Immune profiling of tumor-infiltrating lymphocytes in patients with primary and metastatic soft tissue sarcomas 3352

Abstract Description Immune checkpoint inhibitors have limited activity in most bone and soft tissue sarcomas, which exhibit low neoantigen burden and macrophage predominance over tumor-infiltrating lymphocytes (TILs). In this work, we analyzed TILs and peripheral blood mononuclear cells (PBMCs) from sarcoma patients undergoing routine surgeries using multiplex flow cytometry. Phenotypes, memory/activation states, and expression of checkpoint proteins were compared between matched TILs and PBMCs using FlowJo and Graphpad Prism software with unpaired Mann-Whitney tests. Within 21 paired TIL:PBMC cultures, we found that TILs exhibited a higher CD8: CD4 ratio than PBMCs (median ratio TILs 1.05 [IQR 0.56-2.65] vs PBMCs 0.25 [IQR 0.14-0.43], (p = <0.0001). Within TILs, we detected a higher proportion of CD8+CD103+ CD39+ T cells compared to PBMCs (4.3% [IQR 1.6-10.5) vs 0.09% [IQR 0.02-0.16], p < 0.0001) which have been reported to be tumor-specific TILs with an exhausted tissue-resident memory phenotype. Most TILs were effector memory phenotype (median %CD8+EM+ 61.2 [IQR 41.5-70.6] and %CD4+EM+ 81.6 [IQR 62.8-89.1]). Most CD3- cells in both TILs and PBMCs were CD56+ NK cells. Finally, we found that expression of PD1 was higher in TILs vs. PBMCs (mean MFI 7057 ± SEM 831.8 vs. PBMCs 1924 ± SEM 150.4, p = <0.0001). No significant differences were observed in CTLA4, TIM3, or LAG-3 expression. Correlation of TIL phenotypes with clinical outcomes and response to treatment will be presented at the meeting. Funding Sources Sumra Chaudhry was supported by a Diversity in Cancer Research (DICR) Post Baccalaureate Grant DICR POST-BACC-23-1158368-01-DPBACC from the American Cancer Society Center for Diversity in Cancer Research Training with additional support from the University of Colorado Comprehensive Cancer Center (grant # P30CA046934). Topic Categories Tumor Immunology: Cellular Responses and Tumor Microevironment (TIME)