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Rajiv Khanna

Publications and source records attributed to Rajiv Khanna.

At least 19 recordsLinked to original sources
PubMed2007

Epstein-Barr virus T-cell immunity despite rituximab.

Immunosuppression following solid organ transplantation results in impaired T-cell immunity and risk of Epstein-Barr virus (EBV)-positive post-transplant lymphoproliferative disorders (PTLD). The B-cell targeting antibody rituximab has efficacy in PTLD. As B cells are the principle reservoir for EBV, we investigated the effect of rituximab on the persistence of EBV-specific CD8(+) T-cell immunity. To avoid the confounding factor of concurrent immunosuppression to prevent transplant rejection, immunity was analysed in non-transplanted lymphoma patients (i.e. a non-PTLD setting). Cytomegalovirus-specific T-cell immunity was assessed as an internal control. Our data demonstrated that circulating B cells were not critical for maintaining EBV-specific T-cell immunity.

Aged↗
PubMed2006

Functional reversion of antigen-specific CD8+ T cells from patients with Hodgkin lymphoma following in vitro stimulation with recombinant polyepitope.

Recent studies on Hodgkin's lymphoma (HL) have indicated that patients with active disease display functional impairment of Ag-specific CD8+ T cells due to expansion of regulatory T cells at sites of disease and in the peripheral blood. Adoptive cellular immunotherapy based on EBV-specific CD8+ T cells has been explored with limited success to date. It has been proposed that improved targeting of these CD8+ T cells toward viral Ags that are expressed in HL may enhance future therapeutic vaccine strategies. In this study, we have developed a novel replication-deficient adenoviral Ag presentation system that is designed to encode glycine alanine repeat-deleted EBV nuclear Ag 1 covalently linked to multiple CD8+ T cell epitopes from latent membrane proteins 1 and 2. A single stimulation of CD8+ T cells from healthy virus carriers, and patients with HL with this adenoviral construct in combination with IL-2, was sufficient to reverse the functional T cell impairment and restored both IFN-gamma production and cytolytic function. More importantly, these activated CD8+ T cells responded to tumor cells expressing membrane proteins and recognized novel EBNA1 epitopes. Flow cytometric analysis revealed that a large proportion of T cells expanded from patients with HL were CD62L(high) and CD27(high), and CCR7(low), consistent with early to mid effector T cells. These findings provide an important platform for translation of Ag-specific adoptive immunotherapy for the treatment of EBV-associated malignancies such as HL and nasopharyngeal carcinoma.

Adenoviridae↗
PubMed2006

Expression of LAG-3 by tumor-infiltrating lymphocytes is coincident with the suppression of latent membrane antigen-specific CD8+ T-cell function in Hodgkin lymphoma patients.

In Hodgkin lymphoma (HL), the malignant Hodgkin Reed-Sternberg (HRS) cells constitute only 0.5% of 10% of the diseased tissue. The surrounding cellular infiltrate is enriched with T cells that are hypothesized to modulate antitumor immunity. We show that a marker of regulatory T cells, LAG-3, is strongly expressed on infiltrating lymphocytes present in proximity to HRS cells. Circulating regulatory T cells (CD4+ CD25hi CD45 ROhi, CD4+ CTLA4hi, and CD4+ LAG-3hi were elevated in HL patients with active disease when compared with remission. Longitudinal profiling of EBV-specific CD8+ T-cell responses in 94 HL patients revealed a selective loss of interferon-gamma expression by CD8+ T cells specific for latent membrane proteins 1 and 2 (LMP1/2), irrespective of EBV tissue status. Intratumoral LAG-3 expression was associated with EBV tissue positivity, whereas FOXP3 was linked with neither LAG-3 nor EBV tissue status. The level of LAG-3 and FOXP3 expression on the tumor-infiltrating lymphocytes was coincident with impairment of LMP1/2-specific T-cell function. In vitro pre-exposure of peripheral blood mononuclear cells to HRS cell line supernatant significantly increased the expansion of regulatory T cells and suppressed LMP-specific T-cell responses. Deletion of CD4+ LAG-3+ T cells enhanced LMP-specific reactivity. These findings indicate a pivotal role for regulatory T cells and LAG-3 in the suppression of EBV-specific cell-mediated immunity in HL.

