MSTP Admissions Committee, Stanford School of Medicine (2010 - Present)
Honors & Awards
Career Award for Medical Scientists, Burroughs Wellcome Fund (2008)
Residency:Brigham and Women's Hospital Harvard Medical School (2004) MA
Board Certification: Hematology, American Board of Internal Medicine (2007)
Fellowship:Stanford University Medical Center (2008) CA
Board Certification: Internal Medicine, American Board of Internal Medicine (2005)
Medical Education:University of California San Francisco (2002) CA
Current Research and Scholarly Interests
Acute myeloid leukemia (AML) is a cancer of the blood and bone marrow that is rapidly fatal within months if untreated. Even with aggressive treatment, including high dose chemotherapy and bone marrow transplantation, five-year overall survival rates range between 30-40%. A growing body of evidence indicates that not all cells in this cancer are the same, and that there is a rare population of leukemia stem cells (LSC) that are responsible for maintaining the disease. These findings have led to the idea that in order to cure this cancer, the LSC must be eliminated, while at the same time sparing the normal blood forming stem cells within the bone marrow.
The overall goal of the research is to identify molecular and genetic differences between human AML stem cells and their normal counterparts, and then to develop therapeutic strategies directed against these targets. We have used a bioinformatic analysis to identify genes and pathways preferentially expressed or activated in LSC. From this analysis, we identified a number of cell surface protein markers that are more highly expressed on AML LSC compared to their normal counterparts. We then determined that one of these protein markers, CD47, contributes to leukemia development by blocking the ingestion and removal of leukemia cells by cells of the immune system. Most significantly, we determined that blocking monoclonal antibodies directed against CD47 targeted LSC and depleted leukemia in mouse pre-clinical models.
Currently, our major focus is the development of therapeutic antibodies directed against CD47 and/or additional protein markers present in much larger amounts on the external surface of the LSC compared to the normal blood forming stem cells. It is our hope that we will develop a clinical grade therapeutic antibody for the treatment of AML that will be investigated in clinical trials at the Stanford Cancer Center.
Independent Studies (16)
- Directed Reading in Cancer Biology
CBIO 299 (Aut, Win, Spr, Sum)
- Directed Reading in Immunology
IMMUNOL 299 (Aut, Win, Spr, Sum)
- Directed Reading in Medicine
MED 299 (Aut, Win, Spr, Sum)
- Early Clinical Experience in Immunology
IMMUNOL 280 (Aut, Win, Spr, Sum)
- Early Clinical Experience in Medicine
MED 280 (Aut, Win, Spr, Sum)
- Graduate Research
CBIO 399 (Aut, Win, Spr, Sum)
- Graduate Research
IMMUNOL 399 (Aut, Win, Spr, Sum)
- Graduate Research
MED 399 (Aut, Win, Spr, Sum)
- Graduate Research
STEMREM 399 (Aut, Win, Spr, Sum)
- Medical Scholars Research
MED 370 (Aut, Win, Spr, Sum)
- Out-of-Department Advanced Research Laboratory in Experimental Biology
BIO 199X (Aut, Win, Spr)
- TGR Dissertation
STEMREM 802 (Aut, Win, Sum)
- Teaching in Immunology
IMMUNOL 290 (Aut, Win, Spr, Sum)
- Undergraduate Research
IMMUNOL 199 (Aut, Win, Spr, Sum)
- Undergraduate Research
MED 199 (Aut, Win, Spr, Sum)
- Undergraduate Research
STEMREM 199 (Aut, Spr, Sum)
- Directed Reading in Cancer Biology
Graduate and Fellowship Programs
Preleukemic mutations in human acute myeloid leukemia affect epigenetic regulators and persist in remission.
Proceedings of the National Academy of Sciences of the United States of America
2014; 111 (7): 2548-2553
Cancer is widely characterized by the sequential acquisition of genetic lesions in a single lineage of cells. Our previous studies have shown that, in acute myeloid leukemia (AML), mutation acquisition occurs in functionally normal hematopoietic stem cells (HSCs). These preleukemic HSCs harbor some, but not all, of the mutations found in the leukemic cells. We report here the identification of patterns of mutation acquisition in human AML. Our findings support a model in which mutations in "landscaping" genes, involved in global chromatin changes such as DNA methylation, histone modification, and chromatin looping, occur early in the evolution of AML, whereas mutations in "proliferative" genes occur late. Additionally, we analyze the persistence of preleukemic mutations in patients in remission and find CD34+ progenitor cells and various mature cells that harbor preleukemic mutations. These findings indicate that preleukemic HSCs can survive induction chemotherapy, identifying these cells as a reservoir for the reevolution of relapsed disease. Finally, through the study of several cases of relapsed AML, we demonstrate various evolutionary patterns for the generation of relapsed disease and show that some of these patterns are consistent with involvement of preleukemic HSCs. These findings provide key insights into the monitoring of minimal residual disease and the identification of therapeutic targets in human AML.
