Abstract
A promising vaccine strategy for the treatment of cancer involves the use of vaccines incorporating tumor antigen-derived synthetic peptides that can be coordinately recognized by specific CD4(+) and CD8(+) T-cells. Previously, we reported that a MAGE-A6-derived peptide (MAGE-A6(172-187)) and its highly-immunogenic and cross-reactive homolog derived from Mycoplasma penetrans HF-2 permease (HF-2(216-229)) are promiscuously presented by multiple HLA-DR alleles to responder CD4(+) T-cells obtained from healthy donors and melanoma patients. Here, we investigated whether these same peptides could concomitantly stimulate cross-reactive MAGE-A6-specific CD8(+) T-cell responses in vitro using cells isolated from HLA-A*0201 (HLA-A2)(+) healthy individuals and patients with melanoma. We now show that MAGE-A6(172-187) and, even more so, HF-2(216-229), induce memory CD8(+) T cells that recognize HLA-A2(+) MAGE-A6(+) tumor target cells. The immunogenicity of these peptides was at least partially attributed to their embedded MAGE-A6(176-185) and HF-2(220-229) "homologous" sequences. The functional avidity of HF-2(216-229) peptide-primed CD8(+) T cells for the MAGE-A6(172-187) peptide was more than 100-fold greater than that of CD8(+) T cells primed with the corresponding MAGE-A6 peptide. Additionally, these 2 peptides were recognized in interferon γ (IFNγ) and granzyme B ELISPOT assays by CD8(+) T-cell clones displaying variable T-cell receptor (TCR) Vβ usage. These data suggest that the immune cross-reactivity of the MAGE-A6(172-187) and HF-2(216-229) peptides extends to CD8(+) T cells, at least in HLA-A2(+) donors, and supports the potential translational utility of these epitopes in clinical vaccine formulations and for immunomonitoring of cancer patients.