Blood Vessel Walls in Adult Mice Can Still Produce Blood Stem Cells
The textbook account of how adult blood is made has a clean simplicity to it: bone marrow stem cells do the job, period.
During embryonic development, a remarkable transformation occurs. Certain cells lining the walls of blood vessels — endothelial cells — convert directly into blood-forming stem cells, in a process called endothelial-to-hematopoietic transition. This is how the blood system is built in the developing embryo. After birth, the assumption has long been that the bone marrow takes over entirely, and that endothelial cells settle into their mature role as passive vessel liners, their stem-cell-producing days behind them.
A study published in eLife in April 2026 challenges that assumption with considerable technical rigor. Using in vivo genetic lineage tracing — a method that permanently marks individual cells so their descendants can be tracked — combined with single-cell RNA sequencing and bone marrow transplantation experiments, researchers identified hemogenic endothelial cells in the bone marrow of adult mice. These cells are rare. But they are there, and they are active.
A molecular echo of embryonic life
The newly identified hemogenic endothelial cells carry a molecular signature that resembles what you see in the embryo, but with distinct differences that reflect their adult context. They appear to contribute a small but real stream of new stem cells to the bone marrow pool alongside the established hematopoietic stem cells that handle the bulk of blood production. Whether they serve as an emergency reserve or as a minor but routine component of steady-state blood production remains unclear.
The implications for medicine are potentially significant. Blood disorders including leukemia, aplastic anemia, and immune deficiencies are treated with bone marrow transplants, which replace failing stem cell populations with healthy ones. If endothelial cells in adult bone marrow can independently generate stem cells, this raises the possibility — still distant — of stimulating that capacity as an alternative or complement to transplantation. It also provides a new lens for understanding blood disorders that arise in patients with apparently normal established stem cell populations.
Aging and the fading of a hidden capacity
For longevity researchers, the finding opens a specific question: does this hemogenic capacity decline with age? Aging bone marrow is known to produce a skewed repertoire of blood cells — fewer high-quality immune cells, more of certain white blood cell types that feed chronic inflammation. If endothelial cells contribute meaningfully to the stem cell pool, their age-related deterioration could be part of that story. Whether this capacity diminishes in older animals, and whether it can be restored or maintained, is now a tractable experimental question.