Prevalent role of TCR alpha-chain in the selection of the preimmune repertoire specific for a human tumor-associated self-antigen

Qualitative difference between the cytotoxic T lymphocyte responses to melanocyte antigens in melanoma and vitiligo

Vitiligo is a skin disorder characterized by depigmented macules secondary to melanocyte loss. An unusual facet is its relation to melanoma: cytotoxic T lymphocytes directed to melanocyte antigens are found in both conditions and imply a breakdown of tolerance, yet the resulting immune reaction is the opposite. The mechanisms at the basis of these opposite effects are not known. Here, we performed a direct comparison of whole melanocyte-specific T cell populations in the two diseases. We demonstrate that neither precursor frequencies of Melan-A/MART-1-specific T lymphocytes nor their status of activation differ significantly. However, by using a tetramer-based T cell receptor down-regulation assay, we documented a higher affinity of vitiligo T cells. We calculated that the peptide concentration required for 50% of maximal receptor down-regulation differed by 6.5-fold between the two diseases. Moreover, only vitiligo T cells were capable of efficient receptor down-regulation and IFN-gamma production in response to HLA-matched melanoma cells, suggesting that this difference in receptor affinity is physiologically relevant. The differences in receptor affinity and tumor reactivity were confirmed by analyzing Melan-A/MART-1-specific clones established from the two diseases. Our results suggest that the quality, and not the quantity, of the melanocyte-specific cytotoxic responses differs between the two pathologies.

Adoptive transfer of tumor-reactive Melan-A-specific CTL clones in melanoma patients is followed by increased frequencies of additional Melan-A-specific T cells

In this study, we report the adoptive transfer of highly tumor-reactive Melan-A-specific T cell clones to patients with metastatic melanoma, and the follow-up of these injected cells. These clones were generated from HLA-A*0201 patients by in vitro stimulations of total PBMC with the HLA-A*0201-binding Melan-A peptide analog ELAGIGILTV. Ten stage IV melanoma patients were treated by infusion of these CTL clones with IL-2 and IFN-alpha. The generated T cell clones, of effector/memory phenotype were selected on the basis of their ability to produce IL-2 in response to HLA-A*0201 Melan-A-positive melanoma lines. Infused clones were detected, by quantitative PCR, in the blood of three patients for periods ranging from 7 to 60 days. Six patients showed regression of individual metastases or disease stabilization, and one patient experienced a complete response, but no correlation was found between the detection of the infused clones in PBMC or tumor samples and clinical responses. Nonetheless, frequencies of Melan-A/A2-specific lymphocytes, measured by tetramer labeling, increased after treatment in most patients. In one of these patients, who showed a complete response, this increase corresponded to the expansion of new clonotypes of higher avidity than those detected before treatment. Together, our results suggest that infused CTL clones may have initiated an antitumor response that may have resulted in the expansion of a Melan-A-specific CTL repertoire.

Distinct structural TCR repertoires in naturally occurring versus vaccine-induced CD8+ T-cell responses to the tumor-specific antigen NY-ESO-1

Spontaneous immune responses to the cancer testis antigen NY-ESO-1 are frequently found in cancer patients bearing antigen-expressing tumors. In HLA-A2-expressing patients, naturally elicited NY-ESO-1-specific, tumor-reactive cytotoxic T lymphocytes (CTLs) are mostly directed against an immunodominant epitope corresponding to peptide NY-ESO-1 157-165. NY-ESO-1-specific CTLs can also be induced by synthetic peptide vaccines, but they are heterogeneous in terms of functional avidity and tumor reactivity. The authors investigated the structural bases of this phenomenon by analyzing the TCR features of natural and vaccine-induced NY-ESO-1-specific CTLs. The results indicate that CTLs from the two groups exhibit highly structurally conserved but distinct TCR features, suggesting that the synthetic peptides used for vaccination may fail to faithfully mimic the naturally processed antigen. Together, the results of this study underline the strength of TCR molecular monitoring and will be instrumental for the development and monitoring of vaccines aimed at eliciting CTLs with high tumor reactivity.

