Melan-A/MART-1_51-73 represents an immunogenic HLA-DR4-restricted epitope recognized by melanoma-reactive CD4⁺ T cells

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-γ 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.