Irving L Weissman

Institute for Stem Cell Biology and Regenerative Medicine, Bengalūru, Karnataka, India

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Publications (778)8572.05 Total impact

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    ABSTRACT: CD47 is a cell surface protein that transmits an anti-phagocytic signal, known as the 'don't-eat-me' signal, to macrophages upon engaging its receptor SIRPα. Molecules that antagonize the CD47-SIRPα interaction by binding to CD47 such as anti-CD47 antibodies and the engineered SIRPα variant CV1 have been shown to facilitate macrophage-mediated anti-tumor responses. However, these strategies targeting CD47 are handicapped by large antigen sinks in vivo and indiscriminate cell binding due to ubiquitous expression of CD47. These factors reduce bioavailability and increase the risk of toxicity. Here, we present an alternative strategy to antagonize the CD47-SIRPα pathway by engineering high-affinity CD47 variants that target SIRPα, which has restricted tissue expression. CD47 proved to be refractive to conventional affinity maturation techniques targeting its binding interface with SIRPα. Therefore, we developed a novel engineering approach, whereby we augmented the existing contact interface via N-terminal peptide extension, coined 'Velcro' engineering. The high-affinity variant (Velcro-CD47) bound to the two most prominent human SIRPα alleles with greatly increased affinity relative to wild-type CD47 and potently antagonized CD47 binding to SIRPα on human macrophages. Velcro-CD47 synergizes with tumor-specific monoclonal antibodies to enhance macrophage phagocytosis of tumor cells in vitro, with similar potency as CV1. Finally, Velcro-CD47 interacts specifically with a subset of myeloid-derived cells in human blood, whereas CV1 binds all myeloid, lymphoid, and erythroid populations interrogated. This is consistent with the restricted expression of SIRPα compared to CD47. Herein, we have demonstrated that 'Velcro' engineering is a powerful protein-engineering tool with potential applications to other systems, and that Velcro-CD47 could be an alternative adjuvant to CD47-targeting agents for cancer immunotherapy. Copyright © 2015, The American Society for Biochemistry and Molecular Biology.
    Journal of Biological Chemistry 04/2015; DOI:10.1074/jbc.M115.648220 · 4.60 Impact Factor
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    ABSTRACT: Nonresolving chronic inflammation at the neoplastic site is consistently associated with promoting tumor progression and poor patient outcomes. However, many aspects behind the mechanisms that establish this tumor-promoting inflammatory microenvironment remain undefined. Using bladder cancer (BC) as a model, we found that CD14-high cancer cells express higher levels of numerous inflammation mediators and form larger tumors compared with CD14-low cells. CD14 antigen is a glycosyl-phosphatidylinositol (GPI)-linked glycopro-tein and has been shown to be critically important in the signaling pathways of Toll-like receptor (TLR). CD14 expression in this BC sub-population of cancer cells is required for increased cytokine production and increased tumor growth. Furthermore, tumors formed by CD14-high cells are more highly vascularized with higher myeloid cell infiltration. Inflammatory factors produced by CD14-high BC cells recruit and polarize monocytes and macrophages to acquire immune-suppressive characteristics. In contrast, CD14-low BC cells have a higher baseline cell division rate than CD14-high cells. Importantly, CD14-high cells produce factors that further increase the proliferation of CD14-low cells. Collectively, we demonstrate that CD14-high BC cells may orchestrate tumor-promoting inflammation and drive tumor cell proliferation to promote tumor growth. bladder cancer | CD14 | inflammation | microenvironment S olid tumors represent a complex mass of tissue composed of multiple distinct cell types (1, 2). Cells within the tumor produce a range of soluble factors to create a complex of sig-naling networks within the tumor microenvironment (3–7). One of the outcomes of this crosstalk is tumor-promoting inflammation (TPI) (8, 9). TPI can modulate the functions of tumor-infiltrating myeloid lineage cells including macrophages (10–12). Tumor-associated macrophages (TAMs) consistently display an alternatively activated phenotype (M2) commonly found in sites of wound healing (13–18). These macrophages promote tumor growth while suppressing the host immune response locally (19– 22). Polarization and subversion of tumor-infiltrating macro-phages is accomplished via immune mediators in the tumor microenvironment (23, 24). Adding to the complexity of solid tumors is the heterogeneity of the cancer cells (2). Tumor cells of varying differentiation states and different characteristics coexist within a tumor (25–29). However, the different roles of each tumor cell subset during cancer progression remain undefined. Bladder cancer (BC) represents a growing number of solid tumors characterized by the infiltration of a significant number of myeloid cells in the neoplastic lesion (30, 31). We have previously determined that keratin 14 (KRT14) expression marks the most primitive differentiation state in BC cells (32). KRT14 expression is significantly associated with poor overall patient survival. However, the mechanisms used by KRT14-expressing cells to promote tumor growth remain unclear. In the current study, we found that KRT14+ basal BC cells also express higher levels of CD14. Here, we investigate the strategies used by KRT14+ CD14-high BC cells to promote tumor growth.
