The Food and Drug Administration is cracking down on "unscrupulous" clinics selling unproven and potentially dangerous treatments involving stem cells.

Hundreds of clinics around the country have started selling stem cell therapies that supposedly use stem cells but have not been approved as safe and effective by the FDA, according to the agency.

"There are a small number of unscrupulous actors who have seized on the clinical promise of regenerative medicine, while exploiting the uncertainty, in order to make deceptive, and sometimes corrupt assurances to patients based on unproven and, in some cases, dangerously dubious products," FDA Commissioner Scott Gottlieb said in a statement Monday.

The FDA has taken action against clinics in California and Florida.

The agency sent a warning letter to the US Stem Cell Clinic of Sunrise, Fla., and its chief scientific officer, Kristin Comella, for "marketing stem cell products without FDA approval and significant deviations from current good manufacturing practice requirements."

The clinic is one of many around the country that claim to use stem cells derived from a person's own fat to treat a variety of conditions, including Parkinson's disease, amyotrophic lateral sclerosis ( ALS), and lung and heart diseases, the FDA says.

The Florida clinic had been previously linked to several cases of blindness caused by attempts to use fat stem cells to treat macular degeneration.

The FDA also said it has taken "decisive action" to "prevent the use of a potentially dangerous and unproven treatment" offered by StemImmune Inc. of San Diego, Calif., and administered to patients at California Stem Cell Treatment Centers in Rancho Mirage and Beverly Hills, Calif.

As part of that action, the U.S. Marshals Service seized five vials of live vaccinia virus vaccine that is supposed to be reserved for people at high risk for smallpox but was being used as part of a stem-cell treatment for cancer, according to the FDA. "The unproven and potentially dangerous treatment was being injected intravenously and directly into patients' tumors," according to an FDA statement.

Smallpox essentially has been eradicated from the planet, but samples are kept in reserve in the U.S. and Russia, and vaccines are kept on hand as a result.

But Elliot Lander, medical director of the California Stem Cell Treatment Centers, denounced the FDA's actions in an interview with Shots.

"I think it's egregious," Lander says. "I think they made a mistake. I'm really baffled by this."

While his clinics do charge some patients for treatments that use stem cells derived from fat, Lander says, none of the cancer patients were charged and the treatments were administered as part of a carefully designed research study.

"Nobody was charged a single penny," Lander says. "We're just trying to move the field forward."

In a written statement, U.S. Stem Cell also defended its activities.

"The safety and health of our patients are our number one priority and the strict standards that we have in place follow the laws of the Food and Drug Administration," according to the statement.

"We have helped thousands of patients harness their own healing potential," the statement says. "It would be a mistake to limit these therapies from patients who need them when we are adhering to top industry standards."

But stem-cell researchers praised the FDA's actions.

"This is spectacular," says George Daley, dean of the Harvard Medical School and a leading stem-cell researcher. "This is the right thing to do."

Daley praised the FDA's promise to provide clear guidance soon for vetting legitimate stem-cell therapies while cracking down on "snake-oil salesmen" marketing unproven treatments.

Stem-cell research is "a major revolution in medicine. It's bound to ultimately deliver cures," Daley says. "But it's so early in the field," he adds. "Unfortunately, there are unscrupulous practitioners and clinics that are marketing therapies to patients, often at great expense, that haven't been proven to work and may be unsafe."

Others agreed.

"I see this is a major, positive step by the FDA," says Paul Knoepfler, a professor of cell biology at the University of of California, Davis, who has documented the proliferation of stem-cell clinics.

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