Adolescent↗
PubMed2006

Prolonged illness after infectious mononucleosis is associated with altered immunity but not with increased viral load.

BACKGROUND: Primary Epstein-Barr virus (EBV) infection causes a spectrum of characteristics that range from asymptomatic seroconversion to severe infectious mononucleosis (IM), sometimes with prolonged symptoms and disability. We examined the relationships between clinical course, number of viral copies, and immunological parameters in a prospective cohort of subjects with recent IM. METHODS: Eight case patients with at least 6 months of disabling symptoms and 31 matched control subjects who had recovered promptly were included. Symptom scores were recorded at regular intervals over the course of 12 months. Cellular EBV load, EBV-specific antibody responses, lymphocyte subsets, and EBV-specific interferon (IFN)- gamma induction were measured. RESULTS: In case patients with prolonged illness, the severity of acute-phase symptoms was greater, the development of anti-EBV nuclear antigen-1 immunoglobulin G was more rapid, and the time to development of the peak IFN- gamma response to the majority of latent-cycle EBV peptides was generally slower than those in control subjects. However, in both groups, neither viral nor immune parameters correlated with the severity or duration of symptoms. CONCLUSIONS: The resolution of symptomatic IM is not determined by control of viremia, nor is it easily explained by altered host responses to EBV infection. The detailed determinants of delayed recovery remain to be elucidated.

Adolescent↗
PubMed2006

Plasma Epstein-Barr virus (EBV) DNA is a biomarker for EBV-positive Hodgkin's lymphoma.

PURPOSE: Latent Epstein-Barr virus (EBV) genomes are found in the malignant cells of approximately one-third of Hodgkin's lymphoma (HL) cases. Detection and quantitation of EBV viral DNA could potentially be used as a biomarker of disease activity. EXPERIMENTAL DESIGN: Initially, EBV-DNA viral load was prospectively monitored from peripheral blood mononuclear cells (PBMC) in patients with HL. Subsequently, we analyzed viral load in plasma from a second cohort of patients. A total of 58 patients with HL (31 newly diagnosed, 6 relapsed, and 21 in long-term remission) were tested. Using real-time PCR, 43 PBMC and 52 plasma samples were analyzed. RESULTS: EBV-DNA was detectable in the plasma of all EBV-positive patients with HL prior to therapy. However, viral DNA was undetectable following therapy in responding patients (P = 0.0156), EBV-positive HL patients in long-term remission (P = 0.0011), and in all patients with EBV-negative HL (P = 0.0238). Conversely, there was no association seen for the EBV-DNA load measured from PBMC in patients with active EBV-positive HL patients as compared with EBV-negative HL, or patients in long-term remission. EBV-DNA load in matched plasma/PBMC samples were not correlated. CONCLUSIONS: We show that free plasma EBV-DNA has excellent sensitivity and specificity, and can be used as a noninvasive biomarker for EBV-positive HL and that serial monitoring could predict response to therapy. Additional prospective studies are required to further evaluate the use of free plasma EBV-DNA as a biomarker for monitoring response to treatment in patients with EBV-positive HL.

Adolescent↗
PubMed2006

Transduction of primary lymphocytes with Epstein-Barr virus (EBV) latent membrane protein-specific T-cell receptor induces lysis of virus-infected cells: A novel strategy for the treatment of Hodgkin's disease and nasopharyngeal carcinoma.

