J Pappo

EpiVax, Inc., Providence, Rhode Island, United States

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Publications (37)162.93 Total impact

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    ABSTRACT: Computational methods accelerate vaccine development by rapid identification of potential vaccine candidates. We screened the Helicobacter pylori J99 and 26695 genomes for T-cell epitopes using the epitope mapping algorithm EpiMatrix and selected 150 sequences for experimental validation in a pre-clinical mouse model. Because strains of H. pylori that infect humans do not generally infect mice, and the sequence of the mouse-adapted "Sydney" strain (SS1) is not publicly available, we used targeted PCR to confirm that the epitopes we computationally predicted from the human H. pylori isolates J99 and 26695 are conserved in SS1. Epitopes conserved in SS1 were further analyzed for binding to MHC in vitro and for antigenicity in infected mice to select candidates for an epitope-based vaccine.
    Full-text · Article · May 2008 · Human vaccines
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    ABSTRACT: In recent years, Abs have been considered a correlate rather than an effector of resistance against Helicobacter pylori infection. However, it is still poorly understood to what extent Ab production correlates with gastric immunopathology. Here we report that Abs not only are dispensable for protection, but they are detrimental to elimination of the bacteria and appear to impair gastric inflammatory responses. We found that the initial colonization with H. pylori bacteria was normal in the B cell-deficient (microMT) mice, whereas at later times (>8 wk) most of the bacteria were cleared, concomitant with the development of severe gastritis. In contrast, wild-type (WT) mice exhibited extensive bacterial colonization and only mild gastric inflammation, even at 16 wk after inoculation. Oral immunizations with H. pylori lysate and cholera toxin adjuvant stimulated comparable levels of protection in microMT and WT mice. The level of protection in both strains correlated well with the severity of the postimmunization gastritis. Thus, T cells were responsible for the gastritis, whereas Abs, including potentially host cell cross-reactive Abs, were not involved in causing the gastritis. The T cells in micro MT and WT mice produced high and comparable levels of IFN-gamma to recall Ag at 2 and after 8 wk, whereas IL-4 was detected after 8 wk only, indicating that Th1 activity dominated the early phase of protection, whereas later a mixed Th1 and Th2 activity was seen.
    Full-text · Article · Apr 2004 · The Journal of Immunology
  • Trevor J. Trust · Richard A. Alm · Jacques Pappo
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    ABSTRACT: Helicobacter pylori induces chronic superficial gastritis which in some patients may lead to peptic ulcer disease, while a subset of infected individuals develop gastric cancer or gastric lymphoma. Consensus guidelines recommend that patients with a known H. pylori infection receive eradication treatment. Successful treatment requires that antibiotics be used in combination with acid suppressants or bismuth, and although the list of effective antibacterials is short, regimens such as amoxicillin and clarithromycin or metronidazole and clarithromycin with the proton pump inhibitor omeprazole have achieved eradication rates of ∼90% in trials. However lower eradication rates are probably more common, and strains resistant to clarithromycin or metronidazole, or both, are of concern. Stable amoxycillin resistance has also been reported. Efforts are underway to discover and develop novel therapeutics, both H. pylori specific antibacterial drugs and a therapeutic vaccine. Impetus to these efforts has been provided by the availability of the genome sequences of two different H. pylori isolates. In the case of drug discovery, a genome-based strategy facilitates the expeditious selection of novel lethal targets not used by today's antibiotics, providing the opportunity to identify novel classes of antibacterials. Vaccine discovery and development has largely focused on a small number of antigens selected by conventional means. Recent reports that mucosal and serum antibody titers do not appear to be essential for protection against H. pylori in murine models suggest that that a wider range of H. pylori proteins than those previously considered may be able to induce protective immunity. Progress towards development of new H. pylori therapeutics is discussed. Copyright © 2001 Taylor and Francis Ltd.
