Self-complementary AAV2.5-BMP2-coated Femoral Allografts Mediated Superior Bone Healing Versus Live Autografts in Mice With Equivalent Biomechanics to Unfractured Femur

Abstract

Structural allografts used for critical bone defects have limited osteogenic properties for biointegration. Although ex vivo tissue-engineered constructs expressing bone morphogenetic protein-2 (BMP2) have demonstrated efficacy in critical defect models, similar success has not been achieved with off-the-shelf acellular approaches, including allografts coated with freeze-dried single-stranded adeno-associated virus (ssAAV-BMP2). To see whether the self-complementary AAV serotype 2.5 vector (scAAV2.5-BMP2) could overcome this, we performed side-by-side comparisons in vitro and in the murine femoral allograft model. Although ssAAV-BMP2 was unable to induce BMP2 expression and differentiation of C3H10T1/2 cells in culture, scAAV2.5-BMP2 transduction led to dose-dependent BMP2 expression and alkaline phosphatase activity, and displayed a 25-fold increased transduction efficiency in vivo. After 6 weeks, the ssAAV-BMP2 coating failed to demonstrate any significant effects. However, all allografts coated with 10(10) scAAV2.5-BMP2 formed a new cortical shell that was indistinguishable to that formed by live autografts. Additionally, coated allografts experienced reduced resorption resulting in a threefold increase in graft bone volume versus autograft. This led to biomechanical superiority versus both allografts and autografts, and equivalent torsional rigidity to unfractured femur. Collectively, these results demonstrate that scAAV2.5-BMP2 coating overcomes the major limitations of structural allografts, which can be used to heal critical defects of any size.

Quantifying Massive Allograft Healing of the Canine Femur In Vivo and Ex Vivo: A Pilot Study

“…As a result, investigators have developed preclinical adjuvant therapies [6,11,12,15,19,24,26,[30][31][32][33]. As yet, their clinical application has been unrealized, largely because a large-animal model has not been established, nor have clinically relevant diagnostic tools that can noninvasively quantify graft healing.…”

“…These limitations, in addition to graft type (intercalary/osteochondral), preservation technique, and internal fixation approach, are associated with a 25% to 35% failure rate due to nonunion and fracture [2,14] and a 10-year survival rate of less than 50% due to the accumulation of unremodeled microfractures, which compromise their mechanical properties [29]. To address these shortcomings, investigators have developed biologic adjuvant therapies (ie, BMP-2 [6,15,32], teriparatide [19,24]), stem cell [26,30,33], and gene [11,12,31]), which stimulate integration of cortical allografts. While these technologies have accelerated healing in small-animal models, their application in humans has been unrealized.…”

Specific Biomimetic Hydroxyapatite Nanotopographies Enhance Osteoblastic Differentiation and Bone Graft Osteointegration

“…Additionally, HAP nanotopographies could potentially be used in conjunction with recent cell-based methods to enhance bone formation. 41 This therapeutic approach has the potential to improve patient function and quality of life after bone transplantation and enhance 1710 LOISELLE ET AL.…”

Emerging Ideas: Engineering the Periosteum: Revitalizing Allografts by Mimicking Autograft Healing

“…Combinatorial approaches using MSCs, growth factors, and biomaterials have been used to emulate factors present during periosteum-mediated autograft healing. Growth factors commonly used include bone morphogenetic protein-2 (BMP-2) [27,34,45,46,48], teriparatide (PTH ), the recombinant peptide of parathyroid hormone (PTH) [13,29], vascular endothelial growth factor (VEGF) [21,22,46], receptor activator of nuclear factor kappa-B ligand (RANKL) [21], and the sphingosine 1-phosphate (S1P) receptor agonist, fingolimod (FTY720) [26].…”