最新2013年4月11日《自然》杂志上一篇关于干细胞应用方面的文章，报道了干细胞治疗领域的一个真正实际应用的领域：兽医学。文章的题目是Stem cells boom in vetclinics。文章中提到，在人类干细胞谨慎应用的同时，在马、狗和猫，甚至老虎身上取得了非常令人激动的效果。这应该引起我们的关注和思考。关于干细胞，我们是否过于谨慎，对某些其他手段无能为力的疾病，在一定规范下，大胆使用干细胞是否应该提倡和鼓励。另外，对学者们也有提示作用，也许在人体研究存在困难的情况下，找找动物兄弟帮助，甚至植物，也许可以获得意想不到的收获。干科学有时候也不能太死板。

在美国，病人试图使用未经证实的干细胞疗法会受到政府的限制。但是来自弗吉尼亚的赛马Vinty不需要理会美国政府的规定。毫无困难地获得干细胞注射治疗伤腿的肌腱。它获得意想不到的治疗效果，并得以重新回到训练场。

不过最新的FDA规定可能会限制干细胞在动物医学上的应用，因为老的规定已经使用了10年，面临着更新。据说新的规定年底就会执行，许多人开始担心，这一新规定可能会导致动物们无法尝试这些没有被证实的治疗技术，甚至会间接阻碍人类临床医学的发展。

由于没有明确的限制性规定，这个行业已经悄然兴起。加利福尼亚一个兽医干细胞公司专门提供干细胞治疗各类动物。自2004年，他们已经给超过5000匹马、4300只狗和120只猫等动物患者们进行了干细胞治疗。更厉害的是肯塔基州尼古拉斯维尔的MediVet，他们自2010年以来给超过10000匹马提供干细胞治疗的服务。一些大学的兽医系，独自或经过公司运作，给无数动物提供这种服务。

干细胞在马、狗、猫用的比较多，也有人用于老虎甚至海豚，甚至考虑用干细胞治疗各类肝脏疾病和糖尿病。

许多兽医提供未经证实的干细胞疗法，以满足客户的要求，加州大学戴维斯分校的兽医专业的Borjesson多丽说。“即使没有证据支持，许多兽医临床医生仍积极采用这种方法”。像人类寻求治疗，大部分用于动物治疗的细胞是间充质干细胞，这种干细胞具有可分化成多种细胞类型的能力，包括骨和软骨，已证明间充质干细胞具有很好的抗炎和其他效果。培养这种细胞的技术已经非常成熟，技术人员只需要从脂肪或骨髓中提取间充质，就可以培养出高浓度的能用于治疗的间充质干细胞。

FDA对使用人类骨髓间充质干细胞的态度非常明确，干细胞属于药物，必须首先被证实安全有效才可以应用。目前没有任何MSC治疗被批准。虽然对兽医的要求和人类临床医学不同，FDA虽然没有打击，但也确实没有批准任何一家兽医干细胞疗法。与此形成鲜明对比的是，FDA高调反对给人类提供未经证实的人类干细胞治疗。例如美国德克萨斯州Celltex Therapeutics ofSugar Land曾经将msc用于人类患者，2012年9月因FDA的介入而被中断。

更准确全面的信息，请看以下《自然》上的原文：

Horses, dogs and even a tiger have received the unproven therapies. Now,drug regulators plan to weigh in.

      David Cyranoski

10April 2013

Patients seeking unproven stem-cell therapies in the United States oftenrun up against government restrictions. But Vintage ‘Vinty’ Mark ofLovettsville, Virginia, had no difficulty getting such injections to treat aninjured tendon in his leg. The leg improved dramatically, and Vinty went backto training — to be a racehorse.

New guidance from the US Food and Drug Administration (FDA) could,however, soon rein in veterinary uses of stem cells, a practice that hasexploded in the United States over the past decade, even though most therapiesare unproven. Many researchers and veterinarians say that the guidance, a draftof which the agency plans to issue by the end of the year, is overdue. Butothers worry that FDA interference could hamper research that could benefitanimals — and their human companions.

In the absence of clear regulations, the industry has burgeoned. Vet-Stem,a company based in Poway, California, has provided stem-cell treatments to morethan 5,000 horses, 4,300 dogs and 120 cats since treating its first patient in2004. Kits provided by MediVet America, based in Nicholasville, Kentucky, havebeen used to produce stem-cell injections for more than 10,000 horses since2010. University veterinary departments, independently or through spin-offcompanies, have offered such services to thousands more animals. Veterinarianssend patients’ tissue samples to the centres to have cells extracted or,increasingly, turn to kits that allow them to extract the cells in-house.

Stem cells are most often used to treat horses, dogs and cats, butclinicians have also sought to use them to repair a lumbar fracture in a Bengaltiger and arthritis in pigs. Researchers have also found stem cells in the fatof bottle­nose dolphins, raising hopes for treating the marine-mammal versionsof liver disease and type 2 diabetes. “There’s not a large vet practice that’snot using them,” says Wesley Sutter, a veterinarian at Lexington Equine Surgeryand Sports Medicine in Kentucky. “Some claim [the treatment] cures everything.”

