Stem Cells Aid Dogs With Muscular Dystrophy to Walk More Normally
28 Nov, 2006 06:07 pm
Duchenne muscular dystrophy is a genetic disease that has not treatment and severely limits motility and life expectancy in people. A close animal model with the same symptoms as humans is the golden retriever dog. A recent study shows that stem cells injected into arteries have been able to help dogs with muscular dystrophy walk more normally. This can mean a possible future therapy for Duchenne muscular dystrophy patients.
It’s quite a long story, but to make it short, we’ve been studying how muscles develop and are repaired for many years. About 7 or 8 years ago, we identified a kind of stem cell, a type we’ve named mesoangioblast. It can be grown in culture, can differentiate into different types of muscle, and more importantly, can cross blood vessel walls when injected into arterial circulation. That is because we know that it expresses some of the proteins that white blood cells, leucocytes, use to cross the endothelial and vessel walls. We reasoned that if we were to deliver normal cells to dystrophic animals through the arterial circulation, we would be able to reach an even distribution of the cells in the downstream muscle; the cells would probably cross the vessel walls and to a certain extent get into the muscle. If the muscle regeneration is on-going, as it is in the first stages of muscular dystrophy, then the donor cell would be incorporated into newly-formed fibers, contributing the product of the healthy well type gene to the newly-formed fiber—thus, in this way, being a cure. We tested this approach in dystrophic mice and we published this study in Science in 2003 [1]. Although the mouse is a fitting mother in a genetic, pathological point of view does not have the full spectrum of symptoms that characterize patients with Duchenne muscular dystrophy. The only reliable and close, large animal model is the dog, which has a form of muscular dystrophy that is very similar to Duchenne muscular dystrophy [found in humans]. In 2004, we started treating dystrophic dogs with donor cells [2], but also with autologous cells that had been corrected in vitro and we noticed that when the protocol had been worked out properly, the dogs were maintaining a good level of motility if the treatment was started early. The dogs even regained some motility if the treatment was started a little late, when the dog had already started limping.
What were the results?
We noticed in the dogs, after 5 consecutive injections, that dystrophin was expressed in a large percentage of the muscle fiber. Although this was valuable from muscle to muscle and from biopsy to biopsy, the general parameter of the disease tended to normalize, like the serum level of creatin kinase (CK), and the force of the muscle fiber did not decrease as had happened during the normal progression of the disease. Finally, we noticed the dogs were walking better, especially those for whom we started treatment late. The others maintained a good walking ability for the length of the treatment and also thereafter.
What can be the drawbacks of using stem cell treatment for muscular dystrophy?
There are general drawbacks or risks that one can envision. The first that comes to mind is that we have to inject a lot of cells; there is the fear that some of these cells may undergo mutation and give rise to a tumor. We think this is a concern for embryonic stem cells, but we’re not really worried for adult stem cells. Although anything is possible, we think it’s unlikely, because these cells are normally cells that do not undergo changes in the chromosome content; they stop dividing after about 20 passes. To reach the large number needed, we’d probably inject cells that are quite close to the end of their proliferative life span. Therefore, the probability that they might give rise to tumors, in our opinion, is remote, but still possible. The other concern is that not all the cells we inject end up in the muscle, but some flow through the capillary network, reaching the venous network, eventually ending up in the capillary filter organs, like the liver, lungs, or kidneys. The lungs of many dystrophic patients, or dogs, already suffer because of the weakness of the respiratory muscles. We were worried that the significant number of cells in the lung interstition may create additional respiratory problems. However, as far as we could tell, the veterinary pathologist who was following the dogs did not notice any breathing problems in these animals. The cells in the lung obviously did not cure, but they also did not seem to harm. However, in patients, this could be a matter of concern. These, to me, are problems we might face in trying this therapy one day in patients.
How close do you believe we are in using such a stem cell treatment in clinical trials on humans?
Our rough estimate is a few years—a couple of years if all goes well. We still must have longer follow-up of the treated dogs and we need to raise funds for the forms of the regulatory authorities in Italy. Finally, we’ll need to recruit patients. We think it might 2 years or a little longer, something like that.
[1] Sampaolesi, M. et al., Science. 25 July 2003
[2] Sampaolesi, M. et al., Nature Online. 15 Nov 2006
Dr. Cossu is a researcher in Physiopathology of skeletal muscle development at the San Raffaele Institute in Milan.
Interview by: Thanh-Tam Candice Vu