View details for DOI 10.1073/pnas.1324297111
View details for PubMedID 24550281
Clonal Evolution of Preleukemic Hematopoietic Stem Cells Precedes Human Acute Myeloid Leukemia
SCIENCE TRANSLATIONAL MEDICINE
2012; 4 (149)
Given that most bone marrow cells are short-lived, the accumulation of multiple leukemogenic mutations in a single clonal lineage has been difficult to explain. We propose that serial acquisition of mutations occurs in self-renewing hematopoietic stem cells (HSCs). We investigated this model through genomic analysis of HSCs from six patients with de novo acute myeloid leukemia (AML). Using exome sequencing, we identified mutations present in individual AML patients harboring the FLT3-ITD (internal tandem duplication) mutation. We then screened the residual HSCs and detected some of these mutations including mutations in the NPM1, TET2, and SMC1A genes. Finally, through single-cell analysis, we determined that a clonal progression of multiple mutations occurred in the HSCs of some AML patients. These preleukemic HSCs suggest the clonal evolution of AML genomes from founder mutations, revealing a potential mechanism contributing to relapse. Such preleukemic HSCs may constitute a cellular reservoir that should be targeted therapeutically for more durable remissions.
View details for DOI 10.1126/scitranslmed.3004315
View details for Web of Science ID 000308491600005
View details for PubMedID 22932223
Prospective separation of normal and leukemic stem cells based on differential expression of TIM3, a human acute myeloid leukemia stem cell marker
PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
2011; 108 (12): 5009-5014
Hematopoietic tissues in acute myeloid leukemia (AML) patients contain both leukemia stem cells (LSC) and residual normal hematopoietic stem cells (HSC). The ability to prospectively separate residual HSC from LSC would enable important scientific and clinical investigation including the possibility of purged autologous hematopoietic cell transplants. We report here the identification of TIM3 as an AML stem cell surface marker more highly expressed on multiple specimens of AML LSC than on normal bone marrow HSC. TIM3 expression was detected in all cytogenetic subgroups of AML, but was significantly higher in AML-associated with core binding factor translocations or mutations in CEBPA. By assessing engraftment in NOD/SCID/IL2R?-null mice, we determined that HSC function resides predominantly in the TIM3-negative fraction of normal bone marrow, whereas LSC function from multiple AML specimens resides predominantly in the TIM3-positive compartment. Significantly, differential TIM3 expression enabled the prospective separation of HSC from LSC in the majority of AML specimens with detectable residual HSC function.
View details for DOI 10.1073/pnas.1100551108
View details for Web of Science ID 000288712200061
View details for PubMedID 21383193
Association of a Leukemic Stem Cell Gene Expression Signature With Clinical Outcomes in Acute Myeloid Leukemia
JAMA-JOURNAL OF THE AMERICAN MEDICAL ASSOCIATION
2010; 304 (24): 2706-2715
In many cancers, specific subpopulations of cells appear to be uniquely capable of initiating and maintaining tumors. The strongest support for this cancer stem cell model comes from transplantation assays in immunodeficient mice, which indicate that human acute myeloid leukemia (AML) is driven by self-renewing leukemic stem cells (LSCs). This model has significant implications for the development of novel therapies, but its clinical relevance has yet to be determined.To identify an LSC gene expression signature and test its association with clinical outcomes in AML.Retrospective study of global gene expression (microarray) profiles of LSC-enriched subpopulations from primary AML and normal patient samples, which were obtained at a US medical center between April 2005 and July 2007, and validation data sets of global transcriptional profiles of AML tumors from 4 independent cohorts (n = 1047).Identification of genes discriminating LSC-enriched populations from other subpopulations in AML tumors; and association of LSC-specific genes with overall, event-free, and relapse-free survival and with therapeutic response.Expression levels of 52 genes distinguished LSC-enriched populations from other subpopulations in cell-sorted AML samples. An LSC score summarizing expression of these genes in bulk primary AML tumor samples was associated with clinical outcomes in the 4 independent patient cohorts. High LSC scores were associated with worse overall, event-free, and relapse-free survival among patients with either normal karyotypes or chromosomal abnormalities. For the largest cohort of patients with normal karyotypes (n = 163), the LSC score was significantly associated with overall survival as a continuous variable (hazard ratio [HR], 1.15; 95% confidence interval [CI], 1.08-1.22; log-likelihood P <.001). The absolute risk of death by 3 years was 57% (95% CI, 43%-67%) for the low LSC score group compared with 78% (95% CI, 66%-86%) for the high LSC score group (HR, 1.9 [95% CI, 1.3-2.7]; log-rank P = .002). In another cohort with available data on event-free survival for 70 patients with normal karyotypes, the risk of an event by 3 years was 48% (95% CI, 27%-63%) in the low LSC score group vs 81% (95% CI, 60%-91%) in the high LSC score group (HR, 2.4 [95% CI, 1.3-4.5]; log-rank P = .006). In multivariate Cox regression including age, mutations in FLT3 and NPM1, and cytogenetic abnormalities, the HRs for LSC score in the 3 cohorts with data on all variables were 1.07 (95% CI, 1.01-1.13; P = .02), 1.10 (95% CI, 1.03-1.17; P = .005), and 1.17 (95% CI, 1.05-1.30; P = .005).High expression of an LSC gene signature is independently associated with adverse outcomes in patients with AML.
