BY JON HOLMLUND
A couple of gene-editing news items from this week’s science literature:
First, Nature reports that a group in my “back yard,” at the University of California San Diego, has tested gene editing using the CRISPR approach in mice. Recall that CRISPR is an acronym for a particular molecular mechanism, first discovered in bacteria, that is particularly efficient—though not perfectly so!—at editing genes. The idea is to find a “bad” gene that you’d like to replace, for example to prevent or treat a disease, and edit it to be the normal version of that gene.
The kicker in this particular case in mice is that it tested something called “gene drive.” In classical genetics, humans (and other higher organisms) have two copies of each gene. In sexual reproduction each parent passes one copy of the gene to offspring, so the chance of a particular gene being handed down is 50%.
“Gene drive” is a technique designed to change those odds, and make a particular gene “selfish,” and much more likely to be passed on. In fact, the idea is that transmission would be 100%, or nearly so. If that worked, then a new gene would soon take over a population of organisms, and every member would, in a few generations, have that gene.
Why might that be a good thing? Suppose you are interested in pest control, and you could use the technique to make, say, mosquitoes infertile. Then they would soon all die off. Or if you had some other “desirable” characteristic, you could make it so all members of a species (rodents? Cattle? People?) have that characteristic. Assuming it’s determined by one gene, that is.
And assuming that the technique works. In the mouse experiment, efficiency was only 73%.
That’s probably good news. This is one of those techniques that could have serious unintended consequences if tried in the field. Scientists have been warning about that. It looks like it’s a way off, but something else to fret about.
The second item involves a clinical trial to treat sickle cell anemia. In this one, blood stem cells from a person with the disease are removed from the bloodstream and gene-edited outside the body to make hemoglobin that is not as damaged as in the disease (SCA is an inherited disease in which the red blood cells have abnormal hemoglobin that doesn’t carry oxygen well). Then the altered cells become the therapy, and are given back to the patient.
The FDA has put a “clinical hold” on this clinical trial. Exactly why has not been publicly disclosed (it doesn’t have to be), and it sounds like the trial itself hadn’t started yet, but that the company developing it was getting ready to start. This is, in my view, an approach to gene editing that does not pose special or particularly worrisome ethical issues, because the genetic changes are done on “adult” stem cells to treat an existing individual with a disease in a way that would not entail transmission of altered genes to future generations.
And, probably, it’s a case of “this too shall pass,” and the FDA’s concerns will be answered and the trial will proceed.
But check out the sidebar reporting this in Nature Biotechnology. If you follow the link you will probably get a prompt asking for payment but I was able to sneak a free read on my screen. If you go there, read below the separate quote (itself picked up from The New York Times) from Dr. George Church of Harvard: “Anyone who does synthetic biology [engineering of biological organisms] should be under surveillance, and anyone who does it without a license should be suspect.” Apparently he said that in response to “the publication of an experiment recreating a virus that has engendered fears that such information could be used to create a bioweapon. ”
The old “dual use problem,” eh? We should really fret about that.