In March, a 20-year-old California man named Kris Boesen was driving on a slick road when his car slammed into a telephone pole, breaking three of his vertebrae. Doctors told Boesen’s parents he would likely be permanently paralyzed from the neck down.

Boesen’s parents enlisted him in a clinical trial the University of Southern California, where a team of doctors injected embryonic stem cells into his back. There, they hoped, the cells would mend the damage, allowing signals from his brain to transmit again. Five months later, as KQED reported, Boesen could hold a phone and twist the cap off a bottle of soda. A photo released by USC shows Boesen triumphantly hoisting a barbell over his head.

Though Boesen’s therapy must still be tested in a larger group of study subjects, advocates of embryonic stem-cell research hope remarkable turnarounds like his will become more common if the field is nurtured and funded. That’s also why some scientists and advocacy groups worry that the Trump administration will roll back the modest progress the field has made since restrictions on it were lifted eight years ago.

“We are deeply concerned about the appointment of Tom Price to Secretary of Health and Human Services,” said Mary Bass, the director of public policy for Americans for Cures, a group that advocates for stem-cell research. “The implications for embryonic stem-cell research could be devastating.”

The president-elect is not known for being particularly religious, but he’s surrounding himself with traditional conservatives, including staunch pro-life policymakers like Representative Tom Price of Georgia and Vice-President-elect Mike Pence. At this point, watchers of the field can only speculate as to the Trump administration’s stance on embryonic stem cells. (His team did not return a request for comment). But some fear the new regime may halt stem-cell and fetal-tissue research, which many abortion opponents consider to be life and many scientists regard as the ingredients of breakthroughs.

At issue is the humanity of a cluster of cells that’s created during the in-vitro fertilization process. About a week after a woman’s egg is fertilized with a man’s sperm, it becomes a blastocyst, a 100-cell blob smaller than the head of a needle. After implantation, the couple might donate some of the unused blastocysts for use in stem-cell research.

For years, embryonic stem-cell research was strictly limited by a policy imposed by former President George W. Bush in 2001. “Most Americans share a belief that human life should not be reduced to a tool or a means,” Bush wrote in The New York Times that August, defending his decision. Research on embryonic stem cells was limited to the so-called “Bush lines,” a couple dozen colonies of cells that had already been cultivated. In those days, some scientists would label their lab equipment if it had been purchased with public funds and thus couldn’t touch embryonic cells. During his eight years in office, Bush vetoed bills that would have expanded funding for stem-cell research. President Barack Obama lifted the ban by executive order in 2009, allowing hundreds of new cell lines to flourish.

Embryonic stem-cells are now being tested as possible treatments for juvenile diabetes, Parkinson’s disease, and macular degeneration, among other ailments. Fetal tissue, meanwhile, has been used for studies on the Zika virus and other pathogens. Fetal research, too, has stoked controversy: In the past year several states passed laws—including one Mike Pence signed in Indiana—prohibiting the donation of fetal tissue for research. South Dakota’s law made research on fetal tissue a felony.

To Paul S. Knoepfler, a professor of biology at the Institute for Regenerative Cures at the University of California, today feels like “2006 all over again. Obama opened the door, and now we’re wondering, is the door going to be closed?”

If he is confirmed as HHS secretary, Price would oversee the National Institutes of Health, which gives grants to researchers working on embryonic stem cells and fetal tissue, along with other research areas. Price could decide to cease funding these projects, or Trump could issue an executive order reversing Obama’s policy.

As a congressman, Price repeatedly voted against expanding embryonic stem-cell research, and when Obama lifted the ban in 2009, Price released a statement saying, “Human embryos are the most vulnerable forms of life, yet the Obama administration is creating taxpayer-funded incentives for their destruction.”

In 2005 and 2007, Price co-sponsored “personhood” bills that would define a “human being” from “the moment of fertilization.” And though Price has not recently spoken out against fetal-tissue research, the 2016 Republican party platform states, “We urge all states and Congress to make it a crime to acquire, transfer, or sell fetal tissues from elective abortions for research.” Republicans on the Senate Judiciary Committee released a report this month asking the Justice Department to investigate Planned Parenthood and several research companies for improperly selling fetal tissue—something pro-life lobbyists hope Senator Jeff Sessions, a Republican from Alabama and Trump’s pick for attorney general, will do if confirmed.

Price has, in the past, said he supports spending on science, but only in fiscally practical ways. Meanwhile, Trump’s pick for the White House's Office of Management and Budget, Representative Mick Mulvaney of South Carolina, has questioned whether “we really need government-funded research at all.”

If funding for stem-cell projects is threatened, rather than yanked altogether, there might be a chilling effect on scientists, Knoepfler said. Early-career scientists considering entering into stem-cell research might feel nudged into other domains. Before the stem-cell ban was lifted, some prominent American scientists decamped for Singapore, a nation not exactly known for its liberalism. Investors, sensing trouble, might turn their attention to other promising innovations. Knoepfler points to a 2011 lawsuit that challenged federal funding for embryonic stem-cell research. Though the suit was thrown out, “research was delayed,” he said. “Those events probably permanently steered some scientists away from studying embryonic stem cells.”

Some opponents of embryonic stem-cell research invoke the discovery of something called induced pluripotent stem cells, or IPS cells, as evidence that research on embryos is no longer necessary. These are cells, taken from adults, that can be reprogrammed to resemble embryonic stem cells. They’re just as flexible as embryonic cells, so they can be used in everything from the pancreas to the brain. In a 2009 editorial, Pence cited IPS cells as a reason Obama shouldn’t be “trampling the wishes of millions of Americans who cherish the right to life as a gift of God” with his embryonic stem-cell policy.

But Knoepfler and others said researchers will still need embryonic stem cells to use as controls, and in order to follow through on experiments that are already under way.

As vice president, Pence will not have authority over the NIH, and he cannot issue executive orders. But, as Alta Charo, a professor of law and bioethics at the University of Wisconsin, told me, “he is expected to be an influential member of the administration, and some of these issues are close to his heart.”

As Charo sees it, any coming stem-cell debate will tear back open a decade-old rift: “How much symbolic, political care for embryos is going to trump—no pun intended—the real needs of real patients with real diseases?”