    No preview · Article · Nov 2003
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    ABSTRACT: The regulatory roles of Th1 and Th2 cells in immune protection against Helicobacter infection are not clearly understood. In this study, we report that a primary H. pylori infection can be established in the absence of IL-12 or IFN-gamma. However, IFN-gamma, but not IL-12, was involved in the development of gastritis because IFN-gamma(-/-) (GKO) mice exhibited significantly less inflammation as compared with IL-12(-/-) or wild-type (WT) mice. Both IL-12(-/-) and GKO mice failed to develop protection following oral immunization with H. pylori lysate and cholera toxin adjuvant. By contrast, Th2-deficient, IL-4(-/-), and WT mice were equally well protected. Mucosal immunization in the presence of coadministered rIL-12 in WT mice increased Ag-specific IFN-gamma-producing T cells by 5-fold and gave an additional 4-fold reduction in colonizing bacteria, confirming a key role of Th1 cells in protection. Importantly, only protected IL-4(-/-) and WT mice demonstrated substantial influx of CD4(+) T cells in the gastric mucosa. The extent of inflammation in challenged IL-12(-/-) and GKO mice was much reduced compared with that in WT mice, indicating that IFN-gamma/Th1 cells also play a major role in postimmunization gastritis. Of note, postimmunization gastritis in IL-4(-/-) mice was significantly milder than WT mice, despite a similar level of protection, indicating that immune protection is not directly linked to the degree of gastric inflammation. Only protected mice had T cells that produced high levels of IFN-gamma to recall Ag, whereas both protected and unprotected mice produced high levels of IL-13. We conclude that IL-12 and Th1 responses are crucial for H. pylori-specific protective immunity.
    Full-text · Article · Jan 2003 · The Journal of Immunology
  • Peter B. Ernst · Jacques Pappo
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    ABSTRACT: Approximately 50% of humanity is infected with Helicobacter pylori. This lifelong infection elicits a marked host response, including a robust gastric IgA response. However, natural infection fails to yield protective immunity. Rather than providing protection, the chronic inflammatory response associated with natural infection can contribute to tissue damage and the pathogenesis of gastroduodenal disease, including atrophic gastritis, peptic ulcer, and gastric cancer. These immune responses are attributed to a subset of helper T cells, so-called Th1 cells, that enhance cell-mediated immunity and induce damage to the gastric epithelium. Thus, it is desirable to have effective vaccines that could prevent and cure infection and that may modify the host response in a manner that prevents immune-mediated disease. Using animal models as a tool to understand the immunobiology of Helicobacter infections, several investigators have shown that effective vaccines can be developed. Thus, prophylactic and even therapeutic vaccines have been described in various animal models. The basis for the effectiveness of these vaccines appears related to their ability to alter the gastric immune response, from a homogeneous Th1 response to a mixed Th1 and Th2 response. Interestingly, immunity can occur in the absence of B cells, suggesting that novel IgA-independent mechanisms exist that confer protection against a luminal infection. Thus, H. pylori infection provides a model with which new mechanisms of immunological protection can be identified and applied to other mucosal infections.
    No preview · Article · Sep 2001 · Acta Odontologica Scandinavica
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    ABSTRACT: The majority of humans infected with Helicobacter pylori maintain a lifelong infection with strains bearing the cag pathogenicity island (PAI). H. pylori inhibits T cell responses and evades immunity so the mechanism by which infection impairs responsiveness was investigated. H. pylori caused apoptotic T cell death, whereas Campylobacter jejuni did not. The induction of apoptosis by H. pylori was blocked by an anti-Fas Ab (ZB4) or a caspase 8 inhibitor. In addition, a T cell line with the Fas rendered nonfunctional by a frame shift mutation was resistant to H. pylori-induced death. H. pylori strains bearing the cag PAI preferentially induced the expression of Fas ligand (FasL) on T cells and T cell death, whereas isogenic mutants lacking these genes did not. Inhibiting protein synthesis blocked FasL expression and apoptosis of T cells. Preventing the cleavage of FasL with a metalloproteinase inhibitor increased H. pylori-mediated killing. Thus, H. pylori induced apoptosis in Fas-bearing T cells through the induction of FasL expression. Moreover, this effect was linked to bacterial products encoded by the cag PAI, suggesting that persistent infection with this strain may be favored through the negative selection of T cells encountering specific H. pylori Ags.