Many veterinarians offer unproven stem-cell therapies to satisfy demandingcustomers, says Dori Borjesson, who specializes in veterinary medicine at theUniversity of California, Davis. “Clinicians are sucked into giving treatment”even when there’s not research to back up uses, she says.

Like the treatments sought by humans, most of those used in animalsinvolve mesenchymal stem cells (MSCs), which can mature into a wide variety ofcell types, including bone and cartilage, and have been shown to haveanti-inflammatory and other beneficial effects. MSCs are extracted from fat orbone marrow and can be cultured or prepared for injection in concentrated form.

The FDA’s position on the use of MSCs in humans is clear. It says that thecells are drugs and therefore must be proved safe and effective before they canbe used in treatment, except under certain conditions. No MSC treatments havebeen approved. But the FDA has different regulations for veterinary medicine,and these do not clearly address MSCs. The agency has not approved anyveterinary stem-cell therapies, but neither has it cracked down on any. This isin stark contrast to its high-profile actions against purveyors of unprovenhuman stem-cell treatments, such as Celltex Therapeutics of Sugar Land,Texas,which treated patients with MSCs until the FDA stepped in last September.

That doesn’t mean that the agency is not concerned, says Lynne Boxer, aveterinary medical officer in the FDA’s Office of New Animal Drug Evaluation inRockville, Maryland. “As with any type of drug product, there are risks andbenefits,” she says. “With stem cells, there is the potential for diseasetransmission and tumour formation.” She declines, however, to say whethercurrent practices are against FDA rules, or to elaborate on what the new draftguidance is likely to contain.

The guidance void is irksome, says Karl Nobert, a lawyer at Squire Sandersin Washington DC, who has represented companies seeking direction from the FDA.His concern is not just professional: he is Vinty’s former owner, and says thathe saw “incredible improvement” as the horse healed, with normal tendon fibresrather than scar tissue at the injury site.

Research backs up the benefits of stem-cell treatments in someapplications. A 2007 double-blind study in 21 dogs showed that MSCs improvedchronic osteoarthritis1.A 2010 report showed that injections of tissue rich in MSCs helped damaged legbones to heal in 12 horses2.And a 2012 study, much discussed by veterinarians, showed that MSCs from bonemarrow helped racehorses with tendon injuries avoid re-injury3.

Researchers recognize that many studies of veterinary stem-cell treatmentshave a major weakness: they lack control groups or blinded evaluation, whichare crucial to show whether the treatments truly make a difference. “It isexceptionally difficult to do blinded studies in our patients because theowners or trainers specifically seek an institution for stem-cell therapy,”says Lisa Fortier, a veterinary surgeon at Cornell University in Ithaca, NewYork, and a co-author of the 2010 cartilage study.

Without controlled trials, comparisons between treated and untreatedanimals are difficult. Owners who have paid a few thousand dollars for atherapy are more likely to follow strict rehabilitation protocols than thosewho have not. They are also more likely to rush horses back into action, whichwould skew reported recovery time, a measure of a treatment’s effectiveness.And placebo effects — on the owners — can be powerful. “The cat looks like hellto me but the owner says: ‘She looks so great. I love stem cells’,” saysBorjesson.

Many veterinarians think that studying stem-cell therapies in largeanimals, which are more physiologically similar to humans than the mice oftenused in preclinical research, could be a powerful model for medicine — ifstudies are done right. Borjesson is running studies (with “as much blinding aspossible”) of stem-cell treatments for dry eye, another eye condition calledrecurrent uveitis, and inflammatory bowel disease in clients’ pet dogs. She isalso collaborating with researchers in human regenerative medicine, so that herfindings can inform their studies of experimental therapies. And David Frisbie,a veterinary surgeon at Colorado State University in Fort Collins, is workingwith doctors to apply lessons from animal stem-cell treatments to jointinjuries in humans.

If the pending FDA guidance clearly designates animal stem cells as drugs,veterinarians and companies who want to deploy such treatments will first haveto conduct clinical trials, which Frisbie estimates could cost at least US$5million each. Nobert, meanwhile, is optimistic that veterinary stem-cellcompanies and university researchers will find ways to “design creativeregulatory approval strategies to streamline and expedite thereview-and-approval process” — which might, in turn, influence the humanstem-cell regulatory process.

Still, he worries that overly stringent FDA rules about, for example, howcells are characterized, could “make the ultimate commercial priceunreasonable”.

For Vinty, it’s a moot point. He’s had his stem cells. But even with histendon fixed, he was too slow to race. He now gives riding lessons to children.

Nature496, 148–149 (11 April 2013) doi:10.1038/496148a

References

1.          Black, L. L. et al.Vet. Ther.8, 272–284 (2007).

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3.          Fortier, L. A. et al.J. Bone Joint. Surg. Am.18, 1927–1937 (2010).

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Godwin, E. E., Young, N. J., Dudhia, J.,Beamish, I. C. & Smith, R. K. W. Equine Vet. J.44, 25–32(2012).