Content of LTC-ICs in CD34⁺ cells derived from patients with PNH. (A) Total CD34⁺ cells from 2 patients with PNH and from a normal volunteer were cultured on preformed irradiated allogenic stromal layer. After 5 weeks, cells were plated in methylcellulose for an additional 2 weeks, and colonies were scored (A). Bars represent the total colony numbers obtained from different numbers of input CD34⁺ cells used to initiate the LTBMC. (B) CD34⁺ cells prepared as described in (A) were sorted based on the expression of CD59 antigen using a flow cytometer. Sorted cells were then used for LTBMC.