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Human B cells can be cultured ex vivo for a few weeks,following stimulation of the CD40 cell surface molecule in the presence of recombinant cytokines such as interleukin-4 (IL-4). However,attempts to produce polyclonal antigen-specific human antibodies by in vitro culture of human B cells obtained from immunized donors have not been successful. It has been shown in mice that lipopolysaccharide (LPS) is a potent mitogen for B cells and plays an important role in the generation of antigen-specific antibody responses. Although it has long been believed that LPS has no direct effect on human B cells,recent data indicating that IL-4-activated human B cells are induced to express Toll-like receptor-4,the main LPS receptor,prompted us to study the effects of LPS on the proliferation and antibody secretion of human B cells. Our results showed that LPS caused a reduction in the expansion of CD40-activated human B cells,accompanied by an increase in antigen-specific antibody secretion. This result suggested that some,but not all,B cells were able to differentiate into antibody-secreting cells in response to LPS. This increased differentiation could be explained by the observation that LPS-stimulated human B cells were induced to secrete higher amounts of IL-6,a pleiotropic cytokine well-known for its B-cell differentiation activity. In vivo,the effect of LPS on cytokine secretion by B cells may not only enhance B-cell differentiation but also help to sustain a local ongoing immune response to invading Gram-negative bacteria,until all pathogens have been cleared from the organism. View Publication

Recent compelling evidence indicates that Th17 confer host immunity against a variety of microbes,including extracellular and intracellular pathogens. Therefore,understanding mechanisms for the induction and activation of Ag-specific Th17 is important for the rational design of vaccines against pathogens. To study this,we employed an in vitro system in which influenza hemagglutinin (HA) 1 was delivered to dendritic cells (DCs) via Dectin-1 using anti-human Dectin-1 (hDectin-1)-HA1 recombinant fusion proteins. We found that healthy individuals maintained broad ranges of HA1-specific memory Th17 that were efficiently activated by DCs targeted with anti-hDectin-1-HA1. Nonetheless,these DCs were not able to induce a significant level of HA1-specific Th17 responses even in the presence of the Th17-promoting cytokines IL-1? and IL-6. We further found that the induction of surface IL-1R1 expression by signals via TCRs and common ?-chain receptors was essential for naive CD4(+) T cell differentiation into HA1-specific Th17. This process was dependent on MyD88,but not IL-1R-associated kinase 1/4. Thus,interruptions in STAT3 or MyD88 signaling led to substantially diminished HA1-specific Th17 induction. Taken together,the de novo generation of pathogen-specific human Th17 requires complex,but complementary,actions of multiple signals. Data from this study will help us design a new and effective vaccine strategy that can promote Th17-mediated immunity against microbial pathogens. View Publication

PURPOSE: The propensity of tumor cells to escape immune elimination could limit,if not defeat,the long-term benefits of effective immunotherapeutic protocols. Immunologic targeting of tumor stroma could significantly reduce the ability of tumors to evade immune elimination. Murine studies have shown that inducing immunity against angiogenesis-associated products engenders potent antitumor immunity without significant pathology. It is,however,not known whether T cells corresponding to stromal products are present in humans. In this study,we describe a method to screen for human stromal products that have not triggered significant tolerance and could therefore serve as candidate antigens for cancer immunotherapy. EXPERIMENTAL DESIGN: To identify candidates for human stromal antigens,we used an in vitro-screening method to determine whether dendritic cells transfected with mRNA encoding products,which are overexpressed in the tumor stroma,are capable of stimulating cytotoxic CD8(+) (CTL) responses from human peripheral blood mononuclear cells. RESULTS: CTL responses could be consistently generated against fibroblast activation protein (FAP) but not against matrix metalloproteinase-9 (MMP-9) or MMP-14. To enhance the immunogenicity of the mRNA-translated FAP product,a lysosomal targeting signal derived from lysosome-associated membrane protein-1 (LAMP-1) was fused to the COOH terminus of FAP to redirect the translated product into the class II presentation pathway. Dendritic cells transfected with mRNA encoding the FAP-LAMP fusion product stimulated enhanced CD4(+) and CD8(+) T-cell responses. CONCLUSION: This study identifies FAP,a protease preferentially expressed in tumor-associated fibroblasts,as a candidate human stromal antigen to target in the setting of cancer immunotherapy,and shows that differential expression of stromal products is not a sufficient criteria to indicate its immunogenicity in a vaccination setting. View Publication

