Gene Therapies Receive a Shot in the Arm

Developers of gene therapies are taking advantage of new vector technologies, incorporating CRISPR systems, and augmenting gene therapy with targeted therapies and immunotherapies

All eyes are on the emerging COVID-19 vaccines, but some observers see a little more deeply. They recognize that many of these vaccines incorporate the same kinds of technologies that are found in gene therapies. Progress with COVID-19 vaccines could help bring about progress with gene therapies, and vice versa.

For example, an experimental COVID-19 vaccine called AAVCOVID incorporates an adeno-associated virus (AAV) vector. AAV vectors are already being used as delivery vehicles for two FDA-approved gene therapies—Luxturna (approved in 2017 for a rare inherited retinal dystrophy) and Zolgensma (approved in 2019 for spinal muscular atrophy). Many other AAV-based gene therapies are in development.

AAV vectors are an attractive option for gene therapies because they are not known to cause human disease and because they do not replicate in the human body. They may become even more attractive if the imperative to produce COVID-19 vaccines in great quantities were to create pressure to enhance the manufacture of AAV vectors.

Some of the gene therapies in development use AAV vectors to deliver CRISPR agents that can bring about cut-and-paste treatments for genetic disorders such as sickle-cell disease. AAV vectors are also being used to deliver genetic payloads to target cells, which then use the payloads as templates to express molecules to treat diseases such as macular degeneration.

These latter applications bring to mind the COVID-19 vaccines that deliver genetic material to cells, which then use the material to express the notorious spike protein. Instead of relying on AAV vectors, some of these vaccines rely on lipid nanoparticle vectors, which, not surprisingly, are also being used in gene therapies. For example, there are gene therapies in development that use nanoparticle vectors to bring DNA to target cells, and that also deploy immunotherapies or targeted therapies.

Whatever vectors are needed, gene therapy developers are not content to wait for COVID-19-inspired improvements in vector manufacturing. To facilitate the global commercialization of gene therapy products, many developers are constructing their own GMP facilities.

Opposites attract to fight lung cancer

Cancer can quickly strike and metastasize anywhere in the body, disrupting multiple genes and cellular pathways. Gene therapy strategies are helping reestablish or, conversely, block such disturbed pathways. Genprex is developing new cancer therapeutics initially focusing on non-small cell lung cancers. They represent 84% of all lung cancers and have a 24% five-year survival rate.

“One of the main challenges in this area is delivery of genes to tumor cells,” reports Rodney Varner, president and CEO of Genprex. “There can be multiple tumors in multiple areas. Thus, we need a safe way to perform systemic delivery of therapeutic genes.”

Genprex’s oncology program utilizes a combinational treatment approach coupling their lead product candidate, Reqorsa, which utilizes a nonviral Oncoprex nanoparticle delivery system, with either an approved immunotherapy or targeted therapy.

Reqorsa immunogene therapy diagram
Genprex is developing an immunogene therapy called Reqorsa. Its active ingredient is TUSC2, a tumor suppressor gene. TUSC2 is delivered via the company’s Oncoprex technology, which relies on positively charged lipid nanoparticles that have an affinity for negatively charged cancer cells. Reqorsa interrupts replication and proliferation pathways, stimulates apoptosis, and modulates the immune response against cancer cells.

“Reqorsa consists of an optimized nanoparticle engineered to contain the TUSC2 gene plasmid, a tumor suppressor gene,” explains Michael Redman, Genprex’s executive vice president and COO. “Although there are about 400 tumor suppressor genes, we selected this one based on our collaboration with Jack A. Roth, MD, of the University of Texas MD Anderson Cancer Center, who is the inventor of the technology. The TUSC2 gene codes for a multikinase inhibitor that is reduced or absent in about 80% of all lung cancers.”

Redman says that when the TUSC2 plasmid is encased in nanoparticles, the uptake by tumor cells is up to 33-fold higher than that by normal cells. He elaborates, “Tumors have a different metabolism than normal cells and tend to be more negatively charged compared to healthy cells, which are positively charged or charge neutral. The nanoparticle delivery system is positively charged and, thus, is attracted to cancer cells. The encased plasmid bearing the tumor suppressor gene takes advantage of a cell’s own endocytosis mechanism to foster expression of the protein.”

