Testing for HLA/peptide tetramer-binding to the T cell receptor complex on human T lymphocytes.

HLA/peptide tetramers are frequently used for ex vivo monitoring of disease- or vaccine-induced T cell immune responses and for T cell epitope identification. However, when low-levels HLA/peptide tetramer-positive T cell populations are encountered, it is difficult to ascertain whether this represents a true T cell receptor (TCR)-mediated interaction or background signal. To address this issue, we have developed a method for both HLA class I and class II tetramer assays to confirm tetramer-binding to the TCR/CD3 complex. Preincubation of T cells with anti-CD3 mAb SPV-T3b and subsequent crosslinking interferes with the binding of HLA/peptide tetramers to the TCR/CD3 complex and thereby indicates to what extent HLA/peptide tetramer binds through interaction with TCR/CD3 complex. SPV-T3b pretreatment results in a 2- to 10-fold decrease in tetramer-binding intensity to antigen-specific CD8+ or CD4+ T cells, whereas background reactivity of HLA/peptide tetramers containing HIV-derived peptide in HIV-negative donors remained unchanged. SPV-T3b pretreatment forms a valuable tool to verify tetramer-based detection of antigen-specific T cells during the monitoring of immune responses in clinical studies.

Immunogenicity, including vitiligo, and feasibility of vaccination with autologous GM-CSF-transduced tumor cells in metastatic melanoma patients.

PURPOSE: To determine the feasibility, toxicity, and immunologic effects of vaccination with autologous tumor cells retrovirally transduced with the GM-CSF gene, we performed a phase I/II vaccination study in stage IV metastatic melanoma patients. PATIENTS AND METHODS: Sixty-four patients were randomly assigned to receive three vaccinations of high-dose or low-dose tumor cells at 3-week intervals. Tumor cell vaccine preparation succeeded for 56 patients (88%), but because of progressive disease, the well-tolerated vaccination was completed in only 28 patients. We analyzed the priming of T cells against melanoma antigens, MART-1, tyrosinase, gp100, MAGE-A1, and MAGE-A3 using human leukocyte antigen/peptide tetramers and functional assays. RESULTS: The high-dose vaccination induced the infiltration of T cells into the tumor tissue. Three of 14 patients receiving the high-dose vaccine showed an increase in MART-1- or gp100-specific T cells in the peripheral blood during vaccination. Six patients experienced disease-free survival for more than 5 years, and two of these patients developed vitiligo at multiple sites after vaccination. MART-1- and gp100-specific T cells were found infiltrating in vitiligo skin. Upon vaccination, the T cells acquired an effector phenotype and produced interferon-gamma on specific antigenic stimulation. CONCLUSION: We conclude that vaccination with GM-CSF-transduced autologous tumor cells has limited toxicity and can enhance T-cell activation against melanocyte differentiation antigens, which can lead to vitiligo. Whether the induction of autoimmune vitiligo may prolong disease-free survival of metastatic melanoma patients who are surgically rendered as having no evidence of disease before vaccination is worthy of further investigation.

On the role of melanoma-specific CD8+ T-cell immunity in disease progression of advanced-stage melanoma patients.

Cytotoxic T-cell immunity directed against melanosomal differentiation antigens is arguably the best-studied and most prevalent form of tumor-specific T-cell immunity in humans. Despite this, the role of T-cell responses directed against melanosomal antigens in disease progression has not been elucidated. To address this issue, we have related the presence of circulating melanoma-specific T cells with disease progression and survival in a large cohort of patients with advanced-stage melanoma who had not received prior treatment. In 42 (68%) of 62 patients, melanoma-specific T cells were detected, sometimes in surprisingly large numbers. Disease progression during treatment was more frequent in patients with circulating melanoma-specific T cells, and mean survival of patients with circulating melanoma-specific T cells was equal to the survival of patients without melanoma-specific T cells. These data suggest that the induction of melanosomal differentiation antigen-specific T-cell reactivity in advanced stage melanoma is a late event most likely due to antigen load and spreading and is not accompanied by a clinically significant antitumor effect. These melanoma-specific T cells may be functionally distinct from T cells raised during spontaneous regression or up vaccination.

Human telomerase reverse transcriptase-transduced human cytotoxic T cells suppress the growth of human melanoma in immunodeficient mice.

Immunotherapy of melanoma by adoptive transfer of tumor-reactive T lymphocytes aims at increasing the number of activated effectors at the tumor site that can mediate tumor regression. The limited life span of human T lymphocytes, however, hampers obtaining sufficient cells for adoptive transfer therapy. We have shown previously that the life span of human T cells can be greatly extended by transduction with the human telomerase reverse transcriptase (hTERT) gene, without altering antigen specificity or effector function. We developed a murine model to evaluate the efficacy of hTERT-transduced human CTLs with antitumor reactivity to eradicate autologous tumor cells in vivo. We transplanted the human melanoma cell line melAKR or melAKR-Flu, transduced with a retrovirus encoding the influenza virus/HLA-A2 epitope, in RAG-2(-/-) IL-2Rgamma (-/-) double knockout mice. Adoptive transfer of the hTERT-transduced influenza virus-specific CTL clone INFA24 or clone INFA13 inhibited the growth of melAKR-Flu tumors in vivo and not of the parental melAKR melanoma cells. Furthermore, the hTERT-transduced CTL clone INFA13 inhibited tumor growth to the same extent in vivo as the untransduced CTL clone, as determined by in vivo imaging of luciferase gene-transduced melAKR-Flu tumors, indicating that hTERT did not affect the in vivo function of CTL. These results demonstrate that hTERT-transduced human CTLs are capable of mediating antitumor activity in vivo in an antigen-specific manner. hTERT-transduced MART-1-specific CTL clones AKR4D8 and AKR103 inhibited the growth of syngeneic melAKR tumors in vivo. Strikingly, melAKR-Flu cells were equally killed by the MART-1-specific CTL clones and influenza virus-specific CTL clones in vitro, but only influenza-specific CTLs were able to mediate tumor regression in vivo. The influenza-specific CTL clones were found to produce higher levels of IFNgamma on tumor cell recognition than the MART-1-specific CTL clones, which may result from the higher functional avidity of the influenza virus-specific CTL clones. Also, melAKR-Flu tumors were growing faster than melAKR tumors, which may have surpassed the relatively modest antitumor effect of the MART-1-specific CTL, as compared with the influenza virus-specific CTL. Taken together, the adoptive transfer model described here shows that hTERT-transduced T cells are functional in vivo, and allows us to evaluate the balance between functional activity of the CTL and tumor growth rate in vivo, which determines the efficacy of CTLs to eradicate tumors in adoptive transfer therapy.