In October, 2020, the Nobel Prize in Chemistry was awarded to two women for their discovery of a method in the field of genetics with far-ranging applications. The Nobel Committee, in its announcement, called their effort:
“Genetic scissors: a tool for rewriting the code of life”
“Emmanuelle Charpentier and Jennifer A. Doudna have discovered one of gene technology’s sharpest tools: the CRISPR/Cas9 genetic scissors. Using these, researchers can change the DNA of animals, plants and microorganisms with extremely high precision. This technology has had a revolutionary impact on the life sciences, is contributing to new cancer therapies and may make the dream of curing inherited diseases come true.”
This is exciting news, of course. First, some brief background. CRISPR stands for Clustered Regularly Interspaced Short Palindromic Repeats.
I’ll spare you the intricate story of how the research moved from food scientists studying the Streptococcus bacteria used to make yogurt (who knew?) to the revelations made by Doudna and Charpentier that won them the Nobel Prize.
But it’s explained very clearly in Vox: “A simple guide to CRISPR, one of the biggest science stories of the decade.”
Here’s an example:
“If you haven’t heard of CRISPR yet, the short explanation goes like this: In the past nine years, scientists have figured out how to exploit a quirk in the immune systems of bacteria to edit genes in other organisms — plants, mice, even humans. With CRISPR, they can now make these edits quickly and cheaply, in days rather than weeks or months. (The technology is often known as CRISPR/Cas9, but we’ll stick with CRISPR, pronounced ‘crisper.’)”
Another source writes that
“CRISPR offers the promise to cure any human genetic disease. Which are the candidates to be the first one?”
The author’s answer (with informative links):
- Cancer (a Chinese study is testing it with patients who have advanced esophageal cancer, and another CRISPR trial at the University of Pennsylvania is seeking to alter a molecule on the exterior of immune cells so they can find and attack tumors.
- Blood disorders. I discuss these below. (They should really be listed first, I believe, as you’ll see.)
- Blindness. As many hereditary forms of blindness result from a single mutation, CRISPR is believed able to readily target and change a single gene. One company is working on a therapy for the most common cause of inherited blindness in children: Leber congenital amaurosis.
- AIDS. CRISPR could be used to “cut the DNA of the HIV virus out of its hiding place in the DNA of immune cells,” thus hitting the virus when it’s inactive—apparently the reason that most therapies can’t completely clear the virus. The author cites other CRISPR approaches to combat HIV as well.
- Cystic fibrosis. “Researchers have proven that it is possible to use CRISPR in human lung cells derived from patients with cystic fibrosis and fix the most common mutation behind the disease.” The next step will be testing in humans, though the multiple mutations of CF will require differing methodologies.
- Muscular dystrophy. Mutations in the DMD gene result in progressive deterioration of muscles in affected children. Research in mice has demonstrated using CRISPR to fix the numerous mutations involved, and one group of US researchers found a way to get at “12 strategic ‘mutation hotspots’” involved in most of the roughly 3000 mutations contributing to the disease.
- Huntington’s disease. Since this devastating hereditary disease, tied to a single gene mutation, involves the brain, it will require especially careful application. Two approaches to increase the precision of CRISPR have been developed. US researchers have developed KamiCas9, a CRISPR carrying its own “self-destruct button,” and Polish researchers add an enzyme called nickase to CRISPR to increase its precision.
CRISPR Changes a Patient’s Life
Last year, NPR (National Public Radio) reported on a young woman they’d been following who’d received treatment using CRISPR. Victoria Gray, a Mississippi mother of four, had been suffering her entire life from sickle cell disease, a genetic blood disorder that can be severe. Millions of people are afflicted worldwide. In the US, more than 100,000 are stricken, including many African Americans.
Victoria Gray described its impact:
“Sometimes it feels like lightning strikes in my chest — and real sharp pains all over. And it’s a deep pain. I can’t touch it and make it better. Sometimes, I will be just balled up and crying, not able to do anything for myself….It’s horrible. When you can’t walk or..lift up a spoon to feed yourself, it gets real hard.”
Her life was filled with hospital visits, and she was unable to involve herself in her children’s lives and care as she had hoped.
When she heard about the possibility her condition might be improved or even cured via CRISPR, she was the first person in the US to volunteer.
Said Dr. Francis Collins, director of the National Institutes of Health:
“That first person is an absolute groundbreaker. She’s out on the frontier. Victoria deserves a lot of credit for her courage…All of us are watching with great anticipation.”
Her treatment was difficult. First was chemotherapy to prepare the bone marrow for the cells that would have their genes edited; that left Gray with fatigue and mouth sores inhibiting her ability to eat.
During a two-month hospital stay, doctors removed her blood’s bone marrow cells. Then, using the CRISPR “scissors,” they “edited” those cells, turning on a gene that allows the fetal hemoglobin protein to provide fetuses with oxygen in the womb. Once the baby’s born, the genetic switch stops the red blood cells from making fetal hemoglobin.
