Human engraftment of secondary recipients by BM from a primary recipient of human CD34⁺ cells. (A) Histograms of BM, spleen, and PB cells stained with antibodies against both mu and hu CD45. All secondary recipients from experiments 1 and 7 contained huCD45⁺ cells in these tissues. (B) Typical profiles of the myeloid, lymphoid, and progenitor cells comprising the huCD45⁺ cell fraction of mouse BM are illustrated with histograms from the BM of a secondary recipient. Mouse BM cells were triple-stained and cells within the huCD45⁺ gate were analyzed. Populations of myeloid progenitors (CD33⁺, 2.3%), early myeloid cells (CD13⁺/33⁺, 11.3%), more mature myeloid cells (CD13⁺, 9.5%), monocytes (CD14⁺, 8%), and B cells (CD19⁺, 63%) were observed, while a significant proportion (5.5%) of huCD45⁺ BM cells expressed CD34.