Congenital Human Cytomegalovirus Infection and the Enigma of Maternal Immunity

Delivery of US28 by incoming HCMV particles rapidly attenuates Akt activity to suppress HCMV lytic replication in monocytes

Establishing a nonproductive, quiescent infection within monocytes is essential for the spread of human cytomegalovirus (HCMV). We investigated the mechanisms through which HCMV establishes a quiescent infection in monocytes. US28 is a virally encoded G protein-coupled receptor (GPCR) that is essential for silent infections within cells of the myeloid lineage. We found that preformed US28 was rapidly delivered to monocytes by HCMV viral particles, whereas the de novo synthesis of US28 was delayed for several days. A recombinant mutant virus lacking US28 (US28Δ) was unable to establish a quiescent infection, resulting in a fully productive lytic infection able to produce progeny virus. Infection with US28Δ HCMV resulted in the phosphorylation of the serine and threonine kinase Akt at Ser473 and Thr308, in contrast with the phosphorylation of Akt only at Ser473 after WT viral infection. Inhibiting the dual phosphorylation of Akt prevented the lytic replication of US28Δ, and ectopic expression of a constitutively phosphorylated Akt variant triggered lytic replication of wild-type HCMV. Mechanistically, we found that US28 was necessary and sufficient to attenuate epidermal growth factor receptor (EGFR) signaling induced during the entry of WT virus, which led to the site-specific phosphorylation of Akt at Ser473. Thus, particle-delivered US28 fine-tunes Akt activity by limiting HCMV-induced EGFR activation during viral entry, enabling quiescent infection in monocytes.

Functional Fc receptors are crucial in antibody-mediated protection against cytomegalovirus

Human cytomegalovirus is a medically important pathogen. Previously, using murine CMV (MCMV), we provided evidence that both neutralizing and nonneutralizing antibodies can confer protection from viral infection in vivo. In this study, we report that serum derived from infected animals had a greater protective capacity in MCMV-infected RAG-/- mice than serum from animals immunized with purified virus. The protective activity of immune serum was strictly dependent on functional Fcγ receptors (FcγR). Deletion of individual FcγRs or combined deletion of FcγRI and FcγRIV had little impact on the protection afforded by serum. Adoptive transfer of CD115-positive cells from noninfected donors demonstrated that monocytes represent important cellular mediators of the protective activity provided by immune serum. Our studies suggest that Fc-FcγR interactions and monocytic cells are critical for antibody-mediated protection against MCMV infection in vivo. These findings may provide new avenues for the development of novel strategies for more effective CMV vaccines or antiviral immunotherapies.

Highly stable and immunogenic CMV T cell vaccine candidate developed using a synthetic MVA platform

Human cytomegalovirus (CMV) is the most common infectious cause of complications post-transplantation, while a CMV vaccine for transplant recipients has yet to be licensed. Triplex, a multiantigen Modified Vaccinia Ankara (MVA)-vectored CMV vaccine candidate based on the immunodominant antigens phosphoprotein 65 (pp65) and immediate-early 1 and 2 (IE1/2), is in an advanced stage of clinical development. However, its limited genetic and expression stability restricts its potential for large-scale production. Using a recently developed fully synthetic MVA (sMVA) platform, we developed a new generation Triplex vaccine candidate, T10-F10, with different sequence modifications for enhanced vaccine stability. T10-F10 demonstrated genetic and expression stability during extensive virus passaging. In addition, we show that T10-F10 confers comparable immunogenicity to the original Triplex vaccine to elicit antigen-specific T cell responses in HLA-transgenic mice. These results demonstrate improvements in translational vaccine properties of an sMVA-based CMV vaccine candidate designed as a therapeutic treatment for transplant recipients.

Exploring health disparities in congenital CMV (cCMV): a study in a Somali-American community to assess awareness of cCMV and facilitate understanding of universal cCMV screening

Background

Congenital cytomegalovirus (cCMV) disproportionately impacts black and multiracial infants. While there have been strides made to address this health disparity, strategies to increase awareness and knowledge of cCMV have not been investigated in a Somali community.

Methods

Two survey study strategies (in-person and online), consisting of a pre-survey test, educational intervention, and a post-survey, were designed to gauge knowledge and perceptions about cCMV among Somali women aged 18 to 40 years old.

Results

96 respondents partook in the online module, and 15 in the in-person event. On recruitment, < 45% of women were aware of cCMV. Following the pre-intervention survey, educational modules were conducted, and the survey repeated. For statistical comparisons, a point was assigned for each correct survey query, and the mean of correct responses tabulated for pre- and post-surveys. In the online intervention, mean scores changed from 55 to 87% (paired t-test, p = 0.001), whereas in the in-person intervention, mean scores changed from 65 to 87% (paired t-test, p = 0.007), demonstrating enhanced cCMV awareness upon completion of both interventions. Using multiple linear regression, the expected post-test score was 2% (95% CI [- 8%, 12%]) higher for the online module compared to the in-person module, adjusting for pre-test score.

Conclusion

Both interventions were successful in enhancing knowledge about cCMV in this population, although there was no evidence either intervention was substantially better than the other. Educational efforts will be critical in enhancing the trust required to facilitate diagnostic evaluation and treatment of newborns identified with cCMV in this high-risk population.

Hygiene-based measures for the prevention of cytomegalovirus infection in pregnant women: a systematic review

BACKGROUND

Human Cytomegalovirus (HCMV) is the most frequent congenital infection worldwide causing important sequelae. However, no vaccine or antiviral treatments are currently available, thus interventions are restricted to behavioral measures. The aim of this systematic review was to assess evidence from available intervention studies using hygiene-based measures to prevent HCMV infection during pregnancy.

METHODS

Studies published from 1972 to 2023 were searched in Medline, PsycInfo, and Clinical Trials (PROSPERO, CRD42022344840) according to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines. Methodological quality was assessed by two authors, using ROBE-2 and MINORS.

RESULTS

After reviewing 6 selected articles, the outcome analysis suggested that implementation of hygiene-based interventions during pregnancy prevent, to some extent, the acquisition of congenital HCMV.

CONCLUSIONS

However, these conclusions are based on limited and low-quality evidence available from few studies using this type of intervention in clinical practice. Thus, it would be necessary to perform effective and homogeneous intervention studies using hygiene-based measures, evaluated in high-quality randomized controlled trials (RCTs).

