = 0.40, p = 0.003) compared to CMV+ recipients not possessing a CMV IMD allele, and an overall survival rate similar to their CMV- counterparts. The analysis delineated subgroups within the CMV+ population at greater risk for death due to CMV reactivation.

Generation, maintenance and tissue distribution of T cell responses to human cytomegalovirus in lytic and latent infection

Understanding how the T cell memory response directed towards human cytomegalovirus (HCMV) develops and changes over time while the virus persists is important. Whilst HCMV primary infection and periodic reactivation is well controlled by T cell responses in healthy people, when the immune system is compromised such as post-transplantation, during pregnancy, or underdeveloped such as in new-born infants and children, CMV disease can be a significant problem. In older people, HCMV infection is associated with increased risk of mortality and despite overt disease rarely being seen there are increases in HCMV-DNA in urine of older people suggesting that there is a change in the efficacy of the T cell response following lifelong infection. Therefore, understanding whether phenomenon such as “memory inflation” of the immune response is occurring in humans and if this is detrimental to the overall health of individuals would enable the development of appropriate treatment strategies for the future. In this review, we present the evidence available from human studies regarding the development and maintenance of memory CD8 + and CD4 + T cell responses to HCMV. We conclude that there is only limited evidence supportive of “memory inflation” occurring in humans and that future studies need to investigate immune cells from a broad range of human tissue sites to fully understand the nature of HCMV T cell memory responses to lytic and latent infection.

TCR repertoire evolution during maintenance of CMV-specific T-cell populations

During infections and cancer, the composition of the T-cell receptor (TCR) repertoire of antigen-specific CD8⁺ T cells changes over time. TCR avidity is thought to be a major driver of this process, thereby interacting with several additional regulators of T-cell responses to form a composite immune response architecture. Infections with latent viruses, such as cytomegalovirus (CMV), can lead to large T-cell responses characterized by an oligoclonal TCR repertoire. Here, we review the current status of experimental studies and theoretical models of TCR repertoire evolution during CMV infection. We will particularly discuss the degree to which this process may be determined through structural TCR avidity. As engineered TCR-redirected T cells have moved into the spotlight for providing more effective immunotherapies, it is essential to understand how the key features of a given TCR influence T-cell expansion and maintenance in settings of infection or malignancy. Deeper insights into these mechanisms will improve our basic understanding of T-cell immunology and help to identify optimal TCRs for immunotherapy.

Cytomegalovirus Exposure in the Elderly Does Not Reduce CD8 T Cell Repertoire Diversity

With age, the immune system becomes less effective, causing increased susceptibility to infection. Chronic CMV infection further impairs immune function and is associated with increased mortality in the elderly. CMV exposure elicits massive CD8⁺ T cell clonal expansions and diminishes the cytotoxic T cell response to subsequent infections, leading to the hypothesis that to maintain homeostasis, T cell clones are expelled from the repertoire, reducing T cell repertoire diversity and diminishing the ability to combat new infections. However, in humans, the impact of CMV infection on the structure and diversity of the underlying T cell repertoire remains uncharacterized. Using TCR β-chain immunosequencing, we observed that the proportion of the peripheral blood T cell repertoire composed of the most numerous 0.1% of clones is larger in the CMV seropositive and gradually increases with age. We found that the T cell repertoire in the elderly grows to accommodate CMV-driven clonal expansions while preserving its underlying diversity and clonal structure. Our observations suggest that the maintenance of large CMV-reactive T cell clones throughout life does not compromise the underlying repertoire. Alternatively, we propose that the diminished immunity in elderly individuals with CMV is due to alterations in cellular function rather than a reduction in CD8⁺ T cell repertoire diversity.

Human Cytomegalovirus-Specific Memory CD4+ T-Cell Response and Its Correlation With Virus Transmission to the Fetus in Pregnant Women With Primary Infection

Background

Primary human cytomegalovirus (HCMV) infection during pregnancy is the major cause of congenital viral sequelae. The HCMV-specific T-cell response may have a role in the prevention of virus transmission to the fetus.

Methods

HCMV-specific memory T cells were investigated in the second month after primary infection onset in 44 pregnant women (15 transmitting the infection to the fetus) and 8 pregnant women with remote infection. Peripheral blood mononuclear cells were stimulated for 12 days with peptide pools of HCMV proteins IE-1, IE-2, and pp65, and subsequently restimulated for 24 hours with the same peptide pools in a cultured enzyme-linked immunospot (ELISPOT) assay.

Results

In pregnant women with primary infection, the cultured ELISPOT assay detected a higher T-cell response to pp65 than to IE-1 or IE-2, whereas in remote infection pp65-, IE-1-, and IE-2-specific T cells were detected at comparable levels. During primary infection, the cultured ELISPOT response was mainly mediated by CD4+ T cells, and was lower than in remote infection. Strikingly, the cultured ELISPOT response to pp65 (but not to IE-1 or IE-2) was significantly higher in nontransmitting mothers. To detect other factors potentially associated with nontransmission, different serological parameters were analyzed. Only immunoglobulin G avidity index was higher in nontransmitting mothers, who showed also a lower DNAemia level. These 2 parameters remained associated with congenital infection in multivariate analysis.

