Developing Safer Viral Vectors for Gene Therapy


The chief executive officer of Ring Therapeutics, Tuyen Ong, MD, discussed the potential of anellovirus vectors for use in gene therapy.

The standard approach for gene therapies today consists of adenoviral or lentiviral vectors, which have shown great potential for correcting genetic diseases but also come with high levels of toxicity due to their immunogenicity within the human body. Ring Therapeutics has developed a novel anelloviral vector, coined Ring 46, which may lead to the development of an effective and safe gene therapy agent in humans.

These findings were presented at the American Society of Gene & Cell Therapy 25th Annual Meeting (ASGCT), held in Washington, DC, and virtually May 16-19, 2022, by Dhananjay Nawandar, PhD, associate director, Ring Therapeutics.

CGTLive spoke with the chief executive officer of Ring Therapeutics, Tuyen Ong, MD, to learn more about anelloviruses. He discussed their properties and advantages including low immunogenicity, low preexisting immunity, and immune privilege in humans.

CGTLive: What are some challenges with the current approach and use of viral vectors in gene therapy?

Tuyen Ong, MD: There have been a lot of conversations around challenges with delivery, as well as immunogenicity and immune response. When we typically think about traditional small molecules, it's really focused on pharmacokinetics and pharmacodynamics, which is straightforward. Gene therapy has become much more challenging. Ultimately, as the field continues to blossom, there are a number of areas that we need to address as a community. One is tropism, the second is potency, and the third piece is really relating to immunogenicity and the immune profile. Also, the ability to re-dose, if you don't have durability, or if you need to continue treating for 1 reason – growing children, for example, or insufficient expression of protein as well. Those are the challenges the gene therapy community faces and people are rising up to these challenges in different ways. For us, the optimal solution is anelloviruses, because they've really been able to evolve through millennia, and we have specific tricks that we can harness with them. We're really excited by what anelloviruses can offer.

What makes the anelloviruses an attractive option as a vector?

Anelloviruses are very interesting. They come from the human virome and the majority of the virome consists of viruses that don't cause disease. Ring has built out a whole platform to discover and then vectorize these viruses. We've discovered that they are highly diverse... this is in a publication in Cell Host & Microbe that we published a while back. Essentially, from millions of years of evolution, they've developed a huge amount of genetic diversity that's afforded them very specific properties. One is that intrinsically, they're able to be ubiquitous amongst the general population and are able to reside in different parts of our body. All of those traits have allowed them to be tissue tropic. The second piece is that they've somewhat become immune stealth, they've invaded our immune system and become immune-privileged.

Part of that publication showed that you can transfer anelloviruses between donors and recipients in blood transfusions and those viruses actually persist. In many cases, when the anelloviruses are very similar between the donor and recipient, you can almost re-dose the same virus or vector as well. So we published this exciting data showing anelloviruses as a potential basis for programmable medicines.

What observations and progress have been made with the anellovirus vectors?

About 2 to 3 weeks ago, the National Institutes of Health held a workshop on the humanvirome, and 1 of the challenges is being able to synthetically produce an anellovirus. Ring has been the first and only organization that I'm aware of to be able to synthetically produce anelloviruses. This is a huge milestone for us and it allows us to use ring 46 as a prototype, allowing us to take in another virus and vectorize it, and introduce a transgene tailored within that. What we've shown in the paper is the ability of those trans genes to target a number of different tissues, such as the muscle, retina or the heart. We’re laying the foundation of being able to take an anellovirus, vectorize it, introduce payloads within that, and then show transduction or infectivity into those tissues and ultimately having a therapeutic benefit to patients.

How does low preexisting immunity combat high levels of toxicity associated with current virus vectors?

Low preexisting immunity is the fundamental aspect of why we're so excited by anelloviruses. That pertains mainly to the data we generated with Dr. Ben Larman and the folks at Johns Hopkins that showed that the anellovirus is less antigenic than most viruses in the human virome. They scanned a library of 32,000 peptides from over 800 anelloviruses and tested the immune reactivity of these proteins. When you compare these proteins to the reference library of about 200 species of known viruses, we found that most of the anellovirus peptides were not associated with any detectable antibody responses.

That's an exciting finding for us, because it allows a number of opportunities to open up. One is the lack of preexisting neutralizing antibodies, for example. We've seen that in human intravenous immunoglobulin studies. The fact that anelloviruses are less antigenic means they are less likely to be eliminated by the immune system or mount an immune response. Further down, they have the ability to be re-dosed as well. So we've had interesting findings that are exciting for us in terms of how we can harness those properties.

What are other advantages with anellovirus vectors?

When we look at the Anellogy platform that Ring has built around the anellovirus, instead of looking at small, incremental improvements in the individual components of a platform, what we've done is take a holistic view trying to generate a new gold standard around this. We're innovating on multiple fronts, from discovery to vectorization. Manufacturing is a big bottleneck and the rate limiting step in the gene therapy world, what we've essentially done is to be able to assemble the capsules from our sequences in a recombinant way, which is very different to the traditional AAV approach. That offers us the ability to be much more scalable and modular in terms of how we look at manufacturing.

What will Ring be exploring next with anellovirus vectors?

We've got a substantial body of understanding of how they evade the immune system, which we plan to share in a future conference. We will continue to build out our dominion in the space and understanding about anelloviruses to be able to deploy them in the field of programmable medicines. Ultimately, what it boils down to in this field, is being able to innovate with the nature inside of us and being able to use that to generate therapies for patients in need.

Transcript edited for clarity. To read more coverage of ASGCT 2022, click here.

Nawandar D, Timpona J, Boisvert N, et al. A Novel Gene Delivery Vector with Low Pre-Existing Immunity in Humans. Presented at: ASGCT 25th Annual Meeting, May 16-19, 2022, Washington DC. Abstract #1158.
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