View details for Web of Science ID 000285518000015
View details for PubMedID 21177505
Anti-CD47 Antibody Synergizes with Rituximab to Promote Phagocytosis and Eradicate Non-Hodgkin Lymphoma
2010; 142 (5): 699-713
Monoclonal antibodies are standard therapeutics for several cancers including the anti-CD20 antibody rituximab for B cell non-Hodgkin lymphoma (NHL). Rituximab and other antibodies are not curative and must be combined with cytotoxic chemotherapy for clinical benefit. Here we report the eradication of human NHL solely with a monoclonal antibody therapy combining rituximab with a blocking anti-CD47 antibody. We identified increased expression of CD47 on human NHL cells and determined that higher CD47 expression independently predicted adverse clinical outcomes in multiple NHL subtypes. Blocking anti-CD47 antibodies preferentially enabled phagocytosis of NHL cells and synergized with rituximab. Treatment of human NHL-engrafted mice with anti-CD47 antibody reduced lymphoma burden and improved survival, while combination treatment with rituximab led to elimination of lymphoma and cure. These antibodies synergized through a mechanism combining Fc receptor (FcR)-dependent and FcR-independent stimulation of phagocytosis that might be applicable to many other cancers.
View details for DOI 10.1016/j.cell.2010.07.044
View details for Web of Science ID 000281523200014
View details for PubMedID 20813259
CD47 Is an Adverse Prognostic Factor and Therapeutic Antibody Target on Human Acute Myeloid Leukemia Stem Cells
2009; 138 (2): 286-299
Acute myeloid leukemia (AML) is organized as a cellular hierarchy initiated and maintained by a subset of self-renewing leukemia stem cells (LSC). We hypothesized that increased CD47 expression on human AML LSC contributes to pathogenesis by inhibiting their phagocytosis through the interaction of CD47 with an inhibitory receptor on phagocytes. We found that CD47 was more highly expressed on AML LSC than their normal counterparts, and that increased CD47 expression predicted worse overall survival in three independent cohorts of adult AML patients. Furthermore, blocking monoclonal antibodies directed against CD47 preferentially enabled phagocytosis of AML LSC and inhibited their engraftment in vivo. Finally, treatment of human AML LSC-engrafted mice with anti-CD47 antibody depleted AML and targeted AML LSC. In summary, increased CD47 expression is an independent, poor prognostic factor that can be targeted on human AML stem cells with blocking monoclonal antibodies capable of enabling phagocytosis of LSC.
View details for DOI 10.1016/j.cell.2009.05.045
View details for Web of Science ID 000268277000011
View details for PubMedID 19632179
Dysregulated gene expression networks in human acute myelogenous leukemia stem cells
PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
2009; 106 (9): 3396-3401
We performed the first genome-wide expression analysis directly comparing the expression profile of highly enriched normal human hematopoietic stem cells (HSC) and leukemic stem cells (LSC) from patients with acute myeloid leukemia (AML). Comparing the expression signature of normal HSC to that of LSC, we identified 3,005 differentially expressed genes. Using 2 independent analyses, we identified multiple pathways that are aberrantly regulated in leukemic stem cells compared with normal HSC. Several pathways, including Wnt signaling, MAP Kinase signaling, and Adherens Junction, are well known for their role in cancer development and stem cell biology. Other pathways have not been previously implicated in the regulation of cancer stem cell functions, including Ribosome and T Cell Receptor Signaling pathway. This study demonstrates that combining global gene expression analysis with detailed annotated pathway resources applied to highly enriched normal and malignant stem cell populations, can yield an understanding of the critical pathways regulating cancer stem cells.
View details for DOI 10.1073/pnas.0900089106
View details for Web of Science ID 000263844100075
View details for PubMedID 19218430
Identification of a hierarchy of multipotent hematopoietic progenitors in human cord blood
CELL STEM CELL
2007; 1 (6): 635-645
Mouse hematopoiesis is initiated by long-term hematopoietic stem cells (HSC) that differentiate into a series of multipotent progenitors that exhibit progressively diminished self-renewal ability. In human hematopoiesis, populations enriched for HSC activity have been identified, as have downstream lineage-committed progenitors, but multipotent progenitor activity has not been uniquely isolated. Previous reports indicate that human HSC are enriched in Lin-CD34+CD38- cord blood and bone marrow and express CD90. We demonstrate that the Lin-CD34+CD38- fraction of cord blood and bone marrow can be subdivided into three subpopulations: CD90+CD45RA-, CD90-CD45RA-, and CD90-CD45RA+. Utilizing in vivo transplantation studies and complementary in vitro assays, we demonstrate that the Lin-CD34+CD38-CD90+CD45RA- cord blood fraction contains HSC and isolate this activity to as few as 10 purified cells. Furthermore, we report the first prospective isolation of a population of candidate human multipotent progenitors, Lin-CD34+CD38-CD90-CD45RA- cord blood.
