Purified CD34⁺CD38⁻ cells from patient no. 10 with MDS and +8 and a patient with MDS with del(20q) (see “Patients, materials, and methods”) were seeded at different cell numbers, either alone or together with CD34⁺CD38⁻ cells from a healthy donor onto murine stromal feeders (see “Patients, materials, and methods”). Normal CD34⁺CD38⁻ cells were also cultured in the absence of MDS cells. After 6 weeks of weekly half medium exchange, the LTC-CFC activity was evaluated and colonies were picked to establish the presence of + 8 or del(20q). In patient no. 10, 66% of the starting CD34⁺CD38⁻ cells were + 8, whereas in the other patient, 96.5% of the sorted CD34⁺CD38⁻ cells had del(20q). Colony numbers represent the mean of 3 to 6 replicates.

MDS indicates myelodysplastic syndrome; HSC, hematopoietic stem cell; LTC-CFC, long-term culture–colony forming cells.