Adoptive immunotherapy with in vitro expanded cytotoxic T lymphocytes specific for Epstein-Barr virus (EBV) can successfully treat post-transplant lymphoproliferative disease (PTLD). However, extension of a similar strategy to Hodgkin's disease (HD) and nasopharyngeal carcinoma (NPC) is limited by the poor immunogenicity of the limited set of EBV latency antigens expressed in these malignancies, making T-cell expansion difficult. Retroviral transduction of LMP-specific T-cell receptors (TCR) into activated T lymphocytes may provide a universal, MHC-restricted, means to generate effector cells without the need for tissue culture based methods of CTL expansion. We report the transfer of two LMP2-specific TCRs from human T-cell clones (HLA-A2 and HLA-A23,24 restricted) that confer the ability to lyse EBV-immortalized B-lymphoblastoid cell lines (B-LCL). B-LCL are the best model for native expression of LMP2. We also demonstrate the rapid transfer of the TCR by nucleofection of primary T cells using a simple plasmid-based vector. The ability to detect nucleofected TCRVbeta chain by antibody, fully assembled TCR by tetramer, and peptide-MHC-specific lytic activity indicates that nucleofection can serve as a tool for rapid screening of TCR specificity.

Amino Acid Sequence↗
PubMed2005

Human cytomegalovirus vaccine: time to look for alternative options.

In 1999, the Institute of Medicine (IOM) of the National Academy of Sciences (USA) assigned the highest priority for a vaccine to prevent congenital human cytomegalovirus (HCMV) infection, on the basis of the life-time cost to the health care system and the impact of the virus on human suffering. Subsequently, this priority was also endorsed by the US National Vaccine Program Office, which proposed a series of recommendations including support for increased funding by government agencies for HCMV vaccine research. Despite numerous attempts over the past three decades, successful licensure of a HCMV vaccine formulation remains elusive. Here we review the current status of HCMV vaccine studies and, based on our recent understanding of immune regulation of HCMV infection, we argue that a more realistic goal for vaccine strategies should be preventing HCMV disease rather than infection.

Antibodies, Viral↗
PubMed2005

Contemporaneous fluctuations in T cell responses to persistent herpes virus infections.

The classical paradigm for T cell dynamics suggests that the resolution of a primary acute virus infection is followed by the generation of a long-lived pool of memory T cells that is thought to be highly stable. Very limited alteration in this repertoire is expected until the immune system is re-challenged by reactivation of latent viruses or by cross-reactive pathogens. Contradicting this view, we show here that the T cell repertoire specific for two different latent herpes viruses in the peripheral blood displayed significant contemporaneous co-fluctuations of virus-specific CD8(+) T cells. The coordinated responses to two different viruses suggest that the fluctuations within the T cell repertoire may be driven by sub-clinical viral reactivation or a more generalized 'bystander' effect. The later contention was supported by the observation that, while absolute number of CD3(+) T cells and their subsets and also the cell surface phenotype of antigen-specific T cells remained relatively constant, a loss of CD62L expression in the total CD8(+) T cell population was coincident with the expansion of tetramer-positive virus-specific T cells. This study demonstrates that the dynamic process of T cell expansion and contractions in persistent viral infections is not limited to the acute phase of infection, but also continues during the latent phase of infection.

Amino Acid Sequence↗
PubMed2005

Ex vivo expansion of human cytomegalovirus-specific cytotoxic T cells by recombinant polyepitope: implications for HCMV immunotherapy.

Stem cell transplantation (SCT) remains the most effective curative therapy for the majority of hematopoietic malignancies. Unfortunately, SCT is limited by its toxicity and infectious complications that result from profound immunosuppression. In particular, acquisition of exogenous or reactivation of endogenous human cytomegalovirus (HCMV) is common after SCT. More recently, reconstitution of host immunity through augmentation of anti-HCMV T cell responses has been proposed as an exciting candidate therapy to avoid the requirement for antiviral drug use. Here we have developed a novel antigen presentation system based on a replication-deficient adenovirus that encodes multiple HLA class I-restricted epitopes from eight different antigens of HCMV as a polyepitope (referred to as AdCMVpoly). Ex vivo stimulation of peripheral blood mononuclear cells with AdCMVpoly consistently showed rapid stimulation and expansion of multiple epitope-specific T cells that recognized endogenously processed epitopes presented on virus-infected cells. Interestingly, the AdCMVpoly expression system is capable of expanding antigen-specific T cells even in the absence of CD4(+) T cells. These studies show the effectiveness of a polyepitope antigen presentation system for reproducible expansion of antigen-specific T cells from immunocompetent and immunocompromised settings.

