Patients with end-stage heart failure (ESHF) have a 1-year survival rate of 25% and a 2-year survival rate of 8% with conventional medical therapy (Rose EA et al, NEJM 2001). In fact, this dismal survival rate (not well known to the larger medical community and lay public) is actually significantly worse than patients with AIDS, liver cirrhosis, stroke, and other debilitating diseases. Therapeutic angiogenesis and/or vasculogenesis using cellular transplantation can be a promising and novel strategy to increase blood flow in patients with severe ischemic heart disease and peripheral vascular disease. Previous studies by the PI, co-PI, and collaborators have shown that embryonic stem cells can be differentiated into endothelial cells (ESC-ECs) and that these cells can be used to improve the recovery of cardiac function following myocardial infarction.
Because of the ethical and immunological concerns related to ESCs, transplantation of autologous iPSC-ECs would represent a more realistic therapeutic candidate for ESHF patients. However, from a translational perspective, a number of issues must be addressed before safe and high quality patient-specific iPSCs can be derived for clinical application in the future. First, most of the studies in the literature have used lentiviruses or retroviruses containing reprogramming factors to generate iPSCs, which can lead to insertional mutagenesis and will unlikely to be approved by the FDA as a clinical product. Second, most cell culturing techniques utilize a feeder layer of inactivated mouse embryonic fibroblasts (MEFs) to support the derivation or propagation of iPSCs, which adds the possibility of contaminating the patient-specific iPSCs with animal pathogens. Third, primary cultures of human somatic cells and iPSCs are typically established using media containing fetal bovine serum (FBS) and passaged with animal derived enzymes such as trypsin. Exposure of human cells to animal origin products may increase the risk of non-human pathogen transmission and make them unsuitable for the generation of clinical-grade iPSCs. Hence, the development of integration-free, xeno-free, and feeder-free iPSC lines as outlined in our CIRM Early Translational II Proposal will represent a significant step toward future clinical translation.
Coronary artery disease (CAD) is the number one cause of mortality and morbidity in the US. Following myocardial infarction (MI), the limited ability of the surviving cardiac cells to proliferate thereafter renders the damaged heart susceptible to unfavorable remodeling processes and morbid sequelae such as heart failure. In recent years, stem cell therapy has emerged as a promising candidate for treating ischemic heart disease. In contrast to adult stem cells, human embryonic stem cells (ESCs) have the advantage of being pluripotent, enabling them with the ability to differentiate into virtually every cell type. However, the use of human embryos is controversial, and the problem of immune rejection remains difficult to overcome. One way to circumvent the immunogenicity and ethical issues is to generate human induced pluripotent stem cells (iPSCs). Successful reprogramming of human skin fibroblasts into iPSCs has been reported independently by Shinya Yamanaka and James Thomson.
Despite the significant progress over the past 3-4 years, the use of iPSCs in clinical therapy in the future faces several challenges. First, the lentiviral and retroviral methods of reprogramming used by Yamanaka and Thomson have been shown to place iPSCs at risk for cancerous transformation due to insertional mutagenesis into host cells’ genomes. Second, current iPSC cultivation utilizes almost the same culturing conditions as those for human ESCs. The use of mouse embryonic fibroblasts (MEFs) as feeder layers adds the risk of contaminating the derived patient-specific iPSCs with animal pathogens. Third, the ideal cell source to be isolated from the patients and used for reprogramming must meet the criteria of easy accessibility with minimal risk procedures, availability in large quantities, relatively high reprogramming efficiency, and fast iPSC derivation speed. The majority of published studies thus far have used neonatal fibroblasts as the starting population for reprogramming, which may not be reflective of reprogramming in aged cells in adult patients with comorbid diseases. Finally, the safety and therapeutic applications of iPSC-derived cells must be rigorously tested in appropriate animal models before advancing to any clinical trial.
In this proposal, we seek to improve the derivation technologies, characterization methods, cultivation and differentiation protocols, as well as to gain a better understanding of the reprogramming mechanisms. Our goals are to derive human iPSC lines that are xeno-free, feeder-free, and integration-free and hence are compatible for clinical usage. Through these efforts, we hope to help make patient-specific iPSC therapy for end stage heart failure patients (and patients with other intractable diseases alike) a clinical reality in the future.