Sf9 insect cell growth and beta-galactosidase production in serum and serum-free media

Development of an animal-derived component-free medium for Spodoptera frugiperda (Sf9) cells using response surface methodology

OBJECTIVES

To develop an animal-derived component-free medium for Spodoptera frugiperda (Sf9) growth and green fluorescent protein (GFP) expression.

RESULTS

OSF9-ADCFM contained optimum concentrations of CDLC, YE and ST at 0.5% (v/v), 11.0 g/L, and 3.0 g/L, respectively. A mean viable cell concentration of 1.71 ± 0.14 × 10⁵ cells/mL was obtained from 5 passages (P1-P5). The use of both peptones after 10 kDa ultrafiltration had a significant effect on Sf9 cell growth. Grace's insect medium with 10% FBS gave higher un-infected cell number than SF-900II and OSF9-ADCFM for 4.29 and 5.38 times, respectively. The average cell number of un-infected cells and GFP-fluorescent cells of SF-900II were higher than OSF9-ADCFM 1.25 and 7 times, respectively.

CONCLUSION

In-house OSF9-ADCFM could support growth and GFP expression in Sf9 less than commercial SF-900II. However, it could lower the production cost at least 50% comparing to commercial SF-900II. The development of in- house OSF9-ADCFM would be continued to increase both cell numbers and protein expression in the next step.

Enhanced production of Chikungunya virus-like particles using a high-pH adapted spodoptera frugiperda insect cell line

Chikungunya virus-like particles (VLPs) have potential to be used as a prophylactic vaccine based on testing in multiple animal models and are currently being evaluated for human use in a Phase I clinical trial. The current method for producing these enveloped alphavirus VLPs by transient gene expression in mammalian cells presents challenges for scalable and robust industrial manufacturing, so the insect cell baculovirus expression vector system was evaluated as an alternative expression technology. Subsequent to recombinant baculovirus infection of Sf21 cells in standard culture media (pH 6.2–6.4), properly processed Chikungunya structural proteins were detected and assembled capsids were observed. However, an increase in culture pH to 6.6–6.8 was necessary to produce detectable concentrations of assembled VLPs. Since this elevated production pH exceeds the optimum for growth medium stability and Sf21 culture, medium modifications were made and a novel insect cell variant (SfBasic) was derived by exposure of Sf21 to elevated culture pH for a prolonged period of time. The high-pH adapted SfBasic insect cell line described herein is capable of maintaining normal cell growth into the typical mammalian cell culture pH range of 7.0–7.2 and produces 11-fold higher Chikungunya VLP yields relative to the parental Sf21 cell line. After scale-up into stirred tank bioreactors, SfBasic derived VLPs were chromatographically purified and shown to be similar in size and structure to a VLP standard derived from transient gene expression in HEK293 cells. Total serum anti-Chikungunya IgG and neutralizing titers from guinea pigs vaccinated with SfBasic derived VLPs or HEK293 derived VLPs were not significantly different with respect to production method, suggesting that this adapted insect cell line and production process could be useful for manufacturing Chikungunya VLPs for use as a vaccine. The adaptation of Sf21 to produce high levels of recombinant protein and VLPs in an elevated pH range may also have applications for other pH-sensitive protein or VLP targets.

Metalloproteinase activity is the sole factor responsible for the growth-promoting effect of conditioned medium in Trichoplusia ni insect cell cultures

