PRF1 and neoplasm: For example, in patients with solid tumors, Vδ1 T cells account for a large proportion of tumor-infiltrating γδ T cells; unlike Vδ1 T cells in adjacent non-tumor tissues, tumor-infiltrating γδ T cells do not express granzyme B, perforin, IFN-γ, FasL, TRAIL and NKR, but secrete IL-17 (149–154).