PRF1 and neoplasm: NK cells are involved in innate immunity and exert powerful anti-tumor and anti-viral responses, by (i) the direct killing of tumor or infected cells through perforin and granzyme release, (ii) the stimulation of anti-tumor responses in other effector cells secreting pro-inflammatory cytokines such as IFN-γ, TNF-α, IL-6 and GM-CSF and (iii) recruiting DC and T lymphocytes through the production of chemo-attractant molecules (e.g., CCL5) [39,40].