T-cell development is partially blocked by enforced expression of full-length Helios. (A) Representative FACS analyses of bone marrow, spleen, and thymus from mice reconstituted with bone marrow transduced with the indicated retroviral vectors at 12 to 16 weeks after transplantation. Numbers on the histograms show the percentage of GFP⁺ cells in the indicated organs. (B) Cells were gated for GFP expression and then analyzed for CD4 versus CD8 expression by FACS analysis. (C) Frequency of CD4⁺ and CD8⁺ cells among the total GFP⁺ cells in bone marrow (BM) and spleen (SP) at 12 to 16 weeks after transplantation (GFP, n = 8; Helios, n = 12; Δ49, n = 7). Asterisks indicate statistically significant differences between control and Helios mice (spleen, P < .01; bone marrow, P < .05; for Helios versus GFP control mice). Error bars represent standard deviation from the mean.