Chimeric antigen receptor-engineered T cells in CLL: the next chapter unfolds

The long-standing promise for the application of engineered T lymphocytes to target and eradicate malignancy has begun to be realized recently, with remarkable clinical success reported by a number of groups using Chimeric Antigen Receptor –engineered T cells to target CD19-positive hematologic malignancies. In the September 2 issue of Science Translational Medicine, Porter et al. present the clinical data and correlative analyses for 14 CLL patients treated at the University of Pennsylvania under the pilot clinical trial recently completed at that institution. The initial reports from this trial, published in 2011 documented robust clinical activity in a small cohort of treated patients accompanied by logarithmic expansion, contraction, and long-term functional persistence of engineered T cells, along with cytokine release syndrome as a side-effect of the treatment. In this latest report, updated data are presented from the initial cohort of patients, as well as clinical and correlative data from the remainder of the treated cohort. The robust clinical activity observed in the initial cohort continued to be observed in a subset of the subsequently-treated patients, with molecular remissions documented in that subset; however, in the expanded cohort a subset of partial and non-responding patients was also identified. Collectively, the results from this exciting trial provide evidence to suggest that cellular immunotherapy using engineered T cells is a viable option for treating CLL, reveal a likely requirement for robust in-vivo activation and persistence of engineered cells to effect complete responses, and also highlight the need for a more complete mechanistic understanding of the immune- and tumor- specific processes that define and dictate the success of this powerful treatment modality.