Janelle C. Arthur

Intestinal Inflammation Targets Cancer-Inducing Activity of the Microbiota

Of Microbes and Cancer Inflammation is a well-established driver of tumorigenesis. For example, patients with inflammatory bowel disease have an elevated risk of developing colorectal cancer (CRC). Whether the gut microbiota also contributes to the development of CRC is less well understood. Arthur et al. (p. 120, published online 16 August; see the Perspective by Schwabe and Wang) now show that the microbiota does indeed promote tumorigenesis in an inflammation-driven model of CRC in mice. Although germ-free mice were protected against developing cancer, colonization of mice with Escherichia coli was sufficient to drive tumorigenesis. Microbes resident in the gut can promote colorectal cancer in mice in an inflammation-independent manner. Inflammation alters host physiology to promote cancer, as seen in colitis-associated colorectal cancer (CRC). Here, we identify the intestinal microbiota as a target of inflammation that affects the progression of CRC. High-throughput sequencing revealed that inflammation modifies gut microbial composition in colitis-susceptible interleukin-10–deficient (Il10−/−) mice. Monocolonization with the commensal Escherichia coli NC101 promoted invasive carcinoma in azoxymethane (AOM)–treated Il10−/− mice. Deletion of the polyketide synthase (pks) genotoxic island from E. coli NC101 decreased tumor multiplicity and invasion in AOM/Il10−/− mice, without altering intestinal inflammation. Mucosa-associated pks+ E. coli were found in a significantly high percentage of inflammatory bowel disease and CRC patients. This suggests that in mice, colitis can promote tumorigenesis by altering microbial composition and inducing the expansion of microorganisms with genotoxic capabilities.

Immunogenicity of Recombinant Adenovirus Serotype 35 Vaccine in the Presence of Pre-Existing Anti-Ad5 Immunity

The high prevalence of pre-existing immunity to adenovirus serotype 5 (Ad5) in human populations may substantially limit the immunogenicity and clinical utility of recombinant Ad5 vector-based vaccines for HIV-1 and other pathogens. A potential solution to this problem is to use vaccine vectors derived from adenovirus (Ad) serotypes that are rare in humans, such as Ad35. However, cross-reactive immune responses between heterologous Ad serotypes have been described and could prove a major limitation of this strategy. In particular, the extent of immunologic cross-reactivity between Ad5 and Ad35 has not previously been determined. In this study we investigate the impact of pre-existing anti-Ad5 immunity on the immunogenicity of candidate rAd5 and rAd35 vaccines expressing SIV Gag in mice. Anti-Ad5 immunity at levels typically found in humans dramatically blunted the immunogenicity of rAd5-Gag. In contrast, even high levels of anti-Ad5 immunity did not substantially suppress Gag-specific cellular immune responses elicited by rAd35-Gag. Low levels of cross-reactive Ad5/Ad35-specific CD4+ T lymphocyte responses were observed, but were insufficient to suppress vaccine immunogenicity. These data demonstrate the potential utility of Ad35 as a candidate vaccine vector that is minimally suppressed by anti-Ad5 immunity. Moreover, these studies suggest that using Ad vectors derived from immunologically distinct serotypes may be an effective and general strategy to overcome the suppressive effects of pre-existing anti-Ad immunity.

Cutting Edge: Monarch-1 Suppresses Non-Canonical NF-κB Activation and p52-Dependent Chemokine Expression in Monocytes

CATERPILLER (NOD, NBD-LRR) proteins are rapidly emerging as important mediators of innate and adaptive immunity. Among these, Monarch-1 operates as a novel attenuating factor of inflammation by suppressing inflammatory responses in activated monocytes. However, the molecular mechanisms by which Monarch-1 performs this important function are not well understood. In this report, we show that Monarch-1 inhibits CD40-mediated activation of NF-κB via the non-canonical pathway in human monocytes. This inhibition stems from the ability of Monarch-1 to associate with and induce proteasome-mediated degradation of NF-κB inducing kinase. Congruently, silencing Monarch-1 with shRNA enhances the expression of p52-dependent chemokines.

