Heterogeneous conditions in dissolved oxygen affect N-glycosylation but not productivity of a monoclonal antibody in hybridoma cultures

It is known that heterogeneous conditions exist in large-scale animal cell cultures. However, little is known about how heterogeneities affect cells, productivities, and product quality. To study the effect of non-constant dissolved oxygen tension (DOT), hybridomas were subjected to sinusoidal DOT oscillations in a one-compartment scale-down simulator. Oscillations were forced by manipulating the inlet oxygen partial pressure through a feedback control algorithm in a 220-mL bioreactor maintained at a constant agitation. Such temporal DOT oscillations simulate spatial DOT gradients that can occur in large scales. Different oscillation periods, in the range of 800 to 12,800 s (axis of 7% (air saturation) and amplitude of 7%), were tested and compared to constant DOT (10%) control cultures. Oscillating DOT decreased maximum cell concentrations, cell growth rates, and viability indexes. Cultures at oscillating DOT had an increased glycolytic metabolism that was evidenced by a decrease in yield of cells on glucose and an increase in lactate yield. DOT gradients, even several orders of magnitude higher than those expected under practical large-scale conditions, did not significantly affect the maximum concentration of an IgG(1) monoclonal antibody (MAb). The glycosylation profile of the MAb produced at a constant DOT of 10% was similar to that reported in the literature. However, MAb produced under oscillating culture conditions had a higher amount of triantennary and sialylated glycans, which can interfere with effector functions of the antibody. It was shown that transient excursions of hybridomas to limiting DOT, as occurs in deficiently mixed large-scale bioreactors, is important to culture performance as the oscillation period, and thus the time cells spent at low DOT, affected cell growth, metabolism, and the glycosylation pattern of MAb. Such results underline the importance of monitoring protein characteristics for the development of large-scale processes.

Production of recombinant proteins: challenges and solutions

Efficient strategies for the production of recombinant proteins are gaining increasing importance, as more applications that require high amounts of high-quality proteins reach the market. Higher production efficiencies and, consequently, lower costs of the final product are needed for obtaining a commercially viable process. In this chapter, common problems in recombinant protein production are reviewed and strategies for their solution are discussed. Such strategies include molecular biology techniques, as well as manipulation of the culture environment. Finally, specific problems relevant to different hosts are discussed.

Novel insect cell line capable of complex N-glycosylation and sialylation of recombinant proteins

Paucimannose or oligomannose structures are usually attached to glycoproteins produced by insect cells, while mammalian glycoproteins usually have complex glycans. The lack of complex glycosylation has limited the use of the insect cell baculovirus expression vector system (BEVS), despite its high productivity and versatility. The availability of cell lines capable of complex glycosylation can overcome such a problem and potentially increase the utility of BEVS. In this work the capability of two novel cell lines, one from Pseudaletia unipuncta (A7S) and one from Danaus plexippus (DpN1), to produce and glycosylate a recombinant protein (secreted human placental alkaline phosphatase, SeAP) was assessed. SeAP produced by Tn5B1-4 cells at a low passage number (<200) was utilized for comparison. The optimal conditions for the production of SeAP by DpN1 cells were defined, and the glycosylation profiles of SeAP produced by the cell lines were quantitatively determined. Both the A7S and the DpN1 cells produced lower concentrations of SeAP than the Tn5B1-4 cells. Less than 5% of the glycans attached to SeAP produced by the Tn5B1-4 cells had complex forms. Glycans attached to SeAP from A7S cells contained 4% hybrid and 8% complex forms. Galactosylated biantennary structures were identified. Glycans attached to SeAP produced by the DpN1 cell line had 6% hybrid and 26% complex forms. Of the complex forms in SeAP from DpN1, 13% were identified as sialylated glycans. The galactosyltransferase activity of the three cell lines was measured and correlated to their ability to produce complex forms. Even though neither novel cell line produced as much recombinant protein as the Tn5B1-4 cells, the glycosylation of SeAP expressed by both cell lines was more complete. These novel cell lines represent interesting alternatives for the production of complex glycosylated proteins utilizing the BEVS.

