From stem cells to signaling cells: why scientists renamed the MSC

In 1991, biologist Arnold Caplan popularized the term mesenchymal stem cell. Twenty-six years later, he published a paper arguing it was time to change the name. His proposal, Medicinal Signaling Cells, keeps the familiar initials MSC but reflects a major shift in how scientists understand what these cells actually do.

The original idea: cells as replacement parts

Early on, the thinking was simple. MSCs can develop into bone, cartilage, and fat in a lab dish. So, the reasoning went, perhaps cells placed near an injury would become new tissue and replace what was damaged.

That turned out to be only part of the story. When researchers tracked MSCs in the body, they found that many of the cells did not stay long, and relatively few turned into new tissue. Yet benefits were still observed in many studies. Something else was going on.

The new idea: cells as coordinators

The explanation that emerged is that MSCs work mostly through signaling. Published research describes them as cells that:

• Sense their surroundings, reading chemical cues from nearby tissue.
• Travel toward areas of inflammation and injury, a behavior called homing.
• Release signaling molecules that calm excessive inflammation, encourage blood vessel growth, and prompt the body's own local cells to take up repair.

In other words, MSCs may act less like bricklayers and more like site managers, directing the work rather than doing all of it themselves. That's the insight the name "Medicinal Signaling Cells" tries to capture.

The most important thing these cells may do is not become new tissue, but tell the tissue around them what to do.

Not everyone agrees on the name

Science rarely settles on one term quickly. The International Society for Cell & Gene Therapy has favored mesenchymal stromal cells, partly because many cell populations labeled MSCs don't meet the strict definition of a stem cell. You'll see all three names in the literature. They usually refer to the same cells, identified by standard lab markers and behavior.

Where MSCs are found

MSCs have been isolated from bone marrow, fat, dental pulp, and, notably, from perinatal tissues such as the umbilical cord. The gel-like tissue inside the cord, known as Wharton's jelly, has drawn research interest because it is rich in signaling molecules and structural proteins. Those components are the subject of the next two articles in this series: how cells talk and collagen and hyaluronic acid.

What's still unknown

The signaling model raises important questions that researchers are actively working on. How long do the signals last? How much depends on the health and age of the cells? Can the signals themselves be isolated and used without the cells? Clear answers will take large, well-designed clinical trials. Most uses of MSCs remain investigational.

Medical Disclaimer: This article is for educational purposes only. It summarizes published research on MSCs broadly and does not describe any specific product or treatment. Always consult a qualified healthcare provider before pursuing any regenerative therapy.