PRF1 and neoplasm: The expansion of Vγ9Vδ2 T-lymphocytes is of paramount importance in tumor killing: although Vγ9Vδ2 T-cells are only 5% of circulating T-lymphocytes, they can recognize tumor antigens, kill tumor cells through perforin-granzyme B, Fas/FasL and TRAIL pathways [69], and activate CD8+T-cytotoxic cells and NK cells [70], amplifying the tumor immuno-killing.