Human cytomegalovirus modulates mTORC1 to redirect mRNA translation within quiescently infected monocytes

Human cytomegalovirus (HCMV) utilizes peripheral blood monocytes as a means to systemically disseminate throughout the host. Following viral entry, HCMV stimulates non-canonical Akt signaling leading to the activation of mTORC1 and the subsequent translation of select antiapoptotic proteins within infected monocytes. However, the full extent to which the HCMV-initiated Akt/mTORC1 signaling axis reshapes the monocyte translatome is unclear. We found HCMV entry alone was able to stimulate widescale changes to mRNA translation levels and that inhibition of mTOR, a component of mTORC1, dramatically attenuated HCMV-induced protein synthesis. Although monocytes treated with normal myeloid growth factors also exhibited increased levels of translation, mTOR inhibition had no effect, suggesting HCMV activation of mTOR stimulates the acquisition of a unique translatome within infected monocytes. Indeed, polyribosomal profiling of HCMV-infected monocytes identified distinct prosurvival transcripts that were preferentially loaded with ribosomes when compared to growth factor-treated cells. Sirtuin 1 (SIRT1), a deacetylase that exerts prosurvival effects through regulation of the PI3K/Akt pathway, was found to be highly enriched following HCMV infection in an mTOR-dependent manner. Importantly, SIRT1 inhibition led to the death of HCMV-infected monocytes while having minimal effect on uninfected cells. SIRT1 also supported a positive feedback loop to sustain Akt/mTORC1 signaling following viral entry. Taken together, HCMV profoundly reshapes mRNA translation in an mTOR-dependent manner to enhance the synthesis of select factors necessary for the survival of infected monocytes.IMPORTANCEHuman cytomegalovirus (HCMV) infection is a significant cause of morbidity and mortality among the immunonaïve and immunocompromised. Peripheral blood monocytes are a major cell type responsible for disseminating the virus from the initial site of infection. In order for monocytes to mediate viral spread within the host, HCMV must subvert the naturally short lifespan of these cells. In this study, we performed polysomal profiling analysis, which demonstrated HCMV to globally redirect mRNA translation toward the synthesis of cellular prosurvival factors within infected monocytes. Specifically, HCMV entry into monocytes induced the translation of cellular SIRT1 to generate an antiapoptotic state. Defining the precise mechanisms through which HCMV stimulates survival will provide insight into novel anti-HCMV drugs able to target infected monocytes.

Fully Human Herpesvirus-Specific Neutralizing IgG Antibodies Generated by EBV Immortalization of Splenocytes-Derived from Immunized Humanized Mice

Antiviral neutralizing antibodies (nAbs) are commonly derived from B cells developed in immunized or infected animals and humans. Fully human antibodies are preferred for clinical use as they are potentially less immunogenic. However, the function of B cells varies depending on their homing pattern and an additional hurdle for antibody discovery in humans is the source of human tissues with an immunological microenvironment. Here, we show an efficient method to pharm human antibodies using immortalized B cells recovered from Nod.Rag.Gamma (NRG) mice reconstituting the human immune system (HIS). Humanized HIS mice were immunized either with autologous engineered dendritic cells expressing the human cytomegalovirus gB envelope protein (HCMV-gB) or with Epstein-Barr virus-like particles (EB-VLP). Human B cells recovered from spleen of HIS mice were efficiently immortalized with EBV in vitro. We show that these immortalized B cells secreted human IgGs with neutralization capacities against prototypic HCMV-gB and EBV-gp350. Taken together, we show that HIS mice can be successfully used for the generation and pharming fully human IgGs. This technology can be further explored to generate antibodies against emerging infections for diagnostic or therapeutic purposes.

Vaccine value profile for cytomegalovirus

Cytomegalovirus (CMV) is the most common infectious cause of congenital malformation and a leading cause of developmental disabilities such as sensorineural hearing loss (SNHL), motor and cognitive deficits. The significant disease burden from congenital CMV infection (cCMV) led the US National Institute of Medicine to rank CMV vaccine development as the highest priority. An average of 6.7/1000 live births are affected by cCMV, but the prevalence varies across and within countries. In contrast to other congenital infections such as rubella and toxoplasmosis, the prevalence of cCMV increases with CMV seroprevalence rates in the population. The true global burden of cCMV disease is likely underestimated because most infected infants (85-90 %) have asymptomatic infection and are not identified. However, about 7-11 % of those with asymptomatic infection will develop SNHL throughout early childhood. Although no licensed CMV vaccine exists, several candidate vaccines are in development, including one currently in phase 3 trials. Licensure of one or more vaccine candidates is feasible within the next five years. Various models of CMV vaccine strategies employing different target populations have shown to provide substantial benefit in reducing cCMV. Although CMV can cause end-organ disease with significant morbidity and mortality in immunocompromised individuals, the focus of this vaccine value profile (VVP) is on preventing or reducing the cCMV disease burden. This CMV VVP provides a high-level, comprehensive assessment of the currently available data to inform the potential public health, economic, and societal value of CMV vaccines. The CMV VVP was developed by a working group of subject matter experts from academia, public health groups, policy organizations, and non-profit organizations. All contributors have extensive expertise on various elements of the CMV VVP and have described the state of knowledge and identified the current gaps. The VVP was developed using only existing and publicly available information.

Inhibiting HCMV pUL89-C Endonuclease with Metal-Binding Compounds

Human cytomegalovirus (HCMV) infects individuals of all ages and establishes a lifelong latency. Current antiviral drugs are suboptimal in efficacy and safety and ineffective against resistant/refractory HCMV. Therefore, there is an unmet clinical need for efficacious, safe, and mechanistically novel HCMV drugs. The recent Food and Drug Administration (FDA) approval of letermovir (LTV) validated the HCMV terminase complex as a new target for antiviral development. LTV targets terminase subunit pUL56 but not the main endonuclease enzymatic function housed in the C terminus of subunit pUL89 (pUL89-C). Structurally and mechanistically, pUL89-C is an RNase H-like viral endonuclease entailing two divalent metal ions at the active site. In recent years, numerous studies have extensively explored pUL89-C inhibition using metal-chelating chemotypes, an approach previously used for inhibiting HIV ribonuclease H (RNase H) and integrase strand transfer (INST). Collectively, the work summarized herein validates the use of metal-binding scaffolds for designing potent and specific pUL89-C inhibitors.

Protective effect of pre-existing natural immunity in a nonhuman primate reinfection model of congenital cytomegalovirus infection

Congenital cytomegalovirus (cCMV) is the leading infectious cause of neurologic defects in newborns with particularly severe sequelae in the setting of primary CMV infection in the first trimester of pregnancy. The majority of cCMV cases worldwide occur after non-primary infection in CMV-seropositive women; yet the extent to which pre-existing natural CMV-specific immunity protects against CMV reinfection or reactivation during pregnancy remains ill-defined. We previously reported on a novel nonhuman primate model of cCMV in rhesus macaques where 100% placental transmission and 83% fetal loss were seen in CD4+ T lymphocyte-depleted rhesus CMV (RhCMV)-seronegative dams after primary RhCMV infection. To investigate the protective effect of preconception maternal immunity, we performed reinfection studies in CD4+ T lymphocyte-depleted RhCMV-seropositive dams inoculated in late first / early second trimester gestation with RhCMV strains 180.92 (n = 2), or RhCMV UCD52 and FL-RhCMVΔRh13.1/SIVgag, a wild-type-like RhCMV clone with SIVgag inserted as an immunological marker, administered separately (n = 3). An early transient increase in circulating monocytes followed by boosting of the pre-existing RhCMV-specific CD8+ T lymphocyte and antibody response was observed in the reinfected dams but not in control CD4+ T lymphocyte-depleted dams. Emergence of SIV Gag-specific CD8+ T lymphocyte responses in macaques inoculated with the FL-RhCMVΔRh13.1/SIVgag virus confirmed reinfection. Placental transmission was detected in only one of five reinfected dams and there were no adverse fetal sequelae. Viral whole genome, short-read, deep sequencing analysis confirmed transmission of both reinfection RhCMV strains across the placenta with ~30% corresponding to FL-RhCMVΔRh13.1/SIVgag and ~70% to RhCMV UCD52, consistent with the mixed human CMV infections reported in infants with cCMV. Our data showing reduced placental transmission and absence of fetal loss after non-primary as opposed to primary infection in CD4+ T lymphocyte-depleted dams indicates that preconception maternal CMV-specific CD8+ T lymphocyte and/or humoral immunity can protect against cCMV infection.

