Richard A Koup

University of Maryland, Baltimore, Baltimore, Maryland, United States

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Publications (282)2417.04 Total impact

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    ABSTRACT: Anti-vector immunity may limit the immunogenicity of adenovirus vector vaccines. We tested serum from individuals immunized with adenovirus types 4 and 7 (Ad4, Ad7) vaccine or naturally infected with Ad4 for their ability to neutralize a panel of E1-deleted human and chimpanzee adenoviruses (ChAd). Small, statistically significant, increases in titer were observed to ChAd63, ChAd3, human Ad35 and Ad5. Neutralizing antibodies elicited by Ad4 infection or immunization results in a small amount of adenovirus cross-reactivity.
    Clinical and vaccine Immunology: CVI 03/2014; · 2.60 Impact Factor
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    ABSTRACT: An understanding of the antigen-specific B-cell response to the influenza hemagglutinin (HA) is critical to the development of universal influenza vaccines, but it has not been possible to examine these cells directly, because HA binds to sialic acid (SA) on most cell types. Here, we use structure-based modification of HA to isolate HA-specific B cells by flow cytometry and characterize the features of HA stem antibodies (Abs) required for their development. Incorporation of a previously described mutation (Y98F) to the receptor binding site (RBS) causes HA to bind only those B cells that express HA-specific Abs, but it does not bind non-specifically to B cells, and this mutation has no effect on binding to broadly neutralizing Abs to the RBS. To test the specificity of the Y98F mutation, we first demonstrated that previously described HA nanoparticles mediate hemagglutination and then determined that the Y98F mutation eliminates this activity. Cloning of immunoglobulin genes from HA-specific B cells isolated from a single human subject demonstrates that vaccination with H5N1 can elicit B cells expressing stem mAbs. Although these mAbs mostly originated from the IGHV1-69 germline, a reasonable proportion derived from other genes. Analysis of stem Abs provides insight into the maturation pathways of IGVH1-69-derived stem Abs. Furthermore, this analysis shows that multiple non-IGHV1-69 stem Abs with similar neutralizing breadth develop after vaccination in humans, suggesting that the HA stem response can be elicited in individuals with non-stem reactive IGHV1-69 alleles.IMPORTANCE Universal influenza vaccines would improve immune protection against infection and facilitate vaccine manufacturing and distribution. Flu vaccines stimulate B cells in the blood to produce antibodies that neutralize the virus. These antibodies target a protein on the surface of the virus called HA. Flu vaccines must be reformulated annually, because these antibodies are mostly specific to the viral strains used in the vaccine. But humans can produce broadly neutralizing antibodies. We sought to isolate B cells whose genes encode influenza antibodies from a patient vaccinated for avian influenza. To do so, we modified HA so it would bind only the desired cells. Sequencing the antibody genes of cells marked by this probe proved that the patient produced broadly neutralizing antibodies in response to the vaccine. Many sequences obtained had not been observed before. There are more ways to generate broadly neutralizing antibodies for influenza than previously thought.
    Journal of Virology 02/2014; · 5.08 Impact Factor
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    ABSTRACT: The interaction between follicular T helper cells (TFH) and B cells in the lymph nodes and spleen has a major impact on the development of antigen-specific B cell responses during infection or vaccination. Recent studies described a functional equivalent of these cells among circulating CD4 T cells, referred to as peripheral TFH cells. Here, we characterize the phenotype and in vitro B cell helper activity of peripheral TFH populations, as well as the effect of HIV infection on these populations. In co-culture experiments we confirmed CXCR5+ cells from HIV-uninfected donors provide help to B cells and more specifically, we identified a CCR7(high)CXCR5(high)CCR6(high)PD-1(high) CD4 T cell population that secretes IL-21 and enhances isotype-switched immunoglobulin production. This population is significantly decreased in treatment-naïve, HIV-infected individuals and can be recovered after anti-retroviral therapy. We found impaired immunoglobulin production in co-cultures from HIV-infected individuals and found no correlation between the frequency of peripheral TFH cells and memory B cells, or with neutralization activity in untreated HIV infection in our cohort. Furthermore, we found that within the peripheral TFH population, the expression level of TFH-associated genes more closely resembles a memory, non-TFH population, as opposed to a TFH population. Overall, our data identify a heterogeneous population of circulating CD4 T cells that provides in vitro help to B cells, and challenges the origin of these cells as memory TFH cells.