    Full-text · Article · Aug 2001 · The Journal of Immunology
  • T J Trust · R A Alm · J Pappo
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    ABSTRACT: Helicobacter pylori induces chronic superficial gastritis which in some patients may lead to peptic ulcer disease, while a subset of infected individuals develop gastric cancer or gastric lymphoma. Consensus guidelines recommend that patients with a known H. pylori infection receive eradication treatment. Successful treatment requires that antibiotics be used in combination with acid suppressants or bismuth, and although the list of effective antibacterials is short, regimens such as amoxicillin and clarithromycin or metronidazole and clarithromycin with the proton pump inhibitor omeprazole have achieved eradication rates of approximately 90% in trials. However lower eradication rates are probably more common, and strains resistant to clarithromycin or metronidazole, or both, are of concern. Stable amoxycillin resistance has also been reported. Efforts are underway to discover and develop novel therapeutics, both H. pylori specific antibacterial drugs and a therapeutic vaccine. Impetus to these efforts has been provided by the availability of the genome sequences of two different H. pylori isolates. In the case of drug discovery, a genome-based strategy facilitates the expeditious selection of novel lethal targets not used by today's antibiotics, providing the opportunity to identify novel classes of antibacterials. Vaccine discovery and development has largely focused on a small number of antigens selected by conventional means. Recent reports that mucosal and serum antibody titers do not appear to be essential for protection against H. pylori in murine models suggest that that a wider range of H. pylori proteins than those previously considered may be able to induce protective immunity. Progress towards development of new H. pylori therapeutics is discussed.
    No preview · Article · Feb 2001 · The European journal of surgery. Supplement.: = Acta chirurgica. Supplement
  • P B Ernst · Jacques Pappo
    [Show abstract] [Hide abstract]
    ABSTRACT: Approximately 50% of humanity is infected with Helicobacter pylori. Normally, this is a life-long infection indicating that the host response to natural infection fails to yield protective immunity. Moreover, the chronic inflammatory response associated with this infection can contribute to tissue damage and the pathogenesis of gastroduodenal disease including atrophic gastritis, peptic ulcer and gastric cancer. These damaging immune responses are attributed to a subset of helper T cells, so-called Th1 cells, that enhance cell-mediated immunity and induce damage to the gastric epithelium. Thus, it is desirable to have effective vaccines that could prevent and cure infection or at least, modify the host response in a manner that prevents immune-mediated disease. Using animal models as a tool to understand the immunobiology of Helicobacter infections, several investigators have shown that effective vaccines can be developed. Thus, prophylactic and even therapeutic vaccines have been described in various animal models. The basis for the effectiveness of these vaccines seems to be found in their ability to alter the gastric immune response, perhaps away from a homogeneous Th1 response towards a mixed Th1 and Th2 response. Using these encouraging approaches, vaccines are being developed for use in humans for the treatment and prevention of H. pylori infection and the gastroduodenal diseases associated with this infection.
    No preview · Article · Nov 2000 · Current Pharmaceutical Design
  • Alexander Ibraghimov · Jacques Pappo
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    ABSTRACT: Helicobacter pylori infects about half of the world's population. H. pylori elicits marked immune responses, but the infection is commonly life-long. Some infected individuals remain asymptomatic, while others develop significant gastroduodenal disease. We review the underlying host immune response to H. pylori which programs for persistence and evolution of gastroduodenal disease.