View details for DOI 10.1016/j.stem.2007.10.001
View details for Web of Science ID 000251784300010
View details for PubMedID 18371405
Role of DNMT3A, TET2, and IDH1/2 mutations in pre-leukemic stem cells in acute myeloid leukemia
INTERNATIONAL JOURNAL OF HEMATOLOGY
2013; 98 (6): 648-657
Aberrant changes in the epigenome are now recognized to be important in driving the development of multiple human cancers including acute myeloid leukemia. Recent advances in sequencing technologies have led to the identification of recurrent mutations in genes that regulate DNA methylation including DNA methyltransferase 3A (DNMT3A), ten-eleven translocation 2 (TET2), and isocitrate dehydrogenase 1 (IDH1) and IDH2. These mutations have been shown to promote self-renewal and block differentiation of hematopoietic stem/progenitor cells. Acquisition of these mutations in hematopoietic stem cells can lead to their clonal expansion resulting in a pre-leukemic stem cell (pre-LSC) population. Pre-LSCs retain the ability to differentiate into the full spectrum of mature daughter cells but can become fully transformed with the acquisition of additional driver mutations. Here, we review the effects of mutations in DNMT3A, TET2, and IDH1/2 on mouse and human hematopoiesis, the current understanding of their role in pre-LSCs, and therapeutic strategies to eliminate this population which may serve as a cellular reservoir for relapse.
View details for DOI 10.1007/s12185-013-1407-8
View details for Web of Science ID 000328481700005
View details for PubMedID 23949914
Role of cysteine 288 in nucleophosmin cytoplasmic mutations: sensitization to toxicity induced by arsenic trioxide and bortezomib
2013; 27 (10): 1970-1980
Mutations in exon 12 of the NPM1 gene (NPMc+) define a distinct subset of acute myelogenous leukemias (AML) in which the NPMc+ protein localizes aberrantly to the leukemic cell cytoplasm. We have found that introduction of the most common NPMc+ variant into K562 and 32D cells sensitizes these cells to apoptosis induced by drugs such as bortezomib and arsenic trioxide that induce reactive oxygen species (ROS) formation and that cytotoxicity is prevented in the presence of N-acetyl-1-cysteine, a ROS scavenger. The substitution of tryptophan288 by cysteine occurs in the great majority of NPM1c+ mutations. Mutagenesis of C288 to alanine re-localizes NPMc+ from the cytoplasm to the nucleolus and attenuates the sensitivity of cells expressing this mutation to bortezomib and arsenic trioxide. Primary AML leukemic cells expressing NPMc+ are also significantly more sensitive than other AML cells to apoptosis induced by both drugs at pharmacologically achievable doses. We conclude that the presence of a cysteine moiety at position 288 results in the cytoplasmic localization of NPM1c+ and the increased sensitivity to bortezomib and arsenic trioxide. These data suggest that bortezomib and arsenic trioxide may have increased therapeutic efficacy in NPM1c+ leukemias.Leukemia accepted article preview online, 23 July 2013. doi:10.1038/leu.2013.222.
View details for DOI 10.1038/leu.2013.222
View details for Web of Science ID 000325642600003
View details for PubMedID 23877794
Azacitidine fails to eradicate leukemic stem/progenitor cell populations in patients with acute myeloid leukemia and myelodysplasia
2013; 27 (5): 1028-1036
Epigenetic therapies demonstrate significant clinical activity in acute myeloid leukemia (AML) and myelodysplasia (MDS) and constitute an important new class of therapeutic agents. However hematological responses are not durable and disease relapse appears inevitable. Experimentally, leukemic stem/progenitor cells (LSC) propagate disease in animal models of AML and it has been postulated that their relative chemo-resistance contributes to disease relapse. We serially measured LSC numbers in patients with high-risk AML and MDS treated with 5'-azacitidine and sodium valproate (VAL-AZA). Fifteen out of seventy-nine patients achieved a complete remission (CR) or complete remission with incomplete blood count recovery (CRi) with VAL-AZA therapy. There was no significant reduction in the size of the LSC-containing population in non-responders. While the LSC-containing population was substantially reduced in all patients achieving a CR/CRi it was never eradicated and expansion of this population antedated morphological relapse. Similar studies were performed in seven patients with newly diagnosed AML treated with induction chemotherapy. Eradication of the LSC-containing population was observed in three patients all of whom achieved a durable CR in contrast to patients with resistant disease where LSC persistence was observed. LSC quantitation provides a novel biomarker of disease response and relapse in patients with AML treated with epigenetic therapies. New drugs that target this cellular population in vivo are required.
View details for DOI 10.1038/leu.2012.312
View details for Web of Science ID 000318698300005
View details for PubMedID 23223186
Clonal evolution of acute leukemia genomes
2013; 32 (2): 135-140
In large part, cancer results from the accumulation of multiple mutations in a single cell lineage that are sequentially acquired and subject to an evolutionary process where selection drives the expansion of more fit subclones. Owing to the technical challenge of distinguishing and isolating distinct cancer subclones, many aspects of this clonal evolution are poorly understood, including the diversity of different subclones in an individual cancer, the nature of the subclones contributing to relapse, and the identity of pre-cancerous mutations. These issues are not just important to our understanding of cancer biology, but are also clinically important given the need to understand the nature of subclones responsible for the refractory and relapsed disease that cause significant morbidity and mortality in patients. Recently, advanced genomic techniques have been used to investigate clonal diversity and evolution in acute leukemia. Studies of pediatric acute lymphoblastic leukemia (ALL) demonstrated that in individual patients there are multiple genetic subclones of leukemia-initiating cells, with a complex clonal architecture. Separate studies also investigating pediatric ALL determined that the clonal basis of relapse was variable and complex, with relapse often evolving from a clone ancestral to the predominant de novo leukemia clone. Additional studies in both ALL and acute myeloid leukemia have identified pre-leukemic mutations in some individual cases. This review will highlight these recent reports investigating the clonal evolution of acute leukemia genomes and discuss the implications for clinical therapy.
