All Publications

  • CD47 Blockade Leads to Chemokine-Dependent Monocyte Infiltration and Loss of B Cells from the Splenic Marginal Zone. Journal of immunology (Baltimore, Md. : 1950) Yiu, Y. Y., Hansen, P. S., Torrez Dulgeroff, L. B., Blacker, G., Myers, L., Galloway, S., Gars, E., Colace, O., Mansfield, P., Hasenkrug, K. J., Weissman, I. L., Tal, M. C. 2022


    CD47 is an important innate immune checkpoint through its interaction with its inhibitory receptor on macrophages, signal-regulatory protein alpha (SIRPalpha). Therapeutic blockade of CD47-SIRPalpha interactions is a promising immuno-oncology treatment that promotes clearance of cancer cells. However, CD47-SIRPalpha interactions also maintain homeostatic lymphocyte levels. In this study, we report that the mouse splenic marginal zone B cell population is dependent on intact CD47-SIRPalpha interactions and blockade of CD47 leads to the loss of these cells. This depletion is accompanied by elevated levels of monocyte-recruiting chemokines CCL2 and CCL7 and infiltration of CCR2+Ly6Chi monocytes into the mouse spleen. In the absence of CCR2 signaling, there is no infiltration and reduced marginal zone B cell depletion. These data suggest that CD47 blockade leads to clearance of splenic marginal zone B cells.

    View details for DOI 10.4049/jimmunol.2100352

    View details for PubMedID 35236754

  • Pathology updates and diagnostic approaches to hemophagocytic lymphohistiocytosis. Histopathology Kikuchi, A., Singh, K., Gars, E., Ohgami, R. S. 2021


    Hemophagocytic lymphohistiocytosis (HLH) is a complex, often under-recognized hyperinflammatory immune dysregulation syndrome arising in a diverse range of clinical scenarios and conditions. The accurate and timely diagnosis of HLH is crucial for patient survival, and usually requires a high level of clinical suspicion. The histologic corollary to clinical HLH - hemophagocytosis - is neither necessary nor sufficient for the diagnosis of HLH, as it may be seen in a variety of reactive conditions and may be absent in true HLH. Nevertheless, the finding of hemophagocytosis in specific clinical situations should prompt consideration of HLH and further testing to exclude the condition. While traditionally described in bone marrow, identification of hemophagocytosis in other tissues, including lymphoid, splenic, liver, or neural tissue, can be an important asset to the overall recognition of HLH. In this review we discuss the underlying pathophysiology and etiologies of HLH, morphologic aspects of hemophagocytosis and its associated histologic findings in different tissues, and give a brief overview of diagnostic criteria and clinical evaluation.

    View details for DOI 10.1111/his.14591

    View details for PubMedID 34716920

  • A Morphologic Analysis of Hemophagocytosis in Liver Biopsies Identifies an Association Between Multicellular Erythrophagocytosis, Aggressive NK or T-Cell Lymphomas, and Hemophagocytic Lymphohistiocytosis Kikuchi, A., Gars, E., Kayraklioglu, N., Ruiz-Cordero, R., Gill, R., Wen, K., Mannan, R., Ohgami, R. SPRINGERNATURE. 2021: 971–72
  • A Multi-Institutional Study of Large B-Cell Lymphomas of the Stomach Demonstrates a Male Predominance and Low Incidence of MYC Gene Rearrangements Despite Double-Expressor Phenotype Chaudhari, J., Gars, E., Wen, K., Modi, M., Ohgami, R., Mannan, R. SPRINGERNATURE. 2021: 390–91
  • Vulvar Yolk Sac Tumors Are Somatically Derived SMARCB1 (INI-1)-Deficient Neoplasms. The American journal of surgical pathology Kolin, D. L., Konstantinopoulos, P. A., Campos, S. M., Toumi, G., Kolahi, K. A., Gars, E. J., Howitt, B. E. 2021


