Abstract 5636: Identification of bladder cancer-associated cancer-testis antigens-derived long peptides encompassing both CTL and promiscuous HLA class II-restricted Th cell epitopes

DEP domain containing 1 (DEPDC1) and M-phase phosphoprotein 1 (MPHOSPH1) are human cancer testis antigens that are frequently overexpressed in urinary bladder cancer. The growth of bladder cancer cells was significantly inhibited by knockdown of DEPDC1 or MPHOSPH1 expression using small interfering RNAs; thus, DEPDC1 and MPHOSPH1 are essential for tumor growth and survival, indicating the clinical significance of these antigens as targets for antigen-specific cancer immunotherapy. Subsequent reports further identified highly immunogenic DEPDC1- and MPHOSPH1-derived short peptides (SPs) that can induce HLA-A24-restricted cytotoxic T lymphocytes (CTLs) from peripheral blood mononuclear cells (PBMCs) isolated from patients with bladder cancer. These DEPDC1- and MPHOSPH1-derived SPs vaccine administered to patients with progressive bladder cancer was well tolerated and effectively activated SPs-specific CTLs in vivo, and the better CTL induction was associated with longer survival of patients in a recent phase I and II clinical trial (Obara W et al. Ann. Oncol. 28: 798, 2017). Here, we aimed to identify long peptides (LPs) derived from DEPDC1 and MPHOSPH1 that induced both T-helper (Th) cells and tumor-reactive CTLs. Stimulation of PBMCs isolated from healthy donors with the synthetic DEPDC1- and MPHOSPH1-LPs predicted to bind to promiscuous human HLA class II molecules by a computer algorithm induced specific CD4-positive T cells as revealed by interferon-gamma enzyme-linked immunospot assays. Three of six LPs encompassed SPs recognized by either HLA-A2- or -A24-restricted CTLs, and all six LPs stimulated DEPDC1- or MPHOSPH1-specific Th cells restricted by promiscuous and frequently observed HLA class II molecules in the Japanese population. Some LPs are naturally processed from the proteins in DCs, and the capacity of these LPs to cross-prime SP-specific CTLs was confirmed in vivo using HLA-A2 or -A24 transgenic mice. The LP-specific and HLA class II-restricted T-cell responses were also observed in PBMCs isolated from patients with bladder cancer. Repeated stimulation of PBMCs with DEPDC1-LPs and MPHOSPH1-LPs yielded clonal Th cells expressing specific T-cell receptor (TCR)-alpha and beta genes. These DEPDC1- or MPHOSPH1-derived LPs may have applications in immunotherapy in patients with bladder cancer, and the TCR genes identified may be useful for monitoring of Th cells specific to LPs in vivo. [ This research was supported by a MEXT Grant-in-Aid for Scientific Research on Innovative Areas 22133005; JSPS KAKENHI 23650609, 24300334, 15H04311 and 16H06498 for Scientific Research on Innovative Area "Neo-self"; the Project for Cancer Research And Therapeutic Evolution (P-CREATE) from the Japan Agency for Medical Research and Development, AMED; and OncoTherapy Science, Inc.. ] Citation Format: Yasuharu Nishimura, Miki Tsuruta, Shohei Ueda, Poh Yin Yew, Isao Fukuda, Sachiko Yoshimura, Hiroyuki Kishi, Hiroshi Hamana, Masatoshi Hirayama, Junji Yatsuda, Atsushi Irie, Satoru Senju, Eiji Yuba, Tomomi Kamba, Masatoshi Eto, Hideki Nakayama. Identification of bladder cancer-associated cancer-testis antigens-derived long peptides encompassing both CTL and promiscuous HLA class II-restricted Th cell epitopes [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 5636.