    No preview · Article · Aug 2000 · Microbes and Infection

  • No preview · Article · Apr 2000 · Gastroenterology
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    P Sutton · J Wilson · R Genta · D Torrey · A Savinainen · J Pappo · A Lee
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    ABSTRACT: The importance of host factors in helicobacter induced gastritis has been shown in animal models. Infection of most mouse strains with Helicobacter felis results in a functional atrophic gastritis, while other strains remain gastritis free. To investigate these host factors further by using genetic crosses of responder and non-responder mice. F(1) hybrids of the non-responder CBA/Ca strain and three strains of mice known to develop H felis induced gastritis were infected for three months with H felis. Gastritis was assessed by histopathology and serum antibody responses by ELISA. Infection of CBA/Ca mice and F(1) hybrids induced little or no gastritis. Analyses of the antibody responses in these mice revealed virtually undetectable anti-helicobacter antibody levels despite colonisation with high numbers of H felis. In contrast, infection of H felis responsive strains induced gastritis and a significant humoral immune response. The non-responsiveness of CBA/Ca mice to H felis infection is dominantly inherited. The lack of gastritis in CBA mice and their offspring is probably due to active suppression of the immune response normally mounted against H felis. Investigation of these mechanisms will provide important insights relevant to induction of gastric atrophy and cancer in humans.
    Full-text · Article · Oct 1999 · Gut
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    ABSTRACT: The role of major histocompatibility complex (MHC) class I- and class II-restricted functions in Helicobacter pylori infection and immunity upon oral immunization was examined in vivo. Experimental challenge with H. pylori SS1 resulted in significantly greater (P </= 0.025) colonization of MHC class I and class II mutant mice than C57BL/6 wild-type mice. Oral immunization with H. pylori whole-cell lysates and cholera toxin adjuvant significantly reduced the magnitude of H. pylori infection in C57BL/6 wild-type (P = 0.0083) and MHC class I knockout mice (P = 0.0048), but it had no effect on the H. pylori infection level in MHC class II-deficient mice. Analysis of the anti-H. pylori antibody levels in serum showed a dominant serum immunoglobulin G1 (IgG1) response in immunized C57BL/6 wild-type and MHC class I mutant mice but no detectable serum IgG response in MHC class II knockout mice. Populations of T-cell-receptor (TCR) alphabeta+ CD4(+) CD54(+) cells localized to gastric tissue of immunized C57BL/6 wild-type and MHC class I knockout mice, but TCRalphabeta+ CD8(+) cells predominated in the gastric tissue of immunized MHC class II-deficient mice. These observations show that CD4(+) T cells engaged after mucosal immunization may be important for the generation of a protective anti-H. pylori immune response and that CD4(+) CD8(-) and CD4(-) CD8(+) T cells regulate the extent of H. pylori infection in vivo.
    Preview · Article · Feb 1999 · Infection and Immunity
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    ABSTRACT: Oral immunization with recombinant Helicobacter pylori urease (rUre) coadministered with a mucosal adjuvant protects mice against challenge with Helicobacter felis. In this study, the duration of protection and gastritis after challenge were characterized at sequential time intervals up to 1 year. Outbred Swiss-Webster mice were orally immunized with rUre plus adjuvant and examined for the presence of H. felis infection and leukocyte infiltration into the gastric mucosa. When defined by gastric urease activity, 70%-95% of rUre-immunized mice were protected for between 2 and 57 weeks. Challenge with H. felis increased the inflammatory response in the gastric mucosa of rUre-immunized mice, which also had elevated CD4+ and CD8+ T cells. The CD8+ cells represented a population of gastric intraepithelial cells, which expressed the mucosal alpha E-integrin. Epithelial changes consisting of parietal cell loss and hyperplasia of the epithelium occurred in approximately 20% of the mice. Antimicrobial triple therapy significantly decreased the degree of gastritis and epithelial alteration in the stomach. These results indicate that oral immunization of mice with rUre produces a long-lasting inhibition of H. felis infection but that residual bacteria may produce a persistent lymphocytic infiltration under these experimental conditions.