    So-called primary yolk sac tumors of the vulva are very rare and often have an aggressive disease course. Their molecular features have not been previously characterized. There is also a well-documented group of SMARCB1 (INI-1)-deficient vulvar neoplasms, which includes proximal-type epithelioid sarcoma and myoepithelial carcinoma. Until now, "vulvar yolk sac tumors" and SMARCB1-deficient neoplasms were considered unrelated diseases. After reviewing an index case of a vulvar yolk sac tumor with loss of SMARCB1 by immunohistochemistry, we retrospectively identified 2 additional cases diagnosed as vulvar yolk sac tumors. Patient ages were 34, 32, and 25 years old, and 2 tumors were associated with a pregnancy. All 3 cases showed morphology typical of a yolk sac tumor, and by immunohistochemistry all were positive for SALL4, glypican-3, keratins, and lacked CD34 positivity. All tumors also demonstrated loss of SMARCB1 in tumor cells. Targeted molecular profiling was performed in 2 cases and identified 2 copy deletion of SMARCB1, without genomic alterations typically seen in gonadal yolk sac tumors. In the third case, isochromosome 12p was not identified by fluorescence in situ hybridization. All 3 patients had either local recurrences or distant metastases, and 2 died of disease. One patient had progressive disease while receiving the enhancer of zeste homolog 2 inhibitor tazemetostat. Overall, these findings suggest that vulvar tumors with pure yolk sac-like morphology may represent morphologic variants of SMARCB1-deficient tumors and not veritable germ cell neoplasia. This potential reclassification may have both prognostic and treatment implications and warrants study of additional extragonadal yolk sac tumors.

    View details for DOI 10.1097/PAS.0000000000001777

    View details for PubMedID 34265804

  • Enasidenib drives human erythroid differentiation independently of isocitrate dehydrogenase 2. The Journal of clinical investigation Dutta, R. n., Zhang, T. Y., Köhnke, T. n., Thomas, D. n., Linde, M. n., Gars, E. n., Stafford, M. n., Kaur, S. n., Nakauchi, Y. n., Yin, R. n., Azizi, A. n., Narla, A. n., Majeti, R. n. 2020


    Cancer-related anemia is present in over 60% of newly diagnosed cancer patients and is associated with substantial morbidity and high medical costs. Drugs that enhance erythropoiesis are urgently required to decrease transfusion rates and improve quality of life. Clinical studies have observed an unexpected improvement in hemoglobin and red blood cell (RBC) transfusion-independence in AML patients treated with the isocitrate dehydrogenase 2 (IDH2) mutant-specific inhibitor, enasidenib, leading to improved quality of life without a reduction in AML disease burden. Here, we demonstrate that enasidenib enhanced human erythroid differentiation of hematopoietic progenitors. The phenomenon was not observed with other IDH1/2 inhibitors and occurred in IDH2-deficient CRIPSR-engineered progenitors independently of D-2-hydroxyglutarate. The effect of enasidenib on hematopoietic progenitors was mediated by protoporphyrin accumulation, driving heme production and erythroid differentiation in committed CD71+ progenitors rather than hematopoietic stem cells. Our results position enasidenib as a promising therapeutic agent for improvement of anemia and provide the basis for a clinical trial using enasidenib to decrease transfusion dependence in a wide array of clinical contexts.

    View details for DOI 10.1172/JCI133344

    View details for PubMedID 31895700

  • Upregulation of CD47 Is a Host Checkpoint Response to Pathogen Recognition. mBio Tal, M. C., Torrez Dulgeroff, L. B., Myers, L. n., Cham, L. B., Mayer-Barber, K. D., Bohrer, A. C., Castro, E. n., Yiu, Y. Y., Lopez Angel, C. n., Pham, E. n., Carmody, A. B., Messer, R. J., Gars, E. n., Kortmann, J. n., Markovic, M. n., Hasenkrug, M. n., Peterson, K. E., Winkler, C. W., Woods, T. A., Hansen, P. n., Galloway, S. n., Wagh, D. n., Fram, B. J., Nguyen, T. n., Corey, D. n., Kalluru, R. S., Banaei, N. n., Rajadas, J. n., Monack, D. M., Ahmed, A. n., Sahoo, D. n., Davis, M. M., Glenn, J. S., Adomati, T. n., Lang, K. S., Weissman, I. L., Hasenkrug, K. J. 2020; 11 (3)


