The effects of different cell-based therapies at a critical time point during the soft-tissue healing process

Abstract

Background: Cell-based therapy for soft tissue injuries remains controversial. Adult mesenchymal stem cells (MSCs) are therapeutic candidates given their capacity for self-renewal, immunoprivilege, and differentiation capacity for chondrocyte and tenocyte lineages. Platelet rich plasma (PRP) has been reported to promote collagen synthesis and cell proliferation, influencing the healing of ligaments and cartilage. We hypothesize that allogeneic MSCs and PRP have additive effects on promoting ligament healing in an in-vivo rat medial collateral ligament (MCL) injury model. Methods: MCLs of 20 females Sprague rats were bilaterally transected and treated with either saline (controls) or 1 of 3 treatment groups; (1) allogeneic MSCs (10 5 cells), (2) PRP and (3) allogeneic MSCs & PRP. In addition, five rats were used for the Sham group (surgery + no ligament injury). Rats were sacrificed two weeks post-surgery and the MCLs harvested for histological analysis by hematoxylin and eosin and alcian blue staining. Statistical analysis was performed using Fischer’s exact test with pair-wise comparisons and Bonferroni multiple comparison correction. Results: Histologically, differences across all injured groups (treatment groups and controls) were observed in cellularity (p < 0.0185), regeneration of collagen fibers (p < 0.0084), vascularity (p = 0.0129), inflammation (p = 0.0121) and glycosaminoglycan content (p = 0.0085). From pair-wise comparisons, only the combination allogeneic MSCs & PRP group differed significantly from controls in increased cellularity (p = 9.04 x 10 -4 ) and regeneration of collagen fibers (p = 6.58x10 -4 ). In addition, the PRP group showed significant increase in glycosaminoglycan (p = 0.006) content when compared to the allogeneic MSCs group. Conclusions: The addition of allogeneic MSCs and PRP to an injured MCL show a significant histological increase in degree of cellularity, vascularity and the regeneration of collagen fibers when compared to controls. These data support a possible additive effect of combining allogeneic MSCs and PRP therapy to increase important repair factors during the proliferation/repair phase of post ligament injury. This preliminary study demonstrates that additional functional and biomechanical studies are warranted to determine the role that inflammatory responses versus tissue regeneration are contributing to this mechanism.