Local Transplantation of Ex Vivo Expanded Bone Marrow-Derived CD34-Positive Cells Accelerates Fracture Healing

Abstract

Transplantation of bone marrow (BM) CD34 + cells, an endothelial/hematopoietic progenitor-enriched cell population, has shown therapeutic efficiency in the treatment of ischemic diseases enhancing neovascularization. However, the number of CD34 + cells obtained from bone marrow is not sufficient for routine clinical application. To overcome this issue, we developed a more efficient and clinically applicable CD34 + cell expansion method. Seven-day ex vivo expansion culture of BM CD34 + cells with a cocktail of five growth factors containing VEGF, SCF, IL-6, Flt-3 ligand, and TPO resulted in reproducible more than 20-fold increase in cell number. The favorable effect of the local transplantation of culture expanded (cEx)-BM CD34 + cells on rat unhealing fractures was equivalent or higher than that of nonexpanded (fresh) BM CD34 + cells exhibiting sufficient therapeutic outcome with frequent vasculogenic/osteogenic differentiation of transplanted cEx-BM CD34 + cells and fresh BM CD34 + cells as well as intrinsic enhancement of angiogenesis/osteogenesis at the treated fracture sites. Specifically, cEx-BM CD34 + cell treatment demonstrated the best blood flow recovery at fracture sites compared with the nonexpanded BM CD34 + cells. In vitro, cEx-BM CD34 + cells showed higher colony/tube-forming capacity than nonexpanded BM CD34 + cells. Both cells demonstrated differentiation potential into osteoblasts. Since fresh BM CD34 + cells can be easily collected from fracture sites at the time of primary operation and stored for future use, autologous cEx-BM CD34 + cell transplantation would be not only a simple but also a promising therapeutic strategy for unhealing fractures in the field of orthopedic trauma surgery.