Academic Appointments

  • Instructor, Institute for Stem Cell Biology and Regenerative Medicine


All Publications

  • CD14-expressing cancer cells establish the inflammatory and proliferative tumor microenvironment in bladder cancer PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA Cheah, M. T., Chen, J. Y., Sahoo, D., Contreras-Trujillo, H., Volkmer, A. K., Scheeren, F. A., Volkmer, J., Weissman, I. L. 2015; 112 (15): 4725-4730


    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 glycoprotein and has been shown to be critically important in the signaling pathways of Toll-like receptor (TLR). CD14 expression in this BC subpopulation 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.

    View details for DOI 10.1073/pnas.1424795112

    View details for Web of Science ID 000352856800061

    View details for PubMedID 25825750

  • Macrophages eat cancer cells using their own calreticulin as a guide: Roles of TLR and Btk PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA Feng, M., Chen, J. Y., Weissman-Tsukamoto, R., Volkmer, J., Ho, P. Y., McKenna, K. M., Cheshier, S., Zhang, M., Guo, N., Gip, P., Mitra, S. S., Weissman, I. L. 2015; 112 (7): 2145-2150


    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.

    View details for DOI 10.1073/pnas.1424907112

    View details for Web of Science ID 000349446000075

  • A cell-intrinsic role for TLR2-MYD88 in intestinal and breast epithelia and oncogenesis. Nature cell biology Scheeren, F. A., Kuo, A. H., van Weele, L. J., Cai, S., Glykofridis, I., Sikandar, S. S., Zabala, M., Qian, D., Lam, J. S., Johnston, D., Volkmer, J. P., Sahoo, D., van de Rijn, M., Dirbas, F. M., Somlo, G., Kalisky, T., Rothenberg, M. E., Quake, S. R., Clarke, M. F. 2014; 16 (12): 1238-1248


    It has been postulated that there is a link between inflammation and cancer. Here we describe a role for cell-intrinsic toll-like receptor-2 (TLR2; which is involved in inflammatory response) signalling in normal intestinal and mammary epithelial cells and oncogenesis. The downstream effectors of TLR2 are expressed by normal intestinal and mammary epithelia, including the stem/progenitor cells. Deletion of MYD88 or TLR2 in the intestinal epithelium markedly reduces DSS-induced colitis regeneration and spontaneous tumour development in mice. Limiting dilution transplantations of breast epithelial cells devoid of TLR2 or MYD88 revealed a significant decrease in mammary repopulating unit frequency compared with the control. Inhibition of TLR2, its co-receptor CD14, or its downstream targets MYD88 and IRAK1 inhibits growth of human breast cancers in vitro and in vivo. These results suggest that inhibitors of the TLR2 pathway merit investigation as possible therapeutic and chemoprevention agents.

    View details for DOI 10.1038/ncb3058

    View details for PubMedID 25362351

  • Endoscopic molecular imaging of human bladder cancer using a CD47 antibody SCIENCE TRANSLATIONAL MEDICINE Pan, Y., Volkmer, J., Mach, K. E., Rouse, R. V., Liu, J., Sahoo, D., Chang, T. C., Metzner, T. J., Kang, L., van de Rijn, M., Skinner, E. C., Gambhir, S. S., Weissman, I. L., Liao, J. C. 2014; 6 (260)
  • Engineered SIRPa variants as immunotherapeutic adjuvants to anticancer antibodies. Science Weiskopf, K., Ring, A. M., Ho, C. C., Volkmer, J., Levin, A. M., Volkmer, A. K., Ozkan, E., Fernhoff, N. B., van de Rijn, M., Weissman, I. L., Garcia, K. C. 2013; 341 (6141): 88-91


    CD47 is an antiphagocytic signal that cancer cells employ to inhibit macrophage-mediated destruction. Here, we modified the binding domain of human SIRPα, the receptor for CD47, for use as a CD47 antagonist. We engineered high-affinity SIRPα variants with approximately 50,000-fold increased affinity for human CD47 relative to wild-type SIRPα. As high-affinity SIRPα monomers, they potently antagonized CD47 on cancer cells but did not induce macrophage phagocytosis on their own. Instead, they exhibited remarkable synergy with all tumor-specific monoclonal antibodies tested by increasing phagocytosis in vitro and enhancing antitumor responses in vivo. This "one-two punch" directs immune responses against tumor cells while lowering the threshold for macrophage activation, thereby providing a universal method for augmenting the efficacy of therapeutic anticancer antibodies.

