Endothelial intercellular cell adhesion molecule 1 contributes to cell aggregate formation in CHO cells cultured in serum‐free media

Expansion of Chinese hamster ovary cells via a loose cluster-assisted suspension culture using cell-sized gelatin microcarriers

Technologies for efficiently expanding Chinese hamster ovary (CHO) cells, the primary host cells for antibody production, are of growing industrial importance. Various processes for the use of microcarriers in CHO suspension cultures have been developed, but there have been very few studies on cell-adhesive microcarriers that are similar in size to cells. In this study, we proposed a new approach to suspension cultures of CHO cells using cell-sized condensed and crosslinked gelatin microparticles (GMPs) as carriers. Unlike commercially available carriers with sizes typically greater than 100 μm, each cell can adhere to the surface of multiple particles and form loose clusters with voids. We prepared GMPs of different average diameters (27 and 48 μm) and investigated their effects on cell adhesion and cluster formation. In particular, small GMPs promoted cell proliferation and increased IgG4 production by the antibody-producing CHO cell line. The data obtained in this study suggest that cell-sized particles, rather than larger ones, enhance cell proliferation and function, providing useful insights for improving suspension-culture-based cell expansion and cell-based biologics production for a wide range of applications.

Adaptation process of engineered cell line FCHO/IL-24 stably secreted rhIL-24 in serum-free suspension culture

Interleukin-24 (IL-24) displays tumor cell-specific proliferation inhibition in vitro and in vivo. Recombinant human IL-24 (rhIL-24) has significantly higher activity, yet significantly lower expression level in mammalian cells than in bacteria. To further realize therapeutic potential of IL-24, we enhanced rhIL-24 expression in mammalian cell systems by adapting engineered Flp-In^TMCHO/IL-24 (FCHO/IL-24) cells (adherent cultured in Ham's F12 medium with 10% serum) to serum-free suspension culture. First, MTT assay showed that among four different media (F12, DMEM/F12, 1640 and DMEM), DMEM/F12 medium was the most suitable media for lower-serum adherent culture. Then, cells were adherently cultured in DMEM/F12 with serum concentration reduced from 10% to 0.5% in a gradient manner. Compared to cells in 10% serum, cells in 0.5% serum displayed significantly lower relative cell viability by 40%, increased G0/G1 phase arrest (8.5 ± 2.4%, p < 0.05), decreased supernatant rhIL-24 concentration by 73%, and altered metabolite profiles, such as glucose, lactate and ammonia concentration. Next, the cells were directly adapted to 0.5% serum suspension culture in 125 mL shake flask at 119 rpm with the optimal cell seeding density of 5 × 10⁵ cells/mL (3.3 times higher than that of adherent culture), under which the concentration of rhIL-24 in culture medium was stable at 3.5 ng/mL. Finally, cells adapted to 0.5% serum proliferated better in serum-free medium Eden™-B300S with higher rhIL-24 expression level compared to CDM4CHO. The successful adaptation of engineered cells FCHO/IL-24 laid foundation for adapting cells from adherent culture to suspension serum-free culture to mass produce rhIL-24 protein for therapeutic purposes.

Unveiling the CHO surfaceome: Identification of cell surface proteins reveals cell aggregation-relevant mechanisms

Chinese hamster ovary (CHO) suspension cells are the main production hosts for biopharmaceuticals. For the improvement of production processes, it is essential to understand the interaction between CHO cells and their microenvironment. While the cellular membrane is the crucial surface barrier between the inner and outer cell compartments, the subgroup of cell surface proteins (surfaceome) is of particular interest due to its potential to react to external factors and initiate cell communication and interaction pathways. Therefore, the CHO surfaceome was explored for the first time by enriching exposed N-glycosylated membrane proteins before tandem mass spectrometry (MS/MS) analyses, identifying a total of 449 surface proteins, including 34 proteins specific for production cells. Functional annotation and classification located most proteins to the cell surface belonging mainly to the protein classes of receptors, enzymes, and transporters. In addition, adhesion molecules as cadherins, integrins, Ig superfamily and extracellular matrix (ECM) proteins as collagens, laminins, thrombospondin, fibronectin, and tenascin were significantly enriched, which are involved in mechanisms for the formation of cell junctions, cell-cell and cell-ECM adhesion as focal adhesions. As cell adhesion and aggregation counteracts scalable production of biopharmaceuticals, experimental validation confirmed differential expression of integrin β1 (ITGB1) and β3, CD44, laminin, and fibronectin on the surface of aggregation-prone CHO production cells. The subsequent modulation of the central interaction protein ITGB1 by small interfering RNA knockdown substantially counteracted cell aggregation pointing toward novel engineering routes for aggregation reduction in biopharmaceutical production cells and exemplifying the potential of the surfaceome for specified engineering strategies.