Scientific Resources

The complex process of platelet formation originates with the hematopoietic stem cell,which differentiates through the myeloid lineage,matures,and releases proplatelets into the BM sinusoids. How formed platelets maintain a low basal activation state in the circulation remains unknown. We identify Lepr+ stromal cells lining the BM sinusoids as important contributors to sustaining low platelet activation. Ablation of murine Lepr+ cells led to a decreased number of platelets in the circulation with an increased activation state. We developed a potentially novel culture system for supporting platelet formation in vitro using a unique population of CD51+PDGFRalpha+ perivascular cells,derived from human umbilical cord tissue,which display numerous mesenchymal stem cell (MSC) properties. Megakaryocytes cocultured with MSCs had altered LAT and Rap1b gene expression,yielding platelets that are functional with low basal activation levels,a critical consideration for developing a transfusion product. Identification of a regulatory cell that maintains low baseline platelet activation during thrombopoiesis opens up new avenues for improving blood product production ex vivo. View Publication

Tumors are composed of phenotypically heterogeneous cancer cells that often resemble various differentiation states of their lineage of origin. Within this hierarchy,it is thought that an immature subpopulation of tumor-propagating cancer stem cells (CSCs) differentiates into non-tumorigenic progeny,providing a rationale for therapeutic strategies that specifically eradicate CSCs or induce their differentiation. The clinical success of these approaches depends on CSC differentiation being unidirectional rather than reversible,yet this question remains unresolved even in prototypically hierarchical malignancies,such as acute myeloid leukemia (AML). Here,we show in murine and human models of AML that,upon perturbation of endogenous expression of the lineage-determining transcription factor PU.1 or withdrawal of established differentiation therapies,some mature leukemia cells can de-differentiate and reacquire clonogenic and leukemogenic properties. Our results reveal plasticity of CSC maturation in AML,highlighting the need to therapeutically eradicate cancer cells across a range of differentiation states. View Publication

Laminin and fibronectin are glycoproteins that influence cell behavior and mediate cell/substratum adhesion. We have examined the interaction of these macromolecules with the serine protease plasminogen activator (PA) in two types of extracellular matrices; one produced by the murine Engelbreth-Holm-Swarm (EHS) tumor (Matrigel),and another by normal kidney epithelial cells in culture. Matrigel was found to contain significant quantities of tissue-type PA (tPA). Two of the major components of Matrigel,laminin and type IV collagen,were also examined. Tissue-type PA was associated with purified preparations of laminin; however,it was not found associated with type IV collagen. Normal kidney epithelial cells in culture secrete large amounts of urokinase (UK) and deposit a subepithelial matrix containing both laminin and fibronectin. These matrix macromolecules were isolated from the deposited matrix by immunoprecipitation,examined by zymography,and found to contain UK. The potential role of this interaction in the mechanisms of cell migration and matrix remodeling is discussed. View Publication

Inflammatory bowel disease (IBD) is characterized by severe and recurrent inflammation of the gastrointestinal tract,associated with altered patterns of cytokine synthesis,excessive reactive oxygen species (ROS) production,and high levels of the innate immune protein,lipocalin-2 (LCN-2),in the mucosa. The major source of ROS in intestinal epithelial cells is the NADPH oxidase NOX1,which consists of the transmembrane proteins,NOX1 and p22PHOX,and the cytosolic proteins,NOXO1,NOXA1,and Rac1. Here,we investigated whether NOX1 activation and ROS production induced by key inflammatory cytokines in IBD causally affects LCN-2 production in colonic epithelial cells. We found that the combination of TNFalpha and IL-17 induced a dramatic upregulation of NOXO1 expression that was dependent on the activation of p38MAPK and JNK1/2,and resulted into an increase of NOX1 activity and ROS production. NOX1-derived ROS drive the expression of LCN-2 by controlling the expression of IkappaBzeta,a master inducer of LCN-2. Furthermore,LCN-2 production and colon damage were decreased in NOX1-deficient mice during TNBS-induced colitis. Finally,analyses of biopsies from patients with Crohn's disease showed increased JNK1/2 activation,and NOXO1 and LCN-2 expression. Therefore,NOX1 might play a key role in mucosal immunity and inflammation by controlling LCN-2 expression. View Publication

Circulating Tumor Cells (CTCs) represent an easy,repeatable and representative access to information regarding solid tumors. However,their detection remains difficult because of their paucity,their short half-life,and the lack of reliable surface biomarkers. Flow cytometry (FC) is a fast,sensitive and affordable technique,ideal for rare cells detection. Adapted to CTCs detection (i.e. extremely rare cells),most FC-based techniques require a time-consuming pre-enrichment step,followed by a 2-hours staining procedure,impeding on the efficiency of CTCs detection. We overcame these caveats and reduced the procedure to less than one hour,with minimal manipulation. First,cells were simultaneously fixed,permeabilized,then stained. Second,using low-speed FC acquisition conditions and two discriminators (cell size and pan-cytokeratin expression),we suppressed the pre-enrichment step. Applied to blood from donors with or without known malignant diseases,this protocol ensures a high recovery of the cells of interest independently of their epithelial-mesenchymal plasticity and can predict which samples are derived from cancer donors. This proof-of-concept study lays the bases of a sensitive tool to detect CTCs from a small amount of blood upstream of in-depth analyses. View Publication

