Discovery and Characterization of Interleukin-4-Specific Affibodies for Affinity-Controlled Protein Release and Macrophage Polarization

Interleukin-4 (IL-4) is a key immunoregulatory cytokine that promotes type 2 inflammation, drives macrophage polarization toward an anti-inflammatory M2 phenotype, and supports tissue repair. However, clinical translation of IL-4 therapies to modulate the immune response is limited by the need for precise control over its delivery to avoid immune dysregulation. Here, we report an affinity-based strategy to modulate IL-4 delivery and bioactivity using engineered affibody proteins. A yeast surface display library was screened via magnetic- and fluorescence-activated cell sorting to identify two IL-4-specific affibodies with moderate binding affinities (dissociation constants, K _D = 459 and 141 nM). Circular dichroism confirmed expected alpha-helical folding, and biolayer interferometry characterized the kinetics of IL-4 binding. Structural modeling using AlphaFold3 and RosettaDock and molecular dynamics simulations using GROMACS predicted distinct binding sites for each IL-4-specific affibody on the IL-4 protein and suggested potential interference with receptor complex formation. Bioactivity studies using murine bone marrow-derived macrophages demonstrated that IL-4 complexed with affibodies maintained Ym1 gene expression but significantly reduced Ym1 protein levels, indicating partial inhibition of IL-4 signaling. To enable controlled cytokine delivery via affinity interactions, affibodies were conjugated to polyethylene glycol maleimide (PEG-mal) hydrogels, which were loaded with IL-4. Affibody-conjugated hydrogels achieved high IL-4 loading efficiency (>90%) and exhibited sustained release over 7 days. Increasing affibody-to-IL-4 ratios significantly reduced both the rate and total amount of cytokine release. Overall, this work establishes IL-4-specific affibodies as versatile tools for tuning cytokine presentation and modulating bioactivity and provides a promising approach for regulating inflammatory responses and advancing cytokine-based therapies with improved temporal control.