Virion-associated US28 rapidly modulates Akt activity to suppress HCMV lytic replication in monocytes

Establishing a non-productive quiescent/silent infection within monocytes is essential for spread of human cytomegalovirus (HCMV). Yet, how HCMV establishes a quiescent infection in monocytes remains unclear. US28 is a viral G protein-coupled receptor (GPCR) essential for silent infections within cells of the myeloid lineage. We found virion-associated US28 was rapidly delivered to monocytes, while de novo synthesized US28 was delayed for several days. A recombinant mutant virus lacking US28 (US28Δ) was unable to establish a quiescent infection, resulting in a fully productive lytic replication cycle. Mechanistically, viral entry of US28Δ phosphorylated Akt at both serine 473 (S473) and threonine 308 (T308), which contrasted with the site-specific phosphorylation of Akt at S473 following WT infection. Preventing Akt bi-phosphorylation prevented lytic replication of US28Δ, and ectopic expression of a constitutively phosphorylated Akt variant triggered lytic replication of WT infection. Our data demonstrate that virion-delivered US28 fine-tunes Akt activity to permit HCMV infection to enter a quiescent state following primary infection of monocytes.

Human cytomegalovirus mediates APOBEC3B relocalization early during infection through a ribonucleotide reductase-independent mechanism

The APOBEC3 family of DNA cytosine deaminases comprises an important arm of the innate antiviral defense system. The gamma-herpesviruses Epstein-Barr virus and Kaposi's sarcoma-associated herpesvirus and the alpha-herpesviruses herpes simplex virus (HSV)-1 and HSV-2 have evolved an efficient mechanism to avoid APOBEC3 restriction by directly binding to APOBEC3B and facilitating its exclusion from the nuclear compartment. The only viral protein required for APOBEC3B relocalization is the large subunit of the ribonucleotide reductase (RNR). Here, we ask whether this APOBEC3B relocalization mechanism is conserved with the beta-herpesvirus human cytomegalovirus (HCMV). Although HCMV infection causes APOBEC3B relocalization from the nucleus to the cytoplasm in multiple cell types, the viral RNR (UL45) is not required. APOBEC3B relocalization occurs rapidly following infection suggesting the involvement of an immediate early or early (IE/E) viral protein. In support of this possibility, genetic (IE1 mutant) and pharmacologic (cycloheximide) strategies that prevent the expression of IE/E viral proteins also block APOBEC3B relocalization. In comparison, the treatment of infected cells with phosphonoacetic acid, which interferes with viral late protein expression, still permits A3B relocalization. These results combine to indicate that the beta-herpesvirus HCMV uses an RNR-independent, yet phenotypically similar, molecular mechanism to antagonize APOBEC3B. IMPORTANCE Human cytomegalovirus (HCMV) infections can range from asymptomatic to severe, particularly in neonates and immunocompromised patients. HCMV has evolved strategies to overcome host-encoded antiviral defenses to achieve lytic viral DNA replication and dissemination and, under some conditions, latency and long-term persistence. Here, we show that HCMV infection causes the antiviral factor, APOBEC3B, to relocalize from the nuclear compartment to the cytoplasm. This overall strategy resembles that used by related herpesviruses. However, the HCMV relocalization mechanism utilizes a different viral factor(s) and available evidence suggests the involvement of at least one protein expressed at the early stages of infection. This knowledge is important because a greater understanding of this mechanism could lead to novel antiviral strategies that enable APOBEC3B to naturally restrict HCMV infection.

ADCC-activating antibodies correlate with decreased risk of congenital human cytomegalovirus transmission

Human cytomegalovirus (HCMV) is the most common vertically transmitted infection worldwide, yet there are no vaccines or therapeutics to prevent congenital HCMV (cCMV) infection. Emerging evidence indicates that antibody Fc effector functions may be a previously underappreciated component of maternal immunity against HCMV. We recently reported that antibody-dependent cellular phagocytosis (ADCP) and IgG activation of FcγRI/FcγRII were associated with protection against cCMV transmission, leading us to hypothesize that additional Fc-mediated antibody functions may be important. In this same cohort of HCMV-transmitting (n = 41) and nontransmitting (n = 40) mother-infant dyads, we report that higher maternal sera antibody-dependent cellular cytotoxicity (ADCC) activation is also associated with lower risk of cCMV transmission. We investigated the relationship between ADCC and IgG responses against 9 viral antigens and found that ADCC activation correlated most strongly with sera IgG binding to the HCMV immunoevasin protein UL16. Moreover, we determined that higher UL16-specific IgG binding and FcγRIII/CD16 engagement were associated with the greatest risk reduction in cCMV transmission. Our findings indicate that ADCC-activating antibodies against targets such as UL16 may represent an important protective maternal immune response against cCMV infection that can guide future HCMV correlates studies and vaccine or antibody-based therapeutic development.

HCMV Infection Reduces Nidogen-1 Expression, Contributing to Impaired Neural Rosette Development in Brain Organoids

