Production, purification and immunogenicity of Gag virus-like particles carrying SARS-CoV-2 components.

The virus-like particle (VLP) platform is a robust inducer of humoral and cellular immune responses; hence, it has been used in vaccine development for several infectious diseases. In the current work, VLPs carrying SARS-CoV-2 Spike (S) protein (Wuhan strain) with an HIV-1 Gag core were produced using suspension HEK 293SF-3F6 cells by transient transfection. The Gag was fused with green fluorescent protein (GFP) for rapid quantification of the VLPs. Five different versions of Gag-Spike VLPs (Gag-S-VLPs) consisting of Gag-S alone or combined with other SARS-CoV-2 components, namely Gag-S-Nucleocapsid (N), Gag-S-Matrix (M), Gag-S-Envelope (E), Gag-S-MEN, along with Gag alone were produced and processed by clarification, nuclease treatment, concentration by tangential flow filtration (TFF) and diafiltration. A pilot mouse study was performed to evaluate the immunogenicity of the Gag-S-VLPs through the measurement of the humoral and/or cellular responses against all the mentioned SARS-CoV-2 components. Antibody response to Spike was observed in all variants. The highest number of Spike-specific IFN-γ + T cells was detected with Gag-S-VLPs. No induction of antigen-specific cellular responses to M, N or E proteins were detected with any of the Gag-S, M, E/or N VLPs tested. Therefore, the Gag-S-VLP, by reason of consistently eliciting strong antigen-specific cellular and antibody responses, was selected for further evaluation. The purification process was improved by replacing the conventional centrifugation by serial microfiltration in the clarification step, followed by Spike-affinity chromatography to get concentrated VLPs with higher purity. Three different doses of Gag-S-VLP in conjunction with two adjuvants (Quil-A or AddaVax) were used to assess the dose-dependent antigen-specific cellular and antibody responses in mice. The Gag-S-VLP adjuvanted with Quil-A resulted in a stronger Spike-specific cellular response compared to that adjuvanted with AddaVax. A strong spike neutralisation activity was observed for all doses, independent of the adjuvant combination.

Inducible HEK293 AAV packaging cell lines expressing Rep proteins.

Packaging or producer cell lines for scalable recombinant adeno-associated virus (rAAV) production have been notoriously difficult to create due in part to the cytostatic nature of the Rep proteins required for AAV production. The most difficult challenge being creating AAV packaging cell lines using HEK293 parental cells, currently the best mammalian platform for rAAV production due to the constitutive expression of E1A in HEK293 cells, a key REP transcription activator. Using suspension and serum-free media adapted HEK293SF carrying a gene expression regulation system induced by addition of cumate and coumermycin, we were able to create REP-expressing AAV packaging cells. This was achieved by carefully choosing two of the AAV Rep proteins (Rep 40 and 68), using two inducible promoters with different expression levels and integrating into the cells through lentiviral vector transduction. Three of our best clones produced rAAV titers comparable to titers obtained by standard triple plasmid transfection of their parental cells. These clones were stable for up to 7 weeks under continuous cultures condition. rAAV production from one clone was also validated at scale of 1 L in a wave bioreactor using serum-free suspension culture.

Virus-like particle and viral vector production using the baculovirus expression vector system/insect cell system: adeno-associated virus-based products.

The ability to make a large variety of virus-like particles (VLPs) has been successfully achieved in the baculovirus expression vector system (BEVS)/insect cell system. The production and scale-up of these particles, which are mostly sought as candidate vaccines, are currently being addressed. Furthermore, these VLPs are being investigated as delivery agents for use as therapeutics. Recently, adeno-associated viral (AAV) vectors, which can be potentially used for human gene therapy, have been produced in insect cells using three baculovirus vectors to supply the required genes. The use of host insect cells allows mass production of VLPs in a proven scaleable system. This chapter focuses on the methodology, based on the work done in our lab, for the production of AAV-like particles and vectors in a BEVS/insect cell system.

Validation of a high-performance liquid chromatographic assay for the quantification of Reovirus particles type 3.

An anion exchange high-performance liquid chromatography (HPLC) method for the quantification of human Reovirus type 3 particles was validated according to the performance criteria of precision, specificity, linearity of calibration and working range, limits of detection and quantification, accuracy and recovery. Samples taken at various stages of Reovirus purification were used for the validation of the method. The method was specific for Reovirus which eluted around 9.8min without interference from any other component in the sample. Reovirus can be detected between 0.32E+12 and 2.10E12VP/mL by the proposed method that has the correlation coefficient of linearity equal to 0.9974 and the slope of linearity equal to 5.74E-07 area units/(VPmL).

Production of adeno-associated virus (AAV) serotypes by transient transfection of HEK293 cell suspension cultures for gene delivery.

Adeno-associated virus (AAV) is being used successfully in gene therapy. Different serotypes of AAV target specific organs and tissues with high efficiency. There exists an increasing demand to manufacture various AAV serotypes in large quantities for pre-clinical and clinical trials. A generic and scalable method has been described in this study to efficiently produce AAV serotypes (AAV1-9) by transfection of a fully characterized cGMP HEK293SF cell line grown in suspension and serum-free medium. First, the production parameters were evaluated using AAV2 as a model serotype. Second, all nine AAV serotypes were produced successfully with yields of 10(13)Vg/L cell culture. Subsequently, AAV2 and AAV6 serotypes were produced in 3-L controlled bioreactors where productions yielded up to 10(13)Vg/L similar to the yields obtained in shake-flasks. For example, for AAV2 10(13)Vg/L cell culture (6.8×10(11)IVP/L) were measured between 48 and 64h post transfection (hpt). During this period, the average cell specific AAV2 yields of 6800Vg per cell and 460IVP per cell were obtained with a Vg to IVP ratio of less than 20. Successful operations in bioreactors demonstrated the potential for scale-up and industrialization of this generic process for manufacturing AAV serotypes efficiently.