Engraftment of human fetal thymic and BM tissue implanted in SCID mice by CD4⁻ CD34⁺⁺ Lin⁻ LDFL and CD4⁺ CD34⁺⁺ Lin⁻ LDFL progenitors. Generation of CD3⁺, CD4 SP, and CD8 SP and DP thymocytes by 50 HLA-A3⁻ CD4⁺ CD34⁺⁺ Lin⁻ LDFL cells injected into an HLA-A3⁺ thymic implant 95 days before analysis. Note the presence of a small (<1.9%) fraction of CD3⁺ HLA-A3⁺ host cells (A). Generation of CD34⁺, CD19⁺, and CD33⁺ cells by 200 HLA-A3⁺ CD4⁺ CD34⁺⁺ Lin⁻ LDFL cells injected into human fetal bone fragments (HLA-A3⁻) 125 days before analysis (B). The data are shown using 3% (A) and 2% (B) linear-density contour plots with 1 degree of smoothing. Analysis of CD4 and CD34 expression on Lin⁻ PI⁻ LDFL cells before (C, left) and after FACS (C, center and right). Ten thousand PI⁻ events were collected for the sort reanalysis shown. These sorted cells are donor B in Table 2 and donor D in Table 3.