View details for DOI 10.1038/onc.2012.48
View details for Web of Science ID 000314075500001
View details for PubMedID 22349821
- The cancer stem cell model: B cell acute lymphoblastic leukaemia breaks the mould EMBO MOLECULAR MEDICINE 2013; 5 (1): 7-9
Cyclin-A1 represents a new immunogenic targetable antigen expressed in acute myeloid leukemia stem cells with characteristics of a cancer-testis antigen
2012; 119 (23): 5492-5501
Targeted T-cell therapy is a potentially less toxic strategy than allogeneic stem cell transplantation for providing a cytotoxic antileukemic response to eliminate leukemic stem cells (LSCs) in acute myeloid leukemia (AML). However, this strategy requires identification of leukemia-associated antigens that are immunogenic and exhibit selective high expression in AML LSCs. Using microarray expression analysis of LSCs, hematopoietic cell subpopulations, and peripheral tissues to screen for candidate antigens, cyclin-A1 was identified as a candidate gene. Cyclin-A1 promotes cell proliferation and survival, has been shown to be leukemogenic in mice, is detected in LSCs of more than 50% of AML patients, and is minimally expressed in normal tissues with exception of testis. Using dendritic cells pulsed with a cyclin-A1 peptide library, we generated T cells against several cyclin-A1 oligopeptides. Two HLA A*0201-restricted epitopes were further characterized, and specific CD8 T-cell clones recognized both peptide-pulsed target cells and the HLA A*0201-positive AML line THP-1, which expresses cyclin-A1. Furthermore, cyclin-A1-specific CD8 T cells lysed primary AML cells. Thus, cyclin-A1 is the first prototypic leukemia-testis-antigen to be expressed in AML LSCs. The pro-oncogenic activity, high expression levels, and multitude of immunogenic epitopes make it a viable target for pursuing T cell-based therapy approaches.
View details for DOI 10.1182/blood-2011-07-365890
View details for Web of Science ID 000307391400023
View details for PubMedID 22529286
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
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
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
The CD47-SIRP alpha pathway in cancer immune evasion and potential therapeutic implications
CURRENT OPINION IN IMMUNOLOGY
2012; 24 (2): 225-232
Multiple lines of investigation have demonstrated that the immune system plays an important role in preventing tumor initiation and controlling tumor growth. Accordingly, many cancers have evolved diverse mechanisms to evade such monitoring. While multiple immune cell types mediate tumor surveillance, recent evidence demonstrates that macrophages, and other phagocytic cells, play a key role in regulating tumor growth through phagocytic clearance. In this review we highlight the role of tumor immune evasion through the inhibition of phagocytosis, specifically through the CD47-signal-regulatory protein-? pathway, and discuss how targeting this pathway might lead to more effective cancer immunotherapies.
View details for DOI 10.1016/j.coi.2012.01.010
View details for Web of Science ID 000303187600017
View details for PubMedID 22310103
Treatment advances have not improved the early death rate in acute promyelocytic leukemia
HAEMATOLOGICA-THE HEMATOLOGY JOURNAL
2012; 97 (1): 133-136
Early mortality in acute promyelocytic leukemia has been reported to occur in less than 10% of patients treated in clinical trials. This study reports the incidence and clinical features of acute promyelocytic leukemia patients treated at Stanford Hospital, CA, USA since March 1997, focusing on early mortality. We show that the risk of early death in acute promyelocytic leukemia patients is higher than previously reported. In a cohort of 70 patients who received induction therapy at Stanford Hospital, 19% and 26% died within seven and 30 days of admission, respectively. High early mortality was not limited to our institution as evaluation of the Surveillance, Epidemiology and End Results Database demonstrated that 30-day mortality for acute promyelocytic leukemia averaged 20% from 1977-2007 and did not improve significantly over this interval. Our findings show that early death is now the greatest contributor to treatment failure in this otherwise highly curable form of leukemia.
View details for DOI 10.3324/haematol.2011.046490
View details for Web of Science ID 000299870500022
View details for PubMedID 21993679
Programmed cell removal: a new obstacle in the road to developing cancer
NATURE REVIEWS CANCER
2012; 12 (1): 58-67
The development of cancer involves mechanisms by which aberrant cells overcome normal regulatory pathways that limit their numbers and their migration. The evasion of programmed cell death is one of several key early events that need to be overcome in the progression from normal cellular homeostasis to malignant transformation. Recently, we provided evidence in mouse and human cancers that successful cancer clones must also overcome programmed cell removal. In this Opinion article, we explore the role of programmed cell removal in both normal and neoplastic cells, and we place this pathway in the context of the initiation of programmed cell death.
