PRF1 and HIV-1 infection: In our recent study of activated CD4 and CD8 T cells responding to primary HIV-1 infection and vaccination with vaccinia virus, we confirmed that CD8 T cells express significantly higher levels of perforin and T cell intracellular antigen, TIA-1 [gene name nkg7, also known as granule membrane protein, GMP-17 (54)] compared to CD4 T cells (15).