Human cytomegalovirus (HCMV) is a leading cause of birth defects in humans. These birth defects include microcephaly, sensorineural hearing loss, vision loss, and cognitive impairment. The process by which the developing fetus incurs these neurological defects is poorly understood. To elucidate some of these mechanisms, we have utilized HCMV-infected induced pluripotent stem cells (iPSCs) to generate in vitro brain organoids, modeling the first trimester of fetal brain development. Early during culturing, brain organoids generate neural rosettes. These structures are believed to model neural tube formation. Rosette formation was analyzed in HCMV-infected and mock-infected brain organoids at 17, 24, and 31 days postinfection. Histological analysis revealed fewer neural rosettes in HCMV-infected compared to mock-infected organoids. HCMV-infected organoid rosettes incurred multiple structural deficits, including increased lumen area, decreased ventricular zone depth, and decreased cell count. Immunofluorescent (IF) analysis found that nidogen-1 (NID1) protein expression in the basement membrane surrounding neural rosettes was greatly reduced by virus infection. IF analysis also identified a similar downregulation of laminin in basement membranes of HCMV-infected organoid rosettes. Knockdown of NID1 alone in brain organoids impaired their development, leading to the production of rosettes with increased lumen area, decreased structural integrity, and reduced laminin localization in the basement membrane, paralleling observations in HCMV-infected organoids. Our data strongly suggest that HCMV-induced downregulation of NID1 impairs neural rosette formation and integrity, likely contributing to many of HCMV's most severe birth defects. IMPORTANCE HCMV infection in pregnant women continues to be the leading cause of virus-induced neurologic birth defects. The mechanism through which congenital HCMV (cCMV) infection induces pathological changes to the developing fetal central nervous system (CNS) remains unclear. Our lab previously reproduced identified clinical defects in HCMV-infected infants using a three dimensional (3D) brain organoid model. In this new study, we have striven to discover very early HCMV-induced changes in developing brain organoids. We investigated the development of neural tube-like structures, neural rosettes. HCMV-infected rosettes displayed multiple structural abnormalities and cell loss. HCMV-infected rosettes displayed reduced expression of the key basement membrane protein, NID1. We previously found NID1 to be specifically targeted in HCMV-infected fibroblasts and endothelial cells. Brain organoids generated from NID1 knockdown iPSCs recapitulated the structural defects observed in HCMV-infected rosettes. Findings in this study revealed HCMV infection induced early and dramatic structural changes in 3D brain organoids. We believe our results suggest a major role for infection-induced NID1 downregulation in HCMV-induced CNS birth defects.

Protective effect of pre-existing natural immunity in a nonhuman primate reinfection model of congenital cytomegalovirus infection

Congenital cytomegalovirus (cCMV) is the leading infectious cause of neurologic defects in newborns with particularly severe sequelae in the setting of primary CMV infection in the first trimester of pregnancy. The majority of cCMV cases worldwide occur after non-primary infection in CMV-seropositive women; yet the extent to which pre-existing natural CMV-specific immunity protects against CMV reinfection or reactivation during pregnancy remains ill-defined. We previously reported on a novel nonhuman primate model of cCMV in rhesus macaques where 100% placental transmission and 83% fetal loss were seen in CD4 + T lymphocyte-depleted rhesus CMV (RhCMV)-seronegative dams after primary RhCMV infection. To investigate the protective effect of preconception maternal immunity, we performed reinfection studies in CD4+ T lymphocyte-depleted RhCMV-seropositive dams inoculated in late first / early second trimester gestation with RhCMV strains 180.92 ( n =2), or RhCMV UCD52 and FL-RhCMVΔRh13.1/SIV gag , a wild-type-like RhCMV clone with SIV gag inserted as an immunological marker ( n =3). An early transient increase in circulating monocytes followed by boosting of the pre-existing RhCMV-specific CD8+ T lymphocyte and antibody response was observed in the reinfected dams but not in control CD4+ T lymphocyte-depleted dams. Emergence of SIV Gag-specific CD8+ T lymphocyte responses in macaques inoculated with the FL-RhCMVΔRh13.1/SIV gag virus confirmed reinfection. Placental transmission was detected in only one of five reinfected dams and there were no adverse fetal sequelae. Viral whole genome, short-read, deep sequencing analysis confirmed transmission of both reinfection RhCMV strains across the placenta with ∼30% corresponding to FL-RhCMVΔRh13.1/SIV gag and ∼70% to RhCMV UCD52, consistent with the mixed human CMV infections reported in infants with cCMV. Our data showing reduced placental transmission and absence of fetal loss after non-primary as opposed to primary infection in CD4+ T lymphocyte-depleted dams indicates that preconception maternal CMV-specific CD8+ T lymphocyte and/or humoral immunity can protect against cCMV infection.

Author Summary

Globally, pregnancies in CMV-seropositive women account for the majority of cases of congenital CMV infection but the immune responses needed for protection against placental transmission in mothers with non-primary infection remains unknown. Recently, we developed a nonhuman primate model of primary rhesus CMV (RhCMV) infection in which placental transmission and fetal loss occurred in RhCMV-seronegative CD4+ T lymphocyte-depleted macaques. By conducting similar studies in RhCMV-seropositive dams, we demonstrated the protective effect of pre-existing natural CMV-specific CD8+ T lymphocytes and humoral immunity against congenital CMV after reinfection. A 5-fold reduction in congenital transmission and complete protection against fetal loss was observed in dams with pre-existing immunity compared to primary CMV in this model. Our study is the first formal demonstration in a relevant model of human congenital CMV that natural pre-existing CMV-specific maternal immunity can limit congenital CMV transmission and its sequelae. The nonhuman primate model of non-primary congenital CMV will be especially relevant to studying immune requirements of a maternal vaccine for women in high CMV seroprevalence areas at risk of repeated CMV reinfections during pregnancy.

Inhibition of Cytomegalovirus by Pentacta pygmaea Fucosylated Chondroitin Sulfate Depends on Its Molecular Weight

Many viruses attach to host cells by first interacting with cell surface proteoglycans containing heparan sulfate (HS) glycosaminoglycan chains and then by engaging with specific receptor, resulting in virus entry. In this project, HS–virus interactions were targeted by a new fucosylated chondroitin sulfate from the sea cucumber Pentacta pygmaea (PpFucCS) in order to block human cytomegalovirus (HCMV) entry into cells. Human foreskin fibroblasts were infected with HCMV in the presence of PpFucCS and its low molecular weight (LMW) fractions and the virus yield at five days post-infection was assessed. The virus attachment and entry into the cells were visualized by labeling the purified virus particles with a self-quenching fluorophore octadecyl rhodamine B (R18). The native PpFucCS exhibited potent inhibitory activity against HCMV specifically blocking virus entry into the cell and the inhibitory activities of the LMW PpFucCS derivatives were proportional to their chain lengths. PpFucCS and the derived oligosaccharides did not exhibit any significant cytotoxicity; moreover, they protected the infected cells from virus-induced lytic cell death. In conclusion, PpFucCS inhibits the entry of HCMV into cells and the high MW of this carbohydrate is a key structural element to achieve the maximal anti-viral effect. This new marine sulfated glycan can be developed into a potential prophylactic and therapeutic antiviral agent against HCMV infection.

Primary, Secondary, and Tertiary Prevention of Congenital Cytomegalovirus Infection

Cytomegalovirus infection is the most common congenital infection, affecting about 1% of births worldwide. Several primary, secondary, and tertiary prevention strategies are already available during the prenatal period to help mitigate the immediate and long-term consequences of this infection. In this review, we aim to present and assess the efficacy of these strategies, including educating pregnant women and women of childbearing age on their knowledge of hygiene measures, development of vaccines, screening for cytomegalovirus infection during pregnancy (systematic versus targeted), prenatal diagnosis and prognostic assessments, and preventive and curative treatments in utero.

