By: Steven R. Bauer, Ph.D.
We can admire an individualist for being independent and self-directed. But these traits can be disruptive and troublesome when they’re shared by cells called mesenchymal stem cells (MSCs). When these cells (also called human multipotent stromal cells, or MSCs) are being prepared for use as therapies to treat human diseases or medical conditions, what’s important is predictability.
MSCs are called ‘multipotent’ because they can produce more than one type of specialized cell of the body, but not all types. For example, they will respond to various types of substances called growth factors by differentiating − or specializing − into cartilage, bone, or fat. MSCs may also help the body control inflammation by suppressing immune cell functions. These processes, immunosuppression and differentiation, justify MSC use in regenerative medicine clinical trials investigating their use to protect, restore, or repair tissues in the body.
But there’s a catch. As of January 2018, no MSC-based clinical trials have resulted in FDA-approved treatments. One significant challenge is ensuring that the MSCs will work together to perform the same desired function when they are administered to patients. So FDA scientists have been developing ways to predict whether specific populations of MSCs intended for use as a therapy are made up of individualists or sufficient numbers of team players. It turns out that MSCs are very responsive to their environment. In a lab-based manufacturing process, MSCs are exposed to an environment very different from the body — one that could change the way they respond to growth factors and one that could result in MSC preparations with lots of unexpected – and undesirable – individualism. Additionally, this might change the way the cells behave after they are put into a patient. For example, they might not suppress inflammation very well, might form tissue where it isn’t wanted, might form the wrong tissue, and even form tumors.
Recognizing these potential issues, FDA’s MSC Consortium is trying to develop methods that would predict with more certainty how manufactured or isolated MSCs will behave in patients.
My own laboratory has been developing ways to predict the behavior of MSCs that have been stimulated by growth factors. Our study has involved identifying changes in the size and shape (or morphology) of stimulated MSCs that may predict their future behavior. We call this approach functionally-relevant morphological profiling. It’s made possible by powerful imaging technologies that make it practical for us to routinely monitor and analyze the changes in the size and shape of many thousands of cells in a matter of hours.
Why are sizes and shapes so important to predicting MSC activity?
Think of it this way: you can tell the difference between basketball players and baseball players by looking at their uniforms. And you know what kind of behavior you can anticipate when they’re playing their respective games. Likewise, morphological profiling can help scientists predict whether stimulated MSCs are going to differentiate into specific cells that do specific tasks.
We’ve used this approach to follow MSCs that were stimulated to undergo a process called mineralization, the laying down of minerals that support bone growth. Previously, we had to wait for over a month to see if stimulated MSCs would mineralize. But, by using our profiling method, we can predict with over 90 percent certainty on day three whether the stimulated cells would mineralize by day 35.
In another study, we measured more than 90 morphological features — including their sizes and shapes, and the shapes of internal structures — of stimulated MSCs. Based on our knowledge of the changes in the size and shapes of MSCs that go on to develop immunosuppressive activity, we could predict which MSCs would suppress a certain type of immune cell (T cell). Immunosuppression makes these stimulated MSCs potentially effective treatments for inflammatory diseases, such as Crohn’s disease (chronic inflammation of the intestine), and multiple sclerosis (loss of nerve cell signaling).
In short, this type of profiling allows us to measure the extent to which there are similarities or differences in these cell preparations and to compare our findings with the profile of specific cell types associated with the biological functions we are seeking. That may help us predict whether the cells will perform the function we want if they are administered to patients.
MSC-based therapies are not available yet. But the ability to predict specific functions of different preparations of MSCs in the lab may be a big step toward getting safe and effective FDA-approved treatments to patients. We think our work is widely applicable to a variety of potential stem-cell based products, and it will help us determine if new techniques for stimulating MSCs to differentiate will produce safe and effective therapies.
Steven R. Bauer, Ph.D., is the chief of the Cellular and Tissues Therapy Branch, Division of Cellular and Gene Therapies, in the Office of Cellular, Tissue and Gene Therapy at FDA’s Center for Biologics Evaluation and Research.
The FDA Grand Rounds on March 8 features Steven Bauer discussing his research.