Phenotypic and functional reversal within the early human hematopoietic compartment

Area of Science:

• Hematology
• Stem Cell Biology
• Immunology

Background:

• The behavior and surface marker expression of human hematopoietic stem cells (hHSCs) in culture remain debated.
• Understanding the link between hHSC phenotype and function is crucial for stem cell therapies.

Purpose of the Study:

• To investigate the relationship between early lineage marker (ELM) expression on human umbilical cord blood (UCB) CD34(+) cells and their long-term repopulation activity (LT-SRA).
• To explore the potential for dedifferentiation of hematopoietic progenitor cells into functional HSCs.

Main Methods:

• Analysis of CD33, CD38, and CD71 (ELM) expression on UCB CD34(+) cells.
• Assessing LT-SRA in nonobese diabetic/severe combined immunodeficient (NOD/SCID) mice after transplantation of cultured cells.
• Isolation and transplantation of CD34(+)ELM(-) and CD34(+)ELM(+) fractions from cultured UCB CD34(+) cells.

Main Results:

• LT-SRA was primarily found in the CD34(+)ELM(-) fraction of uncultured UCB samples.
• Culturing UCB CD34(+) cells preserved the CD34(+)ELM(-) population and LT-SRA.
• CD34(+)ELM(+) cells from cultures acquired LT-SRA after losing ELM expression, indicating dedifferentiation.

Conclusions:

• The CD34(+)ELM(-) phenotype is strongly associated with LT-SRA in human hematopoietic stem cells.
• Hematopoietic stem cells may arise from the dedifferentiation of early progenitor cells, challenging traditional differentiation pathways.
• This finding suggests novel strategies for ex vivo expansion of HSCs for transplantation.