Abstract 2510: Immunotherapy targeting MASH2 antigen protects mice against MASH2-expressing transplanted tumors and inhibits the development of colorectal adenomas in APC +/Min-FCCC mice
Authors: Rioux Clément , Clapper Margie , Cooper Harry , Michaud Jean , St Amant Natalie , Koohsari Hossein , Workman Laura , Kaunga Esther , Pilorget Anthony , Gerard Catherine 
Published: August 2015

Abstract
The importance of the host immune system in controlling the growth and development of colorectal cancer (CRC) is highlighted by the prognostic value of immune infiltration, which suggests that cancer immunotherapy could mobilize the immune system for clinical benefit. Human achaete scute homolog 2 (Hash2) and its murine ortholog Mash2 are overexpressed in human and mouse CRC, respectively, and are thus potential targets for immunotherapy.
The present studies assessed the ability of a recombinant MASH2 protein combined with the AS15 immunostimulant to induce an immune response and inhibit tumor growth in mouse models. CB6F1 mice received 4 injections of AS15 or MASH2+AS15 and were subsequently injected with TC1/MASH2 tumor cells. In parallel, APC+/Min-FCCC mice that spontaneously develop MASH2-expressing colorectal adenomas were immunized (x9) with phosphate buffered saline (PBS), AS15 alone or MASH2+AS15, either before (prophylaxis) or after (immunotherapy) colon adenomas were detectable by colonoscopy. MASH2-specific antibody and cellular immune responses (CD4+ and CD8+ cells producing cytokines) were measured by ELISA and flow cytometry, respectively. Colorectal adenomas were diagnosed and characterized by histopathology.
In both CB6F1 and APC+/Min-FCCC mice, MASH2+AS15 induced strong MASH2-specific antibody and CD4+ responses that were not observed after injection with PBS or AS15. CB6F1 mice immunized with MASH2+AS15 showed slower growth of injected TC1/MASH2 tumors and better survival in comparison to mice injected with AS15 alone. In APC+/Min-FCCC mice, the mean number of colon adenomas was 2.6, 2.4 and 3.8 in the MASH2+AS15, AS15 and PBS groups, respectively (p = 0.059 for MASH2+AS15 vs PBS). In these mice, the mean number of colon microadenomas was ∼3-fold lower in the MASH2+AS15 group as compared to PBS control (MASH2+AS15 [0.4], AS15 [0.6], PBS [1.1]; p = 0.001 for MASH2+AS15 vs PBS). MASH2+AS15 was most effective in inhibiting distal colon microadenomas, with the mean number 3-fold lower than that of the PBS group (0.2 for MASH2+AS15, 0.4 for AS15, 0.6 for PBS, p&lt;0.001 for MASH2+AS15 vs PBS, p = 0.032 for MASH2+AS15 vs AS15). Similarly, in the therapeutic study, colon microadenomas were inhibited to the greatest extent after immunization with MASH2+AS15. In conclusion, MASH2+AS15 immunotherapy leads to partial protection of mice against MASH2-expressing transplantable tumors and strongly reduces the mean number of spontaneous colorectal adenomas in APC+/Min-FCCC mice, by inducing MASH2-specific CD4+ T cells and antibodies. These data are very promising and demonstrate the utility of MASH2 immunotherapy, with responses that may be further improved by combining with immunotherapies that induce antigen-specific CD8+ T cells or with immune checkpoint inhibitors.
Funding: GlaxoSmithKline Biologicals SA
Citation Format: Clément Rioux, Margie Clapper, Harry Cooper, Jean Michaud, Natalie St Amant, Hossein Koohsari, Laura Workman, Esther Kaunga, Anthony Pilorget, Catherine Gerard. Immunotherapy targeting MASH2 antigen protects mice against MASH2-expressing transplanted tumors and inhibits the development of colorectal adenomas in APC +/Min-FCCC mice. [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 2510. doi:10.1158/1538-7445.AM2015-2510