Porphyromonas gingivalis induced up-regulation of PD-L1 in colon carcinoma cells

Periodontal pathogens and cancer development

Increasing evidence suggests a significant association between periodontal disease and the occurrence of various cancers. The carcinogenic potential of several periodontal pathogens has been substantiated in vitro and in vivo. This review provides a comprehensive overview of the diverse mechanisms employed by different periodontal pathogens in the development of cancer. These mechanisms induce chronic inflammation, inhibit the host's immune system, activate cell invasion and proliferation, possess anti-apoptotic activity, and produce carcinogenic substances. Elucidating these mechanisms might provide new insights for developing novel approaches for tumor prevention, therapeutic purposes, and survival improvement.

Periodontitis and risk of cancer: Mechanistic evidence

This review aims to critically analyze the pathways of interaction and the pathogenic mechanisms linking periodontitis and oral bacteria with the initiation/progression of cancer at different body compartments. A higher risk of head and neck cancer has been consistently associated with periodontitis. This relationship has been explained by the local promotion of dysbiosis, chronic inflammation, immune evasion, and direct (epi)genetic damage to epithelial cells by periodontal pathobionts and their toxins. Epidemiological reports have also studied a possible link between periodontitis and the incidence of other malignancies at distant sites, such as lung, breast, prostate, and digestive tract cancers. Mechanistically, different pathways have been involved, including the induction of a chronic systemic inflammatory state and the spreading of oral pathobionts with carcinogenic potential. Indeed, periodontitis may promote low-grade systemic inflammation and phenotypic changes in the mononuclear cells, leading to the release of free radicals and cytokines, as well as extracellular matrix degradation, which are all mechanisms involved in carcinogenic and metastatic processes. Moreover, the transient hematogenous spill out or micro-aspiration/swallowing of periodontal bacteria and their virulence factors (i.e., lipopolysaccharides, fimbriae), may lead to non-indigenous bacterial colonization of multiple microenvironments. These events may in turn replenish the tumor-associated microbiome and thus influence the molecular hallmarks of cancer. Particularly, specific strains of oral pathobionts (e.g., Porphyromonas gingivalis and Fusobacterium nucleatum) may translocate through the hematogenous and enteral routes, being implicated in esophageal, gastric, pancreatic, and colorectal tumorigenesis through the modulation of the gastrointestinal antitumor immune system (i.e., tumor-infiltrating T cells) and the increased expression of pro-inflammatory/oncogenic genes. Ultimately, the potential influence of common risk factors, relevant comorbidities, and upstream drivers, such as gerovulnerability to multiple diseases, in explaining the relationship cannot be disregarded. The evidence analyzed here emphasizes the possible relevance of periodontitis in cancer initiation/progression and stimulates future research endeavors.

Specific Intratumor Bacteria Genera and TRG Recombinations Associated with Greater Survival Probability in Alimentary Tract Cancers

INTRODUCTION

There remains a lack of knowledge regarding the effects of the intratumor microbiome on the tumor immune milieu. We aimed to investigate whether intratumoral bacterial RNA sequence abundance in gastric and esophageal cancers is associated with T-cell infiltrate features.

METHODS

We assessed cases representing the stomach adenocarcinoma (STAD) and esophageal cancer (ESCA) databases of The Cancer Genome Atlas. RNA-seq data estimating intratumoral bacterial abundance was obtained from publicly available sources. TCR recombination reads were mined from exome files. Survival models were generated using the lifelines python package.

RESULTS

Increasing levels of the Klebsiella genus were associated with a better OS probability (hazard ratio, 0.5), via a Cox proportional hazards model. The higher Klebsiella abundance was associated with a significantly increased overall (p = 0.0001) and disease-specific survival (p = 0.0289) probability for the STAD dataset. Cases representing the upper 50th percentile of Klebsiella abundance also represented a significantly increased recovery of TRG and TRD recombination reads (p = 0.00192). Analogous results were found for the Aquincola genus in ESCA.

