IL6 and congenital rubella syndrome: The use of ibrutinib before leukapheresis has been linked to a higher incidence and greater severity of CRS in first series [18], but the concomitant administration of ibrutinib and CAR T cells appears to be associated with a lower incidence of ≥ grade 3 CRS [20, 21] and lower levels of pro-inflammatory cytokines (including IL-6, IL2Rα, and MCP-1, in particular) [20].