Absence of central tolerance in Aire-deficient mice synergizes with immune-checkpoint inhibition to enhance antitumor responses.

The endogenous anti-tumor responses are limited in part by the absence of tumor-reactive T cells, an inevitable consequence of thymic central tolerance mechanisms ensuring prevention of autoimmunity. Here we show that tumor rejection induced by immune checkpoint blockade is significantly enhanced in Aire-deficient mice, the epitome of central tolerance breakdown. The observed synergy in tumor rejection extended to different tumor models, was accompanied by increased numbers of activated T cells expressing high levels of Gzma, Gzmb, Perforin, Cxcr3, and increased intratumoural levels of Cxcl9 and Cxcl10 compared to wild-type mice. Consistent with Aire's central role in T cell repertoire selection, single cell TCR sequencing unveiled expansion of several clones with high tumor reactivity. The data suggest that breakdown in central tolerance synergizes with immune checkpoint blockade in enhancing anti-tumor immunity and may serve as a model to unmask novel anti-tumor therapies including anti-tumor TCRs, normally purged during central tolerance.

DAI Senses Influenza A Virus Genomic RNA and Activates RIPK3-Dependent Cell Death.

Influenza A virus (IAV) is an RNA virus that is cytotoxic to most cell types in which it replicates. IAV activates the host kinase RIPK3, which induces cell death via parallel pathways of necroptosis, driven by the pseudokinase MLKL, and apoptosis, dependent on the adaptor proteins RIPK1 and FADD. How IAV activates RIPK3 remains unknown. We report that DAI (ZBP1/DLM-1), previously implicated as a cytoplasmic DNA sensor, is essential for RIPK3 activation by IAV. Upon infection, DAI recognizes IAV genomic RNA, associates with RIPK3, and is required for recruitment of MLKL and RIPK1 to RIPK3. Cells lacking DAI or containing DAI mutants deficient in nucleic acid binding are resistant to IAV-triggered necroptosis and apoptosis. DAI-deficient mice fail to control IAV replication and succumb to lethal respiratory infection. These results identify DAI as a link between IAV replication and RIPK3 activation and implicate DAI as a sensor of RNA viruses.

In Vivo RNAi Screening Identifies MDA5 as a Significant Contributor to the Cellular Defense against Influenza A Virus.

Responding to an influenza A virus (IAV) infection demands an effective intrinsic cellular defense strategy to slow replication. To identify contributing host factors to this defense, we exploited the host microRNA pathway to perform an in vivo RNAi screen. To this end, IAV, lacking a functional NS1 antagonist, was engineered to encode individual siRNAs against antiviral host genes in an effort to rescue attenuation. This screening platform resulted in the enrichment of strains targeting virus-activated transcription factors, specific antiviral effectors, and intracellular pattern recognition receptors (PRRs). Interestingly, in addition to RIG-I, the PRR for IAV, a virus with the capacity to silence MDA5 also emerged as a dominant strain in wild-type, but not in MDA5-deficient mice. Transcriptional profiling of infected knockout cells confirmed RIG-I to be the primary PRR for IAV but implicated MDA5 as a significant contributor to the cellular defense against influenza A virus.

An in vivo RNAi screening approach to identify host determinants of virus replication.

RNA interference (RNAi) has been extensively used to identify host factors affecting virus infection but requires exogenous delivery of short interfering RNAs (siRNAs), thus limiting the technique to nonphysiological infection models and a single defined cell type. We report an alternative screening approach using siRNA delivery via infection with a replication-competent RNA virus. In this system, natural selection, defined by siRNA production, permits the identification of host restriction factors through virus enrichment during a physiological infection. We validate this approach with a large-scale siRNA screen in the context of an in vivo alphavirus infection. Monitoring virus evolution across four independent screens identified two categories of enriched siRNAs: specific effectors of the direct antiviral arsenal and host factors that indirectly dampened the overall antiviral response. These results suggest that pathogenicity may be defined by the ability of the virus to antagonize broad cellular responses and specific antiviral factors.