    No preview · Article · Oct 1997 · Gastroenterology
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    J G Fox · Perkins SE · L Yan · Z Shen · L Attardo · J Pappo
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    ABSTRACT: Helicobacter pylori-infected cats were screened by culture and polymerase chain reaction (PCR) for the presence of H. pylori in salivary secretions, gastric juice, gastric tissue and faeces. H. pylori was cultured from salivary secretions in six of 12 (50%) cats and from gastric fluid samples in 11 of 12 (91%) cats. A 298 base pair polymerase chain reactions (PCR) product specific for an H. pylori 26000 MW surface protein was amplified from dental plaque samples from five of 12 (42%) cats and from the faeces of four of five (80%) cats studied. Analyses of serum and mucosal secretions by enzyme-linked immunosorbent assay (ELISA) revealed an H. pylori-specific immunoglobulin G (IgG) response, and elevated IgA anti-H. pylori antibody levels in salivary and local gastric secretions. Immunohistochemical analyses of gastric tissue revealed the presence of IgM+ B cells assembled into multiple lymphoid follicles surrounded by clusters of CD4+ and CD8+ T cells. The lamina propria also contained single cells or aggregates of IgA+ and IgM+ B cells. These observations show that H. pylori can be identified in feline mucosal secretions, and that a localized IgA immune response develops in gastric tissue of H. pylori-infected cats. The findings suggest a zoonotic risk from exposure to personnel handling H. pylori-infected cats in vivaria.
    Full-text · Article · Aug 1996 · Immunology
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    ABSTRACT: The ability of oral immunization to interfere with the establishment of infection with Helicobacter felis was examined. Groups of Swiss Webster mice were immunized orally with 250 micrograms of Helicobacter pylori recombinant urease (rUrease) and 10 micrograms of cholera toxin (CT) adjuvant, 1 mg of H. felis sonicate antigens and CT, or phosphate-buffered saline (PBS) and CT. Oral immunization with rUrease resulted in markedly elevated serum immunoglobulin G (IgG), serum IgA, and intestinal IgA antibody responses. Challenge with live H. felis further stimulated the urease-specific intestinal IgA and serum IgG and IgA antibody levels in mice previously immunized with rUrease but activated primarily the serum IgG compartment of PBS-treated and H. felis-immunized mice. Intestinal IgA and serum IgG and IgA anti-urease antibody responses were highest in rUrease-immunized mice at the termination of the experiment. Mice immunized with rUrease were significantly protected (P < or = 0.0476) against infection when challenged with H. felis 2 or 6 weeks post-oral immunization in comparison with PBS-treated mice. Whereas H. felis-infected mice displayed multifocal gastric mucosal lymphoid follicles consisting of CD45R+ B cells surrounded by clusters of Thy1.2+ T cells, gastric tissue from rUrease-immunized mice contained few CD45R+ B cells and infrequent mucosal follicles. These observations show that oral immunization with rUrease confers protection against H. felis infection and suggest that gastric tissue may function as an effector organ of the mucosal immune system which reflects the extent of local antigenic stimulation.
    Full-text · Article · Apr 1995 · Infection and Immunity
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    ABSTRACT: In this study, we demonstrate the role of M cells in uptake of poly(D-L-lactic-co-glycolic acid) (PLGA) microspheres and transport into rabbit Peyer's patches. Microspheres 1 to 10 microns in diameter composed of 50:50 lactic acid:glycolic acid were instilled into intestinal segments containing jejunal or ileal Peyer's patches, and uptake by M cells was examined by electron microscopy. PLGA microspheres visualized as electron-lucent, spherical particles were taken up by M cells by pseudopod-like extensions of the M cell apical membrane and translocated to the pocket region containing mononuclear leukocytes within 60 min. These results indicate that PLGA microspheres can be directed to M cell apical surfaces for delivery to immunocompetent cells in gut-associated lymphoid tissues.
