AACR 2002
Abstract #719

Heat shock protein gp96 presentation of antigenic peptides leads to in vitro sensitization and in vivo expansion of tumor-specific T cells

Licia Rivoltini, Chiara Castelli, Paola Squarcina, Agata Cova, Lorenzo Pilla, Matteo Carrabba, Giovanna Andreola, Jorgelina Coppa, Filiberto Belli, Francesco Gallino, Pramod Srivastava, Roberto Camerini, Jonathan J Lewis, Giorgio Parmiani, National Tumor Institute, Milano, Italy; Antigenics Inc., New York, NY; Sigma-Tau S.p.a., Roma, Italy.

Tumor-derived HSP-gp96 has been clearly shown to mediate protection from metastatic spread and cure of established lesions in mice models. This effect appears to be induced by tumor-specific CD8+ T cells, possibly triggered and expanded in vivo by immunogenic peptides derived from tumor antigens and chaperoned by gp96. However, direct evidence of peptide presence in tumor-derived gp96 molecules has been reported only in murine systems, while no data are available in human tumors. To assess the hypothesis that gp96 purified from human neoplastic cells does contain tumor antigen-derived peptides, we took advantage of antigen-specific T-cell clones and oligoclonal lines available in our laboratory for detecting immunogenic epitopes in gp96 extracted either from autologous or HLA-matched tumor cells. HLA-A2.1+ monocytes were pulsed with gp96 from melanoma and colon carcinoma cells and used as targets for HLA-A2–restricted MART-1(27-35)-, EpCAM(263-271)- and Her2neu(654-662)-specific T-cells clones and lines. Anti–MART-1 T cells released IFN-gamma in response to gp96 from different melanomas, but not to gp96 purified from colon carcinoma cells. Such recognition was HLA class I-mediated, since it was significantly blocked by anti-HLA class I, and not by anti-HLA class II, monoclonal antibody. HLA class I blockable recognition of colon carcinoma-derived gp96 pulsed on monocytes was also detected with anti-EpCam and anti–Her2-neu T-cell lines and clones. To assess the immunological and clinical effects of HSP, two Phase I-II clinical trials based on vaccination with autologous tumor-derived HSP-gp96 were performed in our institution. Since in vitro data suggested that tumor-derived gp96 does contain antigen-derived peptides, we wanted to evaluate whether MART–1-, EpCam-, and Her2neu-specific T cells could have been expanded in vivo by vaccination with autologous tumor-derived gp96. Indeed, three out of 12 HLA-A2+ melanoma patients displayed a significant increment of MART-1(27-35) recognition, detectable by Elispot and HLA/peptide tetramer staining. Among the nine HLA-A2.1+ colon carcinoma patients enrolled in the study, two developed a significant enhancement of EpCam and Her2neu peptide recognition, paralleled by increased HLA-A2.1/EpCAM and Her2neu peptide tetramers staining. No change in anti-Flu responses was observed in any of these patients. Two of the three melanoma patients showing increased MART-1 reactivity responded clinically to the vaccine with a complete tumor regression. Altogether, these data suggest that gp96 derived from melanoma and colon carcinoma cells carries tumor-derived peptides that can be processed by APC and presented both in vitro and in vivo to antigen-specific T cells, thus representing a promising tool for vaccine therapy in cancer patients.