View details for DOI 10.1038/nrc3171
View details for Web of Science ID 000298369300014
Extranodal dissemination of non-Hodgkin lymphoma requires CD47 and is inhibited by anti-CD47 antibody therapy
2011; 118 (18): 4890-4901
Non-Hodgkin lymphoma (NHL) presents as both localized and disseminated disease with spread to secondary sites carrying a worse prognosis. Although pathways driving NHL dissemination have been identified, there are few therapies capable of inhibiting them. Here, we report a novel role for the immunomodulatory protein CD47 in NHL dissemination, and we demonstrate that therapeutic targeting of CD47 can prevent such spread. We developed 2 in vivo lymphoma metastasis models using Raji cells, a human NHL cell line, and primary cells from a lymphoma patient. CD47 expression was required for Raji cell dissemination to the liver in mouse xenotransplants. Targeting of CD47 with a blocking antibody inhibited Raji cell dissemination to major organs, including the central nervous system, and inhibited hematogenous dissemination of primary lymphoma cells. We hypothesized that anti-CD47 antibody-mediated elimination of circulating tumor cells occurred through phagocytosis, a previously described mechanism for blocking anti-CD47 antibodies. As predicted, inhibition of dissemination by anti-CD47 antibodies was dependent on blockade of phagocyte SIRP? and required macrophage effector cells. These results demonstrate that CD47 is required for NHL dissemination, which can be therapeutically targeted with a blocking anti-CD47 antibody. Ultimately, these findings are potentially applicable to the dissemination and metastasis of other solid tumors.
View details for DOI 10.1182/blood-2011-02-338020
View details for Web of Science ID 000296714500018
View details for PubMedID 21828138
Surprise! HSC Are Aberrant in Chronic Lymphocytic Leukemia
2011; 20 (2): 135-136
In this issue of Cancer Cell, Kikushige et al. report the surprising finding that, in human chronic lymphocytic leukemia (CLL), hematopoietic stem cells (HSC) aberrantly generate clonal B cells with CLL-like phenotypes, which implicate HSC in the pathogenesis of this mature lymphoid malignancy and has major implications for CLL therapies.
View details for DOI 10.1016/j.ccr.2011.08.001
View details for Web of Science ID 000294099700002
View details for PubMedID 21840478
Single-cell phospho-specific flow cytometric analysis demonstrates biochemical and functional heterogeneity in human hematopoietic stem and progenitor compartments
2011; 117 (16): 4226-4233
The low frequency of hematopoietic stem and progenitor cells (HSPCs) in human BM has precluded analysis of the direct biochemical effects elicited by cytokines in these populations, and their functional consequences. Here, single-cell phospho-specific flow cytometry was used to define the signaling networks active in 5 previously defined human HSPC subsets. This analysis revealed that the currently defined HSC compartment is composed of biochemically distinct subsets with the ability to respond rapidly and directly in vitro to a broader array of cytokines than previously appreciated, including G-CSF. The G-CSF response was physiologically relevant-driving cell-cycle entry and increased proliferation in a subset of single cells within the HSC compartment. The heterogeneity in the single-cell signaling and proliferation responses prompted subfractionation of the adult BM HSC compartment by expression of CD114 (G-CSF receptor). Xenotransplantation assays revealed that HSC activity is significantly enriched in the CD114(neg/lo) compartment, and almost completely absent in the CD114(pos) subfraction. The single-cell analyses used here can be adapted for further refinement of HSPC surface immunophenotypes, and for examining the direct regulatory effects of other factors on the homeostasis of stem and progenitor populations in normal or diseased states.
View details for DOI 10.1182/blood-2010-07-298232
View details for Web of Science ID 000289807600012
View details for PubMedID 21357764
Monoclonal antibody therapy directed against human acute myeloid leukemia stem cells
2011; 30 (9): 1009-1019
Accumulating evidence indicates that many human cancers are organized as a cellular hierarchy initiated and maintained by self-renewing cancer stem cells. This cancer stem cell model has been most conclusively established for human acute myeloid leukemia (AML), although controversies still exist regarding the identity of human AML stem cells (leukemia stem cell (LSC)). A major implication of this model is that, in order to eradicate the cancer and cure the patient, the cancer stem cells must be eliminated. Monoclonal antibodies have emerged as effective targeted therapies for the treatment of a number of human malignancies and, given their target antigen specificity and generally minimal toxicity, are well positioned as cancer stem cell-targeting therapies. One strategy for the development of monoclonal antibodies targeting human AML stem cells involves first identifying cell surface antigens preferentially expressed on AML LSC compared with normal hematopoietic stem cells. In recent years, a number of such antigens have been identified, including CD123, CD44, CLL-1, CD96, CD47, CD32, and CD25. Moreover, monoclonal antibodies targeting CD44, CD123, and CD47 have demonstrated efficacy against AML LSC in xenotransplantation models. Hopefully, these antibodies will ultimately prove to be effective in the treatment of human AML.
