Ruxolitinib, a JAK1/2 inhibitor approved for the treatment of myeloproliferative neoplasms (MPN) and steroid-refractory acute graft-versus-host disease (GVHD) [173, 174], showed feasibility in preventing severe CRS refractory to steroid therapy in four R/R B-ALL patients receiving CD19 or CD22 CAR T-cell therapy [175]. The gene discussed is JAK1; the disease is myeloproliferative neoplasm.