Insect cell entrapment, growth and recovering using a single-use fixed-bed bioreactor. Scaling up and recombinant protein production

Sf9 Cell Metabolism Throughout the Recombinant Baculovirus and Rabies Virus-Like Particles Production in Two Culture Systems

This work aimed to assess the Sf9 cell metabolism during growth, and infection steps with recombinant baculovirus bearing rabies virus proteins, to finally obtain rabies VLP in two culture systems: Schott flask (SF) and stirred tank reactor (STR). Eight assays were performed in SF and STR (four assays in each system) using serum-free SF900 III culture medium. Two non-infection growth kinetics assays and six recombinant baculovirus infection assays. The infection runs were carried out at 0.1 pfu/cell multiplicity of infection (MOI) for single baculovirus bearing rabies glycoprotein (BVG) and matrix protein (BVM) and a coinfection with both baculoviruses at MOI of 3 and 2 pfu/cell for BVG and BVM, respectively. The SF assays were done in triplicate. The glucose, glutamine, glutamate, lactate, and ammonium uptake or release specific rates were quantified over the exponential growth phase and infection stage. The highest uptake specific rate was observed for glucose (42.5 × 10-12 mmol cell/h) in SF and for glutamine (30.8 × 10-12 mmol/cell/h) in STR, in the exponential growth phases. A wave pattern was observed for assessed analytes throughout the infection phase and the glucose had the highest wave amplitude within the 10-10 mmol cell/h order. This alternative uptake and release behavior is in harmony with the lytic cycle of baculovirus in insect cells. The virus propagation and VLP generation were not limited by glucose, glutamine, and glutamate, neither by the toxicity of lactate nor ammonium under the conditions appraised in this work. The findings from this work can be useful to set baculovirus infection processes at high cell density to improve rabies VLP yield, purity, and productivity.

Targeting Prostate Cancer Using Bispecific T-Cell Engagers against Prostate-Specific Membrane Antigen

Prostate cancer (PCa) tops the list of cancer-related deaths in men worldwide. Prostate-specific membrane antigen (PSMA) is currently the most prominent PCa biomarker, as its expression levels are robustly enhanced in advanced stages of PCa. As such, PSMA targeting is highly efficient in PCa imaging as well as therapy. For the latter, PSMA-positive tumors can be targeted directly by using small molecules or macromolecules with cytotoxic payloads or indirectly by engaging the immune system of the host. Here we describe the engineering, expression, purification, and biological characterization of bispecific T-cell engagers (BiTEs) that enable targeting PSMA-positive tumor cells by host T lymphocytes. To this end, we designed the 5D3-αCD3 BiTE as a fusion of single-chain fragments of PSMA-specific 5D3 and anti-CD3 antibodies. Detailed characterization of BiTE was performed by a combination of size-exclusion chromatography, differential scanning fluorimetry, and flow cytometry. Expressed in insect cells, BiTE was purified in monodisperse form and retained thermal stability of both functional parts and nanomolar affinity to respective antigens. 5D3-αCD3's efficiency and specificity were further evaluated in vitro using PCa-derived cell lines together with peripheral blood mononuclear cells isolated from human blood. Our data revealed that T-cells engaged via 5D3-αCD3 can efficiently eliminate tumor cells already at an 8 pM BiTE concentration in a highly specific manner. Overall, the data presented here demonstrate that the 5D3-αCD3 BiTE is a candidate molecule of high potential for further development of immunotherapeutic modalities for PCa treatment.

Optimizing and developing a scalable, chemically defined, animal component-free lentiviral vector production process in a fixed-bed bioreactor

Lentiviral vectors (LVVs) play a critical role in gene delivery for ex vivo gene-modified cell therapies. However, the lack of scalable LVV production methods and the high cost associated with them may limit their use. In this work, we demonstrate the optimization and development of a scalable, chemically defined, animal component-free LVV production process using adherent human embryonic kidney 293T cells in a fixed-bed bioreactor. The initial studies focused on the optimization of the culture process in 2D static cultures. Process changes such as decreasing cell seeding density on day 0 from 2.5 × 10⁴ to 5 × 10³ cells/cm², delaying the transient transfection from 24 to 120 h post-seeding, reducing plasmid DNA to 167 ng/cm², and adding 5 mM sodium butyrate 6 h post-transfection improved functional LVV titers by 26.9-fold. The optimized animal component-free production process was then transferred to the iCELLis Nano bioreactor, a fixed-bed bioreactor, where titers of 1.2 × 10⁶ TU/cm² were achieved when it was operated in perfusion. In this work, comparable functional LVV titers were obtained with FreeStyle 293 Expression medium and the conventional Dulbecco's modified Eagle's medium supplemented with 10% fetal bovine serum both at small and large scale.