View details for DOI 10.1038/onc.2010.511
View details for Web of Science ID 000287964100001
View details for PubMedID 21076471
Therapeutic Antibody Targeting of CD47 Eliminates Human Acute Lymphoblastic Leukemia
2011; 71 (4): 1374-1384
Acute lymphoblastic leukemia (ALL) is the most common pediatric malignancy and constitutes 15% of adult leukemias. Although overall prognosis for pediatric ALL is favorable, high-risk pediatric patients and most adult patients have significantly worse outcomes. Multiagent chemotherapy is standard of care for both pediatric and adult ALL, but is associated with systemic toxicity and long-term side effects and is relatively ineffective against certain ALL subtypes. Recent efforts have focused on the development of targeted therapies for ALL including monoclonal antibodies. Here, we report the identification of CD47, a protein that inhibits phagocytosis, as an antibody target in standard and high-risk ALL. CD47 was found to be more highly expressed on a subset of human ALL patient samples compared with normal cell counterparts and to be an independent predictor of survival and disease refractoriness in several ALL patient cohorts. In addition, a blocking monoclonal antibody against CD47 enabled phagocytosis of ALL cells by macrophages in vitro and inhibited tumor engraftment in vivo. Significantly, anti-CD47 antibody eliminated ALL in the peripheral blood, bone marrow, spleen, and liver of mice engrafted with primary human ALL. These data provide preclinical support for the development of an anti-CD47 antibody therapy for treatment of human ALL.
View details for DOI 10.1158/0008-5472.CAN-10-2238
View details for Web of Science ID 000287352600020
View details for PubMedID 21177380
Human Acute Myelogenous Leukemia Stem Cells Revisited: There's More Than Meets the Eye
2011; 19 (1): 9-10
In this issue of Cancer Cell, Goardon et al. revise earlier conclusions regarding acute myelogenous leukemia (AML) stem cells by demonstrating that in the majority of patients, they reside in two hierarchically related populations most similar to normal hematopoietic progenitors. These findings have implications for therapeutic targeting of these cells.
View details for DOI 10.1016/j.ccr.2011.01.007
View details for Web of Science ID 000287290300005
View details for PubMedID 21251611
Calreticulin Is the Dominant Pro-Phagocytic Signal on Multiple Human Cancers and Is Counterbalanced by CD47
SCIENCE TRANSLATIONAL MEDICINE
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
Second-line mitoxantrone, etoposide, and cytarabine for acute myeloid leukemia: A single-center experience
AMERICAN JOURNAL OF HEMATOLOGY
2010; 85 (11): 877-881
The majority of patients with acute myeloid leukemia (AML) will require second-line chemotherapy for either relapsed or refractory disease. Currently, only allogeneic hematopoietic cell transplantation (HCT) offers a curative option in this setting and no preferred regimen has been established. The reported efficacy of second-line regimens is widely disparate, thus limiting informed clinical decision making. A retrospective review of 77 patients receiving therapy between 2001 and 2008 with relapsed, 42, and refractory, 35, AML was performed to determine overall response rate and survival following mitoxantrone (8 mg/m(2)/day), etoposide (100 mg/m(2)/day), and cytarabine (1,000 mg/m(2)/day) chemotherapy administered over 5 days. Among 77 patients (median age of 54 years and 64% intermediate risk karyotype) with median follow-up of 153 days, 18% achieved a complete response and 8% a morphologic leukemia-free state. Fifty-seven (74%) experienced treatment failure, 10 of whom achieved a remission after additional therapy. Median overall survival (OS) was 6.8 months. Among patients achieving a response, 50% received consolidation with allogeneic HCT, autologous HCT (5%), or consolidation chemotherapy alone (45%). A nonsignificant trend in overall response (50%, 27%, and 23.8%) and median OS (8.3, 6.8, and 4.7 months) was observed by cytogenetic stratification into favorable, intermediate, and unfavorable risk. Patients with refractory versus relapsed disease had similar overall responses (20% and 31%, P = 0.41) and median OS (5.3 and 7.6 months, P = 0.36). Despite risk stratification by the European Prognostic Index, our series demonstrates inferior rates of response and survival, illustrating the limited activity of this regimen in our cohort.
View details for DOI 10.1002/ajh.21857
View details for Web of Science ID 000283568200010
View details for PubMedID 20872554
- Metastatic Cancer Stem Cells: An Opportunity for Improving Cancer Treatment? CELL STEM CELL 2010; 6 (6): 502-503
Macrophages as mediators of tumor immunosurveillance
TRENDS IN IMMUNOLOGY
2010; 31 (6): 212-219
Tumor immunosurveillance is a well-established mechanism for regulation of tumor growth. In this regard, most studies have focused on the role of T- and NK-cells as the critical immune effector cells. However, macrophages play a major role in the recognition and clearance of foreign, aged, and damaged cells. Macrophage phagocytosis is negatively regulated via the receptor SIRPalpha upon binding to CD47, a ubiquitously expressed protein. We recently showed that CD47 is up-regulated in myeloid leukemia and migrating hematopoietic progenitors, and that the level of protein expression correlates with the ability to evade phagocytosis. These results implicate macrophages in the immunosurveillance of hematopoietic cells and leukemias. The ability of macrophages to phagocytose tumor cells might be exploited therapeutically by blocking the CD47-SIRPalpha interaction.
