Should humans be allowed to alter their own genetic code? That question is steeped with controversy—especially since the development of CRISPR-Cas9, a technology that can edit genomes. Now, the National Institutes of Health have approved the first clinical trial of CRISPR in the United States, writes Sara Reardon for Nature News.

By the end of the year, scientists at the University of Pennsylvania will conduct a trial that tests whether the technology is safe for human use, Reardon reports. It’s the first time CRISPR will be used on human genes in the United States and follows its approval in countries like the United Kingdom. The NIH Recombinant DNA Advisory Committee, which provides ethical and research oversight to the agency, reviewed and approved the proposal.

Also known by its longer name, Clustered Regularly Interspaced Short Palindromic Repeats, CRISPR lets scientists switch genes on and off and even swap out parts of DNA. This trial will be funded by by the Parker Institute for Cancer Immunotherapy, which was founded with a $250 million investment earlier this year by Facebook’s former president, Sean Parker.

The trial will target human T cells, a type of white blood cell that is an important component of the immune system that fights off infections and disease. T cells don’t just manage immune responses; they also can hunt down and kill cancerous cells. In this case, says Reardon, researchers will both insert and edit genes within T cells, then put them back into patients’ blood with a goal of turning the cells into even better cancer-fighting machines.

Researchers plan to do this by editing the genes to help T-cells detect and target cancer cells, while also removing a gene that allows the cancer cells to detect and attack them in return. They also plan to remove a protein that could hamper the cancer battle, Reardon reports. These edits to the T-cells will hopefully verify the safety of CRISPR and improve existing cancer therapies.

The approval comes somewhat sooner than expected: As Antonio Regalado writes for MIT Technology Review, a company called Editas that plans to treat blindness using CRISPR was long thought to be the first that would receive approval. But it didn’t come without controversy.

Review board members had concerns that both the University of Pennsylvania and the trial’s lead researcher own patents and companies that could benefit from the recently approved test, Jocelyn Kaiser writes for Science Magazine. The board members also expressed concerns about UPenn’s legacy when it comes to gene therapy. A young man named Jesse Gelsinger died in 1999 while participating in a study led by UPenn researchers. His death occurred just four days after he received an injection of corrective genes intended to treat a deadly form of his metabolic disorder found in babies.

RDAC approval of CRISPR is just the first hurdle faced by those who wish to use the technology to edit human genes in the U.S., writes Kaiser. Now, researchers must wait on ethics board and FDA approvals. But for better or for worse, it appears that CRISPR will soon be more fact than fantasy in the United States. The question is no longer should or even if, but when.