Impact of Gut Microbiome on Cancer Immunotherapy
New Findings from Nature Communications
An intriguing study published in Nature Communications has uncovered the significant role of the gut microbiome in the effectiveness of cancer immunotherapy. The human gut hosts approximately 30 trillion bacteria, collectively known as the microbiome. Historically, the microbiome has primarily been understood for its contributions to digestion and nutrient absorption. Recent research, however, highlights its substantial influence on immune cell functionality.
Research Background
The evolving understanding of gut microbiome interactions has spurred numerous investigations into how these microorganisms affect patient responses to cancer immunotherapy. Despite this progress, the molecular mechanisms underlying these interactions remain inadequately explored.
Key Findings from Sanford Burnham Prebys Medical Discovery Institute
A recent study spearheaded by researchers at the Sanford Burnham Prebys Medical Discovery Institute in the United States has pinpointed a molecular link that explains how the gut microbiome affects cancer immunotherapy outcomes.
Role of the UPR Pathway
The research, involving collaboration among scientists from three different hospitals, revealed that the unfolded protein response (UPR) pathway plays a crucial role in mediating the interaction between the gut microbiome and anti-tumor immunity. This cellular pathway functions as a quality control system, efficiently eliminating damaged and improperly folded proteins.
The study found that this pathway was downregulated in patients who responded positively to cancer immunotherapy, indicating its potential as a diagnostic marker for patient classification prior to treatment.
Importance of the RNF5 Gene
Further investigations revealed that the RNF5 gene is vital for facilitating the interaction between the gut microbiome and the immune system. This relationship is now recognized as a significant factor contributing to therapeutic resistance in cancer immunotherapy patients.
Mice lacking the RNF5 gene demonstrated remarkable efficacy in inhibiting melanoma growth. However, this inhibitory effect was significantly reduced when these mice were treated with antibiotics, suggesting that the gut microbiome and the RNF5 gene together influence the immune response against cancer cells.
Microbial Influence on Immune Response
The researchers identified a combination of 11 distinct microbes present in the guts of RNF5-deficient mice. These bacteria are believed to shape the microbiome environment and impact the characteristics of immune cells in these mice. When these microbes were transferred to germ-free mice—models devoid of normal intestinal flora—these mice also gained the ability to inhibit melanoma growth.
Gene Expression and Patient Responses
In melanoma patients undergoing cancer immunotherapy, the expression levels of genes associated with the UPR pathway were found to correlate significantly with patient responsiveness to treatment.
The researchers aim to identify metabolites secreted by these gut microbes to determine if these compounds affect the strength and nature of the anti-tumor immune response.
Reference
Li, Y., Tinoco, R., Elmen, L., Segota, I., Xian, Y., Fujita, Y., . . . Ronai, Z. A. (2019). Gut microbiota dependent anti-tumor immunity restricts melanoma growth in Rnf5(-/-) mice. Nat Commun, 10(1), 1492. doi:10.1038/s41467-019-09525-y