Identification of early myeloid progenitors as immunosuppressive cells.
ABSTRACT: Growing evidence suggests that hematopoietic stem/progenitor cells (HSPCs), precursors of mature immune cells, may play a direct role in immunosurveillance. Early myeloid progenitors are the major components of HSPCs and they often undergo extensive expansion in stress as a result of myeloid-biased hematopoiesis. Yet, the precise function of early myeloid progenitors remains unclear. Here we show that during tumor progression, mouse granulocyte/macrophage progenitors (GMPs) but not common myeloid progenitors (CMPs) are markedly expanded within the bone marrow and blood of mice. Interestingly, both GMPs and CMPs freshly isolated from either tumor-bearing or naïve animals are capable of inhibiting polyclonal stimuli- and alloantigen-induced T cell proliferation, with tumor host-derived cells having elevated activities. Strikingly, these early myeloid progenitor cells even display much stronger suppressive capacity than the classical myeloid-derived suppressive cells. Analysis of GMPs indicates that they express iNOS and can secrete high levels of NO. Further studies unusing iNOS specific inhibitors reveal that the immunosuppression of GMPs is, to a large extent, NO-dependent. GMPs can also efficiently induce regulatory T cell development. These studies demonstrate that early myeloid progenitors can act as immunosuppressive cells. This finding provides novel insights into the functional diversity and plasticity of early myeloid progenitor cells.
Project description:Granulocyte-monocyte progenitors (GMPs) and monocyte-dendritic cell progenitors (MDPs) produce monocytes during homeostasis and in response to increased demand during infection. Both progenitor populations are thought to derive from common myeloid progenitors (CMPs), and a hierarchical relationship (CMP-GMP-MDP-monocyte) is presumed to underlie monocyte differentiation. Here, however, we demonstrate that mouse MDPs arose from CMPs independently of GMPs, and that GMPs and MDPs produced monocytes via similar but distinct monocyte-committed progenitors. GMPs and MDPs yielded classical (Ly6Chi) monocytes with gene expression signatures that were defined by their origins and impacted their function. GMPs produced a subset of "neutrophil-like" monocytes, whereas MDPs gave rise to a subset of monocytes that yielded monocyte-derived dendritic cells. GMPs and MDPs were also independently mobilized to produce specific combinations of myeloid cell types following the injection of microbial components. Thus, the balance of GMP and MDP differentiation shapes the myeloid cell repertoire during homeostasis and following infection.
Project description:Because PML-RARA-induced acute promyelocytic leukemia (APL) is a morphologically differentiated leukemia, many groups have speculated about whether its leukemic cell of origin is a committed myeloid precursor (e.g. a promyelocyte) versus an hematopoietic stem/progenitor cell (HSPC). We originally targeted PML-RARA expression with CTSG regulatory elements, based on the early observation that this gene was maximally expressed in cells with promyelocyte morphology. Here, we show that both Ctsg, and PML-RARA targeted to the Ctsg locus (in Ctsg-PML-RARA mice), are expressed in the purified KLS cells of these mice (KLS?=?Kit(+)Lin(-)Sca(+), which are highly enriched for HSPCs), and this expression results in biological effects in multi-lineage competitive repopulation assays. Further, we demonstrate the transcriptional consequences of PML-RARA expression in Ctsg-PML-RARA mice in early myeloid development in other myeloid progenitor compartments [common myeloid progenitors (CMPs) and granulocyte/monocyte progenitors (GMPs)], which have a distinct gene expression signature compared to wild-type (WT) mice. Although PML-RARA is indeed expressed at high levels in the promyelocytes of Ctsg-PML-RARA mice and alters the transcriptional signature of these cells, it does not induce their self-renewal. In sum, these results demonstrate that in the Ctsg-PML-RARA mouse model of APL, PML-RARA is expressed in and affects the function of multipotent progenitor cells. Finally, since PML/Pml is normally expressed in the HSPCs of both humans and mice, and since some human APL samples contain TCR rearrangements and express T lineage genes, we suggest that the very early hematopoietic expression of PML-RARA in this mouse model may closely mimic the physiologic expression pattern of PML-RARA in human APL patients.
