The blood stem cell, or hematopoietic stem cell, is a cell that's believed to give rise to all the components of the blood and immune system. Nestled in our bone marrow, it springs into action as necessary and is a key component of bone marrow transplantation procedures (more accurately called hematopoietic stem cell transplantation) conducted to save patients with blood diseases or whose immune systems have been wiped out by large doses of chemotherapy or radiation.
But new research published today in Stem Cell Reports by research associate Eliver Ghosn, PhD, and colleagues in the laboratory of geneticist Leonore Herzenberg suggests that, at least in laboratory mice, this stem cell may not be as omnipotent as previously thought. In particular, it seems unable to give rise to an important subpopulation of B cells, a type of immune cell. As Ghosn explained to me in an email:
Briefly, our findings challenge the idea that a single blood, or hematopoietic, stem cell (HSC) can fully regenerate all components of the immune system. We've shown that transplantation with highly purified HSCs fails to fully regenerate the B lymphocyte compartment, which is needed to protect against infections such as influenza, pneumonia and other infectious diseases, and also to respond to vaccinations.
Further studies conducted by the researchers suggest that these B cells may arise from an alternative fetal progenitor cell distinct from the HSC — perhaps as an evolutionary effort to separate what's known as innate immunity from adaptive immunity. They urge further research into the clinical outcomes of the transplantation of purified HSC in humans. As Ghosn said:
From a clinical standpoint, these findings raise the key question of whether human HSC transplantation, widely used in human regenerative therapies to restore immunity in immune-compromised patients, is sufficient to regenerate human tissue B cells that help protect transplanted patients from subsequent infectious diseases. This is specially relevant today considering that the field is moving toward using highly purified human HSCs in clinical settings.