A universal method for converting blood-making stem cells into heart cells

Scientists from the Johns Hopkins University have developed a simplified, cheaper, all-purpose method that might be usable to more safely turn blood cells into heart cells. This method is virus-free and produces heart cells that beat with nearly 100 percent efficiency. Elias Zambidis, M.D., Ph.D., assistant professor of oncology and pediatrics at the Johns Hopkins Institute for Cell Engineering and the Kimmel Cancer Center said, “We took the recipe for this process from a complex minestrone to a simple miso soup.” Continuing, Zambidis added, “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.

In order to transform cells from one cell type to another, scientists generally use engineered viruses to deliver genes into cells to convert them into different cell types or to turn them into induced pluripotent stem cells. Viruses, however, come with several caveats, the most prevalent of which is the ability of viruses to insert into genes and cause mutations. Some of these mutations can even cause the types of mutations that can initiate cancer-like growth in transformed cells. To insert the genes without using a virus, Zambidis’ team turned to small circles of DNA called plasmids. Once introduced into cells, these rings of DNA replicate only briefly inside cells after which, they are degraded.

If this isn’t bad enough, coaxing stem cells into other cell types is also expensive because of the varied recipe of growth factors, nutrients and conditions that are used to grow stem cells during their transformation. The recipe of this “broth” differs from lab to lab and cell line to cell line. However, Zambidis’ team described what he called a “painstaking, two-year process” to simplify the recipe and environmental conditions that are used to grow cells that are undergoing transformation into heart cells. They found that their recipe worked consistently for at least 11 different stem cell lines tested. They also found that it worked equally well for the embryonic stem cells, and stem cell lines made from adult blood stem cells (this was reported in the April 8 issue of Public Library of Science ONE (PLoS ONE).

How to convert these cells into heart cells? Postdoctoral scientist Paul Burridge examined some 30 papers on techniques to create cardiac cells. After drawing charts of 48 different variables in the creation of heart cells, he tested hundreds of combinations of these variables. Burridge eventually narrowed the choices down to between four to nine essential ingredients at each of three stages of cardiac development. This simplified the protocol for making heart cells, but it had an added benefit: Burridge’s recipe was one-tenth the price of standard media for these cells ($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.

In their experiments, the Hopkins team tested their new growth medium on cord blood stem cells. They used electric pulses to transfer a plasmid into the cells. These plasmids transferred seven genes into the stem cells. These plasmids triggered the cells to revert to a more primitive cell state (induced pluripotent stem cells or iPSCs). Then Burridge bathed the newly formed iPSCs in the simplified recipe of growth media, which they named “universal cardiac differentiation system.” Finally, they incubated the cells in containers that removed oxygen down to a quarter of ordinary atmospheric levels. Burridge noted, “The idea is to recreate conditions experienced by an embryo when these primitive cells are developing into different cell types.” Nine days later, these cells formed clumps of functional, beating cardiac cells, each the size of a needlepoint. Burridge determined that an average of 94.5% of the iPSCs had formed cardiac cells in Petri dishes. Most scientists see an efficiency of 10% on a good day.

Physiological studies showed that these cardiac cells showed the same characteristic muscular pulses seen in a normal human heart. Therefore, virus-free, iPSC-derived cardiac cells could be used in laboratories to test drugs that treat arrhythmia and other conditions. Perhaps, such cells could eventually be engineered to develop grafts of the cells that are implanted into patients who suffered heart attacks.

Zambidis’ team has recently developed similar techniques for turning these blood-derived iPSC lines into retinal, neural and vascular cells.