Epigenetic silencing of innate and adaptive immunity genes underlies the immune evasion cancer hallmark in Theileria-infected B-cells.
Cancer hallmarks are characterized by wide-scale changes in gene expression programs. Pioneering studies showed how viral oncogenes target regulatory pathways, but little is known about tumorigenic mechanisms of non-viral pathogens. Theileria annulata is an intracellular parasite (related to apicomplexa parasites causing malaria) which remarkably transforms bovine leukocytes, hijacking host signaling pathways to induce cancer phenotypes, akin to human leukemias. While some host genes contribute to the proliferative or invasive hallmark phenotypes, there is still limited comprehensive understanding of the impact of Theileria infection on host transcription and transformation. We performed a multi-omics meta-analysis to investigate the effect of Theileria infection on cancer hallmarks in bovine B lymphocytes. Combining transcriptomic, proteomic and epigenomic analysis across multiple datasets, we show that Theileria infection suppresses host immune pathways. Specifically, genes encoding innate and adaptive immune mediators are repressed in T. annulata-infected B cells (and in T. parva infected T cells), including downregulation of genes for Toll-like receptors (TLR), inflammasome components of the guanylate binding protein (GBP) family and major histocompatibility complex class (MHC) II genes. Treatment with distinct theilericidal drugs could partially rescue immune gene expression. Mechanistically, we describe alterations in the host epigenome, including loss of activating histone modifications (e.g., H3K18ac, H3K4me3, H3K27ac) on the promoters of repressed immune genes, and enrichment of silencing marks (H3K27me3) on promoters of the BOLA genes and the gene encoding CIITA, the master transcriptional regulator of MHC class II gene expression. Our results suggest that intracellular T. annulata and T. parva parasites could drive an immune evasion cancer hallmark in host lymphocytes by epigenetic silencing of genes for innate and adaptive immunity.