Conditioned medium (CM) taken from a serum-free culture of Trichoplusia ni (BTI-Tn-5B1-4, High Five) cells on days 2 and 3, shortened the lagphase and increased the maximum cell density when added to T. ni cultures with low-inoculum cell density. Gel filtration fractions of CM, eluting at around 45kDa, stimulated cell proliferation even better than CM. A protein in the gel filtration fraction was identified by N-terminal amino acid sequencing as a proteinase, related to a snake venom metalloproteinase. Casein zymography showed, multiple metalloproteinase bands between 48 and 25kDa, as well as precursor forms above 48kDa. Metalloproteinase bands below the main band at 48kDa were autocatalytic degradation products. Metalloproteinase activity was the sole factor responsible for the growth stimulating effect of CM as shown by using the specific metalloproteinase inhibitor dl-thiorphan. Metalloproteinases have recently been shown to release growth factors from sequestering extracellular proteins. We propose that the metalloproteinase is involved in autocrine regulation of T. ni proliferation in serum-free media. In addition, a gel filtration fraction of CM, eluting at about 10kDa, inhibited cell growth. Apart from a lysozyme precursor protein and a cyclophilin-like protein, a kazal-type proteinase inhibitor could be identified in this fraction.

Growth of an ovarian cell line of Galleria mellonella and its response to immune-inducing factors

Antibacterial proteins are produced in the reproductive tracts of some insect species. The advent of a pupal ovarian cell line of the lepidopteran Galleria mellonella offered an opportunity for exploring the use of ovarian tissue culture to induce antimicrobial proteins in lieu of the larvae. The ovarian cell growth rates and cell yields were maximized by adjusting Grace's medium to pH 6.5, adding 15% (v/v) qualified heat-inactivated fetal calf serum, and lowering the sucrose concentration to 9.3 g/L. Five cell forms and biochemical profiles of the collective cell types were analyzed throughout the culture growth cycle. The final modified culture medium did not affect morphogenesis, whereas it increased the culture growth rate by 50% and the final cell yield threefold. The molting and immunoprotein-inducing hormone, 20-hydroxyecdysone, increased culture growth rate and altered the levels of cell types A and D. Neither 20-hydroxyecdysone nor the larval immunizing agents, apolipophorin-III or Bacillus subtilis, in combination or alone, induced antibacterial activity. The bacterium did induce immunity in both larval and adult stages.

The effect of dissolved oxygen (DO) concentration on the glycosylation of recombinant protein produced by the insect cell-baculovirus expression system

The effect of dissolved oxygen concentration on human secreted alkaline phosphatase (SEAP) glycosylation by the insect cell-baculovirus expression system was investigated in a well-controlled bioreactor. Oligomannose-type N-linked glycans (i.e., Man2 to Man6 and Man3F) were present in SEAP produced by Spodoptera frusiperda Sf-9 (Sf-9) and Trichoplusia ni BTI-Tn-5B1-4 (Tn-5B1-4) insect cell lines. The relative amounts of the most highly processed glycans (i.e., Man3F and Man2 in the SEAP from Sf-9 and Tn-5B1-4 cells, respectively) were significantly higher at 50% of air saturation than at either 10% or 190% of air saturation. That is, glycan processing was inhibited at both low and high dissolved oxygen concentrations.

Design of an efficient medium for insect cell growth and recombinant protein production

We report the development of a new serum-free medium based on the use of factorial experiments. At first, a variety of hydrolysates were screened using a fractional factorial approach with High-Five cells. From this experiment yeastolate ultrafiltrate was found to have, by far, the most important effect on cell growth. Furthermore, Primatone RL was found to remarkably prolong the stationary phase of Sf-9 and High-Five cell cultures. The optimal concentrations for yeastolate and Primatone were determined to be 0.6 and 0.5%, respectively, on the basis of a complete factorial experiment. This new medium, called YPR, supported good growth of both Sf-9 and High-Five cells in batch cultures, with maximal densities of 5.4 and 6.1 x 10(6) cells/ml, respectively. In addition, both cell lines achieved good growth in bioreactor batch culture and had a prolonged stationary phase of 3-4 d in YPR medium compared to Insect-XPRESS medium. The ability of the new medium to support recombinant protein expression was also tested by infecting Sf-9 or High-Five cells at high density (2 x 10(6) cells/ml) with a baculovirus expressing secreted placental alkaline phosphatase (SEAP). The maximum total SEAP concentration after 7 d was about 43 lU/ml (58 mg/L) and 28 lU/ml (39 mg/L) for High-Five and Sf-9 cells, respectively.