Myeloid cells in peripheral blood mononuclear cell concentrates inhibit the expansion of chimeric antigen receptor T cells

Background aims. Autologous chimeric antigen receptor (CAR) T-cell therapies have shown promising clinical outcomes, but T-cell yields have been variable. CD19- and GD2-CART-cell manufacturing records were reviewed to identify sources of variability. Methods. CD19-CAR T cells were used to treat 43 patients with acute lymphocytic leukemia or lymphoma and GD2-CAR T cells to treat eight patients with osteosarcoma and three with neuroblastoma. Both types of CART cells were manufactured using autologous peripheral blood mononuclear cells (PBMC) concentrates and anti-CD3/CD28 beads for T-cell enrichment and simulation. Results. A comparison of the first 6 GD2- and the first 22 CD19-CAR T-cell products manufactured revealed that GD2-CART-cell products contained fewer transduced cells than CD19-CART-cell products (147 +/- 102 x 10(6) vs 1502 +/- 1066 x 10(6); P = 0.0059), and their PBMC concentrates contained more monocytes (31.4 +/- 12.4% vs 18.5 +/- 13.7%; P = 0.019). Among the first 28 CD19-CART-cell products manufactured, four had poor expansion yielding less than 1 x 10(6) transduced T cells per kilogram. When PBMC concentrates from these four patients were compared with the 24 others, PBMC concentrates of poorly expanding products contained greater quantities of monocytes (39.8 +/- 12.9% vs. 15.3 +/- 10.8%, P = 0.0014). Among the patients whose CD19-CART cells expanded poorly, manufacturing for two patients was repeated using cryopreserved PBMC concentrates but incorporating a monocyte depleting plastic adherence step, and an adequate dose of CAR T cells was produced for both patients. Conclusions. Variability in CAR T-cell expansion is due, at least in part, to the contamination of the starting PBMC concentrates with monocytes.