Essential role of MFSD1-GLMP-GIMAP5 in lymphocyte survival and liver homeostasis.

We detected ENU-induced alleles of Mfsd1 (encoding the major facilitator superfamily domain containing 1 protein) that caused lymphopenia, splenomegaly, progressive liver pathology, and extramedullary hematopoiesis (EMH). MFSD1 is a lysosomal membrane-bound solute carrier protein with no previously described function in immunity. By proteomic analysis, we identified association between MFSD1 and both GLMP (glycosylated lysosomal membrane protein) and GIMAP5 (GTPase of immunity-associated protein 5). Germline knockout alleles of Mfsd1, Glmp, and Gimap5 each caused lymphopenia, liver pathology, EMH, and lipid deposition in the bone marrow and liver. We found that the interactions of MFSD1 and GLMP with GIMAP5 are essential to maintain normal GIMAP5 expression, which in turn is critical to support lymphocyte development and liver homeostasis that suppresses EMH. These findings identify the protein complex MFSD1-GLMP-GIMAP5 operating in hematopoietic and extrahematopoietic tissues to regulate immunity and liver homeostasis.

Akkermansia muciniphila induces slow extramedullary hematopoiesis via cooperative IL-1R/TLR signals.

Bacterial infections can activate and mobilize hematopoietic stem and progenitor cells (HSPCs) from the bone marrow (BM) to the spleen, a process termed extramedullary hematopoiesis (EMH). Recent studies suggest that commensal bacteria regulate not only the host immune system but also hematopoietic homeostasis. However, the impact of gut microbes on hematopoietic pathology remains unclear. Here, we find that systemic single injections of Akkermansia muciniphila (A. m.), a mucin-degrading bacterium, rapidly activate BM myelopoiesis and slow but long-lasting hepato-splenomegaly, characterized by the expansion and differentiation of functional HSPCs, which we term delayed EMH. Mechanistically, delayed EMH triggered by A. m. is mediated entirely by the MYD88/TRIF innate immune signaling pathway, which persistently stimulates splenic myeloid cells to secrete interleukin (IL)-1α, and in turn, activates IL-1 receptor (IL-1R)-expressing splenic HSPCs. Genetic deletion of Toll-like receptor-2 and -4 (TLR2/4) or IL-1α partially diminishes A. m.-induced delayed EMH, while inhibition of both pathways alleviates splenomegaly and EMH. Our results demonstrate that cooperative IL-1R- and TLR-mediated signals regulate commensal bacteria-driven EMH, which might be relevant for certain autoimmune disorders.

Targeting erythroid progenitor cells for cancer immunotherapy.

Immunotherapy, especially immune checkpoint blockade therapy, represents a major milestone in the history of cancer therapy. However, the current response rate to immunotherapy among cancer patients must be improved; thus, new strategies for sensitizing patients to immunotherapy are urgently needed. Erythroid progenitor cells (EPCs), a population of immature erythroid cells, exert potent immunosuppressive functions. As a newly recognized immunosuppressive population, EPCs have not yet been effectively targeted. In this review, we summarize the immunoregulatory mechanisms of EPCs, especially for CD45+ EPCs. Moreover, in view of the regulatory effects of EPCs on the tumor microenvironment, we propose the concept of EPC-immunity, present existing strategies for targeting EPCs, and discuss the challenges encountered in both basic research and clinical applications. In particular, the impact of existing cancer treatments on EPCs is discussed, laying the foundation for combination therapies. The aim of this review is to provide new avenues for improving the efficacy of cancer immunotherapy by targeting EPCs.

Interplay of the heart, spleen, and bone marrow in heart failure: the role of splenic extramedullary hematopoiesis.

