Abstract 3266: Classical chemotherapy modulates cytokine secretion in the MSS CRC immune microenvironment and enhances T cell killing
Authors: Carlsen Lindsey , Huntington Kelsey E. , El-Deiry Wafik 
Published: June 2023

Metastatic colorectal cancer (mCRC) is the third deadliest cancer and has a five-year survival rate of 14%. Most patients receive chemotherapies 5-FU and folinic acid combined with oxaliplatin, irinotecan, or both. Immune checkpoint inhibitors (ICI) are effective for 3% of patients with microsatellite instable (MSI) tumors but 97% of patients have ICI-resistant microsatellite stable (MSS) tumors. Chemotherapy-mediated sensitization of MSS CRC to immune cell killing has been described in preclinical models and in the CheckMate 9X8 clinical trial. We hypothesize that chemotherapy modulates cytokine secretion within the MSS CRC tumor microenvironment and can enhance immune cell killing in certain contexts. SW480 and HT29 cells were pre-treated with chemotherapy (IC5072h, 24 hours), then co-cultured with TALL-104 cells -/+ pembrolizumab to measure immune cell-mediated killing. Using the Luminex 200 platform, the levels of 50+ cytokines were measured after chemotherapy treatment of SW480 and HT29 cells (IC5072h, 48 hours) and TALL-104 and NK-92 cells (1 µM or 10 µM, 36 hours). A humanized mouse model was established by injecting HCT 116 tumor-bearing nude mice with TALL-104 cells. Infiltration of injected TALL-104 cells was measured in mice that received either 5-FU + oxaliplatin or 5-FU + irinotecan. 5-FU + folinic acid + oxaliplatin -/+ pembrolizumab enhances TALL-104-mediated killing of SW480 and HT29 cells. In TALL-104 cells, soluble DcR3 increased significantly after low-dose 5-FU + oxaliplatin and the triple treatment but did not change with 5-FU + irinotecan. The triple treatment also slightly reduced GrB levels and MIF trended upward with all treatments. In NK-92 cells, B2M, CHI3L1, IL-10, IFN-γ, CCL3, CCL4, FasL, GrB, and IL-6 significantly decreased after all treatments and M-CSF increased with low-dose triple treatment. In SW480 cells, CHI3L1, IL-10, GrB, CCL2, and VEGF decreased after all treatments. GM-CSF increased only with 5-FU + oxaliplatin. In the humanized mouse model, there was a trend toward increased TALL-104 cell infiltration in chemotherapy pre-treated tumors. Chemotherapy tends to decrease cytokine secretion of TALL-104 and NK-92 cells. GM-CSF increases after 5-FU + oxaliplatin treatment in SW480 and HT29 cells, and pre-treatment with this regimen also enhances TALL-104-mediated killing of SW480 and HT29 cells -/+ ICI, pointing to 5-FU + oxaliplatin-induced GM-CSF as a mediator of chemotherapy-dependent enhancement of T cell killing. Chemotherapy pre-treatment may enhance TALL-104 cell infiltration in MSI tumors. Future directions include evaluation of concurrent vs. sequential chemotherapy + immunotherapy regimens using murine models of MSS colorectal cancer and isolation of circulating tumor cells from patients before and after chemotherapy treatment to measure effects on cytokine secretion and immune cell killing.

Citation Format: Lindsey Carlsen, Kelsey E. Huntington, Wafik El-Deiry. Classical chemotherapy modulates cytokine secretion in the MSS CRC immune microenvironment and enhances T cell killing [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 3266.