The effect of intestinal flora on immune checkpoint inhibitors in tumor treatment: a narrative review

Advances in the role of gut microbiota in the regulation of the tumor microenvironment (Review)

As a protector of human health, the gut microbiota plays an important role in the development of the immune system during childhood, and the regulation of dietary habits, metabolism and immune system during adulthood. Dysregulated gut flora is not pathogenic, but it can weaken the protective effect of the immune system and cause various diseases. The tumor microenvironment is a physiological environment formed during tumor growth, which provides nutrients and growth factors necessary for tumor growth. As an important factor affecting the tumor microenvironment, the intestinal microflora affects the development of tumors through the mechanisms of gut and microflora metabolites, gene toxins and signaling pathways. The present article aimed to review the components and mechanisms of action, clinical applications, and biological targets of gut microbiota in the regulation of the tumor microenvironment. The present review provides novel insights for the future use of intestinal flora, to regulate the tumor microenvironment, to intervene in the occurrence, development, treatment and prognosis of tumors.

Implication of the Gut Microbiome and Microbial-Derived Metabolites in Immune-Related Adverse Events: Emergence of Novel Biomarkers for Cancer Immunotherapy

Immune checkpoint inhibitors (ICIs) have changed how we think about tumor management. Combinations of anti-programmed death ligand-1 (PD-L1) immunotherapy have become the standard of care in many advanced-stage cancers, including as a first-line therapy. Aside from improved anti-tumor immunity, the mechanism of action of immune checkpoint inhibitors (ICIs) exposes a new toxicity profile known as immune-related adverse effects (irAEs). This novel toxicity can damage any organ, but the skin, digestive and endocrine systems are the most frequently afflicted. Most ICI-attributed toxicity symptoms are mild, but some are severe and necessitate multidisciplinary side effect management. Obtaining knowledge on the various forms of immune-related toxicities and swiftly changing treatment techniques to lower the probability of experiencing severe irAEs has become a priority in oncological care. In recent years, there has been a growing understanding of an intriguing link between the gut microbiome and ICI outcomes. Multiple studies have demonstrated a connection between microbial metagenomic and metatranscriptomic patterns and ICI efficacy in malignant melanoma, lung and colorectal cancer. The immunomodulatory effect of the gut microbiome can have a real effect on the biological background of irAEs as well. Furthermore, specific microbial signatures and metabolites might be associated with the onset and severity of toxicity symptoms. By identifying these biological factors, novel biomarkers can be used in clinical practice to predict and manage potential irAEs. This comprehensive review aims to summarize the clinical aspects and biological background of ICI-related irAEs and their potential association with the gut microbiome and metabolome. We aim to explore the current state of knowledge on the most important and reliable irAE-related biomarkers of microbial origin and discuss the intriguing connection between ICI efficacy and toxicity.

The Prediction Potential of the Pretreatment Lung Immune Prognostic Index for the Therapeutic Outcomes of Immune Checkpoint Inhibitors in Patients With Solid Cancer: A Systematic Review and Meta-Analysis

Background

The lung immune prognostic index (LIPI) is recently developed to predict immune checkpoint inhibitors (ICIs) treatment outcomes for non-small cell lung cancer. However, its predictive value for other types of cancer remained unclear. This meta-analysis aimed to evaluate the association between pretreatment LIPI score and therapeutic outcomes in cancer patients treated with ICIs.

Methods

We searched PubMed, Cochrane Library literature databases and EMBASE for abstracts and full-text articles published from the inception of the database until 16th, Nov 2020. Meta-analyses were performed separately for progression-free survival (PFS) and overall survival (OS) by using the random-effects model.

Results

A total of 12 studies involving 4883 patients receiving ICIs treatment were identified for the primary analysis. The pooled results implied that compared with good LIPI score groups, patients with poor or intermediate LIPI score were significantly associated with worse OS (HR=3.33, 95%CI 2.64-4.21, P < 0.001, I² = 64.2%; HR=1.71, 95%CI 1.43-2.04, P < 0.001, I² = 43.6%, respectively) and PFS (HR=2.73,95%CI 2.00-3.73, P < 0.001, I² = 78.2%; HR=1.43, 95%CI 1.28-1.61, P < 0.001, I² = 16.3%, respectively). Also, for 1873 patients receiving chemotherapy, a poor LIPI score was significantly associated with worse OS (HR=2.30, 95%CI 1.73-3.07, P < 0.001; I² = 56.2%) and PFS (HR=1.92,95%CI 1.69-2.17; P < 0.001; I² = 0.0%) compared with good LIPI score groups.

Conclusions

A good LIPI score was significantly correlated with improved OS and PFS in cancer patients receiving ICIs or chemotherapy, regardless of the types of cancer.