(H-312) Delivery of IL-4 mRNA via lipid nanoparticles for the intracellular control of macrophage phenotype

Introduction:: Cell therapy is a quickly growing field in biomedical engineering with a wide range of applications in immunotherapy and tissue regeneration. Due to their role as high-level regulators of healing and angiogenesis, macrophages are an attractive target for cell therapy platforms. Studies have shown that the delivery of macrophages to sites of injury can improve healing outcomes, such as biomaterial integration and blood vessel regrowth. Pro-regenerative IL-4-polarized macrophages in particular have demonstrated some success in promoting angiogenesis. However, macrophage plasticity and rapid response to environmental stimuli can make it difficult to maintain macrophage phenotype in the highly inflammatory injury milieu. In this study, we sought to overcome this problem by designing a biomaterials-based strategy to control macrophage phenotype intracellularly.

Materials and Methods:: Both human and murine primary monocytes were isolated from peripheral blood and bone marrow, respectively, and differentiated into macrophages with MCSF. Macrophages were either maintained in an unactivated phenotype (M0) or M1-activated with interferon-gamma and lipopolysaccharide (inflammatory media). Lipid nanoparticles carrying IL-4 mRNA (IL4-LNPs) were cultured with macrophages for 12 hours to facilitate phagocytosis. After co-culture with IL4-LNPs, macrophages were cultured in normal or inflammatory media. Culture media was collected from days 1-7 for ELISA, and cell lysates were collected on day 2 for gene expression analysis.

Results, Conclusions, and Discussions:: ELISA results showed that macrophages treated with IL4-LNPs were successfully transfected and secreted IL-4, a cytokine not typically produced by macrophages, at detectable levels for at least 7 days. Gene expression data demonstrated that this secreted IL-4 successfully polarized M0 macrophages and re-polarized M1 macrophages to a pro-angiogenic M2 phenotype. M1 macrophages significantly downregulated typical M1 markers, indicating that IL4-LNPs were able to overcome the inflammatory culture conditions of this group. Future work will administer IL4-LNP-carrying murine macrophages to volumetric muscle loss injuries to determine their effects on tissue regeneration and angiogenesis in vivo.

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