Leukemia-associated Macrophages Research Articles

The Lactate Receptor GPR81 is a Mechanism of Leukemia-Associated Macrophage Polarization in the Bone Marrow Microenvironment.

Interactions between acute myeloid leukemia (AML) and the bone marrow microenvironment (BMME) are critical to leukemia progression and chemoresistance. Altered metabolite levels in the tumor microenvironment contribute to immunosuppression in solid tumors, while this has not been studied yet in the leukemic BMME. Metabolomics of AML patient bone marrow serum detected elevated metabolites, including lactate, compared to age- and sex-matched controls. Excess lactate has been implicated in solid tumors for inducing suppressive tumor-associated macrophages (TAMs) and correlates with poor prognosis. We describe the role of lactate in the polarization of leukemia-associated macrophages (LAMs) using a murine model of blast crisis chronic myelogenous leukemia (bcCML) and mice genetically lacking the lactate receptor GPR81. LAMs were CD206hi and suppressive in transcriptomics and cytokine profiling. Yet, LAMs had a largely unique expression profile from other types of TAMs. We demonstrate GPR81 signaling as a mechanism of both LAM polarization and the direct support of leukemia cell growth and self-repopulation. Furthermore, LAMs and elevated lactate diminished the function of hematopoietic progenitors and stromal support, while knockout of GPR81 had modest protective effects on the hematopoietic system. We report microenvironmental lactate as a critical driver of AML-induced immunosuppression and leukemic progression, thus identifying GPR81 signaling as an exciting and novel therapeutic target for treating this devastating disease.

CD74 + Leukemia-Associated Macrophages Supporess T Cell Immune Surveillance and Promote Leukemic Cell Growth in Acute Myeloid Leukemia

The bone marrow microenvironment plays a pivotal role in the recurrence of acute myeloid leukemia (AML). However, the exact mechanisms are not fully understood. Single-cell technologies have emerged as powerful tools for unraveling the immune microenvironment in leukemia. In this study, utilizing scRNA-seq on a cohort of 13 paired AML patients, we have unveiled a distinctive subcluster of tumor-associated macrophages (TAMs) linked to relapse leukemia. To explore the heterogeneity of the bone marrow microenvironment during the progression of AML, we conducted a scRNA-seq analysis on bone marrow cells obtained from 13 paired AML patients at the time of diagnosis (DX) and relapse (RE) (Figure 1A). Employing UMAP for dimensionality reduction, we detected multiple subclusters and observed a notable rise in the Macrophage CD74 cluster in all paired RE patients, suggesting a pivotal role of CD74+ TAMs in AML relapse (Figure 1B-C). Furthermore, CD274, FOS, TGFβ1, and CD163, recognized as markers of M2 macrophages, were significantly enriched in the CD74+ TAMs population (Figure 1D). Intriguingly, a higher proportion of CD74+ TAMs correlated with unfavorable outcomes in TCGA database (Figure 1E). Meanwhile, we found that the ligand macrophage migration inhibitory factor (MIF) of CD74 was associated with poor prognosis of AML (Figure 1F). To investigate the association of CD74+ TAMs with AML cells, Gene Set Variation Analysis (GSVA) was employed and revealed restrained pathways related to T cell function (Figure 2A). Through in vitro experiments on patient samples, we found that CD74+TAM can inhibit the proliferation of T cells and the secretion of IFN-γ. Further monoclonal antibody block experiments unveiled that this inhibitory effect might be attributed to the heightened expression of PD-L1, TGFβ1, and IL-10 by the macrophages (Figure 2B-C). In conclusion, we have substantiated the inhibitory role of CD74+ TAMs on T cells, which hampers their ability to engage in effective tumor killing. To elucidate the interplay between CD74+ TAMs and AML cells, we examined the gene expression profile of cytokines, noting a significant increase in the expression level of IL-6 within the CD74+ TAMs subclusters of the RE group (Figure 3A). Furthermore, upon co-culture with CD74+ TAMs, THP-1 cells exhibited notable activation of IL-6 related pathways (Figure 3B). The injection of CD74+ TAMs resulted in heightened AML initiation and poorer survival in patient-derived xenograft (PDX) model, which was reversed by blocking the IL-6-IL-6R axis (Figure 3C-D). These findings collectively confirm that IL-6 secreted by CD74+ TAMs fosters the malignancy and drug resistance of AML cells. Subsequently, MLL-AF9-induced AML mouse model was employed to explore the spatial interplay between CD74+ TAMs, AML cells and T cells. Immunofluorescence (IF) analysis of mouse bone marrow tissue revealed that after chemotherapy, the proximity between AML cells and CD74+ TAMs decreased (Figure 4A-B). Conversely, the presence of T cells surrounding CD74+ TAMs increased (Figure 4C-D). These findings indicate that CD74+ TAMs can inhibit T cell function and directly influence AML cells within the tumor microenvironment. In summary, our study revealed a notable rise in the proportion of TAMs expressing CD74 in relapsed AML patients. These CD74+ TAMs were found to facilitate leukemia progression while concurrently inhibiting T cell immune surveillance in the context of AML. Thus, our findings indicate that CD74+ TAMs represent a distinct type of macrophages associated with AML relapse.