    No preview · Article · Mar 1995 · Cell and Tissue Research
  • Z Kabok · T H Ermak · J Pappo

    No preview · Article · Feb 1995 · Advances in Experimental Medicine and Biology
  • T H Ermak · H R Bhagat · J Pappo
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    ABSTRACT: Uptake and delivery of antigens to immunocompetent cells in the gut are critical factors for the development of oral vaccines. Particulate antigens are transported within minutes by M cells to intraepithelial lymphocytes and into the follicle dome. The dome contains B cells, CD4+ T cells, and macrophages, indicating that the cells involved in antigen presentation are located below the dome's epithelium. The high number of M cells in rabbits and the development of monoclonal antibodies against rabbit lymphocytes have enabled the detailed study of lymphocytes associated with M cells. The follicle epithelium of rabbit Peyer's patches contains B cells and a population of CD4-/CD8-, major histocompatibility complex class II+ mononuclear cells of unknown function. These cells are phenotypically distinct from T cells in follicle domes, in T cell-dependent areas, in villus epithelium, or in villus lamina propria. In addition, lymphocytes in M-cell pockets express an activation antigen (3B6) not found on CD4+ or CD8+ cells in T cell-dependent areas. These results indicate that M-cell pocket lymphocytes in follicle epithelium form a phenotypically distinct compartment situated at the interface between M-cell-driven antigen uptake and the mucosal immune system.
    No preview · Article · Feb 1994 · The American journal of tropical medicine and hygiene
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    J G Fox · M Blanco · J C Murphy · N S Taylor · A Lee · Z Kabok · J Pappo
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    ABSTRACT: Helicobacter felis inoculated per os into germfree mice and their conventional non-germfree counterparts caused a persistent chronic gastritis of approximately 1 year in duration. Mononuclear leukocytes were the predominant inflammatory cell throughout the study, although polymorphonuclear cell infiltrates were detected as well. Immunohistochemical analyses of gastric mucosa from H. felis-infected mice revealed the presence of mucosal B220+ cells coalescing into lymphoid follicles surrounded by aggregates of Thy-1.2+ T cells; CD4+, CD5+, and alpha beta T cells predominated in organized gastric mucosal and submucosal lymphoid tissue, and CD11b+ cells occurred frequently in the mucosa. Follicular B cells comprised immunoglobulin M+ (IgM+) and IgA+ cells. Numerous IgA-producing B cells were present in the gastric glands, the lamina propria, and gastric epithelium. Infected animals developed anti-H. felis serum IgM antibody responses up to 8 weeks postinfection and significant levels of IgG anti-H. felis antibody in serum, which remained elevated throughout the 50-week course of the study.
    Full-text · Article · Jul 1993 · Infection and Immunity
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    J Pappo · R T Mahlman
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    ABSTRACT: The production of interleukin-1 (IL-1) by rabbit Peyer's patch M cells populating the follicle-associated epithelium (FAE) was studied. Sorted 5D9+ phagocytic epithelial M cells synthesized IL-1 after stimulation with lipopolysaccharide (LPS) in vitro, as evidenced by the ability of culture supernatants to induce the proliferation of the T-cell line D10.G4.1. Fixed LPS-stimulated M cells were less effective at mediating T-cell proliferation than supernatants from LPS-activated M cells. The magnitude of T-cell proliferation was M-cell concentration dependent, and proportional to the dose of LPS. The M-cell-mediated D10.G4.1 cell proliferation was inhibited > 75% with anti-IL-1 alpha, but < 50% with similar concentrations of anti-IL-1 beta. The results show that M cells secrete IL-1, and suggest the participation of M cells in the delivery of a localized co-stimulatory signal for T-cell and B-cell proliferation in the microenvironment of gut-associated lymphoid tissue (GALT).
    Preview · Article · Mar 1993 · Immunology

Publication Stats

2k Citations
162.93 Total Impact Points

Institutions

  • 2008
    • EpiVax, Inc.
      Providence, Rhode Island, United States
  • 2001
    • University of Texas Medical Branch at Galveston
      • Department of Pediatrics
      Galveston, Texas, United States
  • 1992
    • University of Milan
      Milano, Lombardy, Italy
  • 1990-1991
    • San Francisco VA Medical Center
      San Francisco, California, United States
  • 1988-1989
    • University of California, San Francisco
      • Division of Hospital Medicine
      San Francisco, California, United States