Conclusions

Determination of HCMV-specific T cells by cultured ELISPOT, in pregnant women with primary HCMV infection, in association with avidity index and DNAemia may help to assess the risk of HCMV fetal transmission.

Immunodominant cytomegalovirus-specific CD8+ T-cell responses in sub-Saharan African populations

More than 90% of children in Africa are infected with cytomegalovirus (CMV) by the age of 12 months. However, the high-frequency, immunodominant CD8+ T-cell responses that control CMV infection have not been well studied in African populations. We therefore sought to define the immunodominant CMV-specific CD8+ T-cell responses within sub-Saharan African study subjects. Among 257 subjects, we determined the CD8+ T-cell responses to overlapping peptides spanning three of the most immunogenic CMV proteins, pp65, IE-1 and IE-2, using IFN-γ ELISpot assays. A bioinformatics tool was used to predict optimal epitopes within overlapping peptides whose recognition was statistically associated with expression of particular HLA class I molecules. Using this approach, we identified 16 predicted novel CMV-specific epitopes within CMV-pp65, IE-1 and IE-2. The immunodominant pp65-specific, IE-1, IE-2 responses were all either previously well characterised or were confirmed using peptide-MHC tetramers. The novel epitopes identified included an IE-2-specific epitope restricted by HLA*B*44:03 that induced high-frequency CD8+ T-cell responses (mean 3.4% of CD8+ T-cells) in 95% of HLA-B*44:03-positive subjects tested, in one individual accounting for 18.8% of all CD8+ T-cells. These predicted novel CMV-specific CD8+ T-cell epitopes identified in an African cohort will facilitate future analyses of immune responses in African populations where CMV infection is almost universal during infancy.

Cytomegalovirus-Specific T Cells Restricted by HLA-Cw*0702 Increase Markedly with Age and Dominate the CD8+ T-Cell Repertoire in Older People

Cytomegalovirus (CMV) infection elicits a strong T-cell immune response, which increases further during aging in a process termed "memory inflation." CMV downregulates the expression of HLA-A and HLA-B on the surface of infected cells to limit presentation of viral peptides to T-cells although HLA-C is relatively spared as it also engages with inhibitory killer immunoglobulin receptor receptors and therefore reduces lysis by natural killer cells. We investigated the magnitude and functional properties of CMV-specific CD8+ T-cells specific for 10 peptides restricted by HLA-C in a cohort of 53 donors between the age of 23 and 91 years. This was achieved via peptide stimulation of PBMCs followed by multicolor flow cytometry. Three peptides, derived from proteins generated in the immediate-early period of viral replication and restricted by HLA-Cw*0702, elicited strong immune responses, which increased substantially with age such that the average aggregate response represented 37% of the CD8+ T-cell pool within donors above 70 years of age. Remarkably, a single response represented 70% of the total CD8+ T-cell pool within a 91-year-old donor. HLA-Cw*0702-restricted CD8+ T-cell responses were immunodominant over HLA-A and HLA-B-restricted CMV-specific responses and did not show features of exhaustion such as PD-1 or CD39 expression. Indeed, such CTL exhibit a polyfunctional cytokine profile with co-expression of IFN-γ and TNF-α and a strong cytotoxic phenotype with intracellular expression of perforin and granzymeB. Functionally, HLA-Cw*0702-restricted CTL show exceptionally high avidity for cognate peptide-HLA and demonstrate very early and efficient recognition of virally infected cells. These observations indicate that CD8+ T-cells restricted by HLA-C play an important role in the control of persistent CMV infection and could represent a novel opportunity for CD8+ T-cell therapy of viral infection within immunosuppressed patients. In addition, the findings provide further evidence for the importance of HLA-C-restricted T-cells in the control of chronic viral infection.

Cytomegalovirus reactivation posthematopoietic stem cell transplantation (HSCT) and type of graft: A step toward rationalizing CMV testing and positively impacting the economics of HSCT in developing countries

We aimed to determine a correlation between cytomegalovirus reactivation post hematopoeitic stem cell transplantation (post-HSCT) with the type of graft source, defining children at risk. We analyzed data on children less than 18 years of age undergoing HSCT from 2002 to May 2016 (n = 464). Correlation between reactivation and graft source was analyzed statistically. Reactivation occurred in 3% of children with matched-related donor (MRD) transplants, 33.3% with unrelated peripheral blood stem cells, 17.4% with unrelated cords, and 36.5% (15/41) with mismatched or haploidentical grafts (P = <0.0001). MRD does not warrant weekly PCR, unlike unrelated or haploidentical donors, thus defining protocols for developing countries with limited resources.

Cytomegalovirus-Responsive CD8+ T Cells Expand After Solid Organ Transplantation in the Absence of CMV Disease

Cytomegalovirus (CMV) is a major cause of morbidity and mortality in solid organ transplant recipients. Approximately 60% of adults are CMV seropositive, indicating previous exposure. Following resolution of the primary infection, CMV remains in a latent state. Reactivation is controlled by memory T cells in healthy individuals; transplant recipients have reduced memory T cell function due to chronic immunosuppressive therapies. In this study, CD8+ T cell responses to CMV polypeptides immediate-early-1 and pp65 were analyzed in 16 CMV-seropositive kidney and heart transplant recipients longitudinally pretransplantation and posttransplantation. All patients received standard of care maintenance immunosuppression, antiviral prophylaxis, and CMV viral load monitoring, with approximately half receiving T cell-depleting induction therapy. The frequency of CMV-responsive CD8+ T cells, defined by the production of effector molecules in response to CMV peptides, increased during the course of 1 year posttransplantation. The increase commenced after the completion of antiviral prophylaxis, and these T cells tended to be terminally differentiated effector cells. Based on this small cohort, these data suggest that even in the absence of disease, antigenic exposure may continually shape the CMV-responsive T cell population posttransplantation.