View details for DOI 10.1016/j.it.2010.04.001
View details for Web of Science ID 000279427000002
View details for PubMedID 20452821
Immunophenotypic features of acute myeloid leukemia with inv(3)(q21q26.2)/t(3;3)(q21;q26.2)
2010; 34 (5): 594-597
Immunophenotypic identification of myeloid specific antigens is an important diagnostic tool in the management of patients with acute myeloid leukemia (AML). These antigens allow determination of cell of origin and degree of differentiation of leukemia blasts. AML with inv(3)(q21q26.2)/t(3;3)(q21;q26.2) is a relatively rare subtype of AML. The immunophenotypic characteristics of inv(3) AML patients are somewhat limited. We identified 14 new cases of hematological disorders with increased myeloid blasts carrying inv(3)(q21q26.2)/t(3;3)(q21;q26.2). Also, we identified another 13 cases previously published in the literature, where the immunophenotype of inv(3)(q21q26.2) was documented. As a group, patients with AML with inv(3)(q21q26.2) had high levels of early myeloid (CD13, CD33, CD117 and MPO) and uncommitted markers (CD34, HLA-DR and CD56) and a high rate of monosomy 7 in addition to the inv(3)(q21q26.2). Differential karyotype and expression of certain antigens were noted in patients with de novo AML with inv(3)(q21q26.2) vs. those with inv(3)(q21q26.2)-containing blasts.
View details for DOI 10.1016/j.leukres.2009.08.029
View details for Web of Science ID 000276945300009
View details for PubMedID 19781775
CD47 Is Upregulated on Circulating Hematopoietic Stem Cells and Leukemia Cells to Avoid Phagocytosis
2009; 138 (2): 271-285
Macrophages clear pathogens and damaged or aged cells from the blood stream via phagocytosis. Cell-surface CD47 interacts with its receptor on macrophages, SIRPalpha, to inhibit phagocytosis of normal, healthy cells. We find that mobilizing cytokines and inflammatory stimuli cause CD47 to be transiently upregulated on mouse hematopoietic stem cells (HSCs) and progenitors just prior to and during their migratory phase, and that the level of CD47 on these cells determines the probability that they are engulfed in vivo. CD47 is also constitutively upregulated on mouse and human myeloid leukemias, and overexpression of CD47 on a myeloid leukemia line increases its pathogenicity by allowing it to evade phagocytosis. We conclude that CD47 upregulation is an important mechanism that provides protection to normal HSCs during inflammation-mediated mobilization, and that leukemic progenitors co-opt this ability in order to evade macrophage killing.
View details for DOI 10.1016/j.cell.2009.05.046
View details for Web of Science ID 000268277000010
View details for PubMedID 19632178
The Adhesion Molecule Esam1 Is a Novel Hematopoietic Stem Cell Marker
2009; 27 (3): 653-661
Hematopoietic stem cells (HSCs) have been highly enriched using combinations of 12-14 surface markers. Genes specifically expressed by HSCs as compared with other multipotent progenitors may yield new stem cell enrichment markers, as well as elucidate self-renewal and differentiation mechanisms. We previously reported that multiple cell surface molecules are enriched on mouse HSCs compared with more differentiated progeny. Here, we present a definitive expression profile of the cell adhesion molecule endothelial cell-selective adhesion molecule (Esam1) in hematopoietic cells using reverse transcription-quantitative polymerase chain reaction and flow cytometry studies. We found Esam1 to be highly and selectively expressed by HSCs from mouse bone marrow (BM). Esam1 was also a viable positive HSC marker in fetal, young, and aged mice, as well as in mice of several different strains. In addition, we found robust levels of Esam1 transcripts in purified human HSCs. Esam1(-/-) mice do not exhibit severe hematopoietic defects; however, Esam1(-/-) BM has a greater frequency of HSCs and fewer T cells. HSCs from Esam1(-/-) mice give rise to more granulocyte/monocytes in culture and a higher T cell:B cell ratio upon transplantation into congenic mice. These studies identify Esam1 as a novel, widely applicable HSC-selective marker and suggest that Esam1 may play roles in both HSC proliferation and lineage decisions.
View details for DOI 10.1634/stemcells.2008-0824
View details for Web of Science ID 000264706900016
View details for PubMedID 19074415
In vivo evaluation of human hematopoiesis through xenotransplantation of purified hematopoietic stem cells from umbilical cord blood
2008; 3 (12): 1932-1940
Establishment of robust xenograft models is critical to studying human hematopoiesis in a physiologic setting. Using a recently developed immunodeficient mouse strain, we have established long-term multilineage human grafts and demonstrated their serially transplantability using limited numbers of purified human hematopoietic stem cells (HSCs). Herein, we describe our protocol for the isolation of human HSC (Lin-CD34+CD38-CD90+) from umbilical cord blood (CB) as well as the xenotransplantation system that allows stable engraftment of human hematopoietic cells with as few as ten HSCs. Isolation of CB mononuclear cells requires 2-3 h, and cells may be cryopreserved before transplantation. Isolation of HSC requires approximately 2-3 h, and transplantation requires 1 h. Short-term and long-term engraftment is assessed 4-6 weeks and 10-12 weeks post-transplantation, respectively, with preparation and analysis time requiring 4-8 h at each time point.
View details for DOI 10.1038/nprot.2008.194
View details for Web of Science ID 000265781700012
View details for PubMedID 19180077
Early Mortality in Acute Promyelocytic Leukemia May Be Higher Than Previously Reported.
AMER SOC HEMATOLOGY. 2009: 420-421
View details for Web of Science ID 000272725801195
Is Time of the Essence in Adult Acute Myeloid Leukemia (AML)? Time to Blast Clearance and Time to Induction Therapy Fail to Predict Overall Survival (OS).
AMER SOC HEMATOLOGY. 2009: 646-647
View details for Web of Science ID 000272725801797