C-miR146a targets myeloid cell populations and restores miR-146a levels and activity in miR-146a^−/−mice. Dose-dependent biodistribution of miR-146a mimic in organs (A) and in bone marrow (BM) CD11b⁺ myeloid cells and CD11b^– cells (B) of miR-146a–deficient mice. Mice were injected intravenously by using various doses of C-miR146a and euthanized 3 hours later to assess miR-146a levels in BM, spleen, lymph nodes (LN), blood, and enriched BM CD11b⁺ myeloid cells and CD11b^– cells by using qPCR. (C) Biodistribution of systemically injected C-miR146a and miR-146a. C57BL/6 mice engrafted with Cbfb/Myh11/Mpl leukemia were injected intravenously with 5 mg/kg of C-miR146a^Cy3 or miR-146a^Cy3 and euthanized 3 hours later. The percentages of Cy3⁺ cells in BM were assessed by using flow cytometry (T cells, CD3⁺; natural killer [NK] cells, NK1.1⁺; B cells, CD19⁺; short-term hematopoietic stem cells [ST-HSC], Lin^–cKit⁺Sca1⁺Flt3^–CD150^–CD48^–; long-term hematopoietic stem cells [LT-HSC], Lin^–cKit⁺Sca1⁺Flt3^–CD150⁺CD48^–; monocytes, CD11b⁺CD11c^–; macrophages, CD11b⁺F4/80⁺; dendritic cells [DCs], CD11b⁺CD11c⁺; myeloid-derived suppressor cells [MDSCs], CD11b⁺Gr1⁺; and AML cells, GFP⁺). Shown are results representative for 2 independent experiments; means ± SEM (n = 3 mice/group). (D-E) Myeloid cell–selective delivery of miR-146a in vivo. miR-146a^−/− or WT mice were injected intravenously with 5 mg/kg of C-miR146a and euthanized 3 hours later. miR-146a levels in BM and splenocytes and enriched CD11b⁺ myeloid cells, CD19⁺ B cells, and CD3⁺ T cells from spleen were assessed by using qPCR and compared with the same populations in untreated WT mice. Shown are representative results obtained in 3 independent experiments; means ± SEM (n = 3). (F) Single injection of C-miR146a results in transient downregulation of IRAK1 and TRAF6 protein levels. miR-146a^−/− mice were injected intravenously with 5 mg/kg of C-miR146a and euthanized at indicated times. Protein levels of IRAK1 and TRAF6 in BM cells were assessed by using western blot, and the quantified band intensities normalized to β-actin are shown. Shown are results representative for two independent experiments.***P < .001; **P < .01; and *P < .05 compared to untreated or as indicated.