Substantial progress has been made in the treatment of precursor B-cell acute 
lymphoblastic leukemia (B-ALL), but recurrent disease remains a leading cause of 
death in children due to cancer and outcomes for adults with B-ALL remain poor. 
Recently, complete clinical responses have been observed in small numbers of 
patients with B-ALL treated with adoptive immunotherapy using T cells 
genetically engineered to express chimeric antigen receptors (CARs) targeting 
CD19, a cell surface molecule present in essentially all cases of B-ALL. 
Preclinical data suggest that CARs targeting CD22, another antigen present in 
the majority of B-ALL cases, are similarly potent. Several clinical studies 
already under way will soon more clearly define the rate of response to this 
novel therapy in B-ALL. Further work is needed to identify optimal platforms for 
CAR-based adoptive immunotherapy for leukemia, to establish guidelines for 
managing toxicity, and to determine whether the remissions induced by this 
approach can be rendered durable.