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In the equine world, tendon and ligament injuries are bad news indeed. Among the many prized race and performance animals who suffer from bowed tendons or similar maladies each year, just 20% or so make a full recovery, and then only after a long and costly rehabilitation. The suffering and expense these injuries incur has led frustrated horse owners to try a host of different treatments for these injuries over time, some more evidence-based than others, and all without great success. Perhaps it was inevitable, then, that some in the veterinary world would turn to a therapeutic approach that scientists say holds such great promise in humans: stem cells.
In the past few years at least two companies, one in Britain and the other in the United States, have begun offering treatments that they say improve healing of the injuries by means of autologous adult stem cell transplants. The two firms – Vet-Stem, based in Poway, Calif., and VetCell Bioscience, based in London – have very similar names, and both make use of mesenchymal stem cells. Both companies claim that their treatments are effective in about 70% of cases. But the details of their approaches vary significantly, and the proof of the efficacy of such methods is so far less than robust, say experts.
FROM FAT TO TENDONS
Vet-Stem was founded in 2002 by Robert Harman, a veterinarian and biotech entrepreneur. The privately held firm had initial funding from its founders in cash and kind of $1 million, supplemented by series A investment of $1 million and $3 million from series B.
Using technology licensed from Articel in Baltimore, Harman's company uses stem cells harvested from fatty tissue. "We need from a horse about two tablespoons of fat, roughly 10 to 15 grams," Harman explains. "The veterinarian takes it out with a lipectomy under local anesthetic. We provide a collection kit, [which] is sent back refrigerated to San Diego."
Once the package arrives in the Vet-Stem lab, the company's scientists use a combination of flotation and digestion processes to separate the nucleated cells from the fat. "It's the cells in the fat we want," says Harman. The process takes about four hours in the lab, and the company then dispatches back to the veterinarian the cells in suspension, ready-stored in syringes. The whole process takes 48 hours or less from the time the fat is collected until it returns. At that point, the horse's veterinarian will inject a volume and dose, customized for the specific horse and its injury, directly into the relevant tendon, ligament, or joint.
The mechanism of action is a combination of four elements, Harman says: cells that regenerate the tissue by becoming that tissue type; cells that generate a family of growth factors that modulate the healing process; cells that reduce apoptosis; and cells and growth factors that increase the formation of new blood vessels.
Fat is an ideal source of mesenchymal cells, says Harman. "With almost any other source there aren't enough cells in there from one collection. We not only have enough, there's enough to freeze some extra." Roughly two percent of the nucleated cells from the fatty tissue are mesenchymal stem cells, he explains, but cardiac studies suggest that the "major factor of these cells is to produce growth factors, stimulate blood vessels and recruit other cells. They are an extremely powerful little pharmaceutical factory."
BONE MARROW BECOMES TENDON
Meanwhile in Great Britain, VetCell Bioscience, the first-ever spinoff from the Royal Veterinary College, takes a different approach. The company is privately held, and the Royal Veterinary College has a 13% shareholding. The company says it has raised £750,000 in private equity and assisted in the success of £250,000 in research grant money.
Since 2001, VetCell has used a cell-culture system patented by the college's Roger Smith to multiply mesenchymal stem cells derived from an adult horse's bone marrow or from cryogenically stored umbilical cord blood. Research has shown that to achieve an effect, a very large number of these cells are required, says Greg McGarrell, VetCell's CEO. "Because you need so many of these cells is why we culture them," he explains. "If we take bone marrow, about one in 100,000 nucleated cells are mesenchymal; that's why we need to culture. That's what we've patented."
In the case of cells taken from the umbilical cord, after the foaling process and passage of the placenta, a 10-cm section of the umbilical cord is cut, cleaned, and shipped to the company's laboratory in Edinburgh. The mesenchymal cells are extracted, cultured to a minimum of 50 million cells, and stored cryogenically.
From an adult horse, the bone marrow is collected from the sternum under standing sedation. About 20 ml is aspirated in preloaded heparinized syringes and taken to Edinburgh, where the mesenchymal cells are extracted and cultured to a minimum of 10 million cells. The culturing process takes from 10 to 30 days, averaging around 20. "It is important that the cells are not implanted during the inflammatory phase of the injury, as this is likely to drive the cells down a more fibroblastic (scar) lineage rather than the desired tenocyte, approximately three to four weeks postinjury, which is ideal when considering the length of time it takes to culture the cells," says McGarrell.
The VetCell system has been licensed by Vet Biotechnology, a company based in Adelaide, Australia, and by the Japan Racing Association, McGarrell says. "What VetCell, the Royal Veterinary College, and others are doing is trying to produce a real regeneration result. And the only way you can do that is by culturing cells."
WHERE'S THE DATA?
Perhaps understandably, both companies say theirs is the best approach, but making a comparison is difficult. At this point, published data on the efficacy of either system is decidedly thin, says Lisa Fortier, an expert in equine stem cells and orthopedics from Cornell College of Veterinary Medicine in Ithaca, NY. "In fact, the most interesting thing in all of this is that nobody has shown that any cells at all are needed to improve tendon healing," Fortier says. "The only thing we do know is that growth factors do help."
The difficulty for the California firm, she says, is that by separating the cells from their environment, the company is potentially removing any growth factor that might have been present. But on the other hand, the problem for their British counterparts is that little growth factor seems to be present in bone marrow aspirate, as Fortier and colleagues show in an abstract submitted to next year's Orthopedic Research Society meeting.
For Harman however, the proof is in the clinic, or on the racetrack. He says the company has treated about 600 horses so far, with a 75–80% success rate. Among racehorses specifically, he says the company has treated about 100, of which 50 or so have had time to get back on the track. Among those, the success rate is also roughly 70%. Across the Atlantic, VetCell shows "a 73% prognosis return to racing for racehorses treated," McGarrell says.
Fortier suggests caution when interpreting the companies' results. "Even with no treatment, at least 50% of the horses will race one more time," she says. A true proof of success would come after three or more races without repeat injury.
Scott Waterman, executive director of the Racing Medication and Testing Consortium, an industry-funded group trying to establish uniform rules for medication of race horses in the United States, says that the evidence he has heard so far about the efficacy of stem cell treatment is little more than anecdotal. Since the treatment isn't aimed at performance enhancement, it is not likely to violate any rules, he says. "Actually, if this proves to be a useful therapy, it's going to be a positive for racing," says Waterman. "As long as it's a complete heal and you're not putting the horse out there in jeopardy."
ON TO DOGS AND CAMELS
Meanwhile, the entrepreneurs at Vet-Stem are looking forward to expanding their stem-cell service to other conditions in horses, as well as further animal species such as domestic dogs and cats. "Who knows, maybe we'll be in racing camels in Saudi Arabia one day," Harman suggests.
McGarrell takes issue with such talk. "This is not what the field needs at the moment," he says. "There is no clinical proof in veterinary medicine for anything other than tendons or ligaments." Fortier agrees. Vet-Stem "needs to openly present some of their data," she says. "I think they lose credibility by claiming it's a magic bullet."
The company has even treated some arthritic pooches already, with positive results. "The real proof is when you're in real patients," Harman says. "We barreled ahead and said, let's see if it really works."