Engineering Macrophages to Control the Foreign Body Reaction

Abstract

The foreign body reaction (FBR) is an inflammatory response driven by macrophages (MΦs). During the inflammatory response, MΦs influence fibrosis and angiogenesis by secreting certain cytokines. It is still unclear what roles the pro-inflammatory (M1) MΦ and pro-healing (M2) MΦ phenotypes play during these processes. However, given that the FBR leads to a non-vascularized fibrous capsule surrounding most medical devices, better device integration might be possible by controlling the MΦ phenotype at the implant site to lead to decreased fibrosis and increased vessel formation. The research presented in this dissertation describes the development and characterization of engineered pro-inflammatory MΦs, MΦ-cTLR4 cells, which can be activated to a M1-like MΦ phenotype with a small molecule, the chemical inducer of dimerization (CID) drug. It is hypothesized that the engineered MΦ-cTLR4 cells in this study can functionally activate by addition of CID drug and allow better integration of implanted medical devices, by inhibiting fibrosis and priming angiogenesis around implanted medical devices. The MΦ-cTLR4 cells when activated with the CID drug, express increased levels of M1 MФ markers. Activated MΦ-cTLR4 cells stay stimulated for at least 48 hours; once the CID drug is withdrawn, the MΦ-cTLR4 cells return to baseline state within 18 hours. Further, in vitro CID-activated MΦ-cTLR4 cells induce upregulation of adhesion molecules on endothelial cells (ECs) in a TNFα-dependent manner. The MΦ-cTLR4 cells have also been shown to co-localize with pro-inflammatory regions following in vivo injection, which suggest these cells are still present and functionally active. Lastly, CID-treated mice with injected MΦ-cTLR4 cells within a Matrigel matrix exhibited less fibrosis overall in the Matrigel plugs. With the ability to specifically modulate the MФ-cTLR4 cells with the presence or absence of a small molecule, a tool now exists to observe a primarily M1 MФ response during inflammation. Using these engineered cells as a tool, this study has shown that pro-inflammatory MΦ-cTLR4 cells may be capable of inhibiting the fibrosis response, while also being able to prime the angiogenesis response. By controlling these two key processes that relate to the foreign body reaction, better medical device integration might be possible.