Qian Liu is a Senior Group Leader at OXGENE™ (Oxford, UK) and Corinne Branciaroli is Group Leader of the Viral Cell Line Development team at OXGENE. Qian joined OXGENE in 2017 following a PhD and two postdocs focused on regenerative medicine. When Qian first joined OXGENE, she worked on the development of lentiviral packaging and site-specific integration cell lines but she now manages all of OXGENE’s commercial cell line development and viral vector production projects.
Corinne brought a wealth of laboratory experience gained in both commercial and academic laboratories to OXGENE, where she started as a molecular biologist in 2017 and then worked on the development of stable cell lines. She’s been leading OXGENE’s Viral Cell Line Development team since 2019, focusing on the development of stable lentiviral packaging and producer cell lines.
In this interview, Qian and Corinne explore how the needs of cell therapy manufacturers have changed over the last few years with regards to the use of lentiviral vectors. They also discuss the challenges involved in the transfer of genetic information during cell therapy development, the main benefits of packaging and producer cell lines, and what should be considered when choosing a cell line and supplier.
This interview is part of the RegMedNet In Focus on packaging and producer cell lines. Discover expert opinion and top tips for developing lentiviral packaging and producer cell lines in the feature now.
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How have the needs of cell therapy manufacturers changed over recent years with regards to the use of lentiviral vectors?
Back in the 60s, scientists showed that immune cells could kill cancer cells in mice. This was the start of a burgeoning interest in cancer immunotherapy. In the 80s, the first cancer infiltrating lymphocytes were taken from patients, expanded in the lab and reinjected into the patient. In the 90s, an immunologist made the first attempt to engineer T cells using retroviruses to carry new genes into these cells that would ramp up their ability to fight cancer. Together with the discovery of embryonic stem cells in the 80s and more recently of induced pluripotent stem cells in the mid-2000s, these early studies set the scene for cell therapies to be investigated far more widely in recent years. In fact, according to the Alliance of Regenerative Medicine (WA, USA), there were 471 cell-based immune-oncology trials and 204 other cell therapy clinical trials underway worldwide at the end of the first half of 2020.
Much of the early work on engineering viral vectors to carry new genetic information into cells was done in retroviruses. These were attractive candidates for cell therapies because by integrating into the genome, they offered the potential for long-term management of – or even a cure for – genetic diseases. However, in recent years, the related lentiviral vectors have become the more common vector of choice for cell therapies, thanks to their additional advantages of low immunogenicity and the ability to transduce non-dividing cells. The majority of lentiviral vector development over the last few years has been concerned with increasing the safety of these vector types, with subsequent generations of plasmids engineered to further reduce the risk of recombination events occurring that may lead to the accidental generation of any wild-type virus.
In many ways, the needs of cell therapy manufacturers haven’t necessarily changed significantly in recent years – the concerns around patient safety, scaling up manufacture, maintaining quality processes and pricing and reimbursement remain the same, but the expansion of the field has just made these issues more acute. The number of cell therapies being developed for systemic diseases with larger patient populations has certainly led to a more urgent demand for scalable technologies, with the right level of compliance and documentation to smooth the path to regulatory approval.
What are the current challenges in the transfer of genetic information during cell therapy development?
Transfer of genetic information during cell therapy nowadays relies primarily on lentiviral vectors, and the main challenge around this now is how to manufacture a sufficient quantity of these vectors in a cost-effective way, so that these really very promising therapies can become more accessible and affordable. In terms of the manufacturing challenge, there’s an additional need to improve standardization during production and quality control processes to ensure the quality and safety of the therapeutic products. More specific regulatory guidance and support would be helpful in defining these standard procedures.
What are the main benefits of packaging and producer cell lines?
Packaging and producer cell lines have within their genome all the genetic elements needed to encode the viral vector. In the case of producer cell lines, their genome also contains the gene of interest. As well as being easily scalable – all you need to do to produce more viral vector is to grow more cells – it also reduces the number of GMP plasmids required for cell therapy manufacture, reducing both the cost of goods and process complexity required to produce large quantities of viral vectors. Finally, another key benefit is that using packaging or producer cell lines eliminates the batch-to-batch variation that inevitably occurs when relying on transient plasmid transfection to create new batches of viral vectors. This improved process robustness is an important consideration for regulatory approval.
