Abstract
The team carried out a one-time intramuscular administration of adeno-associated virus serotype 1 (AAV1) vector encoding glucokinase and insulin in the rear legs of five diabetic dogs. The therapy “resulted in normalization of fasting glycemia, accelerated disposal of glucose after oral challenge, and no episodes of hypoglycemia during exercise for >4 years after gene transfer,” the researchers wrote.
Results were better than those of dogs treated with exogenous insulin therapy or gene transfer for insulin only. The team said its study will provide the basis for a future clinical veterinary study in companion dogs with diabetes, with that study's results expected to greatly help define the safety and efficacy profile of the team's eventual trial of the therapy in humans.
“One possible limitation of the results presented here is that the dog model of diabetes used in this study does not fully mimic the immunological state of type 1 diabetic patients. However, while future studies in autoimmune models of diabetes are warranted, studies in mice, dogs, and humans would suggest that targeting muscle with AAV vectors may at least partially escape immune recognition,” the team stated in the study.
The research team previously increased glucose uptake and corrected hyperglycemia in diabetic mice by gene therapy, producing promising results by generating a glucose sensor in skeletal muscle through coexpression of glucokinase and insulin.
Leading the team was Fàtima Bosch, leader of the research team and head of Center of Animal Biotechnology and Gene Therapy (CBATEG) at Spain's Universitat Autònoma de Barcelona (UAB). Also involved in the study were researchers from UAB's Departments of Biochemistry and Molecular Biology, Medicine and Animal Surgery, Faculty of Veterinary Science, and Department of Animal Health and Anatomy; as well as the Spanish Biomedical Research Center in Diabetes and Associated Metabolic Disorders (CIBERDEM), and two U.S. institutions, Children's Hospital of Philadelphia and Howard Hughes Medical Institute.
Pexa-Vec is an oncolytic Wyeth strain vaccinia virus with disrupted thymidine kinase gene (tk) for cancer selectivity. The immunotherapy is designed to rapidly debulk tumors via tumor cell lysis, activate an antivascular effect with rapid tumor vascular knockout, and induce a durable immune response against tumors.
Thirty subjects were randomized into the low- and high-dose groups and received three Pexa-Vec treatments over the course of 4 weeks. The results demonstrated that Pexa-Vec treatment at both doses resulted in a reduction in tumor size and decreased blood flow in tumors. The study showed a statistically significant dose-dependent overall survival benefit with a median overall survival of 14.1 months for the high-dose group compared with 6.7 months for the low-dose group.
At both low and high doses, Pexa-Vec treatment induced an immune response against the tumor, as seen by antibody-mediated tumor cell toxicity. Pexa-Vec was well tolerated at both high and low doses, with the most frequent adverse events consisting of fever lasting less than 24 hr.
“This Nature Medicine publication highlights the unique possibility of a meaningful survival benefit combined with short-term, transient and manageable side effects,” said Tony Reid, M.D., Ph.D., professor of medicine at the University of California, San Diego and colead author of the paper.
Further clinical trials with JX-594 for the treatment of advanced solid tumors are warranted, the team concluded. Pexa-Vec has been safely administered to more than 200 patients and is currently in phase 2b clinical development for the treatment of advanced HCC, and is also being evaluated in other solid tumors.
The study was one of two published on consecutive days that detailed the potential of Pexa-Vec. On February 11, Jennerex published in Cancer Research (Breitbach et al., 2013) study results demonstrating the ability of Pexa-Vec to disrupt the blood supply to a tumor.
“Based on this research, it is clear that Pexa-Vec selectively targets and infects tumor-associated endothelial cells, as well as cancer cells, resulting in disruption of the blood supply and destruction of the tumor, a finding that has not been reported in patients with similar agents,” says Caroline Breitbach, director of clinical and translational research at Jennerex and lead author of the paper.