Improvements in therapies for heart failure with preserved ejection fraction (HFpEF) are crucial for improving patient outcomes and quality of life. Although HFpEF is the predominant heart failure type among older individuals, its prognosis is often poor owing to the lack of effective therapies. The roles of the spleen and bone marrow are often overlooked in the context of HFpEF. Recent studies suggest that the spleen and bone marrow could play key roles in HFpEF, especially in relation to inflammation and immune responses. The bone marrow can increase production of certain immune cells that can migrate to the heart and contribute to disease. The spleen can contribute to immune responses that either protect or exacerbate heart failure. Extramedullary hematopoiesis in the spleen could play a crucial role in HFpEF. Increased metabolic activity in the spleen, immune cell production and mobilization to the heart, and concomitant cytokine production may occur in heart failure. This leads to systemic chronic inflammation, along with an imbalance of immune cells (macrophages) in the heart, resulting in chronic inflammation and progressive fibrosis, potentially leading to decreased cardiac function. The bone marrow and spleen are involved in altered iron metabolism and anemia, which also contribute to HFpEF. This review presents the concept of an interplay between the heart, spleen, and bone marrow in the setting of HFpEF, with a particular focus on extramedullary hematopoiesis in the spleen. The aim of this review is to discern whether the spleen can serve as a new therapeutic target for HFpEF.

Idiopathic multicentric Castleman disease with marrow fibrosis and extramedullary hematopoiesis.

BACKGROUND: Idiopathic multicentric Castleman disease (iMCD) is a rare inflammatory disorder mediated by excessive proinflammatory cytokine signaling, most notably by interleukin 6 (IL-6). IL-6-induced extramedullary hematopoiesis (EMH) has been reported in murine models of iMCD. Herein we present four cases of iMCD with EMH in humans. CASE SERIES: The index case is a 24-year-old white woman who presented with pancytopenia, hepatosplenomegaly, and diffuse lymphadenopathy (LAD) with EMH in core lymph node biopsies. We then searched ACCELERATE, a Castleman disease (CD) natural history registry, and identified three additional CD cases with EMH reported in biopsies: A 23-year-old Asian man with fatigue, edema, LAD, and splenomegaly; a 20-year-old white man with fever, dyspnea, LAD, and hepatosplenomegaly; and a 50-year-old white man with constitutional symptoms, LAD, and myelodysplastic syndrome in bone marrow with a KRAS mutation. RESULTS: All four patients presented with thrombocytopenia and fever and/or markedly elevated C-reactive protein. Patient 1 had iMCD-NOS (not otherwise specified) with severe thrombocytopenia, reticulin fibrosis in bone marrow, small volume LAD and organomegaly but no anasarca. The other three patients had iMCD-TAFRO (thrombocytopenia, anasarca, reticulin fibrosis, renal dysfunction, organomegaly). Two had mixed CD and two had hypervascular CD in lymph nodes. All four had bone marrow hypercellularity and megakaryocyte hyperplasia and two had reticulin fibrosis. CONCLUSIONS: This case series demonstrates that EMH can be seen in CD, particularly in iMCD-TAFRO. Given the similarity of this finding to previous murine models of IL-6-induced marrow and lymph node changes we hypothesize that this is an IL-6-mediated phenomenon.

Hematopoietic stem cells and extramedullary hematopoiesis in the lungs.

Hematopoietic stem cells are key players in hematopoiesis as the body maintains a physiologic steady state, and the signaling pathways and control mechanisms of these dynamic cells are implicated in processes from inflammation to cancer. Although the bone marrow is commonly regarded as the site of hematopoiesis and hematopoietic stem cell residence, these cells also circulate in the blood and reside in extramedullary tissues, including the lungs. Flow cytometry is an invaluable tool in evaluating hematopoietic stem cells, revealing their phenotypes and relative abundances in both healthy and diseased states. This review outlines current protocols and cell markers used in flow cytometric analysis of hematopoietic stem and progenitor cell populations. Specific niches within the bone marrow are discussed, as are metabolic processes that contribute to stem cell self-renewal and differentiation, as well as the role of hematopoietic stem cells outside of the bone marrow at physiologic steady state. Finally, pulmonary extramedullary hematopoiesis and its associated disease states are outlined. Hematopoiesis in the lungs is a new and emerging concept, and discovering ways in which the study of lung-resident hematopoietic stem cells can be translated from murine models to patients will impact clinical treatment.