Adenoviridae↗
PubMed2005

Technology insight: Applications of emerging immunotherapeutic strategies for Epstein-Barr virus-associated malignancies.

The Epstein-Barr virus (EBV) is uniquely associated with a broad range of human malignancies. In spite of their diverse cellular origin, most of these malignancies share common features, including the expression of either some or all of the EBV latent proteins, which can be potentially exploited for immune-based therapies. Here we discuss new and emerging strategies to manipulate the immune response to specifically boost T-cell immunity towards viral proteins that are expressed in EBV-associated malignancies. These strategies are used either alone or as an adjuvant therapy in combination with chemotherapy and/or monoclonal antibodies. Overall, this strategy may serve as a new paradigm for the successful multi-modality treatment of malignancies.

Antibodies, Monoclonal↗
PubMed2005

Viruses and lymphoma.

The aetiology of lymphomas is poorly understood and the striking increase in its incidence rate in developed societies remains unexplained. The concept of lymphoma as a virally-induced malignancy is not surprising since viruses are implicated in approximately 15% of all cancers. However, lymphoma represents a complex multistep process and, although viral associations have been identified, integration of the available epidemiological and scientific data poses substantial questions. The study of oncogenic viruses has and will continue to yield major insights into the pathogenesis of lymphoma. Further research is likely to uncover new lymphoma associations between both known and as yet unidentified viruses, may provide cellular and pharmacological targeted antiviral therapy strategies for the treatment of malignant lymphoma, and ultimately may generate the most promising avenue for lymphoma prevention.

Humans↗
PubMed2004

Herpesvirus-specific CD8 T cell immunity in old age: cytomegalovirus impairs the response to a coresident EBV infection.

Aging in humans is associated with increased infections and the reduced proliferative capacity of T cells, part of the more global phenomenon termed immune senescence. The etiology of immune senescence is unknown but the accumulation of virus-specific memory T cells may be a contributory factor. We have examined CD8 T cell responses to two persistent herpesvirus infections, CMV and EBV, and to a recurrent virus infection, influenza, in different age cohorts of healthy donors using HLA-peptide tetramers and intracellular cytokine detection. Of these, CMV appears to be the most immunogenic, with the CD8 T cell response representing over 10% of the CD8 pool in many elderly donors. Interestingly, the effect of age upon EBV-specific responses depends upon donor CMV sero-status. In CMV seropositive donors, the magnitude of the EBV-specific immune response is stable with age, but in CMV seronegative donors, the response to EBV increases significantly with age. By contrast, the influenza-specific CD8 T cell immune response decreases with age, independent of CMV status. The functional activity of the herpesvirus-specific immune response decreases in elderly donors, although the characteristic phenotypes of CMV- and EBV-specific memory populations are retained. This demonstrates that aging is associated with a marked accumulation of CMV-specific CD8 T cells together with a decrease in immediate effector function. Moreover, infection with CMV can reduce prevailing levels of immunity to EBV, another persistent virus. These results suggest that carriage of CMV may be detrimental to the immunocompetent host by suppressing heterologous virus-specific immunity during aging.

Adult↗
PubMed2004

Cross-recognition of human alloantigen by cytomegalovirus glycoprotein-specific CD4+ cytotoxic T lymphocytes: implications for graft-versus-host disease.

Presence of the HLA-DR7 allele in patients who receive transplants has been proposed as a risk factor for human cytomegalovirus (HCMV)-associated complications; however, the precise mechanism of this increased risk remains unresolved. Here we show that HLA-DR7-restricted HCMV-specific CD4(+) cytotoxic T lymphocytes (CTLs) can display an unusual dual specificity toward a glycoprotein-B (gB) epitope and the alloantigen HLA-DR4. However, no HLA-DR4-specific alloreactivity was observed when the gB-specific CTLs were generated from virus carriers expressing both HLA-DR7 and DR4 alleles. This most likely demonstrates the clonal inactivation of potentially self-reactive T cells in humans. Fine specificity analysis showed that gB-specific CTLs from HLA-DR7(+)/DR4(-) individuals displayed a distinct pattern of recognition when compared with CTLs from HLA-DR7(+)/DR4(+) individuals, presumably evading an area of the epitope that mimics a structure presented on HLA-DR4. These data illustrate a possible mechanism for the clinical association between HCMV and graft-versus-host disease.