ADCC-activating antibodies correlate with protection against congenital human cytomegalovirus infection

Human cytomegalovirus (HCMV) is the most common vertically transmitted infection worldwide, yet there are no licensed vaccines or therapeutics to prevent congenital HCMV (cCMV) infection. Emerging evidence from studies of natural infection and HCMV vaccine trials indicates that antibody Fc effector functions may defend against HCMV infection. We previously reported that antibody-dependent cellular phagocytosis (ADCP) and IgG activation of FcγRI/FcγRII were associated with reduced risk of cCMV transmission, leading us to hypothesize that other Fc-mediated antibody functions may also contribute to protection. In this same cohort of HCMV transmitting (n = 41) and non-transmitting (n = 40) mother-infant dyads, we found that higher maternal sera antibody-dependent cellular cytotoxicity (ADCC) activation was also associated with decreased risk of cCMV infection. We determined that NK cell-mediated ADCC responses correlated strongly with anti-HCMV IgG FcγRIII/CD16 activation and IgG binding to the HCMV immunoevasin protein UL16. Notably, anti-UL16 IgG binding and engagement of FcγRIII/CD16 were higher in non-transmitting versus transmitting dyads and interacted significantly with ADCC responses. These findings indicate that ADCC-activating antibodies against novel targets such as UL16 may represent an important protective maternal immune response against cCMV infection, which can guide future HCMV correlates studies and vaccine development.

Novel monoclonal antibody-based therapies: implications for the treatment and prevention of HCMV disease

Human cytomegalovirus (HCMV) is an important pathogen worldwide. Although HCMV infection is often asymptomatic in immunocompetent individuals, it can cause severe or even life-threatening symptoms in immunocompromised patients. Due to limitations of antiviral treatments, it is necessary to search for new therapeutic alternatives. Recent studies have highlighted the contribution of antibodies in protecting against HCMV disease, including neutralizing and non-neutralizing antibodies. Given the immunocompromised target population, monoclonal antibodies (mAbs) may represent an alternative to the clinical management of HCMV infection. In this context, we provide a synthesis of recent data revising the literature supporting and arguing about the role of the humoral immunity in controlling HCMV infection. Additionally, we review the state of the art in the development of therapies based on mAbs.

Repurposing N-hydroxy thienopyrimidine-2,4-diones (HtPD) as inhibitors of human cytomegalovirus pUL89 endonuclease: Synthesis and biological characterization

The terminase complex of human cytomegalovirus (HCMV) is required for viral genome packaging and cleavage. Critical to the terminase functions is a metal-dependent endonuclease at the C-terminus of pUL89 (pUL89-C). We have previously reported metal-chelating N-hydroxy thienopyrimidine-2,4-diones (HtPD) as inhibitors of human immunodeficiency virus 1 (HIV-1) RNase H. In the current work, we have synthesized new analogs and resynthesized known analogs of two isomeric HtPD subtypes, anti-HtPD (13), and syn-HtPD (14), and characterized them as inhibitors of pUL89-C. Remarkably, the vast majority of analogs strongly inhibited pUL89-C in the biochemical endonuclease assay, with IC50 values in the nM range. In the cell-based antiviral assay, a few analogs inhibited HCMV in low μM concentrations. Selected analogs were further characterized in a biophysical thermal shift assay (TSA) and in silico molecular docking, and the results support pUL89-C as the protein target of these inhibitors. Collectively, the biochemical, antiviral, biophysical, and in silico data reported herein indicate that the isomeric HtPD chemotypes 13-14 can serve as valuable chemical platforms for designing improved inhibitors of HCMV pUL89-C.

B cells going viral in the CNS: Dynamics, complexities, and functions of B cells responding to viral encephalitis

A diverse number of DNA and RNA viruses have the potential to invade the central nervous system (CNS), causing inflammation and injury to cells that have a limited capacity for repair and regeneration. While rare, viral encephalitis in humans is often fatal and survivors commonly suffer from permanent neurological sequelae including seizures. Established treatment options are extremely limited, predominantly relying on vaccines, antivirals, or supportive care. Many viral CNS infections are characterized by the presence of antiviral antibodies in the cerebral spinal fluid (CSF), indicating local maintenance of protective antibody secreting cells. However, the mechanisms maintaining these humoral responses are poorly characterized. Furthermore, while both viral and autoimmune encephalitis are associated with the recruitment of diverse B cell subsets to the CNS, their protective and pathogenic roles aside from antibody production are just beginning to be understood. This review will focus on the relevance of B cell responses to viral CNS infections, with an emphasis on the importance of intrathecal immunity and the potential contribution to autoimmunity. Specifically, it will summarize the newest data characterizing B cell activation, differentiation, migration, and localization in clinical samples as well as experimental models of acute and persistent viral encephalitis.

Lessons from Acquired Natural Immunity and Clinical Trials to Inform Next-Generation Human Cytomegalovirus Vaccine Development

Human cytomegalovirus (HCMV) infection, the most common cause of congenital disease globally, affecting an estimated 1 million newborns annually, can result in lifelong sequelae in infants, such as sensorineural hearing loss and brain damage. HCMV infection also leads to a significant disease burden in immunocompromised individuals. Hence, an effective HCMV vaccine is urgently needed to prevent infection and HCMV-associated diseases. Unfortunately, despite more than five decades of vaccine development, no successful HCMV vaccine is available. This review summarizes what we have learned from acquired natural immunity, including innate and adaptive immunity; the successes and failures of HCMV vaccine human clinical trials; the progress in related animal models; and the analysis of protective immune responses during natural infection and vaccination settings. Finally, we propose novel vaccine strategies that will harness the knowledge of protective immunity and employ new technology and vaccine concepts to inform next-generation HCMV vaccine development.

8-Hydroxy-1,6-naphthyridine-7-carboxamides as Inhibitors of Human Cytomegalovirus pUL89 Endonuclease

Human cytomegalovirus (HCMV) replication requires a metal-dependent endonuclease at the C-terminus of pUL89 (pUL89-C) for viral genome packaging and cleavage. We have previously shown that pUL89-C can be pharmacologically inhibited with designed metal-chelating compounds. We report herein the synthesis of a few 8-hydroxy-1,6-naphthyridine subtypes, including 5-chloro (subtype 15), 5-aryl (subtype 16), and 5-amino (subtype 17) variants. Analogs were studied for the inhibition of pUL89-C in a biochemical endonuclease assay, a biophysical thermal shift assay (TSA), in silico molecular docking, and for the antiviral potential against HCMV in cell-based assays. These studies identified eight analogs of 8-hydroxy-1,6-naphthyridine-7-carboxamide subtypes for further characterization, most of which inhibited pUL89-C with single-digit μM IC50 values, and conferred antiviral activity in μM range. TSA and molecular modeling of selected analogs corroborate their binding to pUL89-C. Collectively, our biochemical, antiviral, biophysical and in silico data suggest that 8-hydroxy-1,6-naphthyridine-7-carboxamide subtypes can be used for designing inhibitors of HCMV pUL89-C.

