A microscope image shows neurons created from pluripotent stem cells using modified RNA.

A Harvard researcher has developed a way to make pluripotent stem cells that solves several of the major impediments to using them to treat human diseases.


Derrick Rossi, an assistant professor at Harvard Medical School, created pluripotent stem cells–which can turn into virtually any other type of cell in the body–from non-stem cells without using viruses to tinker with a cell’s genome, as conventional methods do. This means that Rossi’s method could be substantially safer for treating disease. The work is published today in the journal Cell Stem Cell.

“Rossi has figured out how to turn a skin cell into a stem cell without genetic modifications, and to do it efficiently,” said Doug Melton, codirector of the Harvard Stem Cell Institute, where Rossi is a principal faculty member, at a press conference.

Rossi’s innovation, which has not yet been tested in people, was to use messenger RNA instead of DNA to produce the four proteins needed to reprogram the cell. He has started a company called ModeRNA to commercialize this use of messenger RNA. He said the approach may also have potential in gene therapy, which also relies on viruses to deliver treatment, but he declined to talk further about the company or possible gene therapy applications because the work is at such an early stage.

Improving the usability of man-made stem cells is key to helping patients and ending the political morass that has slowed stem-cell research. On Tuesday, a U.S. federal appeals court allowed federal funding of embryonic stem-cell research to continue while a legal case against such funding proceeds.

The human embryonic stem cells used in research were mostly derived from embryonic tissue grown a decade ago. These are the most versatile cells in the body, and the gold standard by which man-made cells are judged.

Four years ago, Japanese researcher Shinya Yamanaka showed that regular cells could be turned into embryonic-like stem cells–called induced pluripotent stem (iPS) cells–through the introduction of four specific proteins. Theoretically, this meant that doctors could take skin cells from a sick or disabled person, transform them into stem cells, and then into a specialized cell to treat them–an insulin-producing islet cell for someone with diabetes or a nerve cell for someone who is paralyzed, for instance. Using iPS cells avoids the need to destroy embryos and, because they can be derived from the patient’s own cells, means less risk of rejection.

But only one in 1,000 or one in 10,000 skin cells could be transformed into a stem cell using Yamanaka’s method. It also changes a cell’s genes in ways that might trigger cancer or other problems.

Rossi ‘s idea was to produce Yamanaka’s four proteins in a different way. Instead of using the DNA that holds the instructions for making proteins, he wanted to use RNA, which carries those instructions to the place in a cell where proteins are made.

His first several attempts were miserable failures. When he tried to change the messages the RNA carried, he triggered a serious immune response and most of the cells shut down or self-destructed. Rossi then tried modifying the RNA chemically and eventually figured out a way to allow his changes to escape immune detection while delivering the message. “This was key to our success,” said Rossi, who is also a researcher at Children’s Hospital Boston. “We could encode RNA for any protein we wanted to express and insert it into a cell.”

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