Generation of NK cells from donor PBMCs is the safest and most favorable option as they carry various NK cell activating markers such as CD16, NKG2D, NKp44, and NKp46 which strongly recognize and kill non-self or tumor cells; however, the percentage of NK cells in peripheral blood is too low, and expansion of NK cells derived from PBMCs is costly and time-consuming (189–191). Here, KLRK1 is linked to neoplasm.