Abstract 2503: Efficient crosspresentation of oncofetal antigen (Glypican-3)-derived long peptides encompassing CTL and promiscuous Th cell epitopes using a novel liposome
Authors: Sayem Mohammad A. , Tomita Yusuke , Yuno Akira , Hirayama Masatoshi , Irie Atsushi , Tsukamoto Hirotake , Senju Satoru , Yuba Eiji , Yoshikawa Toshiaki , Kono Kenji , Nakatsura Tetsuya , Nishimura Yasuharu 
Published: August 2015

Abstract
Glypican-3 (GPC3), a human oncofetal antigen, is specifically overexpressed in hepatocellular carcinoma (HCC) and melanoma cells. GPC3-derived short peptides (SPs) vaccine carrying CTL epitopes were safe, and induced measurable immune and some clinical responses in a phase I clinical trial for treatment of HCC (Clin Cancer Res 18:3686, 2012). In this study we aim to identify GPC3-derived long peptides (LPs) carrying promiscuous HLA class II-binding Th1 cell epitopes. We predicted five candidate LPs using computer algorithm and proved antigenicity of all five GPC3-LPs to induce specific CD4+ T-cells by IFN-γ-ELISPOT assays. To determine the restriction HLA molecules involved in antigen presentation, blocking of antigen-induced IFN-γ production was investigated by adding anti-HLA-class II monoclonal antibodies (mAbs). Determination of specific restriction HLA molecules were carried out using L cells transfected with single pair of HLA class II α and β genes or allogeneic PBMC with shared HLA-class II molecule and found that these Th cells were restricted by seven frequent HLA class II molecules. Majority of these Th cell lines secreted Th1-type cytokines in response to autologous PBMCs pulsed with the cognate LPs. Th cells induced by four GPC3-LPs responded to autologous DCs pre-loaded with recombinant human GPC3 suggesting a possible natural processing of these LPs from GPC3 protein. One of the LPs was well cross-presented to GPC3-SP-specific CTLs when they were cocultured with DCs preloaded with GPC3-LPs encapsulated in a novel pH-sensitive liposome that can deliver LPs from endosome to cytoplasm. HLA-A2 transgenic mice immunized with the same LP showed increased GPC3-SP-specific and HLA-A2-restricted CTL response as compared to mice immunized with GPC3-SP alone. A part of this augmented response may be attributed to the help of CD4+ T cell response, because this LP stimulated specific mouse I-Ab-restricted CD4+ T cell response in vivo. GPC3-LPs-specific and HLA-Class II-restricted T cell responses were also observed in 12 out of 20 HCC patients vaccinated with GPC3-SPs. These GPC3-LPs may be applicable to immunotherapy of HCC.
Citation Format: Mohammad A. Sayem, Yusuke Tomita, Akira Yuno, Masatoshi Hirayama, Atsushi Irie, Hirotake Tsukamoto, Satoru Senju, Eiji Yuba, Toshiaki Yoshikawa, Kenji Kono, Tetsuya Nakatsura, Yasuharu Nishimura. Efficient crosspresentation of oncofetal antigen (Glypican-3)-derived long peptides encompassing CTL and promiscuous Th cell epitopes using a novel liposome. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 2503. doi:10.1158/1538-7445.AM2015-2503