Stem cells can reproduce themselve, although their proliferation rate is very low.
On the other hand there are the so-called "immortalized cell lines" which have a normal or high proliferation rate, and can sustain it over long periods of time.
Can stem cells also be considered to be a kind of such "immortal" cells?
This question is similar to a previous one https://www.researchgate.net/post/What_is_the_difference_between_mechanism_of_immortality_in_normal_stem_cells_vs_cancer_stem_cells
Vad Pérez Stem cells are generally divided into two (very broad) groups, pluripotent stem cells and all other stem cells (such as neural progenitors, muscle progenitors and other progenitor cell types). Pluripotent stem cells can be either embryonic stem cells obtained from embryos ("ES cells") or induced ("iPS cells).
The growth rate of stem cells varies widely depending on the cell type. The same thing can be said about cancer cells. For example, I worked with more than 20 different cancer lines, of which about 8 were neuroblastoma cell lines. Neuroblastoma in particular is very hard to grow, has extremely high cell death rate, is prone to differentiating, and many lines actually grow slowly. Not all cancer cell lines grow rapidly. However, it is true that all of them are immortal (otherwise it would not be called a cell line).
Stem cells, in turn, are very different depending on the cell line, too. For example, now I am working with two human embryonic stem cell lines, KhES-1 and KhES-3. They have very different growth rate, and one grows much better than the other. To illustrate, my KhES-1 is still "passage 4", while my KhES-3 line is already "passage 10", even though I started them and split them always at the same time (because I work on both at the same time). The speed of their growth is quite different. ES and iPS cells can definitely divide just as fast as HeLa or faster. The speed of division does not directly correlate with immortality.
Now, about immortality, yes, all pluripotent stem cells (that is, ES cells and iPS cells) can divide indefinitely. However, whether the mechanism of this immortality is same as in cancer, is not clear. Pluripotent stem cells do activate telomerase, and extension of telomeres happens during reprogramming. They are very similar to cancer cells. The question "what is different between cancer cells and pluripotent stem cells" (i.e. why cancer is so aggressive while pluripotent cells are not, even though both are immortal) has not been answered yet. Whoever answers it, is going to publish pretty high.
Yulia Panina so, a question: if NSCs (ES/iPS) divide at the same rate that CSCs do — it should mean they will also form tumors, isn't?
I am not interested in finding differences between CSCs and iPSs)) my interest is much more narrow (although from your explanation it appears that in NCSs in the organism some mechanism exists decreasing proliferation rates of these cells, and this mechanism is broken in CSCs and their progeny)
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