Phenotypic Analysis of 26 Cultured TILs Derived From Japanese Melanoma Tissues

Purpose Tumor‐infiltrating lymphocyte (TIL) therapy has attracted increasing attention as a promising next‐generation cancer immunotherapy that may overcome some limitations of current immune checkpoint inhibitors. However, the phenotypic characteristics and tumor reactivity of TILs derived from Japanese melanoma tissues remain insufficiently investigated. This study aimed to evaluate the feasibility of expanding TILs from Japanese melanoma specimens and to characterize their phenotype and autologous tumor reactivity. Methods TILs were expanded from 26 Japanese melanoma specimens, including tumors derived from primary and mucosal lesions. The phenotypes of cultured TILs were assessed, and reactivity against autologous tumor cells was evaluated in 9 available TIL samples. Results TILs were successfully expanded from Japanese melanoma tissues, consistent with previous reports from the United States. The phenotypes of cultured TILs varied substantially among cases. Among the 9 TIL samples tested for reactivity against autologous tumor cells, MHC class I‐restricted specific reactivity was detected in 7 samples, including 1 sample derived from mucosal melanoma. No clear association was observed between autologous tumor reactivity and the proportion of CD3 + CD8 + T cells or the expression of specific markers on CD3 + CD8 + T cells. Conclusion This study is the first to characterize cultured TILs established from a series of Japanese melanoma patients. These findings suggest that the expansion of tumor‐reactive TILs from Japanese melanoma tissues is feasible and may provide a basis for the development of TIL therapy in Japan.