Synergistic immunotherapy targeting cancer-associated anemia: prospects of a combination strategy.

Cancer-associated anemia promotes tumor progression, leads to poor quality of life in patients with cancer, and even obstructs the efficacy of immune checkpoint inhibitors therapy. However, the precise mechanism for cancer-associated anemia remains unknown and the feasible strategy to target cancer-associated anemia synergizing immunotherapy needs to be clarified. Here, we review the possible mechanisms of cancer-induced anemia regarding decreased erythropoiesis and increased erythrocyte destruction, and cancer treatment-induced anemia. Moreover, we summarize the current paradigm for cancer-associated anemia treatment. Finally, we propose some prospective paradigms to slow down cancer-associated anemia and synergistic the efficacy of immunotherapy. Video Abstract.

Unraveling the interplay between iron homeostasis, ferroptosis and extramedullary hematopoiesis.

Iron participates in myriad processes necessary to sustain life. During the past decades, great efforts have been made to understand iron regulation and function in health and disease. Indeed, iron is associated with both physiological (e.g., immune cell biology and function and hematopoiesis) and pathological (e.g., inflammatory and infectious diseases, ferroptosis and ferritinophagy) processes, yet few studies have addressed the potential functional link between iron, the aforementioned processes and extramedullary hematopoiesis, despite the obvious benefits that this could bring to clinical practice. Further investigation in this direction will shape the future development of individualized treatments for iron-linked diseases and chronic inflammatory disorders, including extramedullary hematopoiesis, metabolic syndrome, cardiovascular diseases and cancer.

Extramedullary hematopoiesis in an inguinal lymph node: an unusual presentation of primary myelofibrosis.

BACKGROUND: Extramedullary hematopoiesis (EMH) is a proliferation of hematopoietic tissue outside of the bone marrow medullary space. It is a pathophysiologic response, more often associated with either a benign reactive hematological disease or a myeloproliferative neoplasm (MPN). Identification of EMH in adults is always pathologic. It is highly unlikely for a myeloproliferative neoplasm to present with inguinal lymphadenopathy. An unusual and complex case can be precisely diagnosed via a multidisciplinary approach involving experts from various modalities of laboratory. In this regard, the present case highlights the importance of an integrated approach in establishing the diagnosis. CASE PRESENTATION: We report a case of a 61-year-old male patient of primary myelofibrosis who presented with extramedullary hematopoiesis in an inguinal lymph node. The patient initially presented with generalized symptoms including anemia, fatigue, abdominal pain, and weight loss. On examination, massive splenomegaly. Chest X-ray revealed consolidation which was secondary to right-sided pleural effusion. Therefore, he was suspected to have a lung carcinoma. However, lymph node biopsy revealed extensive fibrosis, consequently effacing the nodal architecture. An abnormal blood picture raised the possibility of bone marrow infiltration. Extensive panel of markers is tested on lymph node and bone trephine. Cytogenetic studies with G-banding analysis and fluorescence in situ hybridization (FISH) played a significant role in deriving clinical decision. Translocations identified in conventional cytogenetic workup led to the diagnosis of primary myelofibrosis. The case is being reported due to unusual presentation of PMF. CONCLUSION: In conclusion, it is a distinctive case of myeloproliferative disorder initially presented with extramedullary hematopoiesis and through multidisciplinary workup successfully diagnosed as primary myelofibrosis. Awareness of unique clinical presentations and integrated approach towards diagnosis is the key to such challenging cases.

Fine needle aspiration of hepatic angiomyolipoma with extramedullary hematopoiesis: A case report.

