CRLF2 and leukemia: Since the initiation of our preclinical studies testing the hypothesis that JAKi and TSLPRCART co-therapy would have synergistic anti-leukemia activity against CRLF2-rearranged ALL [38, 39], a few case descriptions have also described successful use of ruxolitinib in patients with tocilizumab- and steroid-refractory CD19CART-induced CRS with decreases in detectable serum cytokine levels following administration of ruxolitinib and clinical resolution of hyperinflammatory signs and symptoms [50, 51].