    PLoS Pathogens 01/2014; 10(1):e1003853. · 8.14 Impact Factor
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    ABSTRACT: A major challenge for the development of a highly effective AIDS vaccine is the identification of mechanisms of protective immunity. To address this question, we used a nonhuman primate challenge model with simian immunodeficiency virus (SIV). We show that antibodies to the SIV envelope are necessary and sufficient to prevent infection. Moreover, sequencing of viruses from breakthrough infections revealed selective pressure against neutralization-sensitive viruses; we identified a two-amino-acid signature that alters antigenicity and confers neutralization resistance. A similar signature confers resistance of human immunodeficiency virus (HIV)-1 to neutralization by monoclonal antibodies against variable regions 1 and 2 (V1V2), suggesting that SIV and HIV share a fundamental mechanism of immune escape from vaccine-elicited or naturally elicited antibodies. These analyses provide insight into the limited efficacy seen in HIV vaccine trials.
    Nature 12/2013; · 38.60 Impact Factor
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    ABSTRACT: Estaquier et al. provide commentary on our paper that elucidated the mechanism by which HIV-1 causes cell death in activated CD4 T lymphocytes. We showed that proviral DNA integration triggers DNA-PK dependent death signaling, leading to p53 phosphorylation and cell demise (Cooper A et al. Nature 498:376-379, 2013). They have raised several hypothetical points that we further clarify here.
    Retrovirology 12/2013; 10(1):150. · 5.66 Impact Factor
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    ABSTRACT: Vaccines constructed from rare-serotype recombinant adenovirus vectors (rAd) such as rAd serotype 28 (rAd28) and rAd35 are currently being explored as alternatives to rAd5-based vaccines because they circumvent the problems with pre-existing immunity that complicate the effectiveness of rAd5 vaccines. However, previous work has demonstrated that the immunogenicity of rAd28 and rAd35 is substantially lower than rAd5. Here we show that rAd28 and rAd35 increase apoptosis of antigen presenting cells (APCs), such as monocytes, relative to rAd5 and mock infected controls. APCs undergoing apoptosis showed an increased loss of vector-insert expression. Loss of vector-insert expression correlated with activation of NK cells, which resulted in apoptosis of co-cultured monocytes. Finally, we show that activation of NK cells is dependent on IFNα which is produced by exposure to rAd28 or rAd35, but not to rAd5. Taken together, these data demonstrate that IFNα-induced activation of NK cells leads to increased monocyte apoptosis and subsequent vector-insert loss. This may be a possible mechanism that results in reduced immunogenicity of rAd28 and rAd35-based vectors.
    Vaccine 12/2013; · 3.77 Impact Factor
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    ABSTRACT: Defining the characteristics of HIV-specific CD8+ T cell responses that lead to viral control is crucial for vaccine development. We evaluated the differential impact of magnitude, polyfunctional capacity and specificity of the CD8+ response at approximately 6 months post infection on viral set point at 12 months in a cohort of HIV-infected individuals. High frequencies of Gag and Nef responses endowed with four functions were the best predictors of a low viral set point.
    Journal of Virology 11/2013; · 5.08 Impact Factor
  • Kapil K Saharia, Richard A Koup
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    ABSTRACT: During HIV infection, the timing of opportunistic infections is not always associated with severity of CD4 T cell depletion, and different opportunistic pathogens reactivate at different CD4 T cell thresholds. Here, we examine how differences in the phenotype and function of pathogen-specific CD4 T cells influence susceptibility to HIV infection. By focusing on three common opportunistic infections (Mycobacterium tuberculosis, human papillomavirus, and cytomegalovirus), we investigate how differential depletion of pathogen-specific CD4 T cells impacts the natural history of these pathogens in HIV infection. A broader understanding of this relationship can better inform treatment strategies against copathogens.
