B-cell progenitors circulate in cord blood: flow cytometry identification and purification of candidate populations.

(A) Three-color surface immunofluorescence studies of lymphoid cells (forward scatter × side scatter gate) show minor CB subsets that coexpress CD34 and either CD10 (0.5%) or CD19 (0.9%), above the background indicated by the quadrant bars, set using isotype-matched antibodies (less than 0.01%; see “Materials and methods”). (B) After gating on the IgM⁻ CD34⁺ cells (2.57%, top panel), the contour plot correlated distribution of CD19 versus CD10 is shown (bottom panel). Four hemopoietic progenitor populations (CD34⁺) are found in CB: CD34⁺CD19⁻CD10⁺ (3.3%), CD34⁺CD19⁺CD10⁺ (6.7%), CD34⁺CD19⁻CD10⁻ (74%), and CD34⁺CD19⁺CD10⁻ (16%). Please note that Coulter flow cytometers display contour plots in a different format than FACS analyzers. The data are not overcompensated. (C) Single cells in the 4 populations are purified using the R1-R4 sorting regions indicated in the bottom panel. CD34⁺ cells are enriched before the sorting step (90%; top panel). (D) On reanalyses to define the sort purity, most cells (more than 99.5%) in every population fall within the predefined sort regions.