    View details for DOI 10.1126/science.1238856

    View details for PubMedID 23722425

  • Anti-CD47 antibody-mediated phagocytosis of cancer by macrophages primes an effective antitumor T-cell response PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA Tseng, D., Volkmer, J., Willingham, S. B., Contreras-Trujillo, H., Fathman, J. W., Fernhoff, N. B., Seita, J., Inlay, M. A., Weiskopf, K., Miyanishi, M., Weissman, I. L. 2013; 110 (27): 11103-11108


    Mobilization of the T-cell response against cancer has the potential to achieve long-lasting cures. However, it is not known how to harness antigen-presenting cells optimally to achieve an effective antitumor T-cell response. In this study, we show that anti-CD47 antibody-mediated phagocytosis of cancer by macrophages can initiate an antitumor T-cell immune response. Using the ovalbumin model antigen system, anti-CD47 antibody-mediated phagocytosis of cancer cells by macrophages resulted in increased priming of OT-I T cells [cluster of differentiation 8-positive (CD8(+))] but decreased priming of OT-II T cells (CD4(+)). The CD4(+) T-cell response was characterized by a reduction in forkhead box P3-positive (Foxp3(+)) regulatory T cells. Macrophages following anti-CD47-mediated phagocytosis primed CD8(+) T cells to exhibit cytotoxic function in vivo. This response protected animals from tumor challenge. We conclude that anti-CD47 antibody treatment not only enables macrophage phagocytosis of cancer but also can initiate an antitumor cytotoxic T-cell immune response.

    View details for DOI 10.1073/pnas.1305569110

    View details for Web of Science ID 000321978000057

  • Anti-KIT monoclonal antibody inhibits imatinib-resistant gastrointestinal stromal tumor growth PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA Edris, B., Willingham, S. B., Weiskopf, K., Volkmer, A. K., Volkmer, J., Muehlenberg, T., Montgomery, K. D., Contreras-Trujillo, H., Czechowicz, A., Fletcher, J. A., West, R. B., Weissman, I. L., van de Rijn, M. 2013; 110 (9): 3501-3506


    Gastrointestinal stromal tumor (GIST) is the most common sarcoma of the gastrointestinal tract and arises from the interstitial cells of Cajal. It is characterized by expression of the receptor tyrosine kinase CD117 (KIT). In 70-80% of GIST cases, oncogenic mutations in KIT are present, leading to constitutive activation of the receptor, which drives the proliferation of these tumors. Treatment of GIST with imatinib, a small-molecule tyrosine kinase inhibitor, inhibits KIT-mediated signaling and initially results in disease control in 70-85% of patients with KIT-positive GIST. However, the vast majority of patients eventually develop resistance to imatinib treatment, leading to disease progression and posing a significant challenge in the clinical management of these tumors. Here, we show that an anti-KIT monoclonal antibody (mAb), SR1, is able to slow the growth of three human GIST cell lines in vitro. Importantly, these reductions in cell growth were equivalent between imatinib-resistant and imatinib-sensitive GIST cell lines. Treatment of GIST cell lines with SR1 reduces cell-surface KIT expression, suggesting that mAb-induced KIT down-regulation may be a mechanism by which SR1 inhibits GIST growth. Furthermore, we also show that SR1 treatment enhances phagocytosis of GIST cells by macrophages, indicating that treatment with SR1 may enhance immune cell-mediated tumor clearance. Finally, using two xenotransplantation models of imatinib-sensitive and imatinib-resistant GIST, we demonstrate that SR1 is able to strongly inhibit tumor growth in vivo. These results suggest that treatment with mAbs targeting KIT may represent an alternative, or complementary, approach for treating GIST.

    View details for DOI 10.1073/pnas.1222893110

    View details for Web of Science ID 000315841900062

  • The CD47-signal regulatory protein alpha (SIRPa) interaction is a therapeutic target for human solid tumors PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA Willingham, S. B., Volkmer, J., Gentles, A. J., Sahoo, D., Dalerba, P., Mitra, S. S., Wang, J., Contreras-Trujillo, H., Martin, R., Cohen, J. D., Lovelace, P., Scheeren, F. A., Chao, M. P., Weiskopf, K., Tang, C., Volkmer, A. K., Naik, T. J., Storm, T. A., Mosley, A. R., Edris, B., Schmid, S. M., Sun, C. K., Chua, M., Murillo, O., Rajendran, P., Cha, A. C., Chin, R. K., Kim, D., Adorno, M., Raveh, T., Tseng, D., Jaiswal, S., Enger, P. O., Steinberg, G. K., Li, G., So, S. K., Majeti, R., Harsh, G. R., van de Rijn, M., Teng, N. N., Sunwoo, J. B., Alizadeh, A. A., Clarke, M. F., Weissman, I. L. 2012; 109 (17): 6662-6667