Clonal hematopoiesis (CH) is a common aging-associated condition with increased risk of hematologic malignancy. Knowledge of the mechanisms driving evolution from CH to overt malignancy has been hampered by a lack of in vivo models that orthogonally activate mutant alleles. Here,we develop independently regulatable mutations in DNA methyltransferase 3A (Dnmt3a) and nucleophosmin 1 (Npm1),observed in human CH and AML,respectively. We find Dnmt3a mutation expands hematopoietic stem and multipotent progenitor cells (HSC/MPPs),modeling CH. Induction of mutant Npm1 after development of Dnmt3a-mutant CH causes progression to myeloproliferative disorder (MPD),and more aggressive MPD is observed with longer latency between mutations. MPDs uniformly progress to acute myeloid leukemia (AML) following transplant,accompanied by a decrease in HSC/MPPs and an increase in myeloid-restricted progenitors,the latter of which propagate AML in tertiary recipient mice. At a molecular level,progression of CH to MPD is accompanied by selection for mutations activating Ras/Raf/MAPK signaling. Progression to AML is characterized by additional oncogenic signaling mutations (Ptpn11,Pik3r1,Flt3) and/or mutations in epigenetic regulators (Hdac1,Idh1,Arid1a). Together,our study demonstrates that Npm1 mutation drives evolution of Dnmt3a-mutant CH to AML and rate of disease progression is accelerated with longer latency of CH. View Publication

The flow cytometric crossmatch (FCXM) assay,which detects the presence of donor specific HLA antibodies in patient sera,is a cornerstone of HLA compatibility testing. Since relatively long FCXM assay turnaround times may contribute to transplant delays and increased graft ischemia time,we developed and validated two modified crossmatch procedures,namely the Halifax and Halifaster FCXM protocols. These protocols reduce FCXM assay time >60{\%} and simplify their set-up without compromising quality or sensitivity. Optimization of the FCXM (the Halifax protocol) includes a 96-well tray platform,reduced wash times,increased serum to cell suspension volume ratio,shortened incubations and higher incubation temperature. The Halifaster protocol is a further modification,employing methods that improve lymphocyte purity compared to density gradient centrifugation (96 ± 2.63{\%} vs 69 ± 19.06{\%}),reduce cell isolation time (by ∼40{\%}) and conserve FCXM assay reagents. Importantly,linear regression analysis of the median channel fluorescence shift (MCFS) values revealed excellent concordance (R2 of 0.98-0.99) among all three FCXM protocols (standard vs Halifax vs Halifaster). Finally,a retrospective review of 2013 crossmatches performed using the Halifax protocol demonstrated excellent correlation with the virtual crossmatch (95.7{\%} and 96.8{\%} specificity and sensitivity,respectively) regarding the identification of donor specific antibodies (HLA-A/B/DR) assigned based on the single antigen bead (SAB) assay testing with a 2000 mean fluorescence intensity (MFI) cutoff. Implementation of the Halifax or Halifaster protocols will expedite pre-transplantation work-up and improve patient care. View Publication

BACKGROUND The goal of antiretroviral therapy (ART) is to suppress HIV-1 replication and reconstitute CD4+ T cells. Here,we report on HIV-infected individuals who had a paradoxical decline in CD4+ T cells despite ART-mediated suppression of plasma HIV-1 load (pVL). We defined such an immunological outcome as extreme immune decline (EXID). METHODS EXID's clinical and immunological characteristics were compared to immunological responders (IRs),immunological nonresponders (INRs),healthy controls (HCs),and idiopathic CD4+ lymphopenia (ICL) patients. T cell immunophenotyping and assembly/activation of inflammasomes were evaluated by flow cytometry. PBMC transcriptome analysis and genetic screening for pathogenic variants were performed. Levels of cytokines/chemokines were measured by electrochemiluminescence. Luciferase immunoprecipitation system and NK-mediated antibody-dependent cellular cytotoxicity (ADCC) assays were used to identify anti-lymphocyte autoantibodies. RESULTS EXIDs were infected with non-B HIV-1 subtypes and after 192 weeks of consistent ART-mediated pVL suppression had a median CD4+ decrease of 157 cells/mul,compared with CD4+ increases of 193 cells/mul and 427 cells/mul in INR and IR,respectively. EXID had reduced naive CD4+ T cells,but similar proportions of cycling CD4+ T cells and HLA-DR+CD38+CD8+ T cells compared with IR and INR. Levels of inflammatory cytokines were also similar in EXID and INR,but the IL-7 axis was profoundly perturbed compared with HC,IR,INR,and ICL. Genes involved in T cell and monocyte/macrophage function,autophagy,and cell migration were differentially expressed in EXID. Two of the 5 EXIDs had autoantibodies causing ADCC,while 2 different EXIDs had an increased inflammasome/caspase-1 activation despite consistently ART-suppressed pVL. CONCLUSIONS EXID is a distinct immunological outcome compared with previously described INR. Anti-CD4+ T cell autoantibodies and aberrant inflammasome/caspase-1 activation despite suppressed HIV-1 viremia are among the mechanisms responsible for EXID. View Publication