    Cell 10/2013; 155(3):505-14. · 31.96 Impact Factor
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    ABSTRACT: Background A safe and effective vaccine for the prevention of human immunodeficiency virus type 1 (HIV-1) infection is a global priority. We tested the efficacy of a DNA prime-recombinant adenovirus type 5 boost (DNA/rAd5) vaccine regimen in persons at increased risk for HIV-1 infection in the United States. Methods At 21 sites, we randomly assigned 2504 men or transgender women who have sex with men to receive the DNA/rAd5 vaccine (1253 participants) or placebo (1251 participants). We assessed HIV-1 acquisition from week 28 through month 24 (termed week 28+ infection), viral-load set point (mean plasma HIV-1 RNA level 10 to 20 weeks after diagnosis), and safety. The 6-plasmid DNA vaccine (expressing clade B Gag, Pol, and Nef and Env proteins from clades A, B, and C) was administered at weeks 0, 4, and 8. The rAd5 vector boost (expressing clade B Gag-Pol fusion protein and Env glycoproteins from clades A, B, and C) was administered at week 24. Results In April 2013, the data and safety monitoring board recommended halting vaccinations for lack of efficacy. The primary analysis showed that week 28+ infection had been diagnosed in 27 participants in the vaccine group and 21 in the placebo group (vaccine efficacy, -25.0%; 95% confidence interval, -121.2 to 29.3; P=0.44), with mean viral-load set points of 4.46 and 4.47 HIV-1 RNA log10 copies per milliliter, respectively. Analysis of all infections during the study period (41 in the vaccine group and 31 in the placebo group) also showed lack of vaccine efficacy (P=0.28). The vaccine regimen had an acceptable side-effect profile. Conclusions The DNA/rAd5 vaccine regimen did not reduce either the rate of HIV-1 acquisition or the viral-load set point in the population studied. (Funded by the National Institute of Allergy and Infectious Diseases; number, NCT00865566 .).
    New England Journal of Medicine 10/2013; · 51.66 Impact Factor
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    ABSTRACT: Elite controllers suppress HIV viremia to below the limit of detection in the absence of antiretroviral therapy (ART). However, precise frequencies of CD4(+) T cells carrying replication-competent HIV and/or the dynamics of the infectious viral reservoirs in response to initiation and discontinuation of ART in elite controllers are unknown. We show that the size of the pool of CD4(+) T cells harboring infectious HIV diminished significantly following initiation of ART and rebounded to baseline upon cessation of therapy. Our data provide compelling evidence that persistent viral replication occurs in untreated elite controllers even in the absence of detectable plasma viremia.
    The Journal of Infectious Diseases 07/2013; · 5.85 Impact Factor
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    ABSTRACT: Programmed Death-1 (PD-1) expression by human/simian immunodeficiency virus (HIV/SIV)-specific CD8 T cells has been associated with defective cytokine production and reduced in vitro proliferation capacity. However, the cellular mechanisms that sustain PD-1(high) virus-specific CD8 T cell responses during chronic infection are unknown. Here, we show that the PD-1(high) phenotype is associated with accelerated in vivo CD8 T cell turnover in SIV-infected rhesus macaques, especially within the SIV-specific CD8 T cell pool. Mathematical modeling of BrdU labeling dynamics demonstrated a significantly increased generation rate of PD-1(high) compared to PD-1(low) CD8 T cells in all memory compartments. Simultaneous analysis of Ki67 and BrdU kinetics revealed a complex in vivo turnover profile, whereby only a small fraction of PD-1(high) cells, but virtually all PD-1(low) cells, returned to rest after activation. Similar kinetics operated in both chronic and acute SIV infection. Our data suggest that the persistence of PD-1(high) SIV-specific CD8 T cells in chronic infection is maintained in vivo by a mechanism involving high production coupled to high disappearance.