    It is well understood that the adaptive immune response to infectious agents includes a modulating suppressive component as well as an activating component. We now show that the very early innate response also has an immunosuppressive component. Infected cells upregulate the CD47 "don't eat me" signal, which slows the phagocytic uptake of dying and viable cells as well as downstream antigen-presenting cell (APC) functions. A CD47 mimic that acts as an essential virulence factor is encoded by all poxviruses, but CD47 expression on infected cells was found to be upregulated even by pathogens, including severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), that encode no mimic. CD47 upregulation was revealed to be a host response induced by the stimulation of both endosomal and cytosolic pathogen recognition receptors (PRRs). Furthermore, proinflammatory cytokines, including those found in the plasma of hepatitis C patients, upregulated CD47 on uninfected dendritic cells, thereby linking innate modulation with downstream adaptive immune responses. Indeed, results from antibody-mediated CD47 blockade experiments as well as CD47 knockout mice revealed an immunosuppressive role for CD47 during infections with lymphocytic choriomeningitis virus and Mycobacterium tuberculosis Since CD47 blockade operates at the level of pattern recognition receptors rather than at a pathogen or antigen-specific level, these findings identify CD47 as a novel potential immunotherapeutic target for the enhancement of immune responses to a broad range of infectious agents.IMPORTANCE Immune responses to infectious agents are initiated when a pathogen or its components bind to pattern recognition receptors (PRRs). PRR binding sets off a cascade of events that activates immune responses. We now show that, in addition to activating immune responses, PRR signaling also initiates an immunosuppressive response, probably to limit inflammation. The importance of the current findings is that blockade of immunomodulatory signaling, which is mediated by the upregulation of the CD47 molecule, can lead to enhanced immune responses to any pathogen that triggers PRR signaling. Since most or all pathogens trigger PRRs, CD47 blockade could be used to speed up and strengthen both innate and adaptive immune responses when medically indicated. Such immunotherapy could be done without a requirement for knowing the HLA type of the individual, the specific antigens of the pathogen, or, in the case of bacterial infections, the antimicrobial resistance profile.

    View details for DOI 10.1128/mBio.01293-20

    View details for PubMedID 32576678

  • Single-cell multiomic analysis identifies regulatory programs in mixed-phenotype acute leukemia. Nature biotechnology Granja, J. M., Klemm, S., McGinnis, L. M., Kathiria, A. S., Mezger, A., Corces, M. R., Parks, B., Gars, E., Liedtke, M., Zheng, G. X., Chang, H. Y., Majeti, R., Greenleaf, W. J. 2019


    Identifying the causes of human diseases requires deconvolution of abnormal molecular phenotypes spanning DNA accessibility, gene expression and protein abundance1-3. We present a single-cell framework that integrates highly multiplexed protein quantification, transcriptome profiling and analysis of chromatin accessibility. Using this approach, we establish a normal epigenetic baseline for healthy blood development, which we then use to deconvolve aberrant molecular features within blood from patients with mixed-phenotype acute leukemia4,5. Despite widespread epigenetic heterogeneity within the patient cohort, we observe common malignant signatures across patients as well as patient-specific regulatory features that are shared across phenotypic compartments of individual patients. Integrative analysis of transcriptomic and chromatin-accessibility maps identified 91,601 putative peak-to-gene linkages and transcription factors that regulate leukemia-specific genes, such as RUNX1-linked regulatory elements proximal to the marker gene CD69. These results demonstrate how integrative, multiomic analysis of single cells within the framework of normal development can reveal both distinct and shared molecular mechanisms of disease from patient samples.

    View details for DOI 10.1038/s41587-019-0332-7

    View details for PubMedID 31792411

  • The life and death of the germinal center. Annals of diagnostic pathology Gars, E., Butzmann, A., Ohgami, R., Balakrishna, J. P., O'Malley, D. P. 2019; 44: 151421


