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Replies to post #190164 on Biotech Values
Intravitreal injection, whereby a needle is pushed into the eye’s vitreous, or gel-like core, is a common drug delivery procedure performed under local anesthetic in a doctor’s office, explained Bennett. But using this routine injection technique in trials of gene therapy for retinal degeneration has thus far proven impossible.
The problem, explained David Schaffer, a professor of chemical and biomolecular engineering, bioengineering, and neuroscience at the University of California, Berkeley, who led the research, is that current AAV vectors are incapable of penetrating deep into the retina where the target cells for retinal diseases are located. “AAV is a respiratory virus and so it evolved to infect lung epithelial cells,” explained Schaffer. “It never evolved to penetrate deep into tissue.”
Patients receiving gene therapy have therefore undergone a direct intraretinal injection, which requires hospitalization and general anesthetic, and can sometimes even damage the retina. If it were possible to inject AAV into the vitreous instead of the retina and still get gene delivery to the target cells, said Bennett, “one could envision the [doctor saying], ‘Ok, well just come into the office and get your gene therapy, tomorrow afternoon at two.’”
With that aim, Schaffer and colleagues evolved AAV to be better at tissue penetration. They injected regular AAV into the vitreous of mouse eyes and one week later collected photoreceptor cells from deep within the retina. The tiny percentage of AAV vectors that made it into those cells were then amplified, repackaged into virus particles and injected into the vitreous again. They repeated the injection, recovery, and amplification a total of six times, finally isolating 48 AAV variants for sequencing. Two thirds of those isolates turned out to the same variant, and Schaffer and colleagues named it 7m8.
The team then performed intravitreal injection of the 7m8 AAV vector to deliver missing genes into two mouse models of retinal degeneration—retinoschisis and Leber’s congenital amaurosis. In both models, the treated mice showed improved retinal function. Mice receiving their missing genes via intravitreal injection of the standard AAV vector, on the other hand, did not.
Lastly, to determine whether the 7m8 vector would be likely to show similar deep penetration in the human retina, Schaffer injected the vector fused to a fluorescent protein into the vitreous of macaque eyes. Primate retinas are considerably thicker than those of mice, and the vector did not consistently reach the deep cell layers—showing a spotty penetration pattern rather than the wide and even pan-retinal penetration that had been seen in the mice. However, 7m8 did effectively target photoreceptor cells of the fovea—a thinner part of the primate retina that is essential for the sharp detailed vision humans use when reading and driving. “That’s a really important region to protect,” said Schaffer. “For the quality of life of patients who are going blind, if you can at least protect the fovea that would be a huge improvement.”
Schaffer and colleagues don’t yet know what makes the 7m8 vector so much better at tissue penetration than its AAV ancestor, but they plan to find out and use that knowledge to further improve its penetration in the primate retina.
They also plan to use similar directed evolution strategies to improve vector penetration into other body tissues “What this paper illustrates is the ability of purpose-directed vector evolution to achieve a specific anatomic transduction goal,” said Kathy High, a University of Pennsylvania professor of pediatrics who was not involved in the study. “And that’s an important development not just for ocular applications but for others like the liver or central nervous system.”
Genzyme recently informed us that it no longer intends to use our HSV-based manufacturing technology to produce the AAV vector being used for the wet AMD product. Genzyme will be responsible for all future clinical trials and commercialization of its wet AMD product candidate.
Our license to Genzyme
In 2004, we entered into a collaboration agreement with Genzyme to develop a recombinant AAV product to treat wet AMD. Our agreement originally provided that the parties would share responsibility for planning, budgeting, workload, decision-making, costs and future revenues. The parties had joint ownership of any intellectual property that arose as a direct result of the work done for the partnership. In collaboration with Genzyme, early product development work, production of materials for animal studies, development of several manufacturing and clinical assays, completion of IND-enabling toxicology and biodistribution studies, technology transfer of our HSV-based manufacturing process to Genzyme, production of the AAV vector under GMP for the Phase 1 human clinical trial, and drafting of the IND were conducted.
