Preexisting antibodies can protect against congenital cytomegalovirus infection in monkeys.

Human cytomegalovirus (HCMV) is the most common congenital infection and a known cause of microcephaly, sensorineural hearing loss, and cognitive impairment among newborns worldwide. Natural maternal HCMV immunity reduces the incidence of congenital infection, but does not prevent the disease altogether. We employed a nonhuman primate model of congenital CMV infection to investigate the ability of preexisting antibodies to protect against placental CMV transmission in the setting of primary maternal infection and subsequent viremia, which is required for placental virus exposure. Pregnant, CD4+ T cell-depleted, rhesus CMV-seronegative (RhCMV-seronegative) rhesus monkeys were treated with either standardly produced hyperimmune globulin (HIG) from RhCMV-seropositive macaques or dose-optimized, potently RhCMV-neutralizing HIG prior to intravenous challenge with an RhCMV mixture. HIG passive infusion provided complete protection against fetal loss in both groups. The dose-optimized, RhCMV-neutralizing HIG additionally inhibited placental transmission of RhCMV and reduced viral replication and diversity. Our findings suggest that the presence of durable and potently neutralizing antibodies at the time of primary infection can prevent transmission of systemically replicating maternal RhCMV to the developing fetus, and therefore should be a primary target of vaccines to eliminate this neonatal infection.

Plasmablast Response to Primary Rhesus Cytomegalovirus (CMV) Infection in a Monkey Model of Congenital CMV Transmission.

Human cytomegalovirus (HCMV) is the most common congenital infection worldwide and the leading infectious cause of neurologic deficits and hearing loss in newborns. Development of a maternal HCMV vaccine to prevent vertical virus transmission is a high priority, yet protective maternal immune responses following acute infection are poorly understood. To characterize the maternal humoral immune response to primary CMV infection, we investigated the plasmablast and early antibody repertoire using a nonhuman primate model with two acutely rhesus CMV (RhCMV)-infected animals-a CD4+ T cell-depleted dam that experienced fetal loss shortly after vertical RhCMV transmission and an immunocompetent dam that did not transmit RhCMV to her infant. Compared to the CD4+ T cell-depleted dam that experienced fetal loss, the immunocompetent, nontransmitting dam had a more rapid and robust plasmablast response that produced a high proportion of RhCMV-reactive antibodies, including the first identified monoclonal antibody specific for soluble and membrane-associated RhCMV envelope glycoprotein B (gB). Additionally, we noted that plasmablast RhCMV-specific antibodies had variable gene usage and maturation similar to those observed in a monkey chronically coinfected with simian immunodeficiency virus (SIV) and RhCMV. This study reveals characteristics of the early maternal RhCMV-specific humoral immune responses to primary RhCMV infection in rhesus monkeys and may contribute to a future understanding of what antibody responses should be targeted by a vaccine to eliminate congenital HCMV transmission. Furthermore, the identification of an RhCMV gB-specific monoclonal antibody underscores the possibility of modeling future HCMV vaccine strategies in this nonhuman primate model.

Maternal Antibody Responses and Nonprimary Congenital Cytomegalovirus Infection of HIV-1-Exposed Infants.

Risk of congenital cytomegalovirus (cCMV) transmission is highly dependent on the presence of preexisting maternal immunity, with the lowest rates observed in CMV-seroimmune populations. Among infants of CMV-seroimmune women, those who are exposed to human immunodeficiency virus (HIV) have an increased risk of acquiring cCMV infection as compared to HIV-unexposed infants. To better understand the risk factors of nonprimary cCMV transmission in HIV-infected women, we performed a case-control study in which CMV-specific plasma antibody responses from 19 CMV-transmitting and 57 CMV-nontransmitting women with chronic CMV/HIV coinfection were evaluated for the ability to predict the risk of cCMV infection. Primary multivariable conditional logistic regression analysis revealed an association between epithelial-tropic CMV neutralizing titers and a reduced risk of cCMV transmission (odds ratio [OR], 0.18; 95% confidence interval [CI], .03-.93; P = .04), although this effect was not significant following correction for multiple comparisons (false-discovery rate, 0.12). Exploratory analysis of the CMV specificity of plasma antibodies revealed that immunoglobulin G (IgG) responses against the glycoprotein B (gB) neutralizing epitope AD-2 had a borderline association with low risk of transmission (OR, 0.72; 95% CI, .51-1.00; P = .05), although this was not confirmed in a post hoc plasma anti-AD-2 IgG blocking assay. Our data suggest that maternal neutralizing antibody responses may play a role in protection against cCMV in HIV/CMV-coinfected populations.

Maternal CD4+ T cells protect against severe congenital cytomegalovirus disease in a novel nonhuman primate model of placental cytomegalovirus transmission.