The company is planning to initiate two Phase I/II trials in the first half of 2021—one with Reqorsa in combination with a targeted therapy (Tagrisso, marketed by AstraZeneca), and another with Reqorsa in combination with an immunotherapy (Keytruda, marketed by Merck & Co). Varner envisions many more opportunities because of the flexibility of the system.

“We were recently granted a fast-track designation by the FDA for the combination of Reqorsa with Tagrisso for patients who have failed prior treatment with Tagrisso,” he discloses. “We are excited to continue assessing even more therapeutic genes and combination therapies.”

Targeting sickle-cell disease

Sickle-cell disease (SCD), an autosomal homozygous illness, results from a single point mutation in the β-globin (HBB) gene that changes a single thymine into an adenine. The shape-shifted β-globin protein, a critical component of hemoglobin, contorts red blood cells into a sickle shape, causing premature cell death and severe pain in patients. Graphite Bio has developed a gene editing platform that takes a patient’s own hematopoietic stem cells (HSCs), corrects the genetic defect, and returns the HSCs back to the patient.

“Our platform utilizes a site-directed approach that builds on CRISPR technology,” reports Josh Lehrer, MPhil, MD, Graphite Bio’s CEO. “We employ CRISPR to create the double-stranded break in DNA, but we take this one step further. We add a DNA donor template from a recombinant AAV that efficiently directs the cell’s own DNA repair mechanism. This process is called homology directed repair.” According to Lehrer, the cut-and-paste approach allows corrected HSCs to give rise to cells that survive and reproduce, restoring normalcy.

The company’s initial clinical candidate, GPH101, will be entering clinical testing this year in the CEDAR trial, a Phase I/II open-label, multicenter trial. “We are,” Lehrer contends, “the first company to provide a potentially curative genetic therapy for SCD that corrects the faulty gene and restores the production of normal hemoglobin and thus normal red blood cells.”

Lehrer indicates that the company is advancing its gene integration pipeline to include other genetic diseases such as X-linked severe combined immunodeficiency syndrome and Gaucher disease, among others.

“We can conceivably correct any genetic disease [by genetically modifying cells such as] airway stem cells, neural stem cells, and keratinocytes,” Lehrer ventures. “This corrective cell therapy approach could extend across numerous applications such as treatments for autoimmunity, cancer, and disorders of the central nervous system.”

One-and-done shot restores vision

Reversal of vision loss, spearheaded by AAV therapeutics, may soon be one shot away from reality. “We are developing a gene therapy candidate that targets ‘wet’ age-related macular degeneration and diabetic macular edema,” informs Laurent Fischer, MD, CEO of Adverum Biotechnologies.

Age-related macular degeneration (AMD) is a leading global cause of blindness in individuals over 50 years of age. Approximately 10% of AMD patients have “wet-AMD,” which accounts for 90% of AMD blindness. Vascular endothelial growth factor (VEGF) plays a pivotal role in the pathogenesis of wet AMD. Typically, patients receive intravitreal injections of an anti-VEGF protein, such as FDA-approved aflibercept.

“Patients need repeated injections every four to eight weeks indefinitely,” Fischer notes. “This represents a large burden to patients and their caregivers. Unlike other ocular gene therapies that require surgery, our treatment, ADVM-022, is designed as a one-and-done outpatient intravitreal injection.”

ADVM-022 gene therapy diagram
A gene therapy for “wet” age-related macular degeneration has been developed by Adverum Biotechnologies. The therapy, which is called ADVM-022, uses a proprietary vector capsid (AAV.7m8) to carry a coding sequence for aflibercept. According to Adverum, a single intravitreal administration of ADVM-022 may provide a safe and effective long-term treatment option.

ADVM-022 utilizes a proprietary vector capsid (AAV.7m8) carrying a coding sequence for aflibercept. “Just one treatment with ADVM-022 results in local and stable production of the therapeutic protein,” Fisher asserts. “This has been a transformative treatment approach for AMD. So far, we have shown robust and sustained efficacy beyond 24 months of successful responses from a single injection.”

