A scalable platform for human embryonic stem cell (hESC)-derived cardiomyocyte (CM) production can provide a readily available source of CMs for cell therapy, drug screening, and cardiotoxicity tests. We have designed and optimized a scalable platform using microcarrier cultures in serum-free media supplemented with SB203580 mitogen-activated protein kinase-inhibitor. Different microcarriers (DE-53, Cytodex-1 and 3, FACT, and TOSOH-10) were used to investigate the effects of type, size, shape, and microcarrier concentrations on the differentiation efficiency. hESCs propagated on TOSOH-10 (protamine derivatized 10-μm beads) at the concentration of 0.125 mg/mL produced 80% beating aggregates, threefold cell expansion, and 20% of CMs (determined by fluorescence-activated cell sorting for myosin heavy chain and α-actinin expression). The ratio of CM/hESC seeded in this system was 0.62 compared to 0.22 in the embryoid body control cultures. The platform robustness has been tested with HES-3 and H1 cell lines, and its scalability was demonstrated in suspended spinner cultures. However, spinner culture yields dropped to 0.33 CM/hESC probably due to shear stress causing some cell death. Cells dissociated from differentiated aggregates showed positive staining for cardio-specific markers such as α-actinin, myosin heavy and light chain, troponin I, desmin, and emilin-2. Finally, CM functionality was also shown by QT-prolongation (QTempo) assay with/without Astemizole. This study represents a new scalable bioprocessing system for CM production using reagents that can comply with Good Manufacturing Practice.

One of the most important limitations of mammalian cell-based processes is the secretion and accumulation of lactate as a by-product of their metabolism. Among the cell lines commonly used in industrial bioprocesses, HEK293 has been gaining importance over the last years. Up recently, HEK293 cells were known to consume lactate in late stages of cell culture usually when glucose and/or glutamine were depleted from media. Remarkably, in both scenarios, no significant cell growth was reported. However, we have observed a different metabolic behavior regarding lactate production and consumption in HEK293 cultures. HEK293 cells were able to co-metabolize glucose and lactate simultaneously, even in exponentially growing cell cultures. Our deep study of the effects of environmental conditions on lactate metabolism revealed that pH was the key to trigger the metabolic shift from lactate production to lactate and glucose concomitant consumption. Remarkably, this shift could be triggered at will when pH was set at 6.8. Even more interesting was the fact that lowering pH to 6.6 and supplementing media with exogenous lactate resulted in co-consumption of glucose and lactate from the beginning of cell culture, without affecting cell growth or protein productivity. On the contrary, cell growth was clearly hampered at this low pH if extracellular lactate was lacking. From our results, we hypothesize that HEK293 cells metabolize extracellular lactate as a strategy for pH detoxification, by means of co-transporting extracellular protons together with lactate into the cytosol. This novel hypothesis for unraveling lactate metabolism in HEK293 cells could open a door to re-direct genetic engineering strategies in order to obtain more efficient cell lines and also to further develop animal cell technology applications.

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The nature of enveloped virus-like particles (VLPs) has triggered high interest in their application to different research fields, including vaccine development. The baculovirus expression vector system (BEVS) has been used as an efficient platform for obtaining large amounts of these complex nanoparticles. To date, most of the studies dealing with VLP production by recombinant baculovirus infection utilize indirect detection or quantification techniques that hinder the appropriate characterization of the process and product. Here, we propose the application of cutting-edge quantification methodologies in combination with advanced statistical designs to exploit the full potential of the High Five/BEVS as a platform to produce HIV-1 Gag VLPs. The synergies between CCI, MOI, and TOH were studied using a response surface methodology approach on four different response functions: baculovirus infection, VLP production, VLP assembly, and VLP productivity. TOH and MOI proved to be the major influencing factors in contrast with previous reported data. Interestingly, a remarkable competition between Gag VLP production and non-assembled Gag was detected. Also, the use of nanoparticle tracking analysis and flow virometry revealed the existence of remarkable quantities of extracellular vesicles. The different responses of the study were combined to determine two global optimum conditions, one aiming to maximize the VLP titer (quantity) and the second aiming to find a compromise between VLP yield and the ratio of assembled VLPs (quality). This study provides a valuable approach to optimize VLP production and demonstrates that the High Five/BEVS can support mass production of Gag VLPs and potentially other complex nanoparticles.

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