Abstract 4221: Characterization of OVA-expressing immunogenic syngeneic tumor models for immune checkpoint inhibitor evaluation
Authors: Nie Chenpan , Zhang Yi , Zheng Jia , An Annie X. , Zhou Jun , Li Henry Q.X. , Wang Jingjing 
Published: June 2022

Abstract
BACKGROUND: Syngeneic mouse tumor models are widely used as preclinical models for immuno-oncology (I/O) research. However, their response to immune checkpoint inhibitors (ICIs) in vivo is limited, despite the increase in tumor infiltrating lymphocytes (TILs), which is potentially due to low intrinsic immunogenicity. Expression of chicken ovalbumin (OVA) engineered into syngeneic tumors has previously been shown to render the cells more immunogenic and increases the response to ICIs such as anti-PD-1. In this study we investigated the potential to increase the response to ICIs through OVA expression and characterized the model for TILs and T cell-mediated immunity compared with parent cell line.
METHODS: A series of murine cells were transduced by lentiviral vector (pLVX-EF1a_IRES-PURO) with a chicken OVA coding cDNA. OVA expression was confirmed by western blot following single clone selection under puromycin. MC38-OVA, B16-F10-OVA, CT26.WT-OVA and EMT6-OVA cells were subcutaneously inoculated into immunocompetent C57BL/6 or BALB/c mice to evaluate the tumorigenicity and their in vivo response to anti-PD-1(10mg/kg, IP) treatment. In the study, blood, spleen and tumors were collected at termination for FACS analysis of the immune cell populations and the OVA-specific T cells. The effects of CD4+ and CD8+ T lymphocyte depletion was investigated using anti-CD4 and anti-CD8 antibodies in the PD-1 cured EMT6-OVA mice. Adoptive cell transfer (ACT) was evaluated by re-challenge studies in both OVA expressing and WT tumor-bearing mice with isolated T cells derived from OVA untreated mice, anti-PD-1 cured mice or OT-I mice.
RESULTS: Anti-PD-1 treatment resulted in complete regression in most mice bearing CT26.WT-OVA, MC38-OVA and EMT6-OVA, whereas an improvement in the response was shown in B16-F10-OVA in vivo. T cell and NK cells expansion was observed after anti-PD-1 treatment in peripheral blood with increased T cells, Treg cells and NK cells in both tumor-draining lymph nodes and spleen. In the re-challenge study anti-PD-1 cured mice generated robust tumor specific memory T cell, which successfully inhibited OVA expressing tumor growth following ACT. CD3+ T cells from EMT6-OVA-bearing mice showed anti-tumor immunity in vivo. CD4 and CD8 depletion studies provided further insight into the T cell role in PD-1 treatment.
CONCLUSIONS: The panel of OVA expressing murine cell lines displayed increased T cell-mediated immunity and enhanced anti-PD-1 responses compared to WT models for different cancer indications in vivo, providing novel immunogenic syngeneic models for preclinical immunotherapy evaluation.
Citation Format: Chenpan Nie, Yi Zhang, Jia Zheng, Annie X. An, Jun Zhou, Henry Q.X. Li, Jingjing Wang. Characterization of OVA-expressing immunogenic syngeneic tumor models for immune checkpoint inhibitor evaluation [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 4221.