    The formation, development and dissolution of germinal centers is a major part of immune system function. It is important to differentiate neoplastic processes from follicular hyperplasia and regressive follicular changes. Better understanding of germinal center development and dissolution also provides diagnostic clues to the underlying pathologic process. It is also important in identifying the immune basis of different pathologic entities as well as in immunotherapy decision making and follow up. In this study, we characterize the immunoarchitecture of lymphoid follicles with a focus on germinal center in one representative case, each of commonly encountered benign and malignant lymph node disorders, with morphologic and immunohistochemical alterations of germinal centers. The cases include reactive follicular hyperplasia (FH), florid follicular hyperplasia (FFH), follicular lymphoma (FL), angioimmunoblastic T-cell lymphoma (AITL), hyaline-vascular Castleman disease (HVCD), progressive transformation of germinal centers, nodular lymphocyte predominant Hodgkin lymphoma (NLPHL), lymphocyte-rich classic Hodgkin lymphoma (LR-CHL), human immunodeficiency virus (HIV)-associated follicular dissolution and chronic lymphocytic leukemia (CLL) with proliferation centers (PC). A panel of antibodies were used namely CD3, CD20, CD10, BCL2, BCL6, CD21, CD23, CD35, FOXP1, GCET1, HGAL/GCET2, LMO2, MUM1, IgD, Ki67, PD1 and PD-L1. We found that these entities show distinct immunoarchitectural patterns of germinal center formation, development and regression, particularly, the distribution of mantle zone B-cells, follicular helper T cells (Tfh) and FDC meshworks, confirming the influence of antigenic stimulation and status of immune system in these changes. This also confirms the interrelationship of underlying immunologic mechanisms in these disease processes.

    View details for DOI 10.1016/j.anndiagpath.2019.151421

    View details for PubMedID 31751845

  • Enasidenib Drives Maturation of Human Erythroid Precursors Independently of IDH2 Dutta, R., Zhang, T. Y., Koehnke, T., Thomas, D., Gars, E., Stafford, M., Nakauchi, Y., Kaur, S., Yin, R., Narla, A., Majeti, R. AMER SOC HEMATOLOGY. 2019
  • Endothelin receptor emerges as a potential target of Hoxa9-mediated leukemogenesis LEUKEMIA RESEARCH Gars, E., Kaur, S., Thomas, D. 2018; 75: 69–70
  • Bone marrow histomorphological criteria can accurately diagnose hemophagocytic lymphohistiocytosis HAEMATOLOGICA Gars, E., Purington, N., Scott, G., Chisholm, K., Gratzinger, D., Martin, B. A., Ohgami, R. S. 2018; 103 (10): 1635–41
  • A replicable CD271+ mesenchymal stromal cell density score: bringing the dysfunctional myelodysplastic syndrome niche to the diagnostic laboratory. Leukemia & lymphoma Gars, E., Yousry, S. M., Babu, D., Kurzer, J. H., George, T. I., Gratzinger, D. 2016: 1-3

    View details for PubMedID 27808583

  • Endothelial cell derived angiocrine support of acute myeloid leukemia targeted by receptor tyrosine kinase inhibition. Leukemia research Drusbosky, L., Gars, E., Trujillo, A., McGee, C., Meacham, A., Wise, E., Scott, E. W., Cogle, C. R. 2015; 39 (9): 984-9


    In acute myeloid leukemia (AML), refractory disease is a major challenge and the leukemia microenvironment may harbor refractory disease. Human AML cell lines KG-1 and HL-60 expressed receptors also found on endothelial cells (ECs) such as VEGFRs, PDGFRs, and cKit. When human AML cells were co-cultured with human umbilical vein endothelial cells (HUVECs) and primary bone marrow endothelial cell (BMECs), the AML cells were more resistant to cytarabine chemotherapy, even in transwell co-culture suggesting angiocrine regulation. Primary BMECs secreted significantly increased levels of VEGF-A and PDGF-AB after exposure to cytarabine. Pazopanib, a receptor tyrosine kinase inhibitor (RTKI) of VEGFRs, PDGFRs, and cKit, removed EC protection of AML cells and enhanced AML cell sensitivity to cytarabine. Xenograft modeling showed significant regression of AML cells and abrogation of BM hypervascularity in RTKI treated cohorts. Together, these results show direct cytotoxicity of RTKIs on AML cells and reversal of EC protection. Combining RTKIs with chemotherapy may serve as promising therapeutic strategy for patients with AML.

    View details for DOI 10.1016/j.leukres.2015.05.015

    View details for PubMedID 26189107

  • Activation of the vascular niche supports leukemic progression and resistance to chemotherapy. Experimental hematology Poulos, M. G., Gars, E. J., Gutkin, M. C., Kloss, C. C., Ginsberg, M., Scandura, J. M., Rafii, S., Butler, J. M. 2014; 42 (11): 976-986.e3


    Understanding the intricate cellular components of the bone marrow microenvironment can lead to the discovery of novel extrinsic factors that are responsible for the initiation and progression of leukemic disease. We have shown that endothelial cells (ECs) provide a fertile niche that allows for the propagation of primitive and aggressive leukemic clones. Activation of the ECs by vascular endothelial growth factor (VEGF)-A provides cues that enable leukemic cells to proliferate at higher rates and also increases the adhesion of leukemia to ECs. Vascular endothelial growth factor A-activated ECs decrease the efficacy of chemotherapeutic agents to target leukemic cells. Inhibiting VEGF-dependent activation of ECs by blocking their signaling through VEGF receptor 2 increases the susceptibility of leukemic cells to chemotherapy. Therefore, the development of drugs that target the activation state of the vascular niche could prove to be an effective adjuvant therapy in combination with chemotherapeutic agents.