Two distinct dendritic cell (DC) subpopulations have been evidenced in mice on the basis of their differential CD8alpha expression and their localization in lymphoid organs. Several reports suggest that CD8alpha(+) and CD8alpha(-) DC subsets could be functionally different. In this study,using a panel of MHC class I- and/or class II-restricted peptides,we analyzed CD4(+) and CD8(+) T cell responses obtained after i.v. injection of freshly purified peptide-pulsed DC subsets. First,we showed that both DC subsets efficiently induce specific CTL responses and Th1 cytokine production in the absence of CD4(+) T cell priming. Second,we showed that in vivo activation of CD4(+) T cells by CD8alpha(+) or CD8alpha(-) DC,injected i.v.,leads to a nonpolarized Th response with production of both Th1 and Th2 cytokines. The CD8alpha(-) subset induced a higher production of Th2 cytokines such as IL-4 and IL-10 than the CD8alpha(+) subset. However,IL-5 was produced by CD4(+) T cells activated by both DC subsets. When both CD4(+) and CD8(+) T cells were primed by DC injected i.v.,a similar pattern of cytokines was observed,but,under these conditions,Th1 cytokines were mainly produced by CD8(+) T cells,while Th2 cytokines were produced by CD4(+) T cells. Thus,this study clearly shows that CD4(+) T cell responses do not influence the development of specific CD8(+) T cell cytotoxic responses induced either by CD8alpha(+) or CD8alpha(-) DC subsets. View Publication

The design of immunogens that elicit broadly reactive neutralizing antibodies (bnAbs) has been a major obstacle to HIV-1 vaccine development. One approach to assess potential immunogens is to use mice expressing precursors of human bnAbs as vaccination models. The bnAbs of the VRC01-class derive from the IGHV1-2 immunoglobulin heavy chain and neutralize a wide spectrum of HIV-1 strains via targeting the CD4 binding site of the envelope glycoprotein gp120. We now describe a mouse vaccination model that allows a germline human IGHV1-2(∗)02 segment to undergo normal V(D)J recombination and,thereby,leads to the generation of peripheral B cells that express a highly diverse repertoire of VRC01-related receptors. When sequentially immunized with modified gp120 glycoproteins designed to engage VRC01 germline and intermediate antibodies,IGHV1-2(∗)02-rearranging mice,which also express a VRC01-antibody precursor light chain,can support the affinity maturation of VRC01 precursor antibodies into HIV-neutralizing antibody lineages. View Publication

Mtb influences DC activity and T cell-mediated immune responses. We show that the treatment of immature monocyte-derived DC with Mtb elicited the formation of mature DC,producing TNF-alpha,IL-1beta,IL-6,and IL-23 and instructing CD4(+) cells to secrete IFN-gamma and IL-17. Mtb-induced cytokine release by DC depended on dectin-1 receptor engagement,whereas MR or DC-SIGN stimulation inhibited this process. A selective dectin-1 binding by the receptor agonist glucan was sufficient to enable DC to generate Th1/Th17 lymphocytes,showing features comparable with those induced by Mtb-treated DC. Interestingly,DC-SIGN or MR engagement inhibited Th17 and increased Th1 generation by glucan- or Mtb-treated DC. Our results indicate that Mtb modulates the lymphocyte response by affecting DC maturation and cytokine release. Dectin-1 engagement by Mtb enables DC to promote a Th1/Th17 response,whereas DC-SIGN and MR costimulation limits dectin-1-dependent Th17 generation and favors a Th1 response,probably by interfering with release of cytokines. View Publication