T cell avidity and tumor recognition: implications and therapeutic strategies

In the last two decades, great advances have been made studying the immune response to human tumors. The identification of protein antigens from cancer cells and better techniques for eliciting antigen specific T cell responses in vitro and in vivo have led to improved understanding of tumor recognition by T cells. Yet, much remains to be learned about the intricate details of T cell – tumor cell interactions. Though the strength of interaction between T cell and target is thought to be a key factor influencing the T cell response, investigations of T cell avidity, T cell receptor (TCR) affinity for peptide-MHC complex, and the recognition of peptide on antigen presenting targets or tumor cells reveal complex relationships. Coincident with these investigations, therapeutic strategies have been developed to enhance tumor recognition using antigens with altered peptide structures and T cells modified by the introduction of new antigen binding receptor molecules. The profound effects of these strategies on T cell – tumor interactions and the clinical implications of these effects are of interest to both scientists and clinicians. In recent years, the focus of much of our work has been the avidity and effector characteristics of tumor reactive T cells. Here we review concepts and current results in the field, and the implications of therapeutic strategies using altered antigens and altered effector T cells.

Molecular tracking of antigen-specific T-cell clones during immune responses

Despite extended international efforts, the mechanisms governing T-cell receptor repertoire selection and kinetics in response to foreign or tumour antigens remain poorly characterized. A central goal of current research is to develop improved, reliable, immunological monitoring methods that measure and combine such parameters as the frequency of antigen-specific T cells and their functional capacities, as well as their clonal expansion during immune responses. Detecting and tracking defined anti-viral- and anti-tumour-specific T-cell responses ex vivo should lead to improvements in therapeutic strategies against viral infection or cancer in the future. During the past few years, highly sensitive tools have been developed to enable the molecular dissection and tracking of clonal T-cell expansion in animal models as well as in humans.

Melanocyte-specific, cytotoxic T cell responses in vitiligo: the effective variant of melanoma immunity?

Vitiligo is a relatively common progressive depigmentary condition that is believed to be due to the autoimmune-mediated loss of epidermal melanocytes. An interesting aspect of vitiligo is its relation to melanoma: cytotoxic T lymphocytes directed to self-antigens shared by normal melanocytes and melanoma cells are found in both conditions and might prove important in melanocyte destruction, yet the resulting immune reactions are completely different. From this standpoint, the selective destruction of pigment cells that occurs in cases of vitiligo is the therapeutic goal sought in melanoma research. In the present article, we will address these issues by reviewing current literature on the subject as well as by posing some speculations.

Analysis of T cell receptor alpha-chain variable region (Valpha) usage and CDR3alpha of T cells infiltrated into lesions of psoriasis patients

Psoriasis is a common inflammatory skin disease and is considered as T cell-mediated immune response. In this study, we analyzed T cell receptor alpha-chain variable region (TCR Valpha) usage in the lesions of psoriasis patients using 5'-RACE. As the results, Valpha1, -2, -7, -8, -10, -11, -12, and -23 were commonly detected in psoriatic lesions and comparison of expressions of these Valpha types between psoriasis patients and healthy individuals showed that Valpha1, -7, -11, and -12 were highly increased in psoriasis patients than in healthy individuals. Compared with atopy dermatitis patients, the expressions of Valpha1 and Valpha7 were increased in psoriasis patients. Then, to identify CDR3alpha of T cells infiltrated in psoriatic lesions, we examined which type of J gene segment was rearranged with Valpha1 or Valpha7, which the expressions was specifically increased in psoriatic lesions. The result showed that the V-J rearrangements between the examined patients were not equivalent and their frequencies were diverse, however, several common rearrangements such as Valpha1-Jalpha13, -23, -27, or -34 and Valpha7-Jalpha12, -33 were detected. The results in this study might provide the clue to define the characteristics of T cells associated with the pathogenesis of psoriasis.

Selective growth, in vitro and in vivo, of individual T cell clones from tumor-infiltrating lymphocytes obtained from patients with melanoma

In recent clinical trials in patients with metastatic melanoma, adoptive transfer of tumor-reactive lymphocytes mediated the regression of metastatic tumor deposits. To better understand the role of individual T cell clones in mediating tumor regression, a 5' RACE technique was used to determine the distribution of TCR beta-chain V region sequences expressed in the transferred cells as well as in tumor samples and circulating lymphocytes from melanoma patients following adoptive cell transfer. We found that dominant T cell clones were present in the in vitro-expanded and transferred tumor-infiltrating lymphocyte samples and certain T cell clones including the dominant T cell clones persisted at relatively high levels in the peripheral blood of the patients that demonstrated clinical responses to adoptive immunotherapy. However, these dominant clones were either undetected or present at a very low level in the resected tumor samples used for tumor-infiltrating lymphocyte generation. These data demonstrated that there was selective growth and survival, both in vitro and in vivo, of individual T cell clones from a relatively small number of T cells in the original tumor samples. These results suggest that the persistent T cell clones played an active role in mediating tumor regression and that 5' RACE analysis may provide an important tool for the analysis of the role of individual T cell clones in mediating tumor regression. A similar analysis may also be useful for monitoring autoimmune responses.

