A team of Hopkins scientists recently developed a method to safely turn blood cells into functional cardiac myocytes. The researchers claim that this method produces virus-free heart cells that beat with nearly a 100 percent efficiency.
According to Elias Zambidis, assistant professor of oncology and pediatrics at the Hopkins Institute for Cell Engineering and the Kimmel Cancer Center, many scientists previously doubted that a non-viral method of converting blood cells into cardiac cells existed. While he hopes that other scientists will test this method themselves, he cautions that the cardiac cells are not ready for human testing.
Generally, scientists develop stem cells taken from one source, such as blood, and into another cell type by virus-assisted gene delivery. This converts the blood cells into stem cells at the risk of the virus mutating genes and initiating cancers in the transformed cells. To avoid using a virus, Zambidis’s team used plasmids, rings of DNA that degrade after replicating briefly inside cells.
Due to the complexity of the process, Zambidis’s team took two years to simplify the environmental conditions, which include growth factors and nutrients, that house the transforming cells. The team found that their recipe worked well for at least 11 different stem cell lines, the more controversial embryonic stem cells and most importantly, stem cell lines generated from adult blood stem cells.
The process was aided by Hopkins postdoctoral scientist Paul Burridge, who extensively studied cardiac cell-creating techniques and charted 48 different variables used to create heart cells such as enzymes, growth factors and the size of compartments used in cell culture plates. After testing many combinations of these variables, he narrowed the choices down to around four to nine essential ingredients at each of the three stages of cardiac development.
Zambidis said that the composition of the growth broth used to house the cells still needs some modification. He also said that the team recently discovered how to remove the fetal bovine serum, a possible source of unwanted viruses, from one step of the procedure.
Using the new growth medium, the team used cord blood stem cells and a plasmid to transfer seven genes into the stem cells. To allow the plasmid to enter the cells, they delivered an electric pulse to bore tiny holes in the cell surface. Once inside the cell, the plasmids induced the cells to become pluripotent stem cells, a more primitive cell state that can differentiate into a variety of different cell types.
After bathing the pluripotent cells in the simplified growth media, the team used special incubation containers to reduce the oxygen content in the cells to a quarter of the normal atmospheric level. According to Burridge, these procedures aimed to mimic conditions experienced by differentiating cells in embryos. Finally, the team added PVA, a chemical that caused the cells to adhere together.
After nine days, the cells turned into functional cardiac myocytes. Burridge found that the success rate of this procedure was 94.5 percent, compared to 10 percent in most other procedures. When an electrocardiograph was applied to the cells, the resulting rhythm resembled the pulses observed in a normal human heart.
These virus-free cells could eventually be used to test drugs that treat arrhythmia or could be developed into grafts, which could be implanted into heart attack patients.
In addition, Zambidis’s team recently developed techniques for converting blood-derived cell lines into retinal, neural and vascular cells.
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