The leukocyte activation marker CD69 is a novel regulator of the immune response,modulating the production of cytokines including transforming growth factor-beta (TGF-beta). We have generated an antimurine CD69 monoclonal antibody (mAb),CD69.2.2,which down-regulates CD69 expression in vivo but does not deplete CD69-expressing cells. Therapeutic administration of CD69.2.2 to wild-type mice induces significant natural killer (NK) cell-dependent antitumor responses to major histocompatibility complex (MHC) class I low RMA-S lymphomas and to RM-1 prostatic carcinoma lung metastases. These in vivo antitumor responses are comparable to those seen in CD69(-/-) mice. Enhanced host NK cytotoxic activity correlates with a reduction in NK-cell TGF-beta production and is independent of tumor priming. In vitro studies demonstrate the novel ability of anti-CD69 mAbs to activate resting NK cells in an Fc receptor-independent manner,resulting in a substantial increase in both NK-cell cytolytic activity and interferon gamma (IFNgamma) production. Modulation of the innate immune system with monoclonal antibodies to host CD69 thus provides a novel means to antagonize tumor growth and metastasis. View Publication

Although microbial infections can alter steady-state hematopoiesis,the mechanisms that drive such changes are not well understood. We addressed a role for IFN-γ signaling in infection-induced bone marrow suppression and anemia in a murine model of human monocytic ehrlichiosis,an emerging tick-borne disease. Within the bone marrow of Ehrlichia muris-infected C57BL/6 mice,we observed a reduction in myeloid progenitor cells,as defined both phenotypically and functionally. Infected mice exhibited a concomitant increase in developing myeloid cells within the bone marrow,an increase in the frequency of circulating monocytes,and an increase in splenic myeloid cells. The infection-induced changes in progenitor cell phenotype were critically dependent on IFN-γ,but not IFN-α,signaling. In mice deficient in the IFN-γ signaling pathway,we observed an increase in myeloid progenitor cells and CDllb(lo)Gr1(lo) promyelocytic cells within the bone marrow,as well as reduced frequencies of mature granulocytes and monocytes. Furthermore,E. muris-infected IFN-γR-deficient mice did not exhibit anemia or an increase in circulating monocytes,and they succumbed to infection. Gene transcription studies revealed that IFN-γR-deficient CDllb(lo)Gr1(lo) promyelocytes from E. muris-infected mice exhibited significantly reduced expression of irf-1 and irf-8,both key transcription factors that regulate the differentiation of granulocytes and monocytes. Finally,using mixed bone marrow chimeric mice,we show that IFN-γ-dependent infection-induced myelopoiesis occurs via the direct effect of the cytokine on developing myeloid cells. We propose that,in addition to its many other known roles,IFN-γ acts to control infection by directly promoting the differentiation of myeloid cells that contribute to host defense. View Publication

Intestinal fibrosis is a serious complication in inflammatory bowel disease (IBD). Despite the remarkable success of recent anti-inflammatory therapies for IBD,incidence of intestinal fibrosis and need for bowel resection have not significantly changed. To clarify the contribution of haematopoietic-derived cells in intestinal fibrosis,we prepared bone marrow (BM) chimeric mice (chimeras),which were reconstituted with BM cells derived from enhanced green fluorescent protein (EGFP)-transgenic mice or CC chemokine receptor 2 (CCR2)-deficient mice. After 2 months of transplantation,BM chimeras were treated with azoxymethane/dextran sodium sulphate. During chronic inflammation,CCR2+ BM-derived monocyte and fibrocyte infiltration into the colon and CC chemokine ligand 2 production increased,leading to colon fibrosis in EGFP BM chimeras. In CCR2-deficient BM chimeras,monocyte and fibrocyte numbers in the colonic lamina propria significantly decreased,and colon fibrosis was attenuated. In colon tissue,mRNA expression of tissue inhibitor of metalloproteinase (TIMP)-1 but not of collagen I,transforming growth factor-beta1 or matrix metalloproteinases was significantly different between the two chimeras. CCR2+ monocytes and fibrocytes showed high Timp1 mRNA expression. Our results suggest that infiltrating CCR2+ monocytes and their progenies,fibrocytes,promote colon fibrosis by inhibiting collagen degradation through TIMP-1 production. View Publication

