A peptide epitope derived from the cancer testis antigen HOM-MEL-40/SSX2 capable of inducing CD4⁺ and CD8⁺ T-cell as well as B-cell responses.

Background: Antigen-derived HLA class I-restricted peptides can generate specific CD8(+) T-cell responses in vivo and are therefore often used as vaccines for patients with cancer. However, only occasional objective clinical responses have been reported suggesting the necessity of CD4(+) T-cell help and possibly antibodies for the induction of an effective anti-tumor immunity in vivo. The SSX2 gene encodes the cancer testis antigen (CTA) HOM-MEL-40/SSX2, which is frequently expressed in a wide spectrum of cancers. Both humoral and cellular immune responses against SSX2 have been described making SSX2 an attractive candidate for vaccine trials.

Methods: SYFPEITHI algorithm was used to predict five pentadecamer peptides with a high binding probability for six selected HLA-DRB1 subtypes (*0101, *0301, *0401, *0701, *1101, *1501) which are prevalent in the Caucasian population.

Results: Using peripheral blood cells of 13 cancer patients and 5 healthy controls, the HOM-MEL-40/SSX2-derived peptide p101-111 was identified as an epitope with dual immunogenicity for both CD4(+) helper and cytotoxic CD8(+) T cells. This epitope also reacted with anti-SSX2 antibodies in the serum of a patient with breast cancer. Most remarkably, SSX2/p101-111 simultaneously induced specific CD8, CD4, and antibody responses in vitro.

Conclusions: p101-111 is the first CTA-derived peptide which induces CD4(+), CD8(+), and B-cell responses in vitro. This triple-immunogenic peptide represents an attractive vaccine candidate for the induction of effective anti-tumor immunity.