Cytomegalovirus Reinfections Stimulate CD8 T-Memory Inflation

Cytomegalovirus (CMV) has been shown to induce large populations of CD8 T-effector memory cells that unlike central memory persist in large quantities following infection, a phenomenon commonly termed “memory inflation”. Although murine models to date have shown very large and persistent CMV-specific T-cell expansions following infection, there is considerable variability in CMV-specific T-memory responses in humans. Historically such memory inflation in humans has been assumed a consequence of reactivation events during the life of the host. Because basic information about CMV infection/re-infection and reactivation in immune competent humans is not available, we used a murine model to test how primary infection, reinfection, and reactivation stimuli influence memory inflation. We show that low titer infections induce “partial” memory inflation of both mCMV specific CD8 T-cells and antibody. We show further that reinfection with different strains can boost partial memory inflation. Finally, we show preliminary results suggesting that a single strong reactivation stimulus does not stimulate memory inflation. Altogether, our results suggest that while high titer primary infections can induce memory inflation, reinfections during the life of a host may be more important than previously appreciated.

MVA vaccine encoding CMV antigens safely induces durable expansion of CMV-specific T cells in healthy adults

Attenuated poxvirus modified vaccinia Ankara (MVA) is a useful viral-based vaccine for clinical investigation, because of its excellent safety profile and property of inducing potent immune responses against recombinant (r) antigens. We developed Triplex by constructing an rMVA encoding 3 immunodominant cytomegalovirus (CMV) antigens, which stimulates a host antiviral response: UL83 (pp65), UL123 (IE1-exon4), and UL122 (IE2-exon5). We completed the first clinical evaluation of the Triplex vaccine in 24 healthy adults, with or without immunity to CMV and vaccinia virus (previous DryVax smallpox vaccination). Three escalating dose levels (DL) were administered IM in 8 subjects/DL, with an identical booster injection 28 days later and 1-year follow-up. Vaccinations at all DL were safe with no dose-limiting toxicities. No vaccine-related serious adverse events were documented. Local and systemic reactogenicity was transient and self-limiting. Robust, functional, and durable Triplex-driven expansions of CMV-specific T cells were detected by measuring T-cell surface levels of 4-1BB (CD137), binding to CMV-specific HLA multimers, and interferon-γ production. Marked and durable CMV-specific T-cell responses were also detected in Triplex-vaccinated CMV-seronegatives, and in DryVax-vaccinated subjects. Long-lived memory effector phenotype, associated with viral control during CMV primary infection, was predominantly found on the membrane of CMV-specific and functional T cells, whereas off-target vaccine responses activating memory T cells from the related herpesvirus Epstein-Barr virus remained undetectable. Combined safety and immunogenicity results of MVA in allogeneic hematopoietic stem cell transplant (HCT) recipients and Triplex in healthy adults motivated the initiation of a placebo-controlled multicenter trial of Triplex in HCT patients. This trial was registered at www.clinicaltrials.gov as #NCT02506933.

Coinfection with Human Cytomegalovirus Genetic Variants in Transplant Recipients and Its Impact on Antiviral T Cell Immune Reconstitution

Reconstitution of T cell immunity is absolutely critical for the effective control of virus-associated infectious complications in hematopoietic stem cell transplant (HSCT) recipients. Coinfection with genetic variants of human cytomegalovirus (CMV) in transplant recipients has been linked to clinical disease manifestation; however, how these genetic variants impact T cell immune reconstitution remains poorly understood. In this study, we have evaluated dynamic changes in the emergence of genetic variants of CMV in HSCT recipients and correlated these changes with reconstitution of antiviral T cell responses. In an analysis of single nucleotide polymorphisms within sequences encoding HLA class I-restricted CMV epitopes from the immediate early 1 gene of CMV, coinfection with genetically distinct variants of CMV was detected in 52% of patients. However, in spite of exposure to multiple viral variants, the T cell responses in these patients were preferentially directed to a limited repertoire of HLA class I-restricted CMV epitopes, either conserved, variant, or cross-reactive. More importantly, we also demonstrate that long-term control of CMV infection after HSCT is primarily mediated through the efficient induction of stable antiviral T cell immunity irrespective of the nature of the antigenic target. These observations provide important insights for the future design of antiviral T cell-based immunotherapeutic strategies for transplant recipients, emphasizing the critical impact of robust immune reconstitution on efficient control of viral infection.

