CD4 and congenital rubella syndrome: It has been reported that non-cytolytic, human CD19 CAR CD4+ Treg compared to human CD19 CAR CD8+ T-cells maintain weights and clinical scores in models of GVHD with no measurable increase in IL-6 production, one of the CRS hallmarks, suggesting CAR Treg may have a lower risk for CRS (233); whether cytolytic CAR19 Treg also prevent CRS will need to be investigated.