Sox13 and M2-like leukemia-associated macrophages contribute to endogenous IL-34 caused accelerated progression of acute myeloid leukemia

Interleukin 34 (IL-34) mainly plays physiologic and pathologic roles through the sophisticated multi-ligand signaling system, macrophage colony-stimulating factor (M-CSF, CSF-1)/IL-34-CSF-1R axis, which exhibits functional redundancy, tissue-restriction and diversity. This axis is vital for the survival, differentiation and function of monocytic lineage cells and plays pathologic roles in a broad range of diseases. However, the role of IL-34 in leukemia has not been established. Here MLL-AF9 induced mouse acute myeloid leukemia (AML) model overexpressing IL-34 (MA9-IL-34) was used to explore its role in AML. MA9-IL-34 mice exhibited accelerated disease progression and short survival time with significant subcutaneous infiltration of AML cells. MA9-IL-34 cells showed increased proliferation. In vitro colony forming assays and limiting dilution transplantation experiments demonstrated that MA9-IL-34 cells had elevated leukemia stem cell (LSC) levels. Gene expression microarray analysis revealed a panel of differential expressed genes including Sex-determining region Y (SRY)-box 13 (Sox13). Furthermore, a positive correlation between the expressions of IL-34 and Sox13 was detected human datasets. Knockdown of Sox13 rescued the enhanced proliferation, high LSC level and subcutaneous infiltration in MA9-IL-34 cells. Moreover, more leukemia-associated macrophages (LAMs) were detected in MA9-IL-34 microenvironment. Additionally, those LAMs showed M2-like phenotype since they expressed high level of M2-associated genes and had attenuated phagocytic potential, suggesting that LAMs should also contribute to IL-34 caused adverse phenotypes. Therefore, our findings uncover the intrinsic and microenvironmental mechanisms of IL-34 in AML and broadens the knowledge of M-CSF/IL-34-CSF-1R axis in malignancies.

Knockdown of let-7b in leukemia associated macrophages inhibit acute myeloid leukemia progression.

Macrophages, critical components of bone marrow microenvironment, are reported to be remodeled into leukemia-associated macrophages (LAMs) in leukemic microenvironment where they contribute to leukemia development, characterized as M2 macrophages with pro-tumor effects. However, how leukemic microenvironment transforms macrophages into LAMs remains unknown. Here, we analyzed the clinical relevance of LAMs and profiled their RNA-Seq from acute myeloid leukemia (AML) patients with complete remission (CR) after induction treatment and refractory AML patients. Our results showed that the proportion and number of LAMs in refractory AML patients was higher than that in CR patients and LAM was a poor prognostic factor of AML patients. Furthermore, let-7b was a potentially aberrant gene in LAMs contributed to M2-subtype characteristics. Knockdown of let-7b in LAMs could inhibit the development of AML by repolarizing LAMs toward M1-subtype characteristics through the activation of Toll-like receptor and NF-κB pathway. Our study provides insight for future LAM-based immunotherapy strategies for AML.

Knockdown of Let-7b in Leukemia Associated Macrophages Inhibit Acute Myeloid Leukemia Progression

As critical components of bone marrow microenvironment, macrophages are significant players in supporting and maintaining hematopoiesis. Macrophages are reported to be remodeled into leukemia-associated macrophages (LAMs) in leukemic microenvironment where they contribute to leukemia development, characterized as M2 macrophages with pro-tumor effects. However, how leukemic microenvironment transforms macrophages into LAMs remains unknown. Here, we analyzed clinical relevance of LAMs and profiled their RNA-Seq from acute myeloid leukemia (AML) patients achieved complete remission (CR) after induction treatment and refractory AML patients. Our results showed that the proportion of LAMs in refractory AML patients was higher than that in CR patients and LAM was a strong indicator of poor prognosis of AML patients. Furthermore, let-7b was a potentially aberrant gene in LAMs contributed to M2-subtype characteristics, which was associated with macrophage polarization. Knockdown of let-7b in LAMs could inhibit the development of AML by repolarizing LAMs towards M1-subtype characteristics through the activation of Toll Like Receptor (TLR) and NF-κB pathway. Our study provides insight for future LAM-based immunotherapy strategies for AML.