Antigens, Viral↗
PubMed2004

Determining virological, serological and immunological parameters of EBV infection in the development of PTLD.

Post-transplant lymphoproliferative disease (PTLD) in Epstein-Barr virus (EBV) seronegative solid organ transplant recipients remains a significant problem, particularly in the first year post-transplant. Immune monitoring of a cohort of high-risk patients indicated that four EBV seronegative transplant recipients developed early-onset PTLD prior to evidence of an EBV humoral response. EBV status has been classically defined serologically, however these patients demonstrated multiple parameters of EBV infection, including the generation of EBV-specific CTL, outgrowth of spontaneous lymphoblastoid cell lines, and elevated EBV DNA levels, despite the absence of a classic EBV antibody response. As EBV serology is influenced by both immunosuppression and cytomegalovirus immunoglobulin treatment, both the EBV-specific CTL response and elevated EBV levels are more reliable indicators of EBV infection post-transplant.

Adolescent↗
PubMed2004

Endogenous presentation of CD8+ T cell epitopes from Epstein-Barr virus-encoded nuclear antigen 1.

Epstein-Barr virus (EBV)-encoded nuclear antigen (EBNA)1 is thought to escape cytotoxic T lymphocyte (CTL) recognition through either self-inhibition of synthesis or by blockade of proteasomal degradation by the glycine-alanine repeat (GAr) domain. Here we show that EBNA1 has a remarkably varied cell type-dependent stability. However, these different degradation rates do not correspond to the level of major histocompatibility complex class I-restricted presentation of EBNA1 epitopes. In spite of the highly stable expression of EBNA1 in B cells, CTL epitopes derived from this protein are efficiently processed and presented to CD8+ T cells. Furthermore, we show that EBV-infected B cells can readily activate EBNA1-specific memory T cell responses from healthy virus carriers. Functional assays revealed that processing of these EBNA1 epitopes is proteasome and transporter associated with antigen processing dependent. We also show that the endogenous presentation of these epitopes is dependent on the newly synthesized protein rather than the long-lived stable EBNA1. Based on these observations, we propose that defective ribosomal products, not the full-length antigen, are the primary source of endogenously processed CD8+ T cell epitopes from EBNA1.

B-Lymphocytes↗
PubMed2004

Induction of therapeutic T-cell responses to subdominant tumor-associated viral oncogene after immunization with replication-incompetent polyepitope adenovirus vaccine.

The EBV-encoded latent membrane proteins (LMP1 and LMP2), which are expressed in various EBV-associated malignancies have been proposed as a potential target for CTL-based therapy. However, the precursor frequency for LMP-specific CTL is generally low, and immunotherapy based on these antigens is often compromised by the poor immunogenicity and potential threat from their oncogenic potential. Here we have developed a replication- incompetent adenoviral vaccine that encodes multiple HLA class I-restricted CTL epitopes from LMP1 and LMP2 as a polyepitope. Immunization with this polyepitope vaccine consistently generated strong LMP-specific CTL responses in HLA A2/K(b) mice, which can be readily detected by both ex vivo and in vivo T-cell assays. Furthermore, a human CTL response to LMP antigens can be rapidly expanded after stimulation with this recombinant polyepitope vector. These expanded T cells displayed strong lysis of autologous target cells sensitized with LMP1 and/or LMP2 CTL epitopes. More importantly, this adenoviral vaccine was also successfully used to reverse the outgrowth of LMP1-expressing tumors in HLA A2/K(b) mice. These studies demonstrate that a replication-incompetent adenovirus polyepitope vaccine is an excellent tool for the induction of a protective CTL response directed toward multiple LMP CTL epitopes restricted through common HLA class I alleles prevalent in different ethnic groups where EBV-associated malignancies are endemic.

Adenoviridae↗