A few weeks ago, at a major conference on Human Genome Editing, He Jiankui announced that he had genetically modified human embryos using CRISPR, and that twin girls with modified genomes had been born.Since my General Genetics class was just about to cover CRISPR and mammalian genome modification, this was a perfect moment to incorporate this very interesting and important news directly into the class. CRISPRis now frequently in the news and I wanted to compareJiankui’s experiments with other methods that are used to modify human genes.
Usually human gene therapy is done very differently from what Jiankui did. First, usually only somatic cells—those that never give rise to sperm or eggs—are modified. This means that changes made in a patient are not transmitted to the patient’s children. But Jiankui changed the genome at a very early stage—in a fertilized egg. This means that the twin girls will pass their altered genes to any offspring they may later have. The researcher created a permanent change to the human race. This has never been done before, and is not legal in many countries, including the United States.
Second, usually genetic therapies are directed against disorders like cancer or genetically inherited diseases where modification of the genome of the patient’s cells is life-saving. In this case, Jiankui chose to modify a gene that would make the children resistant to the HIV virus that causes AIDS. Since AIDS is quite treatable now, some have questioned whether the risk associated with the genetic modification is worth the benefit of potential resistance to AIDS.
Finally,Jiankui used CRISPR to induce the mutation. CRISPR is a relatively uncontrolled process in a cell—the gene is ‘targeted,’ but we know that there are sometimes ‘off-target’ effects in which mutations in other parts of the genome occur as part of the procedure. Many scientists feel that our knowledge about and ability to control these off-target effects makes CRISPR too risky to use in the way that Jiankui did.
What happens next?
Dr.Jiankui has expressed the hope that he has opened the door to future endeavors in this area. However, many members of the scientific community are concerned that premature use of CRISPR in this way can create a backlash that will prevent more reasoned and controlled approaches from moving forward. That would be a real pity, as CRISPR has the potential to provide life-saving therapies for people with cancer or with serious genetically inherited diseases.