    Journal of Virology 07/2013; · 5.08 Impact Factor
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    ABSTRACT: We present an integrated analytical method for analyzing peptide microarray antibody binding data, from normalization through subject-specific positivity calls and data integration and visualization. Current techniques for the normalization of such data sets do not account for non-specific binding activity. A novel normalization technique based on peptide sequence information quickly and effectively reduced systematic biases. We also employed a sliding mean window technique that borrows strength from peptides sharing similar sequences, resulting in reduced signal variability. A smoothed signal aided in the detection of weak antibody binding hotspots. A new principled FDR method of setting positivity thresholds struck a balance between sensitivity and specificity. In addition, we demonstrate the utility and importance of using baseline control measurements when making subject-specific positivity calls. Data sets from two human clinical trials of candidate HIV-1 vaccines were used to validate the effectiveness of our overall computational framework.
    Journal of immunological methods 06/2013; · 2.35 Impact Factor
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    ABSTRACT: Human immunodeficiency virus-1 (HIV-1) has infected more than 60 million people and caused nearly 30 million deaths worldwide, ultimately the consequence of cytolytic infection of CD4(+) T cells. In humans and in macaque models, most of these cells contain viral DNA and are rapidly eliminated at the peak of viraemia, yet the mechanism by which HIV-1 induces helper T-cell death has not been defined. Here we show that virus-induced cell killing is triggered by viral integration. Infection by wild-type HIV-1, but not an integrase-deficient mutant, induced the death of activated primary CD4 lymphocytes. Similarly, raltegravir, a pharmacologic integrase inhibitor, abolished HIV-1-induced cell killing both in cell culture and in CD4(+) T cells from acutely infected subjects. The mechanism of killing during viral integration involved the activation of DNA-dependent protein kinase (DNA-PK), a central integrator of the DNA damage response, which caused phosphorylation of p53 and histone H2AX. Pharmacological inhibition of DNA-PK abolished cell death during HIV-1 infection in vitro, suggesting that processes which reduce DNA-PK activation in CD4 cells could facilitate the formation of latently infected cells that give rise to reservoirs in vivo. We propose that activation of DNA-PK during viral integration has a central role in CD4(+) T-cell depletion, raising the possibility that integrase inhibitors and interventions directed towards DNA-PK may improve T-cell survival and immune function in infected individuals.
    Nature 06/2013; · 38.60 Impact Factor
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    ABSTRACT: Advances in HIV-1 vaccine clinical trials and preclinical research indicate that the virus envelope glycoproteins (Env) are likely to be an essential component of a prophylactic vaccine. Efficient Ag uptake and presentation by dendritic cells (DCs) is important for strong CD4(+) Th cell responses and the development of effective humoral immune responses. In this study, we examined the capacity of distinct primary human DC subsets to internalize and present recombinant Env to CD4(+) T cells. Consistent with their specific receptor expression, skin DCs bound and internalized Env via C-type lectin receptors, whereas blood DC subsets, including CD1c(+) myeloid DCs, CD123(+) plasmacytoid DCs (PDCs), and CD141(+) DCs exhibited a restricted repertoire of C-type lectin receptors and relied on CD4 for uptake of Env. Despite a generally poor capacity for Ag uptake compared with myeloid DCs, the high expression of CD4 on PDCs allowed them to bind and internalize Env very efficiently. CD4-mediated uptake delivered Env to EEA1(+) endosomes that progressed to Lamp1(+) and MHC class II(+) lysosomes where internalized Env was degraded rapidly. Finally, all three blood DC subsets were able to internalize an Env-CMV pp65 fusion protein via CD4 and stimulate pp65-specific CD4(+) T cells. Thus, in the in vitro systems described in this paper, CD4-mediated uptake of Env is a functional pathway leading to Ag presentation, and this may therefore be a mechanism used by blood DCs, including PDCs, for generating immune responses to Env-based vaccines.
