Perforin

Perforin is the pore-forming protein that cytotoxic lymphocytes secrete, together with granzyme proteases, into the immune synapse to elicit programmed cell death in a target cell. It is the effector of the predominant pathway for cellular cytotoxicity, used by both CD8+ cytotoxic T lymphocytes and natural killer cells.

Perforin-knockout (Prf1-/-) mice consequently lack that pathway and are widely used to ask which aspects of tumor progression are normally restrained by cytotoxic lymphocyte killing. The clinical success of immunotherapies that work by boosting cytotoxic lymphocyte activity underlines the importance of this pathway for antitumor immunity.