While we hypothesized that addition of the JAK1/2 inhibitor ruxolitinib to TSLPRCART would have synergistic efficacy against CRLF2-R ALL, we instead observed that simultaneous co-administration of ruxolitinib blunted TSLPRCART cytokine production and expansion, leading to suboptimal leukemia clearance. The gene discussed is JAK1; the disease is acute lymphoblastic leukemia.