PRF1 and neoplasm: Subsequently, CTLs exert cytotoxic effects by releasing granzyme B and perforin or secreting cytokines (e.g., IFN) and FASL-FAS, ultimately resulting in the death of tumor cells.22, 23, 24 CD4+ cells can differentiate into diverse T helper (Th) cell subsets, including Th1, Th2, and Th17 cells.25