The human lung contains phenotypic hematopoietic progenitors with in vitro proliferation and differentiation capacity. (A) Pipeline for flow-cytometric immunophenotyping and evaluation of in vitro colony-forming capacity of progenitors from BM, lung, and PB of organ donors. (B) Normalized flow cytometry plots of BM and PB in the Live/Lin⁻ gate from a representative donor showing stem cell subsets within the multipotent (MP [CD34⁺CD38⁻], light purple) and the hematopoietic progenitor cell (HPC [CD34⁺CD38⁺], light blue) pool. (C) Composition of hematopoietic progenitor subsets in the BM, PB, and lung (n = 8). (D) Numbers of HPC subsets in the BM (white), PB (red), and lung (gray) per 10³ Lin⁻ CD34⁺ cells. N = 8 donors; bars indicate mean number of cells ± standard deviation (SD), and colors of the dots represent individual donors. Analysis of variance (ANOVA) followed by Sidak multiple comparison test, ∗P < .03; ∗∗P < .002; ∗∗∗P < .0001. (E) Frequency of HSCs/MPPs and HPCs as a percentage of total nucleated cells in the lung or BM, respectively. Dot colors represent individual donors, bars indicate mean ± SD. Student t test, ∗∗P < .01. (F) Culture-initiating capacity of lung and BM progenitors in MethoCult (n = 8): representative colonies (scale bar, 500 μm), colony composition, and colony quantity for progenitors derived from the BM and lung. Student t test, ∗∗∗P < .0001. #ANOVA followed by Sidak multiple comparison test. BFU-E (purple), burst-forming unit erythroid; G (orange), granulocyte; M (red), macrophage; GM (pink), granulocyte macrophage; GEMM (black), granulocyte, erythroid, macrophage, and megakaryocyte. (G) Culture-initiating capacity of lung and BM progenitors in MegaCult (n = 6): representative colonies (scale bar, 100 μm), colony quantity, and colony size for progenitors from the BM and lung. Bar graph represents mean number of colonies ± SD, Student t test, ∗∗∗P < .0001. Stacked bars represent mean proportion ± SD, Kruskal-Wallis test, ∗∗∗P < .0001. (H) Proportions of cycling (S-G2-M phase [blue], Ki-67⁺DAPI⁺), preparing/growing (G1 [gray], Ki-67⁺DAPI⁻), and resting cells (G0 [black], Ki-67⁻DAPI⁻) in the HSC/MPP and HPC pool from BM, PB, and lung (n = 7). Stacked bars represent mean proportion ± SD, ANOVA followed by Sidak multiple comparison test, ∗∗P < .01, ∗P < .05. For comparisons not indicated, no statistically significant differences were observed. CFU-Mk, CFU megakaryocyte; CMP, common myeloid progenitor; DAPI, 4′,6-diamidino-2-phenylindole; GMP, granulocyte-macrophage progenitor; MEP, megakaryocyte-erythroid progenitor; MLP, multilymphoid progenitor; ns, not significant.