Biomaterial-based Helper T-cell Therapies for Ischemic Diseases

Abstract

There exists a critical need to develop improved therapies for ischemic diseases, such as peripheral artery disease (PAD). Ideal therapies for PAD not only restore vascularization and blood perfusion to ischemic limbs but also enhance muscle regeneration in the ischemic skeletal muscle. It is becoming increasing appreciated that immune cells, in particular CD4+ T-cells, can regulate both vascular and skeletal muscle regeneration in vivo. Immunomodulatory biomaterials that regulate the recruitment and activation of these immune cells can potentially enhance their ability to locally promote these processes of regeneration. The hypothesis driving this work is that a biomaterial that controls the number and types of CD4+ T-cells cells at sites of ischemic injury can enhance angiogenesis and myogenesis. The ability of different types of CD4+ T-cells (Th1, Th2, Th17, and Treg) was first investigated to identify a subtype of these cells that is conducive for vascular and skeletal muscle regeneration. This was done by collecting secreted factors from these cells in the form of conditioned media (CM) and applying these media to in vitro assays and delivering them to a model of hindlimb ischemia via an injectable biomaterial. Overall, Th2 and Th17 CM were shown to exhibit the most beneficial, long-term effects on regeneration. These CM enhanced angiogenesis in vivo, impart by enhancing endothelial sprouting. Furthermore, Th2 and Th17 CM, and to a lesser extent Th1 CM, enhanced myoblast proliferation in vitro and prolonged early stages of muscle regeneration in vivo. Treg CM showed no discernible effects on these processes in vivo. Having identified that secreted factors from Th2 T-cells enhance angiogenesis in vivo, a biomaterial based therapy was developed to recruit host Th2 T-cells generated from vaccinations to sites of ischemia. Th2 T-cells were generated by vaccinating mice with a model antigen, OVA, in the presence of aluminum hydroxide (ALUM); these antigen-specific T-cells were subsequently recruited and activated at sites of ischemia with a PLG scaffold that provides controlled release of OVA. Combining vaccinations of OVA with ALUM and OVA-releasing scaffolds in a murine model of hindlimb ischemia enhanced the number of Th2, IL-5 producing-cells and eosinophils at sites of ischemic injury. This led to an enhancement of angiogenesis and blood perfusion in ischemic limbs, reducing coagulation necrosis in skeletal muscle downstream of the ligation site. The studies and therapies developed here advance our understanding of how helper T-cells contribute to vascular and skeletal muscle regeneration and demonstrate the utility of biomaterials that manipulate the adaptive immune system to treat ischemic diseases.