HIV-1 is able to replicate in primary human macrophages without stimulating innate immunity despite reverse transcription of genomic RNA into double stranded DNA, an activity that might be expected to trigger innate pattern recognition receptors (PRRs). We hypothesized that, if correctly orchestrated HIV-1 uncoating and nuclear entry is important for evasion of innate sensors, then manipulation of specific interactions between HIV-1 capsid (CA) and host factors that putatively regulate these processes should trigger PRRs and stimulate type 1 interferon secretion. Here we show that HIV-1 CA mutants N74D and P90A, which are impaired for interaction with cofactors Cleavage and Polyadenylation Specificity Factor subunit 6 (CPSF6) and cyclophilins (Nup358 and CypA) respectively(1-2), cannot replicate in primary human monocyte derived macrophages (MDM) because they trigger innate sensors leading to nuclear translocation of NFκB and IRF3, the production of soluble type-1 interferon (IFN) and induction of an antiviral state. Depletion of CPSF6 with shRNA expression allows wild type virus to trigger innate sensors and interferon production. In each case, suppressed replication is rescued by IFN-receptor blockade demonstrating a role for IFN in restriction. IFN production is dependent on viral reverse transcription but not integration suggesting that a viral reverse transcription product comprises the HIV-1 pathogen associated molecular pattern (PAMP). Finally, we show that we can pharmacologically induce wild type HIV-1 infection to stimulate IFN secretion and an antiviral state using a non-immunosuppressive cyclosporine analogue. We conclude that HIV-1 has evolved to utilize CPSF6 and cyclophilins to cloak its replication allowing evasion of innate immune sensors and induction of a cell autonomous innate immune response in primary human macrophages (Extended Data Fig 1).

Marek's disease virus (MDV) is an alphaherpesvirus for which infection is strictly cell associated in permissive cell culture systems. In contrast to most other alphaherpesviruses, no comprehensive ultrastructural study has been published to date describing the different stages of MDV morphogenesis. To circumvent problems linked to nonsynchronized infection and low infectivity titers, we generated a recombinant MDV expressing an enhanced green fluorescent protein fused to VP22, a major tegument protein that is not implicated in virion morphogenesis. Growth of this recombinant virus in cell culture was decreased threefold compared to that of the parental Bac20 virus, but this mutant was still highly replicative. The recombinant virus allowed us to select infected cells by cell-sorting cytometry at late stages of infection for subsequent transmission electron microscopy analysis. Under these conditions, all of the stages of assembly and virion morphogenesis could be observed except extracellular enveloped virions, even at the cell surface. We observed 10-fold fewer naked cytoplasmic capsids than nuclear capsids, and intracellular enveloped virions were very rare. The partial envelopment of capsids in the cytoplasm supports the hypothesis of the acquisition of the final envelope in this cellular compartment. We demonstrate for the first time that, compared to other alphaherpesviruses, MDV seems deficient in three crucial steps of viral morphogenesis, i.e., release from the nucleus, secondary envelopment, and the exocytosis process. The discrepancy between the efficiency with which this MDV mutant spreads in cell culture and the relatively inefficient process of its envelopment and virion release raises the question of the MDV cell-to-cell spreading mechanism.Marek's disease virus (MDV), referred to as Gallid herpesvirus 2, is the etiological agent of Marek's disease in chickens, a multifaceted disease most widely recognized by the induction of a malignant T-cell lymphoma. This major pathogen of chickens is a herpesvirus classified in the Mardivirus genus (Marek's disease-like viruses) within the Alphaherpesvirinae subfamily. MDV can be efficiently propagated in cell culture but remains strictly cell associated without free viral particles being detectable in the supernatant (2, 38). Moreover, infectious MDV virion particles cannot be purified from infected cell lysates as has been described for varicella-zoster virus (VZV) or turkey herpesvirus. Therefore, homologous vaccines commonly used in poultry flocks are frozen viable MDV-infected cells, which require storage and transport in liquid nitrogen (4). This feature makes MDV a unique virus within the herpesvirus family and among animal viruses in general.From electron microscopy (EM) studies of cultured cells infected with various herpesviruses, including mutant viruses with deletions of different tegument proteins or glycoproteins genes, three different pathways for the assembly and morphogenesis of herpesviruses have been proposed (reviewed in references 7, 20, ...

Tetherin is a broadly active antiviral effector that works by tethering nascent enveloped virions to a host cell membrane, thus preventing their release. In this study, we demonstrate that herpes simplex virus 1 (HSV-1) is targeted by tetherin. We identify the viral envelope glycoprotein M (gM) as having moderate anti-tetherin activity. We show that gM but not gB or gD efficiently removes tetherin from the plasma membrane and can functionally substitute for the human immunodeficiency virus type 1 (HIV-1) Vpu protein, the prototypic viral tetherin antagonist, in rescuing HIV-1 release from tetherin-expressing cells. Our data emphasize that tetherin is a broadly active antiviral effector and contribute to the emerging hypothesis that viruses must suppress or evade an array of host cell countermeasures in order to establish a productive infection.