Herpesvirus infections can lead to a number of severe clinical manifestations, particularly when involving the central nervous system (CNS), causing encephalitis and meningitis. However, understanding of the host factors conferring increased susceptibility to these diseases and their complications remains incomplete. Previous studies have uncovered defects in the innate Toll-like receptor 3 pathway and production of type I interferon (IFN-I) in children and adults that predispose them to herpes simplex encephalitis. More recently, there is accumulating evidence for an important role of IFN-independent cell-autonomous intrinsic mechanisms, including small nucleolar RNAs, RNA lariat metabolism, and autophagy, in restricting herpesvirus replication and conferring protection against CNS infection. The present review first describes clinical manifestations of HSV infection with a focus on neurological complications and then summarizes the host–pathogen interactions and innate immune pathways responsible for sensing herpesviruses and triggering antiviral responses and immunity. Next, we review the current landscape of inborn errors of immunity and the underlying genetic defects and disturbances of cellular immune pathways that confer increased susceptibility to HSV infection in CNS. Ultimately, we discuss some of the present outstanding unanswered questions relating to inborn errors of immunity and HSV CNS infection together with some perspectives and future directions for research in the pathogenesis of these severe diseases in humans.

Multiple myeloma (MM), a tumor of germinal center (GC)-experienced plasma cells, comprises distinct genetic subgroups, such as the t(11;14)/CCND1 and the t(4;14)/MMSET subtype. We have generated genetically defined, subgroup-specific MM models by the GC B cell-specific coactivation of mouse Ccnd1 or MMSET with a constitutively active Ikk2 mutant, mimicking the secondary NF-κB activation frequently seen in human MM. Ccnd1/Ikk2ca and MMSET/Ikk2ca mice developed a pronounced, clonally restricted plasma cell outgrowth with age, accompanied by serum M spikes, bone marrow insufficiency, and bone lesions. The transgenic plasma cells could be propagated in vivo and showed distinct transcriptional profiles, resembling their human MM counterparts. Thus, we show that targeting the expression of genes involved in MM subgroup-specific chromosomal translocations into mouse GC B cells translates into distinct MM-like diseases that recapitulate key features of the human tumors, opening the way to a better understanding of the pathogenesis and therapeutic vulnerabilities of different MM subgroups.

The clinical outcome of SARS-CoV-2 infection spans from asymptomatic viral elimination to lethal COVID-19 pneumonia, which is due to type I interferon (IFN) deficiency in at least 15–20% of cases. We report two unrelated male patients with critical COVID-19 who are heterozygous for rare deleterious variants in RB1CC1, encoding the autophagy-related FIP200 protein. Airway epithelial cells genetically deprived of FIP200 or cell lines expressing the RB1CC1/FIP200 patient variants exhibit elevated SARS-CoV-2 replication and impaired autophagic flux. The antiviral function of FIP200 is independent of canonical autophagy and type I IFN, but involves the selective autophagy receptor NDP52. We identify a non-canonical function of FIP200 in a novel lysosomal degradation pathway, in which SARS-CoV-2 virions are targeted to single-membrane compartments for degradation of viral RNA in LC3B-positive acidified vesicles. This pathway is impaired in FIP200-deficient cells and in cells expressing FIP200 patient haplotypes. Collectively, we describe a cell-autonomous anti-SARS-CoV-2 restriction pathway, dependent on FIP200 and NDP52, and independent of canonical autophagy and type I IFN, which can underlie critical COVID-19 pneumonia.

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.

Heligmosomoides polygyrus coinfection is reported to have protective antiviral effects against pulmonary viral infections. To investigate a potential underlying mechanism, we infected C57BL/6 mice with H. polygyrus larvae for 2 weeks. Bone marrow (BM)-derived plasmacytoid dendritic cells (pDCs) were generated and stimulated with Toll-like receptor agonists. We found increased expression of type 1 interferon genes (Ifnα1, Ifnα4, Ifnβ1, Mx1, Isg15), increased TNF, IL-6, IL-10 secretion, and higher expression of antigen presentation markers in BM-derived-pDCs from infected compared to naive control mice. Our findings may partly explain the mechanism of the antiviral protection previously reported in acute helminth infections.

Inborn errors of type I interferon (IFN-I) immunity account for ∼7–8% of herpes simplex encephalitis (HSE) cases in young children, but the pathogenesis of HSE in adults is largely unknown. We report that IFN-I autoantibodies (auto-Abs) in serum/plasma samples drawn before, during, or after HSE in 16/339 Danish adults neutralized 0.1–10 ng/ml of IFN-I. Neutralization was IgG-mediated and was also detected in cerebrospinal fluid in several patients. Patients’ serum impaired the ability of exogenous IFN-I to protect fibroblasts against herpes simplex virus (HSV)-1 infection in vitro. Among patients with neutralizing IFN-I auto-Abs, a larger fraction were HSV-1 IgG seronegative, suggesting that these auto-Abs confer a greater risk of HSE during primary HSV-1 infection. Neutralization was mainly driven by auto-Abs to IFN-ω, and the risk of HSE in adults with auto-Abs was significantly elevated (odds ratio [OR] = 3.1 for IFN-ω and OR = 2.0 for any IFN-I) compared with the general population. Overall, auto-Abs neutralizing IFN-I accounted for ∼5% of adult HSE cases.