Johns Hopkins scientists have developed a new virus-free method that they say can be used to turn blood cells into heart cells more safely.
They claimed the method is simple, cheaper, all-purpose and produces heart cells that beat with nearly 100 percent efficiency.
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, Elias Zambidis, assistant professor of oncology and pediatrics, and his colleagues turned to plasmids, rings of DNA that replicate briefly inside cells and eventually degrade.
The process began with Johns Hopkins postdoctoral scientist Paul Burridge, 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 dollars per bottle lasting about one week.
In their experiments with the new growth medium, the Hopkins team began with cord blood stem cells and a plasmid to transfer seven genes into the stem cells.
They delivered an electric pulse to the cells, making tiny holes in the surface through which plasmids can slip inside. Once inside, the plasmids trigger the cells to revert to a more primitive cell state that can be coaxed into various cell types. At this stage, the cells are called induced pluripotent stem cells (iPSC).
Burridge then 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.
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.
The study appeared in the April 8 issue of PLoS ONE.