Depletion of high-content CD14⁺ cells from apheresis products is critical for successful transduction and expansion of CAR T cells during large-scale cGMP manufacturing

With the US Food and Drug Administration (FDA) approval of four CD19- and one BCMA-targeted chimeric antigen receptor (CAR) therapy for B cell malignancies, CAR T cell therapy has finally reached the status of a medicinal product. The successful manufacturing of autologous CAR T cell products is a key requirement for this promising treatment modality. By analyzing the composition of 214 apheresis products from 210 subjects across eight disease indications, we found that high CD14⁺ cell content poses a challenge for manufacturing CAR T cells, especially in patients with non-Hodgkin's lymphoma and multiple myeloma caused by the non-specific phagocytosis of the magnetic beads used to activate CD3⁺ T cells. We demonstrated that monocyte depletion via rapid plastic surface adhesion significantly reduces the CD14⁺ monocyte content in the apheresis products and simultaneously boosts the CD3⁺ content. We established a 40% CD14⁺ threshold for the stratification of apheresis products across nine clinical trials and demonstrated the effectiveness of this procedure by comparing manufacturing runs in two phase 1 clinical trials. Our study suggests that CD14⁺ content should be monitored in apheresis products, and that the manufacturing of CAR T cells should incorporate a step that lessens the CD14⁺ cell content in apheresis products containing more than 40% to maximize the production success.