In this treatment, the restoration of fetal hemoglobin production is expected to take over from the adult-hemoglobin sickle cells, which are deformed and unable to deliver oxygen, thereby damaging organs and threatening life.
Dr. Haydar Frangoul, the clinician in charge of Gray’s care, said:
“We are trying to introduce enough…fetal hemoglobin in the red blood cell to make the red blood cell go back to being happy and squishy and not spicy and hard, so it can go deliver oxygen where it’s supposed to.”
More than 2 billion edited cells were then inserted into Gray’s body.
When Gray left the hospital, she knew it could be quite a while before there were signs that the procedure had been successful.
The good news is that when NPR checked on her one year later, she was doing well: free of the need for blood transfusions, free of pain, and spared hospital visits. The gene edited cells have now remained with her for a full year, indicating that they could last for her entire life.
“It’s amazing. It’s better than I could have imagined. I feel like I can do what I want now.”
Similar success was seen with two other patients treated for sickle cell disease and seven treated for beta thalassemia, another blood disorder.
“All the patients appear to have responded well. The only side effects have been from the intense chemotherapy they’ve had to undergo before getting the billions of edited cells infused into their bodies.”
“Doctors will have to follow Gray for years and study many additional patients to answer the most important questions: Are the cells really helping patients live healthier lives? Will they keep working? Will they keep working safely? and will the cells actually help patients live longer?”
NPR quoted Jennifer Doudna, one of the Nobel Prize recipients:
“I’m very excited to see the results. Patients appear to be cured of their disease, which is simply remarkable.”
Clearly, any time we are considering making changes to our genetic makeups, alarm bells go off—and they should. There was the story of the Chinese scientist who claimed he’d created a set of twins with CRISPR-edited genes that would make them resistant to HIV. (It’s still not clear that he did so.)
His actions received worldwide condemnation, as germline genetic editing (to affect the next generation) is widely frowned upon. There are, however, varying ethical guidelines, I’ve learned, from “restrictive” in the US, to “legal prohibition” in the UK, to “ambiguous” in various other countries, ranging from Russia to Iceland.
But a STAT piece in 2019 headlined “CRISPR is ascending again, after scientists find ‘elegant’ fix for cancer worry.” And a 2020 Nature article found “People with cancer show no serious side effects after treatment with gene-edited immune cells.”
Also in 2018, geneticist Allan Bradley of the Wellcome Sanger Institute in England said that CRISPR unleashes DNA damage that’s been “seriously underestimated.” He led a study published in Nature Biotechnology that cited deletions of thousands of DNA bases, including at spots far from the CRISPR’s cuts. Reportedly, some of the deletions can silence genes that should be active and activate genes that should be silent, including cancer-causing genes. “This should be a wakeup call,” said Bradley.
His study found that although the targeted DNA was changed as expected, “that set off a chain reaction that engulfed genes far from the target.”
STAT noted that critics of the cancer studies had asked why, if CRISPR’d cells can initiate cancer, no CRISPR’d mice had turned up with tumors, so scientists raised similar questions about the new genomic havoc finding, Why don’t scientists see it when they analyze the DNA of CRISPR’d cells?
“You find what you look for. No one is looking at the impact [of these DNA changes] on downstream genes.”
Bradley also noted that the standard way to search for the deletions requires PCR (polymerase chain reaction, a method that vastly replicates a small DNA sample so that scientists can study it in detail), which must attach to binding sites. But if CRISPR deletes the binding sites, the damage goes undetected.
Bradley’s study was called “well done and credible…a cautionary note to the [genome editing] community” by a prominent CRISPR developer who declined to be identified because he has business relationships with relevant companies. This expert also said the findings of DNA rearrangements and deletions were consistent with other reports.
I haven’t been able to find any refutation of Bradley’s article or a follow-up. But that doesn’t mean one doesn’t exist.
What to Make of All This?
The negative studies were available in 2018, yet Victoria Gray’s treatment began in 2019, and the Nobel Committee awarded its prize in 2020. I can only assume that those involved in all these efforts are cognizant of the potential drawbacks.
There are currently clinical trials using CRISPR in multiple myeloma, lung, bladder and prostate cancer, HIV-1, human papilloma virus, leukemia, melanoma, solid tumors, gastrointestinal infections—as well as sickle cell disease and esophageal cancer.
So we’ll just have to hope that the researchers go slowly, recognizing that CRISPR requires precision that may not have been fully appreciated previously, and watching for any signs of problems.
I saw one reference to the fact that “few studies conduct full-out genome sequencing of CRISPR’d cells.” From my non-medical perspective, I wonder if such sequencing could/should be a part of the protocol for every clinical trial involving CRISPR—sort of a “recheck your work” approach. Perhaps a reader with greater knowledge can respond to this question.
The promise seems so great–a potentially huge breakthrough. But the excitement and early apparent successes—and the vast monetary rewards—must not overshadow the possibility of unintended consequences.