'Hygienic' lymphocytes convey increased cancer risk

Commensal bacteria modulate the tumor microenvironment

It has been recently shown that gut microbes modulate whole host immune and hormonal factors impacting the fate of distant preneoplastic lesions toward malignancy or regression. This raises the possibility that the tumor microenvironment interacts with broader systemic microbial-immune networks. These accumulated findings suggest novel therapeutic opportunities for holobiont engineering in emerging tumor microenvironments.

Role of the microbiome in non-gastrointestinal cancers

“The forgotten organ”, the human microbiome, comprises a community of microorganisms that colonizes various sites of the human body. Through coevolution of bacteria, archaea and fungi with the human host over thousands of years, a complex host-microbiome relationship emerged in which many functions, including metabolism and immune responses, became codependent. This coupling becomes evident when disruption in the microbiome composition, termed dysbiosis, is mirrored by the development of pathologies in the host. Among the most serious consequences of dysbiosis, is the development of cancer. As many as 20% of total cancers worldwide are caused by a microbial agent. To date, a vast majority of microbiome-cancer studies focus solely on the microbiome of the large intestine and the development of gastrointestinal cancers. Here, we will review the available evidence implicating microbiome involvement in the development and progression of non-gastrointestinal cancers, while distinguishing between viral and bacterial drivers of cancer, as well as “local” and “systemic”, “cancer-stimulating” and “cancer-suppressing” effects of the microbiome. Developing a system-wide approach to cancer-microbiome studies will be crucial in understanding how microbiome influences carcinogenesis, and may enable to employ microbiome-targeting approaches as part of cancer treatment.

Beneficial bacteria inhibit cachexia

Muscle wasting, known as cachexia, is a debilitating condition associated with chronic inflammation such as during cancer. Beneficial microbes have been shown to optimize systemic inflammatory tone during good health; however, interactions between microbes and host immunity in the context of cachexia are incompletely understood. Here we use mouse models to test roles for bacteria in muscle wasting syndromes. We find that feeding of a human commensal microbe, Lactobacillus reuteri, to mice is sufficient to lower systemic indices of inflammation and inhibit cachexia. Further, the microbial muscle-building phenomenon extends to normal aging as wild type animals exhibited increased growth hormone levels and up-regulation of transcription factor Forkhead Box N1 [FoxN1] associated with thymus gland retention and longevity. Interestingly, mice with a defective FoxN1 gene (athymic nude) fail to inhibit sarcopenia after L. reuteri therapy, indicating a FoxN1-mediated mechanism. In conclusion, symbiotic bacteria may serve to stimulate FoxN1 and thymic functions that regulate inflammation, offering possible alternatives for cachexia prevention and novel insights into roles for microbiota in mammalian ontogeny and phylogeny.

Gut bacteria and cancer

Microbiota on the mucosal surfaces of the gastrointestinal (GI) tract greatly outnumbers the cells in the human body. Effects of antibiotics indicate that GI tract bacteria may be determining the fate of distal cancers. Recent data implicate dysregulated host responses to enteric bacteria leading to cancers in extra-intestinal sites. Together these findings point to novel anti-cancer strategies aimed at promoting GI tract homeostasis.