Neutralizing Antibodies and CD8+ T Lymphocytes both Contribute to Immunity to Adenovirus Serotype 5 Vaccine Vectors

ABSTRACT The high prevalence of preexisting immunity to adenovirus serotype 5 (Ad5) in human populations will likely limit the immunogenicity and clinical utility of recombinant Ad5 vector-based vaccines for human immunodeficiency virus type 1 and other pathogens. Ad5-specific neutralizing antibodies (NAbs) are thought to contribute substantially to anti-Ad5 immunity, but the potential importance of Ad5-specific T lymphocytes in this setting has not been fully characterized. Here we assess the relative contributions of Ad5-specific humoral and cellular immune responses in blunting the immunogenicity of a rAd5-Env vaccine in mice. Adoptive transfer of Ad5-specific NAbs resulted in a dramatic abrogation of Env-specific immune responses following immunization with rAd5-Env. Interestingly, adoptive transfer of Ad5-specific CD8+ T lymphocytes also resulted in a significant and durable suppression of rAd5-Env immunogenicity. These data demonstrate that NAbs and CD8+ T lymphocytes both contribute to immunity to Ad5. Novel adenovirus vectors that are currently being developed to circumvent the problem of preexisting anti-Ad5 immunity should therefore be designed to evade both humoral and cellular Ad5-specific immune responses.

A Human T-Cell Leukemia Virus Type 1 Regulatory Element Enhances the Immunogenicity of Human Immunodeficiency Virus Type 1 DNA Vaccines in Mice and Nonhuman Primates

ABSTRACT Plasmid DNA vaccines elicit potent and protective immune responses in numerous small-animal models of infectious diseases. However, their immunogenicity in primates appears less potent. Here we investigate a novel approach that optimizes regulatory elements in the plasmid backbone to improve the immunogenicity of DNA vaccines. Among various regions analyzed, we found that the addition of a regulatory sequence from the R region of the long terminal repeat from human T-cell leukemia virus type 1 (HTLV-1) to the cytomegalovirus (CMV) enhancer/promoter increased transgene expression 5- to 10-fold and improved cellular immune responses to human immunodeficiency virus type 1 (HIV-1) antigens. In cynomolgus monkeys, DNA vaccines containing the CMV enhancer/promoter with the HTLV-1 R region (CMV/R) induced markedly higher cellular immune responses to HIV-1 Env from clades A, B, and C and to HIV-1 Gag-Pol-Nef compared with the parental DNA vaccines. These data demonstrate that optimization of specific regulatory elements can substantially improve the immunogenicity of DNA vaccines encoding multiple antigens in small animals and in nonhuman primates. This strategy could therefore be explored as a potential method to enhance DNA vaccine immunogenicity in humans.

Recruitment and expansion of dendritic cells in vivo potentiate the immunogenicity of plasmid DNA vaccines

DCs are critical for priming adaptive immune responses to foreign antigens. However, the utility of harnessing these cells in vivo to optimize the immunogenicity of vaccines has not been fully explored. Here we investigate a novel vaccine approach that involves delivering synergistic signals that both recruit and expand DC populations at the site of antigen production. Intramuscular injection of an unadjuvanted HIV-1 envelope (env) DNA vaccine recruited few DCs to the injection site and elicited low-frequency, env-specific immune responses in mice. Coadministration of plasmids encoding the chemokine macrophage inflammatory protein-1alpha (MIP-1alpha) and the DC-specific growth factor fms-like tyrosine kinase 3 ligand with the DNA vaccine resulted in the recruitment, expansion, and activation of large numbers of DCs at the site of inoculation. Consistent with these findings, coadministration of these plasmid cytokines also markedly augmented DNA vaccine---elicited cellular and humoral immune responses and increased protective efficacy against challenge with recombinant vaccinia virus. These data suggest that the availability of mature DCs at the site of inoculation is a critical rate-limiting factor for DNA vaccine immunogenicity. Synergistic recruitment and expansion of DCs in vivo may prove a practical strategy for overcoming this limitation and potentiating immune responses to vaccines as well as other immunotherapeutic strategies.

Cutting Edge: NLRP12 Controls Dendritic and Myeloid Cell Migration To Affect Contact Hypersensitivity

Nucleotide-binding domain leucine-rich repeat (NLR) proteins are regulators of inflammation and immunity. Although first described 8 y ago, a physiologic role for NLRP12 has remained elusive until now. We find that murine Nlrp12, an NLR linked to atopic dermatitis and hereditary periodic fever in humans, is prominently expressed in dendritic cells (DCs) and neutrophils. Nlrp12-deficient mice exhibit attenuated inflammatory responses in two models of contact hypersensitivity that exhibit features of allergic dermatitis. This cannot be attributed to defective Ag processing/presentation, inflammasome activation, or measurable changes in other inflammatory cytokines. Rather, Nlrp12−/− DCs display a significantly reduced capacity to migrate to draining lymph nodes. Both DCs and neutrophils fail to respond to chemokines in vitro. These findings indicate that NLRP12 is important in maintaining neutrophils and peripheral DCs in a migration-competent state.

