TORONTO - Gordie Howe's son says the hockey legend's stroke symptoms have improved since his treatment with stem cells at a Mexican clinic in early December and he wants him to repeat the procedure.

But regenerative medicine experts say there's no scientific evidence such therapies work, and in some cases they can be seriously harmful or even deadly.

The 86-year-old Howe suffered two disabling strokes late last year. In December, the family took him to a Tijuana clinic where he received stem cell injections as part of a clinical trial being run under a licensing agreement with Stemedica Cell Technologies of San Diego, Calif.

The experimental treatment involved injecting neural stem cells into Howe's spinal canal, along with intravenous infusions of mesenchymal stem cells, which are found in bone marrow, fat and umbilical cord blood.

Marty Howe said his father can walk again, his speech is improving and he is regaining some of the weight he lost following the strokes.

"After his stem cell treatment, the doctor told us it was kind of an awakening of the body, and it was all that," he told The Canadian Press while in Calgary for a hockey promotion event Tuesday. "They call it the miracle of stem cells and it was nothing less than a miracle."

However, experts in the field question whether stem cells are responsible for Howe's improvement and caution that most so-called stem cell therapies have not gone through rigorous scientific trials, nor have they been approved as treatments by Health Canada or the U.S. Food and Drug Administration.

Mick Bhatia, director of McMaster University's Stem Cell and Cancer Research Institute, said there are many unknowns in Howe's case, such as how many stem cells were administered, were tests done to see whether they migrated to the targeted area of the body, and did they take up residence where they might have some effect or simply disappear?

"Is this a transient effect, or is it really a perceived or somewhat of a placebo effect and is there something really happening? Scientifically and biologically that is important," Bhatia said Wednesday from Hamilton.

And because Howe received adult stem cells produced from donor cells, he may have needed to take drugs to prevent an immune reaction as well as anti-inflammatory medications, he said.

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Gordie Howe's stem cell therapy raises concerns among experts