Role of CAR-T cell therapy in B-cell acute lymphoblastic leukemia

Chimeric antigen receptor (CAR) T cells are genetically engineered cells containing fusion proteins combining an extracellular epitope-specific binding domain, a transmembrane and signaling domains of the T cell receptor. The CD19-CAR T cell product tisagenlecleucel has been approved by the US Food and Drug Administration and the European Medicines Agency for therapy of children and young adults under 25 years with relapsed/refractory B‑cell acute lymphoblastic leukemia (ALL) due to a high overall response rate of 81% at 3 months after therapy. The rates of event-free and overall survival were 50 and 76% at 12 months. Despite the high initial response rate with CD19-CAR‑T cells in B‑ALL, relapses occur in a significant fraction of patients. Current strategies to improve CAR‑T cell efficacy focus on improved persistence of CAR‑T cells in vivo, use of multispecific CARs to overcome immune escape and new CAR designs. The approved CAR‑T cell products are from autologous T cells generated on a custom-made basis with an inherent risk of production failure. For large scale clinical applications, universal CAR‑T cells serving as “off-the-shelf” agents would be of advantage. During recent years CAR‑T cells have been frequently used for bridging to allogeneic hematopoietic stem cell transplantation (HSCT) in patients with relapsed/refractory B‑ALL since we currently are not able to distinguish those CAR‑T cell induced CRs that will persist without further therapy from those that are likely to be short-lived. CAR‑T cells are clearly of benefit for treatment following relapse after allogeneic HSCT. Future improvements in CAR‑T cell constructs may allow longer term remissions without additional HSCT.