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Keeping it simple: A higher-yielding process for manufacturing dendritic cells

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Science Translational Medicine  06 Nov 2019:
Vol. 11, Issue 517, eaaz9749
DOI: 10.1126/scitranslmed.aaz9749

Abstract

An optimized protocol using a hollow-fiber bioreactor produces a complete dose of dendritic cell–based immunotherapies in a single batch.

When he was quizzed about his views on optimization, Albert Einstein said, “Everything should be made as simple as possible, but not simpler.” Never has this principle been more relevant than in bioprocess engineering for the manufacture of personalized dendritic cell vaccines. Dendritic cells are a heterogeneous population of leukocytes that mediate immunity in our bodies. However, dendritic cell vaccines typically include a single subgroup of highly active cells that originate from monocytes. The manufacture of monocyte-derived dendritic cells (Mo-DCs) starts with the isolation of monocytes from patient-derived peripheral blood mononuclear cells using counterflow elutriation, followed by ex vivo differentiation of the monocytes through controlled supplementation of cytokines, such as granulocyte-macrophage colony–stimulating factor, interleukin-4, and other maturation factors. This process typically yields 1.6 × 109 monocytes from each patient, which are then diluted to 1 × 106 cells/mL in cell culture bags for differentiation to Mo-DCs.

Although Uslu et al. routinely used this protocol to manufacture Mo-DCs, they observed that the process is costly, time consuming, and inconsistent. Consequently, they investigated the use of the Quantum hollow-fiber bioreactor, a fully automated and U.S. Food and Drug Administration–approved product, for monocyte differentiation. The bioreactor has an annular design, and its two chambers are separated by a membrane that is impervious to cells, fully permeable to metabolites, and semipermeable to cytokines. The hollow fibers must normally be treated with fibronectin and later digested with trypsin to facilitate culturing and harvesting, respectively. Not only do these treatments add extra steps to the workflow, but they also reduce the production capacity of the bioreactor 10-fold. Uslu et al. addressed this problem by first replacing fibronectin with human serum albumin in the priming medium. Then, they optimized the concentrations of the maturation factors and the perfusion rates of the culturing medium in both chambers of the reactor and entirely eliminated the use of trypsin. The optimized protocol generated a homogeneous population of Mo-DCs with comparable stability, survival rates, morphology, and functional maturity to the established bag-based protocol. In fact, the two sets of Mo-DCs were indistinguishable in their ability to stimulate allogeneic T cell proliferation.

Saliently, even though the optimized protocol uses more expensive reagents for priming medium and higher concentrations of cytokines in the culturing medium, it is still cheaper and easier to execute and can process enough Mo-DCs for a single dose of the vaccine in one batch. However, the compatibility of the bioreactor product with downstream operations, such as antigen-loading, vaccine formulation, and storage, remains to be tested. Nevertheless, it is an important advance and lays a strong foundation for dendritic cell manufacturing.

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