Biology subjects

Ramer-Tait, A.

Publications and source records attributed to Ramer-Tait, A..

4 recordsLinked to original sources

bioRxiv2026

Tryptophan degradation by intestinal Bacteroides induces anti-tumor immunity and limits melanoma growth

Defining mechanisms used by gut microbiota to control anti-tumor immunity may offer novel therapeutic modalities. Here, we demonstrate that Bacteroides rodentium and closely related Bacteroides uniformis species induce anti-tumor immunity and limit melanoma development when colonized in either germ-free (GF) mice, mice with a complex microbiome, or WT mice. Enhanced CD8+ T cell infiltration seen in tumors of mice harboring B. rodentium coincided with increased expression of immune-stimulating pathways and activation of bone marrow-derived dendritic cells that were co-cultured with the B. rodentium secretome. Metabolomic analyses of cecal samples from GF mice colonized with Altered Shedlar Flora (ASF) plus B. rodentium revealed lower tryptophan levels than in ASF-colonized controls, and WT mice fed a tryptophan-deficient diet exhibited inhibition of melanoma development. In silico genomic reconstruction of metabolic pathways revealed that both B. rodentium and B. uniformis harbor tryptophanase A (TnaA) and aromatic amino transferase (ArAT) genes, both of which function in tryptophan degradation. Administration of a B. uniformis harboring TnaA mutant failed to inhibit melanoma growth in gnotobiotic mice. Notably, administration of indoles, but not kynurenines, also effectively inhibited melanoma development, increasing immune cell infiltration into the tumors. Correspondingly, levels of bacterially encoded tryptophan-degrading enzymes were higher in cohorts of melanoma patients responding to immune checkpoint blockade. These findings highlight a novel mechanism of anti-tumor immunity and tumor growth inhibition dependent on the tryptophan degradation products, indoles, produced by intestinal Bacteroides species.

cancer biology↗

bioRxiv2025

Gut Competition Dynamics of Live Bacterial Therapeutics Are Shaped by Microbiome Complexity, Diet, and Therapeutic Transgenes

Competitive exclusion is conventionally believed to prevent the establishment of a secondary strain of the same bacterial species in the gut microbiome, raising concerns for the deployment of live bacterial therapeutics (LBTs), especially if the bacterial chassis is a strain native to the gut. In this study, we investigated factors influencing competition dynamics in the murine gut using isogenic native Escherichia coli strains. We found that competition outcomes are context-dependent, modulated by microbiome complexity, LBT transgene expression, intestinal inflammation, and host diet. Furthermore, we demonstrated that native LBTs can establish long-term engraftment in the gut alongside a parental strain, with transgene-associated fitness effects influencing competition. We identified various interventions, including strategic dosing and dietary modulation, that significantly enhanced LBT colonization levels by 2 to 3 orders of magnitude. These insights provide a framework for optimizing LBT engraftment and efficacy, supporting their potential translation for human therapeutic applications.

microbiology↗

bioRxiv2020

Alterations in the gut microbiome by HIV-1 infection or a high-fat diet associates with systemic immune activation and inflammation in double humanized-BLT mice

BackgroundWhile the translatability of gut microbiome studies utilizing animal models to humans has proven difficult, studying the gut microbiome directly in humans is also challenging due to the existence of many confounding variables. Therefore, we utilized double humanized mice, which have both an engrafted stable human-like gut microbiome and functional human immune system. With this model, we were able to determine the in vivo impact of HIV-1 infection or a high-fat diet (HFD) on gut human microbiome composition, and its relationship with human immune cell activation and systemic inflammation. ResultsSurgery was performed on NSG mice to create humanized bone-marrow, liver, thymus mice (hu-mice). In order to create double hu-mice, the hu-mice were treated with broad spectrum antibiotics to deplete murine gut bacteria and subsequently transplanted with human fecal material from healthy human donors. We characterized 262 fecal samples from hu-mice, double hu-mice, and human fecal donors to determine the impact of HIV-1 infection or HFD on the gut microbiome and systemic immune activation and inflammation. We found that HIV-1 infection altered the human-like gut microbiome of double hu-mice, which was associated with decreased human CD4 T cells and increased systemic inflammation and immune activation. Further, using a HFD we induced gut microbial dysbiosis in double hu-mice which corresponded with increased systemic immune activation and inflammation. ConclusionsHere, we describe the changes in the human gut microbiome and human immune system due to HIV-1 infection or HFD using our double hu-mice model. HIV-1 infection led to changes in the composition of the human-like gut microbiome that was associated with human CD4 T cell loss and high levels of inflammation and immune activation. The HFD quickly changed the composition of the gut microbiome and led to systemic immune activation and inflammation. We further identified a subset of gut bacteria in HIV-1 infected and HFD fed double hu-mice that was closely associated with systemic inflammation and immune activation. This study demonstrated how double humanized mice can be used to study the complex in vivo interactions of the gut microbiome and human immune system in the context of both disease and diet.

microbiology↗

bioRxiv2019

Stable Engraftment of a Human Gut Bacterial Microbiome in Double Humanized BLT-mice

BackgroundHumanized mice featuring a functional human immune system are an important pre-clinical model for examining immune responses to human-specific pathogens. This model has been widely utilized to study human diseases that are otherwise impossible or difficult to investigate in humans or with other animal models. However, one limitation of using humanized mice is their native murine gut microbiome, which significantly differs from the one found in humans. These differences may be even greater for mice housed and bred in specific pathogen free conditions. Given the importance of the gut microbiome to human health and disease, these differences may profoundly impact the ability to translate the results from humanized mice studies to human disease. Further, there is a critical need for improved pre-clinical models to study the complex in vivo relationships of the gut microbiome, immune system, and human disease. We therefore created double humanized mice with both a functional human immune system and stable human-like gut microbiome.\n\nResultsSurgery was performed on NOD.Cg-PrkdcscidII2rgtm1Wjl/SzJ (NSG) mice to create bone-marrow, liver, thymus (BLT) humanized mice. After immune reconstitution, mice were treated with broad spectrum antibiotics to deplete murine gut bacteria and then transplanted with fecal material from healthy human donors. Characterization of 173 fecal samples obtained from 45 humanized mice revealed that double humanized mice had unique 16S rRNA gene profiles consistent with those of the individual human donor samples. Importantly, transplanted human-like gut microbiomes were stable in mice for the duration of the study, up to 14.5 weeks post-transplant. Microbiomes of double humanized mice also harbored predicted functional capacities that more closely resembled those of the human donors compared to humanized mice.\n\nConclusionsHere, we describe successful engraftment of a stable human microbiome in BLT humanized mice to further improve this preclinical humanized mouse model. These double humanized mice represent a unique and tractable new model to study the complex relationships between the human gut microbiome, human immune system, and human disease in vivo.

microbiology↗