Affinity-based controlled release of interleukin-4 from scaffolds via biotin-streptavidin interactions for immunomodulation

Immunomodulatory cytokines like interleukin-4 (IL-4) can modulate host immune cell behavior to improve tissue integration, but versatile strategies for modifying complex biomaterials to control the release of such cytokines are limited. Bioconjugation strategies using biotin-avidin interactions offer a promising approach since biotin can be conjugated to proteins, biomaterials, and even cells, without compromising their function. Although it is known that conjugation of biotin to large biomolecules reduces its binding affinity for avidin and avidin variants, the potential to control the release of biotinylated molecules by leveraging these changes in affinity interactions has not been thoroughly investigated. Moreover, the effects of biotin and avidin variants on innate immunity are poorly understood. Therefore, the goals of this study were to determine if biotin-avidin interactions could be manipulated to control the release of IL-4 from biomaterials and to investigate the subsequent effects on primary human macrophage phenotype. First, we characterized the effects of soluble biotin, avidin, and avidin variants, streptavidin and CaptAvidin, on the phenotype of primary human macrophages from 8 different donors using RNA sequencing, finding that CaptAvidin influenced macrophage gene expression much more than the other variants. Then, after evaluating how bioconjugation parameters influenced biotin density and avidin variant binding to porous gelatin scaffolds, we found that biotin-avidin affinity interactions sustained the release of biotinylated IL-4 (bIL-4) from biotinylated and desthiobiotinylated scaffolds bound with either avidin or streptavidin for up to 14 days in vitro. Finally, we measured the response of primary human macrophages from 5 donors to the bIL-4-releasing scaffolds, finding an increase in reparative macrophage phenotype gene expression when bIL-4 was released via biotin-streptavidin interactions compared to scaffolds that relied solely on desorption-based release. These results highlight how biotin-streptavidin interactions can be leveraged for controlled release to achieve an immunomodulatory drug delivery system.