process has causal agent T cell cell killing leukocyte mediated cytotoxicity T cell mediated cytotoxicity Note that either or both mechanisms mentioned in the definition may be used in this process. Note that both granule release and the engagement of death receptors on target cells result in the induction of apoptosis in the target cell. Note that both CD4 and CD8 positive T cells can mediate apoptosis of target cells, independently of their definition as 'helper' T cells or not. T cell mediated immunity