    Proceedings of the National Academy of Sciences 03/2015; 112(15). DOI:10.1073/pnas.1424795112 · 9.81 Impact Factor
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    ABSTRACT: Most cell-surface receptors for cytokines and growth factors signal as dimers, but it is unclear whether remodeling receptor dimer topology is a viable strategy to “tune” signaling output. We utilized diabodies (DA) as surrogate ligands in a prototypical dimeric receptor-ligand system, the cytokine Erythropoietin (EPO) and its receptor (EpoR), to dimerize EpoR ectodomains in non-native architectures. Diabody-induced signaling amplitudes varied from full to minimal agonism, and structures of these DA/EpoR complexes differed in EpoR dimer orientation and proximity. Diabodies also elicited biased or differential activation of signaling pathways and gene expression profiles compared to EPO. Non-signaling diabodies inhibited proliferation of erythroid precursors from patients with a myeloproliferative neoplasm due to a constitutively active JAK2V617F mutation. Thus, intracellular oncogenic mutations causing ligand-independent receptor activation can be counteracted by extracellular ligands that re-orient receptors into inactive dimer topologies. This approach has broad applications for tuning signaling output for many dimeric receptor systems.
    Cell 03/2015; 160:1-13. DOI:10.1016/j.cell.2015.02.011 · 33.12 Impact Factor
  • Kipp Weiskopf, Irving L Weissman
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    ABSTRACT: Macrophages are innate immune cells that derive from circulating monocytes, reside in all tissues, and participate in many states of pathology. Macrophages play a dichotomous role in cancer, where they promote tumor growth but also serve as critical immune effectors of therapeutic antibodies. Macrophages express all classes of Fcγ receptors, and they have immense potential to destroy tumors via the process of antibody-dependent phagocytosis. A number of studies have demonstrated that macrophage phagocytosis is a major mechanism of action of many antibodies approved to treat cancer. Consequently, a number of approaches to augment macrophage responses to therapeutic antibodies are under investigation, including the exploration of new targets and development of antibodies with enhanced functions. For example, the interaction of CD47 with signal-regulatory protein α (SIRPα) serves as a myeloid-specific immune checkpoint that limits the response of macrophages to antibody therapies, and CD47-blocking agents overcome this barrier to augment phagocytosis. The response of macrophages to antibody therapies can also be enhanced with engineered Fc variants, bispecific antibodies, or antibody-drug conjugates. Macrophages have demonstrated success as effectors of cancer immunotherapy, and further investigation will unlock their full potential for the benefit of patients.
    mAbs 02/2015; DOI:10.1080/19420862.2015.1011450 · 4.73 Impact Factor
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    ABSTRACT: Macrophage-mediated programmed cell removal (PrCR) is an important mechanism of eliminating diseased and damaged cells before programmed cell death. The induction of PrCR by eat-me signals on tumor cells is countered by don't-eat-me signals such as CD47, which binds macrophage signal-regulatory protein α to inhibit phagocytosis. Blockade of CD47 on tumor cells leads to phagocytosis by macrophages. Here we demonstrate that the activation of Toll-like receptor (TLR) signaling pathways in macrophages synergizes with blocking CD47 on tumor cells to enhance PrCR. Bruton's tyrosine kinase (Btk) mediates TLR signaling in macrophages. Calreticulin, previously shown to be an eat-me signal on cancer cells, is activated in macrophages for secretion and cell-surface exposure by TLR and Btk to target cancer cells for phagocytosis, even if the cancer cells themselves do not express calreticulin.
