Abnormal monocyte differentiation and function in chronic myelomonocytic leukemia.

PURPOSE OF REVIEW: Monocytes serve as the phagocytic defense surveillance system of the human body. Although there is comprehensive evidence regarding monocyte development, characterization and function under steady state hematopoietic continuum, the deviations and complexities in the monocyte secretome during myeloid malignancies have not been comprehensively examined and delineated. RECENT FINDINGS: This review summarizes the aspects of development, functions, transcriptional and cytokine-mediated regulation of monocytes during steady state hematopoiesis and also contrasts the aberrations observed in myelomonocytic leukemias like chronic myelomonocytic leukemia (CMML). It presents the findings from the major studies highlighting the novel markers for identifying CMML monocytes, altered signaling cascades, roles in disease progression and potential therapeutic interventions to reduce the monocyte mediated inflammatory milieu for disease amelioration. SUMMARY: Recent findings provide rationale for the development of therapeutic strategies aimed at disrupting the leukemic initiating cells and malignant monocyte axis.

TP53 mutations in myelodysplastic syndromes and secondary AML confer an immunosuppressive phenotype.

Somatic gene mutations are key determinants of outcome in patients with myelodysplastic syndromes (MDS) and secondary AML (sAML). In particular, patients with TP53 mutations represent a distinct molecular cohort with uniformly poor prognosis. The precise pathogenetic mechanisms underlying these inferior outcomes have not been delineated. In this study, we characterized the immunological features of the malignant clone and alterations in the immune microenvironment in patients with TP53-mutant and wild-type MDS or sAML. Notably, PDL1 expression is significantly increased in hematopoietic stem cells of patients with TP53 mutations, which is associated with MYC upregulation and marked downregulation of MYC's negative regulator miR-34a, a p53 transcription target. Notably, patients with TP53 mutations display significantly reduced numbers of bone marrow-infiltrating OX40+ cytotoxic T cells and helper T cells, as well as decreased ICOS+ and 4-1BB+ natural killer cells. Further, highly immunosuppressive regulatory T cells (Tregs) (ie, ICOShigh/PD-1-) and myeloid-derived suppressor cells (PD-1low) are expanded in cases with TP53 mutations. Finally, a higher proportion of bone marrow-infiltrating ICOShigh/PD-1- Treg cells is a highly significant independent predictor of overall survival. We conclude that the microenvironment of TP53 mutant MDS and sAML has an immune-privileged, evasive phenotype that may be a primary driver of poor outcomes and submit that immunomodulatory therapeutic strategies may offer a benefit for this molecularly defined subpopulation.

Functional Interference in the Bone Marrow Microenvironment by Disseminated Breast Cancer Cells.

Skeletal metastasis of breast cancer is associated with a poor prognosis and significant morbidity. Investigations in other solid tumors have revealed an impairment in hematopoietic function upon bone marrow invasion. However, the interaction between disseminated breast cancer cells and the bone marrow microenvironment which harbors them has not been addressed comprehensively. Employing advanced co-culture assays, proteomic studies, organotypic models as well as in vivo xenotransplant models, we define the consequences of this interaction on the stromal compartment of bone marrow, affected molecular pathways and subsequent effects on the hematopoietic stem and progenitor cells (HSPCs). The results showed a basic fibroblast growth factor (bFGF)-mediated, synergistic increase in proliferation of breast cancer cells and mesenchymal stromal cells (MSCs) in co-culture. The stromal induction was associated with elevated phosphoinositide-3 kinase (PI3K) signaling in the stroma, which coupled with elevated bFGF levels resulted in increased migration of breast cancer cells towards the MSCs. The perturbed cytokine profile in the stroma led to reduction in the osteogenic differentiation of MSCs via downregulation of platelet-derived growth factor-BB (PDGF-BB). Long term co-cultures of breast cancer cells, HSPCs, MSCs and in vivo studies in NOD.Cg-Prkdc(scid) Il2rg(tm1Wjl) /SzJ (NSG) mice showed a reduced support for HSPCs in the altered niche. The resultant non- conducive phenotype of the niche for HSPC support emphasizes the importance of the affected molecular pathways in the stroma as clinical targets. These findings can be a platform for further development of therapeutic strategies aiming at the blockade of bone marrow support to disseminated breast cancer cells. Stem Cells 2016;34:2224-2235.

Breast cancer cells compete with hematopoietic stem and progenitor cells for intercellular adhesion molecule 1-mediated binding to the bone marrow microenvironment.

Adhesion-based cellular interactions involved in breast cancer metastasis to the bone marrow remain elusive. We identified that breast cancer cells directly compete with hematopoietic stem and progenitor cells (HSPCs) for retention in the bone marrow microenvironment. To this end, we established two models of competitive cell adhesion-simultaneous and sequential-to study a potential competition for homing to the niche and displacement of the endogenous HSPCs upon invasion by tumor cells. In both models, breast cancer cells but not non-tumorigenic cells competitively reduced adhesion of HSPCs to bone marrow-derived mesenchymal stromal cells (MSCs) in a tumor cell number-dependent manner. Higher adhesive force between breast cancer cells and MSCs, as compared with HSPCs, assessed by quantitative atomic force microscopy-based single-cell force spectroscopy could partially account for tumor cell mediated reduction in HSPC adhesion to MSCs. Genetic inactivation and blockade studies revealed that homophilic interactions between intercellular adhesion molecule 1 (ICAM-1) expressed on tumor cells and MSCs, respectively, regulate the competition between tumor cells and HSPCs for binding to MSCs. Moreover, tumor cell-secreted soluble ICAM-1(sICAM-1) also impaired HSPC adhesion via blocking CD18-ICAM-1 binding between HSPCs and MSCs. Xenotransplantation studies in NOD.Cg-Prkdc(scid) Il2rg(tm1Wjl)/SzJ mice revealed reduction of human HSPCs in the bone marrow via metastatic breast cancer cells. These findings point to a direct competitive interaction between disseminated breast cancer cells and HSPCs within the bone marrow micro environment. This interaction might also have implications on niche-based tumor support. Therefore, targeting this cross talk may represent a novel therapeutic strategy.

