HEMATOPOIETIC PROGENITOR-CELL DIFFERENTIATION - FLOW CYTOMETRIC ASSESSMENT IN BONE-MARROW AND THYMUS

We have recently shown that expression of any of the lineage-associate d molecules CD2, CD7, CD10, CD19 or CD33 does not ensure lineage-commi tment of CD34(+) progenitor cells. Further, normal progenitor cells an d leukaemic blast cells have been shown to coexpress molecules associa ted with more than one haemopoietic lineage. Five-dimensional now cyto metric analysis of normal bone marrow cells was exploited to investiga te the hypothesis of a developmental stage in haemopoiesis comprising CD34(+) cells coexpressing CD2, CD5, CD7, CD10, CD19 and CD33 or any c ombination of these molecules. We report on a subpopulation of CD34(+) bone marrow cells constituting < 5% of the CD34(+) cells and characte rized by extensive coexpression of several molecules associated with t he B lymphoid, T lymphoid and myeloid lineages, There is every probabi lity that some cells display the CD34(+) CD2(+) CD5(+) CD7(+) CD10(+) CD19(+) CD33(+) phenotype, Studies on postnatal thymocytes suggest tha t this may be the phenotype or one of a few phenotypes of a candidate thymus-seeding progenitor cell population. Finally, our findings that CD34(+) as well as CD34(+) CD5(+) thymocytes can be driven into non-T- lymphoid differentiation by cytokines, support the notion that the thy mus is seeded by uncommitted progenitors.