Abstract 15060: Protein-Engineered Hydrogels for Improved Efficacy of Stem Cell-Based Injection Therapy in a Murine Model of Peripheral Arterial Disease

Introduction: Stem cell injection is a minimally invasive approach for treatment of cardiovascular diseases including peripheral arterial disease (PAD), which affects over 8 million patients in the US. However, poor cell survival and low cell retention at injection site are critical bottlenecks to the efficacy of stem cell therapy. We developed a shear-thinning and self-healing hydrogel system with controllable rigidity for stem cell encapsulation so as to enhance transplant cell viability. Hypothesis: The injectable hydrogel system will prolong cell survival under ischemic conditions and maintain cellular phenotype, in comparison to cell injection in saline. Methods: We developed a hydrogel comprised of two complementary engineered proteins that self-assemble upon simple mixing. The hydrogel network incorporates a polyethylene glycol physical crosslinker that modulates hydrogel stiffness and degradation. Bioluminescently-labeled human induced pluripotent stem cell-derived endothelial cells (iPSC-ECs) were encapsulated within the hydrogel with controllable stiffness (G'~10-800 Pa) under conditions of hypoxia (1% O2). The cells within hydrogel were then subjected to an in vitro model of injection and assayed for cell survival, proliferation, and endothelial phenotype for up to 14 days. To verify these results in an experimental model of PAD, 10^6 cells were injected in saline or in 400 Pa hydrogel into the ischemic limb in SCID mice. Results: Acutely after injection, the survival of iPSC-ECs in saline was 65%, whereas survival of iPSC-ECs in hydrogels with stiffnesses of 10, 100, 400, and 800 Pa was 94%. Bioluminescence imaging of cell viability in hypoxia for 14 days demonstrated the highest proliferation in the hydrogel with 400 Pa stiffness. In the 400 Pa hydrogel, iPSC-ECs maintained elongated morphology with robust expression of endothelial phenotypic marker, CD31. In the ischemic hindlimb, iPSC-EC retention was markedly increased with hydrogel encapsulation, compared to saline delivery. Conclusions: These findings demonstrate that stem cell encapsulation within this protein hydrogel improves cell viability, which may have therapeutic benefit for treatment of PAD and broadly to myocardial ischemia.