STEM CELL PHENOTYPIC AND FUNCTIONAL CHARACTERIZATION

-       Identification and origin of HSCs can be determined by immunophenotypic analysis using flow cytometry.

-       earliest identifiable human HSCs capable of initiating long-term cultures

Ø  CD34+, CD38−, HLA-DRlow, Thy1low, and Lin−.

v  This population of marrow cells is enriched in primitive progenitors.

-       Expression of CD38 and HLA-DR is associated with a loss of stemness.

-       Acquisition of CD33 and CD38 is seen on committed myeloid progenitors, and the expression of CD10 and CD38 is seen on committed lymphoid progenitors. The expression of CD7 is seen on T lymphoid progenitor cells and natural killer cells, and the expression of CD19 is seen on B lymphoid progenitor cells.

-       Functional characterization of HSCs can be accomplished through in-vitro techniques using long-term culture assays.

-       These involve the enumeration of colony-forming units (e.g., CFU-GEMM) on semisolid media such as methylcellulose.

Ø  Primitive progenitor cells, such as the high proliferative potential colony-forming cell and the long-term colony initiating cell, have also been identified.

Ø  These hematopoietic precursor cells give rise to colonies that can survive for 5 to 8 weeks but can be replated

-       Treatment of hematologic disorders is based on fundamental understanding of the biologic principles of HSC proliferation and maturation.