Contribution of proliferation and conservation to overall LTC-IC expansion. Single cell assays were performed as described in Methods and Fig 2 legend. In addition, we used data from a study previously published by our group in which LTC-IC were assessed in a single cell assay based on bone marrow (BM) stroma–conditioned media supplemented with IL-3 and MIP-1 in the absence of a stromal feeder.37 Significantly greater LTC-IC expansion is seen in AFT024/Flt3-L/SCF/IL-7 cultures than in AFT024/IL-3/MIP-1 cultures or SCM/AFT024/IL-3/MIP-1 cultures. This is a result of both increased proliferation and conservation when compared with AFT024/IL-3/MIP-1 cultures. The equivalent LTC-IC expansion seen in AFT024/IL-3/MIP-1 and SCM/IL-3/MIP-1 cultures is caused by different mechanisms: extensive self-renewal (80.5% ± 7.0%) of only 33.9% ± 6.0% conserved LTC-IC in SCM/IL-3/MIP-1 cultures and minimal self-renewal (13.9% ± 8.6%) of 84.8% ± 11.5% conserved LTC-IC in AFT024/IL-3/MIP-1 cultures. *P < 0.05; **P < 0.01.