Patients who have undergone vascular trauma resulting from penetrating (e.g. blast injury) or blunt (e.g. fracture and contusion from a traffic accident) trauma often experience severe damage to their small-diameter peripheral arteries (2-4mm, e.g. tibial or brachial arteries) and require surgical intervention to bypass or replace the injured vessel segments. As the accessibility of saphenous veins may be low in patients of vascular trauma due to severe injuries or loss of more than one lower extremity as a result of blast injury or severe traffic accident, and the application of synthetic vascular grafts can be hindered by the potential risk of infection due to the contagious nature of these types of injuries, an alternative source of vascular graft is in dire need. Acellular tissue engineered vascular grafts (TEVGs) therefore may offer a readily available treatment for emergency care for patients of vascular trauma. Although TEVGs of significant mechanical strength can be developed from culturing primary human vascular smooth muscle cells (VSMCs) followed by decellularization, this platform has several obstacles which prevent it from ultimately serving victims of vascular trauma. The finite expandability, limited accessibility, and donor-to-donor functional variations among primary VSMCs may hinder the efficiency of TEVG production. Further, as small-diameter TEVGs require autologous endothelial cell (EC) coating prior to implantation to avoid blood clothing, potential dysfunction of patient ECs due to either advanced age or disease, as well as the significant time required to derive and expand the patient's autologous ECs, could prevent applicability in treating acute vascular injury. Human induced pluripotent stem cells (hiPSCs), self-renewable cells derived from somatic cells by the ectopic expression of stem cell factors, provide an excellent alternative to address the complications of primary cell based TEVGs. As hiPSCs can be differentiated into virtually any somatic cell type, including VSMCs and ECs (hiPSC-VSMCs and hiPSC-ECs), these cells provide an unlimited cell source to obtain vascular cells to construct TEVGs of comparable quality (hiPSC-TEVGs). Further, by engineering the expression of human leukocyte antigen (HLA) proteins, non- or low-immunogenic universal hiPSCs could be established, making the hiPSC-TEVGs suitable for implantation into any patient. Through utilizing the hiPSC platform, TEVGs for patients of vascular trauma can be developed on a massive scale, and of predictable and reproducible mechanical strength. Additionally, through developing and cryopreserving allogeneic universal hiPSC-ECs, these cells could be immediately applied to endothelialize TEVGs for small-diameter vascular intervention. Using hiPSC-VSMCs, we have successfully developed TEVGs with mechanical strength approaching that of saphenous veins, the common native grafts in vascular injury repair. Therefore, to achieve this future application of hiPSC-TEVGs, it is essential to establish the approach to efficiently decellularize the hiPSC-TEVGs, provide a luminal layer of hiPSC-ECs, and assess subsequent mechanical properties in vivo for preclinical efficacy as detailed in this proposal.
Current practices employing native autologous vessels or primary cell-based tissue engineered vascular grafts (TEVGs) for victims of penetrating (e.g. blast injury) or blunt (e.g. fracture and contusion from a traffic accident) vascular trauma have been successful, but are inherently limited in scope with regard to the rapid intervention necessary to limit the extent of morbidity or mortality for these patients, and may be totally unable to benefit patient populations with severe vascular injury, who may have no functionally available native vessels for bypass, or those patients of advanced age or with diseases such as diabetes which may cause required cell types to be dysfunctional for therapeutic efficacy. The human induced pluripotent stem cell (hiPSC) platform offers a unique, unlimited cell source to produce TEVGs on a mass scale of comparable quality, which could be further genetically modified to create minimally or non-immunogenic universal cells suitable for transplant into any patient. This project details our current and future efforts to create clinically suitable hiPSC-based TEVGs of robust mechanical strength, further provision of an hiPSC-derived endothelial layer to prevent clotting in small-diameter vascular grafts (3-4 mm, e.g. tibial or brachial arteries) for patients with peripheral artery injury, and assessing therapeutic efficacy of these TEVGs through in vivo experimentation with both a nude rat and porcine carotid preclinical model.
