Affinity Controlled Co-Delivery of Immunomodulatory and Osteogenic Proteins to Enhance Bone Repair

Musculoskeletal injuries to the extremities account for nearly half of all traumatic injuries experienced by military service members and civilians and can cause substantial disability. Bone morphogenetic protein-2 (BMP-2) is a potent osteoinductive protein that is delivered clinically to repair large bone defects. However, the combination of supraphysiological protein doses and the clinical collagen sponge delivery vehicle that provides poor BMP-2 localization within injury sites can cause significant soft tissue inflammation and abnormal ossification. To address this challenge, we will use directed evolution of a yeast surface display library of affibody proteins to generate specific protein binding partners with tunable affinities. We will use these protein binding partners to tune the delivery of therapeutic proteins. Since the early immune response to bone injury can drastically influence healing outcomes, this project specifically focuses on codelivery of BMP-2 with the immunoregulatory cytokine interleukin-4 (IL-4), which is a key driver of musculoskeletal repair. Combining immunomodulation with BMP-2 may be a promising strategy for bone repair that lowers required protein doses. To easily integrate these binding partners into the clinical collagen sponge delivery vehicle, we will create fusion proteins in which half of the protein contains a collagen-binding domain that binds to the collagen sponge and the other half of the protein contains an affibody binding partner that binds to either IL-4 or BMP-2. We will test the hypothesis that sequential release of IL-4 followed by BMP-2 using protein binding partners integrated into the clinical collagen sponge will resolve the inflammatory response to bone injury and enhance bone repair.