Efficient identification of mutated cancer antigens recognized by T cells associated with durable tumor regressions (TUM2P.878)

Cancer immunotherapy with adoptive transfer of tumor infiltrating lymphocytes (TILs) represents an effective treatment for patients with metastatic melanoma, with the objective regressions in up to 72% of patients in three sequential pilot clinical trials. However, the antigen targets recognized by effective TILs remain largely unclear. Melanoma patients 2359 and 2591 both experienced durable complete regressions of metastases ongoing beyond five years following adoptive TIL transfer. A novel approach was developed to identify mutated T-cell antigens by screening a tandem minigene library, which comprised non-synonymous mutation sequences identified by whole-exome sequencing of autologous tumors. The screening of tandem minigene libraries resulted in the identification of mutated kinesin family member 2C (KIF2C) antigen as a target of TIL 2359, and mutated DNA polymerase alpha subunit B (POLA2) antigen as a target of TIL 2591. Both KIF2C and POLA2 have been found to play important roles in cell proliferation. These findings suggest that the minigene screening approach may facilitate the antigen repertoire analysis of tumor reactive T cells, and lead to the development of novel adoptive cell therapies based on the in vitro stimulation of T cells that recognize candidate mutated antigens derived from genes essential for the carcinogenesis.