The development of cancer treatments and diagnostic tools using CRISPR/Cas9 and other gene-editing technology is a promising area of research in the United States, although the field is moving into human studies at a relatively slow pace.
Jiankui He, PhD
The development of cancer treatments and diagnostic tools using CRISPR/Cas9 and other gene-editing technology is a promising area of research in the United States, although the field is moving into human studies at a relatively slow pace. Outrage recently generated by reports that twin girls were born in China from genetically modified embryos has injected an additional note of caution into the research.
American regulatory officials called for better controls worldwide on human gene-editing experiments after Jiankui He, PhD, announced in November that he had successfully changed a gene in the twins’ embryos to confer resistance to HIV. He, who is an associate professor at Southern University of Science and Technology in Shenzhen, China, described the research in a YouTube video and later at the Second International Summit on Human Gene Editing.1,2 He’s statements about the research, which has not yet been presented in peer-reviewed form, sparked a debate about the ethics of the experiment.
The controversy comes at a time when ongoing efforts to move genetically modified cancer treatments from the lab to the clinic in the United States have been proceeding more slowly than some had hoped. Investigators at the University of Pennsylvania have started to enroll patients in a multicenter trial testing CRISPR-edited T cells, but other phase I trials that American investigators had hoped to launch in 2018 are not yet underway.
In China, the development of gene-edited anticancer therapies has progressed more rapidly. In June, Chinese investigators reported encouraging findings in a small phase I study of T cells engineered with CRISPR to knock out the PD-1 immune checkpoint in patients with metastatic PD-L1—positive non–small cell lung cancer.
Of 8 evaluable patients treated across 4 dosing cohorts, 2 reached stable disease and 6 progressed. The median progression-free survival was 7.7 weeks (range, 5.6-28.0). and the median overall survival was 42.6 weeks (range, 13.4-52.4).3 Additional CRISPR trials for potential anticancer therapies are ongoing in China, according to studies registered on ClinicalTrials.gov.
There are many other signs of progress in the field. The underlying technologies and techniques of gene modification continue to improve,4,5 and preclinical research continues to identify potential ways to apply tools such as CRISPR to cancer care. In addition, 2 groups are making plans for the first US human clinical trials of gene editing in sickle cell disease.6
“The preclinical results that different groups have achieved by using tools like CRISPR to modify immune cells have been, and continue to be, extremely promising. Many people, including me, are very eager to move to trials, but everyone understands the need for caution. That was true before the events in China, but when something like that happens, it’s natural for those with oversight responsibility to take a step back and make sure they have all the safeguards we need in place to prevent anything like that from happening again,” said Saad J. Kenderian, MB, ChB, a senior associate consultant in the Division of Hematology at Mayo Clinic in Rochester, Minnesota, who leads an immunotherapy engineering team.
“I don’t think the long-term picture has changed,” he said. “Promising treatments will move on to trials, and the process of getting trials designed and approved will speed up as we establish best practices. But we need to do it responsibly.”The prospect of altering genes, even to cure illness, has long raised concerns about protecting human clinical study participants, but medical gene-editing efforts had gone 19 years without a major misstep.7 Then He announced that he had overseen the modification of the CCR5 gene in twin girls who had already been born and at least 1 other still-gestating fetus.
He said he recruited 8 couples who were undergoing in vitro fertilization (IVF) to avoid passing HIV from infected fathers to their children and proposed the genetic alteration as a means of greatly reducing the chance that any resulting children could contract HIV later in life.8 (Standard IVF techniques could have resulted in HIV-free children at birth, but people born without the CCR5 gene would be highly resistant to contracting HIV.) According to He’s presentation, the modification successfully removed both copies of CCR5 in 1 girl but left 1 copy of the gene in the second child. He has not yet published an account of his work in any independent journal, and there are no reports of independent authorities examining the girls or their DNA.2
News of the experiment, which leaked several days before his appearance at the gene-editing conference in Hong Kong on November 28, generated widespread condemnation that the presentation did little to quell. Some of the criticism focused on He’s selfreported technique, which struck some experts as a dangerously second-rate way to use CRISPR. Other scientists focused on He’s decision to implant an edited embryo that still had a working copy of the CCR5 gene, which means the child may face other health risks without enjoying much, if any, immunity to HIV. Most of the criticism, however, focused on the ethics of even attempting the experiment in the first place.2
No single organization has the power to regulate genetic editing across the globe, but the international scientific community has embraced a consensus on what might justify editing germline (hereditary) genes. That consensus emphasizes publicly announced and independently overseen experiments on inevitable and untreatable conditions with simple genetic causes via edits that have been successfully practiced in numerous preclinical trials.
He’s trial, however, focused on a gene that does not directly cause any disease or even create abnormal risk of any disease, and it used germline edits that have rarely been studied in preclinical trials. Some experts said the experiment put at least 2 children and their descendants at risk of future health problems, simply to make them resistant but not immune to a condition that is both avoidable and treatable.