The study was a follow-up to the 2008 study by the NIH National Eye Institute (NEI), in which 15 patients received one or more injections of genetically modified RPE65-AAV vector into select areas of the retina of one eye. The other eye served as a control. Within days after treatment, vision in the participants' treated eye significantly improved. A 3-year follow-up study by the team in 2011 (Jacobson et al., 2011) showed that visual gains were retained.
The latest follow-up study, however, focused on whether the gene therapy stopped or slowed the degeneration of photoreceptors. Artur V. Cideciyan, Ph.D., a professor of ophthalmology at the University of Pennsylvania Scheie Eye Institute, led the research team in estimating the rate of thinning of the photoreceptor layer in the retinas of treated and untreated eyes over a period lasting up to 6.5 years, using optical coherence tomography (OCT), a noninvasive technique.
Using OCT, the scientists were able to accurately measure the thickness of the photoreceptor cell layer in treated and untreated eyes as well as of untreated areas within treated eyes. The scientists also measured the rate of thinning in an additional eight participants with LCA who were not treated with gene therapy.
“Based on our latest study, photoreceptor cell loss in eyes treated with RPE65 gene therapy continues at a rate no different than the expected natural progression of the disease,” said Samuel G. Jacobson, M.D., Ph.D., professor of ophthalmology, also at the University of Pennsylvania Scheie Eye Institute, and a coauthor of the study, in a statement (National Eye Institute, 2013). “When compared, the photoreceptor cell layers of treated and untreated eyes became thinner at a similar pace, decreasing at about 9.6% a year.”
Researchers aren't sure why the retinal degeneration continued, but speculated that the lack of a normal-functioning RPE65 gene promotes cellular stress and the subsequent onset of apoptosis. Once initiated, the cell death cannot be reversed simply by restoring RPE65 gene function. The report also showed that RPE65 gene therapy did not halt photoreceptor cell degeneration in animals if administered at a time in the disease process comparable to that in humans.
“The practical implication of our results is that human treatments of RPE65-LCA should address the need to slow or arrest the retinal degeneration that is present and ongoing in these patients, no matter how young they are when considered for enrollment in clinical trials,” the team concluded.
Ricki Lewis, who chronicled 8-year-old Corey Haas' experience in receiving the gene therapy and aftermath in the book The Forever Fix: Gene Therapy and the Boy Who Saved It, wrote in her blog (
Dogs with LCA2, Lewis noted, have a few years when their rods and cones are just fine, and stay that way if gene therapy occurs during that period. Gene therapy done after the rods and cones have begun to decline can't save them.
“Unlike dogs, in a baby with LCA2 the photoreceptors are already dying. The dogs in the trial may have been too young to exactly mimic the situation in people,” Lewis said. “Perhaps gene therapy in people should be done as early as possible—which researchers had already suspected because of the increasing severity of the disease with age.”
Without comment, the high court on January 7 turned back a certiorari plea by the coplaintiffs in Sherley v. Sebelius—James L. Sherley, M.D., Ph.D., an adult stem cell researcher at Boston Biomedical Research Institute (Watertown, MA), and Theresa Deisher, Ph.D., founder, CEO, and R&D director at AVM Biotechnology (Seattle, WA).
Drs. Sherley and Deisher filed suit in 2009 against the U.S. Department of Health and Human Services (HHS), HHS Secretary Kathleen Sebelius, the NIH, and NIH Director Francis S. Collins, M.D., Ph.D., seeking to overturn the NIH 2009 Guidelines on Human Stem Cell Research. The guidelines were intended to codify President Barack Obama's executive order that lifted restrictions on hESC research enacted by his predecessor, President George W. Bush.
The resulting federal case produced one major surprise alarming to the biopharma industry in 2010, when Royce C. Lamberth, Chief Judge of the U.S. District Court for the District of Columbia, issued a preliminary injunction temporarily blocking federal funding of hESC research. He reasoned at the time that the coplaintiffs stood more than a chance of overturning the NIH guidelines. However, the preliminary injunction was overturned and remanded back to Judge Lamberth, who issued a 38-page decision siding with the HHS, Sebelius, and Dr. Collins. It was that decision that the Supreme Court upheld.