    The Journal of Immunology 05/2013; · 5.52 Impact Factor
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    ABSTRACT: Ebola virus (EBOV) infections are characterized by deficient T lymphocyte responses, T lymphocyte apoptosis and lymphopenia, in the absence of direct infection of lymphocytes. In contrast, dendritic cells (DC) are infected but fail to mature appropriately, thereby impairing the T cell response. We investigated the contribution of EBOV proteins in modulating DC maturation by generating recombinant viruses expressing enhanced green fluorescent protein and carrying mutations affecting several potentially immunomodulating domains. These included envelope glycoprotein (GP) domains as well as innate response antagonist domains (IRADs) previously identified in the VP24 and VP35 proteins. GP expressed by an unrelated vector, but not the wild-type EBOV, was found to strongly induce DC maturation, and infections with recombinant EBOV carrying mutations disabling GP functional domains did not restore DC maturation. In contrast, each of the viruses carrying mutations disabling any IRAD in VP35 induced a dramatic upregulation of DC maturation markers. This was dependent on infection, but not interaction with GP. Disabling of IRADs also resulted in a several hundred fold increase in secretion of cytokines and chemokines. Furthermore, these mutations induced formation of homotypic DC clusters, which represent close correlates of their maturation, and presumably facilitate transfer of antigen from migratory DC to lymph node DC. Thus, an individual IRAD is insufficient to suppress DC maturation; rather, the suppression of DC maturation and the "immune paralysis" observed during EBOV infections results from a cooperative effect of two or more individual IRADs.
    Journal of Virology 04/2013; · 5.08 Impact Factor
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    ABSTRACT: Background. Correlates of immune protection in patients with HIV-associated cryptococcal meningitis (CM) are poorly defined. A clearer understanding of these immune responses is essential to inform rational development of immunotherapies.Methods. Cryptococcal-specific peripheral CD4 T-cell responses were measured in 44 patients with HIV-associated CM at baseline and during follow-up. Responses were assessed following ex-vivo cryptococcal mannoprotein stimulation using 13-color flow-cytometric analysis. The relationships between cryptococcal-specific CD4 T-cell responses, clinical parameters at presentation, and outcome were investigated.Results. Cryptococcal-specific CD4 T-cell responses were characterized by the production of MIP1α, IFNγ and TNFα. Conversely, minimal IL-4 and IL-17 production was detected. Patients surviving to 2-weeks had significantly different functional CD4 T-cell responses compared to those who died. Patients with a response predominantly consisting of IFNγ or TNFα production had a 2-week mortality of 0% (0/20) vs 25% (6/24) in those without (p=0.025). Such patients also had lower fungal burdens (10,400 vs 390,000&emsp14;cfu/ml, p<0.001), higher CSF lymphocyte counts (122 vs 8 cells/μL, p<0.001) and a trend towards faster rates of clearance of infection.Conclusions. The phenotype of the peripheral CD4 T-cell response to Cryptococcus was associated with disease severity and outcome in HIV-associated CM. IFNγ/TNFα predominant responses were associated with survival.
    The Journal of Infectious Diseases 03/2013; · 5.85 Impact Factor
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    ABSTRACT: Highly multiplexed, single cell technologies reveal important heterogeneity within cell populations. Recently, technologies to simultaneously measure expression of 96 (or more) genes from a single cell have been developed for immunologic monitoring. Here, we report a rigorous, optimized, quantitative methodology for using this technology. Specifically: we describe a unique primer/probe qualification method necessary for quantitative results; we show that primers do not compete in highly multiplexed amplifications; we define the limit of detection for this assay as a single mRNA transcript; and, we show that the technical reproducibility of the system is very high. We illustrate two disparate applications of the platform: a "bulk" approach that measures expression patterns from 100 cells at a time in high throughput to define gene signatures, and a single-cell approach to define the coordinate expression patterns of multiple genes and reveal unique subsets of cells.
