MART-1 (51-73)

We performed a phase 1/2 trial testing the safety, toxicity, and immune response of a vaccine consisting of autologous dendritic cells (DCs) transduced with a replication-defective adenovirus (AdV) encoding the full-length melanoma antigen MART-1/Melan-A (MART-1). This vaccine was designed to activate MART-1-specific CD+8 and CD4+ T cells. Metastatic melanoma patients received 3 injections of 10(6) or 10(7) DCs, delivered intradermally. Cell surface phenotype and cytokine production of the DCs used for the vaccines were tested, and indicated intermediate maturity. CD8+ T-cell responses to MART-1 27-35 were assessed by both major histocompatibility complex class I tetramer and interferon (IFN)-gamma enzyme-linked immunosorbent spot (ELISPOT) before, during, and after each vaccine and CD4+ T-cell responses to MART-1 51-73 were followed by IFN-gamma ELISPOT. We also measured antigen response breadth. Determinant spreading from the immunizing antigen MART-1 to other melanoma antigens [gp100, tyrosinase, human melanoma antigen-A3 (MAGE-A3)] was assessed by IFN-gamma ELISPOT. Twenty-three patients were enrolled and 14 patients received all 3 scheduled DC vaccines. Significant CD8+ and/or CD4+ MART-1-specific T-cell responses were observed in 6/11 and 2/4 patients evaluated, respectively, indicating that the E1-deleted adenovirus encoding the cDNA for MART-1/Melan-A (AdVMART1)/DC vaccine activated both helper and killer T cells in vivo. Responses in CD8+ and CD4+ T cells to additional antigens were noted in 2 patients. The AdVMART1-transduced DC vaccine was safe and immunogenic in patients with metastatic melanoma.

Melan-A/MART1 is a melanocytic differentiation antigen expressed by tumor cells of the majority of melanoma patients and, as such, is considered as a good target for melanoma immunotherapy. Nonetheless, the number of class I and II restricted Melan-A epitopes identified so far remains limited. Here we describe a new Melan-A/MART-1 epitope recognized in the context of HLA-DQa1*0101 and HLA-DQb1*0501, -DQb1*0502 or -DQb1*0504 molecules by a CD4+ T cell clone. This clone was obtained by in vitro stimulation of PBMC from a healthy donor by the Melan-A51-73 peptide previously reported to contain a HLA-DR4 epitope. The Melan-A51-73 peptide, therefore contains both HLA-DR4 and HLA-DQ5 restricted epitope. We further show that Melan-A51-63 is the minimal peptide optimally recognized by the HLA-DQ5 restricted CD4+ clone. Importantly, this clone specifically recognizes and kills tumor cell lines expressing Melan-A and either HLA-DQb1*0501, -DQb1*0504 or -DQb1*0502 molecules. Moreover, we could detect CD4+ T cells secreting IFN-gamma in response to Melan-A51-63 and Melan-A51-73 peptides among tumor infiltrating and blood lymphocytes from HLA-DQ5+ patients. This suggests that spontaneous CD4+ T cell responses against this HLA-DQ5 epitope occur in vivo. Together these data significantly increase the fraction of melanoma patients susceptible to benefit from a Melan-A class II restricted vaccine approach.

The human Melan-A/MART-1 gene encodes an HLA-A2-restricted peptide epitope recognized by melanoma-reactive CD8(+) cytotoxic T lymphocytes. Here we report that this gene also encodes at least one HLA-DR4-presented peptide recognized by CD4(+) T cells. The Melan-A/MART-1(51-73) peptide was able to induce the in vitro expansion of specific CD4(+) T cells derived from normal DR4(+) donors or from DR4(+) patients with melanoma when pulsed onto autologous dendritic cells. CD4(+) responder T cells specifically produced IFN-gamma in response to, and also lysed, T2.DR4 cells pulsed with the Melan-A/MART-1(51-73) peptide and DR4(+) melanoma target cells naturally expressing the Melan-A/MART-1 gene product. Interestingly, CD4(+) T cell immunoreactivity against the Melan-A/MART-1(51-73) peptide typically coexisted with a high frequency of anti-Melan-A/MART-1(27-35) reactive CD8(+) T cells in freshly isolated blood harvested from HLA-A2(+)/DR4(+) patients with melanoma. Taken together, these data support the use of this Melan-A/MART-1 DR4-restricted melanoma epitope in future immunotherapeutic trials designed to generate, augment, and quantitate specific CD4(+) T cell responses against melanoma in vivo.