Human iPSC-derived trigeminal neurons lack constitutive TLR3-dependent immunity that protects cortical neurons from HSV-1 infection

Severe influenza pneumonitis in children with inherited TLR3 deficiency

Autosomal recessive IRF7 and IRF9 deficiencies impair type I and III IFN immunity and underlie severe influenza pneumonitis. We report three unrelated children with influenza A virus (IAV) infection manifesting as acute respiratory distress syndrome (IAV-ARDS), heterozygous for rare TLR3 variants (P554S in two patients and P680L in the third) causing autosomal dominant (AD) TLR3 deficiency. AD TLR3 deficiency can underlie herpes simplex virus-1 (HSV-1) encephalitis (HSE) by impairing cortical neuron-intrinsic type I IFN immunity to HSV-1. TLR3-mutated leukocytes produce normal levels of IFNs in response to IAV. In contrast, TLR3-mutated fibroblasts produce lower levels of IFN-β and -λ, and display enhanced viral susceptibility, upon IAV infection. Moreover, the patients' iPSC-derived pulmonary epithelial cells (PECs) are susceptible to IAV. Treatment with IFN-α2b or IFN-λ1 rescues this phenotype. AD TLR3 deficiency may thus underlie IAV-ARDS by impairing TLR3-dependent, type I and/or III IFN-mediated, PEC-intrinsic immunity. Its clinical penetrance is incomplete for both IAV-ARDS and HSE, consistent with their typically sporadic nature.

Lund Human Mesencephalic (LUHMES) Neuronal Cell Line Supports Herpes Simplex Virus 1 Latency In Vitro

Lund human mesencephalic (LUHMES) cells are human embryonic neuronal precursor cells that can be maintained as proliferating cells due to the expression of a tetracycline-regulatable (Tet-off) v-myc transgene. They can be differentiated to postmitotic neurons by the addition of tetracycline, glial cell-derived neurotrophic factor (GDNF), and dibutyryl cAMP. We demonstrate that these cells can be infected with herpes simplex virus 1 (HSV-1) at a multiplicity of infection (MOI) of 3 with the majority of cells surviving. By 6 days postinfection, there is a loss of lytic gene transcription and an increase in the numbers of neurons that express the latency-associated transcripts (LATs). Importantly, the virus can then be reactivated by the addition of a phosphoinositide 3-kinase inhibitor, which has previously been shown to reactivate HSV-1 in rat neuron cultures. While rodent primary culture neuron systems have been described, these are limited by their lack of scalability, as it is difficult to obtain more than 500,000 neurons to employ for a given experiment. Several recent papers have described a human dorsal root ganglion (DRG) neuron culture model and human induced pleuripotent stem cell (iPSC) neuron culture models that are scalable, but they require that the presence of an antiviral suppression be maintained following HSV-1 infection. The human LUHMES cell model of HSV-1 infection described here may be especially useful for studying HSV-1 latency and reactivation on account of its scalability, its amenability to maintenance of latency without the continual use of antiviral inhibitors, and its latent gene expression profile which mirrors many properties observed in vivo, importantly, the heterogeneity of cells expressing the LATs.IMPORTANCE Herpes simplex virus (HSV) is responsible for significant morbidity in humans due to its ability to cause oral and genital lesions, ocular disease, and encephalitis. While antivirals can attenuate the severity and frequency of disease, there is no vaccine or cure. Understanding the molecular details of HSV latency and reactivation is key to the development of new therapies. One of the difficulties in studying HSV latency has been the need to rely on establishment of latent infections in animal models. While rodent primary neuron culture models have shown promise, they yield relatively small numbers of latently infected neurons for biochemical and molecular analyses. Here we present the use of a human central nervous system (CNS)-derived conditionally proliferating cell line that can be differentiated into mature neurons and latently infected with HSV-1. This model shows promise as a scalable tool to study molecular and biochemical aspects of HSV-1 latency and reactivation in human neurons.

Herpes Simplex Virus Type 1 Infection of the Central Nervous System: Insights Into Proposed Interrelationships With Neurodegenerative Disorders

Herpes simplex virus type 1 (HSV-1) is highly prevalent in humans and can reach the brain without evident clinical symptoms. Once in the central nervous system (CNS), the virus can either reside in a quiescent latent state in this tissue, or eventually actively lead to severe acute necrotizing encephalitis, which is characterized by exacerbated neuroinflammation and prolonged neuroimmune activation producing a life-threatening disease. Although HSV-1 encephalitis can be treated with antivirals that limit virus replication, neurological sequelae are common and the virus will nevertheless remain for life in the neural tissue. Importantly, there is accumulating evidence that suggests that HSV-1 infection of the brain both, in symptomatic and asymptomatic individuals could lead to neuronal damage and eventually, neurodegenerative disorders. Here, we review and discuss acute and chronic infection of particular brain regions by HSV-1 and how this may affect neuron and cognitive functions in the host. We review potential cellular and molecular mechanisms leading to neurodegeneration, such as protein aggregation, dysregulation of autophagy, oxidative cell damage and apoptosis, among others. Furthermore, we discuss the impact of HSV-1 infection on brain inflammation and its potential relationship with neurodegenerative diseases.

Application of induced pluripotent stem cells to primary immunodeficiency diseases

Primary immunodeficiency diseases (PIDs) are a heterogeneous group of rare immune disorders with genetic causes. Effective treatments using hematopoietic stem cells or pharmaceutical agents have been around for decades. However, for many patients, these treatment options are ineffective, partly because the rarity of these PIDs complicates the diagnosis and therapy. Induced pluripotent stem cells (iPSCs) offer a potential solution to these problems. The proliferative capacity of iPSCs allows for the preparation of a large, stable supply of hematopoietic cells with the same genome as the patient, allowing for new human cell models that can trace cellular abnormalities during the pathogenesis and lead to new drug discovery. PID models using patient iPSCs have been instrumental in identifying deviations in the development or function of several types of immune cells, revealing new molecular targets for experimental therapies. These models are only in their early stages and for the most part have recapitulated results from existing models using animals or primary cells. However, iPSC-based models are being used to study complex diseases of other organs, including those with multigenic causes, suggesting that advances in differentiation processes will expand iPSC-based models to complex PIDs as well.