PRF1 and neoplasm: Furthermore, Vδ2Vγ9 T cells possess the characteristics of self-activation and release the Th1-type cytokine interferon gamma (IFN-γ) and other cytotoxic cytokines, such as tumor necrosis factor (TNF), perforin, and granzymes (granzyme A and B), to eliminate tumor cells (8, 13, 14).