Using Bispecific Antibodies to Redose AAV Gene Therapy

Nicholas Giovannone, PhD, a senior principal scientist at Regeneron

Despite the advantages of adeno-associated virus (AAV) vectors for gene therapy products, a major drawback to AAV vector-based approaches is that redosing of the same product, or other products based on AAV vectors, is usually limited by immune responses. At the American Society of Gene & Cell Therapy (ASGCT) 28th Annual Meeting, held May 13 to 17, 2024, in New Orleans, Nicholas Giovannone, PhD, a senior principal scientist at Regeneron,Nicholas Giovannone, PhD, a senior principal scientist at Regeneron, presented on a potential method intended to overcome this limitation.

At the conference, CGTLive® spoke with Giovannone about the research. He gave some background about the concept and described the key results, noting that in nonhuman primate studies, a bispecific antibody approach successfully suppressed the immune response, allowing for AAV redosing.

CGTLive: Can you give some background context about your presentation at ASGCT this year?

Nicholas Giovannone, PhD: My group and Regeneron broadly is really interested in tackling this challenge of immune responses to AAV gene therapies, which has emerged as, in some ways, an unexpected problem. In other ways, in terms of the antibody response and the challenges of inability to redose it's less-so unexpected, but that's been a really big challenge from the beginning with AAV gene therapy. We wanted to tackle that challenge by immunomodulation approaches that you can give before the AAV is administered, and in doing so, you could prevent the AAV antibody response from ever forming. In doing that, you could potentially keep a patient seronegative so that they can receive an AAV gene therapy in the future. That's been a focus of my group for the past several years.

What are the key results you are presenting?

As I mentioned, we're very interested in this concept of prophylactic immunomodulation, which isn't necessarily new to the field, but the approach that we're taking is like all we do at Regeneron: trying to understand the basic science and really develop a strategy that makes sense based on that basic science. So rather than taking a broad immunosuppression approach, we went back to first immunological principles and said, "Okay, what is one of the key players in generation of antibody response?" One of those key players is CD40. As such, one of the approaches that we're testing is this antibody reversible mediated blockade of this key receptor interaction in development of antibody response. Then separately, we also tested a more conventional approach—this is all done in nonhuman primates—a more conventional approach of depleting the B-cells that go on to become antibody-secreting cells. But instead of the conventional methods of B-cell depletion through rituximab, for instance, which is actually commonly used in the clinic for AAV therapies, we wanted to understand why rituximab so far has failed in the clinic to enable redosing.

One of the things we learned from looking at the data with rituximab versus more advanced therapies like one that we developed at Regeneron, a CD20xCD3 bispecific antibody approach—one of the things we found was that rituximab is not so great at depleting B-cells in the critical areas you need to deplete them to prevent an antibody response: namely, the lymph nodes and spleen. And so we tested an approach using this bispecific antibody that we found is a much better depleter in those tissues.

We found both this CD40 blockade approach and the B-cell depletion approach with this bispecific antibody, CD20xCD3, were really effective at preventing the antibody response to AAV in different ways, which I'm happy to elaborate on. But the end result was that we were able to redose with a second AAV vector in the monkeys and achieved much higher levels of transduction than monkeys that received no immunomodulation. I want to emphasize again that these approaches are meant to be transient. The idea, again, is to temporarily block the AAV antibody response so that during that time the AAV is around, you're preventing an immune reaction, and then you can redose in the future—so how do we keep somebody seronegative even after receiving the AAV?

This transcript has been edited for clarity.

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