Immune modulation with primed mesenchymal stem cells delivered via biodegradable scaffold to repair an Achilles tendon segmental defect

Tendon healing is a complex coordinated series of events resulting in protracted recovery, limited regeneration, and scar formation. Mesenchymal stem cell (MSC) therapy has shown promise as a new technology to enhance soft tissue and bone healing. A challenge with MSC therapy involves the ability to consistently control the inflammatory response and subsequent healing. Previous studies suggest that preconditioning MSCs with inflammatory cytokines, such as IFN-, TNF-, and IL-1 may accelerate cutaneous wound closure. The objective of this study was to therefore elucidate these effects in tendon. That is, the in vivo healing effects of TNF- primed MSCs were studied using a rat Achilles segmental defect model. Rat Achilles tendons were subjected to a unilateral 3mm segmental defect and repaired with either a PLG scaffold alone, MSC-seeded PLG scaffold, or TNF--primed MSC-seeded PLG scaffold. Achilles tendons were analyzed at 2 and 4 weeks post-injury. In vivo, MSCs, regardless of priming, increased IL-10 production and reduced the inflammatory factor, IL-1. Primed MSCs reduced IL-12 production and the number of M1 macrophages, as well as increased the percent of M2 macrophages, and synthesis of the anti-inflammatory factor IL-4. Primed MSC treatment also increased the concentration of type I procollagen in the healing tissue and increased failure stress of the tendon 4 weeks post-injury. Taken together delivery of TNF- primed MSCs via 3D PLG scaffold modulated macrophage polarization and cytokine production to further accentuate the more regenerative MSC-induced healing response. (c) 2016 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 35:269-280, 2017.