What applications would someone use a packaging cell line for, and when would a producer line be more appropriate?
Packaging cell lines are a cost-effective solution for preclinical or early-stage cell and gene therapy companies looking for a single flexible platform from which to test multiple transgenes, or variants of a transgene. For example, companies engaged in developing T-cell-based cancer immunotherapies could use the same packaging cell line and transfect in different lentiviral vector plasmids to target multiple cancer types. This may also be of interest to companies developing ex vivo cell therapies for immune reprogramming, where it might be valuable to test multiple antigen/cytokine combinations from the same packaging system to determine the best combination for optimal immune cell stimulation.
Producer cell lines on the other hand are the ideal solution for companies ready to take a lead candidate through to large-scale manufacture for clinical trials or commercial production.
There are several stable lentiviral cell lines on the market. What should you consider when choosing a cell line and supplier?
Good question. Obviously manufacturers will want to consider the cell line’s performance and what characteristics will best suit their purposes – for example, whether it would be preferable to use a cell line that might grow fast but produce slightly lower titers, versus one that grows slower but produces a higher lentiviral yield.
Second, regulatory approval is always going to be at the front of a manufacturer’s mind, so making sure that whoever you work with for your packaging and producer cell lines can provide a full documentation pack, detailing cell line provenance as well as all steps of the process is really important.
Finally, and probably equally importantly, it can be really beneficial to choose to work with a supplier who will work in partnership with you. Especially in the early stages of transitioning from a transient to stable production process there are a lot of variables and a few unknowns to take into consideration. It can be helpful to work with a partner who will support you through this, offer ongoing technical advice and discussion, support you through process development and optimization, and finally who can help facilitate technology transfer and onboarding in your manufacturing facility of choice. Close communication between the solutions provider and cell therapy developer is so important to the success of projects like this, so it’s important to choose a partner who recognizes and emphasizes this.
How can OXGENE’s process development service help improve titer after final packaging and producer cell line selection? How much of an improvement might there be?
OXGENE’s process development team is made up of experts in upstream process development, downstream process development and analytics. They played a hugely important part in developing our new lentiviral packaging and producer cell lines. For example, once our cell line development team select the top performing packaging and producer clonal cell lines, the upstream process development experts will design experiments using a design-of-experiments approach to test all the factors that could impact lentiviral production (e.g., cell seeding density, media composition, induction timing and dose, feeding regime and – for packaging cell lines – transfection conditions). They’ll screen all these different conditions on various platforms including shake flasks, deep-well plates and AMBR15 system, in multiple rounds.
Once they’ve identified the best conditions, they will verify and optimize these further in scaled-up productions in stirred tank bioreactor systems (1–10L). This type of process optimization makes an enormous difference in improving production yields for packaging and producer cell lines, while optimizing the bioreactor process will also enable rapid transition from benchtop production to large-scale manufacture.
We haven’t yet finished all the process development for our new packaging and producer cell lines but we can report that for the pre-packaging cell line, the precursor of the packaging and producer lines, process development increased production titer by more than tenfold.
In your opinion, how might the use of lentiviral vectors in the field of regenerative medicine evolve over the next 5–10 years?
As technologies become more scalable and cost of goods decreases, ex vivo cell therapies are likely to become more accessible and therefore a more mainstream treatment option. For example, there’s a huge – and growing – interest in precision medicine at the moment, particularly in oncology where there’s a large amount of resource invested in the further development and commercialization of CAR-T therapies.
As we mentioned before, there are currently over 600 cell therapy clinical trials active worldwide, and as the results of these start to be published, and some of these treatments move closer to the clinic, it’s likely to have a knock-on effect on research and investment in this area, meaning more research, more trials and hopefully more of these therapies reaching the market, probably for even more diverse and complex disease types. Overall, I think that overcoming some of the obstacles in the way of large-scale manufacture of cell therapies is likely to increase the number of lentiviral-based cell therapies available over the next few years.
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The opinions expressed in this interview are those of the interviewees and do not necessarily reflect the views of RegMedNet or Future Science Group.