One year before the wave of CCR5 discoveries, a Seattle man named Timothy Ray Brown was diagnosed with HIV while studying in Berlin. He staved off the disease using the antiretroviral drug cocktail, but in 2006, after attending a wedding in New York, fell ill upon his return home. His doctor diagnosed anemia, but a painful biopsy revealed that Brown had acute myelogenous leukemia. The only treatment was a bone marrow transplant: fortunately, a search for potential donors turned up more than 250 matches. Brown’s hematologist had the idea to select a donor who had the defective CCR5 gene. On the list of prospects, donor number sixty-one possessed the Δ32 variant.
Brown didn’t want to be a guinea pig,25 but he signed up for a transplant. Three months after the operation in February 2007, the virus was undetectable in Brown’s blood and he ceased taking his HIV medications. After his leukemia returned, Brown had a second operation in February 2008. Doctors eventually declared him HIV-free with a normal T cell count.26 “My name is Timothy Ray Brown and I am the first person in the world to be cured of HIV,” the Berlin Patient proudly wrote.
Brown’s experience gave Sangamo a lot to chew on. Mutation repair was still the Holy Grail for many diseases but inactivating key genes could have important medical benefits in certain situations, including the one Ando was advocating. The goal was to attempt “to recreate this HIV-protective genotype in the cells of HIV-positive individuals, in the hopes of essentially creating a compartment of the immune system that is protected from HIV infection,” Urnov recalled.27
With Holmes leading the HIV program, Sangamo finally entered the clinic in 2009, in collaboration (as Ando had advocated) with Carl June, a leading gene therapy physician at the University of Pennsylvania. Five years later, Sangamo reported results on the first dozen HIV patients who had been treated with their own CCR5-edited T cells.28 The results were mixed: the therapy was safe and there was some evidence of an antiviral effect, enabling some subjects to remain off standard antiretroviral therapy. In 2015, Sangamo received approval from the U.S. Food and Drug Administration (FDA) to extend the concept from T cells to stem cells, with the goal of protecting other cellular compartments of the immune system from harboring HIV. To date, Sangamo has treated more than one hundred HIV patients.
While Sangamo is known as the zinc finger specialist, a French company has taken the TALEN gene-editing technology to the clinic. The CEO of Cellectis, André Choulika, thought CRISPR was “super cool” when he first heard about it, but decided to stick with TALENs, mostly for immunotherapies. “We found them to be more accurate, precise, and powerful, and we thought they would be safer for patients,” he says.29
Lanphier retired from Sangamo in June 2016 after twenty-one years, partly for health reasons but also because he felt it was time “to bring in the real pros.” On CNBC’s Mad Money, Jim Cramer asked Lanphier about CRISPR and Sangamo’s faith in the ZFN platform. “The key to human therapeutics is specificity—the ability to target exactly the gene you want and only that gene,” Lanphier replied. “That’s where zinc finger nucleases have a complete monopoly.”30 Years later, I asked Lanphier if he still felt the same way. “CRISPR is bacterial. It’s nonspecific. It’s immunogenic,” he said. “It’s a great research tool. It’s going to give a lot of visibility to genome editing. And when people actually want to use it therapeutically, that’s where they’ll end up talking to us.” It must have been a wrench to remove that vanity license plate. “Nobody can do it the way Sangamo does it, on this scale, with the kind of precision,” he said.
Before retiring, Lanphier launched therapeutic programs in blood disorders, including sickle-cell disease, beta thalassemia, and hemophilia. Ed Rebar came up with a clever strategy to switch on genes in the liver. Albumin, the most abundant protein in human blood, is produced by a gene that is extremely active in the liver. Rebar reckoned: what was to stop Sangamo from smuggling in a gene like a Trojan horse and taking advantage of this powerful albumin gene promoter? The method, dubbed in vivo protein replacement, or “invisible mending”, involved snipping the albumin gene in the first intron, plugging in a transgene into this “safe harbor,” and using the constitutive power of the albumin promoter to fire up the gene of interest. That fueled programs to target rare inherited disorders of genes normally expressed in the liver such as mucopolysaccharidosis (MPS) types I and II (also known as Hurler and Hunter syndromes, respectively) and hemophilia B.
On November 13, 2017, forty-four-year-old Brian Madeux climbed onto a bed in Room 1037—the Infusion Room—of the UCSF Benioff Children’s Hospital in Oakland. Dressed in a gray sweatshirt and khaki shorts, Madeux nervously watched a nurse hook up an IV. He was no stranger to hospitals, having endured more than two dozen surgeries for hernias, bunions, spinal, eye, and ear problems resulting from Hunter syndrome. Surrounded by doctors, nurses, and a film crew, he was about to become the first patient to receive a direct infusion of a gene-editing drug. “It’s kind of humbling,” he told the Associated Press.31
Madeux’s infusion took place on the centenary of the first description of his disease. Charles Hunter, a Scottish physician who had emigrated to Winnipeg, Canada, published a case report of two brothers, ages ten and eight, with a syndrome of physical abnormalities that would later bear his name.32 The brothers had several common features—undersized, large head, short neck, broad chest, easily winded. We now know the disease is caused by a deficiency of an enzyme called iduronate-2-sulphatase. Hunter syndrome patients are unable to break down two particular carbohydrates, which consequently accumulate in various tissues. Enzyme replacement treatments involve weekly infusions that can cost more than $100,000 per year. Madeux’s doctors hoped his treatment would stem the progression of his disease and serve as an inspiration for other patients. For the first few days, he felt weak and dizzy, later he suffered a partially collapsed lung (probably unrelated to the therapy). Encouragingly, his liver appeared to be functioning normally. More patients were enrolled, some receiving higher doses. But initial results were equivocal.
Lanphier’s successor, Sandy Macrae, is a Scottish physician who trained in the 1990s as a molecular biologist with the great Sydney Brenner. “My wife said it would never be of any use to me, and then this job came up,” Macrae jokes. After revising the name of the company to Sangamo Therapeutics, he began inking deals for different disease targets with big pharma partners. Sangamo wasn’t going to discard decades of expertise on ZFNs, but it is no longer just a zinc finger company. “If I was back doing my postdoc, I’d be using CRISPR,” Macrae admitted.
Rarely does a biotech CEO acknowledge mistakes or failures, but Macrae has done both. Success in clinical genome editing comes down to three things: editing, delivery, and biology. The Hunter syndrome story showed that the albumin promoter strategy works beautifully in cells and animal models, and appears safe in human patients. Any complications in the trials were due to the AAV vector that was used. The trial was a “remarkably unremarkable event,” Macrae said.33 But the boost in enzyme levels only proved significant in a patient who received the highest dose. He then developed a side effect called transaminitis, which shut down production of the enzyme. “We succeeded in the editing, but it wasn’t good enough for the biology,” Macrae said. A new effort in the clinic with improved vectors is underway.