Zambidis' team has recently developed similar techniques for turning these blood-derived iPSC lines into retinal, neural and vascular cells.
Zambidis says, "many scientists previously thought that a nonviral method of inducing blood cells to turn into highly functioning cardiac cells was not within reach, but "we've found a way to do it very efficiently and we want other scientists to test the method in their own labs." However, he cautions that the cells are not yet ready for human testing.
To get stem cells taken from one source (such as blood) and develop them into a cell of another type (such as heart), scientists generally use viruses to deliver a package of genes into cells to, first, get them to turn into stem cells. However, viruses can mutate genes and initiate cancers in newly transformed cells. To insert the genes without using a virus, Zambidis' team turned to plasmids, rings of DNA that replicate briefly inside cells and eventually degrade.
A Universal System for Highly Efficient Cardiac Differentiation of Human Induced Pluripotent Stem Cells That Eliminates Interline Variability
The process began with Johns Hopkins postdoctoral scientist Paul Burridge, Ph.D., who studied some 30 papers on techniques to create cardiac cells. He drew charts of 48 different variables used to create heart cells, including buffers, enzymes, growth factors, timing, and the size of compartments in cell culture plates. After testing hundreds of combinations of these variables, Burridge narrowed the choices down to between four to nine essential ingredients at each of three stages of cardiac development.
Beyond simplification, an added benefit is reduced cost. Burridge used a cheaper growth media that is one-tenth the price of standard media for these cells at $250 per bottle lasting about one week.
Zambidis says that he wants other scientists to test the method on their stem cell lines, but also notes that the growth "soup" is still a work in progress. "We have recently optimized the conditions for complete removal of the fetal bovine serum from one brief step of the procedure -- it's made from an animal product and could introduce unwanted viruses," he says.
Burridge bathed the newly formed iPSCs in the now simplified recipe of growth media, which they named "universal cardiac differentiation system." The growth media recipe is specific to creating cardiac cells from any iPSC line.
Finally, they incubated the cells in containers that removed oxygen down to a quarter of ordinary atmospheric levels. "The idea is to recreate conditions experienced by an embryo when these primitive cells are developing into different cell types," says Burridge. They also added a chemical called PVA, which works like glue to make cells stick together.
Nine days later, the nonviral iPSCs turned into functional, beating cardiac cells, each the size of a needlepoint.
Burridge manually counted how often iPSCs formed into cardiac cells in petri dishes by peering into a microscope and identifying each beating cluster of cells. In each of 11 cell lines tested, each plate of cells had an average of 94.5 percent beating heart cells. "Most scientists get 10 percent efficiency for IPSC lines if they're lucky," says Zambidis
The production of cardiomyocytes from human induced pluripotent stem cells (hiPSC) holds great promise for patient-specific cardiotoxicity drug testing, disease modeling, and cardiac regeneration. However, existing protocols for the differentiation of hiPSC to the cardiac lineage are inefficient and highly variable. We describe a highly efficient system for differentiation of human embryonic stem cells (hESC) and hiPSC to the cardiac lineage. This system eliminated the variability in cardiac differentiation capacity of a variety of human pluripotent stem cells (hPSC), including hiPSC generated from CD34+ cord blood using non-viral, non-integrating methods.
This efficient and cost-effective universal system for cardiac differentiation of hiPSC allows a potentially unlimited production of functional cardiomyocytes suitable for application to hPSC-based drug development, cardiac disease modeling, and the future generation of clinically-safe nonviral human cardiac cells for regenerative medicine.
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