Maternal Fc-mediated non-neutralizing antibody responses correlate with protection against congenital human cytomegalovirus infection

Human cytomegalovirus (HCMV) is the most common congenital infection and a leading cause of stillbirth, neurodevelopmental impairment, and pediatric hearing loss worldwide. Development of a maternal vaccine or therapeutic to prevent congenital HCMV has been hindered by limited knowledge of the immune responses that protect against HCMV transmission in utero. To identify protective antibody responses, we measured HCMV-specific IgG binding and antiviral functions in paired maternal and cord blood sera from HCMV-seropositive transmitting (n = 41) and non-transmitting (n = 40) mother-infant dyads identified via a large, US-based, public cord blood bank. We found that high-avidity IgG binding to HCMV and antibody-dependent cellular phagocytosis (ADCP) were associated with reduced risk of congenital HCMV infection. We also determined that HCMV-specific IgG activation of FcγRI and FcγRII was enhanced in non-transmitting dyads and that increased ADCP responses were mediated through both FcγRI and FcγRIIA expressed on human monocytes. These findings suggest that engagement of FcγRI/FcγRIIA and Fc effector functions including ADCP may protect against congenital HCMV infection. Taken together, these data can guide future prospective studies on immune correlates against congenital HCMV transmission and inform HCMV vaccine and immunotherapeutic development.

Modestly protective cytomegalovirus vaccination of young children effectively prevents congenital infection at the population level

A vaccine to prevent congenital cytomegalovirus infection (cCMV) is a public health priority. cCMV results from maternal primary or non-primary CMV infection (reinfection, or reactivation of chronic infection) during pregnancy. Young children are a major source of transmission to pregnant women because they shed CMV at high viral loads for prolonged periods. CMV vaccines evaluated in clinical trials so far have demonstrated only approximately 50% efficacy against maternal primary infection. None of these have been approved, as higher levels of vaccine efficacy are assumed to be required to substantially reduce cCMV prevalence. Here, we designed a mathematical model to capture the relationship between viral shedding by young children and maternal CMV infections during pregnancy. Using this model, we were able to quantify the impact of CMV post-infection immunity on protecting against reinfection and viral shedding. There was a 36% reduction in the risk of infection to a seropositive person with post-infection immunity (reinfection) versus a seronegative person without this immunity (primary infection), given the same exposure. Viral shedding following reinfection was only 34% the quantity of that following primary infection. Our model also predicted that a vaccine that confers the equivalent of post-infection immunity, when given to young children, would markedly reduce both CMV transmission to pregnant women and the prevalence of cCMV. Thus, we predict that existing vaccine candidates that have been shown to be only modestly protective may in fact be highly effective at preventing cCMV by interrupting child-to-mother transmission.

Polymorphic Forms of Human Cytomegalovirus Glycoprotein O Protect against Neutralization of Fibroblast Entry by Antibodies Targeting Epitopes Defined by Glycoproteins H and L

Human cytomegalovirus (CMV) utilizes different glycoproteins to enter into fibroblast and epithelial cells. A trimer of glycoproteins H, L, and O (gH/gL/gO) is required for entry into all cells, whereas a pentamer of gH/gL/UL128/UL130/UL131A is selectively required for infection of epithelial, endothelial, and some myeloid-lineage cells, but not of fibroblasts. Both complexes are of considerable interest for vaccine and immunotherapeutic development but present a conundrum: gH/gL-specific antibodies have moderate potency yet neutralize CMV entry into all cell types, whereas pentamer-specific antibodies are more potent but do not block fibroblast infection. Which cell types and neutralizing activities are important for protective efficacy in vivo remain unclear. Here, we present evidence that certain CMV strains have evolved polymorphisms in gO to evade trimer-specific neutralizing antibodies. Using luciferase-tagged variants of strain TB40/E in which the native gO is replaced by gOs from other strains, we tested the effects of gO polymorphisms on neutralization by monoclonal antibodies (mAbs) targeting four independent epitopes in gH/gL that are common to both trimer and pentamer. Neutralization of fibroblast entry by three mAbs displayed a range of potencies that depended on the gO type, a fourth mAb failed to neutralize fibroblast entry regardless of the gO type, while neutralization of epithelial cell entry by all four mAbs was potent and independent of the gO type. Thus, specific polymorphisms in gO protect the virus from mAb neutralization in the context of fibroblast but not epithelial cell entry. No influence of gO type was observed for protection against CMV hyperimmune globulin or CMV-seropositive human sera, suggesting that antibodies targeting protected gH/gL epitopes represent a minority of the polyclonal neutralizing repertoire induced by natural infection.

Amniocentesis to diagnose congenital cytomegalovirus infection following maternal primary infection

BACKGROUND

Congenital cytomegalovirus infection following maternal primary cytomegalovirus infection affects approximately 0.4% of newborns in the United States but may be hard to diagnose prenatally.

OBJECTIVE

To evaluate the current sensitivity and specificity of amniocentesis in detecting congenital cytomegalovirus infection.

STUDY DESIGN

Secondary analysis of a multicenter randomized placebo-controlled trial designed to evaluate whether cytomegalovirus hyperimmune globulin reduces congenital cytomegalovirus infection in neonates of individuals diagnosed with primary cytomegalovirus infection before 24 weeks of gestation. At randomization, subjects had no clinical evidence of fetal infection. Eligible subjects were randomized to monthly infusions of cytomegalovirus hyperimmune globulin or placebo until delivery. Although not required by the trial protocol, amniocentesis following randomization was permitted. The fetuses and neonates were tested for the presence of cytomegalovirus at delivery. Comparisons were made between those with and without amniocentesis and between those with cytomegalovirus-positive and negative results, using chi-square or Fisher exact test for categorical variables and the Wilcoxon rank sum test or t test for continuous variables. A P value of <.05 was considered significant.

RESULTS

From 2012 to 2018, 397 subjects were included, of whom 55 (14%) underwent amniocentesis. Cytomegalovirus results were available for 53 fetuses and neonates. Fourteen amniocenteses were positive (25%). Gestational age at amniocentesis was similar between those with and without cytomegalovirus present, as was the interval between maternal diagnosis and amniocentesis. The prevalence of fetal or neonatal infection was 26% (14/53). The neonates of all 12 subjects with a positive amniocentesis and available results had cytomegalovirus infection confirmed at delivery, as did 2 neonates from the group of 41 subjects with a negative amniocentesis, with a sensitivity of 86% (95% confidence interval, 57-98), specificity of 100% (95% confidence interval, 91-100), positive predictive value of 100% (95% confidence interval, 74-100), and negative predictive value of 95% (95% confidence interval, 83-99). Amniocentesis-positive pregnancies were delivered at an earlier gestational age (37.4 vs 39.6 weeks; P<.001) and had lower birthweights (2583±749 vs 3428±608 g, P=.004) than amniocentesis-negative pregnancies.

CONCLUSION

Amniocentesis results are an accurate predictor of congenital cytomegalovirus infection.

