Our data indicate that the adoptive transfer of antigen-specific T cells in melanoma patients can induce clinical tumor-specific immune responses without major adverse effects.

Adoptive T cell therapy has been successfully used for treatment of viral and malignant diseases. However, little is known about the fate and trafficking of transferred Ag-specific T cells. Using the tetramer (TM) technology which allows for detection and quantification of Ag-specific CTL, we assessed the frequency of circulating Melan-A-specific CTL in advanced melanoma patients during adoptive T cell therapy. Melan-A-specific CTL were generated from HLA-A2.1+ patients by in vitro stimulation of CD8+ T cells with dendritic cells pulsed with a mutated HLA-A2-binding Melan-A (ELAGIGILTV) peptide. Eight patients received three infusions of 0.25–11 × 108 Melan-A-specific CTL i.v. at 2-wk intervals along with low-dose IL-2. The transferred T cell product contained a mean of 42.1% Melan-A-TM+ CTL. Before therapy, the frequencies of Melan-A-specific CTL in patients’ circulating CD8+ T cells ranged from 0.01 to 0.07%. Characterization of the TM frequencies before and at different time points after transfer revealed an increase of circulating Melan-A-specific CTL up to 2%, correlating well with the number of transferred CTL. An elevated frequency of TM+ T cells was demonstrated up to 14 days after transfer, suggesting long-term survival and/or proliferation of transferred CTL. Combining TM analysis with a flow cytometry-based cytokine secretion assay, unimpaired production of IFN-γ was demonstrated in vivo for at least 24 h after transfer. Indium-111 labeling of Melan-A-specific CTL demonstrated localization of transferred CTL to metastatic sites as early as 48 h after injection. Overall, the results suggest that in vitro-generated Melan-A-specific CTL survive intact in vivo for several weeks and localize preferentially to tumor.

Tumor-reactive T cells play an important role in cancer immunosurveillance. Applying the multimer technology, we report here an unexpected high frequency of Melan-A-specific CTLs in a melanoma patient with progressive lymph node metastases, consisting of 18 and 12.8% of total peripheral blood and tumor-infiltrating CD8 ؉ T cells, respectively. Melan-A-specific CTLs revealed a high cytolytic activity against allogeneic Melan-A-expressing target cells but failed to kill the autologous tumor cells. Loading of the tumor cells with Melan-A peptide reversed the resistance to killing, suggesting impaired function of the MHC class I antigen processing and presentation pathway. Mutations of the coding region of the HLA-A2 binding Melan-A 26 -35 peptide or down-regulation of the MHC class I heavy chain, the antigenic peptide TAP, and tapasin could be excluded. However, PCR and immunohistochemical analysis revealed a deficiency of the immunoproteasomes low molecular weight protein 2 and low molecular weight protein 7 in the primary tumor cells, which affects the quantity and quality of generated T-cell epitopes and might explain the resistance to killing. This is supported by our data, demonstrating that the resistance to killing can be partially reversed by pre-exposure of the tumor cells to IFN-␥, which is known to induce the immunoproteasomes. Overall, this is the first report of an extremely high frequency of tumor-specific CTLs that exhibit competent T-cell-effector functions but fail to lyse the autologous tumor cells. Immunotherapeutic approaches should not only focus on the induction of a robust antitumor immune response, but should also have to target tumor immune escape mechanisms.

The adoptive transfer of in vitro induced and expanded tumor antigen-specific cytotoxic T lymphocytes (CTL) provides a promising approach to the immunotherpy of cancer. We have previously shown that antigen-specific CTL can be generated from HLA-A2.1+ cancer patients by 4 rounds of in vitro stimulation of purified CD8+ T cells with autologous dendritic cells pulsed with HLA-A2 binding tumor-associated peptides. Based on these results we have initiated a pilot study of adoptive T cell therapy in advanced melanoma patients demonstrating that in vitro generated Melan-A (ELAGIGILTV)-specific CTL survive intact in vivo for several weeks and localize preferentially to tumor. Here we report on the clinical results of a phase I study of 11 HLA-A2+ melanoma patients that received at least three i.v. infusions of Melan-A-specific CTL i.v. at 2-week intervals. Each T cell infusion was accompanied by a 6-day course of s.c. IL-2 (3x106 IU daily). A total of 51 T-cell infusions were administered, averaging 2.1 x108 Melan-A specific T cells per infusion, with a range from 0.11 – 13.1 x108 T cells per infusion. Clinical side effects were mild and consisted of chills and low-grade fever (WHO grade I–II) in 7 out of 11 patients that typically occurred within 6 to 8 h post infusion. Hematological effects, observed after T cell transfer, included an increase in eosinophils up to 50% in 7 out of 11 patients, peaking 24h post transfer. Clinical and immunological responses consisted of antitumor responses in 3 out of 11 patients (1 CR, 1 PR, 1 mixed response), an elevated frequency of circulating Melan-A multimer+ T cells up to 2% of total CD8+ T cells for 2 weeks post T cell infusion, suggesting long-term survival and/or proliferation of transferred CTL, and a complete loss of Melan-A expression in lymph node metastases of 2 patients after T cell transfer. Our data indicate that the adoptive transfer of antigen-specific T cells in cancer patients is capable of inducing clinical and systemic tumor-specific immune responses without provoking major side effects.

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