    CD47, a "don't eat me" signal for phagocytic cells, is expressed on the surface of all human solid tumor cells. Analysis of patient tumor and matched adjacent normal (nontumor) tissue revealed that CD47 is overexpressed on cancer cells. CD47 mRNA expression levels correlated with a decreased probability of survival for multiple types of cancer. CD47 is a ligand for SIRP?, a protein expressed on macrophages and dendritic cells. In vitro, blockade of CD47 signaling using targeted monoclonal antibodies enabled macrophage phagocytosis of tumor cells that were otherwise protected. Administration of anti-CD47 antibodies inhibited tumor growth in orthotopic immunodeficient mouse xenotransplantation models established with patient tumor cells and increased the survival of the mice over time. Anti-CD47 antibody therapy initiated on larger tumors inhibited tumor growth and prevented or treated metastasis, but initiation of the therapy on smaller tumors was potentially curative. The safety and efficacy of targeting CD47 was further tested and validated in immune competent hosts using an orthotopic mouse breast cancer model. These results suggest all human solid tumor cells require CD47 expression to suppress phagocytic innate immune surveillance and elimination. These data, taken together with similar findings with other human neoplasms, show that CD47 is a commonly expressed molecule on all cancers, its function to block phagocytosis is known, and blockade of its function leads to tumor cell phagocytosis and elimination. CD47 is therefore a validated target for cancer therapies.

    View details for DOI 10.1073/pnas.1121623109

    View details for Web of Science ID 000303249100065

    View details for PubMedID 22451913

  • Antibody therapy targeting the CD47 protein is effective in a model of aggressive metastatic leiomyosarcoma PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA Edris, B., Weiskopf, K., Volkmer, A. K., Volkmer, J., Willingham, S. B., Contreras-Trujillo, H., Liu, J., Majeti, R., West, R. B., Fletcher, J. A., Beck, A. H., Weissman, I. L., van de Rijn, M. 2012; 109 (17): 6656-6661


    Antibodies against CD47, which block tumor cell CD47 interactions with macrophage signal regulatory protein-?, have been shown to decrease tumor size in hematological and epithelial tumor models by interfering with the protection from phagocytosis by macrophages that intact CD47 bestows upon tumor cells. Leiomyosarcoma (LMS) is a tumor of smooth muscle that can express varying levels of colony-stimulating factor-1 (CSF1), the expression of which correlates with the numbers of tumor-associated macrophages (TAMs) that are found in these tumors. We have previously shown that the presence of TAMs in LMS is associated with poor clinical outcome and the overall effect of TAMs in LMS therefore appears to be protumorigenic. However, the use of inhibitory antibodies against CD47 offers an opportunity to turn TAMs against LMS cells by allowing the phagocytic behavior of resident macrophages to predominate. Here we show that interference with CD47 increases phagocytosis of two human LMS cell lines, LMS04 and LMS05, in vitro. In addition, treatment of mice bearing subcutaneous LMS04 and LMS05 tumors with a novel, humanized anti-CD47 antibody resulted in significant reductions in tumor size. Mice bearing LMS04 tumors develop large numbers of lymph node and lung metastases. In a unique model for neoadjuvant treatment, mice were treated with anti-CD47 antibody starting 1 wk before resection of established primary tumors and subsequently showed a striking decrease in the size and number of metastases. These data suggest that treatment with anti-CD47 antibodies not only reduces primary tumor size but can also be used to inhibit the development of, or to eliminate, metastatic disease.

    View details for DOI 10.1073/pnas.1121629109

    View details for Web of Science ID 000303249100064

    View details for PubMedID 22451919

  • Three differentiation states risk-stratify bladder cancer into distinct subtypes PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA Volkmer, J., Sahoo, D., Chin, R. K., Ho, P. L., Tang, C., Kurtova, A. V., Willingham, S. B., Pazhanisamy, S. K., Contreras-Trujillo, H., Storm, T. A., Lotan, Y., Beck, A. H., Chung, B. I., Alizadeh, A. A., Godoy, G., Lerner, S. P., van de Rijng, M., Shortliffe, L. D., Weissman, I. L., Chan, K. S. 2012; 109 (6): 2078-2083


