Human cells in tissues of NOD/SCID mice engrafted with human CD34⁺HPC. Immunofluorescence and confocal microscopy analysis of frozen tissue sections from organs of NOD/SCID mice engrafted with human CD34⁺ HPC. Staining of skin (A), liver (B), and lung (C) sections with anti–human CD45-FITC. Control staining on spleen sections include isotype control and anti–human CD45-FITC staining on tissue from mice that did not receive human cells (not shown). Sections are from tissues harvested from the same one mouse (no. 4 from experiment 1 in Table 1, which received a transplant of 3 × 10⁵ cord blood CD34⁺ HPCs). CD45 staining was found in tested samples, harvested from different cohorts of engrafted mice, of skin from 5 mice, liver from 10 mice, and lung from 10 mice. Original magnification, × 63.