Myeloid progenitor cluster formation drives emergency and leukaemic myelopoiesis

Although many aspects of blood production are well understood, the spatial organization of myeloid differentiation in the bone marrow remains unknown. Here we use imaging to track granulocyte/macrophage progenitor (GMP) behaviour in mice during emergency and leukaemic myelopoiesis. In the steady state, we find individual GMPs scattered throughout the bone marrow. During regeneration, we observe expanding GMP patches forming defined GMP clusters, which, in turn, locally differentiate into granulocytes. The timed release of important bone marrow niche signals (SCF, IL-1β, G-CSF, TGFβ and CXCL4) and activation of an inducible $\textit{Irf8}$ and β-catenin progenitor self-renewal network control the transient formation of regenerating GMP clusters. In leukaemia, we show that GMP clusters are constantly produced owing to persistent activation of the self-renewal network and a lack of termination cytokines that normally restore haematopoietic stem-cell quiescence. Our results uncover a previously unrecognized dynamic behaviour of GMPs $\textit{in situ}$, which tunes emergency myelopoiesis and is hijacked in leukaemia.This work was supported by NIH K01DK098315 award to E.M.P.; a Bloodwise and CRUK program grants and Wellcome Trust funding to the Cambridge Stem Cell Institute to B.G.; and NIH R01HL092471, R01HL111266 and P30DK063720 grants, Rita Allen Scholar Award and Leukemia Lymphoma Society Scholar Award to E.P

The Critical Role for Type-2 Dendritic Cells in Antitumor Immune Responses

The clinical successes in immunotherapy have been both astounding and at the same time unsatisfactory. Countless patients with varied tumor types have seen pronounced clinical response with immunotherapeutic intervention; however, many more patients have experienced minimal or no clinical benefit when provided the same treatment. Even as our ability to isolate and assay individual immune components from the tumor microenvironment (TME) has improved, the immunological features that dictate therapeutic success or failure are poorly understood. As technology has advanced, so has the understanding of the complexity and diversity of the immune context of the TME and its influence on response to therapy. As cancer treatments move away from broadly eliminating dividing cells to specifically activating components of the immune system within the TIME, our understanding of the cell types critical for eliciting antitumor responses must be better understood.Just as tumors can been subcategorized based on pathological and genetic features, categorizing tumors based on their TIME is equally informative. Specific combinations of immune populations within TIME can be highly predictive of both survival and response to immunotherapy. Antigen presenting cells (APCs), and in particular dendritic cells (DC), are emerging as critical components of a responsive TIME. DC have long been recognized for their exquisite ability to bridge detection of a harmful pathogen or virus with the activation of an adaptive T cell response. More recent work from our lab and others has highlighted the function that specific DC populations have in activating CD8+ T cells within the tumor-draining lymph node (tdLN) and tumor. However, CD4+ conventional T cells (Tconv) are emerging as critical partners for productive antitumor responses, but the conditions required for effective CD4+ Tconv activation remain poorly understood. Differentiation of proinflammatory CD4+ conventional T cells (Tconv) are critical for productive antitumor responses yet their elicitation remains poorly understood. We exhaustively characterized myeloid cells in tumor draining lymph nodes (tdLN) of mice and identified two subsets of conventional type-2 dendritic cells (cDC2) that traffic from tumor to tdLN and present tumor-derived antigens to CD4+ Tconv, but then fail to support antitumor CD4+ Tconv differentiation. Regulatory T cell (Treg) depletion enhanced their capacity to elicit strong CD4+ Tconv responses and ensuing antitumor protection. Analogous cDC2 populations were identified in patients, and as in mice their abundance relative to Treg predicts protective ICOShi PD-1lo CD4+ Tconv phenotypes and survival. Further, in melanoma patients with low Treg abundance, intratumoral cDC2 density alone correlates with abundant CD4+ Tconv and with responsiveness to anti-PD-1 therapy. Together, this highlights a pathway which restrains cDC2, and whose reversal enhances CD4+ Tconv abundance and controls tumor growth

FOXO3A directs a protective autophagy program in haematopoietic stem cells.

Blood production is ensured by rare, self-renewing haematopoietic stem cells (HSCs). How HSCs accommodate the diverse cellular stresses associated with their life-long activity remains elusive. Here we identify autophagy as an essential mechanism protecting HSCs from metabolic stress. We show that mouse HSCs, in contrast to their short-lived myeloid progeny, robustly induce autophagy after ex vivo cytokine withdrawal and in vivo calorie restriction. We demonstrate that FOXO3A is critical to maintain a gene expression program that poises HSCs for rapid induction of autophagy upon starvation. Notably, we find that old HSCs retain an intact FOXO3A-driven pro-autophagy gene program, and that ongoing autophagy is needed to mitigate an energy crisis and allow their survival. Our results demonstrate that autophagy is essential for the life-long maintenance of the HSC compartment and for supporting an old, failing blood system

FOXO3A directs a protective autophagy program in haematopoietic stem cells.