Angiomyolipoma, a perivascular epithelioid cell tumour, is easily identifiable as a benign tumour in the kidneys. However, when occurring in extrarenal sites it can mimic malignancy (Cancer Cytopathol. 2017;125:257). Pathologists must be aware of the classical morphological features of this lesion, its pitfalls in extrarenal sites, and the need for immunohistochemistry in order to establish the correct diagnosis (World J Gastroenterol. 2000;6:608). We report a case of angiomyolipoma with extramedullary hematopoiesis presenting as a large hepatic mass, diagnosed by cytology through endoscopic ultrasound guided fine needle aspiration. Our case exemplifies the classic cytological findings that are important in the differentiation between hepatic angiomyolipoma (HAML) and differentials in this organ such as hepatocellular carcinoma (HCC) and focal nodular hyperplasia. A brief literature review and comparison of significant features between HAML and HCC are presented.

Immunohistopathological Analysis of Extramedullary Hematopoiesis and Angiogenesis of Spleen in a Case of Primary Myelofibrosis with Huge Splenomegaly.

Although splenomegaly is one of the important signs of primary myelofibrosis, the differential diagnosis varies from malignant disorders to benign disorders, including malignant lymphoma and sarcoidosis. The patient was a 67-year-old male who developed anemia and huge splenomegaly. The laboratory findings include human T-cell leukemia virus type 1 (HTLV-1) antibody, elevated soluble interleukin-2 receptor, hypocellular bone marrow, and uptake in the spleen on positron emission tomography/computed tomography scan. Additionally, we performed laparoscopic splenectomy to alleviate the clinical symptoms and to rule out malignant lymphoma. Histological findings revealed extramedullary hematopoiesis, characterized by the presence of erythroid islands and clusters of dysplastic megakaryocytes with increased reticulin fibrosis. Immunohistochemical staining revealed the presence of von Willebrand factor, dysplastic megakaryocytes, myeloperoxidase, myeloid-predominant proliferations, and CD34 immature myeloid cells. Furthermore, regarding the angiogenesis in the spleen, the endothelial cells of the capillaries and those of the sinusoidal vascular system that were reactive for CD34 and CD8, respectively, were also detected. Consequently, the histological findings revealed both extramedullary hematopoiesis and angiogenesis in spleen. Based on the histological findings and the identification of Janus activating kinase 2 (JAK-2) mutation, the patient was diagnosed with primary myelofibrosis. Splenectomy reduces blood transfusion requirements after surgery. The patient was carefully followed-up without further treatments. Thus, primary myelofibrosis is the crucial differential diagnosis of huge splenomegaly.

Advanced extramedullary hematopoiesis with a marked increase in reticulin fibers and hemorrhage on various organs: the first autopsy case report.

Myelofibrosis is characterized by stem cell-derived clonal proliferation potentially resulting in bone marrow fibrosis. As the disease progresses, extramedullary hematopoiesis is frequently detected in the spleen and the liver but rarely in other organs. We report a case of a 68-year-old woman with myelofibrosis with a JAK2 mutation, showing extramedullary hematopoiesis (EMH) in various organs with a marked increase in reticulin fibers, and myeloproliferative neoplasm (MPN)-related necrotizing crescent glomerulonephritis. She was admitted to our hospital owing to respiratory discomfort. Computed tomography revealed a mass in the anterior mediastinum. Ten days later, the patient died owing to respiratory distress. At autopsy, EMH were detected in the anterior mediastinum, heart, lung, spleen, and the kidney with a marked increase in reticulin fibers. We considered that respiratory distress was partially caused by EMH. In the kidney, necrotizing crescent glomerulonephritis was observed. Immunohistochemically, the glomerular basement and mesangial area were IgA- and C3d-positive. Ultrastructural examination revealed the presence of dense deposits in the subendothelial space and the mesangial and paramesangial areas. Thus, we suspected that MPN-related necrotizing crescentic glomerulonephritis harbored a pathogenesis similar to that of IgA-dominant post-infectious glomerulonephritis or IgA nephropathy. This case report could widen the spectrum of MPN- or EMH-related lesions.