    Current clinical judgment in bladder cancer (BC) relies primarily on pathological stage and grade. We investigated whether a molecular classification of tumor cell differentiation, based on a developmental biology approach, can provide additional prognostic information. Exploiting large preexisting gene-expression databases, we developed a biologically supervised computational model to predict markers that correspond with BC differentiation. To provide mechanistic insight, we assessed relative tumorigenicity and differentiation potential via xenotransplantation. We then correlated the prognostic utility of the identified markers to outcomes within gene expression and formalin-fixed paraffin-embedded (FFPE) tissue datasets. Our data indicate that BC can be subclassified into three subtypes, on the basis of their differentiation states: basal, intermediate, and differentiated, where only the most primitive tumor cell subpopulation within each subtype is capable of generating xenograft tumors and recapitulating downstream populations. We found that keratin 14 (KRT14) marks the most primitive differentiation state that precedes KRT5 and KRT20 expression. Furthermore, KRT14 expression is consistently associated with worse prognosis in both univariate and multivariate analyses. We identify here three distinct BC subtypes on the basis of their differentiation states, each harboring a unique tumor-initiating population.

    View details for DOI 10.1073/pnas.1120605109

    View details for Web of Science ID 000299925000058

    View details for PubMedID 22308455

  • An antibody against SSEA-5 glycan on human pluripotent stem cells enables removal of teratoma-forming cells NATURE BIOTECHNOLOGY Tang, C., Lee, A. S., Volkmer, J., Sahoo, D., Nag, D., Mosley, A. R., Inlay, M. A., Ardehali, R., Chavez, S. L., Pera, R. R., Behr, B., Wu, J. C., Weissman, I. L., Drukker, M. 2011; 29 (9): 829-U86


    An important risk in the clinical application of human pluripotent stem cells (hPSCs), including human embryonic and induced pluripotent stem cells (hESCs and hiPSCs), is teratoma formation by residual undifferentiated cells. We raised a monoclonal antibody against hESCs, designated anti-stage-specific embryonic antigen (SSEA)-5, which binds a previously unidentified antigen highly and specifically expressed on hPSCs--the H type-1 glycan. Separation based on SSEA-5 expression through fluorescence-activated cell sorting (FACS) greatly reduced teratoma-formation potential of heterogeneously differentiated cultures. To ensure complete removal of teratoma-forming cells, we identified additional pluripotency surface markers (PSMs) exhibiting a large dynamic expression range during differentiation: CD9, CD30, CD50, CD90 and CD200. Immunohistochemistry studies of human fetal tissues and bioinformatics analysis of a microarray database revealed that concurrent expression of these markers is both common and specific to hPSCs. Immunodepletion with antibodies against SSEA-5 and two additional PSMs completely removed teratoma-formation potential from incompletely differentiated hESC cultures.

    View details for DOI 10.1038/nbt.1947

    View details for Web of Science ID 000294718400024

    View details for PubMedID 21841799

  • Calreticulin Is the Dominant Pro-Phagocytic Signal on Multiple Human Cancers and Is Counterbalanced by CD47 SCIENCE TRANSLATIONAL MEDICINE Chao, M. P., Jaiswal, S., Weissman-Tsukamoto, R., Alizadeh, A. A., Gentles, A. J., Volkmer, J., Weiskopf, K., Willingham, S. B., Raveh, T., Park, C. Y., Majeti, R., Weissman, I. L. 2010; 2 (63)


    Under normal physiological conditions, cellular homeostasis is partly regulated by a balance of pro- and anti-phagocytic signals. CD47, which prevents cancer cell phagocytosis by the innate immune system, is highly expressed on several human cancers including acute myeloid leukemia, non-Hodgkin's lymphoma, and bladder cancer. Blocking CD47 with a monoclonal antibody results in phagocytosis of cancer cells and leads to in vivo tumor elimination, yet normal cells remain mostly unaffected. Thus, we postulated that cancer cells must also display a potent pro-phagocytic signal. Here, we identified calreticulin as a pro-phagocytic signal that was highly expressed on the surface of several human cancers, but was minimally expressed on most normal cells. Increased CD47 expression correlated with high amounts of calreticulin on cancer cells and was necessary for protection from calreticulin-mediated phagocytosis. Blocking the interaction of target cell calreticulin with its receptor, low-density lipoprotein receptor-related protein, on phagocytic cells prevented anti-CD47 antibody-mediated phagocytosis. Furthermore, increased calreticulin expression was an adverse prognostic factor in diverse tumors including neuroblastoma, bladder cancer, and non-Hodgkin's lymphoma. These findings identify calreticulin as the dominant pro-phagocytic signal on several human cancers, provide an explanation for the selective targeting of tumor cells by anti-CD47 antibody, and highlight the balance between pro- and anti-phagocytic signals in the immune evasion of cancer.