IMPORTANCE

Infection and disease caused by human cytomegalovirus (CMV) remain a significant burden in patients undergoing hematopoietic stem cell transplantation (HSCT). The establishment of efficient immunological control, primarily mediated by cytotoxic T cells, plays a critical role in preventing CMV-associated disease in transplant recipients. Recent studies have also begun to investigate the impact genetic variation in CMV has upon disease outcome in transplant recipients. In this study, we sought to investigate the role T cell immunity plays in recognizing and controlling genetic variants of CMV. We demonstrate that while a significant proportion of HSCT recipients may be exposed to multiple genetic variants of CMV, this does not necessarily lead to immune control mediated via recognition of this genetic variation. Rather, immune control is associated with the efficient establishment of a stable immune response predominantly directed against immunodominant conserved T cell epitopes.

Reconstitution of cytomegalovirus-specific T-cell response in allogeneic hematopoietic stem cell recipients: the contribution of six frequently recognized, virus-encoded ORFs

BACKGROUND

The reactivation of human cytomegalovirus (HCMV) in immunosuppressed patients is associated with significant morbidity. Testing HCMV-specific T-cell responses can help determine which patients are at high risk of HCMV disease. We optimized selection of HCMV antigens for detection of T-cell response of patients after allogeneic hematopoietic stem cell transplantation (HSCT) with the aim of identifying patients with insufficient control of HCMV reactivation.

METHODS

T-cell immune response to HCMV was monitored in 30 patients during the first year after HSCT. The HSCT recipients were classified according to their anti-HCMV T-cell response and the presence of HCMV DNA in the blood.

RESULTS

We observed an inverse relationship between the magnitude of HCMV-specific T-cell responses against CMV lysate, phosphoprotein (pp) 65, immediate early-1 (IE-1), UL36, and UL55, but not to US3 and US29 detected by interferon-gamma (IFNγ)- ELISPOT and the level of HCMV DNA in the blood of patients during the 30 days following sampling. The study has revealed that patients who received a graft from a seronegative donor have a lower T-cell response against HCMV and increased probability of HCMV reactivation in comparison to the patients who had received their graft from a seropositive donor.

CONCLUSION

The individual peptide pools and native HCMV antigens were useful for monitoring the time course of the anti-HCMV response by IFNγ-ELISPOT, which proved to have a prognostic value. Besides widely employed peptide pools of pp65 and IE-1, the use of antigens UL36 and UL55, but not US3 or US29, increased sensitivity of the test.

Comparison of the Cytomegalovirus (CMV) Enzyme-Linked Immunosorbent Spot and CMV QuantiFERON Cell-Mediated Immune Assays in CMV-Seropositive and -Seronegative Pregnant and Nonpregnant Women

Human cytomegalovirus (CMV) infection is a major cause of congenital infection leading to birth defects and sensorineural anomalies, including deafness. Recently, cell-mediated immunity (CMI) in pregnant women has been shown to correlate with congenital CMV transmission. In this study, two interferon gamma release assays (IGRA), the CMV enzyme-linked immunosorbent spot (ELISPOT) and CMV QuantiFERON assays, detecting CMV-specific CMI were compared. These assays were performed for 80 CMV-infected (57 primarily and 23 nonprimarily) pregnant women and 115 controls, including 89 healthy CMV-seropositive pregnant women without active CMV infection, 15 CMV-seronegative pregnant women, and 11 seropositive or seronegative nonpregnant women. Statistical tests, including frequency distribution analysis, nonparametric Kruskal-Wallis equality-of-populations rank test, Wilcoxon rank sum test for equality on unmatched data, and lowess smoothing local regression, were employed to determine statistical differences between groups and correlation between the assays. The CMV ELISPOT and CMV QuantiFERON assay data were not normally distributed and did not display equal variance. The CMV ELISPOT but not CMV QuantiFERON assay displayed significant higher values for primarily CMV-infected women than for the healthy seropositive pregnant and nonpregnant groups (P = 0.0057 and 0.0379, respectively) and those with nonprimary infections (P = 0.0104). The lowess local regression model comparing the assays on an individual basis showed a value bandwidth of 0.8. Both assays were highly accurate in discriminating CMV-seronegative pregnant women. The CMV ELISPOT assay was more effective than CMV-QuantiFERON in differentiating primary from the nonprimary infections. A substantial degree of variability exists between CMV ELISPOT and CMV QuantiFERON assay results for CMV-seropositive pregnant women.

A Diverse Repertoire of CD4 T Cells Targets the Immediate-Early 1 Protein of Human Cytomegalovirus

T-cell responses to the immediate-early 1 (IE-1) protein of human cytomegalovirus (HCMV) are associated with protection from viral disease. Thus, IE-1 is a promising target for immunotherapy. CD8 T-cell responses to IE-1 are generally strong. In contrast, CD4 T-cell responses to IE-1 were described to be comparatively infrequent or undetectable in HCMV carriers, and information on their target epitopes and their function has been limited. To analyze the repertoire of IE-1-specific CD4 T cells, we expanded them from healthy donors with autologous IE-1-expressing mini-Epstein–Barr virus-transformed B-cell lines and established IE-1-specific CD4 T-cell clones. Clones from seven out of seven HCMV-positive donors recognized endogenously processed IE-1 epitopes restricted through HLA-DR, DQ, or DP. Three to seven IE-1 epitopes were recognized per donor. Cumulatively, about 27 different HLA/peptide class II complexes were recognized by 117 IE-1-specific clones. Our results suggest that a highly diversified repertoire of IE-1-specific CD4 T cells targeting multiple epitopes is usually present in healthy HCMV carriers. Therefore, multiepitope approaches to immunomonitoring and immunotherapy will make optimal use of this potentially important class of HCMV-specific effector cells.

