Growth, differentiation, transplantation and survival of human skeletal myofibers on biodegradable scaffolds

Skeletal muscle transplantation strategies for muscle repair or gene therapy involve either the injection of proliferating myoblasts followed by fusion with host myofibers or implantation of ex vivo differentiated myofibers; however, both implant procedures are associated with significant cell loss. Biodegradable porous, gas-foamed poly-lactide-co-glycolide (PLG) scaffolds have desirable characteristics for cell transfer and were used to study attachment, growth, differentiation and survival of human myogenic cells. Primary human myoblasts suspended in clinical grade extracellular matrixes (ECMs) and adhered to PLG scaffolds differentiated in vitro into high-density tropomyosin positive myofibers. An immunodeficient non-obese diabetic/severe combined immunodeficiency (NOD/SCID) mouse implant model was used to study the transfer and in vivo survival of differentiated human myofibers on these scaffolds. Scaffold rigidity allowed the myofibers to be maintained under tension in vitro and following subcutaneous transplantation in vivo. Following implantation, myofiber density on the PLG scaffolds decreased linearly by 78% over a 4-week period. ECM composed of either Tisseel fibrin or Zyderm collagen type I did not significantly affect in vivo cell viability over the 4-week period. Varying PLG scaffold microsphere content (10-100%) also had little effect on cell survival in vivo. In contrast, when the residual NK cell population in the immunodeficient NOD/SCID mouse model was depleted with anti-asialo GM1 (ASGM1) antiserum, in vivo cell survival significantly increased from 22% to 34% after 4 weeks. With further improvements in cell survival, PLG scaffolds may prove useful for the implantation of primary human myofibers in future clinical applications.