Major Advance in Gene Therapy for Hemophilia B
As reported by the New York Times on December 10th and by a wide variety of other media outlets, medical researchers in Britain have successfully used gene therapy to treat six individuals with Factor IX deficiency also known as hemophilia B. The results represent a major advance not only in the treatment of hemophilia but also in the field of gene therapy which has experienced many setbacks and false starts over the last twenty years.
According to the Times, “the general concept of gene therapy — replacing the defective gene in any genetic disease with the intact version — has long been alluring. But carrying it out in practice, usually by loading the replacement gene onto a virus that introduces it into human cells, has been a struggle. The immune system is all too effective at killing the viruses before the genes can take effect.”
“The success with hemophilia B, reported online Saturday in The New England Journal of Medicine, embodies several minor improvements developed over many years by different groups of researchers. The delivery virus, carrying a good version of the human gene for the clotting agent known as Factor IX, was prepared by researchers at St. Jude Children’s Research Hospital in Memphis. The patients had been recruited and treated with the virus in England by a team led by Dr. Amit C. Nathwani of University College London; researchers at the Children’s Hospital of Philadelphia monitored their immune reactions.”
“Dr. Nathwani and his team reported that they treated the patients by infusing the delivery virus into their veins. The virus homes in on the cells of the liver, and the gene it carries then churns out correct copies of Factor IX. A single injection enabled the patients to produce small amounts of Factor IX, enough that four of the six could stop the usual treatment, injections of Factor IX concentrate prepared from donated blood. The other two patients continued to need concentrate, but less frequently."
“The patients have continued to produce their own Factor IX for up to 22 months, said Dr. Edward G. D. Tuddenham, director of the Hemophilia Center at the Royal Free Hospital in London. One patient, a geologist, had a good response at first, but his level of Factor IX has declined to 1 percent of normal, the level at which the disease kicks in.We attribute this to the fact that he had an inflammation, and although we treated it promptly, we should have been quicker off the mark,” Dr. Tuddenham said.
“Twenty more patients will be treated to assess the best dose of the virus, the goal being the highest dose that does not set off an immune system attack, Dr. Tuddenham said. “We are pretty close to the sweet spot,” he said. If all goes well, a genetic treatment for hemophilia B “could be available for widespread use in a couple of years.”
Stanford Studies Confirm that Hemophilia B is an Excellent Candidate for Gene Therapy
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"We demonstrated prolonged therapeutic levels of hFIX in this knockout mouse model of hemophilia B over a 6-month time" according to Dr. A. Keravala and colleagues at the Stanford University School of Medicine. "Additionally, we observed sustained FIX activity in plasma and phenotypic correction of bleeding after tail clip in phiC31-treated mice" The researchers concluded: "These studies suggest the possibility that a similar approach in large animals and humans could lead to a simple and successful gene therapy for hemophilia."
For additional information, contact A. Keravala, Dept. of Genetics, Stanford University School of Medicine, Stanford, CA, United States.
New Technique Cures Hemophilia in Mice
Using an innovative gene therapy technique called genome editing that hones in on the precise location of mutated DNA, scientists have treated the blood clotting disorder hemophilia in mice. This is the first time that genome editing has been done in a living animal and achieved clinically meaningful results. As such, it represents an important step forward in the decades-long scientific progression of gene therapy whereby a genetic condition is treated by correcting a problematic DNA sequence. In this new study, researchers used two versions of a genetically engineered virus - one carrying enzymes that cut DNA in an exact spot and one carrying a replacement gene to be copied into the DNA sequence. All of this occurred in the liver cells of living mice.
“Our research raises the possibility that genome editing can correct a genetic defect at a clinically meaningful level,” said the study leader, Katherine A. High, MD, a hematologist and gene therapy expert at The Children’s Hospital of Philadelphia. High, a Howard Hughes Medical Institute Investigator, directs the Center for Cellular and Molecular Therapeutics at Children’s Hospital, and has investigated gene therapy for hemophilia for more than a decade.High’s research, a collaboration with scientists at Sangamo BioSciences, Inc., makes use of genetically engineered enzymes called zinc finger nucleases (ZFNs) that act as “molecular word processors”, editing mutated sequences of DNA. Scientists have learned how to design ZFNs custom-matched to a specific gene location. ZFNs specific for the factor 9 gene were designed and used in conjunction with a DNA sequence that restored normal gene function lost in hemophilia.