In 2018, Adverum reported that the FDA had granted fast track designation for ADVM-022 for the treatment of wet AMD. The company is currently conducting a multicenter Phase I trial in patients with wet AMD who received frequent anti-VEGF treatment. A Phase II trial is underway using ADVM-022 for the treatment of recently diagnosed diabetic macular edema, a complication of diabetes that can lead to blindness.

Adverum’s scalable platform will eventually also be utilized to treat rare ocular diseases. Creation of appropriate vectors relies on the use of the company’s multistep directed evolution process that screens libraries with millions of AAVs for desired characteristics such as efficient transduction, robust expression, and evasion of immune responses. To support the expected global commercialization of ADVM-022 and future products, the company is investing in a GMP facility in North Carolina.

Fischer reflects on his personal experience with the trials: “As a physician, I find it incredibly heartwarming to see patients, who would otherwise be experiencing rapid vision loss, respond to treatment.”

Aiming at rare diseases

Although about 7,000 rare diseases have been identified, only a handful of treatments are approved. Since nearly 80% of rare diseases have a monogenic origin, gene therapy holds a particularly relevant promise.

Rare, devastating neurological diseases are being targeted by Neurogene, a developer of AAV-based gene therapies that makes a point of collaborating with academic partners. It recently partnered with Stuart Cobb, PhD, a principal investigator at the University of Edinburgh (and Neurogene’s CSO), to combine the company’s manufacturing and drug development capabilities with the multiple gene therapy platform capabilities at Edinburgh.

Neurogene is also pursuing preclinical studies employing AAV-based gene therapy as a potential treatment for aspartylglucosaminuria, a rare lysosomal storage disorder and neurodegenerative disease. Aspartylglucosaminuria is caused by a variant in the AGA gene.

“SIRVE-ing” designer AAV vectors

AAV vectors continue to lead the field of gene therapy vectors for treating a variety of human diseases. There are more than 200 current interventional clinical trials in the United States. Recombinant AAV capsids feature the same sequence and structure that are seen in their wild-type counterparts, yet the genomes of recombinant AAVs lack all AAV protein-coding sequences and instead substitute gene expression cassettes. However, factors such as capsid content, cassette genome structure, and protein product all can interact with elements of the host’s immune system.

Kriya Therapeutics provides a platform for rational vector design, analytical characterization, and scalable manufacturing. “We are aiming to deliver the next generation of gene therapies, utilizing computational tools to methodically design vectors and efficient manufacturing systems to make them at scale,” says Shankar Ramaswamy, MD, the company’s co-founder and CEO.

The company’s intelligent vector design platform, SIRVE (System for Intelligent Rational Vector Engineering), couples sophisticated computational tools developed in-house with the latest understandings in the field of AAV biology. Ramaswamy elaborates, “There is no one size that fits all in recombinant AAV vector design. You have to design the best possible vectors and select the right targets with modularity in mind.”

The overall goal of the SIRVE platform is multifold: to reduce immunogenicity through targeted sequence modification; to engineer cassettes for optimal expression; to improve tissue specificity through design and targeted delivery; and to enhance manufacturability of the final product.

The company’s initial pipeline includes gene therapy programs for the treatment of diabetes, ophthalmic diseases, and solid tumors. However, Ramaswamy notes that Kriya aims to deploy its technology and manufacturing platform more broadly to address a range of diseases across therapeutic areas. Kriya recently opened a 51,350-square-foot manufacturing facility located in Research Triangle Park, NC.

“Manufacturing is critical to success in gene therapy,” he explains. “This facility will support critical activities in manufacturing from early research through commercial launch across a number of products. Additionally, we believe our technology-enabled manufacturing platform makes us a partner of choice to help translate promising research in gene therapy coming out of academia.”

When Ramaswamy looks into his crystal ball, he sees an exciting future: “We are at a tremendous inflection point as a field. AAV-based gene therapy holds incredible promise, and we hope to help drive innovations to unleash its full potential.”