T cells that are genetically modified to express single-chain chimeric antigen receptors (CAR) have shown promise in early cancer immunotherapy clinical trials. Unfortunately, 2 recent deaths in cancer patients treated with CAR T cells have created some uncertainty on how to best mitigate patient risk, while continuing to advance this very promising therapeutic avenue. In order to address these concerns, the Recombinant DNA Advisory Committee (RAC) held a symposium, the objectives of which were to first review the reported treatment-associated toxicities and, second, to discuss methods for improving safety and efficacy. This report highlights the issues raised as part of this discussion, with a specific focus on protocols infusing CAR T cells. Because this was not a consensus conference, the opinions described should not be construed to represent those of any individual RAC member, the RAC as a body, conference participants, the National Institutes of Health, or the U.S. Food and Drug Administration.