CD99 mice demonstrate no overt hematopoietic defects at steady state. (A) Representative flow cytometry histogram showing CD99 expression, as measured on CD3⁺ T cells from CD99 Gt/Gt, CD99 Gt/+, and WT mice. (B) Representative flow cytometry histogram (left) and summary (right) of CD99 expression on WT HSCs (LSK CD34^–), MPPs (LSK CD34⁺), CMPs (lineage-negative [LN] c-kit⁺sca-1^–CD34⁺CD16/32^–), GMPs (LN c-kit⁺sca-1^–CD34⁺CD16/32⁺), and MEPs (LN c-kit⁺sca-1^–CD34^–CD16/32^–; n = 3). (C) BM cellularity of 10 to 12-week-old CD99 Gt/Gt (n = 6) and WT mice (n = 6). (D) Absolute number of CMP, GMP, and MEP (n = 6 per genotype). (E) Absolute number of LSK cells, HSCs (LSK CD34^–CD150⁺), MPP A (LSK CD34⁺CD150⁺), and MPP B (LSK CD34⁺CD150^–) cells (n = 6 per genotype). (F-G) Complete blood counts of WT and CD99 KO mice, showing WBC and platelet counts, as well as hemoglobin, hematocrit, and mean corpuscular volume (n = 6 per genotype). (H) Numbers of colonies formed 10 days after plating of 150 HSCs from 3 mice in methylcellulose containing myeloid-erythroid cytokines. Numbers of colonies 10 days after 30 000 cells were resuspended from the initial plating and replated for 4 successive rounds. Statistical significance was assessed using 2-tailed Student t tests (∗P < .05; ∗∗P < .01; ∗∗∗P < .005). All data are represented as mean ± standard error. MFI, mean fluorescence intensity; WBC, white blood cell.