Pathogenic Idiopathic Extramedullary Hematopoiesis in a Yellow-Collared Macaw (Primolius auricollis).

1.5-year-old yellow-collared macaw (Primolius auricollis) was presented as a referral case for chronic breathing difficulties and coelomic distension. The bird was in poor body condition, and coelomic distension and green-colored urates were noted during the physical examination. Radiographic images revealed a large coelomic space-occupying soft-tissue lesion that was ultrasonographically confirmed to be hepatomegaly; the liver had a heterogeneous echogenic pattern. An ultrasound-guided fine needle aspirate of the liver was performed. The cytological results revealed immature hematopoietic cells with signs of dyserythropoiesis and were consistent with extramedullary hematopoiesis (EMH). The plasma biochemistry panel revealed a marked increase in aspartate aminotransferase and bile acids, consistent with severe hepatic disease. Following the results of the diagnostic tests, chemotherapy was initiated using hydroxyurea. Two weeks after the initial presentation and treatment, the bird died and a full postmortem examination was performed. Macroscopic examination confirmed severe hepatomegaly and severe splenomegaly. Histopathological examination of tissue samples confirmed severe EMH in the liver and spleen, splenic and renal hemosiderosis, and acute pulmonary congestion. The bone marrow was normal. The final diagnosis was pathogenic idiopathic EMH, and this case was unusual in both its presentation and severity. Extramedullary hematopoiesis is usually related to myeloid proliferative disorder, chronic blood loss, hemolytic disease, or chronic inflammatory disease. Mycobacteriosis and parasitic infection have been reported to be associated with EMH in birds; however, the inflammatory patterns seen in those cases were lacking in this case. Myeloproliferative neoplasia also appears an unlikely disease condition in this case considering that histopathology found normal architecture in the studied bone marrow; however, bone marrow abnormalities in locations other than the one sampled could not be excluded. A short review of homeostatic and pathogenic hematopoiesis in birds is provided to support the likely diagnosis of idiopathic EMH.

Targeting the Spleen as an Alternative Site for Hematopoiesis.

Bone marrow is the main site for hematopoiesis in adults. It acts as a niche for hematopoietic stem cells (HSCs) and contains non-hematopoietic cells that contribute to stem cell dormancy, quiescence, self-renewal, and differentiation. HSC also exist in resting spleen of several species, although their contribution to hematopoiesis under steady-state conditions is unknown. The spleen can however undergo extramedullary hematopoiesis (EMH) triggered by physiological stress or disease. With the loss of bone marrow niches in aging and disease, the spleen as an alternative tissue site for hematopoiesis is an important consideration for future therapy, particularly during HSC transplantation. In terms of harnessing the spleen as a site for hematopoiesis, here the remarkable regenerative capacity of the spleen is considered with a view to forming additional or ectopic spleen tissue through cell engraftment. Studies in mice indicate the potential for such grafts to support the influx of hematopoietic cells leading to the development of normal spleen architecture. An important goal will be the formation of functional ectopic spleen tissue as an aid to hematopoietic recovery following clinical treatments that impact bone marrow. For example, expansion or replacement of niches could be considered where myeloablation ahead of HSC transplantation compromises treatment outcomes.

Myeloid, mast cell, histiocytic and dendritic cell neoplasms and proliferations involving the spleen.

Splenic involvement and consequent splenomegaly are usually seen as part of systemic involvement by myeloid neoplasms as well as mast cell and histiocytic neoplasms. Primary splenic involvement by these neoplasms is rare. Splenectomy is usually not performed for establishing a diagnosis of these entities. However, in rare instances, the pathologist may need to evaluate the spleen secondary to splenic rupture or palliative splenectomy to alleviate symptoms related to splenomegaly. This review article describes the clinicopathologic features of a broad group of myeloid, mastocytic, and histiocytic proliferative and neoplastic disorders.

Intratumoral extramedullary hematopoiesis in solitary fibrous tumor of the breast.

