Of particular concern are CRS and neurotoxicity (CRES or ICANS).11, 29, 59 Both CRS and neurotoxicity are a consequence of cytokine production by activated CAR T cells, which in turn leads to activation of host myeloid cells to amplify cytokine production and enhance inflammation via IL‐1 and IL‐6.11, 29, 59. Here, IL6 is linked to congenital rubella syndrome.