By precisely targeting a specific site along a chromosome, ZFNs have an advantage over conventional gene therapy techniques that may randomly deliver a replacement gene into an unfavorable location, bypassing normal biological regulatory components controlling the gene. This imprecise targeting carries a risk of “insertional mutagenesis,” in which the corrective gene causes an unexpected alteration, such as triggering leukemia.
In the current study, the researchers used genetic engineering to produce mice with hemophilia B, modeling the disease in people. Before treatment, the mice had no detectable levels of clotting factor IX.
Previous studies by other researchers had shown that ZFNs could accomplish genome editing in cultured stem cells that were then injected into mice to treat sickle cell disease. However, this ex vivo approach is not feasible for many human genetic diseases, which affect whole organ systems. Therefore the current study tested whether genome editing was effective when directly performed in vivo (in a living animal).
High and colleagues designed two versions of a vector, or gene delivery vehicle, using adeno-associated virus (AAV). One AAV vector carried ZFNs to perform the editing, the other delivered a correctly functioning version of the F9 gene. Because different mutations in the same gene may cause hemophilia, the process replaced seven different coding sequences, covering 95 percent of the disease-carrying mutations in hemophilia B.
The researchers injected mice with the gene therapy vector, which was designed to travel to the liver, where clotting factors are produced. The mice that received the ZFN/gene combination then produced enough clotting factor to reduce blood clotting times to nearly normal levels. Control mice receiving vectors lacking the ZFNs or the F9 minigene had no significant improvements in circulating factor or in clotting times.
The improvements persisted over the eight months of the study, and showed no toxic effects on growth, weight gain or liver function, clues that the treatment was well-tolerated.
“We established a proof of concept that we can perform genome editing in vivo, to produce stable and clinically meaningful results,” said High. “We need to perform further studies to translate this finding into safe, effective treatments for hemophilia and other single-gene diseases in humans, but this is a promising strategy for gene therapy.” She continued, “The clinical translation of genetic therapies from mouse models to humans has been a lengthy process, nearly two decades, but we are now seeing positive results in a range of diseases from inherited retinal disorders to hemophilia. In vivo genome editing will require time to mature as a therapeutic, but it represents the next goal in the development of genetic therapies.”
Source: Children's Hospital of Philadelphia Press Release, June 27, 2011
Michigan Researchers Develop Hemophilia-Specific Stem Cell Line
Researchers from the University of Michigan (U-M) in Ann Arbor have developed the state’s first embryonic stem cell lines that carry genes linked to specific inherited diseases, including hemophilia.
On April 4, U-M announced the creation of two stem cell lines: one carries the gene for hemophilia B (factor IX deficiency) and the other for Charcot-Marie-Tooth disease, a neurological disorder that causes progressive degeneration of the foot, lower leg and hand muscles.
Stem cells are unspecialized cells that can renew themselves for prolonged periods. They can also develop into many different cell types, making them a potentially renewable source of replacement cells that could be used in the future to treat many conditions. The creation of such stem cell lines will open the door to an enhanced understanding of the origin and progression of congenital disorders, and hopefully to new treatments based on those findings. “These stem cell lines hold so much promise for medical science, and for this reason, they will be of tremendous interest to researchers around the world,” said Eva L. Feldman, MD, PhD, director of U-M’s A. Alfred Taubman Medical Research Institute.
Access to embryonic stem cells was first made possible in Michigan in November 2008, when voters approved Proposal 2, a state constitutional amendment. The law allows investigators to generate new lines from unused embryos donated by fertility clinics. Instead of discarding the embryos, which in some instances carry the genes responsible for congenital disorders, scientists now have a new approach for advancing research.