    View details for DOI 10.1016/j.exphem.2014.08.003

    View details for PubMedID 25179751

    View details for PubMedCentralID PMC4254082

  • Human ESC-derived hemogenic endothelial cells undergo distinct waves of endothelial to hematopoietic transition. Blood Rafii, S., Kloss, C. C., Butler, J. M., Ginsberg, M., Gars, E., Lis, R., Zhan, Q., Josipovic, P., Ding, B. S., Xiang, J., Elemento, O., Zaninovic, N., Rosenwaks, Z., Sadelain, M., Rafii, J. A., James, D. 2013; 121 (5): 770-80


    Several studies have demonstrated that hematopoietic cells originate from endotheliumin early development; however, the phenotypic progression of progenitor cells during human embryonic hemogenesis is not well described. Here, we define the developmental hierarchy among intermediate populations of hematopoietic progenitor cells (HPCs) derived from human embryonic stem cells (hESCs). We genetically modified hESCs to specifically demarcate acquisition of vascular (VE-cadherin) and hematopoietic (CD41a) cell fate and used this dual-reporting transgenic hESC line to observe endothelial to hematopoietic transition by real-time confocal microscopy. Live imaging and clonal analyses revealed a temporal bias in commitment of HPCs that recapitulates discrete waves of lineage differentiation noted during mammalian hemogenesis. Specifically, HPCs isolated at later time points showed reduced capacity to form erythroid/ megakaryocytic cells and exhibited a tendency toward myeloid fate that was enabled by expression of the Notch ligand Dll4 on hESC-derived vascular feeder cells. These data provide a framework for defining HPC lineage potential, elucidate a molecular contribution from the vascular niche in promoting hematopoietic lineage progression, and distinguish unique subpopulations of hemogenic endothelium during hESC differentiation.Live imaging of endothelial to hematopoietic conversion identifies distinct subpopulations of hESC-derived hemogenic endothelium. Expression of the Notch ligand DII4 on vascular ECs drives induction of myeloid fate from hESC-derived hematopoietic progenitors.

    View details for DOI 10.1182/blood-2012-07-444208

    View details for PubMedID 23169780

  • Development of a vascular niche platform for expansion of repopulating human cord blood stem and progenitor cells. Blood Butler, J. M., Gars, E. J., James, D. J., Nolan, D. J., Scandura, J. M., Rafii, S. 2012; 120 (6): 1344-7


    Transplantation of ex vivo expanded human umbilical cord blood cells (hCB) only partially enhances the hematopoietic recovery after myelosuppressive therapy. Incubation of hCB with optimal combinations of cytokines and niche cells, such as endothelial cells (ECs), could augment the efficiency of hCB expansion. We have devised an approach to cultivate primary human ECs (hECs) in serum-free culture conditions. We demonstrate that coculture of CD34(+) hCB in direct cellular contact with hECs and minimal concentrations of thrombopoietin/Kit-ligand/Flt3-ligand resulted in a 400-fold expansion of total hematopoietic cells, 150-fold expansion of CD45(+)CD34(+) progenitor cells, and 23-fold expansion of CD45(+) Lin(-)CD34(hi+)CD45RA(-)CD49f(+) stem and progenitor cells over a 12-day period. Compared with cytokines alone, coculture of hCB with hECs permitted greater expansion of cells capable of multilineage engraftment and serial transplantation, hallmarks of long-term repopulating hematopoietic stem cells. Therefore, hECs establish a cellular platform for expansion of hematopoietic stem and progenitor cells and treatment of hematologic disorders.

    View details for DOI 10.1182/blood-2011-12-398115

    View details for PubMedID 22709690

    View details for PubMedCentralID PMC3418723