    Proceedings of the National Academy of Sciences 02/2015; DOI:10.1073/pnas.1424907112 · 9.81 Impact Factor
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    ABSTRACT: Germline transcription has been described for both immunoglobulin and T-cell receptor (TCR) genes, raising questions of their functional significance during haematopoiesis. Previously, an immature murine T-cell line was shown to bind antibody to TCR-Vβ8.2 in absence of anti-Cβ antibody binding, and an equivalent cell subset was also identified in the mesenteric lymph node. Here, we investigate whether germline transcription and cell surface Vβ8.2 expression could therefore represent a potential marker of T-cell progenitors. Cells with the TCR phenotype of Vβ8.2(+) Cβ(-) are found in several lymphoid sites, and among the lineage-negative (Lin(-) ) fraction of hematopoietic progenitors in bone marrow (BM). Cell surface marker analysis of these cells identified subsets reflecting common lymphoid progenitors, common myeloid progenitors and multipotential progenitors. To assess whether the Lin(-) Vβ8.2(+) Cβ(-) BM subset contains hematopoietic progenitors, cells were sorted and adoptively transferred into sub-lethally irradiated recipients. No T-cell or myeloid progeny were detected following introduction of cells via the intrathymic or intravenous routes. However, B-cell development was detected in spleen. This pattern of restricted in vivo reconstitution disputes Lin(-) Vβ8.2(+) Cβ(-) BM cells as committed T-cell progenitors, but raises the possibility of progenitors with potential for B-cell development. © 2015 The Authors. Journal of Cellular and Molecular Medicine published by John Wiley & Sons Ltd and Foundation for Cellular and Molecular Medicine.
    Journal of Cellular and Molecular Medicine 02/2015; DOI:10.1111/jcmm.12572 · 3.70 Impact Factor
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    Ayelet Voskoboynik, Irving L. Weissman
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    ABSTRACT: The decline of tissue regenerative potential with the loss of stem cell function is a hallmark of mammalian aging. We study Botryllus schlosseri, a colonial chordate which exhibits robust stem cell-mediated regeneration capacities throughout life. Larvae, derived by sexual reproduction and chordate development, metamorphose to clonal founders that undergo weekly formation of new individuals by budding from stem cells. Individuals are transient structures which die through massive apoptosis, and successive buds mature to replicate an entire new body. As a result, their stem cells, which are the only self-renewing cells in a tissue, are the only cells which remain through the entire life of the genotype and retain the effects of time. During aging, a significant decrease in the colonies’ regenerative potential is observed and both sexual and asexual reproductions will eventually halt. When a parent colony is experimentally separated into a number of clonal replicates, they frequently undergo senescence simultaneously, suggesting a heritable factor that determines lifespan in these colonies. The availability of the recently published B. schlosseri genome coupled with its unique life cycle features promotes the use of this model organism for the study of the evolution of aging, stem cells, and mechanisms of regeneration.
    Invertebrate Reproduction and Development 01/2015; 59. DOI:10.1080/07924259.2014.944673 · 0.67 Impact Factor
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    ABSTRACT: How are skeletal tissues derived from skeletal stem cells? Here, we map bone, cartilage, and stromal development from a population of highly pure, postnatal skeletal stem cells (mouse skeletal stem cells, mSSCs) to their downstream progenitors of bone, cartilage, and stromal tissue. We then investigated the transcriptome of the stem/progenitor cells for unique gene-expression patterns that would indicate potential regulators of mSSC lineage commitment. We demonstrate that mSSC niche factors can be potent inducers of osteogenesis, and several specific combinations of recombinant mSSC niche factors can activate mSSC genetic programs in situ, even in nonskeletal tissues, resulting in de novo formation of cartilage or bone and bone marrow stroma. Inducing mSSC formation with soluble factors and subsequently regulating the mSSC niche to specify its differentiation toward bone, cartilage, or stromal cells could represent a paradigm shift in the therapeutic regeneration of skeletal tissues. Copyright © 2015 Elsevier Inc. All rights reserved.