Blockade of Tigit on AML-Derived M2 Macrophages Results in Reprograming into the M1 Phenotype and Enhances CD47-Mediated Phagocytosis

Blockade of Tigit on AML-Derived M2 Macrophages Results in Reprograming into the M1 Phenotype and Enhances CD47-Mediated Phagocytosis

Inhibiting Efferocytosis in Acute Myeloid Leukemia Decreases Checkpoint Blockade through Decreased CCL5/STAT6 Signaling and Increases Activation through NF-Kb

Efferocytosis is a tolerogenic wound-healing process carried out by macrophages including phagocytosis of cellular debris and production of T cell suppressive cytokines. MerTK, the prototypic efferocytic receptor, is expressed on macrophages in tissues that harbor high leukemic burden, or “leukemia-associated macrophages” (LAMs), and therefore efferocytosis is co-opted by leukemia for immune evasion. We previously reported that in acute myeloid leukemia (AML) models blocking efferocytosis through inhibition of MerTK led to increased serum [IL-18] and downregulation of checkpoint ligands PD-L1 and PD-L2 on LAMs, which was not attributable to decreased [INF-γ] given that INF-γ was actually increased with MerTK inhibition.To evaluate a potential mechanism of PD-L1/PD-L2 downregulation when efferocytosis is inhibited, we evaluated for IL-4, IL-10 and IL-6 - all previously associated with checkpoint ligand expression - in serum samples of C57Bl/6 mice inoculated with a syngeneic MLL-ENL AML, and treated with a MerTK efferocytosis inhibitor (MRX-2843, n=15) or vehicle (PBS, n=14). There was no appreciable [IL-4] or [IL-10] detected in either treatment group. There was decreased serum [IL-6] in some MRX-2843-treated samples (mean: 45.4pg/ml) compared to controls (mean: 379.1pg/ml, p=0.3), however nearly all treated and untreated samples were <40pg/ml. We then evaluated several additional serum cytokines from these mice. CCL5/RANTES, known to promote M2 macrophage polarization and modulate PD-L1/PD-L2, was significantly decreased in mice treated with MRX-2843 (12.92pg/ml) compared to vehicle (28.63pg/ml, p<0.001). To validate this as relevant signaling pathway in LAMs, we evaluated STAT6 phosphorylation by western blot analysis in bone marrow derived macrophages (BMDM) from C57Bl/6 mice co-cultured with AML cells and treated with MRX-2843 or vehicle. When MerTK was inhibited, STAT6 phosphorylation was consistently decreased compared to vehicle-treated BMDM. This CCL5/STAT6 axis alteration may be a potential mechanism of PD-L1/PD-L2 downregulation when efferocytosis is inhibited.We next sought to evaluate whether there was LAM autocrine cytokine signaling within tissues of high leukemic burden, which were not detected by serum cytokine analysis. BMDM co-cultured with AML cells, and treated with MRX-2843 or vehicle were harvested after 12 hours and RT-qPCR was performed. mRNA levels of IFN-β and IL-1β in BMDM treated with MRX-2843 were twice that of controls, suggesting classic macrophage activation. These BMDM did not amplify appreciable levels of IL-4, IL-10, or TGF-β mRNA.Given the increased IL-1β mRNA and previously reported increased IL-18 associated with MerTK inhibition in LAMs, we evaluated NF-κB activation and subsequent inflammasome assembly. By RT-qPCR we did not detect any consistent alteration in p105 (precursor of p50) or RelA (p65), however when BMDM co-cultured with AML cells and treated with MRX-2843 or vehicle, western blot analysis consistently demonstrated increased phosphorylation of p65 as well as increased NLRP3 when MerTK was inhibited.In conclusion, blocking efferocytosis through MerTK in LAMs decreased CCL5/STAT6 signaling, which likely contributes to decreased LAM PD-L1 and PD-L2 expression. Furthermore, MerTK inhibition led to activation of NF-κB p65, inflammasome assembly, and production of IL-1β and IL-18. Taken together, these data demonstrate a mechanism by which MerTK inhibition alters antigen presentation through decreased co-inhibition and augmented activating cytokine production. Given that MerTK inhibitors are currently in clinical trials for relapsed/refractory malignancies, these data are relevant, timely, and could provide additional justification for their use in acute leukemias. DisclosuresVerneris: Fate Therapeutics: Consultancy; Novartis: Other: advisory board; jazz: Other: advisory board.

