The Harry M. Zweig Memorial Fund for Equine Research

Characteristics of Stem Cells Derived from Bone Marrow
Aspirate, Adipose Tissue and Muscle

Dr. Lisa Fortier

FortierThe application of stem cells in equine veterinary therapeutics is an emerging field.  In horses, stem cells hold tremendous promise for the treatment of any disease that involves cell death such as nerve injury (roarers and wobblers), arthritis, bowed tendons, and suspensory ligament tears.  Stem cells are generically defined as cells that are capable of continued self-renewal through replication, and of becoming cells of specific tissue types. Typically, cells such as those from skin, are only capable of dividing a couple of times before they die, and unlike stem cells they cannot turn into cells of tissue types that are different than their origin.  For example, skin cells cannot turn into nerve cells, and muscle cells cannot turn into cartilage cells.  However, it is the capacity of stem cells to continuously replicate and turn into nearly any cell type in the body that makes them attractive assets for tissue regeneration.

There are an increasing number of methods/biologics being developed and utilized under the guise of “stem cell therapy”, particularly to treat bowed tendons.  For example, bone marrow aspirate taken from a horse’s breast bone (sternum) is said to contain stem cells, and there is a company (Vet-Stem, Poway, CA) that claims to isolate stem cells out of fat taken from a horse’s rump.  There are also assertions that stem cells are readily isolated from muscle tissue.  Although a large body of information is available on stem cells, there is a generally over-simplified view of stem cells with respect to their definitions, availability, and ability to turn into assorted tissues. The presumption by many is that any cell which sticks to a tissue culture dish is a stem cell, and no further characterizations are performed.  Clinically, these simplified presumptions have lead to the relatively common procedure of injecting bone marrow aspirate into tendons and suspensory ligaments, and the increasing use of fat-derived cells, even though there is no data available concerning the absolute number of stem cells that can be obtained from either source.  Further, there is no information comparing the ability of stem cells, obtained from different tissues, to turn into other tissues such as nerve, tendon or cartilage. Therefore, no objective clinical recommendations regarding the optimal source of stem cells for treatment of different injuries can be made.

The premise for this proposal is to simply answer two fundamental questions so that the best possible source of stem cells for therapeutic applications can be identified. We will ask: 1) How many stem cells can be obtained from bone marrow aspirate, fat, or muscle, and 2) Which tissue source, bone marrow, fat, or muscle, provides stem cells with the greatest capacity to turn into cartilage or bone.  We will not investigate the ability of stem cells to turn into tendon since there are no established methods to drive stem cells into tendon.  More importantly, there are no molecular markers specific to tendon cells, rendering interpretation of outcome data problematical.  This one-year proposal will build on the results of our 2006 Harry M. Zweig Memorial Fund for Equine Research proposal in which we successfully generated a panel of ten cell surface markers that can be used to identify adult-derived stem cells.  This marker panel is the first of its kind that can be used to define equine adult-tissue derived stem cells.  The broad objectives of the present proposal are to compare the quantity and quality of stem cells obtained from equine bone marrow aspirate, adipose tissue, and muscle, in order to provide a scientific and objective basis for the clinical application of stem cell therapies in athletic horses.

Stem cells obtained from bone marrow, fat, or muscle are attractive since they can be auto-transplanted, i.e. obtained from and re-inserted into the same patient. Auto-transplantion of cells avoids potential donor-host immune rejection and disease transmission issues.  In contrast, embryonic stem cells may be subject to host-immune rejection, and although we have made tremendous progress (with Zweig funding in 2003/2004) in establishing several embryonic stem cell lines, there are not yet enough cells in our bank for experimental purposes. Therefore this proposal will focus solely on stem cells derived from adult tissues.