Naive T-cell Deficits at Diagnosis and after Chemotherapy Impair Cell Therapy Potential in Pediatric Cancers

Translational data on chimeric antigen receptor (CAR) T-cell trials indicate that the presence of naive T cells in the premanufacture product is important to clinical response and persistence. In anticipation of developing CAR trials for other tumors, we investigated the T-cell distribution from children with solid tumors and lymphomas at diagnosis and after every cycle of chemotherapy. We found that patients with T cells enriched for naive and stem central memory cells expanded well in vitro, but the majority of tumor types showed chemotherapy-related depletion of early lineage cells with a corresponding decline in successful ex vivo stimulation response. Unexpectedly, many pediatric patients with solid tumors had low numbers of naive T cells prior to any therapy. These data indicate the ex vivo manufacture of CART cells may need to be customized based on the nature of T cells available in each disease type. SIGNIFICANCE: Cumulative chemotherapy cycles deplete naive T cells in many pediatric cancer regimens, reducing expansion potential associated with successful adoptive cellular therapies. Naive T-cell deficits can be seen at diagnosis as well, implying immune deficits that exist prior to chemotherapy, which may also affect the development of immune-based therapies.