The precise cell type hosting latent human cytomegalovirus (HCMV) remains elusive. Here, we report that HCMV reprogrammes human haematopoietic progenitor cells (HPCs) into a unique monocyte subset to achieve latency. Unlike conventional monocytes, this monocyte subset possesses higher levels of B7-H4, IL-10 and inducible nitric oxide synthase (iNOS), a longer lifespan and strong immunosuppressive capacity. Cell sorting of peripheral blood from latently infected human donors confirms that only this monocyte subset, representing less than 0.1% of peripheral mononuclear cells, is HCMV genome-positive but immediate-early-negative. Mechanistic studies demonstrate that HCMV promotes the differentiation of HPCs into this monocyte subset by activating cellular signal transducer and activator of transcription 3 (STAT3). In turn, this monocyte subset generates a high level of nitric oxide (NO) to silence HCMV immediate-early transcription and promote viral latency. By contrast, the US28-knockout HCMV mutant, which is incapable of activating STAT3, fails to reprogramme the HPCs and achieve latency. Our findings reveal that via activating the STAT3-iNOS-NO axis, HCMV differentiates human HPCs into a longevous, immunosuppressive monocyte subset for viral latency.

The CRISPR/Cas9 system has been applied in the genome editing and disruption of latent infections for herpesviruses such as the herpes simplex virus, Epstein–Barr virus, cytomegalovirus, and Kaposi’s sarcoma-associated herpesvirus. CRISPR/Cas9-directed mutagenesis can introduce similar types of mutations to the viral genome as can bacterial artificial chromosome recombination engineering, which maintains and reconstitutes the viral genome successfully. The cleavage mediated by CRISPR/Cas9 enables the manipulation of disease-associated viral strains with unprecedented efficiency and precision. Additionally, current therapies for herpesvirus productive and latent infections are limited in efficacy and cannot eradicate viruses. CRISPR/Cas9 is potentially adapted for antiviral treatment by specifically targeting viral genomes during latent infections. This review, which focuses on recently published progress, suggests that the CRISPR/Cas9 system is not only a useful tool for basic virology research, but also a promising strategy for the control and prevention of herpesvirus latent infections.

Interferon-γ (IFN-γ) represents one of the most important innate immunity responses in a host to combat infections of many human viruses including human herpesviruses. Human N-myc interactor (Nmi) protein, which has been shown to interact with signal transducer and activator of transcription (STAT) proteins including STAT1, is important for the activation of IFN-γ induced STAT1-dependent transcription of many genes responsible for IFN-γ immune responses. However, no proteins encoded by herpesviruses have been reported to interact with Nmi and inhibit Nmi-mediated activation of IFN-γ immune responses to achieve immune evasion from IFN-γ responses. In this study, we show strong evidence that the UL23 protein of human cytomegalovirus (HCMV), a human herpesvirus, specifically interacts with Nmi. This interaction was identified through a yeast two-hybrid screen and co-immunoprecipitation in human cells. We observed that Nmi, when bound to UL23, was not associated with STAT1, suggesting that UL23 binding of Nmi disrupts the interaction of Nmi with STAT1. In cells overexpressing UL23, we observed (a) significantly reduced levels of Nmi and STAT1 in the nuclei, the sites where these proteins act to induce transcription of IFN-γ stimulated genes, and (b) decreased levels of the induction of the transcription of IFN-γ stimulated genes. UL23-deficient HCMV mutants induced higher transcription of IFN-γ stimulated genes and exhibited lower titers than parental and control revertant viruses expressing functional UL23 in IFN-γ treated cells. Thus, UL23 appears to interact directly with Nmi and inhibit nuclear translocation of Nmi and its associated protein STAT1, leading to a decrease of IFN-γ induced responses and an increase of viral resistance to IFN-γ. Our results further highlight the roles of UL23-Nmi interactions in facilitating viral immune escape from IFN-γ responses and enhancing viral resistance to IFN antiviral effects.

We report a study of the dynamics of molecular reorientation and segmental mobility of a ferroelectric liquid crystal in the smectic-C* ͑Sm-C*͒ phase having 2-hydroxy-benzilidenianiline as the mesogen core and (S)-2-chloro-3-methylbutanoyl as the chiral terminal group, at different temperatures during electric-field-induced switching between the two surface-stabilized states by use of a time-resolved Fourier-transform infrared technique. From polarized infrared spectra under static dc electric fields, details of mutual arrangement of different molecular segments in the Sm-C* phase have been obtained. Contrary to the usual expectations, the average alkyl chain axis does not coincide with the mesogen axis and is less tilted with respect to the layer normal than the mesogen. On the other hand, motion of the carbonyl groups is found to be strongly hindered and the distribution function for the CvO bonds is not cylindrically symmetric with respect to the long molecular axis. Time-resolved infrared measurements at different temperatures and voltages have revealed that, on switching the polarity of the electric field, the hydrogen-bonded CvO group moves with the mesogen which reaches equilibrium orientations at a faster rate compared to the alkyl chain at the temperatures and voltages employed in this study. ͓S1063-651X͑97͒09209-X͔