Orchard Therapeutics' Hot Pursuit Of A Stable Cell Line For Lentiviral Vector Production
By Anna Rose Welch, Editorial & Community Director, Advancing RNA
When Dr. Bobby Gaspar founded Orchard Therapeutics and came on, first as its CSO prior to becoming CEO, he set four goals for the company to successfully manufacture a gene therapy. The first was to select the appropriate stem cell population. The second was to investigate the use of and potentially develop novel transduction enhancers to make the currently finicky transduction process more efficient. The final two — which remain works in progress for a large number of cell and gene therapy (CGT) players today — were to implement automation and to develop a stable producer cell line for lentiviral vector production.
To this day, Gaspar is confident these have been and continue to be the appropriate steps to successfully manufacture its ex-vivo hematopoietic stem cell (HSC) gene therapy (currently approved in the EU as Libmeldy). But he laughed when I asked him what advice he would give himself if he went back to the beginning, knowing what he does now about the manufacturing challenges facing CGT companies. In fact, it will most likely ring true for most of you in this field.
“Number one, give yourself more time than you anticipate you will need,” he said. “In the CGT space, you have to move development along as quickly as possible. But any startup will inevitably face the growing pains of not having everything it needs right off the bat in terms of space, facilities, and people. You’re building things as you go along, so you have to be realistic about what you can achieve over a certain period of time because it takes so much to get there.”
This advice is exceptionally true when we’re talking about transitioning from legacy viral vector manufacturing processes to what is heralded as the exciting new chapter in viral-vector-based CGT development: the stable producer cell line.
In the first of this two-part article, Gaspar fills me in on the “why” and “how” of the company’s investment in this nascent but alluring technology. Though, like many areas in the CGT manufacturing space, maturity of this production method (i.e., clinical and commercial development) is out of reach today by more than a few arms-lengths, Gasper homed in on one milestone he thinks will be key for unlocking the future promise of stable producer cell lines.
In addition to that fantastic Airplane gif in the subhead, my mind inevitably associates current viral vector manufacturing challenges with another movie quote (sort of) from The Pirates of the Caribbean: “But why is the [vector] gone?!” It’s no doubt a common phrase uttered within CGT analytical departments the world over as they try to run analytical tests requiring larger sample sizes of viral vectors than are currently available. (Like Captain Jack Sparrow, these experts may also be asking why all the rum is gone, too.)
Vector scale-up is one of the most commonly cited issues CGT companies are facing today. Afterall, as Gaspar admitted, “We’re making viral vectors the way we’ve made them for the last 20 years, and it’s time to move forward.”
Today, transient transfection remains the go-to practice for developing lentiviral vectors (LVV), despite its notable inefficiencies. Not only do companies need to source and/or develop multiple plasmids and large quantities of reagents, the transient transfection process is renowned for producing inconsistent titer. The industry’s reliance on adherent cell culture also doesn’t exactly bode well for commercial scale vector production (unless, of course, companies are cool with constructing high-rises or owning their own football-fields, plural…). It should come as no surprise then to note that the chatter around stable producer cell lines increases in volume with each passing year.
In the non-pharma world, we’re all familiar with the phrase, “Why choose one when you can have both?” This is a fabulous argument when you’re picking ice cream flavors. But in the CGT industry, which tends to fly in the face of tradition, the saying gets a bit reversed when we approach the transfection process: “Why transfect HEK 293T cells with multiple plasmids when you could only do it with one?”
As Gaspar explained, integrating all the information from multiple plasmids into a single plasmid and then performing the transfection process is a winning proposition, both from a supply chain and an efficiency standpoint. Ideally, a company could then select the clone that promises the highest titer and yield for scaling up in suspension culture and create a master cell bank. Once that clone is well characterized and the master cell bank is established, the company has a solid basis from which to scale-up a cell line and produce vector in a more consistent and repeatable fashion.
The industry’s progress toward stable producer cell lines will be a long journey, but the technology is slowly but surely emerging. Perhaps the most well-known method to date is that of GSK, which is already being licensed out to other biotechs, including Orchard. However, licensing the technology is only the beginning.
“You have to put a process in place from the moment you have identified the most promising clone,” he explained. “Right now, we’re asking ourselves the following questions: ‘How are we going to grow and scale that clone? What media will we use to best grow the clonal cell line? How will we harvest and purify the vector?’ We know we can identify a clonal line; now we have to work out what our processes are for growing that line to the desired scale.”
Though the stable producer cell line is a highly anticipated solution for more sustainable lentiviral vector production, we have yet to see the technology integrated into a clinical program and/or at a large scale. In order to accomplish this crucial progression, Gaspar anticipates that the industry will have to buckle down on advancing the analytical paradigm for CGTs. Afterall, we can’t ignore the comparability challenge such a transition to the stable producer cell line will inevitably pose for companies. (“Demonstrating comparability” sounds kind of like The Hunger Games, doesn’t it?)
Though the company has its work cut out for it in process development, Gaspar earmarked comparability as one of the biggest hurdles companies will face in adopting the technology. A clinical-stage company will need to demonstrate that the CGT product relying on a vector produced the new way (i.e., stable producer cell line) is highly similar to the product using vector developed the conventional way (i.e., transient transfection). But as we know, comparability — both as a concept and in practice — is a common pitfall for CGT companies today. We can apportion some blame on the biological complexity of these treatments’ mechanisms of action. The lack of overarching reference standards, insufficient identification of a therapy’s critical quality attributes (CQAs), and/or inconsistencies in the analytical measurement of these CQAs also cause their own fair share of comparability headaches.
Having a strong understanding of a therapies’ CQAs, how they evolve (or don’t evolve) following manufacturing changes, and the clinical implications of any changes will be essential to industry-wide adoption and success with stable producer cell lines. In fact, Gaspar is less inclined to believe that stable producer cell line technology will run into any fundamental, technical barriers rendering it ill-equipped for large-scale CGT therapy development. Rather, he expects that the long-term success of stable cell lines will be determined in large part by a company’s ability to thoroughly characterize its process.
Streamlining the vector production process is an essential step for improving the manufacturing paradigm of CGTs. But for ex-vivo products, developing the vector is only one of several critical steps on the path to manufacturing a CGT. The industry also has a current bone to pick with the transduction process. Stay tuned for part 2, in which Gaspar and I delve into the innovations he expects will enable a more productive transduction process.