Identification of HLA‐A2‐ and A24‐restricted T‐cell epitopes derived from SOX6 expressed in glioma stem cells for immunotherapy

Abstract

Malignant gliomas are the most aggressive human primary brain tumors and are currently incurable. Immunotherapies have the potential to target glioma and glioma stem cells (GSCs) that are resistant to conventional therapies. We previously identified SOX6 as a human glioma antigen and demonstrated that vaccination with SOX6 DNA induced cytotoxic T lymphocytes (CTLs) specific for glioma, thereby exerting therapeutic antitumor responses in glioma-bearing mice. In this study, we attempted to identify SOX6-derived peptides as specific targets for effective and safe T-cell-mediated immunotherapy targeting SOX6-positive glioma and GSCs. In vitro stimulation with human leukocyte antigen (HLA)-A*2402 (A24)-restricted peptides, RFENLGPQL (SOX6 504 ) and PYYEEQARL (SOX6 628 ) or the HLA-A*0201 (A2)-restricted peptide, ALFGDQDTV (SOX6 447 ) was capable of inducing SOX6 peptide-specific CTLs in peripheral blood mononuclear cells derived from healthy donors and glioma patients. These CTLs were able to lyse a majority of glioma cell lines and a GSC line derived from human glioblastoma in an HLA Class I-restricted and an antigen-dependent manner. Furthermore, peptide vaccines of SOX6 628 , which was conserved in the murine SOX6 protein and expected to bind to major histocompatibility complex (MHC) H-2 d , induced CTLs specific for SOX6 628 in H-2 d mice. Normal autologous cells from mice, in which SOX6-specific immune responses were generated, were not destroyed. These results suggest that these SOX6 peptides are potnetially immunogenic in HLA-A24 or -A2 positive glioma patients and should be considered as a promising strategy for safe and effective T-cell-based immunotherapy of patients with gliomas.

The mechanisms of cancer immunoescape and development of overcoming strategies

“…Cytotoxic T lymphocytes (CTLs) specific for SOX2, which is reported to be expressed in CSCs, may eliminate SOX2-positive cancer stem-like cells in patients with monoclonal gammopathy of undetermined significance (MGUS), a precursor lesion to multiple myeloma [6]. We have identified that SOX6 might be expressed in human glioma stem-like cells enriched by sphere forming methods, which had high tumor-initiating ability and differentiation ability to both glial cells and neurons, and SOX6-specific CTL could lyse the glioma stem-like cells [7]. However, CSCs may also have immunoresistant property in some cases.…”

Development of Personalized Combination Cancer Immunotherapy Based on the Patients’ Immune Status

“…We proposed the development of following methods for modulation of the different key regulation points, and their appropriate combinations for effective cancer immunotherapy (Kawakami et al 2013b ) (Fig. 20.2 ): (1) We have been working on these immune-modulating methods, including the identifi cation of better tumor antigens (e.g., SOX6, mutant BRAF) (Ueda et al 2004(Ueda et al , 2010, DC-stimulating new adjuvants [e.g., Mycobacterium bovis Bacillus Calmette-Guérin-cell wall skeleton (BCG-CWS)] (Udagawa et al 2006 ), oncolytic herpes simplex virus (HSV) (Toda et al 2002 ;Ohkusu-Tsukada et al 2011 ), new TLR-stimulating compounds, cultured anti-tumor T cells (e.g., anti-tumor TILs, new TCR/CAR transduced T cells), various molecular-targeted drugs which act on both cancer cells, and activating and inhibiting immune cells Yaguchi et al 2012 ;Kudo-Saito et al 2012 ;Nishio et al 2014 ;Sumimoto et al 2006 ). We have previously reported that mutant BRAF depletion not only inhibits cell proliferation and invasion of human melanoma cells, but also inhibits production of multiple immunosuppressive cytokines such as IL-10, IL-6, and vascular endothelial growth factor (VEGF).…”

Brain cancer immunoediting: novel examples provided by immunotherapy of malignant gliomas

“…Ideally, glioma antigens should be highly expressed by the majority of glioma cells, have greater expression in tumor than in normal cells, strongly immunogenic, and present in multiples in order to avoid immune escape. Expression in CSCs could be a further requisite [133]: SOX2 and SOX6 provide interesting examples of candidate glioma antigens [134,135].…”