PDCD1 and neoplasm: Besides PD-1, other inhibitory receptors such as TIGIT (T cell immunoreceptor with Ig and ITIM domains), LAG-3 (lymphocyte-activation gene 3), and TIM-3 (T-cell immunoglobulin and mucin domain 3) [150,151] are also potential targets for combination therapies aimed at enhancing NK cell-mediated tumour destruction.