Jordan Gauthier, MD, MSc, Fred Hutchinson Cancer Research Center, Seattle, WA, discusses the relationship between interleukin-15 (IL-15) serum concentrations, anti-tumor efficacy, and in vivo CAR T-cell kinetics in patients treated with anti-CD19 CAR T-cell therapies. IL-15 serum concentrations are associated with higher probabilities of response and higher CAR T-cell in vivo expansion and persistence. This interview took place during the Transplantation & Cellular Therapy (TCT) 2021 Meetings.