In previous posts, we have examined the debate that surrounds a population of stem cells called “Very Small Embryonic-Like Stem Cells” or VSELs. Ratajczak and his colleagues have published several papers describing the isolation and characterization of VSELs from bone marrow. VSELs express some of the same genes as embryonic stem cells (Oct4, Nanog, and Sox2), and are also very small, and have the capacity to differentiate into a wide variety of cell types.
The debate over VSELs exists because although some scientists have been able to reproduce Ratajczak’s work, but several important scientists have not been able to do so. Therefore a debate rages as to whether or not VSELs exist.
On top of this debate comes findings by several laboratories of small stem cells in bone marrow that possess the ability to divide and differentiate into several different cell types. For example Shmilovici in 2007 and Charles Vacanti at Harvard University in 2001 reported the isolation of “spore-like cells” from human bone marrow. These cells were reportedly smaller than 6 micrometers in diameter and were activated by harsh conditions or injury. However, a paper by Danova-Alt and others in 2012 examined very small embryonic-like stem cells from umbilical cord blood and was unable to confirm that these cells possesses the properties of stem cells. Stout and others in 2007 isolated “blastomere-like stem cells” from pig skeletal muscle and showed that they were mobilized into circulating blood after trauma. Also, last year, the laboratory of Muhammad Ashraf at the University of Cincinnati Medical Center isolated small juvenile stem cells from aged human bone marrow. Therefore, even though prominent laboratories have not been able to confirm the existence of VSELs, it seems very likely that some sort of small-sized stem cells are present in bone marrow. However, the nature of these cells and their capacity to proliferate and differentiate remains uncertain to date.
A recent paper from researchers at StemBios Technologies has reported the isolation and characterization of small stem cells from bone marrow that they call “SB cells.” These SB cells are less than 6 micrometers in diameter and are present in human bone marrow and peripheral blood. Even more interestingly, these SB cells express several cell surface proteins not found in other bone marrow cells (Lgr5, for example). They also did not express several of the markers found on the surfaces of VSELs (i.e. CD133). Thus these SB cells seems to constitute a unique bone marrow-based stem cell population.
When differentiated in culture, SB cells formed liver cells, fat cells, and neuron-like cells. When injected into the tail veins of a mouse, SB cells spread throughout the mouse body and were found in the brain, liver, skeletal muscles. Further work established that the SB cells had in fact differentiated into liver cells, neurons, and skeletal muscles in the bodies of the host mice.
These cells represent a potential rich source of material for regenerative medicine. In fact, Stem Bios Technologies Inc have begun planning a human clinical trial using SB cells to determine their efficacy in treating human maladies. If this trial proves successful, then SB cells and their isolation and mobilization might play a remarkable role in future regenerative treatments.