Immunotherapy with Donor T Cells Sensitized with Overlapping Pentadecapeptides for Treatment of Persistent Cytomegalovirus Infection or Viremia

We conducted a phase I trial of allogeneic T cells sensitized in vitro against a pool of pentadecapeptides (15-mer peptides) spanning the sequence of CMVpp65 for adoptive therapy of 17 allogeneic hematopoietic cell transplant recipients with cytomegalovirus (CMV) viremia or clinical infection persisting despite prolonged treatment with antiviral drugs. All but 3 of the patients had received T cell-depleted transplants without graft-versus-host disease (GVHD) prophylaxis with immunosuppressive drugs after transplantation. The CMVpp65-specific T cells (CMVpp65CTLs) generated were oligoclonal and specific for only 1 to 3 epitopes, presented by a limited set of HLA class I or II alleles. T cell infusions were well tolerated without toxicity or GVHD. Of 17 patients treated with transplant donor (n = 16) or third-party (n = 1) CMVpp65CTLs, 15 cleared viremia, including 3 of 5 with overt disease. In responding patients, the CMVpp65CTLs infused consistently proliferated and could be detected by T cell receptor Vβ usage in CMVpp65/HLA tetramer + populations for period of 120 days to up to 2 years after infusion. Thus, CMVpp65CTLs generated in response to synthetic 15-mer peptides of CMVpp65 are safe and can clear persistent CMV infections in the post-transplantation period.

Diversified phenotype of antigen specific CD8+ T cells responding to the immunodominant epitopes of IE and pp65 antigens of human cytomegalovirus

To study the cytomegalovirus (CMV)-specific CD8+ T cells in individuals with HLA A*1101, A*0201 and A*2402, our findings showed that peptide SK-10-2, KI-10 and KV-10 of CMV IE and pp65 antigens were immunodominant in 198 individuals with HLA A*1101, A*0201 and A*2402, the most frequent genotypes in Chinese. Interestingly, SK-10-2 induced the strongest T cell response to produce IFN-γ whereas the others did not induce prominent IFN-γ production despite they all induced remarkable T cell proliferation. The peptides induced different phenotypes including IFN-γ(high)TNF-α(low) and TNF-α(low)Foxp3(low). It suggests that only some of CMV-reactive CD8+ T cells are real protective IFN-γ(high) cytotoxic T cells.

Cytomegalovirus drives Vδ2neg γδ T cell inflation in many healthy virus carriers with increasing age

Cytomegalovirus (CMV) usually causes lifelong asymptomatic infection, but over time can distort immune profiles. Recent reports describe selective expansion of Vδ2^neg γδ T cells in healthy and immunocompromised CMV carriers. Having shown previously that virus-specific CD8⁺ and CD4⁺ T cell responses are increased significantly in elderly CMV carriers, probably driven by chronic stimulation, we hypothesized that Vδ2^neg γδ T cells may also be expanded with age. Our results show that Vδ2^neg γδ T cells are increased significantly in CMV-seropositive healthy individuals compared to CMV-seronegative controls in all age groups. The differences were most significant in older age groups (P < 0·0001). Furthermore, while Vδ2^neg γδ T- cells comprise both naive and memory cells in CMV-seronegative donors, highly differentiated effector memory cells are the dominant phenotype in CMV carriers, with naive cells reduced significantly in numbers in CMV-seropositive elderly. Although phenotypically resembling conventional CMV-specific T cells, Vδ2^neg γδ T cells do not correlate with changes in magnitude of CMV-specific CD4⁺ or CD8⁺ T cell frequencies within those individuals, and do not possess ex-vivo immediate effector function as shown by CMV-specific CD4⁺ and CD8⁺ T cells. However, after short-term culture, Vδ2^neg γδ T cells demonstrate effector T cell functions, suggesting additional requirements for activation. In summary, Vδ2^neg γδ T cells are expanded in many older CMV carriers, demonstrating a further level of lymphocyte subset skewing by CMV in healthy individuals. As others have reported shared reactivity of Vδ2^neg γδ T cells towards tumour cells, the composition of γδ T cell subsets may also have implications for risk of developing cancer in elderly people.

CD8 T cell-evasive functions of human cytomegalovirus display pervasive MHC allele specificity, complementarity, and cooperativity

Immunoevasive proteins ("evasins") of human CMV (HCMV) modulate stability and localization of MHC class I (MHC I) molecules, and their supply of antigenic peptides. However, it is largely unknown to what extent these evasins interfere with recognition by virus-specific CD8 T cells. We analyzed the recognition of HCMV-infected cells by a panel of CD8 T cells restricted through one of nine different MHC I allotypes. We employed a set of HCMV mutants deleted for three or all four of the MHC I modulatory genes US2, US3, US6, and US11. We found that different HCMV evasins exhibited different allotype-specific patterns of interference with CD8 T cell recognition of infected cells. In contrast, recognition of different epitopes presented by the same given MHC I allotype was uniformly reduced. For some allotypes, single evasins largely abolished T cell recognition; for others, a concerted action of evasins was required to abrogate recognition. In infected cells whose Ag presentation efficiency had been enhanced by IFN-γ pretreatment, HCMV evasins cooperatively impared T cell recognition for several different MHC I allotypes. T cell recognition and MHC I surface expression under influence of evasins were only partially congruent, underscoring the necessity to probe HCMV immunomodulation using specific T cells. We conclude that the CD8 T cell evasins of HCMV display MHC I allotype specificity, complementarity, and cooperativity.