In This Issue

In This Issue

Effects of Macrophage Colony-Stimulating Factor Isoforms on Leukemia Progression in Mouse Acute Myeloid Leukemia Model

Oncogenic events occur by a variety of mechanisms, including point mutations, in-frame deletions or insertions, epigenetic modifications or even surrounding changes. As an important growth factor, M-CSF plays different roles in complicated pathological context and there are complex heterogeneities between M-CSF different splicing isoforms (sM-CSF and mM-CSF). The role of M-CSF and the difference between the two isoforms in hematological malignancies, which are significantly different from solid tumors, is poorly understood. In this study, we studied the different effects of mM-CSF and sM-CSF on both intrinsic factor-leukemia cells and surrounding linker-macrophage in acute myeloid leukemia mice model.The high level expression of M-CSF was found in myeloid leukemia patients from bloodspot database. We established MLL-AF9 induced AML mouse model with high level expression of sM-CSF or mM-CSF. We found mM-CSF could delay the progression of leukemia. Subsequently, we investigated the effect of the two isoforms on both leukemia cells and macrophages. More proliferative cells were detected in leukemia cells with high level M-CSF isoforms. In vitro colony assay experiments showed sM-CSF could promote the self-renew of leukemia cells. Morphological and flow cytometry analysis indicated M-CSF isoforms had different potential in promoting leukemia cell differentiation. Moreover, myeloid differentiation associated transcription factor-Cebpe and Runx1 might account for differentiation promoting effect by mM-CSF. As for macrophages, M-CSF isoforms could increase monocytes and macrophages in leukemic microenvironment by both growth-promoting and recruitment effects. Additionally, mM-CSF promoted the expression of both M1 and M2-associated genes. Meanwhile mM-CSF promoted the specific phagocytosis potential of macrophages to leukemia cells. Furthermore, the gene expression profiles of LAMs (leukemia associated macrophages) revealed mM-CSF did make macrophages a special phenotype with enhanced oxidative phosphorylation, metabolism and phagocytosis pathway. Moreover, phagocytosis of LAMs educated by mM-CSF may be mediated by oxidative phosphorylation.Our results suggested that the diverse effects of M-CSF two isoforms in leukemic microenvironment and mM-CSF delayed the leukemia course by affecting both leukemia cell differentiation and macrophage frequencies along with specific phagocytosis to leukemia cells. The work reveals that both the intrinsic and surrounding factors participate in tumor progression and the complex of carcinogenesis and the interaction between tumor cell itself and microenvironment linkers should be further studied.This work was supported by Grants 81370634 and 81570153 from the National Natural Science Foundation of China (NSFC); program 2016-I2M-2-006 from CAMS Initiative for Innovative Medicine; grant 17JCZDJC35000 from the Tianjin Science and Technology Committee. DisclosuresNo relevant conflicts of interest to declare.

MiR-451a enhances the phagocytosis and affects both M1 and M2 polarization in macrophages

Leukemia associated macrophages (LAMs), which are different from tumor-associated macrophages as well as classical M1 and M2 macrophages, are specifically activated by leukemic microenvironment. We have reported the heterogeneity of gene expression profiles in LAMs. However, the expression profiles of microRNA (miRNA) in LAMs and their regulatory mechanisms have not been established. Here, the expression profiles of miRNA in LAMs from bone marrow and spleen of acute myeloid leukemia mice were analyzed. Then, the effects of miR-451a, which was upregulated in LAMs, on macrophages were studied by transfecting miRNA mimic to peritoneal macrophages. The results showed that overexpression of miR-451a altered the morphology, enhanced the phagocytic ability of macrophages, and promotes the expression of differentiation marker CD11b in macrophages. Furthermore, miR-451a increased the proliferation capacity of both M1- and M2-polarized macrophages, but not M0 macrophages. Moreover, miR-451a further enhanced the expression of iNOS upon M1 activation. Therefore, our results reveal the miRNA expression profiles in LAMs, and broaden the knowledge about miRNA regulation in macrophages.