CONCLUSIONS

This is the first report of associations between low biomass bacterial samples from primary tumor samples with patient survival and with an increased gamma-delta T cell infiltrate. Results indicate that the gamma-delta T cells potentially play a role in the dynamics of the bacterial infiltration of primary tumors of the alimentary tract.

The presence of intratumoral Porphyromonas gingivalis correlates with a previously defined pancreatic adenocarcinoma, immune cell expression phenotype and with tumor resident, adaptive immune receptor features

The association between pancreatic adenocarcinoma (PAAD) and the pancreatic microbiome is not fully understood, although bacteria may decrease the effectiveness of chemotherapy and lead to anti-apoptotic, pro-inflammatory microenvironments. To better understand the relationship between the PAAD microbiome and the microenvironment, we identified Porphyromonas gingivalis-positive PAAD samples and found a strong association between intratumoral P. gingivalis and: (i) an immune cell gene expression phenotype previously defined by others as gene program 7; and (ii) recovery of immunoglobulin recombination, sequencing reads. We applied a novel chemical complementarity scoring algorithm, suitable for a big data setting, and determined that the previously established P. gingivalis antigen, rpgB had a reduced chemical complementarity with T-cell receptor (TCR) complementarity-determining region-3 amino acid sequences recovered from PAAD samples with P. gingivalis in comparison to TCR-rpgB chemical complementarity represented by the PAAD samples that lacked P. gingivalis. This finding strengthens the existing body of evidence correlating P. gingivalis with PAAD, which may have implications for the treatment and prognosis of patients. Furthermore, demonstrating the correlation of P. gingivalis and gene program 7 raises the question of whether P. gingivalis infection is responsible for the gene program 7 subdivision of PAAD?

Letter on "Role of gut microbiome in immune regulation and immune checkpoint therapy of colorectal cancer"

Investigations that decipher the human microbiome have reformed the way medicine is focusing on bacteria. An interesting research review recently published in the journal of Digestive Diseases and Sciences conceivably linked adjunctive commensal intestinal bacteria with the capacity to modulate the immune microenvironment towards immune checkpoint inhibitor (ICIs) efficacy of cancer immunotherapy. Evidence has emerged that the intestinal microbiome can modulate outcomes to ICIs therapies via two major mechanisms, namely mechanisms that are antigen-specific (i.e., epitopes are shared between microbial and tumour antigens that can enhance or reduce anti-tumour immune responses) and those mechanisms that are antigen-independent (i.e., modulation of responses to ICIs by engaging innate and/or adaptive immune cells).

PD-1/PD-L1 pathway: A double-edged sword in periodontitis

Periodontitis is a disease caused by infection and immunological imbalance, which often leads to the destruction of periodontal tissue. Programmed death protein 1 (PD-1) and its ligand: programmed death ligand 1 (PD-L1) are important "immune checkpoint" proteins that have a negative regulatory effect on T cells and are targets of immunotherapy. Studies have shown that the expression of PD-1 and PD-L1 in patients with periodontitis is higher than that in healthy individuals. The keystone pathogen Porphyromonas gingivalis (P. gingivalis) is believed to be the main factor driving the upregulation of PD-1/PD-L1. High expression of PD-1/PD-L1 can inhibit the inflammatory response and reduce the destruction of periodontal supporting tissues, but conversely, it can promote the "immune escape" of P. gingivalis, thus magnifying infections. In addition, the PD-1/PD-L1 pathway is also associated with various diseases, such as cancer and Alzheimer's disease. In this review, we discuss the influence and mechanism of the PD-1/PD-L1 pathway as a "double-edged sword" affecting the occurrence and development of periodontitis, as well as its function in periodontitis-related systemic disorders. The PD-1/PD-L1 pathway could be a new avenue for periodontal and its related systemic disorders therapy.

