Indeed, a recent trial of CAR-NK cells targeting the CD19 antigen in patients with acute leukemias reported impressive anti-tumor responses with no observed graft-vs-host disease (GVHD) or cytokine release syndrome (CRS), toxicities typical of other CAR-expressing cytotoxic effectors such as T cells [1,2,3]. This evidence concerns the gene CD19 and graft versus host disease.