"Our gene therapy candidates utilize piggyBac in combination with AAV delivery and our innovative nanoparticle technology to overcome the limitations of traditional gene therapies that rely strictly on viral delivery."

Eric Ostertag M.D., Ph.D.


May 21, 2021

How have you seen the field of gene therapy evolve over the course of your career?

I was the first graduate of the gene therapy program at the University of Pennsylvania approximately two decades ago. Since then, I have seen incredible advances in the field of gene therapy. Today we are closer than ever to my lifelong dream: to create cell and gene therapies that don’t just have the possibility of prolonging life but could potentially provide single treatment cures for cancer and other genetic diseases.

I did research 25 years ago in Jim Wilson's lab at Penn, and at that time, all gene therapy was gene addition. There was no such thing as gene editing. Gene addition used viruses to deliver genes into the genome. However, the problem with viruses is that people have evolved defense mechanisms against them. Some of these defense mechanisms can not only eliminate your therapeutic transgene expression but could cause potentially fatal inflammatory reactions. The strategy back then was to try to strip out genes from viruses to accommodate cargo capacity for therapeutic transgenes and also attempt to eliminate some of the immunity problems with viruses. Despite 25 years of work, that method has not been entirely successful. In response, the first big trend has been to go to completely non-viral genetic engineering technologies. To do that, you need two components. One, you have to replace the ability to get into the cell, which the virus normally would do via infection. We think the non-viral solution to getting into cells will be nanoparticles. These make up an artificial shell that encapsulates the therapeutic transgene and will get into specific cells of a person.

That is only half the story, because you would also want that therapeutic transgene to go into the patient's genome and result in long-term stable expression. If you can achieve this, you can then think about gene therapy as a potential single treatment cure. However, just delivering DNA into the cell cytoplasm would not do that. It would be a transient approach, which is where most of our competitors are right now. At Poseida, we solve that half of the problem by using a non-viral DNA delivery technology called a transposon that we refer to as Super piggyBac™ (SPB), which can stably integrate a therapeutic transgene into a patient’s genome and thereby create a potential single treatment cure. If you combine these two things, a nanoparticle and SPB, you have created a substitute for a virus but with none of the problems that we had with viruses for gene therapy over the last 25 years.

The other big advance is the advent of gene editing allows you to do more than just deliver a therapeutic transgene. Now you can edit as little as a single nucleotide in the genome. There again, the field has evolved over the last eight to 10 years, where the first gene editing tools were somewhat awkward and cumbersome to use and design. TALENs and zinc-finer nucleuses are examples, but then the CRISPR technology came out. It is easy to use, low cost and has multiplexing ability, which means you can knock out more than one gene at a time. The big problem with CRISPR is that it creates unwanted off-target mutations, which could potentially cause cancer. We invented a site-specific gene-editing system called Cas-CLOVER™, which is the best of both worlds. It is easy to use, you can multiplex it, and it is low cost, similar to CRISPR, but it does not have any of the unwanted and potentially unsafe off target mutations.

What are the advantages of nanoparticle delivery technology and why is it easier to manufacture a nanoparticle than AAV, or adeno-associated virus technology?

For the in vivo gene therapies, if you compare a nanoparticle versus the older viral technologies, virus is expensive, it is time consuming and costly to make, and there are issues with AAV having empty capsids, where your transgene is not even in the AAV. The nanoparticle is far easier to manufacture. There are many contract manufacturing organizations, or CMOs, now that will do viral manufacturing, but it would be very cost-prohibitive to manufacture in-house and it requires huge investments. In contrast, nanoparticle is relatively easy to manufacture, and at Poseida we are planning on manufacturing nanoparticles in-house. In fact, we have a biodegradable nanoparticle that allows you to re-dose a patient, and that biodegradable nanoparticle manufacturing can also be done in-house. Furthermore, there are no cargo limitations. When you have a virus like AAV, you take out its insides in order to accommodate a therapeutic transgene, but still only have a few kilobases of cargo. Because nanoparticle does not have cargo limitations, you can start to think about treating indications that you could not touch with AAV. In our case we are going after hemophilia A, where the transgene, factor VIII, is very large and too big for AAV.

What is the value proposition of cell and gene therapies?

At Poseida we are developing therapies to revolutionize the treatment of cancers and genetic disease in pursuit of single treatment cures. With our genetic engineering platform technologies, our goal is to transform the treatment of life-threatening diseases. It’s important to consider the curative potential of our therapies as compared to current modalities, which may require a lifetime of doctor’s visits, treatments, lifetime drug therapies, or hospitalizations. We believe our novel approach can drive better patient outcomes with less toxicity across our pipeline.

Our gene therapy candidates utilize piggyBac in combination with AAV delivery and our innovative nanoparticle technology to overcome the limitations of traditional gene therapies that rely strictly on viral delivery. PiggyBac’s ability to deliver large capacity genetic cargo and permanently integrate into DNA enables us to extend our technologies into diseases beyond the reach of transient viral-based delivery methods. Our potential to enable durable gene expression, even in tissues with rapidly dividing cells, allows us to pursue a wide spectrum of genetic diseases, including many indications within the pediatric population.

We can talk about cell therapies separately. For us, CAR-T cell therapy is an ex vivo form of gene therapy where you are taking out a patient's T cells, modifying them genetically to educate them to kill cancer, and then you put them back in. Right now, that is mostly done by autologous or individualized therapies. If somebody gets cancer, you manufacture their cells and put them back into the patient. Consequently, it is a very expensive process, it is time consuming, and the clinical trials are expensive and time consuming as well. Both Poseida and the field are headed toward a fully allogeneic process, which means we take cells from a healthy donor, manufacture them and then potentially give them “off the shelf” to many patients. That drops the cost of manufacturing while greatly expanding patient access.

Most companies with CAR-T right now are only able to make somewhere between six to 12 doses from a single manufacturing run. However, with the help of our “booster molecule,” we have shown we can make hundreds of doses from a single manufacturing run and that takes the cost of manufacturing CAR-T from well over US$100,000 to just a few thousand dollars, putting it in the same range as a monoclonal antibody or a bispecific therapy. At Poseida, we are using our proprietary technology to revolutionize cell and gene therapy. Ultimately, we are proud to be developing new therapies with the capacity to cure for patients with very high unmet medical needs.


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