Treatment of Patients with T Cells Expressing a Fully-Human Anti-BCMA CAR with a Heavy-Chain AntigenRecognition Domain Caused High Rates of Sustained Complete Responses and Relatively Mild Toxicity

Multiple myeloma (MM) is a malignancy of plasma cells that is nearly always incurable. T cells expressing chimeric antigen receptors (CAR) that target B-cell maturation antigen (BCMA) can recognize and eliminate MM. The murine or other non-human sequences in the single-chain variable fragments (scFv) of many anti-BCMA CARs can elicit recipient immune responses against CAR T cells. We constructed a CAR incorporating an anti-BCMA fully-human heavy-chain variable domain designated FHVH33. FHVH33 lacks the light chain, the artificial linker sequence, and the 2 linker-associated junctions of a scFv, so FHVH33 is smaller than a scFv and is likely to be less immunogenic. The FHVH33-containing CAR utilized in this clinical trial also incorporated a CD8a hinge and transmembrane domain, a 4-1BB domain, and a CD3z domain. The CAR was designated FHVH33-CD8BBZ and was encoded by a gamma-retroviral vector. T cells expressing FHVH33-CD8BBZ were designated FHVH33-T. The FHVH33-T production process was initiated with unsorted peripheral blood mononuclear cells and took 7 days. The treatment protocol was 300 mg/m 2 of cyclophosphamide and 30 mg/m 2 of fludarabine on days -5 to -3 followed by infusion of FHVH33-T on day 0.