I have written a number of times in this blog about iPSCs (induced pluripotent stem cells) including the exciting possibility of closing the loop in the stem cell supply chain and thereby enabling very long lives. See the posts IPSCs, telomerase, and closing the loop in the stem cell supply chain, Progress in closing the stem cell supply chain loop and The stem cell supply chain – closing the loop for very long lives. I have also pointed out in a recent presentation(ref) that, for this concept to become real, a number of technical challenges must be overcome including: a) obtaining iPSCs that are free of DNA contamination, and that have long telomeres and full hESC pluripotency, b) developing reliable means for assuring differentiation into adult stem cells of various types, and c) developing reliable and safe means for introducing those cells into their respective body niches. I further stated that although much research is being devoted to these approaches, 10-20 years are likely to be required before the stem cell supply chain can truly be closed in humans. I believe the main challenges that will have to be faced are of a bioengineering nature.
There is another application for iPSCs which is likely to become very important in the immediate future: supplying large quantities of specialized body cells for research and drug testing purposes. It appears that the engineering challenges of producing industrial-quantities of high grade cardiomyocytes suitable for drug-testing purposes have already been solved. The article iPSC-Derived Human Cardiomyocytes appearing in the May 15 issue of Genetic Engineering & Biotechnology News describes the development, the work of a company Cellular Dynamics International. Also, the development is covered in an article in PharmTech. Cardiomyocytes are the cells that make up cardiac muscle.
The engineering challenges of obtaining large numbers of pure cardiomyocytes are not simple. According to the Gen article “The pharmaceutical industry requires large numbers of purified cell types for screening candidate molecules for efficacy and unintentional toxicity, and the industrialized use of terminal cell types derived from iPSCs has been severely hampered, if not prohibited, by the difficulties of culturing stem cells. — iPSCs, while highly proliferative, are sensitive to manipulation; improper handling can severely restrict their pluripotency and drastically reduce the numbers of subsequently differentiated healthy cells. — Furthermore, while producing terminally differentiated cell types from stem cells using embryoid body (EB) and directed differentiation techniques are well known, the efficiency with which these methods produce terminally differentiated cells is highly variable; a common theme to both techniques is difficulty in producing highly pure (>90%) populations of terminally differentiated cells.”
“Therefore, the key to utilizing stem cell technology on an industrial scale is to develop processes that are both scalable and standardizable for both iPSC maintenance and differentiation. — Cellular Dynamics International’s (CDI) iCell™ Cardiomyocytes are human iPSC-derived cardiomyocytes that possess expected cardiac characteristics, form electrically connected syncytial layers, and exhibit expected electrophysiological and biochemical responses upon exposure to exogenous agents. CDI’s new technology overcomes barriers in both iPSC maintenance, terminal cell type differentiation, and purification by generating standardized and scalable protocols. The primary production constraint of iPSC husbandry was eliminated by developing a culture system that uses standard single-cell splitting techniques and small molecules to minimize operator-specific effects(ref).”
Cardiomyocytes are highly specialized muscle cells(ref) which contract in a coordinated manner producing heart beats. This video on the CDI web site shows a monolayer of iPSC-produced cardiomyocytes that is spontaneously beating. The iPSC-produced cardiomyocytes’ biochemical and electrophysiological properties and gene expression profiles have been tested and appear to match those of human-derived cardiomyocytes(ref). The cardiomyocytes can be customized. “–because iPSCs can be derived from individuals with identifiable phenotypes and genotypes, targeted human subpopulation models can be employed early in the discovery and toxicity screening processes(ref).”
CDI has developed technology for directing differentiation of iPSCs, for their proliferation, and for purifying them. Their basic breakthrough has been in engineering an accurate and efficient production process. “CDI’s new technology overcomes barriers in both iPSC maintenance, terminal cell type differentiation, and purification by generating standardized and scalable protocols. The primary production constraint of iPSC husbandry was eliminated by developing a culture system that uses standard single-cell splitting techniques and small molecules to minimize operator-specific effects.– iPSC culture scalability was incorporated into the process by building the cell culture system in a parallel fashion to enable the production of billions of iPSCs through the use of CellSTACK® culture chambers (Corning). — Differentiation of iPSCs into iCell Cardiomyocytes is built on CDI’s platform that utilizes recombinant genetic engineering and antibiotic selection. Prior to iPSC clonal expansion, genes encoding antibiotic resistance and an optional marker under control of a cell-type specific promoter (pan-cardiac for iCell Cardiomyocytes) are introduced into the iPSCs through homologous recombination. — After curation and quality control (QC), the iPSC clone carrying the selectable marker is expanded using iPSC maintenance procedures, harvested, and placed into the directed differentiation protocol of choice. Subsequent to differentiation initiation, the cultures are exposed to the selection agent to leave a pure, targeted cell population. — In the case of iCell Cardiomyocytes, the directed differentiation method produces cardiomyocyte purities greater than 50%, while antibiotic selection subsequently increases this purity to approximately 100%, a level that is necessary to ensure that the observed experimental outcome is due to an effect on cardiomyocytes rather than noncardiac “contaminating” cells. — This process, as currently practiced at CDI, is capable of meeting the foreseeable demand for purified iPSC-derived human cardiomyocytes and is scalable by more than two orders of magnitude, without difficulty, if necessary(ref).”
It is likely that variants of this technique can be used to produce a variety of other cell types “”We intend to launch liver, nerve, and blood vessel cell products over the next 18 months,” said Chris Parker, CDI’s Chief Commercial Officer(ref).” CDI has recently raised $40.6 million in private equity funding with a total of $70 million since 2004(ref).
The iPSC-derived cells should be more reliable for drug toxicity testing than existing cell lines. “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 fundamental 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(ref).”
Developing a viable and robust cardiomyocyte product line based on iPSCs basically required overcoming a number of serious bioengineering challenges. I think the same will be the case for closing the loop in the stem cell supply chain.