Nurse-Like Cells and Chronic Lymphocytic Leukemia B Cells: A Mutualistic Crosstalk inside Tissue Microenvironments.

Chronic lymphocytic leukemia (CLL) is the most common adult leukemia in Western countries and is an example of hematological disease where cooperation between genetic defects and tumor microenvironmental interaction is involved in pathogenesis. CLL is a disease that is considered as “addicted to the host”; indeed, the crosstalk between leukemic cells and the tumor microenvironment is essential for leukemic clone maintenance supporting CLL cells’ survival, proliferation, and protection from drug-induced apoptosis. CLL cells are not innocent bystanders but actively model and manipulate the surrounding microenvironment to their own advantage. Besides the different players involved in this crosstalk, nurse-like cells (NLC) resemble features related to leukemia-associated macrophages with an important function in preserving CLL cell survival and supporting an immunosuppressive microenvironment. This review provides a comprehensive overview of the role played by NLC in creating a nurturing and permissive milieu for CLL cells, illustrating the therapeutic possibilities in order to specifically target and re-educate them.

Effects of MiR-451a on the Phagocytosis and Polarization of Macrophages

Macrophages are important member in tissue microenvironments and play diverse physiologic and pathologic roles. Leukemia associated macrophages (LAM) are a kind of specifically activated macrophages in leukemia microenvironment, which are different from M1, M2 and TAMs. We have reported the heterogeneities in gene expression profiles of LAMs. However, MicroRNA expression profiles of LAMs and regulatory mechanism are still unknown. Here, a MLL-AF9 induced mouse acute myeloid leukemia (AML) model was used, and LAMs in the spleen and bone marrow were sorted for microRNA sequencing. The microRNA expression profiles of LAMs in bone marrow and spleen in AML mice were different from macrophages from control mice. Based on the volcano plot, more than 100 microRNAs were differentially expressed in LAMs compared with macrophages in control mice. Next, five differentially expressed microRNAs were selected and verified by qRT-PCR in LAMs from spleen. The results showed that miR-451a and miR-155-5p in spleen LAMs were significantly upregulated in LAMs from spleen. Overexpression of miR-451a altered the morphology of macrophages, enhanced the phagocytic ability of macrophages, and promotes the expression of macrophage differentiation marker CD11b. Furthermore, overexpression of miR-451a had little effect on M0 macrophages, but increased the proliferation capacity of macrophages upon stimulation toward M1 or M2 phenotype. MiR-451a overexpressed-macrophages had higher level of iNOS when stimulated with LPS or IL-4 whereas there was no difference in the expression of IL-1β, IL-6, CD206 and Arg-1 between MiR-451a overexpressed-macrophages and control macrophage. Therefore, our data revealed the characteristics of the microRNA expression profile of LAMs for the first time, and verified the effect of miR-451a on macrophage in vitro. Disclosures No relevant conflicts of interest to declare.

Monocyte-Derived Leukemia-Associated Macrophages Facilitate Extramedullary Distribution of T-cell Acute Lymphoblastic Leukemia Cells.

Macrophages play important roles in both physiologic and pathologic processes and arise from successive waves of embryonic and adult hematopoiesis. Monocyte-derived macrophages (MOMF) exert distinct functions under pathologic conditions, and leukemia-associated macrophages (LAM) show considerable diversities in activation and functional phenotype. However, their origin and pathologic roles have not been well elucidated. Here we used wild-type and CCR2-/- mice to study the pathologic roles of monocyte-derived LAM in extramedullary tissues in models of Notch1-induced T-cell acute lymphoblastic leukemia (T-ALL). MOMF existed in the resting liver and spleen. In the spleen, Ly6C+ monocytes gave rise to the Ly6C+ macrophage subset. Furthermore, an increase of monocyte-derived LAM, including the Ly6C+ subset, was detected in the extramedullary tissues in leukemic mice. More monocyte-derived LAM, including Ly6C+ LAM, was detected in the spleens of leukemic mice transplanted with exogeneous mononuclear cells. Moreover, Ly6C+ LAM exhibited increased M1-related characteristics and contributed to sterile inflammation. In CCR2-/- leukemic mice, reduced Ly6C+ LAM, relieved sterile inflammation, and reduced distribution of leukemia cells were detected in extramedullary tissues. In addition, monocyte-derived Ly6C+ LAM expressed high levels of CCL8 and CCL9/10. Blocking CCR1 and CCR2 relieved hepatosplenomegaly and inhibited the extramedullary distribution of leukemia cells in T-ALL mice. Collectively, our findings reveal the multifaceted pathologic roles of monocyte-derived LAM in T-ALL progression. SIGNIFICANCE: This study links monocyte-derived leukemia-associated macrophages with noninfectious inflammation and extramedullary distribution of leukemia cells during leukemia progression, providing new insight into macrophage-based immunotherapy in leukemia.