Because IL-1beta plays an important role in inflammation in human and murine arthritis,we investigated the contribution of the inflammasome components ASC,NALP-3,IPAF,and caspase-1 to inflammatory arthritis. We first studied the phenotype of ASC-deficient and wild-type mice during Ag-induced arthritis (AIA). ASC(-/-) mice showed reduced severity of AIA,decreased levels of synovial IL-1beta,and diminished serum amyloid A levels. In contrast,mice deficient in NALP-3,IPAF,or caspase-1 did not show any alteration of joint inflammation,thus indicating that ASC associated effects on AIA are independent of the classical NALP-3 or IPAF inflammasomes. Because ASC is a ubiquitous cytoplasmic protein that has been implicated in multiple cellular processes,we explored other pathways through which ASC may modulate inflammation. Ag-specific proliferation of lymph node and spleen cells from ASC-deficient mice was significantly decreased in vitro,as was the production of IFN-gamma,whereas IL-10 production was enhanced. TCR ligation by anti-CD3 Abs in the presence or absence of anti-CD28 Abs induced a reduction in T cell proliferation in ASC(-/-) T cells compared with wild-type ones. In vivo lymph node cell proliferation was also significantly decreased in ASC(-/-) mice,but no effects on apoptosis were observed either in vitro or in vivo in these mice. In conclusion,these results strongly suggest that ASC modulates joint inflammation in AIA through its effects on cell-mediated immune responses but not via its implication in inflammasome formation. View Publication

BACKGROUND AND AIMS: Atherosclerosis is known to be an inflammatory disease and there is increasing evidence that chylomicron remnants (CMR),the lipoproteins which carry dietary fats in the blood,cause macrophage foam cell formation and inflammation. In early atherosclerosis the frequency of activated monocytes in the peripheral circulation is increased,and clearance of CMR from blood may be delayed,however,whether CMR contribute directly to monocyte activation and subsequent egress into the arterial wall has not been established. Here,the contribution of CMR to activation of monocyte pro-inflammatory pathways was assessed using an in vitro model. METHODS AND RESULTS: Primary human monocytes and CMR-like particles (CRLP) were used to measure several endpoints of monocyte activation. Treatment with CRLP caused rapid and prolonged generation of reactive oxygen species by monocytes. The pro-inflammatory chemokines MCP-1 and IL-8 were secreted in nanogram quantities by the cells in the absence of CRLP. IL-8 secretion was transiently increased after CRLP treatment,and CRLP maintained secretion in the presence of pharmacological inhibitors of IL-8 production. In contrast,exposure to CRLP significantly reduced MCP-1 secretion. Chemotaxis towards MCP-1 was increased in monocytes pre-exposed to CRLP and was reversed by addition of exogenous MCP-1. CONCLUSION: Our findings indicate that CRLP activate human monocytes and augment their migration in vitro by reducing cellular MCP-1 expression. Our data support the current hypothesis that CMR contribute to the inflammatory milieu of the arterial wall in early atherosclerosis,and suggest that this may reflect direct interaction with circulating blood monocytes. View Publication

The immune system can act as an extrinsic suppressor of tumors. Therefore,tumor progression depends in part on mechanisms that downmodulate intrinsic immune surveillance. Identifying these inhibitory pathways may provide promising targets to enhance antitumor immunity. Here,we show that Stat3 is constitutively activated in diverse tumor-infiltrating immune cells,and ablating Stat3 in hematopoietic cells triggers an intrinsic immune-surveillance system that inhibits tumor growth and metastasis. We observed a markedly enhanced function of dendritic cells,T cells,natural killer (NK) cells and neutrophils in tumor-bearing mice with Stat3(-/-) hematopoietic cells,and showed that tumor regression requires immune cells. Targeting Stat3 with a small-molecule drug induces T cell- and NK cell-dependent growth inhibition of established tumors otherwise resistant to direct killing by the inhibitor. Our findings show that Stat3 signaling restrains natural tumor immune surveillance and that inhibiting hematopoietic Stat3 in tumor-bearing hosts elicits multicomponent therapeutic antitumor immunity. View Publication