Colony formation in the TAR syndrome.

(A) CFU-MK colony formation from peripheral blood CD34⁺cells of TAR syndrome patients. CD34⁺ cells from blood of 4 TAR patients and 2 normal controls were purified by an immunomagnetic procedure followed by cell sorting and were cultured in the serum-free fibrin clot assay; 2000 CD34⁺ cells were seeded in the presence of PEG-rHuMGDF alone, SCF plus PEG-rHuMGDF, or a combination of 3 cytokines (IL-3, SCF, and IL-6) in triplicate. Colonies were scored at day 12 after staining with an anti-CD61 MoAb. CFU-MK was considered as aggregates of more than 2 CD61⁺ cells. A marked reduction in CFU-MK colony formation was observed in TAR syndrome patients compared to controls. In addition, colonies were composed of aggregates of a maximum of 5 cells. (B) Comparison of CFU-MK colony formation from blood and marrow CD34⁺ cells in 2 other TAR syndrome patients. The same technique was used as in Figure 1A. A marked parallel decrease in CFU-MK colony formation was observed with both blood and marrow CD34⁺ cells. Combination of 3 cytokines was more efficient than PEG-rHuMGDF alone or SCF plus PEG-rHuMGDF in the induction of CFU-MK growth. (C) BFU-E and CFU-GM colony formation from peripheral blood CD34⁺ cells of TAR syndrome patients. Peripheral blood CD34⁺ cells were purified as described above and were plated in methylcellulose in the presence of a combination of PEG-rHuMGDF, SCF, G-CSF, IL-6, IL-3, and Epo for 14 to 16 days. Colonies were scored under an inverted microscope. No alteration in CFU-GM and BFU-E colony formation was found in 4 TAR syndrome patients. All results are expressed per 2000 CD34⁺ cells.