Inherited chromosomally integrated HHV-6 demonstrates tissue-specific RNA expressionin vivothat correlates with increased antibody immune response

Abstract

35 Human herpesvirus-6A and 6B (HHV-6A, HHV-6B) are human viruses capable of 36 chromosomal integration. Approximately 1% of the human population carry one copy of HHV-37 6A/B integrated into every cell in their body, referred to as inherited chromosomally integrated 38 human herpesvirus 6A/B (iciHHV-6A/B). Whether iciHHV-6A/B is transcriptionally active in vivo 39 and how it shapes the immunological response is still unclear. Here, we screened DNA-Seq 40 and RNA-Seq data for 650 individuals available through the Genotype-Tissue Expression 41 (GTEx) project and identified 2 iciHHV-6A and 4 iciHHV-6B positive candidates. When 42 corresponding tissue-specific gene expression signatures were analyzed, low levels HHV-6A/B 43 gene expression was found across multiple tissues, with the highest levels of gene expression 44 in the brain (specifically for iciHHV-6A), testis, esophagus, and adrenal gland. U90 and U100 45 were the most highly expressed HHV-6 genes in both iciHHV-6A and iciHHV-6B individuals. To 46 assess whether tissue-specific gene expression from iciHHV-6A/B influences the immune 47 response, a cohort of 15,498 subjects was screened and 85 iciHHV-6A/B + subjects were 48 identified. Plasma samples from iciHHV-6A/B + and age and sex matched controls were 49 analyzed for antibodies to control antigens (CMV, EBV, FLU) or HHV-6A/B antigens. Our results 50 indicate that iciHHV-6A/B + subjects have significantly more antibodies against the U90 gene 51 product (IE1) relative to non-iciHHV-6 individuals. Antibody responses against EBV and FLU 52 antigens or HHV-6A/B gene products either not expressed or expressed at low levels, such as 53 U47, U57 or U72, were identical between controls and iciHHV-6A/B+ subjects. CMV 54 seropositive individuals with iciHHV-6A/B + have more antibodies against CMV pp150, relative to 55 CMV seropositive controls. These results argue that spontaneous gene expression from 56 integrated HHV-6A/B leads to an increase in antigenic burden that translates into a more robust 57 HHV-6A/B specific antibody response.58 59 Importance 60 3 HHV-6A/B are human herpesviruses that have the unique property of being able to 61 integrate into the subtelomeric regions of human chromosomes. Approximately 1% of the 62 world's population carries integrated HHV-6A/B genome in every cell of their body. Whether 63 viral genes are transcriptionally active in these individuals is unclear. By taking advantage of a 64 unique tissue-specific gene expression dataset, we show the majority of tissues from iciHHV-6 65 individuals do not show HHV-6 gene expression. Brain and testes showed the highest tissue-66 specific expression of HHV-6 genes in two separate datasets. Two HHV-6 genes, U90 67 (immediate early 1 protein) and U100 (glycoproteins Q1 and Q2), were found to be selectively 68 and consistently expressed across several human tissues. Expression of U90 translates into an 69 increase in antigen-specific antibody response in iciHHV-6A/B + subjects relative to controls. 70Future studies will be needed to determine...

Fetal inheritance of chromosomally integrated human herpesvirus 6 predisposes the mother to pre-eclampsia

“…We only studied placental expression of the virus following birth, but the clinical consequences of iciHHV-6 may depend on viral replication earlier in pregnancy. Chromosomally integrated HHV-6 appears to be capable of viral reactivation 18 , 19 and we also detected multiple viral transcripts in the placentas with HHV-6 ( Extended Data Figure 2 ). The presence of HHV-6 during extravillous trophoblast invasion of the maternal vessels could derange the cross talk between trophoblast and maternal immune cells, leading to abnormal placentation.…”

Endogenization and excision of human herpesvirus 6 in human genomes

“…While confirming that the risk of excision and thus potential reactivation of integrated HHV-6B is real, full-length integrated HHV-6 genomes with two DRs identical to the solo-DR were not observed, and thus the likelihood of the excision event remains difficult to quantify. Studies with somatic tissues sampled from many sites may be useful for this purpose [ 48 ]. Furthermore, while recombination resulting in a solo-DR “scar” is one of the proposed routes of excision and reactivation, another involves “scarless” excision due to recombination of telomeric repeats flanking the virus genome [ 34 ].…”

“…With data from completed or ongoing population WGS projects, a global assessment of integrated HHV-6 prevalence, evolution, and association with disease should soon be possible. In addition, understanding any immune responses engendered by endogenous HHV-6, either humoral [ 48 ] or cell-intrinsic [ 51 ], are relevant to understanding the biological significance of this phenomenon.…”

Endogenization and excision of human herpesvirus 6 in human genomes

“…These data confirm that the risk of excision and thus potential reactivation of integrated HHV-6B is real, though how often this occurs remains difficult to quantify. Studies with somatic tissues sampled from many sites may be useful for this purpose {Peddu, 2019}. While recombination resulting in a single DR “scar” is one of the proposed routes of excision and reactivation, another involves “scarless” excision due to recombination of telomeric repeats flanking the virus genome{Wood, 2017}.…”

“…With data from completed or ongoing population WGS projects, a global assessment of integrated HHV-6 prevalence, evolution, and association with disease should soon be possible. In addition, understanding any immune responses engendered by endogenous HHV-6, either conventional {Peddu, 2019} or genomic {Ophinni, 2019}, are relevant to understanding the biological significance of this phenomenon.…”