Sensitizing cancer cells to immune checkpoint inhibitors by microbiota-mediated upregulation of HLA class I.

Recent data have shown that gut microbiota has a major impact on the clinical response to immune checkpoint inhibitors (ICIs) in the context of solid tumors. ICI-based therapy acts by unlocking cognate cytotoxic T lymphocyte (CTL) effector responses, and increased sensitivity to ICIs is due to an enhancement of patients' tumor antigen (TA)-specific CTL responses. Cancer clearance by TA-specific CTL requires expression of relevant TAs on cancer cells' HLA class I molecules, and reduced HLA class I expression is a common mechanism used by cancer cells to evade the immune system. Here, we show that metabolites released by bacteria, in particular, phytosphingosine, can upregulate HLA class I expression on cancer cells, sensitizing them to TA-specific CTL lysis in vitro and in vivo, in combination with immunotherapy. This effect is mediated by postbiotic-induced upregulation of NLRC5 in response to upstream MYD88-NF-κB activation, thus significantly controlling tumor growth.

VID22 counteracts G-quadruplex-induced genome instability.

Genome instability is a condition characterized by the accumulation of genetic alterations and is a hallmark of cancer cells. To uncover new genes and cellular pathways affecting endogenous DNA damage and genome integrity, we exploited a Synthetic Genetic Array (SGA)-based screen in yeast. Among the positive genes, we identified VID22, reported to be involved in DNA double-strand break repair. vid22Δ cells exhibit increased levels of endogenous DNA damage, chronic DNA damage response activation and accumulate DNA aberrations in sequences displaying high probabilities of forming G-quadruplexes (G4-DNA). If not resolved, these DNA secondary structures can block the progression of both DNA and RNA polymerases and correlate with chromosome fragile sites. Vid22 binds to and protects DNA at G4-containing regions both in vitro and in vivo. Loss of VID22 causes an increase in gross chromosomal rearrangement (GCR) events dependent on G-quadruplex forming sequences. Moreover, the absence of Vid22 causes defects in the correct maintenance of G4-DNA rich elements, such as telomeres and mtDNA, and hypersensitivity to the G4-stabilizing ligand TMPyP4. We thus propose that Vid22 is directly involved in genome integrity maintenance as a novel regulator of G4 metabolism.

Identification of a choroid plexus vascular barrier closing during intestinal inflammation.

Up to 40% of patients with inflammatory bowel disease present with psychosocial disturbances. We previously identified a gut vascular barrier that controls the dissemination of bacteria from the intestine to the liver. Here, we describe a vascular barrier in the brain choroid plexus (PVB) that is modulated in response to intestinal inflammation through bacteria-derived lipopolysaccharide. The inflammatory response induces PVB closure after gut vascular barrier opening by the up-regulation of the wingless-type, catenin-beta 1 (Wnt/ß-catenin) signaling pathway, rendering it inaccessible to large molecules. In a model of genetically driven closure of choroid plexus endothelial cells, we observed a deficit in short-term memory and anxiety-like behavior, suggesting that PVB closure may correlate with mental deficits. Inflammatory bowel disease­related mental symptoms may thus be the consequence of a deregulated gut­brain vascular axis.