Abstract 3104: Inverse correlation of circulating CD8+ T cells with tumor burden from immune checkpoint treatment in humanized orthotopic model of renal cell carcinoma
Authors: Zhang Xin , Bhattarai Amita , Moret Ravan , Maresh Grace , Ray Alicia Nicole , Woods David , Graham Rachel , Latis Maria , Bardot Stephen , Li Li 
Published: June 2022

Background: Renal cell carcinoma (RCC) is a highly heterogeneous and metastatic disease with a widely varying prognosis. RCC is the first solid tumor treated with immune checkpoint blockade and approved by the FDA for showing improvement of clinical outcomes. Immune checkpoints physiologically regulate immune response via appropriate signals to T cells and maintain homeostasis, while pathologically they can be co-opted by cancer cells to evade the immune system. Here we developed a humanized (Hu)-mice model with adaptive transferred human immune cells to test the role of ICB [anti-PD-1/PD-L1, or anti-CTLA-4 antibody (Ab)] in an orthotopic human RCC tumor-bearing xenograft mouse model and analyzed the correlation of innate immune cells with tumor burden.

Methods: Luciferase-tagged RCC cell line 786-O were injected intra-kidney into immune-deficient Rag2 mice. After tumor formation, mice were humanized by intraperitoneal injection of donor PBMCs (20×106/per mouse). Treatment groups included control, anti-PD-1/PD-L1 Abs or anti-CTLA-4 Ab (all Abs 200 µg/mouse, iv) weekly for 4 weeks. Tumor growth was measured by weekly bioluminescent imaging (BLI) and tumor weight at necropsy. The presence of human immune cells and tumor infiltrating lymphocytes was confirmed by flow cytometry and immunohistochemistry staining. The significance of the differences between groups was determined by student t test. The Pearson correlation coefficient was obtained by analysis of correlation between different study parameters.

Results: BLI level showed a steady xenograft tumor progression for nine weeks. Anti-PD-1/PD-L1 Abs treatment trended toward reducing tumor BLI level while anti-CTLA-4 Ab significantly decreased tumor BLI level (p&lt;0.01). Furthermore, anti-PD-1/PD-L1 Abs reduced lung metastasis with a significant decrease of BLI level compared to control group (p&lt;0.05). Meanwhile, humanization was evidenced by robust, elevated levels of human CD45+ lymphocytes in the peripheral blood compared to non-reconstituted Rag2 mice. Infiltrated human CD3+CD8+ cells were found in mouse blood and spleen. Granzyme B+ cells, CD31+ cells, and pan-cytokeratin+ cells were found in tumors. Interestingly, we observed inverse correlation between circulating human CD8+ T cells and mouse RCC tumor burden.

Conclusion: We successfully generated a humanized RCC mouse model which allows the RCC xenograft to grow steadily within the human immune system reconstituted Rag2 mice. Circulating CD8+ T cells are inversely correlated to tumor growth in this model. The PD-1/PD-L1 or CTLA-4-targeted immunotherapies showed distinct therapeutic effects in our humanized orthotopic xenograft model, which may lead to personalized treatment targeting different immune checkpoints to reinvigorate anti-tumor responses in RCC patients.

Citation Format: Xin Zhang, Amita Bhattarai, Ravan Moret, Grace Maresh, Alicia Nicole Ray, David Woods, Rachel Graham, Maria Latis, Stephen Bardot, Li Li. Inverse correlation of circulating CD8+ T cells with tumor burden from immune checkpoint treatment in humanized orthotopic model of renal cell carcinoma [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 3104.