Multi-layered control of PD-L1 expression in Epstein-Barr virus-associated gastric cancer

Genomic landscape of virus-associated cancers

It has been estimated that 15%-20% of human cancers are attributable to infections, mostly by carcinogenic viruses. The incidence varies worldwide, with a majority affecting developing countries. Here, we present a comparative analysis of virus-positive and virus-negative tumors in nine cancers linked to five viruses. We find that virus-positive tumors occur more frequently in males and show geographical disparities in incidence. Genomic analysis of 1,658 tumors reveals virus-positive tumors exhibit distinct mutation signatures and driver gene mutations and possess a lower somatic mutation burden compared to virus-negative tumors of the same cancer type. For example, compared to the respective virus-negative counterparts, virus-positive cases across different cancer histologies had less often mutations of TP53 and deletions of 9p21.3/ CDKN2 A- CDKN1A ; Epstein-Barr virus-positive (EBV+) gastric cancer had more frequent mutations of EIF4A1 and ARID1A and less marked mismatch repair deficiency signatures; and EBV-positive cHL had fewer somatic genetic lesions of JAK-STAT, NF-κB, PI3K-AKT and HLA-I genes and a less pronounced activity of the aberrant somatic hypermutation signature. In cHL, we also identify germline homozygosity in HLA class I as a potential risk factor for the development of EBV-positive Hodgkin lymphoma. Finally, an analysis of clinical trials of PD-(L)1 inhibitors in four virus-associated cancers suggested an association of viral infection with higher response rate in patients receiving such treatments, which was particularly evident in gastric cancer and head and neck squamous cell carcinoma. These results illustrate the epidemiological, genetic, prognostic, and therapeutic trends across virus-associated malignancies.

EBV-associated diseases: Current therapeutics and emerging technologies

EBV is a prevalent virus, infecting >90% of the world's population. This is an oncogenic virus that causes ~200,000 cancer-related deaths annually. It is, in addition, a significant contributor to the burden of autoimmune diseases. Thus, EBV represents a significant public health burden. Upon infection, EBV remains dormant in host cells for long periods of time. However, the presence or episodic reactivation of the virus increases the risk of transforming healthy cells to malignant cells that routinely escape host immune surveillance or of producing pathogenic autoantibodies. Cancers caused by EBV display distinct molecular behaviors compared to those of the same tissue type that are not caused by EBV, presenting opportunities for targeted treatments. Despite some encouraging results from exploration of vaccines, antiviral agents and immune- and cell-based treatments, the efficacy and safety of most therapeutics remain unclear. Here, we provide an up-to-date review focusing on underlying immune and environmental mechanisms, current therapeutics and vaccines, animal models and emerging technologies to study EBV-associated diseases that may help provide insights for the development of novel effective treatments.

miR-105-5p regulates PD-L1 expression and tumor immunogenicity in gastric cancer

Cancer immunotherapies targeting the interaction between Programmed death 1 (PD-1) and Programmed death ligand 1 (PD-L1) have recently been approved for the treatment of multiple cancer types, including gastric cancer. However, not all patients respond to these therapies, while some eventually acquire resistance. A partial predictive biomarker for positive response to PD-1/PD-L1 therapy is PD-L1 expression, which has been shown to be under strict post-transcriptional control in cancer. By fractionating the PD-L1 3' untranslated region (3'UTR) into multiple overlapping fragments, we identified a small 100-nucleotide-long cis-acting region as being necessary and sufficient for post-transcriptional repression of PD-L1 expression in gastric cancer. In parallel, we performed a correlation analysis between PD-L1 expression and all host miRNAs in stomach cancer patient samples. A single miRNA, miR-105-5p, was predicted to bind to the identified cis-acting 3'UTR region and to negatively correlate with PD-L1 expression. Overexpression of miR-105-5p in gastric cancer cell lines resulted in decreased expression of PD-L1, both at the total protein and surface expression levels, and induced CD8⁺ T cell activation in co-culture assays. Finally, we show that expression of miR-105-5p in gastric cancer is partly controlled by DNA methylation of a cancer- and germline-specific promoter of its host gene, GABRA3. Dysregulation of miR-105-5p is observed in many cancer types and this study shows the importance of this miRNA in controlling the immunogenicity of cancer cells, thus highlighting it as a potential biomarker for PD-1/PD-L1 therapy and target for combinatorial immunotherapy.