Abstract 4654: Differential immunomodulation following checkpoint blockade in the orthotopic ID8-luc ovarian model
Authors: Barnes Sheri , Zaitouna Anita , Kucharczyk Lauren , Wise Scott 
Published: June 2023

Abstract
Syngeneic tumor models for ovarian cancer are limited in preclinical research. One of these models, ID8-luc, is established intraperitoneally with disease progression resulting in the accumulation of ascites fluid. Treatment efficacy can be determined by non-invasive bioluminescence imaging (BLI), but solid ID8-luc tumors do not form in the peritoneal cavity, making assessment of immunomodulation challenging. To this end, we have developed the ID8-luc model as a tool to investigate immuno-modulatory drug candidates by utilizing tissues in the peritoneal cavity of diseased animals for ex vivo analyses. Specifically, flow cytometry of diseased ovaries was employed to examine the effects of checkpoint inhibition on T cell phenotypes and NK cell infiltration. To identify tumor deposits in organs from mice bearing ID8-luc disease for analysis tumor infiltrate, the model was established in untreated C57BL/6 albino mice, and ovaries, liver, peritoneal wall, pancreas, and spleen were evaluated pathologically. Progressive establishment of tumor deposits were seen in the ovaries, pancreas, and peritoneal wall of untreated mice, but not in naïve mice. Further, immune infiltration in ovaries were markedly higher compared to naïve mice. To assess immunomodulation, disease was established in a second cohort of mice, and mice were treated with anti-mPD-1, anti-mPD-L1, and anti-mCTLA-4. Disease progression was monitored by BLI, and following treatment, ovaries containing tumor deposits were collected and lymphoid infiltrate was analyzed by flow cytometry. Checkpoint blockade did not result in efficacy under the conditions tested. However, differences in T cell infiltration were notable with treatment of anti-PD-1 and anti-mPD-L1. Particularly, a marked increase of five to ten fold CD8+ and CD4+ T cells by absolute counts was seen with anti-mPD-1 and anti-mPD-L1 treatment compared to control. Further, the percentage of CD8+ T cells expressing the activation markers CD69 and ICOS as well as PD-1, TIM-3, and LAG-3 checkpoint proteins increased with anti-mPD-1 treatment. Less prominent yet similar trends in this biomarker expression were seen with anti-mPD-L1 treatment. NK and NKT infiltration also increased five to eight fold in ovaries following anti-mPD-1 treatment. Interestingly, anti-mCTLA-4 treatment did not result in any remarkable changes in infiltration or activation marker dynamics. Taken together, these findings are suggestive of a mounting immune response following PD-1 and PD-L1 blockade, but not CTLA-4 blockade, characterized by changes in the lymphocyte compartment in the ovaries. This response is seen in the absence of efficacy, suggesting the potential that this immunomodulation can be exploited in rational combination strategies with checkpoint blockade for immune-oncology drug candidates using the ID8-luc ovarian tumor model.
Citation Format: Sheri Barnes, Anita Zaitouna, Lauren Kucharczyk, Scott Wise. Differential immunomodulation following checkpoint blockade in the orthotopic ID8-luc ovarian model. [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 4654.