TCR Analyses

T-cells play a crucial role in immune surveillance against transformed cells and intracellular infections; they are involved in auto-immune reactions. They recognize their targets, i.e. MHC / peptide complexes, trough the T-cell receptor. TCR usage determines the molecular interaction of the immune system with biologically relevant MHC/peptide molecules. The TCR coding genes (variable, diversity and junctional) determine the molecular composition of the TCR alpha and beta heterodimer. The random association of the VDJ genes constitutes the complementarity determining region 3 (CDR3) responsible for antigen recognition and TCR specificity. The molecular composition of a T-cell population can be objectively defined by measuring the CDR3 region. Qualitative and quantitative comparisons of the TCR composition in different anatomic compartments, or longitudinally over time, allow to asses the entire TCR repertoire. This methodology can be supplemented with functional T-cell based assays and aids to objectively describe any alteration in the T-cell pool. TCR CDR3 analysis is useful in immunomonitoring, e.g. examining patients after BMT or solid organ transplantation, patients with HAART therapy, or patients receiving molecularly defined vaccines.

Therapeutic effectiveness of recombinant cancer vaccines is associated with a prevalent T-cell receptor alpha usage by melanoma-specific CD8+ T lymphocytes

Definition of immune variables that correlate with the antitumor activity of cancer vaccines is critical for monitoring immunotherapy protocols. To define surrogate end points predictive of the therapeutic efficacy of recombinant vaccines based on melanoma antigen tyrosinase-related protein (TRP)-2, we evaluated several properties of antigen-specific CD8(+) T lymphocytes in single mice undergoing either prophylactic or therapeutic immunization. Predictive markers for the efficacy of genetic vaccination were identified in the prophylactic model used. Interestingly, the number of tetramer(+) CD8(+) T lymphocytes expanded in vitro after a single cycle of stimulation with the immunodominant TRP-2 peptide was of the highest predictive value. In the therapeutic model, no variable examined at a single mouse level predicted the long-term therapeutic effect. Mice that survived did not show the highest expansion of antigen-specific lymphocytes or the more functionally active effectors, ex vivo or after in vitro culture with the peptide antigen. Successful therapy correlated strictly with the skewing of the T-cell receptor repertoire of tetramer-sorted, TRP-2-specific CD8(+) T lymphocytes, which showed a preferential alpha chain usage with a common CDR3 region.

GAD65-specific CD4+ T-cells with high antigen avidity are prevalent in peripheral blood of patients with type 1 diabetes

Negative selection of self-reactive T-cells during thymic development, along with activation-induced cell death in peripheral lymphocytes, is designed to limit the expansion and persistence of autoreactive T-cells. Autoreactive T-cells are nevertheless present, both in patients with type 1 diabetes and in at-risk subjects. By using MHC class II tetramers to probe the T-cell receptor (TcR) specificity and avidity of GAD65 reactive T-cell clones isolated from patients with type 1 diabetes, we identified high-avidity CD4+ T-cells in peripheral blood, coexisting with low-avidity cells directed to the same GAD65 epitope specificity. A variety of cytokine patterns was observed, even among T-cells with high MHC-peptide avidity, and the clones utilize a biased set of TcR genes that favor two combinations, Valpha12-beta5.1 and Valpha17-Vbeta4. Presence of these high-avidity TcRs indicates a failure to delete autoreactive T-cells that likely arise from oligoclonal expansion in response to autoantigen exposure during the progression of type 1 diabetes.

T-cell clonotypes in cancer

Cells of the immune system spontaneously recognize autologous tumor cells and T cells are believed to be the main effector cells for the immune surveillance of cancer. Recent advances in our understanding of basic and tumor immunology together with methodological developments implies that tumor specific T cells can now be studied functionally, phenotypically as well as molecularly. T cells recognize peptide antigens in the context of MHC molecules through the clonally distributed T-cell receptor (TCR), thus, the clonal distribution of the TCR offers the means to detect and track specific T cells based upon detection of the unique TCR. In this review, we present and discuss available data on TCR utilization of tumor specific T cells in murine models as well as spontaneous and treatment induced anti-tumor T-cell responses in humans.