Inherited chromosomally integrated HHV-6 demonstrates tissue-specific RNA expression in vivo that correlates with increased antibody immune response.

Human herpesvirus-6A and 6B (HHV-6A, HHV-6B) are human viruses capable of chromosomal integration. Approximately 1% of the human population carry one copy of HHV-6A/B integrated into every cell in their body, referred to as inherited chromosomally integrated HHV-6A/B (iciHHV-6A/B). Whether iciHHV-6A/B is transcriptionally active in vivo and how it shapes the immunological response is still unclear. Here, we screened DNA-Seq and RNA-Seq data for 650 individuals available through the Genotype-Tissue Expression (GTEx) project and identified 2 iciHHV-6A and 4 iciHHV-6B positive individuals. When corresponding tissue-specific gene expression signatures were analyzed, low levels HHV-6A/B gene expression was found across multiple tissues, with the highest levels of gene expression in the brain (specifically for iciHHV-6A), testis, and esophagus. U90 and U100 were the most highly expressed HHV-6 genes in both iciHHV-6A/B individuals. To assess whether this gene expression influences the HHV-6A/B immune response, a cohort of 15,498 subjects was screened and 85 iciHHV-6A/B+subjects were identified. Plasma samples from iciHHV-6A/B+and age- and sex-matched controls were analyzed for antibodies to control antigens or HHV-6A/B antigens. Our results indicate that iciHHV-6A/B+ subjects have significantly more antibodies against the U90 gene product (IE1) relative to non-iciHHV-6 individuals. Antibody responses against EBV and FLU antigens or HHV-6A/B gene products either not expressed or expressed at low levels, such as U47, U57 or U72, were identical between controls and iciHHV-6A/B+ subjects. These results argue that spontaneous gene expression from integrated HHV-6A/B leads to an increase in antigenic burden that translates into a more robust HHV-6A/B-specific antibody response.