Growth and Development Symposium: Stem cell therapy in equine tendon injury.

Tendon injuries affect all levels of athletic horses and represent a significant loss to the equine industry. Accumulation of microdamage within the tendon architecture leads to formation of core lesions. Traditional approaches to tendon repair are based on an initial period of rest to limit the inflammatory process followed by a controlled reloading program designed to promote the maturation and linear arrangement of scar tissue within the lesion. However, these treatment protocols are inefficient, resulting in prolonged recovery periods and frequent recurrence. Current alternative therapies include the use of bone marrow-derived mesenchymal stem cells (BMSC) and a population of nucleated cells from adipose containing adipose-derived mesenchymal stem cells (AdMSC). Umbilical cord blood-derived stem cells (UCB) have recently received attention for their increased plasticity in vitro and potential as a therapeutic aid. Both BMSC and AdMSC require expansion in culture before implantation to obtain a pure stem cell population, limiting the time frame for implantation. Collected at parturition, UCB can be cryopreserved for future use. Furthermore, the low immunogenicity of the UCB population allows for allogeneic implantation. Current research indicates that BMSC, AdMSC, and UCB can differentiate into tenocyte-like cells in vitro, increasing expression of scleraxis, tenascin c, and extracellular matrix proteins. When implanted, BMSC and AdMSC engraft into the tendon and improve tendon architecture. However, treatment with these stem cells does not decrease recovery period. Furthermore, the resulting regeneration is not optimal, as the resulting tissue is still inferior to native tendon. Umbilical cord blood-derived stem cells may provide an alternate source of stem cells that promote improved regeneration of tendon tissue. A more naïve cell population, these cells may have a greater rate of engraftment as well as an increased ability to secrete bioactive factors and recruit additional reparative cells. Further work should clarify the role of distinct stem cell sources in the regenerating tendon and the need for a naïve or differentiated cell type for implantation.