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    ABSTRACT: The generation of pluripotent stem cells by somatic cell nuclear transfer (SCNT) has recently been achieved in human cells and sparked new interest in this technology. The authors reporting this methodical breakthrough speculated that SCNT would allow the creation of patient-matched embryonic stem cells, even in patients with hereditary mitochondrial diseases. However, herein we show that mismatched mitochondria in nuclear-transfer-derived embryonic stem cells (NT-ESCs) possess alloantigenicity and are subject to immune rejection. In a murine transplantation setup, we demonstrate that allogeneic mitochondria in NT-ESCs, which are nucleus-identical to the recipient, may trigger an adaptive alloimmune response that impairs the survival of NT-ESC grafts. The immune response is adaptive, directed against mitochondrial content, and amenable for tolerance induction. Mitochondrial alloantigenicity should therefore be considered when developing therapeutic SCNT-based strategies. Copyright © 2015 Elsevier Inc. All rights reserved.
    Cell Stem Cell 11/2014; DOI:10.1016/j.stem.2014.11.003 · 22.15 Impact Factor
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    ABSTRACT: In the last decade there has been a rapid expansion in clinical trials using mesenchymal stromal cells (MSCs) from a variety of tissues. However, despite similarities in morphology, immunophenotype and differentiation behavior in vitro, MSCs sourced from distinct tissues do not necessarily have equivalent biological properties. We performed a genome-wide methylation, transcription and in vivo evaluation of MSCs from human bone marrow (BM), white adipose tissue, umbilical cord and skin cultured in humanized media. Surprisingly, only BM-derived MSCs spontaneously formed a bone marrow cavity through a vascularized cartilage intermediate in vivo that was progressively replaced by hematopoietic tissue and bone. Only BM-derived MSCs exhibited a chondrogenic transcriptional program with hypomethylation and increased expression of RUNX3, RUNX2, BGLAP, MMP13 and ITGA10 consistent with a latent and primed skeletal developmental potential. The humanized MSC-derived microenvironment permitted homing and maintenance of long-term murine SLAM(+) hematopoietic stem cells (HSCs) as well as human CD34(+)/CD38(-)/CD90(+)/CD45RA(+) HSCs after cord blood transplantation. These studies underscore the profound differences in developmental potential between MSC sources independent of donor age with implications for their clinical use. We also demonstrate a tractable human niche model for studying homing and engraftment of human hematopoietic cells in normal and neoplastic states. Copyright © 2014 American Society of Hematology.
    Blood 11/2014; 125(2). DOI:10.1182/blood-2014-04-572255 · 9.78 Impact Factor
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    ABSTRACT: Small numbers of hematopoietic stem cells (HSCs) generate large numbers of mature effector cells through the successive amplification of transiently proliferating progenitor cells. HSCs and their downstream progenitors have been extensively characterized based on their cell-surface phenotype and functional activities during transplantation assays. These cells dynamically lose and acquire specific sets of surface markers during differentiation, leading to the identification of markers that allow for more refined separation of HSCs from early hematopoietic progenitors. Here, we describe a marker, CD11A, which allows for the enhanced purification of mouse HSCs. We show through in vivo transplantations that upregulation of CD11A on HSCs denotes the loss of their long-term reconstitution potential. Surprisingly, nearly half of phenotypic HSCs (defined as Lin(?)KIT(+)SCA-1(+)CD150(+)CD34(?)) are CD11A(+) and lack long-term self-renewal potential. We propose that CD11A(+)Lin(?)KIT(+)SCA-1(+)CD150(+)CD34(?) cells are multipotent progenitors and CD11A(?)Lin(?)KIT(+)SCA-1(+)CD150(+)CD34(?) cells are true HSCs.
