Natural killer cell therapy or NK therapy, involves using natural killer cells in the blood. They are derived from a human leukocyte antigen. It has recently been studied as a way to treat leukemia and other types of cancer.
One research study (1) looked at natural killer cell therapy and the treatment of leukemia. It noted that natural killer cell therapy alloreactivity comes from a mismatch between donor natural killer cells and recipient cells.
They found that transplanting natural killer cells from HLA-matched donors seemed to control the growth of acute myeloid leukemia relapses and improves the placement of the graft without resulting in graft versus host disease.
Source: 1.Ruggeri L, et al. Natural killer cell alloreactivity for leukemia therapy. J Immunother. 2005 May-Jun;28(3):175-82.