Background: Clinical significance of tumor-infiltrating lymphocytes (TILs) was demonstrated in many tumor types. In the clinical trials, immune checkpoint inhibitors showed significant clinical efficacy in some tumor types with high mutation burden such as melanoma, bladder cancer, and smoking-induced lung cancer, while there were little effects in cancers with lower mutation rates such as breast cancer. Recently, selection and adoptive transfer of autologous mutation specific TILs showed successful regression of metastatic cancer in an estrogen receptor-positive breast cancer patient. In this study, we analyzed in vitro reactivity of cultured TILs against autologous breast cancer cells.

Methods: We cultured TILs and cancer cells derived from 31 breast tumor tissues obtained from the surgery (13 of hormone receptor-positive, one of HER2-positive, and 17 of triple-negative breast cancer [TNBC]). Reactivity of TILs against cancer cells was determined by IFN-gamma ELISA analysis after co-culture of TILs and cancer cells for 24 hours. Epithelial cell markers (cytokeratin and EpCAM) for cancer cells and T cell markers [memory types (CD45RO, CCR7, and CD62L), T-cell activation and exhaustion markers (PD-1, 4-1BB, OX40, CD39, CD107a, TIM3, TIGIT, KLRG1, and LAG3), and regulatory T cells markers (CD25, CD127, and FOXP3)] for expanded TILs were analyzed by flow cytometry.

Results: Seven cases showed in vitro reactivity, which was defined by increased secretion (more than twice) of IFN-gamma from TILs upon cancer cell interaction. Interestingly, most of reactive TILs were from TNBC (6/7) and all of TNBCs showing in vitro reactivity were derived from resection specimens after neoadjuvant chemotherapy (NAC, 6/11). The remaining one case with in vitro reactivity was derived from HER2-positive breast cancer. TNBC cancer cells of cases with in vitro reactivity had more EpCAM-positive cells (p = 0.02) than those of nonreactive cases. Most T cells in TIL cultures showed effector memory phenotype (CD45RO+/CCR7-; CD4 T cells, median 97.4 % (73.7-99.9); CD8 T cells, median 98.8% (93.8-99.8)). TILs of TNBC cases with in vitro reactivity expressed higher levels of PD-1 (p value < 0.01) on CD4 T cells. PD-1 expression levels on CD8 T cells in reactive group tended to be higher than nonreactive group (p = 0.05). Expression of other markers was not different between reactive and nonreactive groups.

Conclusion: Among 17 TNBC cases, 35% showed in vitro TIL reactivity against autologous tumor cells. All reactive TNBCs were NAC-resistant tumors, which have high risk of tumor recurrence and high mortality rates. Adoptive TIL therapy might be a promising therapeutic modality for TNBC patients.

Citation Format: Heejae Lee, Young-Ae Kim, Hye Seon Park, Won Seon Bang, In Ah Park, Miseon Lee, Gyungyub Gong, Hee Jin Lee. Antitumor reactivity of human breast tumor-infiltrating lymphocytes (TILs) [abstract]. In: Proceedings of the AACR Special Conference on Tumor Immunology and Immunotherapy; 2018 Nov 27-30; Miami Beach, FL. Philadelphia (PA): AACR; Cancer Immunol Res 2020;8(4 Suppl):Abstract nr A41.