Identification of functionally important domains of human cytomegalovirus gO that act after trimer binding to receptors

Human cytomegalovirus (HCMV) entry involves trimer (gH/gL/gO) that interacts with PDGFRα in fibroblasts. Entry into epithelial and endothelial cells requires trimer, which binds unidentified receptors, and pentamer (gH/gL/UL128-131), which binds neuropilin-2. To identify functionally important domains in trimer, we screened an overlapping 20-mer gO peptide library and identified two sets of peptides: 19/20 (a.a. 235–267) and 32/33 (a.a. 404–436) that could block virus entry. Soluble trimer containing wild type gO blocked HCMV entry, whereas soluble trimers with the 19/20 or 32/33 sequences mutated did not block entry. Interestingly, the mutant trimers retained the capacity to bind to cellular receptors including PDGFRα. Peptide 19/20 and 32/33 sequences formed a lobe extending from the surface of gO and an adjacent concave structure, respectively. Neither of these sets of sequences contacted PDGFRα. Instead, our data support a model in which the 19/20 and 32/33 trimer sequences function downstream of receptor binding, e.g. trafficking of HCMV into endosomes or binding to gB for entry fusion. We also screened for peptides that bound antibodies (Abs) in human sera, observing that peptides 20 and 26 bound Abs. These peptides engendered neutralizing Abs (NAbs) after immunization of rabbits and could pull out NAbs from human sera. Peptides 20 and 26 sequences represent the first NAb epitopes identified in trimer. These studies describe two important surfaces on gO defined by: i) peptides 19/20 and 32/33, which apparently act downstream of receptor binding and ii) peptide 26 that interacts with PDGFRα. Both these surfaces are targets of NAbs.

Human cytomegalovirus (HCMV) infects 80% of the world population, causing severe morbidity and mortality in transplant patients and can be transmitted to the developing fetus leading to severe neurological defects. The current anti-viral agents used to treat HCMV are not very effective as viruses can develop resistance and there is no licensed HCMV vaccine available. Recently, there has been intense interest in the HCMV envelope glycoproteins involved in entry as a component of vaccines. One glycoprotein complex, the gH/gL/gO trimer is especially intriguing as it is required for infection of extracellular virus in all cell types. Here, we identify domains in the trimer that have an essential function in entry downstream of receptor binding and are also epitopes recognized by naturally induced neutralizing antibodies. These results will have implications for advancing the efforts to develop novel HCMV therapeutics.

4,5-Dihydroxypyrimidine Methyl Carboxylates, Carboxylic Acids, and Carboxamides as Inhibitors of Human Cytomegalovirus pUL89 Endonuclease

Human cytomegalovirus (HCMV) terminase complex entails a metal-dependent endonuclease at the C-terminus of pUL89 (pUL89-C). We report herein the design, synthesis, and characterization of dihydroxypyrimidine (DHP) acid (14), methyl ester (13), and amide (15) subtypes as inhibitors of HCMV pUL89-C. All analogs synthesized were tested in an endonuclease assay and a thermal shift assay (TSA) and subjected to molecular docking to predict binding affinity. Although analogs inhibiting pUL89-C in the sub-μM range were identified from all three subtypes, acids (14) showed better overall potency, substantially larger thermal shift, and considerably better docking scores than esters (13) and amides (15). In the cell-based antiviral assay, six analogs inhibited HCMV with moderate activities (EC₅₀ = 14.4-22.8 μM). The acid subtype (14) showed good in vitro ADME properties, except for poor permeability. Overall, our data support the DHP acid subtype (14) as a valuable scaffold for developing antivirals targeting HCMV pUL89-C.

High prevalence of asymptomatic CMV shedding in healthy children attending the minnesota state fair

BACKGROUND

Young children in the household are a known risk factor for maternal CMV infection and consequently, congenital infection in infants. However, little is known about viral shedding in pre-school aged children.

OBJECTIVES

To estimate the prevalence of CMV DNA shedding and CMV antibodies among healthy children and their mothers.

STUDY DESIGN

A study of children ages 0 through 5 years was undertaken at the 2019 Minnesota State Fair. Children and their mothers were assessed for CMV shedding by procurement of a saliva swab for CMV PCR testing. An optional finger-stick for capillary blood was used to assess CMV antibodies.

RESULTS

A total of 109 children and 85 mothers were enrolled. The prevalence of CMV saliva shedding among children (mean age 3.1 years, SE=0.16) and their mothers was 12/109 (11.0%) and 1/85 (1.2%), respectively. The prevalence of CMV DNA among children peaked at 3 years of age (26%) while the mean viral load was greatest at one year of age (236,693 IU/mL). CMV IgG antibodies among those who agreed to a finger-stick were detected in 16/35 mothers (45.7%) and 0/7 children (0%). Mothers of children aged 5 years or greater had the highest seroprevalence (61.5%).

CONCLUSIONS

The prevalence of CMV salivary shedding in this unselected sample of young children was approximately 11.0%. The overall maternal seroprevalence in our sample was <50%, suggesting these women are at risk for acquisition of a primary CMV infection in subsequent pregnancies.

Cytomegalovirus DNA detection in pregnant women with a high IgG avidity index: a valuable tool for diagnosing non-primary infections?

BACKGROUND/AIM

Congenital human cytomegalovirus infection (cCMV) is the commonest congenital infection, and it can result in hearing loss and neurodevelopmental delay. Even if primary infections are more frequent and cause more severe congenital cCMV manifestations compared to NPIs, and despite partial protection from maternal immunity, the highest birth prevalence of cCMV is observed in seropositive women with non-primary CMV infection (NPI). Given that NPI contribute significantly to the overall burden of cCMV, their accurate diagnosis of NPI remains clinically important. Considering that the serological testing for CMV infection is not always reliable, we sought to determine whether detection of CMV DNA in pregnant women with a high IgG avidity index (AI) can help diagnose NPI.

MATERIALS AND METHODS

Human CMV serology screening (IgG, IgM, and IgG AI) was performed for confirmation of CMV infection in serum samples from mainly pregnant women with indications of CMV infection due to IgG⁺ and IgM⁺-positive samples in other laboratories. Pregnant women (or those with termination of pregnancy during the last period) with adequate IgG levels to perform IgG AI were included. Demographic data and mean gestation week at the time of screening were recorded. Serological testing was performed using CE-IVD commercial kits. CMV DNAemia detection by real time PCR (RT-PCR) was applied to confirm suspected CMV infection.

RESULTS

Nine-hundred and thirty-four pregnant women CMV IgG positive with adequate IgG titers for AI testing were included in the study. The percentage of women with a high AI was 71.8% (671/934); among them, nearly 2.4% (16/671) had presence of CMV DNA. Also, 12.4% of women (116/934) had intermediate IgG AI and 15.7% of women (147/934) had low IgG AI. The presence of CMV DNA was observed in 13.8% (16/116) and 39.5% (58/147) of the groups with intermediate and low IgG AI, respectively. A high CMV IgG AI was associated with a negative CMV PCR status (p-value <.00001).

