Genetically heterozygous - transcriptionally homozygous IRF7 deficiency underlies herpesvirus CNS infections in humans

Inborn errors of immunity (IEI) impairing brain-intrinsic immune defenses can underlie herpes simplex virus encephalitis. By whole-exome sequencing of cohorts of herpesvirus-associated recurrent lymphocytic meningitis and acute retinal necrosis, we identified two patients heterozygous for variants in interferon (IFN) regulatory factor 7 (IRF7). The expression of the Q185X (patient 1, P1) and A86Rfs23X (P2) IRF7 variants in HEK293T cells resulted in truncated IRF7 proteins that lacked IFN-transactivating ability. Peripheral blood mononuclear cells from P1 exhibited reduced type I IFN responses to HSV-2 infection. Genetic knock-in of the IRF7 Q185X variant in THP-1 cells and stem cell-derived plasmacytoid dendritic cells (pDC) confirmed the disrupted IFN expression, resulting in impaired paracrine antiviral protection of meningeal fibroblasts. Strikingly, genetically heterozygous index patient pDC, but not those of healthy carrier family members, showed expression of only the pathogenic IRF7 Q185X allele, resulting in a homozygous transcriptotype. Collectively, this study identifies genetically heterozygous but transcriptionally homozygous IRF7 deficiency as an IEI underlying herpesvirus central nervous system infection.