Tiny Microfluidic Device Makes Cell Therapy Safer For Spinal Cord Injury Patients

For spinal cord injuries, these pluripotent stem cells are coaxed into becoming progenitor cells, which then differentiate into spinal cord cells. Once transplanted back into the patient, these new cells can regenerate parts of the injured spinal cord. However, a significant risk in this therapy is that pluripotent stem cells that do not fully differentiate into progenitors may form tumors. Undifferentiated induced pluripotent stem cells pose a cancer risk, which remains a major challenge in cell therapy. Clinicians and researchers attempt to identify and eliminate these cells by searching for specific surface markers, but a unique marker for these undifferentiated cells has not been found. Alternatively, chemical methods that selectively destroy these cells can harm the differentiated cells.

Now, scientists at MIT (Cambridge, MA, USA) and the Singapore-MIT Alliance for Research and Technology (SMART, Singapore; ) have developed a microfluidic cell sorter that can remove about half of the undifferentiated cells – those with tumor-forming potential – from a batch, without damaging the mature progenitor cells. This device, which is tiny and high-throughput, does not require special chemicals and can sort over three million cells per minute. Moreover, connecting multiple devices can sort over 500 million cells per minute, enhancing the safety of cell therapy treatments. This chip, containing the microfluidic cell sorter, is inexpensive to mass-produce, making the device feasible for widespread use.

Previously used to sort immune cells and mesenchymal stromal cells, this high-throughput microfluidic sorter, which sorts cells based on size, is now being adapted for other stem cell types, including induced pluripotent stem cells. Pluripotent stem cells are generally larger than their progenitor derivatives, likely because the nucleus in an undifferentiated cell contains numerous active genes that shrink as the cell differentiates and suppresses unnecessary genes. The sorter uses this size difference, sorting cells through microfluidic channels in a small plastic chip with an inlet, a spiral, and four outlets for different-sized cells. As cells move through the spiral at high speeds, various forces focus them into specific stream locations based on their size, sorting them through separate outlets.

The sorter's effectiveness is enhanced by running it at two different speeds, first to sort smaller cells and then to larger cells. Unlike a centrifuge, the microfluidic sorter does not require manual intervention to separate cells. It successfully removed about 50% of the larger cells in one pass, with experiments confirming these larger cells were associated with higher tumor risk. The low-cost, filter-free, scalable device is now being tested in larger studies and animal models to evaluate the performance of the purified cells in vivo. Removing more non-differentiated cells could not only improve the safety but also the efficacy of cell therapies.

“We are interested in regenerative strategies to enhance tissue repair after spinal cord injuries, as these conditions lead to devastating functional impairment. Unfortunately, there is currently no effective regenerative treatment approach for spinal cord injuries,” said Sing Yian Chew, a CAMP principal investigator. “Spinal cord progenitor cells derived from pluripotent stem cells hold great promise, since they can generate all cell types found within the spinal cord to restore tissue structure and function. To be able to effectively utilize these cells, the first step would be to ensure their safety, which is the aim of our work.”

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