Just a day and a half into this year’s World Stem Cell Summit in San Antonio and there have been numerous highlights. But a pair of sessions on gene editing grabbed the attention of many of the scientists at the meeting. One of the renown leaders in the field, Harvard’s George Church wowed the scientists, but I fear the heavy dose of scientific detail may have overwhelmed many of the patient advocates that make the attendee mix at this meeting special.
In 2013, Church first published results using a new gene-editing tool he helped perfect called CRISPR, and almost immediately it became the most talked-about tool for advancing stem cell research. As powerful as stem cells may be by themselves, in many situations, they become even more powerful—especially if you use them to deliver a gene that corrects an error in a patient’s cells. Before 2013 we had a few ways to edit genes in living cells and all were modestly effective at making the desired change and relatively specific in making only a few unwanted changes, called “off target” edits.
In some uses, particularly when cells are being modified in the lab for specific and small targets, these other editing techniques are probably OK. This is what several CIRM-funded teams (links) are doing with diseases like sickle cell anemia and HIV, where you can target blood-forming stem cells and even giving a small percentage the proper gene edit may be sufficient to cure the disease. But with something like muscular dystrophy where the gene editing would be required throughout the body and have to be done in the patient not in the lab, you need to improve the efficiency and precision.
After that first publication CRISPR was viewed as a home run in efficiency, taking the number of cells with the gene correction from a few percent to 50 percent or more. But it still had off-target effects. Yet only a year after the technology was introduced, a few teams developed so-called “next generation” CRISPR that comes close to perfect precision, causing an unintended edit in just one in a billion cells, by Church’s estimate.
I have never seen the full name of CRISPR spelled out in a scientific presentation, and after a visit to Wikipedia I know why. Here it is: Clustered Regularly Interspersed Short Palindromic Repeats. Basically, Church took advantage of something that occurs naturally in many bacteria. Just as we are susceptible to viruses, bacteria have their version known as phages. When those parasites integrate their DNA into the bacteria’s genes, part of the bacterial DNA forms CRISPRs that can partner with a protein called Cas to cut the phage DNA and keep the phage from hurting the host bacteria.
In a research setting, creating that “nick” in the DNA is the first step in harnessing CRISPR to insert a desired gene. So, that extreme precision in finding spots on our DNA where we want to create an opening for inserting a new gene became this valuable research tool. It can create a nick as precise as a single nucleotide base, the building blocks of our DNA.
Church and two additional speakers gave detailed descriptions about how the technology has improved and how it is being used to model disease today and is expected to be used to treat disease in the near future. An exciting future is in store.