Regulatory effects of oral microbe on intestinal microbiota and the illness

Over the past decade, the association between oral health, intestinal microbiota, and systemic diseases has been further validated. Some oral microbial species have been isolated from pathological intestine mucosa or feces and identified as biomarkers for intestinal diseases. A small proportion of oral microbiome passes through or colonizes the lower gastrointestinal tract, even in healthy individuals. Opportunistic pathogens from the oral cavity may expand and participate in the occurrence and progression of intestinal diseases when the anatomical barrier is disrupted. These disruptors interact with the intestinal microbiota, disturbing indigenous microorganisms, and mucosal barriers through direct colonization, blood circulation, or derived metabolite pathways. While interacting with the host's immune system, oral-derived pathogens stimulate inflammation responses and guide the transition of the intestinal microenvironment from a healthy state to a pre-disease state. Therefore, the oral-gut microbiome axis sheds light on new clinical therapy options, and gastrointestinal tract ecology balance necessitates simultaneous consideration of both oral and gut microbiomes. This review summarizes possible routes of oral microbes entering the intestine and the effects of certain oral bacteria on intestinal microbiota and the host's immune responses.

The difference of human gut microbiome in colorectal cancer with and without metastases

Metastasis of colorectal cancer is deemed to be closely related to the changes in the human gut microbiome. The purpose of our study is to distinguish the differences in gut microbiota between colorectal cancer with and without metastases. Firstly, this study recruited colorectal cancer patients who met the established inclusion and exclusion criteria in the Oncology Department of Zhejiang Hospital of Traditional Chinese Medicine from February 2019 to June 2019. Fresh stool samples from healthy volunteers, non-metastatic patients, and metastatic patients were collected for 16S rRNA gene sequencing, to analyze the diversity and abundance of intestinal microorganisms in each group. The results showed that the microbial composition of the control group was more aplenty than the experimental group, while the difference also happened in the Tumor and the metastases group. At the phylum level, the abundance of Bacteroidetes significantly declined in the Tumor and the metastases group, compared with the control group. At the class level, Bacilli increased in experimental groups, while its abundance in the Tumor group was significantly higher than that in the metastases group. At the order level, the Tumor group had the highest abundance of Lactobacillales, followed by the metastases group and the control group had the lowest abundance. Overall, our study showed that the composition of the flora changed with the occurrence of metastasis in colorectal cancer. Therefore, the analysis of gut microbiota can serve as a supplement biological basis for the diagnosis and treatment of metastatic colorectal cancer which may offer the potential to develop non-invasive diagnostic tests.

PD-L1, a Potential Immunomodulator Linking Immunology and Orthodontically Induced Inflammatory Root Resorption (OIIRR): Friend or Foe?

Orthodontically induced inflammatory root resorption (OIIRR) is considered an undesired and inevitable complication induced by orthodontic forces. This inflammatory mechanism is regulated by immune cells that precede orthodontic tooth movement (OTM) and can influence the severity of OIIRR. The process of OIIRR is based on an immune response. On some occasions, the immune system attacks the dentition by inflammatory processes during orthodontic treatment. Studies on the involvement of the PD-1/PD-L1 immune checkpoint have demonstrated its role in evading immune responses, aiming to identify possible novel therapeutic approaches for periodontitis. In the field of orthodontics, the important question arises of whether PD-L1 has a role in the development of OIIRR to amplify the amount of resorption. We hypothesize that blocking of the PD-L1 immune checkpoint could be a suitable procedure to reduce the process of OIIRR during orthodontic tooth movement. This review attempts to shed light on the regulation of immune mechanisms and inflammatory responses that could influence the pathogenesis of OIIRR and to acquire knowledge about the role of PD-L1 in the immunomodulation involved in OIIRR. Possible clinical outcomes will be discussed in relation to PD-L1 expression and immunologic changes throughout the resorption process.

