random mutations than occur during the normal life of a cell—or that the mutations they might incur will have any bearing on health. He uses Li-Fraumeni Syndrome as an example. Even with a damaged p53 gene that should let tumors proceed unchecked, people born with Li-Fraumeni sometimes go years, even into adolescence, before developing a detectable cancer.
In other words, people working on therapeutics may not always need to know exactly where, and how often, their gene-editing tools are making unintended cuts. There are degrees of understanding, and of risk, in every therapeutic undertaking. Regulators charged with public safety know this. Patients with life-threatening diseases know this. Investors who back cutting-edge biotech startups know this.
As Corn builds out his lab at the new Innovative Genomics Initiative center on the UC Berkeley campus, he says he also wants to foster a “deeper conversation beyond these three papers” in Nature Biotech. (The third study, from scientists in Southern California and China, took a similar approach to Joung and colleagues but instead of an oligonucleotide used a defanged lentivirus as the “tag” that was taken up when the cell repaired its DNA.)
Corn agrees with Porteus that early worries about off-target effects “haven’t played out yet, but I don’t want to get into a situation where we do things too fast in patients.”
Still, every gene therapy or editing program that advances in the clinic under regulatory watch gives everyone more confidence about, in Rumsfeldian terms, the known unknowns. As mentioned previously, Sangamo has received the FDA’s blessing to test two of its therapies in humans. The company gets high praise from its peers for characterizing—understanding and describing—well known off-target effects of its zinc finger technology. “They don’t know the comprehensive spectrum, but they know the critical ones,” says Caribou Biosciences chief scientific officer Andy May, whose company, cofounded by Berkeley’s Doudna, is building a suite of CRISPR/Cas9 tools for human therapeutics, agriculture science, and more. (It has exclusively licensed the therapeutic uses of its tools to Intellia Therapeutics of Cambridge, MA, as I wrote about here.)
CEO Edward Lanphier and other Sangamo officials have described to me in the past how they have developed tools and methods to minimize off-target hits with their zinc-finger therapies. And they have questioned whether CRISPR/Cas9, which uses a less complicated guide to move its nucleases—its enzymatic scissors—into place, will ever reach the same level of specificity. (Sangamo officials did not return requests for comment for this article.)
Will the quality control tools soon be good enough for drug developers to use? Joung says he thinks GUIDE-Seq would help developers do two things: choose the right guide RNAs for their targeted gene, and after the cells are edited, serve as a check for unwanted mutations.
May, who as an Intellia board member was privy to that company’s landmark deal with Novartis (NYSE: [[ticker:NVS]]) to explore CRISPR/Cas9 in Novartis’s CAR-T immunotherapy program, wants to see more work from GUIDE-Seq and the other two systems. “All have their pros and cons,” he says. “None are unbiased.” The next step, he says, is for the systems to test a wider array of guides and scissors: “To understand the phenomenon, you need to use a much larger set.”
