Shall We Dance Transduce? A CGT CEO's Quest For More Efficient Transduction

By Anna Rose Welch, Editorial & Community Director, Advancing RNA

In the first of this two-part article, I shared how Dr. Bobby Gaspar, CEO of Orchard Therapeutics, is guiding the company through the challenging — but promising — process of a developing a stable producer cell line for more efficient lentiviral vector production. However, as our conversation continued, we seamlessly moved from one complicated T-word — triple transfection — to another: Transduction.

There were two things in particular that struck me as we discussed some of the hang-ups in the current transduction process. One is that, there’s an intriguing contradiction taking shape in the world of CGT manufacturing today, at least as it relates to viral-vector-based therapies. While a central goal in the CGT industry today is to produce larger volumes of high-quality vector in general, when it comes to the transduction of a patient’s cells (and an in vivo gene therapy), the goal is actually to reduce the amount of vector needed to achieve the necessary levels of cell correction. To put it another way: we’re in the pursuit of making more to, ultimately (and hopefully), use less.

Secondly: I had a very hard time not envisioning the current transduction process as a poorly coordinated tango between two dancers that have never met before and/or have never danced together — and, in some cases, don’t actually want to dance at all. (Or, if cute animals are more your thing, think of the current transduction process as this cat [the viral vector] trying to get to the chipmunk [the patient’s cell] through the window.)

At the end of the day, sometimes all a stubborn wallflower at a dance really needs is a strong cocktail.

Enter transduction enhancers, which are already being explored and used in clinical trials today. Much like a good alcoholic beverage can ease tensions between estranged dancers, there are several ways transduction enhancers also work as a “social lubricant,” if you will, between cells and lentiviral vectors. They can bring the vector and cell into closer proximity to encourage more physical contact. They can also increase the permeability of the cell membrane and make it more amenable to the vector.

For Orchard, which is working with the HSC population, these enhancers will facilitate the viral vector’s entrance into the cell without causing cell division. As Gaspar explained, HSCs do not divide easily, which makes it much harder for a lentiviral vector to enter the cell. (Think of the HSCs as a gaggle of inseparable girls at a homecoming dance, making it infinitely more intimidating for a shy someone to approach and ask for a dance.) Such stubbornness on the cells’ part ultimately increases the amount of vector needed to successfully transduce the cells — which, in turn, ratchets up the overall COGS.

As Gaspar points out, “I see these transduction enhancers playing a critical role in the reducing overall COGS because they ultimately lower the amount of vector you need to successfully transduce your cells.” This is one big reason why Orchard is developing some of its own proprietary transduction enhancers to complement those that are currently available on the market.

Of course, another way companies can improve the overall transduction process is to have the best possible cells to transduce in the first place.

“HSCs are not a discrete population; they’re a hierarchical population of cells,” Gaspar clarified. “While the cells selected will all express the same protein marker on their surface — in this case, CD34 — some will be considered true stem cells, while others will be more committed. What we’ve found is that the true stem cell population is more likely to repopulate in vivo in the long-term. So, if you were able to select and correct those purer cells from the beginning, you would also be improving your transduction efficiency.” (The fewer cells you have, the less vector you’d need, as well.)

Today, singling out the members of that purer population may be akin to the dizzying pursuit of “Waldo” throughout the entire series of Where’s Waldo? books. After all, these true stem cells only represent 5 percent or so of a stem cell’s total population, Gaspar qualified. However, identifying the cell surface markers intrinsic to these purer stem cells is another goal the C&G industry is adding to its list to benefit the overall transduction process in the foreseeable future.

Gaspar is optimistic. As he concluded, “I can envisage in a number of years, you will be correcting only a small subset of the CD34 HSC population, as opposed to the total population.”