Upstream bioprocessing for manufacturing viral vectors, part 2

In this blog post, we will continue to explore the different technologies used for viral vector manufacturing.

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Scale-up suspension cell for vector manufacturing

Investigators in the viral vector field are exploring use of suspension-adapted cell lines for transient transfection-based vector production. Adapting attachment-dependent cell lines to a suspension culture mode can extend the timeline for the development phase. However, once optimal cells are generated, the use of substrates for cell attachment and growth is no longer required.

Suspension cell cultures have a significant number of benefits over adherent cells. These include:

• Easy scale-up from laboratory scale shaker or spinner flask platforms to bioreactor scale, without cell attachment and detachment.

• The variety of HEK293 cell lines used for vector production are easy to adapt to suspension mode when cultured in chemically defined or serum-free medium.

• Animal component-free medium further adds benefits at manufacturing scale by reducing downstream purification steps, as well as lowering the regulatory risk associated with adventitious agents.

Stirred tank bioreactors have been used by the industry for commercial manufacturing of recombinant proteins and monoclonal antibodies for decades. These offer many advantages, including:

• Technology that has been adopted by the industry and optimized for production of biologics.

• Many drugs produced in this platform have been approved for use by global regulatory agencies.

• Proven ability to scale-up at large manufacturing volume.

This type of bioreactor platform can be used for both adherent cells by using microcarriers for attachment-dependent cells, and for suspension cells for large scale vector production.

Stable producer cell lines

Stable producer cell lines are genetically modified to express the helper genes via inducible promoters, packaging genes, and the gene of interest for viral vector production. Stable producer cell lines can simplify viral vector manufacturing steps by eliminating transfection steps with multiple plasmids, reducing cost by removing requirement of costly cGMP plasmid, and minimizing regulatory requirements by generating a cell line with clear history.

Currently approved or late clinical phase gene therapy therapeutics are mainly focused on treatment of rare genetic disorders, where targeted patient population numbers and viral particle requirements per dose are relatively small. However, commercialization of treatments for conditions such as Alzheimer’s, Parkinson’s, rheumatoid arthritis, and hemophilia poses a significant manufacturing challenge because the viral particle per dose can increase significantly (by logs) and the patient populations are much larger.

The development of stable cell lines is expected to significantly improve viral vector production at scales needed for these therapies with large therapeutic demand and higher viral vector titers.

Stable producer cell line development can involve lengthy development timelines, which will increase the time to market. However, once the producer cell line is engineered and cloned to produce higher cell density and viral vector titer, the process should be ultimately more productive as well as scalable.

Many companies are actively pursuing the development of engineered human cell lines that are adapted to grow in serum-free medium in suspension culture. It is hoped that the shift towards stable human producer cell lines will ease regulatory safety concerns and provide higher in vivo stability to viral vectors by providing human glycosylation patterns.

It is clear that the landscape for gene therapy is changing rapidly, and the advances in technology are poised to facilitate entry into this revolutionary field of medicine. Cytiva is dedicated to providing enabling technologies and fully integrated single-use platforms that will allow for production of high quality and affordable gene therapy products.

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