A secretive experiment revealed this week, in which neurosurgeons transplanted brain cells into a patient with Parkinson’s disease, made medical history. It was the first time such “reprogrammed” cells, produced from stem cells that had been created in the lab from the man’s own skin cells, had been used to try to treat the degenerative brain disease. But it was also a bioethics iceberg, with some issues in plain sight and many more lurking.

Doctors use stem cell transplants to treat patients with certain cancers or blood disorders. And donors, whose blood or bone marrow is used for the procedures, are typically young, for a variety of reasons. But a pilot study released Wednesday raised the possibility that such donors are also passing along mutations in stem cells that could lead to health problems for some recipients.

Some private clinics are charging UK patients thousands of pounds for unproven and unregulated treatments using the “healing powers” of stem cells.

A five-year regulatory free-for-all in regenerative medicine has given the industry a boost. But patients might be paying the price.

Clusters of living brain cells are teaching scientists about diseases like autism. With a new finding, some experts wonder if these organoids may become too much like the real thing.

Japan has approved a stem-cell treatment for spinal-cord injuries. The event marks the first such therapy for this kind of injury to receive government approval for sale to patients.

“This is an unprecedented revolution of science and medicine, which will open a new era of healthcare,” says oncologist Masanori Fukushima, head of the Translational Research Informatics Center, a Japanese government organization in Kobe that has been giving advice and support to the project for more than a decade.

But independent researchers warn that the approval is premature. Ten specialists in stem-cell science or spinal-cord injuries, who were approached for comment by Nature and were not involved in the work or its commercialization, say that evidence that the treatment works is insufficient. Many of them say that the approval for the therapy, which is injected intravenously, was based on a small, poorly designed clinical trial.

Most Americans say it would be OK to use gene-editing technology to create babies protected against a variety of diseases — but a new poll finds they’d draw the line at changing DNA so children are born smarter, faster or taller.

A month after startling claims of the births of the world’s first gene-edited babies in China, the poll by The Associated Press-NORC Center for Public Affairs Research finds people are torn between the medical promise of a technology powerful enough to alter human heredity and concerns over whether it will be used ethically.

Brisbane, Calif.-based Aimmune Therapeutics recently sparked optimistic headlines after releasing clinical trial results that its allergy product, AR101, would reduce the risks linked to an accidental exposure to peanuts.

Chinese scientists have raced ahead in experimenting with gene-editing on humans in the last few years, using a powerful new tool called Crispr-Cas9 to edit the DNA of dozens of cancer patients.

Information gathered by The Wall Street Journal shows one such trial has lost touch with patients whose DNA was altered, alarming some Western scientists who say subjects should be monitored for many years.

Twelve patients became seriously ill after receiving injections that supposedly contained stem cells from umbilical cord blood, according to the Food and Drug Administration, which issued a warning to the California company, Genetech, that made the blood product they were given.

(The company has no connection with Genentech, the biotechnology corporation.)

The F.D.A. said on Thursday that it had also written to 20 clinics that offer unapproved stem cell treatments, warning them that such products are generally regulated by the agency and encouraging the clinics to contact federal regulators before November 2020, when enforcement will tighten. The names of the clinics have not been released.