    Journal of immunological methods 03/2013; · 2.35 Impact Factor
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    ABSTRACT: Background. The licensing of Zostavax has demonstrated that therapeutic vaccination can help control chronic viral infection. Unfortunately, HIV therapeutic vaccine trials have shown only marginal efficacy.Methods. Seventeen HIV-infected individuals with viral loads <50 copies/ml and CD4 T cell counts >350 cells/µl were randomized to the vaccine or placebo arm. Vaccine recipients received three intramuscular injections of HIV DNA (4&emsp14;mg) coding for clade B Gag, Pol, Nef, and clade A, B, C Env, followed by a replication-deficient Ad5 boost (1010 PFU) encoding all DNA vaccine antigens, except Nef. Humoral, total T cell and CD8 cytotoxic T lymphocyte (CTL) responses were studied pre- and post-vaccination. Single copy viral loads and latently infected CD4 T cell frequencies were determined. VRC 101 is a double-blind trial registered with (NCT00270465).Results. Vaccination was safe and well tolerated. Significantly stronger HIV-specific T cell responses against Gag, Pol, and Env, with increased polyfunctionality and a broadened epitope-specific CTL repertoire, were observed post-vaccination. No changes in single copy viral load or the frequency of latent infection were observed.Conclusions. Vaccination of individuals with existing HIV-specific immunity improved the magnitude, breadth and polyfunctionality of HIV-specific memory T cell responses, but did not impact markers of viral control.
    The Journal of Infectious Diseases 03/2013; · 5.85 Impact Factor
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    ABSTRACT: Recombinant adenoviral vectors (rAds) are the most potent recombinant vaccines for eliciting CD8(+) T cell-mediated immunity in humans; however, prior exposure from natural adenoviral infection can decrease such responses. In this study we show low seroreactivity in humans against simian- (sAd11, sAd16) or chimpanzee-derived (chAd3, chAd63) compared with human-derived (rAd5, rAd28, rAd35) vectors across multiple geographic regions. We then compared the magnitude, quality, phenotype, and protective capacity of CD8(+) T cell responses in mice vaccinated with rAds encoding SIV Gag. Using a dose range (1 × 10(7)-10(9) particle units), we defined a hierarchy among rAd vectors based on the magnitude and protective capacity of CD8(+) T cell responses, from most to least, as: rAd5 and chAd3, rAd28 and sAd11, chAd63, sAd16, and rAd35. Selection of rAd vector or dose could modulate the proportion and/or frequency of IFN-γ(+)TNF-α(+)IL-2(+) and KLRG1(+)CD127(-)CD8(+) T cells, but strikingly ∼30-80% of memory CD8(+) T cells coexpressed CD127 and KLRG1. To further optimize CD8(+) T cell responses, we assessed rAds as part of prime-boost regimens. Mice primed with rAds and boosted with NYVAC generated Gag-specific responses that approached ∼60% of total CD8(+) T cells at peak. Alternatively, priming with DNA or rAd28 and boosting with rAd5 or chAd3 induced robust and equivalent CD8(+) T cell responses compared with prime or boost alone. Collectively, these data provide the immunologic basis for using specific rAd vectors alone or as part of prime-boost regimens to induce CD8(+) T cells for rapid effector function or robust long-term memory, respectively.
    The Journal of Immunology 02/2013; · 5.52 Impact Factor
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    ABSTRACT: OBJECTIVES:: To study whether in vivo recruitment of dendritic cells (DCs) in response to antigen administration in the skin is altered during HIV-1 infection. DESIGN:: Skin punch biopsies were collected from HIV-1+ as well as seronegative individuals at 48 hours post intradermal injection of inactivated antigens of mumps virus, Candida albicans or purified protein derivate (PPD) from Mycobacterium tuberculosis. METHODS:: Cryosections were analyzed by in situ staining and computerized imaging. RESULTS:: Control skin biopsies showed that there was no difference in the number of skin-resident DCs between seronegative and HIV-1+ individuals. Antigen injection resulted in substantial infiltration of DCs compared to the frequencies found in donor-matched control skin. In HIV-1+ individuals, CD123+/CD303+ plasmacytoid DCs and CD11c+ myeloid DCs, including the CD141+ cross-presenting subset, were recruited at lower levels compared to healthy controls in response to PPD and mumps but not C. albicans. The level of DC recruitment correlated with the frequencies of T cells infiltrating the respective antigen sites. Ki67+ cycling T cells at the injection sites were much more frequent in response to each of the antigens in the HIV-1+ individuals, including those with AIDS, compared to healthy controls. CONCLUSIONS:: Multiple DC subsets infiltrate the dermis in response to antigen exposure. There was no obvious depletion or deficiency in mobilization of DCs in response to antigen skin tests during chronic HIV-1 infection. Instead, the levels of antigen-specific memory T cells that accumulate at the antigen site may determine the level of DC infiltration.
