Abstract A010: Development of OVA-expressing immunogenic syngeneic mouse tumor models: CT26-OVA and B16-OVA

Abstract

Abstract Background: Syngeneic homograft mouse tumor models have been the workhorse for investigating immuno-oncology (I/O) therapeutics. However, there are limited number of such models available, and among them, only a few respond to immune checkpoint inhibitors (ICI). One potential reason for the ICI-insensitivity may be their intrinsic low-/non-immunogenicity. Chicken ovalbumin (OVA) is a protein known to be highly immunogenic, and engineered syngeneic cell line expressing OVA could potentially render the cell more immunogenic, thus providing further tools for I/O research. To this end, we developed immunogenic variants of both colon cancer CT26.WT and melanoma B16-F10 syngeneic tumors by introducing the OVA transgene. Method: CT26.WT and B16-F10 cells were transduced by lentiviral vector (pLVX-EF1a-IRES-PURO) with a chicken ovalbumin coding cDNA and selected in culture in the presence of the antibiotic puromycin. OVA expression was confirmed by Western blotting analysis and the cells denoted as CT26-OVA and B16-OVA. The engineered cells were evaluated for tumorigenicity following subcutaneous (SC) implantation in immune competent mice and for in vivo/in vitro response to anti-PD-1 treatment. Mice bearing CT26-OVA and B16-OVA tumors were treated with anti-PD-1 antibodies (10mg/kg) or vehicle (intraperitoneally (IP) twice weekly for 3 weeks). Tumors were collected at termination and subjected to flow analysis for the frequency of total tumor-infiltrating CD8+T cells and H-2Kb-restricted OVA tetramer (SIINFEKL)-positive cells. Results: OVA-expressing models showed slower SC tumor growth compared to the parental lines, which was probably due to immune-mediated rejection. Both B16-OVA and CT26-OVA produced a higher sensitivity to anti-PD-1 treatment, superior to corresponding untransduced parental models. In addition, adoptive T cell transfer was conducted by isolating CD3+ T cells from the cured mice and subsequent inoculation into recipient mice in order to verify the presence of tumor-specific memory T cells. Conclusion: Our preliminary results indicate that CT26.WT and B16-F10 OVA-expressing engineered syngeneic models had a higher immunogenic profile, which resulted in enhanced response to ICI, thus providing additional models for I/O research. Citation Format: Ying Jin, Phillip Shuzong Wang, Zhongliang Li, Annie Xiaoyu An, Jiahua Zhou, Henry Qixiang Li, Davy Xuesong Ouyang. Development of OVA-expressing immunogenic syngeneic mouse tumor models: CT26-OVA and B16-OVA [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference on Molecular Targets and Cancer Therapeutics; 2019 Oct 26-30; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2019;18(12 Suppl):Abstract nr A010. doi:10.1158/1535-7163.TARG-19-A010