Extramedullary hematopoiesis (EMH) is most often associated with underlying hematologic disorders, such as myeloproliferative neoplasms and thalassemia. EMH in the setting of solitary fibrous tumor (SFT) is exceedingly rare, with only 3 cases reported to date in the English literature. Herein, we describe our experience with a unique case of SFT arising in the breast with intratumoral foci of EMH in a 57-year-old woman who presented with an incidentally found right axillary mass on routine screening mammography. To the best of our knowledge, this is the first reported case of mammary SFT with concurrent intratumoral EMH.

Myeloid diseases in the lung and pleura.

Myeloid diseases detected as primary or secondary lesions in the lung and pleura are rare. Clinical presentations and radiographic results may vary significantly depending on the nature of the diseases. The most common diseases associated with lung and pleura involvement are myeloid sarcoma/acute myeloid leukemia (AML) and extramedullary hematopoiesis (EMH). AML typically represents localized involvement by systemic acute leukemia, while EMH is frequently secondary to underlying benign hematolymphoid disorders or myeloproliferative neoplasms. This review provides an overview of the pathogenesis, clinical presentations, radiologic/imaging studies, pathologic and genetic findings, and treatment/outcomes associated with myeloid diseases in the lung and pleura.

Novel Detection of CALR-Mutated Cells in Myeloproliferative Neoplasm-Related Glomerulopathy With Interstitial Extramedullary Hematopoiesis: A Case Report.

Myeloproliferative neoplasms (MPNs) are associated with somatic mutations of genes including JAK2, CALR, or MPL in hematopoietic stem cells. Various glomerular lesions are known to be involved in MPN-related glomerulopathy, including mesangial hypercellularity, segmental sclerosis, features of chronic thrombotic microangiopathy, and intracapillary hematopoietic cell infiltration. Renal extramedullary hematopoiesis (EMH) is uncommon, but it is reported to occur in the setting of MPN; however, to our knowledge, there have been no reports of renal EMH with pathologically verified mutations. We report the case of a 65-year-old woman with MPN who had a CALR mutation and developed nephrotic syndrome. Kidney biopsy showed the typical findings of MPN-related glomerulopathy. CALR mutation-specific immunostaining of the kidney revealed immunopositive cells in the EMH lesion of the interstitium, indicating that renal EMH was caused by CALR-mutated cells. Based on these findings, we diagnosed nephrotic syndrome caused by MPN-related glomerulopathy. After initiation of steroid therapy, the patient's proteinuria gradually decreased and she achieved an incomplete remission. Additionally, the patient was prescribed the JAK inhibitor ruxolitinib and maintained incomplete remission. There is no established treatment for MPN-related glomerulopathy; therefore, further studies are needed to elucidate its pathophysiology.

Stem Cell Defect in Ubiquitin-Green Fluorescent Protein Mice Facilitates Engraftment of Lymphoid-Primed Hematopoietic Stem Cells.

Transgenic mice expressing green fluorescent protein (GFP) are useful in transplantation experiments. When we used ubiquitin-GFP (UBC-GFP) transgenic mice to study the availability of niches for transplanted hematopoietic stem and progenitor cells, the results were strikingly different from the corresponding experiments that used congenic mice polymorphic in the CD45 antigen. Analysis of these unexpected results revealed that the hematopoiesis of UBC-GFP mice was outcompeted by the hematopoiesis of wild-type (WT) mice. Importantly, UBC-GFP mice engrafted the transplanted bone marrow of WT mice without conditioning. There was a significant bias toward lymphopoiesis in the WT branch of chimeric UBC-GFP/WT hematopoiesis. A fraction of immature Sca-1+ cells in the spleen of UBC-GFP mice expressed GFP at a very high level. The chimeric hematopoiesis was stable in the long term and also after transplantation to secondary recipient mice. The article thus identifies a specific defect in the hematopoiesis of UBC-GFP transgenic mice that compromises the lymphoid-primed hematopoietic stem cells in the bone marrow and spleen. Stem Cells 2018;36:1237-1248.