The findings of a single-arm cohort study involving 42 patients with refractory and/or relapsed B-cell lymphoblastic leukaemia (B-ALL) indicate that low-dose (1 × 105/kg) chimeric antigen receptor (CAR) T cells are safe and effective in this setting. 90% of patients entered complete remission, or complete remission with an incomplete count recovery, with only mild, or mild-to-moderate cytokine-release syndrome reported in most patients. These findings indicate a need for comparative studies designed to explore the efficacy of this approach.