Segregation and characterization of lymphohematopoietic stromal elements

Area of Science:

• Hematopoiesis and Stem Cell Biology
• In vitro culture systems
• Cellular microenvironment

Background:

• Long-term maintenance of multipotent hematopoietic stem cells (HSCs) in vitro typically requires an adherent layer.
• The composition of this adherent layer and the presence of stem cells influence HSC maintenance and differentiation.
• Previous methods relied on specific serum and hormone conditions to establish functional adherent layers.

Purpose of the Study:

• To compare the role of the adherent layer versus stem cells in maintaining hematopoiesis in vitro.
• To investigate the effects of irradiation on stem cell function within the adherent layer.
• To analyze the cellular composition of the adherent layer and its influence on supernatant cell differentiation.

Main Methods:

• Established two types of adherent layer cultures: intact (with stem cells) and stem cell-depleted.
• Assessed colony-forming units (CFUs) in the supernatant of these cultures.
• Irradiated donor animals and adherent layers in vitro at varying doses and evaluated CFU production.
• Analyzed the cellular composition of the adherent layers using microscopy and cell counting.
• Transplanted cloned stromal cell lines to assess their ability to support hematopoiesis.

Main Results:

• Intact adherent layers, containing primitive stem cells, were major contributors to supernatant CFUs.
• Stem cell-depleted adherent layers required fresh bone marrow repletion for CFU production.
• Irradiation of donor animals or the adherent layer reduced supernatant CFU production in a dose-dependent manner.
• Low-dose irradiation (5 rads) significantly reduced CFUs, suggesting stem cell inactivation or reduced self-renewal, not just cell killing.
• Adherent layer composition differed, with stem cell-depleted cultures having more endothelial cells and producing more granulocytes, while intact cultures produced more macrophages.

Conclusions:

• The adherent layer plays a critical role in HSC maintenance in vitro, housing stem cells that contribute to hematopoiesis.
• Irradiation effects on stem cells in the adherent layer suggest inactivation or impaired self-renewal rather than direct cell death.
• The cellular composition of the adherent layer influences the differentiation pathways of hematopoietic cells in the supernatant.