    11/2014; 3(5):707-15. DOI:10.1016/j.stemcr.2014.09.007
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    ABSTRACT: A combination of optical imaging technologies with cancer-specific molecular imaging agents is a potentially powerful strategy to improve cancer detection and enable image-guided surgery. Bladder cancer is primarily managed endoscopically by white light cystoscopy with suboptimal diagnostic accuracy. Emerging optical imaging technologies hold great potential for improved diagnostic accuracy but lack imaging agents for molecular specificity. Using fluorescently labeled CD47 antibody (anti-CD47) as molecular imaging agent, we demonstrated consistent identification of bladder cancer with clinical grade fluorescence imaging systems, confocal endomicroscopy, and blue light cystoscopy in fresh surgically removed human bladders. With blue light cystoscopy, the sensitivity and specificity for CD47-targeted imaging were 82.9 and 90.5%, respectively. We detected variants of bladder cancers, which are diagnostic challenges, including carcinoma in situ, residual carcinoma in tumor resection bed, recurrent carcinoma following prior intravesical immunotherapy with Bacillus Calmette-Guérin (BCG), and excluded cancer from benign but suspicious-appearing mucosa. CD47-targeted molecular imaging could improve diagnosis and resection thoroughness for bladder cancer.
    Science translational medicine 10/2014; 6(260):260ra148. DOI:10.1126/scitranslmed.3009457 · 14.41 Impact Factor
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    ABSTRACT: Current methods for the isolation of fibroblasts require extended ex vivo manipulation in cell culture. As a consequence, prior studies investigating fibroblast biology may fail to adequately represent cellular phenotypes in vivo. To overcome this problem, we describe a detailed protocol for the isolation of fibroblasts from the dorsal dermis of mice that bypasses the need for cell culture thereby preserving the physiologic transcriptional and proteomic profiles of each cell. Using the described protocol we characterized the transcriptional programs and the surface expression of 176 CD markers in cultured vs. uncultured fibroblasts. The differential expression patterns we observed highlight the importance of a live harvest for investigations of fibroblast biology.
    Tissue Engineering Part C Methods 10/2014; 21(3). DOI:10.1089/ten.TEC.2014.0118 · 4.64 Impact Factor
  • Journal of the American College of Surgeons 09/2014; 219(3):S82-S83. DOI:10.1016/j.jamcollsurg.2014.07.195 · 4.45 Impact Factor
  • Journal of the American College of Surgeons 09/2014; 219(3):S82. DOI:10.1016/j.jamcollsurg.2014.07.193 · 4.45 Impact Factor
  • Journal of the American College of Surgeons 09/2014; 219(3):S86. DOI:10.1016/j.jamcollsurg.2014.07.204 · 4.45 Impact Factor
  • Experimental Hematology 08/2014; 42(8S):S24. DOI:10.1016/j.exphem.2014.07.083 · 2.81 Impact Factor
  • European Journal of Cancer 07/2014; 50:S13. DOI:10.1016/S0959-8049(14)50050-0 · 4.82 Impact Factor
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    ABSTRACT: The requirement and influence of the peripheral nervous system on tissue replacement in mammalian appendages remain largely undefined. To explore this question, we have performed genetic lineage tracing and clonal analysis of individual cells of mouse hind limb tissues devoid of nerve supply during regeneration of the digit tip, normal maintenance, and cutaneous wound healing. We show that cellular turnover, replacement, and cellular differentiation from presumed tissue stem/progenitor cells within hind limb tissues remain largely intact independent of nerve and nerve-derived factors. However, regenerated digit tips in the absence of nerves displayed patterning defects in bone and nail matrix. These nerve-dependent phenotypes mimic clinical observations of patients with nerve damage resulting from spinal cord injury and are of significant interest for translational medicine aimed at understanding the effects of nerves on etiologies of human injury.