Breast carcinoma cells modulate the chemoattractive activity of human bone marrow-derived mesenchymal stromal cells by interfering with CXCL12.

We investigated whether breast tumor cells can modulate the function of mesenchymal stromal cells (MSCs) with a special emphasis on their chemoattractive activity towards hematopoietic stem and progenitor cells (HSPCs). Primary MSCs as well as a MSC line (SCP-1) were cocultured with primary breast cancer cells, MCF-7, MDA-MB231 breast carcinoma or MCF-10A non-malignant breast epithelial cells or their conditioned medium. In addition, the frequency of circulating clonogenic hematopoietic progenitors was determined in 78 patients with breast cancer and compared with healthy controls. Gene expression analysis of SCP-1 cells cultured with MCF-7 medium revealed CXCL12 (SDF-1) as one of the most significantly downregulated genes. Supernatant from both MCF-7 and MDA-MB231 reduced the CXCL12 promoter activity in SCP-1 cells to 77% and 47%, respectively. Moreover, the CXCL12 mRNA and protein levels were significantly reduced. As functional consequence of lower CXCL12 levels, we detected a decreased trans-well migration of HSPCs towards MSC/tumor cell cocultures or conditioned medium. The specificity of this effect was confirmed by blocking studies with the CXCR4 antagonist AMD3100. Downregulation of SP1 and increased miR-23a levels in MSCs after contact with tumor cell medium as well as enhanced TGFß1 expression were identified as potential molecular regulators of CXCL12 activity in MSCs. Moreover, we observed a significantly higher frequency of circulating colony-forming hematopoietic progenitors in patients with breast cancer compared with healthy controls. Our in vitro results propose a potential new mechanism by which disseminated tumor cells in the bone marrow may interfere with hematopoiesis by modulating CXCL12 in protected niches.

Progenitor Hierarchy of Chronic Myelomonocytic Leukemia Identifies Inflammatory Monocytic-Biased Trajectory Linked to Worse Outcomes.

Myeloblast expansion is a hallmark of disease progression and comprises CD34+ hematopoietic stem and progenitor cells (HSPC). How this compartment evolves during disease progression in chronic myeloid neoplasms is unknown. Using single-cell RNA sequencing and high-parameter flow cytometry, we show that chronic myelomonocytic leukemia (CMML) CD34+ HSPC can be classified into three differentiation trajectories: monocytic, megakaryocyte-erythroid progenitor (MEP), and normal-like. Hallmarks of monocytic-biased trajectory were enrichment of CD120b+ inflammatory granulocyte-macrophage progenitor (GMP)-like cells, activated cytokine receptor signaling, phenotypic hematopoietic stem cell (HSC) depletion, and adverse outcomes. Cytokine receptor diversity was generally an adverse feature and elevated in CD120b+ GMPs. Hypomethylating agents decreased monocytic-biased cells in CMML patients. Given the enrichment of RAS pathway mutations in monocytic-biased cells, NRAS-competitive transplants and LPS-treated xenograft models recapitulated monocytic-biased CMML, suggesting that hematopoietic stress precipitates the monocytic-biased state. Deconvolution of HSPC compartments in other myeloid neoplasms and identifying therapeutic strategies to mitigate the monocytic-biased differentiation trajectory should be explored. SIGNIFICANCE: Our findings establish that multiple differentiation states underlie CMML disease progression. These states are negatively augmented by inflammation and positively affected by hypomethylating agents. Furthermore, we identify HSC depletion and expansion of GMP-like cells with increased cytokine receptor diversity as a feature of myeloblast expansion in inflammatory chronic myeloid neoplasms. This article is highlighted in the In This Issue feature, p. 476.

Memory Reactivation and Its Effect on Exercise Performance and Heart Rate.

Neuronal ensemble and brain plasticity both play an important role in memory consolidation and subsequently memory reactivation. To date, many studies have been designed to study the effect of exercise, heart-rate variability, and other factors on brain plasticity and memory. Here, we present a case study in which we have demonstrated the effect of neuronal ensemble and memory formed during High-intensity aerobic training (VO2 max) and Target Heart-Rate (THR) training and the effect of reactivation of same memory on THR and performance. Of note is the fact that the reactivation and recreation of memory stimulus learned and formed during High-intensity training, such as place, time, odor, and other conditions, can elevate the THR to the same previous peak zone even at low intensity. This demonstrates that reactivation of previously acquired memory or using the stimulation from the neuronal ensemble of consolidated memory during the specific event of training may exert similar physiological effects on exercise or the body to those that are learned during the memory acquisition phase. Hence, as exercise has an effect on memory, the memories may have an effect on exercise performances.