Non-viral Gene Therapy Shows Promise in Hemophilia A Animal Models

Note: This story was updated Jan. 8, 2021, to clarify that the second set of experiments in mice and non-human primates used a research construct, not the gene therapy.

Generation Bio has announced new data showing that its investigational non-viral gene therapy platform can increase levels of the clotting protein factor VIII (FVIII) in mouse and non-human primate models of hemophilia A.

The data support the selection of a final candidate therapy for clinical development later this year, the company said in a press release.

Hemophilia A is caused by missing or defective FVIII due to mutations in the gene that provides instructions to make this protein. Conceptually, the aim of gene therapy for hemophilia A is to deliver a non-mutated version of this gene to the body’s cells, thereby allowing the body to produce functional FVIII.

Most gene therapies in development deliver their genetic payload using an engineered virus. However, this approach has several drawbacks, including cost and safety concerns.

Rather than a virus, Generation Bio’s platform uses closed-ended DNA (ceDNA) delivered via a cell-targeted lipid nanoparticle (ctLNP) system;  basically, a special coating of fat molecules containing a molecule called N-acetyl galactosamine is used to get the DNA into liver cells. The company previously received $110 million in funding to facilitate the development of its platform.

Now, the company reports that administering the construct to mice engineered to mimic symptoms of hemophilia A results in a dose-dependent increase in human FVIII expression (production). Specifically, mice given the therapy at a dose of 0.5 mg/kg had mean FVIII expression of 9% of normal after 10 days. A dose of 1 mg/kg resulted in 16% of normal, and a dose of 2 mg/kg resulted in 23% of normal.

According to Generation Bio, the expression levels seen in mice correspond to, or exceed, the threshold that has been clinically proven to prevent serious bleeds in patients, which is 5% of normal levels.

Another set of experiments tested a research construct in mice and in non-human primates, which are more biologically similar to humans than mice. After five days, treatment with the 2 mg/kg dose resulted in approximately 3% of normal FVIII levels in mice and 1% in primates.

This expression ratio across species is similar to what has been reported for other LNP-based systems, according to Generation Bio.

Doses of the therapy up to 2 mg/kg (the highest tested) were well-tolerated in both the mice and non-human primates. No adverse side effects were found.

“These data are significant milestones as we create a new class of genetic medicine to overcome the limitations of viral gene therapy,” said Geoff McDonough, MD, president and CEO of Generation Bio.

Generation Bio previously reported that a single dose of the gene therapy approach results in durable factor IX (FIX) expression in mice, with expression of the protein in the liver lasting for months after administration. FIX is the protein missing or defective in hemophilia B.

In addition, redosing five weeks after the initial dose has been shown to increase FIX activity levels in mice, from 5–10% initially up to 10–20% after redosing. Notably, redosing typically is not feasible with virus-based therapies, because the body’s immune system will generate a response to the virus after the first exposure (the same basic biological principle by which vaccines work).

“We have now demonstrated in preclinical studies the key features of our platform, including durability, titration and redosing and, importantly, translation of our novel, liver-directed ctLNPs. With predictable species translation and potent murine expression levels in line with our target product profile, we are on track to initiate [studies that would support applications to start clinical trials] for our hemophilia A program this year,” McDonough said.

Added Marisa Stanton, PhD, the company’s chief scientific officer: “Non-viral gene therapy has been an elusive goal for scientists for more than 40 years. Today’s data are a significant step toward reaching that objective for the first time.

“Lipid nanoparticles have demonstrated remarkably predictable species translation from NHPs to patients,” Stanton said. “We believe the high levels of factor VIII expression in mice using our ceDNA development construct and the demonstrated translation of expression from mice to NHP for our ctLNP delivery system are important proof points for our platform.”