Identification and HLA-tetramer-validation of human CD4+ and CD8+ T cell responses against HCMV proteins IE1 and IE2

Human cytomegalovirus (HCMV) is an important human pathogen. It is a leading cause of congenital infection and a leading infectious threat to recipients of solid organ transplants as well as of allogeneic hematopoietic cell transplants. Moreover, it has recently been suggested that HCMV may promote tumor development. Both CD4+ and CD8+ T cell responses are important for long-term control of the virus, and adoptive transfer of HCMV-specific T cells has led to protection from reactivation and HCMV disease. Identification of HCMV-specific T cell epitopes has primarily focused on CD8+ T cell responses against the pp65 phosphoprotein. In this study, we have focused on CD4+ and CD8+ T cell responses against the immediate early 1 and 2 proteins (IE1 and IE2). Using overlapping peptides spanning the entire IE1 and IE2 sequences, peripheral blood mononuclear cells from 16 healthy, HLA-typed, donors were screened by ex vivo IFN-γ ELISpot and in vitro intracellular cytokine secretion assays. The specificities of CD4+ and CD8+ T cell responses were identified and validated by HLA class II and I tetramers, respectively. Eighty-one CD4+ and 44 CD8+ T cell responses were identified representing at least seven different CD4 epitopes and 14 CD8 epitopes restricted by seven and 11 different HLA class II and I molecules, respectively, in total covering 91 and 98% of the Caucasian population, respectively. Presented in the context of several different HLA class II molecules, two epitope areas in IE1 and IE2 were recognized in about half of the analyzed donors. These data may be used to design a versatile anti-HCMV vaccine and/or immunotherapy strategy.

Naïve and memory CD8 T cell pool homeostasis in advanced aging: impact of age and of antigen-specific responses to cytomegalovirus

Alterations in the circulating CD8+ T cell pool, with a loss of naïve and accumulation of effector/effector memory cells, are pronounced in older adults. However, homeostatic forces that dictate such changes remain incompletely understood. This observational cross-sectional study explored the basis for variability of CD8+ T cell number and composition of its main subsets: naïve, central memory and effector memory T cells, in 131 cytomegalovirus (CMV) seropositive subjects aged over 60 years. We found great heterogeneity of CD8+ T cell numbers, which was mainly due to variability of the CD8 + CD28- T cell subset regardless of age. Analysis, by multiple regression, of distinct factors revealed that age was a predictor for the loss in absolute number of naïve T cells, but was not associated with changes in central or effector memory CD8+ T cell subsets. By contrast, the size of CD8+ T cells specific to pp65 and IE-1 antigens of CMV, predicted CD28 - CD8+ T cell, antigen-experienced CD8+ T cell, and even total CD8+ T cell numbers, but not naïve CD8+ T cell loss. These results indicate a clear dichotomy between the homeostasis of naïve and antigen-experienced subsets of CD8+ T cells which are independently affected, in human later life, by age and antigen-specific responses to CMV, respectively.

ESAT-6-gpi DNA vaccine augmented the specific antitumour efficacy induced by the tumour vaccine B16F10-ESAT-6-gpi/IL-21 in a mouse model

In this study, we hypothesized that the mice immunized with the glycosylphosphatidylinositol (GPI) anchored 6-kDa early-secreted antigenic target (ESAT-6) DNA vaccine (ESAT-6-gpi) and the tumour vaccine B16F10-ESAT-6-gpi/IL-21 might significantly enhance immune responses and antimelanoma efficacy. Our experimental results indicated that the anti-ESAT-6 antibody induced by the DNA vaccine ESAT-6-gpi bound ESAT-6 to the surface of tumour vaccine to activate a complement classical pathway and resulted in the B16F10 tumour cell lysis and apoptosis, which served as a potential trigger for breaking melanomatous immune tolerance to elicit an initiation of natural antimelanoma immunity. Our innovative approach of using the DNA vaccine ESAT-6-gpi priming and the tumour vaccine B16F10-ESAT-6-gpi/IL-21 boosting induced strong antimelanoma immunity that inhibited melanomatous growth. These findings highlighted the DNA vaccine ESAT-6-gpi as an immune enhancer to augment the immune efficacy of the tumour vaccine B16F10-ESAT -6-gpi/IL-21 against melanoma in a mouse model.