Project description:Emerging evidence demonstrates that proangiogenic cells (PACs) originate from the BM and are capable of being recruited to sites of ischemic injury where they contribute to neovascularization. We previously determined that among hematopoietic progenitor stem cells, common myeloid progenitors (CMPs) and granulocyte-macrophage progenitor cells (GMPs) differentiate into PACs and possess robust angiogenic activity under ischemic conditions. Herein, we report that a TGF-?1-responsive Krüppel- like factor, KLF10, is strongly expressed in PACs derived from CMPs and GMPs, ? 60-fold higher than in progenitors lacking PAC markers. KLF10(-/-) mice present with marked defects in PAC differentiation, function, TGF-? responsiveness, and impaired blood flow recovery after hindlimb ischemia, an effect rescued by wild-type PACs, but not KLF10(-/-) PACs. Overexpression studies revealed that KLF10 could rescue PAC formation from TGF-?1(+/-) CMPs and GMPs. Mechanistically, KLF10 targets the VEGFR2 promoter in PACs which may underlie the observed effects. These findings may be clinically relevant because KLF10 expression was also found to be significantly reduced in PACs from patients with peripheral artery disease. Collectively, these observations identify TGF-?1 signaling and KLF10 as key regulators of functional PACs derived from CMPs and GMPs and may provide a therapeutic target during cardiovascular ischemic states.
Project description:Autoimmune diseases often induce dysregulated hematopoiesis with altered number and function of hematopoietic stem and progenitor cells (HSPCs). However, there are limited studies on the direct regulation of HSPCs on T cells, which are often detrimental to autoimmunity. Here, we found that in a murine model of Concanavalin A-induced autoimmune hepatitis, LSK (Lineage-Sca-1+c-Kit+)-like cells accumulated in liver, spleen, and bone marrow (BM), which were myeloid progenitors (Lineage-Sca-1-c-Kit+) that upregulated Sca-1 expression upon T cell-derived IFN-? stimulation. Strikingly, BM LSK-like cells from mice induced by Con A to develop autoimmune hepatitis or alternatively myeloid progenitors from wild-type mice possessed strong in vitro suppressive ability. Their suppressive function depended on T cell-derived IFN-? in a paracrine fashion, which induced STAT1 phosphorylation, inducible nitric oxide synthase expression, and nitric oxide production. Blocking IFN-?/IFN-? receptor interaction, knockout of STAT1, or iNOS inhibition abrogated their suppressive function. In addition, the suppressive function was independent of differentiation; mitomycin C-treated myeloid progenitors maintained T cell suppressive ability in vitro. Our data demonstrate a mechanism of inflammation induced suppressive function of myeloid progenitors, which may participate directly in suppressing T cell-mediated immunopathology.
Project description:Langerhans cells (LCs) are antigen-presenting cells (APCs) residing in the epidermis that play a major role in skin immunity. Our earlier studies showed that when skin is inflamed LCs are replaced by bone marrow-derived progenitor cells, while during steady-state conditions LCs are able to self-renew in the skin. Identification of the LC progenitors in bone marrow would represent a critical step toward identifying the factors that regulate LC generation as well as their trafficking to the skin. To determine LC lineage origin, we reconstituted lethally irradiated CD45.2 mice with rigorously purified lymphoid and myeloid progenitors from CD45.1 congenic mice. Twenty-four hours later, we exposed the mice to UV light to deplete resident LCs and induce their replacement by progenitors. Reconstitution with common myeloid progenitors (CMPs), common lymphoid progenitors (CLPs), granulocyte-macrophage progenitors (GMPs), or early thymic progenitors led to LC generation within 2 to 3 weeks. CMPs were at least 20 times more efficient at generating LCs than CLPs. LCs from both lineages were derived almost entirely from fetal liver kinase-2+ (Flk-2+) progenitors, displayed typical dendritic-cell (DC) morphology, and showed long-term persistence in the skin. These results indicate that LCs are derived mainly from myeloid progenitors and are dependent on Flt3-ligand for their development.
Project description:Clinical studies using bone marrow-derived proangiogenic cells (PACs) have demonstrated modest improvements of function and/or perfusion of ischemic myocardium or skeletal muscle. Because the identities of these PACs and their functional ability to promote neovascularization remain poorly understood, it is possible that a subset of robust PACs exists but is obscured by the heterogeneous nature of this cell population. Herein, we found that common myeloid progenitors (CMPs) and granulocyte-macrophage progenitors (GMPs) preferentially differentiate into PACs compared with megakaryocyte-erythrocyte progenitors, hematopoietic stem cells, and common lymphoid progenitors. In vivo hindlimb ischemia studies and Matrigel plug assays verified the enhanced neovascularization properties uniquely associated with PACs derived from CMPs and GMPs. Taken together, these observations identify CMPs and GMPs as key bone marrow progenitors for optimal PAC function in vitro and in vivo and provide a foundation for novel therapeutic approaches to modulate angiogenesis.
