The human αIIb gene promoter confined transgene expression to platelets. (A) The human αIIb promoter confined expression of a GFP reporter gene within the platelet lineage. Entities exhibiting the forward (FSC) and side (SSC) scattering properties of platelets (Plt), white blood cells (WBC), and red blood cells (RBC) isolated from circulating whole blood of a β3^+/+ mouse that received a transplant of –889GFPII-transduced bone marrow (column 1, density plot) were used to construct flow cytometric histograms comparing untransduced and GFP-transduced lineages (column 2). The transplant recipient showed significant levels of GFP in platelets (row 1, column 2, shaded peak) compared with the MFI for platelets from a β3^+/+ control that did not receive a bone marrow transplant (open overlay histogram). In contrast, GFP was not detected above background levels within the WBCs or RBCs of the mouse that underwent transplantation. The result shown is representative of the outcome from analysis of peripheral blood collected from one mouse on 5 separate occasions. (B) Two-color flow cytometric analysis showed that the human αIIb promoter targeted expression of human β3 to platelets. A panel of antibodies that react with surface markers (x-axis, bottom) of specific murine cell lineages (x-axis, top) was used in conjunction with an antibody to human β3 (y-axis). The percentage of cells coexpressing both markers is indicated in each density plot (top right quadrant). Human β3 was not detected in cells from β3^–/–, β3^+/–, and β3^+/+ controls (rows 1-3), while mouse D had significant levels of β3 detectable only in platelets (row 4). Plt indicates platelet; B-Lym, B lymphocyte; T-Lym, T lymphocyte; Gr/E/Nu, granulocyte/eosinophil/neutrophil; Mac/NK, macrophage/natural killer cell; and RBC, red blood cell. The result shown is representative of the outcome observed in 4 experiments that analyzed peripheral blood collected from 2 mice on 2 separate occasions.