Adipose mesenchymal stem cells in canine regenerative medicine

Mesenchymal stem cells (MSCs) are being increasingly used in clinical applications due to their capacity for self-renewal and multipotent differentiation, as well as their immunomodulatory properties.

The willingness of the VMD to permit such novel therapeutic approaches, using biologicals with a light regulatory touch – as well as encouraging post-treatment data from years of use in the equine sector¹ – has allowed the application of these cells to a range of new treatments in companion animals.

Two approaches exist for the therapeutic use of adipose-derived stem cells. Firstly, adipose tissue can be collected, processed and returned for implant without culture; this material is referred to as the stromal vascular fraction (SVF).

Processing is minimal and can involve a laboratory, or can be achieved using an automated system and, therefore, be done in practice. The output of this process will be a pellet of cells ready for implantation, but it is worth noting some variability will exist in the product².

One advantage of this approach is collection, processing and re-implantation of the cells can be done on the same day, or within two days if the sample is sent to a laboratory for processing; but the disadvantage is many of the cells introduced into the site of injury or disease are not stem cells, but a heterogeneous population of MSCs along with endothelial cells, smooth muscle cells, fibroblasts, preadipocytes and immune cells³.

An alternative approach is the cells are isolated and cultured for several days until they number many millions. This highly purified population of cells is then ready to be re-implanted, suspended in autologous serum or plasma.

As performed at the authors’ laboratory, both approaches are autologous, so only material removed from the patient at sampling is returned at implant with no extra additives or carrier solutions.

Use of SVF allows for a more rapid treatment, and is generally less expensive, but consensus is growing a dose-dependent response may occur when using implanted MSCs – so it would be reasonable to suggest the culture of a large number of highly purified cells may prove to be more efficacious in many cases.

Adipose tissue can be collected from several sites. It is most commonly taken from a fat pad behind the scapula, but several sites have been suggested as appropriate sources, including retroperitoneal adipose tissue⁴, lateral thoracic area⁵, gluteal fat⁶ and the inguinal region⁷.

Cells are isolated and, where appropriate, cultured using standard practices⁸, and have been shown to be present in adipose tissue in large numbers. They have also been observed to show a high proliferative value compared to those found in bone marrow; an equal volume of adipose tissue can yield 10 million cells in half the time taken by a bone marrow-derived culture.

In dogs, adipose-derived cells have been shown to be the best available for therapeutic use, compared to bone marrow, Wharton’s jelly and umbilical cord blood⁹. Furthermore, although a limited reduction exists in availability and proliferative potential of MSCs in adipose tissue as animals age, these cells have been shown to be present in therapeutically useful numbers in dogs in their teens.

Indications

A growing number of practices are advertising stem cell treatment in dogs and citing joint problems as the main target for the therapy – especially those conditions that end up as arthritis, such as hip dysplasia, elbow dysplasia and osteochondrosis.

One main benefit of this treatment is its utility in intractable cases, where pain medication is no longer effective or cannot be used. Repeat applications of cells has been advocated and facilitated by the fact cells can be stored long term by cryopreservation, and, therefore, administered to chronic cases without the expense and additional trauma associated with further tissue harvesting and processing.

Secondary to OA is treatment of a range of bone and tendon injuries. Furthermore, on a case-by-case basis, they have been used in the treatment of a range of conditions, including inflammatory bowel disease, degenerative myelopathy, acute and chronic renal failure, chronic obstructive pulmonary disease, autoimmune diseases and spinal trauma.

Success of these applications can be difficult to judge, but evidence exists of improvements post-treatment – both anecdotal and published^10,11. A number of studies are ongoing to further assess the impact of these cells in regenerative medicine.

Research

A range of diseases are being experimentally treated using stem cells in dogs – many with a view to developing veterinary solutions, rather than as animal models. However, only a small number of these studies are in naturally affected dogs; most involved induced lesions¹².

Several studies exist into the use of allogeneic adipose-derived stem cells to treat a range of diseases, including keratoconjunctivitis sicca¹³, inflammatory bowel disease¹⁴, hip dysplasia¹¹ and bone regeneration¹⁵. However, the use of allogeneic transplants renders it unlikely this type of approach will be licensed in the UK in the near future, as the VMD restricts all procedures using MSCs to autologous cells and has shown no desire to change this.

Regulation

All cell culture must be performed at an approved scientific manufacturing centre licensed by the VMD.

A range of indications exist for the use of these cells, but – as has been the case in the equine sector, where MSCs have been used to treat animals for more than 14 years – the veterinary surgeon treating the case has overall responsibility for when and how cells are used.

The increasing scope of the potential application of these cells is pushing forward technology and breaking new ground at a rapid pace.