Manufacturing and validation of Good Manufacturing Practice-compliant regulatory dendritic cells for infusion into organ transplant recipients

Background aims: Regulatory (or "tolerogenic") dendritic cells (DCregs) are a highly promising, innovative cell therapy for the induction or restoration of antigen-specific tolerance in immune-mediated inflammatory disorders. These conditions include organ allograft rejection, graft-versus-host disease following bone marrow transplantation and various autoimmune disorders. DCregs generated for adoptive transfer have potential to reduce patients' dependence on non-specific immunosuppressive drugs that can induce serious side effects and enhance the risk of infection and certain types of cancer. Here, our aim was to provide a detailed account of our experience manufacturing and validating comparatively large numbers of Good Manufacturing Practice-grade DCregs for systemic (intravenous) infusion into 28 organ (liver) transplant recipients and to discuss factors that influence the satisfaction of release criteria and attainment of target cell numbers. Results: DCregs were generated in granulocyte-macrophage colony stimulating factor and interleukin (IL)-4 from elutriated monocyte fractions isolated from non-mobilized leukapheresis products of consenting healthy adult prospective liver transplant donors. Vitamin D3 was added on day 0 and 4 and IL-10 on day 4 during the 7-day culture period. Release and post-release criteria included cell viability, purity, phenotype, sterility and functional assessment. The overall conversion rate of monocytes to DCregs was 28 +/- 8.2%, with 94 +/- 5.1% product viability. The mean cell surface T-cell co-inhibitory to co-stimulatory molecule (programmed death ligand-1:CD86) mean fluorescence intensity ratio was 3.9 +/- 2.2, and the mean ratio of anti-inflammatory:pro-inflammatory cytokine product (IL-10:IL-12p70) secreted upon CD40 ligation was 60 +/- 63 (median = 40). The mean total number of DCregs generated from a single leukapheresis product (n = 25 donors) and from two leukapheresis products (n = 3 donors) was 489 +/- 223 x 106 (n = 28). The mean total number of DCregs infused was 5.9 +/- 2.8 x 106 per kg body weight. DCreg numbers within a target cell range of 2.5-10 x 106/kg were achieved for 25 of 27 (92.6%) of products generated. Conclusions: High-purity DCregs meeting a range of quality criteria were readily generated from circulating blood monocytes under Good Manufacturing Practice conditions to meet target cell numbers for infusion into prospective organ transplant recipients. (c) 2022 International Society for Cell & Gene Therapy. Published by Elsevier Inc. All rights reserved.