Antibody-Mediated Osseous Regeneration: The Early Events in the Healing Response

Abstract

Bone engineering strategies often exploit modulation of the extracellular environment, including delivery of cell and growth factors to repair and regenerate damaged tissues. During bone healing, the expression of endogenous bone morphogenetic proteins is an essential component of the healing response. However, in some situations, the inherent reparative capacity available in the local microenvironment is exceeded by the requirements of the defects. We have recently reported on a novel strategy, that exploits the specificity of antibodies to capture and make available endogenous osteogenic growth factors, referred to as "antibody-mediated osseous regeneration" (AMOR). The objective of the present study was to identify some of the cellular and molecular events involved in AMOR in an effort to begin to elucidate the mechanism of AMOR. The rat critical-sized calvarial defect model was used, where anti-bone morphogenetic protein (BMP)-2 monoclonal antibody (mAb), isotype-control mAb, or recombinant human (rh)BMP-2 were immobilized on absorbable collagen calvarial sponge (ACS) by adsorption, and then implanted into calvarial defects. The results demonstrated persistence of implanted mAbs for short term from 1 to 2 weeks after implantation. Increased cell infiltration was found in defects treated with anti-BMP-2 mAb. Examination of proteins on ACS scaffolds retrieved from defect sites demonstration increased levels of BMP-2, BMP-4, and BMP-7 proteins in sites implanted with anti-BMP-2 mAb. Moreover, BMP-2, BMP-4, and BMP-7 gene expression levels were increased in sites implanted with anti-BMP-2 mAb. Micro-computed tomography and histological analysis demonstrated that the bone within calvarial defects was fully regenerated in sites implanted with either anti-BMP-2 mAb or rhBMP-2. However, rhBMP-2-regenerated bone exhibited aberrant histomorphology with dystrophic calcification and invasion of subjacent areas. Altogether, the results revealed evidence for anti-BMP-2 mAbs to form an immune complex with BMP-2, BMP-4, and BMP-7, and bind to cells to mediate osteogenesis bone regeneration in vivo. This approach suggests a significant role for antibodies in regenerative orthopedic medicine.

Collagen Sponge Functionalized with Chimeric Anti-BMP-2 Monoclonal Antibody Mediates Repair of Critical-Size Mandibular Continuity Defects in a Nonhuman Primate Model

“…Based on previous dose-response data, 25  μ g/mL was selected as the optimal dose of chimeric anti-BMP-2 mAb for all experiments [15, 18]. …”

Co-encapsulation of anti-BMP2 monoclonal antibody and mesenchymal stem cells in alginate microspheres for bone tissue engineering

“…Recently, Freire et al . reported a bone regenerative therapy, in which anti-BMP2 monoclonal antibodies were capable of capturing endogenous BMP growth factors from the local host-graft site, with demonstrated efficacy in promoting bone repair and regeneration [20, 21]. Additionally, other studies have shown that a short treatment of MSCs with BMP2 ligand stimulated Runx-2 and osteopontin gene expression, leading to enhanced bone regeneration [30, 31].…”

“…However, there are a number of limitations to the application of exogenous growth factors, including significant side effects, reduced efficacy compared to endogenous counterparts, high cost, difficulty of achieving optimal kinetics for delivery, and temporal and spatial requirements for their availability [16-19]. As an alternative to using r ecombinant h uman b one m orphogenetic p rotein 2 (rhBMP2) as an exogenous growth factor, investigators have recently shown the ability of specific monoclonal antibodies (mAb) directed against BMP2 to capture endogenous BMP2 ligands from the engraftment site and present them to progenitor stem cells, promoting bone repair and regeneration [20, 21]. Therefore, one can envision that combining the stem cells with antibodies selected for their capacity to capture therapeutic ligands could enhance the quality and quantity of stem cell-mediated bone regeneration.…”

Biomechanical analysis of engineered bone with anti‐BMP2 antibody immobilized on different scaffolds

“…immobilized murine antibodies (mAbs) against BMP-2 on absorbable collagen sponge (ACS) and implanted them within rat calvarial defects. 21, 22 More recently, we demonstrated the ability of chimeric anti-BMP-2 monoclonal antibodies (mAb) immobilized on different types of scaffold materials to mediate de novo bone formation. 23 …”