TET enzymes are dioxygenases that promote DNA demethylation by oxidizing the methyl group of 5-methylcytosine to 5-hydroxymethylcytosine (5hmC). Here,we report a close correspondence between 5hmC-marked regions,chromatin accessibility and enhancer activity in B cells,and a strong enrichment for consensus binding motifs for basic region-leucine zipper (bZIP) transcription factors at TET-responsive genomic regions. Functionally,Tet2 and Tet3 regulate class switch recombination (CSR) in murine B cells by enhancing expression of Aicda,which encodes the activation-induced cytidine deaminase (AID) enzyme essential for CSR. TET enzymes deposit 5hmC,facilitate DNA demethylation,and maintain chromatin accessibility at two TET-responsive enhancer elements,TetE1 and TetE2,located within a superenhancer in the Aicda locus. Our data identify the bZIP transcription factor,ATF-like (BATF) as a key transcription factor involved in TET-dependent Aicda expression. 5hmC is not deposited at TetE1 in activated Batf-deficient B cells,indicating that BATF facilitates TET recruitment to this Aicda enhancer. Our study emphasizes the importance of TET enzymes for bolstering AID expression and highlights 5hmC as an epigenetic mark that captures enhancer dynamics during cell activation. View Publication

Human pluripotent cell lines hold enormous promise for the development of cell-based therapies. Safety,however,is a crucial prerequisite condition for clinical applications. Numerous groups have attempted to eliminate potentially harmful cells through the use of suicide genes1,but none has quantitatively defined the safety level of transplant therapies. Here,using genome-engineering strategies,we demonstrate the protection of a suicide system from inactivation in dividing cells. We created a transcriptional link between the suicide gene herpes simplex virus thymidine kinase (HSV-TK) and a cell-division gene (CDK1); this combination is designated the safe-cell system. Furthermore,we used a mathematical model to quantify the safety level of the cell therapy as a function of the number of cells that is needed for the therapy and the type of genome editing that is performed. Even with the highly conservative estimates described here,we anticipate that our solution will rapidly accelerate the entry of cell-based medicine into the clinic. View Publication

Reduced quantity and quality of stem cells in aged individuals hinders cardiac repair and regeneration after injury. We used young bone marrow (BM) stem cell antigen 1 (Sca-1) cells to reconstitute aged BM and rejuvenate the aged heart,and examined the underlying molecular mechanisms. BM Sca-1+ or Sca-1- cells from young (2-3 months) or aged (18-19 months) GFP transgenic mice were transplanted into lethally irradiated aged mice to generate 4 groups of chimeras: young Sca-1+,young Sca-1-,old Sca-1+,and old Sca-1- . Four months later,expression of rejuvenation-related genes (Bmi1,Cbx8,PNUTS,Sirt1,Sirt2,Sirt6) and proteins (CDK2,CDK4) was increased along with telomerase activity and telomerase-related protein (DNA-PKcs,TRF-2) expression,whereas expression of senescence-related genes (p16INK4a,P19ARF,p27Kip1 ) and proteins (p16INK4a,p27Kip1 ) was decreased in Sca-1+ chimeric hearts,especially in the young group. Host cardiac endothelial cells (GFP- CD31+ ) but not cardiomyocytes were the primary cell type rejuvenated by young Sca-1+ cells as shown by improved proliferation,migration,and tubular formation abilities. C-X-C chemokine CXCL12 was the factor most highly expressed in homed donor BM (GFP+ ) cells isolated from young Sca-1+ chimeric hearts. Protein expression of Cxcr4,phospho-Akt,and phospho-FoxO3a in endothelial cells derived from the aged chimeric heart was increased,especially in the young Sca-1+ group. Reconstitution of aged BM with young Sca-1+ cells resulted in effective homing of functional stem cells in the aged heart. These young,regenerative stem cells promoted aged heart rejuvenation through activation of the Cxcl12/Cxcr4 pathway of cardiac endothelial cells. View Publication

Both targeted therapy and immunotherapy have been used successfully to treat melanoma,but the development of resistance and poor response rates to the individual therapies has limited their success. Designing rational combinations of targeted therapy and immunotherapy may overcome these obstacles,but requires assessment in preclinical models with the capacity to respond to both therapeutic classes. Herein,we describe the development and characterization of a novel,immunogenic variant of the BrafV600ECdkn2a-/-Pten-/- YUMM1.1 tumor model that expresses the immunogen,ovalbumin (YOVAL1.1). We demonstrate that,unlike parental tumors,YOVAL1.1 tumors are immunogenic in vivo and can be controlled by immunotherapy. Importantly,YOVAL1.1 tumors are sensitive to targeted inhibitors of BRAFV600E and MEK,responding in a manner consistent with human BRAFV600E melanoma. The YOVAL1.1 melanoma model is transplantable,immunogenic and sensitive to clinical therapies,making it a valuable platform to guide strategic development of combined targeted therapy and immunotherapy approaches in BRAFV600E melanoma. View Publication