Background: 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 α_E/β₇ integrin, which binds E-cadherin on epithelial cells.

Methods: 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.

Results: 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.

Conclusions: 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. Clin Cancer Res; 20(2); 434–44. ©2013 AACR.