Project description:The differentiation of myeloid progenitors to mature, terminally differentiated cells is a highly regulated process. Here, we showed that conditional disruption of the c-myb proto-oncogene in adult mice resulted in dramatic reductions in CMP, GMP and MEP myeloid progenitors, leading to a reduction of neutrophils, basophils, monocytes and platelets in peripheral blood. In addition, c-myb plays a critical role at multiple stages of myeloid development, from multipotent CMP and bipotent GMP to unipotent CFU-G and CFU-M progenitor cells. c-myb controls the differentiation of these cells and is required for the proper commitment, maturation and normal differentiation of CMPs and GMPs. Specifically, c-myb regulates the precise commitment to the megakaryocytic and granulo-monocytic pathways and governs the granulocytic-monocytic lineage choice. c-myb is also required for the commitment along the granulocytic pathway for early myeloid progenitor cells and for the maturation of committed precursor cells along this pathway. On the other hand, disruption of the c-myb gene favors the commitment to the monocytic lineage, although monocytic development was abnormal with cells appearing more mature with atypical CD41 surface markers. These results demonstrate that c-myb plays a pivotal role in the regulation of multiple stages in adult myelogenesis.
Project description:Hematopoietic stem cells (HSCs) are maintained in a perivascular niche in bone marrow, in which leptin receptor+ (LepR) stromal cells and endothelial cells synthesize factors required for HSC maintenance, including stem cell factor (SCF). An important question is why LepR+ cells are one hundred times more frequent than HSCs. Here, we show that SCF from LepR+ cells is also necessary to maintain many c-kit+-restricted hematopoietic progenitors. Conditional deletion of Scf from LepR+ cells depleted common myeloid progenitors (CMPs), common lymphoid progenitors (CLPs), granulocyte-macrophage progenitors (GMPs), megakaryocyte-erythrocyte progenitors (MEPs), pre-megakaryocyte-erythrocyte progenitors (PreMegEs), and colony-forming units-erythroid (CFU-Es), as well as myeloid and erythroid blood cells. This was not caused by HSC depletion, as many other restricted progenitors were unaffected. Moreover, Scf deletion from endothelial cells depleted HSCs, but not progenitors. Early erythroid progenitors were closely associated with perisinusoidal LepR+ cells. This reveals cellular specialization within the niche: SCF from LepR+ cells is broadly required by HSCs and restricted progenitors while SCF from endothelial cells is required mainly by HSCs.
Project description:Cancer is associated with a profound perturbation in myelopoiesis that results in the accumulation of myeloid-derived suppressor cells (MDSCs) to promote disease progression. Recent studies in mice suggest that tumor-derived factors could regulate the differentiation of hematopoietic stem and progenitor cells (HSPCs) in the bone marrow and subsequently contribute to dysregulation of hematopoiesis. However, the nature and role of HPSCs in patients with cancer remain unknown. Here we show, in detailed studies of the peripheral blood from 133 untreated patients with seven different types of tumors, that the composition of circulating HSPCs was significantly altered in patients with solid tumors. The frequencies of circulating granulocyte-monocyte progenitors (GMPs) were increased four to seven fold in all types of tumors examined, and the circulating hematopoietic precursors exhibited myeloid bias with a skew toward granulocytic differentiation in patients with solid tumors. These myeloid precursors are selectively enriched in tumor tissues, and the high levels of circulating GMPs were positively correlated with disease progression. By using cord blood-derived CD34(+) cells, we developed an in vitro short-term culture model to effectively induce the rapid generation of MDSCs. We found that, among the factors produced by various tumors, GM-CSF, granulocyte colony-stimulating factor, and IL-6 could not only promote the myeloid-biased differentiation, but also induce the differentiation of myeloid precursors into functional MDSCs. These findings suggest that the altered circulating HSPCs may serve as an important link between dysregulated bone marrow hematopoiesis and accumulated MDSCs in patients with cancer.
Project description:The hierarchy of human hemopoietic progenitor cells that produce lymphoid and granulocytic-monocytic (myeloid) lineages is unclear. Multiple progenitor populations produce lymphoid and myeloid cells, but they remain incompletely characterized. Here we demonstrated that lympho-myeloid progenitor populations in cord blood - lymphoid-primed multi-potential progenitors (LMPPs), granulocyte-macrophage progenitors (GMPs) and multi-lymphoid progenitors (MLPs) - were functionally and transcriptionally distinct and heterogeneous at the clonal level, with progenitors of many different functional potentials present. Although most progenitors had the potential to develop into only one mature cell type ('uni-lineage potential'), bi- and rarer multi-lineage progenitors were present among LMPPs, GMPs and MLPs. Those findings, coupled with single-cell expression analyses, suggest that a continuum of progenitors execute lymphoid and myeloid differentiation, rather than only uni-lineage progenitors' being present downstream of stem cells.