Presentation of an immunodominant immediate-early CD8+ T cell epitope resists human cytomegalovirus immunoevasion

Control of human cytomegalovirus (HCMV) depends on CD8+ T cell responses that are shaped by an individual's repertoire of MHC molecules. MHC class I presentation is modulated by a set of HCMV-encoded proteins. Here we show that HCMV immunoevasins differentially impair T cell recognition of epitopes from the same viral antigen, immediate-early 1 (IE-1), that are presented by different MHC class I allotypes. In the presence of immunoevasins, HLA-A- and HLA-B-restricted T cell clones were ineffective, but HLA-C*0702-restricted T cell clones recognized and killed infected cells. Resistance of HLA-C*0702 to viral immunoevasins US2 and US11 was mediated by the alpha3 domain and C-terminal region of the HLA heavy chain. In healthy donors, HLA-C*0702-restricted T cells dominated the T cell response to IE-1. The same HLA-C allotype specifically protected infected cells from attack by NK cells that expressed a corresponding HLA-C-specific KIR. Thus, allotype-specific viral immunoevasion allows HCMV to escape control by NK cells and HLA-A- and HLA-B-restricted T cells, while the virus becomes selectively vulnerable to an immunodominant population of HLA-C-restricted T cells. Our work identifies a T cell population that may be of particular efficiency in HCMV-specific immunotherapy.

Identification and elimination of an immunodominant T-cell epitope in recombinant immunotoxins based on Pseudomonas exotoxin A

Recombinant immunotoxins (RITs) are chimeric proteins that are being developed for cancer treatment. We have produced RITs that contain PE38, a portion of the bacterial protein Pseudomonas exotoxin A. Because the toxin is bacterial, it often induces neutralizing antibodies, which limit the number of treatment cycles and the effectiveness of the therapy. Because T cells are essential for antibody responses to proteins, we adopted an assay to map the CD4(+) T-cell epitopes in PE38. We incubated peripheral blood mononuclear cells with an immunotoxin to stimulate T-cell expansion, followed by exposure to overlapping peptide fragments of PE38 and an IL-2 ELISpot assay to measure responses. Our observation of T-cell responses in 50 of 50 individuals correlates with the frequency of antibody formation in patients with normal immune systems. We found a single, highly immunodominant epitope in 46% (23/50) of the donors. The immunodominant epitope is DRB1-restricted and was observed in subjects with different HLA alleles, indicating promiscuity. We identified two amino acids that, when deleted or mutated to alanine, eliminated the immunodominant epitope, and we used this information to construct mutant RITs that are highly cytotoxic and do not stimulate T-cell responses in many donors.

Sequential anti-cytomegalovirus response monitoring may allow prediction of cytomegalovirus reactivation after allogeneic stem cell transplantation

BACKGROUND

Reconstitution of cytomegalovirus-specific CD3(+)CD8(+) T cells (CMV-CTLs) after allogeneic hematopoietic stem cell transplantation (HSCT) is necessary to bring cytomegalovirus (CMV) reactivation under control. However, the parameters determining protective CMV-CTL reconstitution remain unclear to date.

DESIGN AND METHODS

In a prospective tri-center study, CMV-CTL reconstitution was analyzed in the peripheral blood from 278 patients during the year following HSCT using 7 commercially available tetrameric HLA-CMV epitope complexes. All patients included could be monitored with at least CMV-specific tetramer.

RESULTS

CMV-CTL reconstitution was detected in 198 patients (71%) after allogeneic HSCT. Most importantly, reconstitution with 1 CMV-CTL per µl blood between day +50 and day +75 post-HSCT discriminated between patients with and without CMV reactivation in the R+/D+ patient group, independent of the CMV-epitope recognized. In addition, CMV-CTLs expanded more daramtaically in patients experiencing only one CMV-reactivation than those without or those with multiple CMV reactivations. Monitoring using at least 2 tetramers was possible in 63% (n = 176) of the patients. The combinations of particular HLA molecules influenced the numbers of CMV-CTLs detected. The highest CMV-CTL count obtained for an individual tetramer also changed over time in 11% of these patients (n = 19) resulting in higher levels of HLA-B*0801 (IE-1) recognizing CMV-CTLs in 14 patients.

CONCLUSIONS

Our results indicate that 1 CMV-CTL per µl blood between day +50 to +75 marks the beginning of an immune response against CMV in the R+/D+ group. Detection of CMV-CTL expansion thereafter indicates successful resolution of the CMV reactivation. Thus, sequential monitoring of CMV-CTL reconstitution can be used to predict patients at risk for recurrent CMV reactivation.

Immunotherapeutic strategies to prevent and treat human herpesvirus 6 reactivation after allogeneic stem cell transplantation

Human herpesvirus (HHV) 6 causes substantial morbidity and mortality in the immunocompromised host and has no approved therapy. Adoptive transfer of virus specific T cells has proven safe and apparently effective as prophylaxis and treatment of other virus infections in immunocompromised patients; however, extension to subjects with HHV6 has been hindered by the paucity of information on targets of cellular immunity. We now characterize the cellular immune response from 20 donors against 5 major HHV6B antigens predicted to be immunogenic and define a hierarchy of immunodominance of antigens based on the frequency of responding donors and the magnitude of the T-cell response. We identified specific epitopes within these antigens and expanded the HHV6 reactive T cells using a GMP-compliant protocol. The expanded population comprised both CD4(+) and CD8(+) T cells that were able to produce multiple effector cytokines and kill both peptide-loaded and HHV6B wild-type virus-infected target cells. Thus, we conclude that adoptive T-cell immunotherapy for HHV6 is a practical objective and that the peptide and epitope tools we describe will allow such cells to be prepared, administered, and monitored in human subjects.