Performance Comparison of Recombinant Baculovirus and Rabies Virus-like Particles production Using Two Culture Platforms

This work aimed to assess, following upstream optimization in Schott flasks, the scalability from this culture platform to a stirred-tank bioreactor in order to yield rabies-recombinant baculovirus, bearing genes of G (BVG) and M (BVM) proteins, and to obtain rabies virus-like particles (VLP) from them, using Sf9 insect cells as a host. Equivalent assays in Schott flasks and a bioreactor were performed to compare both systems and a multivariate statistical approach was also carried out to maximize VLP production as a function of BVG and BVM's multiplicity of infection (MOI) and harvest time (HT). Viable cell density, cell viability, virus titer, BVG and BVM quantification by dot-blot, and BVG quantification by Enzyme-Linked Immunosorbent Assay (ELISA) were monitored throughout the assays. Furthermore, transmission electron microscopy was used to characterize rabies VLP. The optimal combination for maximum VLP expression was BVG and BVM MOI of 2.3 pfu/cell and 5.1 pfu/cell, respectively, and 108 h of harvest time. The current study confirmed that the utilization of Schott flasks and a benchtop bioreactor under the conditions applied herein are equivalent regarding the cell death kinetics corresponding to the recombinant baculovirus infection process in Sf9 cells. According to the results, the hydrodynamic and chemical differences in both systems seem to greatly affect the virus and VLP integrity after release.

Benchmarking of Scale-X Bioreactor System in Lentiviral and Adenoviral Vector Production

We have previously produced viral vectors (lentiviral vector, adenoviral vector, and adeno-associated viral vector) in small and in commercial scale in adherent cells using Pall fixed-bed iCELLis^® bioreactor. Recently, a company called Univercells has launched a new fixed-bed bioreactor with the same cell growth surface matrix material, but with different fixed-bed structure than is used in iCELLis bioreactor. We sought to compare the new scale-X™ hydro bioreactor (2.4 m²) and iCELLis Nano system (2.67 m²) to see if the difference has any effect on cell growth or lentiviral vector and adenoviral vector productivity. Runs were performed using parameters optimized for viral vector production in iCELLis Nano bioreactor. Cell growth was monitored by counting nuclei, as well as by following glucose consumption and lactate production. In both bioreactor systems, cells grew well, and the cell distribution was found quite homogeneous in scale-X bioreactor. Univercells scale-X bioreactor was proven to be at least equally efficient or even improved in both lentiviral vector and adenoviral vector production. Based on the results, the same protocol and parameters used in viral vector production in iCELLis bioreactor can also be successfully used for the production in scale-X bioreactor system.

Evaluation of the Single-Use Fixed-Bed Bioreactors in Scalable Virus Production

The accelerating development of gene therapy from research towards clinical trials and beyond has elevated the demand for practical viral vector-manufacturing solutions. The use of disposable upstream technology is gaining traction in clinical manufacturing. Packed-bed or fixed-bed reactors, where column is packed with immobilized biocatalyst particles providing surface to constrain the cells in a particular region of the reactor, have been widely used in bioprocessing applications since mid-1900s. However, the world's first single-use, fully integrated, high cell density, fixed-bed bioreactor was launched only approximately a decade ago. By now, several single-use, fixed-bed technology solutions have been developed in a small scale. Scaling-up the manufacturing can be challenging and for commercial-scale manufacturing, there is practically only one single-use, good manufacturing practice-compliant option available. This study reviews the latest, fully disposable, fixed-bed bioreactors; compares the virus production in the different systems; and discusses important manufacturing cost-related topics. It is predicted that single-use, fixed-bed bioreactors will receive even more attention in the field of viral vector manufacturing and commercialization, especially with the need for higher virus titers and virus yields.

