Manufacturing has been the key factor limiting rollout of vaccination during the COVID-19 pandemic, requiring rapid development and large-scale implementation of novel manufacturing technologies. ChAdOx1 nCoV-19 (AZD1222, Vaxzevria) is an efficacious vaccine against SARS-CoV-2, based upon an adenovirus vector. We describe the development of a process for the production of this vaccine and others based upon the same platform, including novel features to facilitate very large-scale production. We discuss the process economics and the "distributed manufacturing" approach we have taken to provide the vaccine at globally-relevant scale and with international security of supply. Together, these approaches have enabled the largest viral vector manufacturing campaign to date, providing a substantial proportion of global COVID-19 vaccine supply at low cost.

HEK293 cell lines are used for the production of recombinant proteins, virus-like particles and viral vectors. Recent work has generated molecular (systems level) characterisation of HEK293 variants that has enabled re-engineering of the cells towards enhanced use for manufacture-scale production of recombinant biopharmaceuticals (assessment of 'safe harbours' for gene insertion, engineering of new variants for stable, amplifiable expression). In parallel, there have been notable advances in the bioprocessing conditions (suspension adaptation, development of defined serum-free media) that offer the potential for large-scale manufacture, a feature especially important in the drive to produce viral vectors at large-scale and at commercially viable costs for gene therapy. The combination of cell-based and bioprocess-based modification of existing HEK293 cell processes, frequently informed by understandings transferred from developments with Chinese hamster ovary cell lines, seems destined to place the HEK293 cell systems firmly as a critical platform for production of future biologically based therapeutics.

Since the emergence of the biopharmaceutical industry in the 1980's, Escherichia coli, has played an important role in the industrial production of recombinant proteins and plasmid DNA for therapeutic use. Currently, advanced biopharmaceutical products, including rationally designed recombinant proteins and viral-vector gene therapies, offer unprecedented promise for the long-term management, and even cure of disease. As such, E. coli remains an important production host for the biopharmaceutical industry. This review provides insight into the industrially relevant strain engineering approaches used to enhance both the quantity and quality of these therapeutic products.

BACKGROUND:The secretion of recombinant disulfide-bond containing proteins into the periplasm of Gram-negative bacterial hosts, such as E. coli, has many advantages that can facilitate product isolation, quality and activity. However, the secretion machinery of E. coli has a limited capacity and can become overloaded, leading to cytoplasmic retention of product; which can negatively impact cell viability and biomass accumulation. Fine control over recombinant gene expression offers the potential to avoid this overload by matching expression levels to the host secretion capacity.RESULTS:Here we report the application of the RiboTite gene expression control system to achieve this by finely controlling cellular expression levels. The level of control afforded by this system allows cell viability to be maintained, permitting production of high-quality, active product with enhanced volumetric titres.CONCLUSIONS:The methods and systems reported expand the tools available for the production of disulfide-bond containing proteins, including antibody fragments, in bacterial hosts.

Targeting of recombinant proteins to the Escherichia coli periplasm is a desirable industrial processing tool to allow formation of disulphide bonds, aid folding and simplify recovery. Proteins are targeted across the inner membrane to the periplasm by an N-terminal signal peptide. The sequence of the signal peptide determines its functionality, but there is no method to predict signal peptide function for specific recombinant proteins, so multiple signal peptides must be screened for their ability to translocate each recombinant protein, limiting throughput. We present a screening system for optimising signal peptides for translocation of a single chain variable (scFv) antibody fragment employing TEM1 β-lactamase (Bla) as a C-terminal reporter of periplasmic localisation. The Pectobacterium carotovorum PelB signal peptide was selected as the starting point for a mutagenic screen. β-lactamase was fused to the C-terminal of scFv and β-lactamase activity was correlated against scFv translocation. Signal peptide libraries were generated and screened for β-lactamase activity, which correlated well to scFv::Bla production, although only some high activity clones had improved periplasmic translocation of scFv::Bla. Selected signal peptides were investigated in fed-batch fermentations for production and translocation of scFv::Bla and scFv without the Bla fusion. Improved signal peptides increased periplasmic scFv activity by ~40%.

Since the emergence of the biopharmaceutical industry in the 1980's, Escherichia coli, has played an important role in the industrial production of recombinant proteins and plasmid DNA for therapeutic use. Currently, advanced biopharmaceutical products, including rationally designed recombinant proteins and viral-vector gene therapies, offer unprecedented promise for the long-term management, and even cure of disease. As such, E. coli remains an important production host for the biopharmaceutical industry. This review provides insight into the industrially relevant strain engineering approaches used to enhance both the quantity and quality of these therapeutic products.

As high-level recombinant protein production (RPP) exerts a massive stress on the production host, an extensive literature on RPP optimization focuses on separating the growth phase from RPP production once sufficient biomass has been obtained. The aim of the current investigation was to optimize the benefits of the relatively neglected alternative strategy to achieve high-level RPP during growth by minimizing stress on the host. High yields of the biopharmaceutical recombinant human tumour necrosis factor alpha (rhTNFα) were obtained by fed-batch fermentation relevant to industrial production based upon parameters that most severely affected RPP in preliminary laboratory scale batch cultures. Decreasing the inducer concentration and growth temperature, but increasing the production period, were far more effective for increasing RPP yields than changing the growth phase at which production was induced. High yields of up to 5 g l-1 of rhTNFα were obtained with minimal plasmid loss, even in synthetic media that lack animal-derived components and are therefore fully compliant with regulatory requirements. Most of the product was soluble and biologically active. In summary, stress minimization was shown to be an effective way to optimize the production of rhTNFα. Data generated in shake-flask experiments allowed the design of intensified bioreactor cultures in which RPP and growth could be balanced, leading to higher yield of both rhTNFα and biomass than with previous fermentations. An additional benefit of this approach is avoidance of lysis during harvesting and downstream processing.

Recombinant adeno-associated virus (AAV) represents one of the most promising delivery vehicles for genetic medicines. However, the manufacture of plasmid DNA for the production of AAV presents a number of significant challenges, including scalability, fidelity, mis-incorporation of plasmid-derived DNA sequences, high costs and long lead times for GMP production. Touchlight has developed a novel, rapid, in vitro, enzymatic technology for multi-gram scale GMP manufacture of DNA that addresses all of the issues of DNA manufacture for AAV production. The process combines the use of two enzymes; Phi29 DNA polymerase and a protelomerase to generate covalently closed, linear DNA constructs known as doggyboneTM DNA or dbDNATM. The process is rapid, cost effective, of high fidelity and eliminates antibiotic resistance genes. Here we present a case study, with data generated by Cobra Biologics as part of an on-going Innovate UK-funded collaboration, demonstrating that AAV particles can be produced using dbDNATM with total and genomic titres equivalent to AAV particles made with plasmid DNA. In parallel experiments, with an academic collaborator, we have seen in vivo expression of reporter genes after administration of AAV vectors manufactured using dbDNATM (unpublished data). As such, we believe that dbDNATM has the potential to resolve a number of significant challenges in the production of AAV vectors at both clinical and commercial scale.