Tumor-Infiltrating Lymphocytes Expressing the Tissue Resident Memory Marker CD103 Are Associated with Increased Survival in High-Grade Serous Ovarian Cancer

The presence of CD8(+) tumor-infiltrating lymphocytes (TIL) is associated with prolonged survival in high-grade serous ovarian cancer (HGSC) and other epithelial cancers. Survival is most strongly associated with intraepithelial versus intrastromal CD8(+) TILs; however, the mechanisms that promote the intraepithelial localization of TILs remain poorly understood. We hypothesized that intraepithelial CD8(+) TILs, like normal mucosal intraepithelial lymphocytes, might express CD103, a subunit of αE/β7 integrin, which binds E-cadherin on epithelial cells.A large collection of primary ovarian tumors (HGSC, endometrioid, mucinous, and clear cell) was analyzed by immunohistochemistry for the presence of TIL-expressing CD103. The activation and differentiation status of CD103(+) TILs were assessed by flow cytometry. The prognostic significance of TIL subsets was evaluated by Kaplan-Meier analysis.CD103(+) TILs were present in all major ovarian cancer subtypes and were most abundant in HGSC. CD103(+) TILs were preferentially localized to epithelial regions of tumors and were comprised predominantly of CD8(+) T cells expressing activation (HLA-DR, Ki-67, PD-1) and cytolytic (TIA-1) markers, as well as CD56(+) NK cells. Tumor infiltration by CD103(+) TILs was strongly associated with patient survival in HGSC. Tumors containing CD8(+) TILs that were CD103(-) showed poor prognosis equivalent to tumors lacking CD8(+) TILs altogether.CD103(+) TILs comprise intraepithelial, activated CD8(+) T cells, and NK cells and are strongly associated with patient survival in HGSC. CD103 may serve as a useful marker for enriching the most beneficial subsets of TILs for immunotherapy.