seven weeks out are producing 4 and 8 percent of normal Factor VIII, while another patient is producing 21 percent after six weeks.
Carter says so far that there appears to be a spike in Factor VIII expression around nine weeks after treatment, which means BioMarin’s numbers could look better soon. Still, it’s an unknown. “The only way we can really assess the variability is to follow all of these people out longer,” he says.
The trial’s lead investigator John Pasi, a professor at Barts and The London School of Medicine and Dentistry, says all six patients on high doses have been off preventative treatment since achieving “measurable” levels of Factor VIII. One of those patients had a bleed early on in the trial, but that was before the gene therapy kicked in, he said.
Like other companies developing gene therapies for hemophilia, BioMarin is reporting a rise in patients’ liver enzyme levels, a sign of an immune system response to the treatment.
The potential problem is alleviated with steroids, but it’s worth watching going forward. In BioMarin’s trial, according to Pasi, steroids haven’t temporarily caused the expression of the clotting factor to drop, as they have in some other hemophilia B studies.
Biomedical researchers and drug developers have wrestled for decades to turn gene therapy—a method of using viruses to shuttle genetic fixes into patients—into a weapon against hemophilia, as I wrote last year.
But the technology has advanced faster for hemophilia B and its smaller population than hemophilia A. Researchers at St. Jude Children’s Research Hospital in Memphis, TN, and University College London published a study in the New England Journal of Medicine in 2011 that many consider proof that the method can work. Baxalta and UniQure (NASDAQ: [[ticker:QURE]]) have already produced early clinical data in hemophilia B, and several others like Spark Therapeutics (NASDAQ: [[ticker:ONCE]]) and Dimension Therapeutics (NASDAQ: [[ticker:DMTX]]) are following closely behind.
Hemophilia A has been a tougher challenge because the gene for the Factor VIII protein is larger than the gene for Factor IX, the protein that hemophilia B patients lack. The larger the gene, the harder it is to pack into a virus and deliver to patients. Carter says BioMarin has taken out part of the gene to make it small enough to fit. So far, that’s given BioMarin the chance to be the first to the finish line with a gene therapy in hemophilia A. No one else has reached clinical testing.
“It’s a really steep learning curve,” Pasi says. “But it’s a very exciting learning curve to be on.”