    AIDS (London, England) 01/2013; · 4.91 Impact Factor

Publication Stats

25k Citations
2,417.04 Total Impact Points


  • 2013
    • University of Maryland, Baltimore
      Baltimore, Maryland, United States
    • St George's, University of London
      • Center for Infection and Immunity Research
      London, ENG, United Kingdom
  • 2005–2013
    • Karolinska Institutet
      • Department of Medicine, Huddinge
      Stockholm, Stockholm, Sweden
  • 2002–2013
    • National Institute of Allergy and Infectious Diseases
      • Laboratory of Immunoregulation
      Maryland, United States
  • 2012
    • Vaccine & Gene Therapy Institute of Florida
      Port St. Lucie, Florida, United States
    • Ludwig-Maximilian-University of Munich
      • Department of Infectious Diseases and Tropical Medicine
      München, Bavaria, Germany
    • Hospital Universitario Virgen del Rocío
      • Infectious Diseases Service
      Hispalis, Andalusia, Spain
  • 2008–2012
    • University of Oxford
      • • Weatherall Institute of Molecular Medicine
      • • MRC Human Immunology Unit
      Oxford, ENG, United Kingdom
  • 2004–2012
    • National Institute of Allergy and Infectious Disease
      Maryland, United States
    • University Hospital of Lausanne
      Lausanne, Vaud, Switzerland
  • 2001–2012
    • National Institutes of Health
      • • Laboratory of Immunology
      • • Section on Cellular Neurobiology
      Bethesda, MD, United States
  • 1998–2012
    • The Rockefeller University
      New York City, New York, United States
  • 2011
    • McGill University Health Centre
      Montréal, Quebec, Canada
  • 2010–2011
    • United States Army Medical Research Institute for Infectious Diseases
      Maryland, United States
  • 2009–2010
    • National Institute for Communicable Diseases
      Johannesburg, Gauteng, South Africa
    • University of Cape Town
      • Faculty of Health Sciences
      Cape Town, Province of the Western Cape, South Africa
  • 2006–2009
    • Sun Yat-Sen University
      • Zhongshan School of Medicine
      Shengcheng, Guangdong, China
    • Fred Hutchinson Cancer Research Center
      • Statistical Center for HIV/AIDS Research and Prevention
      Seattle, Washington, United States
  • 2007
    • National Heart, Lung, and Blood Institute
      • Hematology Branch
      Bethesda, MD, United States
  • 1997–2006
    • Massachusetts General Hospital
      • Division of Infectious Diseases
      Boston, Massachusetts, United States
  • 2003
    • NCI-Frederick
      Maryland, United States
    • National Eye Institute
      Maryland, United States
  • 1998–2002
    • University of Texas Southwestern Medical Center
      • • Department of Internal Medicine
      • • Department of Pathology
      • • Medical School
      Dallas, TX, United States
  • 2000
    • Harvard University
      • Center for AIDS Research
      Cambridge, MA, United States
  • 1999
    • University of Amsterdam
      • Faculty of Medicine AMC
      Amsterdam, North Holland, Netherlands
  • 1996–1998
    • Progenics Pharmaceuticals, Inc.
      Tarrytown, New York, United States
  • 1994
    • New York University
      • Medicine
      New York City, NY, United States
  • 1989–1992
    • University of Massachusetts Medical School
      • Department of Pediatrics
      Worcester, MA, United States