Uniform 40µm Pore Diameter Precision Templated Scaffolds Promote a Pro-Healing Host Response by Extracellular Vesicle Immune Communication

J Tissue Eng Regen Med. 2020 Nov 20. doi: 10.1002/term.3160. Online ahead of print.

Abstract

Implanted porous precision templated scaffolds (PTS) with 40µm spherical pores reduce inflammation and foreign body reaction (FBR) while increasing vascular density upon implantation. Larger or smaller pores, however, promote chronic inflammation and FBR. While macrophage (MØ) recruitment and polarization participates in perpetuating this pore size mediated phenomenon, the driving mechanism of this unique pro-healing response is poorly characterized. We hypothesized that the primarily myeloid PTS resident cells release small extracellular vesicles (sEVs) that induce pore size dependent pro-healing effects in surrounding T cells. Upon profiling resident immune cells and their sEVs from explanted 40µm- (pro-healing) and 100µm-pore diameter (inflammatory) PTS, we found that PTS pore size did not affect PTS resident immune cell population ratios or the proportion of myeloid sEVs generated from explanted PTS. However, quantitative transcriptomic assessment indicated cell and sEV phenotype were pore size dependent. In vitro experiments demonstrated the ability of PTS cell derived sEVs to stimulate T cells transcriptionally and proliferatively. Specifically, sEVs isolated from cells inhabiting explanted 100μm PTS significantly upregulated Th1 inflammatory gene expression in immortalized T cells. sEVs isolated from cell inhabiting both 40μm and 100μm PTS upregulated essential Treg transcriptional markers in both primary and immortalized T cells. Finally, we investigated the effects of Treg depletion on explanted PTS resident cells. FoxP3+ cell depletion suggests Tregs play a unique role in balancing T cell subset ratios, thus driving host response in 40μm PTS. These results indicate that predominantly 40µm PTS myeloid cell-derived sEVs affect T cells through a distinct, pore size mediated modality. This article is protected by copyright. All rights reserved.

Keywords: T cells; biomaterial implant; extracellular vesicles; immune polarization; macrophages; sEV.