Stem cell source site has been debated among researchers in recent years as stem cells have been gaining popularity in equine medicine. A research group at Colorado State University recently compared the use of bone marrow-derived mesenchymal stem cells from two sites on the horse's body to determine which might be most effective for treating specific soft tissue injuries. Laurie Goodrich, DVM, PhD, Dipl. ACVS, presented results at the 2011 American Association of Equine Practitioners Convention, held Nov. 18-22 in San Antonio, Texas.

According to Goodrich, stem cells are particularly useful for treating tissues such as joints and tendons-these tissues lack regenerative capability due to a deficiency in local stem cell response. Stem cells have been derived from adipose tissue (fat) and bone-marrow. However, for tendon healing, bone marrow-derived cells yield better matrix and collagen production, she noted.

The research team compared bone marrow-derived mesenchymal stem cells (BM-MSCs) from the two most common extraction sites in the horse: the sternum (breastbone) and the ilium (hip). For BM-MSC therapy to be effective, Goodrich said two aspects are crucial: using large numbers of cells (roughly 5-10 million cells/centimeter in tendon and 5-10 million cells/joint) and implanting the cells early during the critical period between the inflammatory and fibroblastic phases of healing.

Goodrich discussed previously noted advantages and disadvantages for each site:

For the sternum:

• Advantages
  • The bone marrow aspirate flows better into the syringe;
  • The amount of aspirate is not influenced by age of the horse; and
  • Cells are easier to collect.
• Disadvantages:
  • The site is close to vital structures (heart, lungs); and
  • The collector must crouch under the horse.

For the ilium:

• Advantages
  • Practitioner doesn't have to crouch while obtaining cells; and
  • There's no risk of jabbing the heart or lungs.
• Disadvantages
  • It's more difficult to get adequate cell volume;
  • The sample size is age-dependent; and
  • Ilial samples often result in unsuccessful culture.

Researchers and clinicians had also noticed that the cells from sternal samples appeared different from those in ilial bone marrow samples.

Goodrich's study sought to provide clinicians with better information to guide selection site and on whether the health of the MSCs varied between separate samples or (fractions) of bone marrow drawn from a site at one time. Goodrich and her co-authors examined two sequential 5 mL samples from both sternal and ilial bone marrow aspirates of seven horses (they "plated" cells from the sample/grew them in culture, referred to as a "passage"). They found that:

• The first fractions of both samples yielded the highest cell counts;
• The cells of the first fraction were no healthier than those of the second;
• The health of the sternal and ilial samples was the same;
• By the second and third culture passages, cell morphologies were similar between the two sites; and
• Aspirates greater than 5-10 mL produced insignificant increases to the nucleated cell count.
• Goodrich noted the following limitations to the study:
• A relatively small number of horses was used;
• There was some variability in age and gender of the horses; and
• They didn't calculate the cell-doubling times, although the measurement of cell numbers at each passage was more relevant.

Goodrich's team concluded that bone marrow aspiration site should depend on clinician preference, since the cells of one site do not appear to be superior to the other.

Disclaimer: Seek the advice of a qualified veterinarian before proceeding with any diagnosis, treatment, or therapy.