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Comment 03

Please cite this contribution as follows: Ilya [Bozo]. Dear Colleagues! Despite the seeming triviality of the issue and. Blog comment, Maximow Award contest, May 2012. Cell Ther Transplant/Maximow Award, May 2012;blog-comment_03. doi:10.3205/maximowaward_2012_blog-comment_03

This contribution is provided under the following license: Creative Commons Attribution 3.0 Unported (CC BY 3.0)

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Ilya. May 29, 2012 at 8:40 pm

Dear Colleagues!

Despite the seeming triviality of the issue and excessive theorizing, it is very important. Often, medical (biomedical) concepts, principles and terms are very different even in various cities within a country. I am sure that terminological differences between the scientific communities of different countries is even more significant.

Before talking about the HSC, I’ll start with the other example, which is even more striking, in my opinion. There are two types of cells (“pericytes” and “perivascular cells”) in the nomenclature of the Russian histology school. Perivascular cells are located around the vessels, these cells are also called “adventitial cells”. In contrast, pericytes are located into the wall of blood vessels closer to the intima, where contact with endothelial cells. It is completely different types of cells in understanding of Russian scientists. However, some researchers from other countries often equate these two terms.

To answer the question about interpretation of the term “hematopoietic stem cells” (HSC), we must first define the concepts and principles of histological schools in different countries. So, the concept of “cellular-differon organization” (клеточно-дифферонной организации) is well recognized in Russia (you can believe me because I am from Russia). I can explain this concept in a few words: “a life is continual”. I’ll try to expound. Life is constantly moving, regardless of our mood, worldview, perceptions, irrespective of the moment in which we look at it, evaluate and interpret it. If today you saw a person in a suit, it does not mean that he will wear it again tomorrow. He can wear a coat or shirt, depending on the weather or other reasons. He can changes an appearance or even a sex . However, there are absolutely immutable things. Namely, a biological sense any man has initial (a zygote) and end points of development.

As for the cells, the situation is similar. “Cell differon” is a continual cytogenetic line of single cellular type from “stem” to a “specialized” cell. In other words, each cell goes a way of development, during which the constantly changing its properties and functional characteristics. Life of cells are continuous and proceeds from the initial point (“stem cell”) to the end point as well. We can identify its characteristics only in concrete moment of time when we perform some studies (as though we have stopped time). As all types of stem cells (the initial points) can be counted on the fingers and there are a lot of specialized cells types it is quite clear that one type of stem cells can gives rise to different cellular differons.

In this regard, HSC is a population of stem cells which gives rise to differons of the all blood cells (and other differentiation pathways was described but the main is hematopoietic). Thus, HSC is the initial point. There are a lot of opportunities to study the HSC population and to divide into many subpopulations by the use of dozens methods, hundreds of immunophenotypic antibodies, etc. But in my opinion, it is a conceptual error. It is important that the HSC as the initial point (true stem cells) of several cellular differons can not have a determination for differentiation into any cell lines. True HSC should be “neutral”. In this regard, some terminological hypothesis are debatable. For example, Yana Onikiychuk (post above) proposed to use the terminology of Muller-Sieburg et al. (2012), which consists in dividing HSC into three subpopulations by their differentiation capacity: myeloid-biased, balanced, and lymphoid-biased HSCs. However, from the perspective of the classical school of histology two of these subpopulations are not HSCs because these cells already have a bias toward one of differons. What does it means? It means that these cells have already left the the initial point and move to the end point. Its can be called such as “undifferentiated precursors of myeloid or lymphoid cell lines”, but not HSCs. At the same time, the population was called “balanced” by Muller-Sieburg et al. more consistent with the true HSC.

Thus, the term “HSC” has a conceptual significance. It means a single self-renewing population of cells which possess capacity to give rise to different types of blood cells (first of all) equally. Close derivatives of HSC (cells that have been starting differentiation already) could be attributed to HSC population due to poor technological opportunities at the time of Maximow, for ex. Possessing modern technologies it is important to remember the fundamental concepts and distinguish between the true HSCs and their immediate descendants which nowise should be considered as a subpopulations of HSCs.
Sorry for my bad English.

This contribution is provided under the following license: Creative Commons Attribution 3.0 Unported (CC BY 3.0)

Please cite this contribution as follows: Ilya [Bozo]. Dear Colleagues! Despite the seeming triviality of the issue and. Blog comment, Maximow Award contest, May 2012. Cell Ther Transplant/Maximow Award, May 2012;blog-comment_03. doi:10.3205/maximowaward_2012_blog-comment_03

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