The amendment led to a partnership between U-M’s Consortium for Stem Cell Therapies (CSCT) and Detroit-based Genesis Genetics, a company specializing in pre-implantation genetic diagnosis (PGD), a test used to identify days-old embryos carrying disease-causing genetic mutations. This partnership now gives patients the option of donating embryos that test positive for a genetic disorder to the CSCT.
While the use of disease-specific embryonic stem cell lines looks promising, scientists are still in the relatively early stages of investigation. It will take years of preclinical and clinical research before actual treatments for diseases, such as hemophilia, become available.
“We are producing tools that can be of immeasurable aid to scientists studying such disorders as hemophilia and Huntington's disease. And we are just beginning to scratch the surface of this new scientific frontier,” said A. Alfred Taubman, founder and chair of the A. Alfred Taubman Medical Research Institute.
Source: University of Michigan news release dated April 4, 2011
FDA Approves Treatment for Factor XIII Deficiency
The U.S. Food and Drug Administration (FDA) has approved Corifact™, a plasma-derived factor XIII product, for the routine prophylactic treatment of congenital factor XIII (FXIII) deficiency. The FDA approval was made after positive results of a clinical study of 14 patients with congenital FXIII deficiency.
FXIII deficiency is a rare disease that affects 1 out of every 3 to 5 million people in the U.S., or approximately 150 people. The condition is characterized by blood that clots normally, but the clots are unstable, so bleeding recurs. FXIII deficiency can cause umbilical cord bleeding in some newborns, soft tissue bruising, mucosal bleeding, and potentially fatal intracranial hemorrhage (ICH). Studies have shown that 25% to 60% of people with FXIII deficiency experience at least one ICH during their lifetime.
Corifact™, the only FXIII concentrate approved in the U.S., received orphan drug designation from the FDA’s Office of Orphan Products Development. This allows for accelerated approval, so that drugs or biologics become available to patients with rare, life-threatening diseases who need effective treatments. More than 1,400 drugs and biologics have been designated as orphan drugs. Since 1983, more than 250 of them have been approved for marketing.
“This product helps fill an important need,” said Karen Midthun, MD, director of the FDA’s Center for Biologics Evaluation and Research. Prior to the drug’s approval, patients with FXIII deficiency were treated with cryoprecipitate or fresh frozen plasma. Corifact is given intravenously every 28 days. The most common side effects are allergies and rashes, chills, fever, joint pain, headache and elevated liver enzymes.
According to a CSL press release, Corifact™ is already available for use in 12 countries worldwide under the trade name Fibrogammin®-P.
Sources: FDA news release date February 17, 2011, and CSL Behring news release dated February 18, 2011
FXIII deficiency is a rare disease that affects 1 out of every 3 to 5 million people in the U.S., or approximately 150 people. The condition is characterized by blood that clots normally, but the clots are unstable, so bleeding recurs. FXIII deficiency can cause umbilical cord bleeding in some newborns, soft tissue bruising, mucosal bleeding, and potentially fatal intracranial hemorrhage (ICH). Studies have shown that 25% to 60% of people with FXIII deficiency experience at least one ICH during their lifetime.
Corifact™, the only FXIII concentrate approved in the U.S., received orphan drug designation from the FDA’s Office of Orphan Products Development. This allows for accelerated approval, so that drugs or biologics become available to patients with rare, life-threatening diseases who need effective treatments. More than 1,400 drugs and biologics have been designated as orphan drugs. Since 1983, more than 250 of them have been approved for marketing.
“This product helps fill an important need,” said Karen Midthun, MD, director of the FDA’s Center for Biologics Evaluation and Research. Prior to the drug’s approval, patients with FXIII deficiency were treated with cryoprecipitate or fresh frozen plasma. Corifact is given intravenously every 28 days. The most common side effects are allergies and rashes, chills, fever, joint pain, headache and elevated liver enzymes.
According to a CSL press release, Corifact™ is already available for use in 12 countries worldwide under the trade name Fibrogammin®-P.
Sources: FDA news release date February 17, 2011, and CSL Behring news release dated February 18, 2011