In early 2010, as the product candidate was moving into human clinical trials required for wet AMD, we renegotiated our agreement to take the form of a license of our HSV-based manufacturing technology and interest in the wet AMD program to Genzyme. The license provides for modest late-stage milestone payments to us and royalties on sales, as well as forgiveness of our share of development costs from mid-2006 to the date the license was signed. Genzyme is responsible for all further development and commercialization of the wet AMD product candidate. We maintain non-exclusive rights to jointly developed technology. Genzyme also has options, expiring in 2015 and 2017, to license our manufacturing technology, as it existed at the time of the license, for specified genes associated with diseases outside our current area of focus. Genzyme recently informed us that it no longer intends to use our HSV-based manufacturing technology to produce the AAV vector being used for the wet AMD product. Our license agreement with Genzyme was further amended in December 2013 to reflect this fact and, among other things, to terminate our exclusive license to Genzyme for use of our HSV-based manufacturing technology in wet AMD except as to specified pending research activities, and to eliminate restrictions on our activities in the field of treatments for ocular neovascularization disorders, including AMD.
We currently do not expect to derive substantial revenue from our license to Genzyme, but a successful outcome of the clinical trials for which Genzyme is responsible would contribute significantly to the perception and prospects of our gene therapy platform.
Vector manufacturing: our HAVE method
We have developed a proprietary, high-yield vector manufacturing process using scalable technologies for herpes-assisted vector expansion, which we refer to as our HAVE manufacturing method. While the HAVE manufacturing method uses the herpes virus as a helper in the first step of a four-step AAV vector manufacturing process, there is no herpes virus in the final product. Our HAVE manufacturing method addresses problems of low productivity and low efficacy that have historically plagued efforts to manufacture AAV vectors and enables us to produce vectors with improved potency, efficiency and safety over processes previously used by us and others. It also enables us to produce a more purified and concentrated end product, as evidenced by an approximately 25- to 30-fold reduction in non-infectious viral contaminants as compared to vectors used in previous clinical trials.
Our manufacturing process has been reviewed by both the FDA and the European Medicines Agency, or EMA, and has been authorized for production of product candidates for use in clinical trials in the United States and Europe. Our manufacturing process is also reproducible and scalable. It has been transferred successfully to Genzyme and to SAFC Pharma, our contract manufacturing organization, where it is used in manufacturing clinical materials pursuant to the FDA’s current good manufacturing practices, or GMP, requirements.
We and SAFC Pharma have successfully produced the necessary material for the clinical trials we have conducted to date, and have more than enough manufacturing capacity to meet the requirements of our planned future trials. We are currently investing in the development of mid- to large-scale manufacturing processes with a view towards supporting our product candidates, if approved, at commercial scale.
We hold or have licensed 79 issued and 28 pending patents covering our manufacturing technology. We believe that our core competency and intellectual property estate in vector manufacturing differentiate us competitively and provide a key element of our gene therapy platform.
Our HAVE method
The four key steps involved in our proprietary HAVE manufacturing method are as follows:
First, the therapeutic gene and the appropriate AAV capsid genes are inserted into individual HSV helpers, and these helpers are individually grown in a complementing cell line called V27. The complementing cell line is required to provide critical functions that allow the replication-incompetent HSV helpers to grow; the same cell line is used to produce HSV helpers for all disease targets. This step occurs in disposable culture vessels of increasing size, up to and including disposable stirred tank bioreactors. The HSV helpers are harvested, minimally processed and concentrated to prepare them for use in producing our AAV vectors. These HSV helpers can be stored frozen for years before use.
Next, the two HSV helpers are used together to infect a cell line called sBHK, allowing for packaging of the therapeutic gene into the AAV capsid and to produce our AAV vectors. The sBHK cell line does not provide the critical functions that would allow for growth of the HSV helpers, which provides an added layer of safety. The same sBHK cell line is used to produce AAV vectors for all disease targets. This step occurs in disposable culture vessels of increasing size depending on the amount of AAV vector that is required. The AAV vector is recovered by using a detergent solution to break open the sBHK cells and release the AAV vectors. This step also destroys any residual HSV helpers that were used to infect the sBHK cells.
The third step is to purify the harvested AAV vector using two chromatography columns. The exact method used to column-purify our AAV vectors varies depending on the AAV capsid used in the product candidate; we have developed purification methods for multiple AAV capsids. We have shown in formal clearance studies that the combination of detergent treatment and two chromatography columns can remove up to 1014 (100 trillion) units of HSV. This step also helps to eliminate any remaining parts, such as proteins or DNA, of the HSV helpers and sBHK production cells.
The final step is to formulate, filter and fill the AAV vector in appropriate containers for use in animal or human studies. This filled AAV vector drug product can be stored frozen for years before use.
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