When injecting stem cells into a patient, how do the cells know where to go? How do they know to travel to a specific damage site, without getting distracted along the way?

Scientists are now discovering that, in some cases they do but in many cases, they don’t. So engineers have found a way to give stem cells a little help.

As reported in today’s Cell Reports, engineers at Brigham and Women’s Hospital (BWH) in Boston, along with scientists at the pharmaceutical company Sanofi, have identified a suite of chemical compounds that can help the stem cells find their way.

“There are all kinds of techniques and tools that can be used to manipulate cells outside the body and get them into almost anything we want, but once we transplant cells we lose complete control over them,” said Jeff Karp, the paper’s co-senior author, in a news release, highlighting just how difficult it is to make sure the stem cells reach their destination.

So, Karp and his team—in collaboration with Sanofi—began to screen thousands of chemical compounds, known as small molecules, that they could physically attach to the stem cells prior to injection and that could guide the cells to the appropriate site of damage. Not unlike a molecular ‘GPS.’

Starting with more than 9,000 compounds, the Sanofi team narrowed down the candidates to just six. They then used a microfluidic device—a microscope slide with tiny glass channels designed to mimic human blood vessels. Stem cells pretreated with the compound Ro-31-8425 (one of the most promising of the six) stuck to the sides. An indication, says the team, Ro-31-8425 might help stem cells home in on their target.

But how would these pre-treated cells fare in animal models? To find out, Karp enlisted the help of Charles Lin, an expert in optical imaging at Massachusetts General Hospital. First, the team injected the pre-treated cells into mouse models each containing an inflamed ear. Then, using Lin’s optical imaging techniques, they tracked the cells’ journey. Much to their excitement, the cells went immediately to the site of inflammation—and then they began to repair the damage.

According to Oren Levy, the study’s co-first author, these results are especially encouraging because they point to how doctors may someday soon deliver much-needed stem cell therapies to patients:

“There’s a great need to develop strategies that improve the clinical impact of cell-based therapies. If you can create an engineering strategy that is safe, cost effective and simple to apply, that’s exactly what we need to achieve the promise of cell-based therapy.”