Microbial genomic analysis reveals the essential role of inflammation in bacteria-induced colorectal cancer

Enterobacteria, especially Escherichia coli, are abundant in patients with inflammatory bowel disease or colorectal cancer (CRC). However, it is unclear whether cancer is promoted by inflammation-induced expansion of E. coli and/or changes in expression of specific microbial genes. Here we use longitudinal (2, 12 and 20 weeks) 16S rRNA sequencing of luminal microbiota from ex-germ free mice to show that inflamed Il10−/− mice maintain a higher abundance of Enterobacteriaceae than healthy wild-type mice. Experiments with mono-colonized Il10−/− mice reveal that host inflammation is necessary for E. coli cancer-promoting activity. RNA-sequence analysis indicates significant changes in E. coli gene catalogue in Il10−/− mice, with changes mostly driven by adaptation to the intestinal environment. Expression of specific genes present in the tumor-promoting E. coli pks island are modulated by inflammation/CRC development. Thus, progression of inflammation in Il10−/− mice supports Enterobacteriaceae and alters a small subset of microbial genes important for tumor development.

Stochastic changes over time and not founder effects drive cage effects in microbial community assembly in a mouse model

Maternal transmission and cage effects are powerful confounding factors in microbiome studies. To assess the consequences of cage microenvironment on the mouse gut microbiome, two groups of germ-free (GF) wild-type (WT) mice, one gavaged with a microbiota harvested from adult WT mice and another allowed to acquire the microbiome from the cage microenvironment, were monitored using Illumina 16S rRNA sequencing over a period of 8 weeks. Our results revealed that cage effects in WT mice moved from GF to specific pathogen free (SPF) conditions take several weeks to develop and are not eliminated by the initial gavage treatment. Initial gavage influenced, but did not eliminate a successional pattern in which Proteobacteria became less abundant over time. An analysis in which 16S rRNA sequences are mapped to the closest sequenced whole genome suggests that the functional potential of microbial genomes changes significantly over time shifting from an emphasis on pathogenesis and motility early in community assembly to metabolic processes at later time points. Functionally, mice allowed to naturally acquire a microbial community from their cage, but not mice gavaged with a common biome, exhibit a cage effect in Dextran Sulfate Sodium-induced inflammation. Our results argue that while there are long-term effects of the founding community, these effects are mitigated by cage microenvironment and successional community assembly over time, which must both be explicitly considered in the interpretation of microbiome mouse experiments.

Probiotic Bacteria Produce Conjugated Linoleic Acid Locally in the Gut That Targets Macrophage PPAR γ to Suppress Colitis

Background Inflammatory bowel disease (IBD) therapies are modestly successful and associated with significant side effects. Thus, the investigation of novel approaches to prevent colitis is important. Probiotic bacteria can produce immunoregulatory metabolites in vitro such as conjugated linoleic acid (CLA), a polyunsaturated fatty acid with potent anti-inflammatory effects. This study aimed to investigate the cellular and molecular mechanisms underlying the anti-inflammatory efficacy of probiotic bacteria using a mouse model of colitis. Methodology/Principal Findings The immune modulatory mechanisms of VSL#3 probiotic bacteria and CLA were investigated in a mouse model of DSS colitis. Colonic specimens were collected for histopathology, gene expression and flow cytometry analyses. Immune cell subsets in the mesenteric lymph nodes (MLN), spleen, blood and colonic lamina propria cells were phenotypically and functionally characterized. Fecal samples and colonic contents were collected to determine the effect of VSL#3 and CLA on gut microbial diversity and CLA production. CLA and VSL#3 treatment ameliorated colitis and decreased colonic bacterial diversity, a finding that correlated with decreased gut pathology. Colonic CLA concentrations were increased in response to probiotic bacterial treatment, but without systemic distribution in blood. VSL#3 and CLA decreased macrophage accumulation in the MLN of mice with DSS colitis. The loss of PPAR γ in myeloid cells abrogated the protective effect of probiotic bacteria and CLA in mice with DSS colitis. Conclusions/Significance Probiotic bacteria modulate gut microbial diversity and favor local production of CLA in the colon that targets myeloid cell PPAR γ to suppress colitis.