When infused in two different humanized mouse models, differently from reports with anti-CD19 CAR-Tconvs, Fox19CAR-Tregs did not cause B cell aplasia, Cytokine Release Syndrome (CRS) nor hemophagocytic lymphohystiocytosis (HLH), thus confirming the stability of their immunosuppressive phenotype53,54. The gene discussed is CD19; the disease is hemophagocytic syndrome.