The leaders of the FDA and the National Institutes of Health (NIH) criticized both He’s study and what they perceived as an insufficiently severe response from the international scientific community. FDA Commissioner Scott Gottlieb, MD, said that the scientific community had failed to “selfpolice” and had registered “a far too slow and far too tepid response,” which would force governments to act.9 NIH Director Francis Collins, MD, PhD, called for the development of binding international agreements that would make trials such as He’s illegal everywhere.10
At the same time, Gottlieb and Collins confined their condemnation to trials of germline gene editing of embryos. In a strongly worded statement, Collins stressed that the NIH does not support gene editing of human embryos.11 In 2015, Congress moved to prevent the FDA from evaluating any therapy that involves genetically changing a human embryo, essentially exposing scientists engaging in such research to hefty fines and potential criminal penalties.12
However, both Gottlieb and Collins voiced their belief in the medical potential of the research into somatic gene editing that investigators in the United States have been conducting. In January 2018, the NIH announced plans to award $190 million in grants over 6 years, pending the availability of funds, for research into the use of CRISPR and other gene-editing tools to modify somatic genes implicated in diseases.13
“I do hope that this very visible misadventure does not cause a cloud over the entire area of gene editing for therapeutic benefit. When it comes to somatic applications, I’m extremely excited about the potential to come up with not just treatments, but cures for hundreds and maybe thousands of diseases that currently have no available treatment—and this could be the best hope,” Collins said in an interview with Science.10In the United States, a first-in-human geneediting study for the development of anticancer therapies has undergone extensive regulatory reviews. Investigators at the University of Pennsylvania worked for more than 2 years to secure FDA approval for the first American trial of CRISPRed T cells, which is taking place at 3 American facilities: their own hospital in Philadelphia, the University of California, San Francisco, and MD Anderson Cancer Center in Houston (NCT03399448). The Parker Institute for Cancer Immunotherapy and Tmunity Therapeutics, a biotech company, are providing funding, according to a University of Pennsylvania spokesman.
The study is seeking to recruit 18 heavily pretreated patients with multiple myeloma, melanoma, or sarcoma who test positive for human leukocyte antigen-A*201 with expression of NY-ESO-1, a cancer-testis antigen, on tumor tissue. The process involves harvesting the patient’s T cells, transducing those cells with a lentiviral vector to express NY-ESO-1, and then using CRISPR to disrupt expression of T-cell receptors α and β and PD-1. The engineered T cells would then be reinfused into the patient.
“All arms of the study are currently enrolling patients,” a university spokesman, who declined to give any further details about progress to date or timing going forward, said in an interview with OncLive®. “Findings from the trial will be shared at an appropriate time via a medical meeting presentation or peerreviewed publication.”
As for other US-based efforts to move treatments from laboratory studies and animal trials to human patients, another trial was registered at ClinicalTrials.gov but then canceled (NCT03538613). The National Cancer Institute had planned a phase I/II trial testing genetically engineered tumor-infiltrating lymphocytes (TILs) in patients with metastatic gastrointestinal epithelial cancer. The study would have involved extracting TILs from the patient and then using CRISPR to edit out the CISH gene, a negative immune system regulator.
A spokeswoman for the NIH said in an interview that the team had decided to pursue more promising treatment approaches, “one of which is the retroviral insertion of mutation-specific T-cell receptors in the patient’s peripheral blood cells.”
Investigators at Memorial Sloan Kettering Cancer Center (MSK) in New York, New York, also had hopes of starting a phase I trial of chimeric antigen receptor (CAR) T cells built with CRISPR rather than older technologies. The study team used CRISPR to place a CD-19—directed CAR exactly where T cells normally code for their targets at the TRAC locus, rather than using viruses to place it at a random point in the cell’s DNA.
Preclinical trial findings show the CAR can be reliably placed on target and that such CAR T cells perform better in animal models than their traditional counterpart. At the highest dose, every TRAC-CAR T-cell mouse was alive 40 days after injection while every mouse that received another type of CAR T cell was dead, according to study findings. At the lowest dose, half of all TRAC-CAR T-cell mice were alive at 30 days while all the mice that received different types of CAR T cells were dead at 20 days.14
Michel Sadelain, MD, PhD, director of the Center for Cell Engineering at MSK and leader of the TRAC-CAR T-cell study team, said that he hopes to have a phase I trial with about 20 patients up and running by the second half of 2019.
“If we were just removing genes, we’d be starting in a few months, but we need CARs to insert into the T cells, and the facilities for making them are not as numerous or as fast as we’d like, so we will have to wait a few extra months,” Sadelain said in an interview. “We’d love to get started faster, because the animal results suggest that using CRISPR to place CARs will make treatment both safer and more effective, but recent events clearly demonstrate the need to move carefully and submit to proper oversight.”
Another group based at the University of Washington in Seattle has designed a trial that will use CRISPR to help diagnose cancer rather than treating it. Investigators will recruit 25 patients with ovarian cancer from whom they will take Pap smear and uterine lavage samples and then test those tissues for TP53 mutations with CRISPR-Duplex sequencing. Those results will be compared with sequences derived from tumor tissue to see if the new sequencing technology may be good enough to use Pap smears and uterine lavage samples, rather than tumor tissue samples, to detect tumor-derived TP53 mutations when sequencing newly diagnosed cancers (NCT03606486).
Meanwhile, investigators based at Children’s National Health System in Washington, DC, have launched a trial that will collect stem cells from patients with NF1-mutant cancers of the central nervous system, reprogram those cells to be pluripotent stem cells, use CRISPR to fix the mutant NF1 allele in some of those cells, and test libraries of existing and experimental treatments against both the regular and repaired cells in hopes of finding potential treatments (NCT03332030).
Recently published study findings point to even more possible applications for geneediting tools. Kenderian’s team at Mayo, for example, found that blocking the cytokine granulocyte-macrophage colony-stimulating factor (GM-CSF) with the antibody lenzilumab increased CAR T-cell efficacy and reduced adverse effects in mouse models. They then found they could use CRISPR to edit the CARs so they produced less GM-CSF.15 The finding suggests that such CARs might prove safer and more effective in human subjects, and the Mayo team is eager to test the theory in clinical trials.