3204 - The Phenotypic Characteristics of Leukemia-Associated Macrophages are Shaped by Organ-Specific Leukemic Microenvironments and Targeting IRF7-SAPK/JNK Pathway Eliminates Their Pro-Leukemic Effects

3204 - The Phenotypic Characteristics of Leukemia-Associated Macrophages are Shaped by Organ-Specific Leukemic Microenvironments and Targeting IRF7-SAPK/JNK Pathway Eliminates Their Pro-Leukemic Effects

Repolarizing heterogeneous leukemia-associated macrophages with more M1 characteristics eliminates their pro-leukemic effects

ABSTRACT Macrophages exhibit phenotypic heterogeneity under both physiological and pathological conditions. Applications targeting M2-like tumor-associated macrophages (TAMs) improve outcome in solid tumors. Considerable differences are detected between leukemia-associated macrophages (LAMs) and TAMs. However, application to induce M1 characteristics in heterogeneous LAMs has not been established. Here we analyzed clinical relevance of macrophage phenotypes in human acute myeloid leukemia (AML), studied phenotypic evolution of bone marrow (BM) and spleen (SP) LAMs in mouse AML and T cell acute lymphoblastic leukemia (T-ALL) models, explored mechanism leading to different LAM phenotypes and tried to eliminate pro-leukemic effects by inducing M1 characteristics. The results showed that more M2-like LAMs but not total LAMs correlated with worse prognosis in AML patients. Heterogeneity of LAM activation in tissue-specific leukemic microenvironments was observed in both AML and ALL models, i.e. SP LAMs evolved with more M2 characteristics while BM LAMs with more M1 characteristics. Furthermore, IRF7 contributed to M1 characteristics through the activation of SAPK/JNK pathway. Moreover, targeting IRF7-SAPK/JNK pathway to induce M1 characteristics in LAMs contributed to prolonged survival in leukemia mice. Our study provides the potential target for macrophage based immuno-therapy strategy against leukemia.

Heterogeneous effects of M-CSF isoforms on the progression of MLL-AF9 leukemia.

Macrophage colony-stimulating factor (M-CSF) regulates both malignant cells and microenvironmental cells. Its splicing isoforms show functional heterogeneity. However, their roles on leukemia have not been well established. Here, the expression of total M-CSF in patients with hematopoietic malignancies was analyzed. The roles of M-CSF isoforms on the progression of acute myeloid leukemia (AML) were studied by establishing MLL-AF9-induced mouse AML models with high level membrane-bound M-CSF (mM-CSF) or soluble M-CSF (sM-CSF). Total M-CSF was highly expressed in myeloid leukemia patients. Furthermore, mM-CSF but not sM-CSF prolonged the survival of leukemia mice. While sM-CSF was more potent to promote proliferation and self-renew, mM-CSF was more potent to promote differentiation. Moreover, isoforms had different effects on leukemia-associated macrophages (LAMs) though they both increase monocytes/macrophages by growth-promoting and recruitment effects. In addition, mM-CSF promoted specific phagocytosis of leukemia cells by LAMs. RNA-seq analysis revealed that mM-CSF enhanced phagocytosis-associated genes and activated oxidative phosphorylation and metabolism pathway. These results highlight heterogeneous effects of M-CSF isoforms on AML progression and the mechanisms of mM-CSF, that is, intrinsically promoting AML cell differentiation and extrinsically enhancing infiltration of macrophages and phagocytosis by macrophages, which may provide potential clues for clinical diagnosis and therapy.

