Drug toxicity that emerges either in late-stage clinical trials or following market launch has been a long-term problem for the pharmaceutical industry. The fundamential challenge is that existing preclinical models do not adequately predict the toxicity of new chemical entities. Current cell models are either primary cell cultures derived from non-human animals or immortal cell lines derived from tumors. Because of their non-human nature or neoplastic life history, they are imperfect predictors of drug toxicity in humans. Recent advances in stem-cell technology hold the potential to overcome such limitations.
Induced pluripotent stem cells (iPSCs), on the other hand, possess the advantages of ESCs, avoid the associated ethical implications, and have the intrinsic ability to be a more flexible cell-based research tool. iPSCs are produced from somatic cells that are induced to a pluripotent state by the incorporation of genetic and small-molecule factors that reprogram the somatic cell to a stem cell (2–4). iPSCs have the same pluripotent capabilities of ESCs and the advantages of originating from individuals with identifiable phenotypes and genotypes, thus enabling the use of targeted human subpopulation models early in drug discovery and toxicity screening.Producing cardiomyocytes from human ESCs and iPSCs using the embryoid body (EB) and directed differentiation methods is well documented (5, 6). The efficiency with which these methods can differentiate ESCs and IPSCs into cardiomyocytes is highly variable, but consistent among both methods is a difficulty in producing highly pure (> 90%) populations of cardiomyocytes. Additional comparisons of cardiomyocyte generation from human ESCs and iPSCs suggest that both starting materials have an equivalent cardiogenic capacity (7), and further molecular and electrophysiological analyses demonstrate that both starting materials produce differentiated cardiomyocytes with phenotypes consistent with atrial, ventricular, and nodal cardiomyocyte subtypes (5, 6).
As described above, human iPSCs have particular advantages over ESCs for drug discovery and toxicity testing when induced to differentiate into a mature cell type. The significant challenge for commercialization of such cells is the ability to consistently produce both starting material iPSCs and the differentiated cells in the quantity, quality, and purity required by the pharmaceutical industry. Here we will describe a process by which we have industrialized the manufacture of iPSC-derived human cardiomyocytes. This process, as currently practiced at Cellular Dynamics International (CDI), is capable of meeting the foreseeable demand for purified iPSC-derived human cardiomyocytes and is scalable by more than two orders of magnitude if necessary without difficulty. We will illustrate the purification process and show that the human cardiomyocytes generated from this process express the same genes, proteins, electrophysiological properties, and responses to cytotoxic substances and ion channel blockers expected of cardiomyocytes.