Nanoparticle-based adjuvant for enhanced protective efficacy of DNA vaccine Ag85A-ESAT-6-IL-21 against Mycobacterium tuberculosis infection

The goal of this study was to evaluate the protective efficacy of a cationic nanoparticle-based DNA vaccine expressing antigen 85A (Ag85A) and 6-kDa early secretory antigen target (ESAT-6) of Mycobacterium tuberculosis as well as cytokine interleukin-21 (IL-21) against M. tuberculosis infection. The results of this indicated that the anti-M. tuberculosis immune responses were induced in mice that had received the different DNA vaccines. More importantly, compared with using DNA vaccine Ag85A-ESAT-6-IL-21 alone, the nanoparticle-based DNA vaccine Ag85A-ESAT-6-IL-21 showed a statistically significant increase in the protective efficacy against M. tuberculosis infection in the immunized mice. We concluded that the nanoparticle-based DNA vaccine induced a strong immune response and markedly inhibited the growth of the M. tuberculosis in the mice. These findings highlighted the potential utility of Fe3O4-Glu-polyethyleneimine nanoparticles encapsulated with the DNA vaccine as a prophylactic vaccine in the M. tuberculosis-infected mouse model.

FROM THE CLINICAL EDITOR

This study emphasizes the potential utility of Fe3O4-Glu-polyethyleneimine nanoparticles encapsulated with DNA vaccine against TB as a prophylactic vaccine. The authors demonstrated a strong immune response and marked growth inhibition of mycobacterium tuberculosis in the mice.

Natural and adoptive T-cell immunity against herpes family viruses after allogeneic hematopoietic stem cell transplantation

Reactivated infections with herpes family-related cytomegalovirus, Epstein-Barr virus and varicella zoster virus are serious and sometimes life-threatening complications for patients undergoing allogeneic hematopoietic stem cell transplantation. The pathogenesis of these infections critically involves the slow and inefficient recovery of antiviral T-cell immunity after transplantation. Although efficient drugs to decrease viral load during this vulnerable period have been developed, long-term control of herpes viruses and protection from associated diseases require the sufficient reconstitution of virus-specific memory T cells. To heal the deficiency by immunotherapeutic means, numerous research groups have developed antiviral vaccines and strategies based on the adoptive transfer of virus-specific T cells. This article summarizes the substantial progress made in this field during the past two decades and gives future perspectives about challenges that need to be addressed before antigen-specific immunotherapy against herpes family viruses can be implemented in general clinical practice.

Novel strategies for adoptive therapy following HLA disparate transplants

Transplants of SBA-E- allogeneic marrow or G-CSF mobilized CD34+ (ISOLEX) E- peripheral blood progenitor cells which are adequately depleted of T-cells, when administered without post-transplant immunosuppression now induce consistent engraftment with low incidences of acute and chronic GVHD both in HLA matched and HLA disparate recipients. Furthermore, the incidence of relapse post transplant is not increased in patients transplanted for AML, MDS or ALL. In our series, the incidence of severe infections in HLA-matched recipients of such T-cell depleted grafts also does not differ from that detected following similarly matched unmodified grafts. However, in recipients of HLA-haplotype disparate T-cell depleted grafts, the risk of lethal viral infections is increased and prolonged. In many cases, this risk is closely correlated with failures of immunodominant virus-specific donor T-cells transferred in the graft to recognize infected host cells because they are restricted by HLA alleles not shared by the host. To address this limitation, we have developed a panel of artificial antigen presenting cells, each expressing a single prevalent HLA-allele. Using this panel, we are able to selectively generate virus-specific cytotoxic T-cells of desired HLA restriction, to insure their effectiveness in HLA haplotype-disparate transplant recipients. We have also shown that partially HLA-matched, third party-derived EBV-specific T-cells, selected from our bank of previously generated and characterized GMP-grade cell lines on the basis of their HLA restriction, can induce durable remissions of rituximab-refractory EBV lymphomas. These approaches may thus provide new, immediately accessible resources for the generation and broad application of immune cell therapies to treat and prevent severe viral diseases post transplant.

Recombinant antibodies encoded by IGHV1-69 react with pUL32, a phosphoprotein of cytomegalovirus and B-cell superantigen

Leukemia cells from patients with chronic lymphocytic leukemia (CLL) express a highly restricted immunoglobulin heavy variable chain (IGHV) repertoire, suggesting that a limited set of antigens reacts with leukemic cells. Here, we evaluated the reactivity of a panel of different CLL recombinant antibodies (rAbs) encoded by the most commonly expressed IGHV genes with a panel of selected viral and bacterial pathogens. Six different CLL rAbs encoded by IGHV1-69 or IGHV3-21, but not a CLL rAb encoded by IGHV4-39 genes, reacted with a single protein of human cytomegalovirus (CMV). The CMV protein was identified as the large structural phosphoprotein pUL32. In contrast, none of the CLL rAbs bound to any other structure of CMV, adenovirus serotype 2, Salmonella enterica serovar Typhimurium, or of cells used for propagation of these microorganisms. Monoclonal antibodies or humanized rAbs of irrelevant specificity to pUL32 did not react with any of the proteins present in the different lysates. Still, rAbs encoded by a germ line IGHV1-69 51p1 allele from CMV-seropositive and -negative adults also reacted with pUL32. The observed reactivity of multiple different CLL rAbs and natural antibodies from CMV-seronegative adults with pUL32 is consistent with the properties of a superantigen.