    View details for DOI 10.1126/scitranslmed.3001375

    View details for Web of Science ID 000288444900003

    View details for PubMedID 21178137

  • Cancer stem cells in bladder cancer: a revisited and evolving concept CURRENT OPINION IN UROLOGY Chan, K. S., Volkmer, J., Weissman, I. 2010; 20 (5): 393-397


    Recently, the prospective isolation and characterization of cancer stem cells (CSCs) from various human malignancies revealed that they are resistant to radiation and chemotherapies. Therefore, CSCs may be the 'roots' and ideal target for therapeutic intervention. Here, we will focus on reviewing the historical perspective, recent literatures on bladder cancer stem cells and their clinical implications.CSCs have been prospectively isolated from bladder cancer tissues from patient specimens, established cancer cell lines and xenografts, based on the expression of a combination of cell surface receptors, cytokeratin markers, drug transporters and the efficient efflux of the Hoechst 33,342 dye (side population). Further, global gene expression profiling of CSCs revealed an activated gene signature of CSCs similar to that of aggressive bladder cancer, supporting the concept that a tumor cell subpopulation is contributing to bladder cancer progression. Finally, our studies on the preclinical targeting of bladder CSCs in vitro and in xenografts using a blocking antibody for CD47 reveal promising efficacy.Functionally distinct CSCs exist in human bladder cancer and can be prospectively isolated. Continuing research will be important to identify their cell of origin, programs balancing self-renewal and differentiation and to identify additional therapeutic options to target bladder CSCs.

    View details for DOI 10.1097/MOU.0b013e32833cc9df

    View details for Web of Science ID 000280552100009

    View details for PubMedID 20657288

  • Gene expression analysis of human red blood cells INTERNATIONAL JOURNAL OF MEDICAL SCIENCES Kabanova, S., Kleinbongard, P., Volkmer, J., Andree, B., Kelm, M., Jax, T. W. 2009; 6 (4): 156-159


    Understanding of molecular mechanisms governing the enucleating phenomena of human erythrocytes is of major importance in both fundamental and applied studies. Total RNA (n=7) from human RBCs (purity of erythrocyte preparation >99,99%) was tested using 2100 Bioanalyzer (Agilent, USA), and transcribed to cDNA. Microarray analysis was performed with the Human Genome Focus GeneChip (Affymetrix, USA), containing 8500 transcripts corresponding to 8400 human genes. Here we report that human RBCs contain typical eukaryotic RNA with 28S- and18S-rRNA standard bands. Microarray studies revealed the presence of transcripts of 1019 different genes in erythrocytic RNA. Gene Ontology analysis recognized 859 genes involved in general biological processes: 529 genes for cellular metabolism, 228 genes for signal transduction, 104 genes for development, 107 genes for immune response, 62 genes for protein localization, 53 genes for programmed cell death, and 5 genes for autophagy. A number of genes responsible for transcription, translation, RNA-stabilisation as well as for apoptosis and anti-apoptosis have been identified for the first time in circulating human RBCs. The presented data shed new light on the genetic determination of erythropoiesis, apoptosis and may have implications on the pathophysiology and diagnosis of various diseases involving red blood cells.

    View details for Web of Science ID 000273404800002

    View details for PubMedID 19421340

  • "Cancer stem cells"-Lessons from Hercules to fight the Hydra UROLOGIC ONCOLOGY-SEMINARS AND ORIGINAL INVESTIGATIONS Moltzahn, F. R., Volkmer, J., Rottke, D., Ackermann, R. 2008; 26 (6): 581-589


    Following the initial identification of hematopoietic tumor stem cells, such cells were also found in several solid tumor types. In urology, cancer stem cells have only been found in prostate tumors so far. The concept and detection of tumor stem cells rely heavily on findings derived from stem cell research. Therefore, in addition to identifying and characterizing urologic tumor stem cells, research in uro-oncology should also aim at better understanding the stem-cell biology of urologic organs. Insights in similarities and differences gleaned from these studies could be used to develop strategies for targeted destruction of tumor stem cells while sparing the physiological stem cells. The main target of future curative therapies in uro-oncology must therefore be the central, immortal head of the Hydra, the tumor stem cell.

    View details for DOI 10.1016/j.urolonc.2008.07.009

    View details for Web of Science ID 000261285100004

    View details for PubMedID 18818107

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