Strategies for manipulating the relative concentration of recombinant rotavirus structural proteins during simultaneous production by insect cells

Adequate production strategies of virus-like particles are among the challenges that must be addressed before such complex multimeric structures find practical applications as vaccines. Attainment of the correct stoichiometric relation between proteins that constitute virus-like particles should result in an increased productivity by maximizing the concentration of assembled proteins and preventing the accumulation of waste monomers. In this work, strategies for manipulating the relative concentration between two of the structural proteins that constitute rotavirus-like particles (VP2 and VP6) were explored using the insect cell baculovirus expression vector system. It was shown that multiplicity of infection is a useful tool for manipulating protein production rates and maximum concentrations in cultures expressing one or two recombinant proteins. Thus, multiplicity of infection can be employed for improving production of rotavirus-like particles. VP2 and VP6 production rates obtained during individual infections remained unchanged when both were simultaneously produced, indicating that such rates can be utilized for estimating protein concentrations during coexpression. Manipulation of the time of infection between the two recombinant baculoviruses, proposed here for the first time, also proved to be effective for controlling the relative protein concentrations. The use of such sequential infections constituted an effective production alternative that does not require high amounts of virus stocks and is easy to implement. In addition to VP2 and VP6, kinetic parameters for the individual production of the other two proteins (VP4 and VP7) that constitute rotavirus-like particles were also obtained.

Comparison of growth and recombinant protein expression in two different insect cell lines in attached and suspension culture

Culture conditions required for obtaining maximum recombinant protein concentrations from two cell lines, Spodoptera frugiperda (IPLBeta-Sf21-AE) and Trichoplusia ni (Tn 5Beta-1-4), were determined in this work. Conditions studied include mode of culture (suspended vs attached), agitation rates, inoculum sizes, cell concentration at the time of infection, and various serum-free media (SFM). Results were compared with the performance of attached cultures in TnM-FH with 10% fetal bovine serum. Growth rates in the different culture media tested were similar, but the cell numbers achieved (i.e., yield) improved 2 to 2.7-fold in SFM over cultures in TnM-FH. Agitation rates of 150-160 rpm were necessary for maximum growth of suspended Tn 5Beta-1-4 cells compared to 125-150 rpm for Sf-21 cells. An inoculum size of 5 x 10(5) cells/mL gave good growth rates and optimum biomass yields for both cell lines. Cultures of both cell lines were infected with viruses encoding for beta-galactosidase or human secreted alkaline phosphatase (seAP). Protein expression in TnM-FH in attached culture showed that Tn 5Beta-1-4 cells are 2-4.5 times more productive on a per cell basis than Sf-21 cells grown under similar conditions. Production of beta-galactosidase in Sf-21 cells increased 50% in suspension cultures with SFM compared to attached cultures in TnM-FH, but seAP expression was essentially unchanged by culture techniques. The Tn 5Beta-1-4 cells produced 2.6-4.4 and 2.7-3 times more beta-galactosidase and seAP, respectively, in SFM in suspension compared to Sf-21 cells. EX-CELL 401 and Sf900-II were formulated as optimized SFM for Sf cell lines. However, in Sf-21 cultures EX-CELL 400 performed better than the other two media, as it increased the beta-galactosidase yield up to 25%. Surprisingly, EX-CELL 401 was the best medium for the production of beta-galactosidase by Tn 5Beta-1-4 cells, resulting in 25% and 69% higher volumetric and specific yields, respectively, compared to EX-CELL 405 which was formulated for this specific cell line. These results show that even when culture media are designed for maximal growth of a specific cell line, other media may provide the best conditions for protein production.

Evidence of Pluronic F-68 direct interaction with insect cells: impact on shear protection, recombinant protein, and baculovirus production*

Pluronic F-68 has been widely used to protect animal cells from hydrodynamic stress, but its mechanism of action is still debatable. Published evidence indicates that Pluronic F-68 interacts with cells, yet scarce information exists of its effect on recombinant protein and virus production by insect cells. In this work, the effect of Pluronic F-68 on production of recombinant baculovirus and rotavirus protein VP7 was determined. Evidence of Pluronic F-68 direct interaction with Sf-9 insect cells also was obtained. Maximum recombinant VP7 concentration and yield increased 10x, whereas virus production decreased by 20x, in spinner flask cultures with 0.05% (w/v) Pluronic F-68 compared to controls lacking the additive. No differences were observed in media rheology, nor kinetics of growth and infection (as inferred from cell size) between both cultures. Hence, Pluronic F-68 influenced cell physiology independently of its shear protective effect. Cells subjected to a laminar shear rate of 3000 s(-1) for 15 min, without gas/liquid interfaces, were protected by Pluronic F-68 even after its removal from culture medium. Furthermore, the protective action was immediate in vortexed cells. The results shown here indicate that Pluronic F-68 physically interacts with cells in a direct, strong, and stable mode, not only protecting them from hydrodynamic damage, but also modifying their capacity for recombinant protein and virus production.