Flow cytometric analysis of transgene-expressing cells in peripheral blood subpopulations and BM CD34⁺ cells. (A) The percentage of transgene-positive cells in different leukocyte subpopulations in the peripheral blood of monkeys that received an EGFP-expressing vector at days 67 and 174 (J02370), or days 116 and 441 (T04228) after transplantation. In these monkeys, EGFP-expressing cells were found in all lineages examined. (B) Flow cytometry data for EGFP expression in different lineages from animal T04228 at day 441. Each lineage was identified with a phycoerythrin (PE)–labeled antibody. The percentages shown are for the total number of EGFP- and lineage-positive cells over the total number of lineage positive cells. (C) Gating on red blood cells (RBCs) and platelets (PLTs) was based on scatter characteristics (S-SC is side scatter and F-SC is forward scatter). (D) EGFP-expressing red blood cells (top panels) and platelets (bottom panels) are plotted with side scatter for a control animal and for animal J02370. Because of the overlapping positive and negative populations due to low fluorescence intensity, especially in red blood cells, the percentages of marked cells (5.6% in red blood cells, 6.7% in platelets) likely underestimate the actual percentage of EGFP-expressing cells.