Blood production is ensured by rare, self-renewing haematopoietic stem cells (HSCs). How HSCs accommodate the diverse cellular stresses associated with their life-long activity remains elusive. Here we identify autophagy as an essential mechanism protecting HSCs from metabolic stress. We show that mouse HSCs, in contrast to their short-lived myeloid progeny, robustly induce autophagy after ex vivo cytokine withdrawal and in vivo calorie restriction. We demonstrate that FOXO3A is critical to maintain a gene expression program that poises HSCs for rapid induction of autophagy upon starvation. Notably, we find that old HSCs retain an intact FOXO3A-driven pro-autophagy gene program, and that ongoing autophagy is needed to mitigate an energy crisis and allow their survival. Our results demonstrate that autophagy is essential for the life-long maintenance of the HSC compartment and for supporting an old, failing blood system

Myeloproliferative Neoplasia Remodels the Endosteal Bone Marrow Niche into a Self-Reinforcing Leukemic Niche

SummaryMultipotent stromal cells (MSCs) and their osteoblastic lineage cell (OBC) derivatives are part of the bone marrow (BM) niche and contribute to hematopoietic stem cell (HSC) maintenance. Here, we show that myeloproliferative neoplasia (MPN) progressively remodels the endosteal BM niche into a self-reinforcing leukemic niche that impairs normal hematopoiesis, favors leukemic stem cell (LSC) function, and contributes to BM fibrosis. We show that leukemic myeloid cells stimulate MSCs to overproduce functionally altered OBCs, which accumulate in the BM cavity as inflammatory myelofibrotic cells. We identify roles for thrombopoietin, CCL3, and direct cell-cell interactions in driving OBC expansion, and for changes in TGF-β, Notch, and inflammatory signaling in OBC remodeling. MPN-expanded OBCs, in turn, exhibit decreased expression of many HSC retention factors and severely compromised ability to maintain normal HSCs, but effectively support LSCs. Targeting this pathological interplay could represent a novel avenue for treatment of MPN-affected patients and prevention of myelofibrosis

Visualizing Synaptic Transfer of Tumor Antigens among Dendritic Cells

Generation of tumor-infiltrating lymphocytes begins when tumor antigens reach the lymph node (LN) to stimulate T cells, yet we know little of how tumor material is disseminated among the large variety of antigen-presenting dendritic cell (DC) subsets in the LN. Here, we demonstrate that tumor proteins are carried to the LN within discrete vesicles inside DCs and are then transferred among DC subsets. A synapse is formed between interacting DCs and vesicle transfer takes place in the absence of free exosomes. DCs -containing vesicles can uniquely activate T cells, whereas DCs lacking them do not. Understanding this restricted sharing of tumor identity provides substantial room for engineering better anti-tumor immunity

Holistic Characterization of Tumor Monocyte-to-Macrophage Differentiation Integrates Distinct Immune Phenotypes in Kidney Cancer

Abstract The tumor immune microenvironment (TIME) is commonly infiltrated by diverse collections of myeloid cells. Yet, the complexity of myeloid cell identity and plasticity has challenged efforts to define bona fide populations and determine their connections to T cell function and their relation to patient outcome. Here we leverage single-cell RNA-sequencing (scRNA-seq) analysis of several mouse and human tumors and find that monocyte-macrophage diversity is characterized by a combination of conserved lineage states as well as transcriptional programs accessed along the differentiation trajectory. Using mouse models, we also find that tumor monocyte-to-macrophage progression is profoundly tied to regulatory T cell (Treg) abundance. Importantly, in human kidney cancer, heterogeneity in macrophage accumulation and myeloid composition corresponded to variance in, not only Treg density, but also the quality of infiltrating CD8 + T cells. In this way, holistic analysis of monocyte-to-macrophage differentiation creates a framework for critically different immune states in kidney tumors

Critical role for CD103 + /CD141 + dendritic cells bearing CCR7 for tumor antigen trafficking and priming of T cell immunity in melanoma

Intratumoral dendritic cells (DC) bearing CD103 in mice or CD141 in humans drive intratumoral CD8+ T cell activation. Using multiple strategies, we identified a critical role for these DC in trafficking tumor antigen to lymph nodes (LN), resulting in both direct CD8+ T cell stimulation and antigen hand-off to resident myeloid cells. These effects all required CCR7. Live imaging demonstrated direct presentation to T cells in LN, and CCR7 loss specifically in these cells resulted in defective LN T cell priming and increased tumor outgrowth. CCR7 expression levels in human tumors correlate with signatures of CD141+ DC, intratumoral T cells, and better clinical outcomes. This work identifies an ongoing pathway to T cell priming, which should be harnessed for tumor therapies