Hematopoietic stem cells: concepts, definitions, and the new reality

Area of Science:

• Hematology
• Stem Cell Biology
• Immunology

Background:

• Hematopoietic stem cells (HSCs) are crucial for blood cell production, with their study beginning in the 1950s.
• Early research identified serially transplantable colonies as a measure of HSC function, leading to the concept of self-renewing multipotent HSCs.
• Variability in HSC self-renewal outcomes has long been observed, prompting the development of sophisticated research tools.

Purpose of the Study:

• To review the historical development and current understanding of hematopoietic stem cell research.
• To highlight recent findings on HSC heterogeneity and its implications.
• To underscore the need for advanced models accommodating HSC pluralistic features.

Main Methods:

• Historical review of hematopoietic stem cell research methodologies.
• Analysis of studies examining individual purified HSCs and their progeny.
• Integration of findings from refined tools for assessing hematopoietic cell subsets.

Main Results:

• Definitive evidence for linearly transmitted heterogeneity in individual hematopoietic stem cell states has been established.
• Complex hierarchical models of hematopoiesis have been developed, incorporating numerous regulatory elements.
• Variability in HSC self-renewal and lineage output is a key characteristic.

Conclusions:

• Hematopoietic stem cell research has progressed from basic rescue experiments to complex regulatory models.
• Recent findings emphasize inherent heterogeneity within HSC populations.
• Future research requires new technologies to model the pluralistic nature of HSCs and their regulation.