Deeply Dormant Stem Cell Reserve Discovered Powering Lifelong Blood Regeneration

Every day, the mammalian body manufactures billions of new blood cells to transport oxygen and fight off pathogens. This massive production line relies on a finite pool of stem cells in the bone marrow, which must be carefully managed to prevent exhaustion over a lifetime.[1][5]

To protect this critical supply, the body keeps a portion of these cells in a state of suspended animation. Now, researchers at the German Cancer Research Center (DKFZ) and the Heidelberg Institute for Stem Cell Technology and Experimental Medicine (HI-STEM) have identified a previously hidden tier of this reserve.[4][5]

Writing in the journal Cell Stem Cell in October 2026, the team detailed a deeply dormant population of hematopoietic stem cells that sleep longer than any previously known group. The discovery fundamentally alters the biological map of how mammals sustain their immune defenses into old age.[2][5]

"We show here that blood stem cells do not represent a uniform cell population, but comprise different subgroups with different properties and tasks," said Dawn S. Lin, the study's first author. This heterogeneity ensures the blood system can respond to both daily needs and long-term survival.[2][4]

The EPCR marker and deep dormancy

For years, biologists have relied on a specific surface protein, CD150, to identify and isolate blood stem cells. Because the newly discovered cells lack this CD150 marker—making them "CD150-negative"—they were routinely overlooked in standard stem cell counts and laboratory assays.[1][2]

Instead, the DKFZ researchers found that this elusive population is characterized by a different surface protein known as EPCR. By tracking cells with the EPCR marker in mice, the team observed a group of stem cells that react far more cautiously to inflammatory signals.[4][5]

While standard blood stem cells will wake up and divide when the body signals an infection, the EPCR-marked cells resist the call. This reluctance to divide protects them from the cellular exhaustion that typically follows repeated inflammatory stress over a lifetime.[4][5]

The depth of this dormancy is stark when measured over time. The researchers found that after more than 200 days, only about two percent of conventional blood stem cells still exhibited a chemical marker of quiescence.[4][5]

In contrast, between 10 and 15 percent of the newly characterized EPCR-positive stem cells retained their resting marker over the same 200-day period. This extended inactivity appears to be the exact mechanism that preserves their regenerative capacity for the long haul.[4][5]

A specialized immune reserve

Beyond their sleeping habits, the deeply dormant cells serve a distinctly different biological purpose when they finally do awaken. The Heidelberg team discovered a clear division of labor between the two stem cell populations during the formation of new blood.[1][5]

The traditional CD150-positive stem cells are primarily oriented toward generating red blood cells and platelets, the components necessary for oxygen transport and clotting. They handle the bulk of the routine, daily hematopoiesis required to keep the cardiovascular system functioning.[4][5]

The newly identified "deep sleepers," however, show a strong bias toward differentiating into immune cells, particularly lymphocytes. This suggests the EPCR-marked reserve acts as a dedicated, long-term backup system specifically designed to replenish the adaptive immune system.[1][4]

This immune-focused role has immediate implications for understanding how the body ages. As mammals grow older, their immune systems typically become less effective—a phenomenon known as immunosenescence—partly because the stem cell pools that generate lymphocytes become depleted or dysfunctional.[6]

Implications for leukemia and aging

If researchers can learn how to manipulate this deeply dormant reserve, it could open new avenues for preserving immune function in older adults. The mechanisms that keep these cells pristine could theoretically be applied to prevent the broader decline of the blood system.[6]

The findings also carry significant weight for clinical oncology, particularly in the treatment of blood cancers. Bone marrow transplants rely entirely on the regenerative power of infused stem cells to rebuild a patient's blood system after high-dose chemotherapy.[5][6]

"Blood stem cells form the basis for stem cell transplants, which are used for leukemias and other severe blood diseases," said Andreas Trumpp, the study's lead investigator and managing director of HI-STEM. He noted that understanding these cells' longevity is critical for clinical advances.[4][5]

"A better understanding of how these cells remain functional even in old age could help further improve these therapies in the future and prevent our blood and immune systems from becoming less effective as we age," Trumpp explained.[4][5]

The search for human equivalents

Currently, the existence of this deeply dormant, EPCR-marked stem cell population has only been definitively proven in murine models. Translating these findings into human medicine requires confirming that the exact same cellular architecture exists in human bone marrow.[1][5]

The research team is already moving to bridge that gap. "We already have initial evidence of this—that's our next project," Trumpp confirmed, pointing to ongoing work to isolate the human equivalent of the CD150-negative reserve.[4][5]

If confirmed in humans, the discovery will force a rewrite of standard laboratory protocols. Clinics and research labs will need to adjust their cell-sorting techniques to ensure they are not inadvertently discarding the most potent, long-lived stem cells in their samples.[6]