CD19 and neoplasm: Systematic studies examining the influence of scFv-based CAR (e.g., CD19 CAR) affinity on CAR T cell efficacy and toxicity will be necessary to further examine the hypothesis that T cells expressing traditional nanomolar affinity CARs are operating sub-optimally and may be more prone to exhaustion and excessive cytokine release, ultimately facilitating off-tumor toxicity or tumor relapse.