The frequent expression of cancer/testis antigens provides opportunities for immunotherapeutic targeting of sarcoma.

Sarcomas are rare but aggressive malignant tumors associated with high mortality, for which the efficacy of standard therapies remains limited. In order to develop immunotherapeutic approaches for the treatment of sarcoma, we studied the relevance of cancer/testis antigens (CTAs), a group of antigens whose expression is developmentally regulated and that is specifically found in some tumor types, as sarcoma vaccine targets. CTA expression was assessed by PCR and/or immunohistochemistry (IHC) in sarcoma tumor samples that included different histological subtypes and sarcoma cell lines. Expression of HLA class I was assessed by IHC in tumor samples and by FACS analysis in cell lines. More than 70% of the tumor samples expressed at least one CTA. The majority of tumors and cell lines expressed normal levels of HLA class I. HLA class I expression in cell lines was enhanced upon treatment with IFN-gamma. CTA expression was enhanced or induced by treatment with the demethylating agent 5-aza-2'-deoxycytidine, resulting in recognition by specific CTLs. Interestingly, a spontaneous humoral and CD8+ T cellular response to the CTA NY-ESO-1 was detected in a synovial sarcoma patient. Together, these findings strongly support the implementation of CTA-based immunotherapy of sarcoma as a means to improve the efficacy of the standard therapy.

Identification of an SSX-2 epitope presented by dendritic cells to circulating autologous CD4+ T cells.

Accumulating evidence supports the requirement for both tumor-specific CD8(+) and CD4(+) T cell responses for efficient tumor rejection to occur. Because of its expression in different tumor types, the cancer/testis Ag encoded by the synovial sarcoma X breakpoint 2 (SSX-2) gene is among the most relevant candidates for the development of generic cancer vaccines. The immunogenicity of SSX-2 has been previously corroborated by detection of specific humoral and CD8(+) T cell responses in cancer patients. In this study we report identification of the first CD4(+) T cell epitope encoded by SSX-2. The identified epitope mapped to the 19-34 region of the protein and was recognized by CD4(+) T cells from an Ag-expressing melanoma patient in association with HLA-DPB1*0101. The absence of detectable response in healthy donors and other patients suggests that SSX-2-specific CD4(+) T cells in the responder patient had been previously expanded in vivo in response to the autologous tumor. The epitope did not appear to be presented on the surface of tumor cells at levels sufficient to allow direct recognition. In contrast, it was efficiently presented by autologous dendritic cells, supporting the concept that processing by professional APC is the main pathway through which the CD4(+) T cell immunoresponse to tumor Ags occurs in vivo.

SSX antigens as tumor vaccine targets in human sarcoma.

The efficacy of current standard therapies for the treatment of sarcoma remains limited. With the aim of identifying target antigens relevant to the development of vaccine-based immunotherapy of sarcoma, we have addressed the relevance of tumor-specific antigens encoded by genes belonging to the SSX family as vaccine targets in sarcoma tumors. Expression of SSX-1 to -5 was analyzed in a collection of sarcoma tumors of diverse histological subtypes and in sarcoma cell lines. We found expression of at least one SSX-encoded antigen in 42% of sarcoma tumors, including 5 of 7 different histological subtypes, and in 50% of sarcoma cell lines. SSX-1 was the most frequently expressed family member, followed by SSX-4, -2 and -5. Expression of SSX-3 was detected in only one sample. Importantly, most SSX positive samples co-expressed more than one family member. In addition, assessment of CD8+ T cell recognition of HLA-A2+ SSX-2+ sarcoma cells showed that the latter were efficiently recognized and lysed by SSX-2-specific CTLs. The results of this study indicate that SSX antigens are relevant targets for the development of vaccine-based immunotherapy of sarcoma and encourage the start of vaccination trials using SSX-derived immunogens in sarcoma patients.