Role of tumor-associated macrophages in hematological malignancies

Macrophages constitute an important component of the microenvironment. They exhibit a remarkable plasticity in their phenotypes and functions. Recent studies have not only revealed the morphological, phenotypic, and functional characteristics of different macrophage subpopulations under physiological conditions but also clarified the mechanisms of alteration in macrophages under pathological conditions. Macrophages present in the tumor microenvironment are known as tumor-associated macrophages (TAMs), which are involved in tumor proliferation, angiogenesis, invasion, metastasis, and chemotherapy resistance. In hematological malignancies, macrophages infiltrate into the tissues that are invaded by myeloma, lymphoma, leukemia, and other malignant cells, acquire a specific activated phenotype, and participate in the progression of the disease. The term TAMs is generally used in myeloma and lymphoma, and in leukemia, it is modified as leukemia-associated macrophages (LAMs), acute leukemia-associated macrophages (AAMs), or “nurse-like cells” (NLCs). This review summarizes the knowledge regarding the progression of macrophages in hematological malignancies.

Hepatic leukemia-associated macrophages exhibit a pro-inflammatory phenotype in Notch1-induced acute T cell leukemia

Tumor-associated macrophages (TAMs) are well accepted and the pathological role of macrophages in hematopoietic malignancies have been proposed. Hepatomegaly is frequently observed in T cell acute lymphoblastic leukemia (T-ALL) patients with poor prognosis. However, the role of leukemia-associated macrophages (LAMs) in hepatic microenvironment remains unclear. Here, the characteristics of hepatic LAMs (H-LAMs) were studied in Notch1 induced T-ALL model. Increase in proportion and absolute counts of H-LAMs was detected with infiltration of inflammatory cells. Furthermore, H-LAMs exhibited a more M1-like phenotype distinct from that of TAMs in hepatocellular carcinoma and LAMs from BM or spleen in leukemia. Moreover, H-LAMs expressed increased level of cytokines in charge of recruiting inflammatory cells, which contributed to pro-inflammatory hepatic microenvironment.

Hepatic leukemic microenvironment educates leukemia-associated macrophages to a pro-inflammatory phenotype in notch1-induced acute T cell leukemia

Hepatic leukemic microenvironment educates leukemia-associated macrophages to a pro-inflammatory phenotype in notch1-induced acute T cell leukemia

Leukemia-Associated Macrophages Educated By Organ-Specific Leukemic Microenvironment Acquire Diverse Functions and Gene-Expression Signatures

Macrophages are important components of microenvironments and participate diverse physiological and pathological processes. Though CD68+macrophages have been demonstrated a potentially clinical marker to predict adverse prognosis in lymphoma, the role of macrophages in leukemia have not been fully elucidated. Most recently, we reported leukemia-associated macrophages (LAMs), which showed leukemia-promoting effects, in Notch1-induced mouse T-ALL leukemic microenvironment. In the present study, we studied the characteristics of LAMs from BM and spleen in MLL-AF9 induced mouse AML model, and compared the gene expression diversities among LAMs from BM and SP of AML and T-ALL models.LAMs were sorted from leukemic BM and spleen in the middle stage of AML, control macrophages were sorted from normal mouse. Then LAMs were cocultured with AML cells for 24, 48 and 72hrs. Cell count, BrdU incorporation assay and Annexin V assay were used to detect the proliferation and apoptosis of leukemia cells, respectively. Significant increase of BrdU positive and decrease of apoptotic AML cells were detected in leukemia cells cocultured with LAMs than control Mϕ. Latex-beads uptaken assay and transwell assay were used to detect the phagocytosis and migration of LAMs. Significant decrease of phagocytosis and increase of migration ability were detected in LAMs than control Mϕ. Furthermore, T cell coculture assay revealed that spleen LAMs suppress the CD25 and CD69 expression in both CD4+ and CD8+T cells but increase induction of Treg cells than BM LAMs. Moreover SP LAMs had a significantly higher proliferation promoting effect on leukemia cells than BM LAMs. To explore the diverse effect among LAMs from BM and spleen, we compared the transcriptional data of LAMs from BM and spleen from AML and T-ALL. The ordered list algorithm revealed the similarity score in LAM samples with same microenvironment (991.8) is higher than those with same type of leukemia (709.1), also the expression pattern analysis revealed that LAMs from leukemic BM and spleen are much more different, the phenotypic gene validated by qRT-PCR revealed that the BM LAMs are more M1-like while the spleen LAMs are more M2-like.Our results suggested that the diverse response of LAMs to leukemia are largely determined by organ-specific leukemic microenvironment.The work was supported by the Grants 81370634, 81570153, 81300376 from the National Natural Science Foundation of China (NSFC). DisclosuresNo relevant conflicts of interest to declare.