T lymphocyte colonies are the progeny of single cells

T lymphocyte colonies, arising from phytohemagglutinin (PHA) stimulated mononuclear cells cultured in a semi-solid agar matrix, could be the progeny of single cells (monoclonal) or of multiple cells (polyclonal). We have conducted several studies to determine if these colonies are monoclonal or polyclonal in origin. Normal human peripheral blood mononuclear cells from male-female, HLA-A and B disparate donor pairs were incubated for 18 h in RPMI 1640 containing PHA and fetal calf serum (FCS) and then cultured in a two-layer semi-solid agar system. After 5 days of incubation, the clonality of the colonies was assessed by in situ Y chromatin analysis, and by analysis of HLA-A and B locus antigens. Overlayers were stained with quinicrine dihydrochloride and the number of cells in the T cell colonies with Y chromatin enumerated using fluorescence microscopy. In other studies, colonies were picked from the agar with a capillary pipette and expanded in culture media. After 17 days of culture, cells were harvested and HLA-A and B phenotypes were determined. The results indicate that 87% of the T cell colonies had cells of either male or female origin. In addition, 90% of the colonies possessed HLA-phenotypes of only one donor. We conclude that Y chromatin and HLA analysis of individual colonies from cocultures suggest the monoclonality of T lymphocyte colonies.