When Gov. Rick Perry emerged from back surgery on July 1, he tweeted that his “little procedure” — a spinal fusion and nerve decompression designed to treat a recurring injury — had gone “as advertised.”

The possible presidential contender didn’t reveal that he’d undergone an experimental injection of his own stem cells, a therapy that isn’t FDA approved, has mixed evidence of success and can cost upwards of tens of thousands of dollars.

The governor’s procedure did not involve embryonic stem cells, which he and many other conservatives ardently oppose using for medical research on both religious and moral grounds. His treatment involved removing his own adult stem cells from healthy tissue and injecting them back into his body at the time of surgery, with the belief that the cells would assist tissue regeneration and speed recovery.

In a statement on Wednesday, Perry spokesman Mark Miner called the procedure “successful” and confirmed that it included “the innovative use of his own adult stem cells.”

While some doctors and biomedical engineers swear by the benefits of this relatively new science and offer the therapy to patients with everything from slipped discs to cardiac disease, stem cell experts say there’s still little clinical evidence — aside from research on animals and small-scale human studies — that it’s effective.

The FDA, which is in litigation over its authority to regulate new stem cell clinics, has not approved the use of adult stem cells for anything other than bone marrow transplants, which have been used for decades to treat cancer and sickle cell anemia patients. This has largely kept doctors from openly advertising these stem cell injections, but not from capitalizing on them by offering the therapy to their patients.

It also hasn’t stopped Perry from pushing for adult stem cell research and industry in Texas. During the governor’s 2009 State of the State address, he called on state leaders to invest in adult stem cell companies. Later that year, his Emerging Technology Fund awarded a $5 million grant to the Texas A&M Health Science Center Institute of Regenerative Medicine and $2.5 million to Helotes-based America Stem Cell to develop new adult stem cell technology.

Last month, three weeks after his adult stem cell treatment, Perry wrote a letter to the Texas Medical Board, which is considering new rules regarding adult stem cells, saying that he hoped Texas would “become the world’s leader in the research and use of adult stem cells.” He asked board members to “recognize the revolutionary potential that adult stem cell research and therapies have on our nation’s health, quality of life and economy.”

In the weeks since the procedure, the governor has traded his cowboy boots for orthopedic shoes and donned a back brace, raising questions that his recovery may be slow-going. Still, he has traveled extensively; in an interview with The Associated Press last week, Perry said he felt 80 percent recovered and was swimming and using the treadmill.

As for the high cost of such stem cell injections, Miner said that whatever state health insurance didn’t pay for, “Perry did.” By rule, the state's Employees Retirement System would not confirm or deny whether Perry is on the health plan. But officials said the state health plan does not cover experimental treatments like such stem cell therapy.

In Perry's procedure, his doctor, Houston orthopedic spine surgeon Stanley Jones, said he pulled stem cells from fatty tissue in the governor's hip, left the cells to expand in culture for several weeks at a Sugar Land lab, then injected the cells back into the governor during his back surgery, into the spine and into Perry's blood stream.

In May 2010, Jones made a high-profile trip to Kyoto, Japan, to get infused with his own stem cells to treat autoimmune arthritis. A January press release from RNL BIO, the South Korea-based stem cell company that treated him, reported that he had a complete recovery within five months.

The infusion of adult stem cells to repair tissue and organ damage is highly controversial. For every Bartolo Colon, the New York Yankees pitcher whose near-miraculous comeback is being attributed to the procedure, researchers say there are botched jobs and patients who spend tens of thousands of dollars with no results.

The biomedical engineers and spinal clinics developing stem cell products and performing the procedure say they’re seeing terrific results.

“They have been outstanding given how new the field is,” said Kevin Dunworth, founder and CEO of Austin-based Celling Technologies and SpineSmith, which prepares the adult stem cells for about 450 procedures in the U.S. every month, a quarter of them in Texas. “The added value of stem cells is that they’re wonderful at mitigating pain on a long-term basis, and they do it quite rapidly, within three to five days.”

But researchers say that despite the great potential adult stem cells may have, so far they’ve seen nothing more definitive than the so-called “placebo effect” — patients who convince themselves they’re feeling better simply by nature of having had the procedure. In some lab tests, stem cells that have been effectively deprogrammed to help regenerate a particular organ have appeared to turn cancerous. In others, patients have traveled around the world, spending $10,000 to $50,000 for stem cells that simply die off, with no effect on health.

“Most of this stuff is pretty experimental at this point,” said Heather Rooke, the science director for the International Society for Stem Cell Research. “People are pushing these things into the clinic before there’s real evidence of safety or an indication that they’ll work.”