Isolation and characterization of rapidly self-renewing stem cells from cultures of human marrow stromal cells

Abstract

Background: The adult stem cells from BM, known as non-hematopoietic mesenchymal stem cells, or marrow stromal cells (MSCs), readily generate single-cell-derived colonies, but the cultures are known to contain cells with at least two different morphologies and different properties of differentiation. Recently, we tried to identify the earliest progenitors in the cultures.

Methods: Human MSCs were plated at very low initial densities of about 3 cells/cm(2), and the growth of colonies was followed by phase microscopy.

Results: The two kinds of morphologically distinct cells reported by others were readily discerned: large, slowly replicating cells and spindle-shaped, more rapidly replicating cells. In addition, we observed very small cells, with diameters of only about 7 microm, that very rapidly replicated, both symmetrically and asymmetrically. The small rapidly self-renewing (RS) cells had different surface epitopes and profiles of expressed proteins than other cells in the same cultures. They also had a greater capacity for multilineage differentiation.

Discussion: RS cells are apparently the earliest progenitors and most rapidly replicating cells in cultures of MSCs. They have properties that appear to make them ideal candidates for studying differentiation and probably make them well-suited for cell and gene therapy.