In combination with CAR T cell therapy, we observed improved immune infiltration and tumour control in vitro, in xenografts, and in a humanized NOG (HuNOG) model reconstituted with human CD34+ haematopoietic stem cells, where CXCL10 knock-in increased intratumoural leukocyte and CAR T cell infiltration and prolonged tumour control within a reconstituted human immune microenvironment, supporting this synergistic paradigm. The gene discussed is CXCL10; the disease is neoplasm.