Activation of double-stranded RNA (dsRNA)-mediated pathways contributes to the innate immune response to viral infection. Among the genes involved in this antiviral response are several interferon-induced genes, including those encoding protein kinase R (PKR) and 2Ј-5Ј oligoadenylate synthetase (OAS). After binding to dsRNA, PKR dimerizes, autophosphorylates, and then phosphorylates the translation initiation factor eukaryotic initiation factor 2␣ (eIF2␣). Phosphorylated eIF2␣ inhibits guanine nucleotide exchange factor eIF2B, preventing restoration of the eIF2␣-tRNA Met -GTP ternary complex and thus halting protein synthesis at the level of initiation (reviewed in reference 20). OAS catalyzes the synthesis of 2Ј-5Ј oligoadenylates, which activate latent RNase L, resulting in degradation of single-stranded mRNA and rRNA (reviewed in reference 44). Together, activation of the PKR and OAS pathways results in an antiviral environment by causing a shutdown of protein synthesis.Since viral replication requires protein synthesis, many viruses have had to evolve strategies for evading these dsRNAmediated antiviral response pathways (32, 36). For example, the vaccinia virus (VV) E3L protein binds to dsRNA and prevents activation of both PKR and OAS (14,28,50). VV lacking E3L (VV⌬E3L) is sensitive to interferon, has a limited cellular host range, and is avirulent in mice (5, 9, 51). Replication of VV⌬E3L in cell culture can be rescued by dsRNAbinding proteins (dsRBPs) from other viruses (30). For example, the dsRBPs pIRS1 and pTRS1 of human cytomegalovirus (HCMV) can inhibit eIF2␣ phosphorylation and RNase L activation, prevent the shutoff of protein synthesis, and rescue viral replication in VV⌬E3L-infected human cells (17). In murine CMV (MCMV), two US22 family members, pm142 and pm143, have functions similar to those of pIRS1 and pTRS1 in that they rescue the replication of VV⌬E3L in otherwise nonpermissive cells, and together they bind to dsRNA and block PKR activation (11,16,18,48).Deletions of individual dsRNA-binding genes have differing consequences in MCMV and HCMV systems. Deletion of either m142 or m143 from the MCMV genome eliminates viral replication and results in the activation of PKR and the inhibition of protein synthesis (48). Thus, both genes are essential and likely act together as a complex (16,18). In contrast, neither TRS1 nor IRS1 is essential for HCMV replication. Several viruses with deletions of IRS1 have been reported, and each replicates as well as wild-type virus (6, 21, 31). Deletion of TRS1 inhibits viral replication, but only by approximately 2 log units and primarily after low multiplicity of infection (MOI) (6). TRS1 appears to have a role in viral assembly late in infection that accounts for the modest replication defect of the TRS1 deletion mutant (1). Notably, deletion of TRS1 does not appear to cause a defect in viral protein synthesis (6). Therefore, unlike MCMV, neither of the two PKR evasion genes of HCMV is essential.To determine whether HCMV relies on having at least one of the...

An integral part of the antiviral innate immune response is the APOBEC3 family of single-stranded DNA cytosine deaminases, which inhibits virus replication through deamination-dependent and -independent activities. Viruses have evolved mechanisms to counteract these enzymes, such as HIV-1 Vif-mediated formation of a ubiquitin ligase to degrade virus-restrictive APOBEC3 enzymes. A new example is Epstein-Barr virus (EBV) ribonucleotide reductase (RNR)-mediated inhibition of cellular APOBEC3B (A3B). The large subunit of the viral RNR, BORF2, causes A3B relocalization from the nucleus to cytoplasmic bodies and thereby protects viral DNA during lytic replication. Here, we use coimmunoprecipitation and immunofluorescence microscopy approaches to ask whether this mechanism is shared with the closely related gammaherpesvirus Kaposi’s sarcoma-associated herpesvirus (KSHV) and the more distantly related alphaherpesvirus herpes simplex virus 1 (HSV-1). The large RNR subunit of KSHV, open reading frame 61 (ORF61), coprecipitated multiple APOBEC3s, including A3B and APOBEC3A (A3A). KSHV ORF61 also caused relocalization of these two enzymes to perinuclear bodies (A3B) and to oblong cytoplasmic structures (A3A). The large RNR subunit of HSV-1, ICP6, also coprecipitated A3B and A3A and was sufficient to promote the relocalization of these enzymes from nuclear to cytoplasmic compartments. HSV-1 infection caused similar relocalization phenotypes that required ICP6. However, unlike the infectivity defects previously reported for BORF2-null EBV, ICP6 mutant HSV-1 showed normal growth rates and plaque phenotypes. Combined, these results indicate that both gamma- and alphaherpesviruses use a conserved RNR-dependent mechanism to relocalize A3B and A3A and furthermore suggest that HSV-1 possesses at least one additional mechanism to neutralize these antiviral enzymes. IMPORTANCE The APOBEC3 family of DNA cytosine deaminases constitutes a vital innate immune defense against a range of different viruses. A novel counterrestriction mechanism has recently been uncovered for the gammaherpesvirus EBV, in which a subunit of the viral protein known to produce DNA building blocks (ribonucleotide reductase) causes A3B to relocalize from the nucleus to the cytosol. Here, we extend these observations with A3B to include a closely related gammaherpesvirus, KSHV, and a more distantly related alphaherpesvirus, HSV-1. These different viral ribonucleotide reductases also caused relocalization of A3A, which is 92% identical to A3B. These studies are important because they suggest a conserved mechanism of APOBEC3 evasion by large double-stranded DNA herpesviruses. Strategies to block this host-pathogen interaction may be effective for treating infections caused by these herpesviruses.

Congenital human cytomegalovirus (HCMV) infection can result in in severe and permanent neurological injury in newborns, and vaccine development is accordingly a major public health priority. HCMV can also cause disease in solid organ (SOT) and hematopoietic stem cell transplant (HSCT) recipients, and a vaccine would be valuable in prevention of viremia and end-organ disease in these populations. Currently there is no licensed HCMV vaccine, but progress toward this goal has been made in recent clinical trials. A recombinant HCMV glycoprotein B (gB) vaccine has been shown to have some efficacy in prevention of infection in young women and adolescents, and provided benefit to HCMV-seronegative SOT recipients. Similarly, DNA vaccines based on gB and the immunodominant T-cell target, pp65 (ppUL83), have been shown to reduce viremia in HSCT patients. This review provides an overview of HCMV vaccine candidates in various stages of development, as well as an update on the current status of ongoing clinical trials. Protective correlates of vaccine-induced immunity may be different for pregnant woman and transplant patients. As more knowledge emerges about correlates of protection, the ultimate licensure of HCMV vaccines may reflect the uniqueness of the target populations being immunized.

Group B streptococci overcome neutrophils in placental membranes, inducing fetal injury and preterm labor.