    Proceedings of the National Academy of Sciences 06/2014; 111(27). DOI:10.1073/pnas.1410097111 · 9.81 Impact Factor
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    ABSTRACT: The mammalian heart has long been considered a postmitotic organ, implying that the total number of cardiomyocytes is set at birth. Analysis of cell division in the mammalian heart is complicated by cardiomyocyte binucleation shortly after birth, which makes it challenging to interpret traditional assays of cell turnover [Laflamme MA, Murray CE (2011) Nature 473(7347):326-335; Bergmann O, et al. (2009) Science 324(5923):98-102]. An elegant multi-isotope imaging-mass spectrometry technique recently calculated the low, discrete rate of cardiomyocyte generation in mice [Senyo SE, et al. (2013) Nature 493(7432):433-436], yet our cellular-level understanding of postnatal cardiomyogenesis remains limited. Herein, we provide a new line of evidence for the differentiated α-myosin heavy chain-expressing cardiomyocyte as the cell of origin of postnatal cardiomyogenesis using the "mosaic analysis with double markers" mouse model. We show limited, life-long, symmetric division of cardiomyocytes as a rare event that is evident in utero but significantly diminishes after the first month of life in mice; daughter cardiomyocytes divide very seldom, which this study is the first to demonstrate, to our knowledge. Furthermore, ligation of the left anterior descending coronary artery, which causes a myocardial infarction in the mosaic analysis with double-marker mice, did not increase the rate of cardiomyocyte division above the basal level for up to 4 wk after the injury. The clonal analysis described here provides direct evidence of postnatal mammalian cardiomyogenesis.
    Proceedings of the National Academy of Sciences 06/2014; 111(24):8850. DOI:10.1073/pnas.1408233111 · 9.81 Impact Factor

Publication Stats

83k Citations
8,572.05 Total Impact Points


  • 2009–2015
    • Institute for Stem Cell Biology and Regenerative Medicine
      Bengalūru, Karnataka, India
  • 1971–2015
    • Stanford University
      • • Institute for Stem Cell Biology and Regenerative Medicine
      • • Department of Pathology
      • • Department of Developmental Biology
      • • Department of Medicine
      • • Hopkins Marine Station
      Palo Alto, California, United States
  • 1974–2014
    • Stanford Medicine
      • • Department of Developmental Biology
      • • Department of Pathology
      • • Institute for Stem Cell Biology and Regenerative Medicine
      • • Department of Radiation Oncology
      • • Division of Immunology and Rheumatology
      • • Department of Medicine
      Stanford, California, United States
    • University of Michigan
      Ann Arbor, Michigan, United States
    • University of California, San Francisco
      • School of Dentistry
      San Francisco, California, United States
  • 2013
    • Stem Cell And Brain Research Institute
      Lyons, Rhône-Alpes, France
  • 2004–2013
    • University of California, Los Angeles
      • Division of Cardiology
      Los Angeles, CA, United States
  • 2012
    • Indiana Blood and Marrow Transplantation
      Indianapolis, Indiana, United States
  • 2010
    • Boston Children's Hospital
      Boston, Massachusetts, United States
  • 2008
    • Harvard Medical School
      • Department of Pathology
      Boston, MA, United States
  • 2007
    • Bar Ilan University
      Gan, Tel Aviv, Israel
    • Cornell University
      • Cell and Developmental Biology
      Итак, New York, United States
  • 1990–2006
    • Howard Hughes Medical Institute
      Ashburn, Virginia, United States
    • Kyoto University
      Kioto, Kyōto, Japan
    • Duke University
      • Department of Medicine
      Durham, North Carolina, United States
  • 2005
    • University of Pittsburgh
      Pittsburgh, Pennsylvania, United States
  • 2003
    • Harvard University
      Cambridge, Massachusetts, United States
    • Duke University Medical Center
      Durham, North Carolina, United States
  • 2000
    • Union College
      New York City, New York, United States
  • 1998
    • University of Tsukuba
      Tsukuba, Ibaraki, Japan
  • 1997
    • VU University Amsterdam
      • Department of Molecular Cell Biology and Immunology
      Amsterdamo, North Holland, Netherlands
  • 1993
    • McGill University
      Montréal, Quebec, Canada
  • 1991
    • Oklahoma Medical Research Foundation
      • Immunobiology and Cancer Program
      Oklahoma City, Oklahoma, United States
    • National Institute of Allergy and Infectious Diseases
      Maryland, United States
  • 1989
    • University of Southern California
      • Department of Medicine
      Los Angeles, CA, United States
    • Palo Alto Institute for Research and Education
      Palo Alto, California, United States
  • 1988
    • University of Alberta
      • Department of Biochemistry
      Edmonton, Alberta, Canada
  • 1986
    • St. Jude Children's Research Hospital
      • Department of Biochemistry
      Memphis, Tennessee, United States
  • 1980
    • Pasadena City College
      Pasadena, Texas, United States