In so doing, the justices brushed off the coplaintiffs' contention, expressed by Drs. Sherley and Deisher in a court filing, that: “The federally sponsored hESC research that the guidelines support inevitably creates a substantial risk—indeed, a virtual certainty—that more human embryos will be destroyed in order to derive more hESCs for research purposes.”
That risk, they continued, violates the Dickey-Wicker Amendment of 1996, which says it is illegal to use federal funds for research “in which a human embryo or embryos are destroyed, discarded, or knowingly subjected to risk of injury or death greater than that allowed for research on fetuses in utero.”
Although the trial is headquartered in Toronto, a major role will be played by physicians and scientists in Calgary, where the laboratory at Foothills Medical Centre has specialized expertise in the stem cell-filtering process to be used in the clinical trial. Technologists led by Nicole Prokopishyn, Ph.D., director of the Calgary Laboratory Services Cellular Therapy Laboratory, have processed the blood of donor patient Christopher Armstrong, a 34-year-old Calgarian with Fabry disease.
For key initial experiments in the trial's current preclinical phase, the researchers isolated from Armstrong's blood nearly a billion CD34+ stem cells, which will be sent to the laboratory of Jeffrey Medin, Ph.D., at the University Health Network (Toronto, ON). Dr. Medin—principal investigator of the pan-Canada team supporting the trial—will use a lentivirus to insert a new, working copy of the GLA gene into Armstrong's CD34+ cells, where the working copy will direct the production of the missing enzyme.
“When the corrected cells circulate in the blood, they also secrete the enzyme, which is then taken up by unmodified cells. This effectively extends the therapy afforded by the modified stem cells,” Dr. Medin, who is also a professor in the Department of Medical Biophysics at the University of Toronto, said in a statement. Dr. Medin's laboratory performed gene therapy in mice that yielded promising results, leading to the trial.
As part of the preclinical phase, researchers also hope to demonstrate that Armstrong's corrected stem cells are able to provide a source of enzyme in a specially adapted mouse model of Fabry disease. The second phase will repeat the experiment, using a new donor. Once the preclinical experimental results have satisfied the regulatory requirements of Health Canada, the team aims to treat the first human patient with Fabry disease, which they estimate will be within 2 years.
The project is being funded by the Canadian Institutes of Health Research and the Kidney Foundation of Canada.
“With the approval of the first gene therapy in 2012, the CAT is paving the way for the approval of similarly complex medicines in the future, as more gene therapies for rare diseases, personalized medicines and nano-medicines are on their way,” CAT Chair Christian Schneider said in a statement.
Acknowledging that the number of MAAs for advanced therapies is still limited, the CAT added that the research and development pipeline is large, based on an analysis of ATMPs under clinical evaluation published in 2012 in the journal Molecular Therapy. The amount of scientific advice provided to companies by the CAT and the number of classified ATMPs are also signs that more of them are on the way to regulators for review.
“As a consequence, a high number of MAAs for advanced therapies is expected over the next 5 to 10 years,” the CAT concluded.
Among ATMPs under development, according to the CAT, three-quarters are cell-based medicinal products whereas the rest represent gene therapies. For the most part, these products are being developed for cancers, cardiovascular diseases, and hematology-related conditions. Also of interest, ATMPs are being developed mainly by noncommercial sponsors (60%) and micro-, small-, and medium-sized enterprises (38%), rather than biopharma giants.
This year, the CAT expects numbers of ATMPs similar to what it saw last year, when 17 applications were submitted for a scientific recommendation on advanced-therapy classification. The CAT classified 14 of these as ATMPs, compared with 12 submitted and 12 adopted in 2011.