RT Journal Article SR Electronic T1 Systematic analysis of CD39, CD103, CD137 and PD-1 as biomarkers for naturally occurring tumor antigen-specific TILs JF bioRxiv FD Cold Spring Harbor Laboratory SP 2021.03.29.437255 DO 10.1101/2021.03.29.437255 A1 Monika A. Eiva A1 Dalia K. Omran A1 Jessica Chacon A1 Daniel J. Powell, Jr. YR 2021 UL http://biorxiv.org/content/early/2021/03/29/2021.03.29.437255.abstract AB The detection of tumor-specific T cells in solid tumors is integral to the interrogation of endogenous antitumor responses and to the advancement of downstream therapeutic applications, such as checkpoint immunotherapy and adoptive cell transfer. A number of biomarkers are reported to identify endogenous tumor-specific tumor infiltrating lymphocytes (TILs), namely CD137, PD-1, CD103, and CD39, however a direct comparison of these molecules has yet to be performed. Here, we evaluate these biomarkers in primary human high-grade serous ovarian tumor samples using single-cell mass cytometry to characterize and compare their relative phenotypic profiles, as well as their response to autologous tumor cells ex vivo. CD137+, PD-1+, CD103+, and CD39+ TILs are all detectable in tumor samples with CD137+ TILs being the least abundant. PD-1+, CD103+, and CD39+ TILs all express a subset of CD137+ cells, while CD137+ TILs highly co-express the aforementioned markers. CD137+ TILs exhibit the highest expression of cytotoxic effector molecules, such as IFNγ and Granzyme B, compared to PD-1+, CD103+ or CD39+ TILs. Removal of CD137+ TILs from PD-1+, CD103+, or CD39+ TILs results in lower secretion of IFNγ in response to autologous tumor stimulation, while CD137+ TILs highly secrete IFNγ in an HLA-dependent manner. CD137+ TILs exhibited an exhausted phenotype with CD28 co-expression, suggestive of antigen recognition and receptiveness to reinvigoration via immune checkpoint blockade. Together, our findings demonstrate that the antitumor abilities of PD-1+, CD103+, and CD39+ TILs are mainly derived from a subset of TILs expressing CD137, implicating CD137 is a more selective biomarker for naturally occurring tumor-specific TILs.Competing Interest StatementDJP holds a patent on CD137 enrichment for efficient tumor infiltrating lymphocyte selection (U.S. Pat. No. 10,233,425) and receives fees for advisory services from InsTIL Bio on TIL therapy.(TILs)tumor-infiltrating lymphocytes(CI)confidence interval