Engineered Fragments of the PSMA-Specific 5D3 Antibody and Their Functional Characterization

Prostate-Specific Membrane Antigen (PSMA) is an established biomarker for the imaging and experimental therapy of prostate cancer (PCa), as it is strongly upregulated in high-grade primary, androgen-independent, and metastatic lesions. Here, we report on the development and functional characterization of recombinant single-chain Fv (scFv) and Fab fragments derived from the 5D3 PSMA-specific monoclonal antibody (mAb). These fragments were engineered, heterologously expressed in insect S2 cells, and purified to homogeneity with yields up to 20 mg/L. In vitro assays including ELISA, immunofluorescence and flow cytometry, revealed that the fragments retain the nanomolar affinity and single target specificity of the parent 5D3 antibody. Importantly, using a murine xenograft model of PCa, we verified the suitability of fluorescently labeled fragments for in vivo imaging of PSMA-positive tumors and compared their pharmacokinetics and tissue distribution to the parent mAb. Collectively, our data provide an experimental basis for the further development of 5D3 recombinant fragments for future clinical use.

Expression of hNeuritin protein in a baculovirus expression system and the analysis of its activity

Neuritin plays an important role in the development and regeneration of the nervous system, and shows good prospects in the treatment and protection of the nervous system. To characterize neuritin function, we constructed a baculovirus expression system of neuritin, and identified the biological activity of the neuritin protein. The results and showed that the expression product could promote the neurite growth of dorsal root ganglion in chicken embryos. The neuritin open reading frame was amplified and cloned into the plasmid pFastBac™HTA. The pFastBac™HTA-neuritin was confirmed to be correct by PCR and DNA sequencing, and then transformed into Escherichia coli DH10Bac. The high purity recombinant Bacmid-neuritin (shuttle vectors) was obtained from DH10Bac through screening and identification. Recombinant virus, including the neuritin gene (virus-neuritin), was produced by transfection of SF9 cells using the bacmid-neuritin, and then amplified repeatedly to express the neuritin fusion protein. Finally, we identified the fusion protein with SDS-PAGE and western blotting, and optimized the best expression time of the neuritin fusion protein. We also analyzed the activity of the expressed protein by dorsal root ganglion from chicken embryos.

Optimization of lentiviral vector production for scale-up in fixed-bed bioreactor

Lentiviral vectors (LVs) are promising tools for gene therapy. However, scaling up the production methods of LVs in order to produce high-quality vectors for clinical purposes has proven to be difficult. In this article, we present a scalable and efficient method to produce LVs with transient transfection of adherent 293T cells in a fixed-bed bioreactor. The disposable iCELLis bioreactors are scalable with a large three-dimensional (3D) growth area range between 0.53 and 500 m², an integrated perfusion system, and a controllable environment for production. In this study, iCELLis Nano (2.67–4 m²) was used for optimizing production parameters for scale-up. Transfections were first done using traditional calcium phosphate method, but in later runs polyethylenimine was found to be more reliable and easier to use. For scalable LV production, perfusion rate control by measuring cell metabolite concentrations in the bioreactor leads to higher productivity and reduced costs. Optimization of cell seeding density for targeted cell concentration during transfection, use of low compaction fixed-bed and lowering the culture pH have a positive effect on LV productivity. These results show for the first time that iCELLis bioreactor is scalable from bench level to clinical scale LV production.

Production of Recombinant Rabies Virus Glycoprotein by Insect Cells in a Single-Use Fixed-Bed Bioreactor

A single-use fixed-bed bioreactor (iCELLis nano) can be used for cultivating non adherent insect cells, which can be then recovered for scaling up or for harvesting a membrane-associated viral glycoprotein with high quality in terms of preserved protein structure and biological function. Here, we describe the procedures for establishing genetically modified Drosophila melanogaster Schneider 2 (S2) cell cultures in the iCELLis nano bioreactor and for quantifying by ELISA the recombinant rabies virus glycoprotein (rRVGP) synthesized. By using the described protocol of production, the following performance can be regularly achieved: 1.7 ± 0.6 × 1E10 total cells; 2.4 ± 0.8 × 1E7 cells/mL and 1.2 ± 0.9 μg of rRVGP/1E7 cells; 1.5 ± 0.8 mg of total rRVGP.