Elucidation of maternal immune correlates of protection against congenital cytomegalovirus (CMV) is necessary to inform future vaccine design. Here, we present a novel rhesus macaque model of placental rhesus CMV (rhCMV) transmission and use it to dissect determinants of protection against congenital transmission following primary maternal rhCMV infection. In this model, asymptomatic intrauterine infection was observed following i.v. rhCMV inoculation during the early second trimester in two of three rhCMV-seronegative pregnant females. In contrast, fetal loss or infant CMV-associated sequelae occurred in four rhCMV-seronegative pregnant macaques that were CD4(+) T-cell depleted at the time of inoculation. Animals that received the CD4(+) T-cell-depleting antibody also exhibited higher plasma and amniotic fluid viral loads, dampened virus-specific CD8(+) T-cell responses, and delayed production of autologous neutralizing antibodies compared with immunocompetent monkeys. Thus, maternal CD4(+) T-cell immunity during primary rhCMV infection is important for controlling maternal viremia and inducing protective immune responses that prevent severe CMV-associated fetal disease.

Perinatal cytomegalovirus and varicella zoster virus infections: epidemiology, prevention, and treatment.

Mother-to-child transmission of cytomegalovirus (CMV) and varicella zoster virus (VZV) can lead to severe birth defects and neurologic impairment of infants. Congenital CMV complicates up to 1% of all pregnancies globally. Although antiviral treatment of infants congenitally infected with CMV can ameliorate the CMV-associated hearing loss and developmental delay, interventions to prevent congenital CMV infection and the associated neurologic impairments are still being evaluated. Congenital VZV infection is rare. Active and passive immunization strategies to prevent perinatal CMV infection with similar efficacy to those established to prevent perinatal VZV infections are critically needed in pediatric health.

Specific nucleoprotein residues affect influenza virus morphology.

Influenza virus strains are often pleiomorphic, a characteristic that is largely attributed to specific residues in matrix protein 1 (M1). Although the mechanism by which M1 controls virion morphology has not yet been defined, it is suggested that the M1 interaction with other viral proteins plays an important role. In this study, we rescued recombinant virus WSN-AichiM1 containing the spherical A/WSN/33 (WSN) backbone and the M1 protein from A/Aichi/2/68 (Aichi). Aichi M1 differs from WSN M1 by 7 amino acids but includes those identified to be responsible for filamentous virion formation. Interestingly, Aichi virus produced spherical virions, while WSN-AichiM1 exhibited a long filamentous morphology, as detected by immunofluorescence and electron microscopy. Additional incorporation of Aichi nucleoprotein (NP) but not the hemagglutinin (HA), neuraminidase (NA), or M2 gene to WSN-AichiM1 abrogated filamentous virion formation, suggesting that specific M1-NP interactions affect virion morphology. Further characterization of viruses containing WSN/Aichi chimeric NPs identified residues 214, 217, and 253 of Aichi NP as necessary and sufficient for the formation of spherical virions. NP residues 214 and 217 localize at the minor groove between the two opposite-polarity NP helical strands of viral ribonucleocapsids, and residue 253 also localizes near the surface of the groove. These findings indicate that NP plays a critical role in influenza virus morphology, possibly through its interaction with the M1 layer during virus budding.

Specific residues in the 2009 H1N1 swine-origin influenza matrix protein influence virion morphology and efficiency of viral spread in vitro.

In April 2009, a novel influenza virus emerged as a result of genetic reassortment between two pre-existing swine strains. This highly contagious H1N1 recombinant (pH1N1) contains the same genomic background as North American triple reassortant (TR) viruses except for the NA and M segments which were acquired from the Eurasian swine lineage. Yet, despite their high degree of genetic similarity, we found the morphology of virions produced by the pH1N1 isolate, A/California/04/09 (ACal-04/09), to be predominantly spherical by immunufluorescence and electron microscopy analysis in human lung and swine kidney epithelial cells, whereas TR strains were observed to be mostly filamentous. In addition, nine clinical pH1N1 samples collected from nasal swab specimens showed similar spherical morphology as the ACal-04/09 strain. Sequence analysis between TR and pH1N1 viruses revealed four amino acid differences in the viral matrix protein (M1), a known determinant of influenza morphology, at positions 30, 142, 207, and 209. To test the role of these amino acids in virus morphology, we rescued mutant pH1N1 viruses in which each of the four M1 residues were replaced with the corresponding TR residue. pH1N1 containing substitutions at positions 30, 207 and 209 exhibited a switch to filamentous morphology, indicating a role for these residues in virion morphology. Substitutions at these residues resulted in lower viral titers, reduced growth kinetics, and small plaque phenotypes compared to wild-type, suggesting a correlation between influenza morphology and efficient cell-to-cell spread in vitro. Furthermore, we observed efficient virus-like particle production from cells expressing wild-type pH1N1 M1, but not M1 containing substitutions at positions 30, 207, and 209, or M1 from other strains. These data suggest a direct role for pH1N1 specific M1 residues in the production and release of spherical progeny, which may contribute to the rapid spread of the pandemic virus.