Virus-Free Method Turns Blood Into Heart Cells

Turning one type of cell into another generally requires using viruses that carry the necessary genes for the job. Viruses, though, are prone to causing unwanted changes in DNA that can lead to cancer formation. Avoiding viruses altogether, researchers at Johns Hopkins are using non-integrating episomal plasmids to transform blood cells into cardiac cells:

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.
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. “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.