ALTERING THE IMMUNE LANDSCAPE TO AUGMENT BONE REGENERATION

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PROJECT SUMMARY The overarching hypothesis of this project is that bone regeneration can be enhanced by exploiting vaccination status and recruiting adaptive immunity to the injury site through controlled release of an antigen. To test this hypothesis, the general approach in this project will be to immunize mice and then perform in vivo bone tissue engineering studies to test the impact of antigen delivery from the scaffold on bone formation and the immune response. The mice will specifically be vaccinated against influenza due to high annual vaccine coverage in the U.S. population, and influenza-derived hemagglutinin (HAG) peptide will be delivered from implanted scaffolds. Testing will be performed in mice using two experimental models, calvarial defects and femoral defects. In both models, the bone defects will be treated with hydrogel scaffolds releasing HAG peptide alone or in combination with therapeutic or sub-therapeutic doses of recombinant human bone morphogenetic protein-2 (BMP-2). All treatments will be duplicated in an unvaccinated control group using both male and female mice to test for gender effects. There are two Specific Aims. Aim 1 is focused on evaluating bone formation and defect regeneration, which will be evaluated at 3 weeks and 6 weeks after treatment by microcomputed tomography analysis and histology. The results will be benchmarked against defect treatment with a therapeutic dose of BMP-2 delivered from a collagen sponge, which will serve as a clinical control treatment. Aim 2 is focused on evaluating the effects of HAG peptide delivery on the immune response. Immune cell infiltration in the regenerating defects will be evaluated at 3 weeks and 6 weeks after treatment by immunostaining. In addition, transcriptomic changes will be evaluated 1 week after treatment by single-cell RNA sequencing. If successful, this project will lead to novel regenerative immunotherapies with high translational potential.