Macrophages: A communication network linking Porphyromonas gingivalis infection and associated systemic diseases

Porphyromonas gingivalis (P. gingivalis) is a Gram-negative anaerobic pathogen that is involved in the pathogenesis of periodontitis and systemic diseases. P. gingivalis has recently been detected in rheumatoid arthritis (RA), cardiovascular disease, and tumors, as well as Alzheimer’s disease (AD), and the presence of P. gingivalis in these diseases are correlated with poor prognosis. Macrophages are major innate immune cells which modulate immune responses against pathogens, however, multiple bacteria have evolved abilities to evade or even subvert the macrophages’ immune response, in which subsequently promote the diseases’ initiation and progression. P. gingivalis as a keystone pathogen of periodontitis has received increasing attention for the onset and development of systemic diseases. P. gingivalis induces macrophage polarization and inflammasome activation. It also causes immune response evasion which plays important roles in promoting inflammatory diseases, autoimmune diseases, and tumor development. In this review, we summarize recent discoveries on the interaction of P. gingivalis and macrophages in relevant disease development and progression, such as periodontitis, atherosclerosis, RA, AD, and cancers, aiming to provide an in-depth mechanistic understanding of this interaction and potential therapeutic strategies.

The Microbiome in Pancreatic Cancer-Implications for Diagnosis and Precision Bacteriophage Therapy for This Low Survival Disease

While the mortality rates for many cancers have decreased due to improved detection and treatments, that of pancreatic cancer remains stubbornly high. The microbiome is an important factor in the progression of many cancers. Greater understanding of the microbiome in pancreatic cancer patients, as well as its manipulation, may assist in diagnosis and treatment of this disease. In this report we reviewed studies that compared microbiome changes in pancreatic cancer patients and non-cancer patients. We then identified which bacterial genera were most increased in relative abundance across the oral, pancreatic, duodenal, and faecal tissue microbiomes. In light of these findings, we discuss the potential for utilising these bacteria as diagnostic biomarkers, as well as their potential control using precision targeting with bacteriophages, in instances where a causal oncogenic link is made.

Microbial Protein Binding to gC1qR Drives PLA2G1B-Induced CD4 T-Cell Anergy

The origin of the impaired CD4 T-cell response and immunodeficiency of HIV-infected patients is still only partially understood. We recently demonstrated that PLA2G1B phospholipase synergizes with the HIV gp41 envelope protein in HIV viremic plasma to induce large abnormal membrane microdomains (aMMDs) that trap and inactivate physiological receptors, such as those for IL-7. However, the mechanism of regulation of PLA2G1B activity by the cofactor gp41 is not known. Here, we developed an assay to directly follow PLA2G1B enzymatic activity on CD4 T-cell membranes. We demonstrated that gp41 directly binds to PLA2G1B and increases PLA2G1B enzymatic activity on CD4 membrane. Furthermore, we show that the conserved 3S sequence of gp41, known to bind to the innate sensor gC1qR, increases PLA2G1B activity in a gC1qR-dependent manner using gC1qR KO cells. The critical role of the 3S motif and gC1qR in the inhibition of CD4 T-cell function by the PLA2G1B/cofactor system in HIV-infected patients led us to screen additional microbial proteins for 3S-like motifs and to study other proteins known to bind to the gC1qR to further investigate the role of the PLA2G1B/cofactor system in other infectious diseases and carcinogenesis. We have thus extended the PLA2G1B/cofactor system to HCV and Staphylococcus aureus infections and additional pathologies where microbial proteins with 3S-like motifs also increase PLA2G1B enzymatic activity. Notably, the bacteria Porphyromonas gingivalis, which is associated with pancreatic ductal adenocarcinoma (PDAC), encodes such a cofactor protein and increased PLA2G1B activity in PDAC patient plasma inhibits the CD4 response to IL-7. Our findings identify PLA2G1B/cofactor system as a CD4 T-cell inhibitor. It involves the gC1qR and disease-specific cofactors which are gC1qR-binding proteins that can contain 3S-like motifs. This mechanism involved in HIV-1 immunodeficiency could play a role in pancreatic cancer and several other diseases. These observations suggest that the PLA2G1B/cofactor system is a general CD4 T-cell inhibitor and pave the way for further studies to better understand the role of CD4 T-cell anergy in infectious diseases and tumor escape.