CONCLUSIONS

CMV DNA was present in 2.4% of seropositive women with high IgG AI, indicating active NPI and thus, harboring the risk of cCMV sequelae to the fetus. Moreover, the incidence of NPI may have been underestimated due to single timepoint testing. In order to detect CMV NPI in a seropositive woman, regular and frequent serology testing as well as detection of CMV DNAemia are required which render the whole diagnostic process impractical and not cost-effective.

Human Brain Organoids as an In Vitro Model System of Viral Infectious Diseases

Brain organoids, or brainoids, have shown great promise in the study of central nervous system (CNS) infection. Modeling Zika virus (ZIKV) infection in brain organoids may help elucidate the relationship between ZIKV infection and microcephaly. Brain organoids have been used to study the pathogenesis of SARS-CoV-2, human immunodeficiency virus (HIV), HSV-1, and other viral infections of the CNS. In this review, we summarize the advances in the development of viral infection models in brain organoids and their potential application for exploring mechanisms of viral infections of the CNS and in new drug development. The existing limitations are further discussed and the prospects for the development and application of brain organs are prospected.

Protection against Congenital CMV Infection Conferred by MVA-Vectored Subunit Vaccines Extends to a Second Pregnancy after Maternal Challenge with a Heterologous, Novel Strain Variant

Maternal reinfection of immune women with novel human cytomegalovirus (HCMV) strains acquired during pregnancy can result in symptomatic congenital CMV (cCMV) infection. Novel animal model strategies are needed to explore vaccine-mediated protections against maternal reinfection. To investigate this in the guinea pig cytomegalovirus (GPCMV) model, a strictly in vivo-passaged workpool of a novel strain, the CIDMTR strain (dose, 1 × 10⁷ pfu) was used to infect dams that had been challenged in a previous pregnancy with the 22122 strain, following either sham-immunization (vector only) or vaccination with MVA-vectored gB, gH/gL, or pentameric complex (PC) vaccines. Maternal DNAemia cleared by day 21 in the glycoprotein-vaccinated dams, but not in the sham-immunized dams. Mean pup birth weights were 72.85 ± 10.2, 80.0 ± 6.9, 81.4 ± 14.1, and 89.38 ± 8.4 g in sham-immunized, gB, gH/gL, and PC groups, respectively (p < 0.01 for control v. PC). Pup mortality in the sham-immunized group was 6/12 (50%), but reduced to 3/35 (8.6%) in combined vaccine groups (p = 0.0048). Vertical CIDMTR transmission occurred in 6/12 pups (50%) in the sham-vaccinated group, compared to 2/34 pups (6%) in the vaccine groups (p = 0.002). We conclude that guinea pigs immunized with vectored vaccines expressing 22122 strain-specific glycoproteins are protected after a reinfection with a novel, heterologous clinical isolate (CIDMTR) in a second pregnancy.

Pathogenesis of wild-type-like rhesus cytomegalovirus strains following oral exposure of immune-competent rhesus macaques

Rhesus cytomegalovirus (RhCMV) infection of rhesus macaques (Macaca mulatta) is a valuable nonhuman primate model of human CMV (HCMV) persistence and pathogenesis. In vivo studies predominantly use tissue culture-adapted variants of RhCMV that contain multiple genetic mutations compared to wild-type (WT) RhCMV. In many studies, animals have been inoculated by non-natural routes (e.g., subcutaneous, intravenous) that do not recapitulate disease progression via the normative route of mucosal exposure. Accordingly, the natural history of RhCMV would be more accurately reproduced by infecting macaques with strains of RhCMV that reflect the WT genome using natural routes of mucosal transmission. Herein, we tested two WT-like RhCMV strains, UCD52 and UCD59, and demonstrated that systemic infection and frequent, high-titer viral shedding in bodily fluids occurred following oral inoculation. RhCMV disseminated to a broad range of tissues, including the central nervous system and reproductive organs. Commonly infected tissues included the thymus, spleen, lymph nodes, kidneys, bladder, and salivary glands. Histological examination revealed prominent nodular hyperplasia in spleens and variable levels of lymphoid lymphofollicular hyperplasia in lymph nodes. One of six inoculated animals had limited viral dissemination and shedding, with commensurately weak antibody responses to RhCMV antigens. These data suggest that long-term RhCMV infection parameters might be restricted by local innate factors and/or de novo host immune responses in a minority of primary infections. Together, we have established an oral RhCMV infection model that mimics natural HCMV infection. The virological and immunological parameters characterized in this study will greatly inform HCMV vaccine designs for human immunization. IMPORTANCE Human cytomegalovirus (HCMV) is globally ubiquitous with high seroprevalence rates in all communities. HCMV infections can occur vertically following mother-to-fetus transmission across the placenta and horizontally following shedding of virus in bodily fluids in HCMV infected hosts and subsequent exposure of susceptible individuals to virus-laden fluids. Intrauterine HCMV has long been recognized as an infectious threat to fetal growth and development. Since vertical HCMV infections occur following horizontal HCMV transmission to the pregnant mother, the nonhuman primate model of HCMV pathogenesis was used to characterize the virological and immunological parameters of infection following primary mucosal exposures to rhesus cytomegalovirus.

Tegument Protein pp150 Sequence-Specific Peptide Blocks Cytomegalovirus Infection

Human cytomegalovirus (HCMV) tegument protein pp150 is essential for the completion of the final steps in virion maturation. Earlier studies indicated that three pp150nt (N-terminal one-third of pp150) conformers cluster on each triplex (Tri1, Tri2A and Tri2B), and extend towards small capsid proteins atop nearby major capsid proteins, forming a net-like layer of tegument densities that enmesh and stabilize HCMV capsids. Based on this atomic detail, we designed several peptides targeting pp150nt. Our data show significant reduction in virus growth upon treatment with one of these peptides (pep-CR2) with an IC₅₀ of 1.33 μM and no significant impact on cell viability. Based on 3D modeling, pep-CR2 specifically interferes with the pp150–capsid binding interface. Cells pre-treated with pep-CR2 and infected with HCMV sequester pp150 in the nucleus, indicating a mechanistic disruption of pp150 loading onto capsids and subsequent nuclear egress. Furthermore, pep-CR2 effectively inhibits mouse cytomegalovirus (MCMV) infection in cell culture, paving the way for future animal testing. Combined, these results indicate that CR2 of pp150 is amenable to targeting by a peptide inhibitor, and can be developed into an effective antiviral.

Association between Congenital Cytomegalovirus Infection and Brain Injury in Neonates: A Meta-analysis of Cohort Studies

Objective

To assess association between congenital cytomegalovirus (CMV) infection and brain injury in neonates.

Methods

The literatures from inception to November 4, 2020, were searched through PubMed, Embase, Cochrane Library, and Web of Science. Heterogeneity test was conducted for each indicator and measured by I ² statistics. If I ² ≥ 50%, the random effects model was applied; otherwise, the fixed effects model was used. Sensitivity analysis was performed for all models. Weighed mean difference (WMD) was used as the effect size for measurement data, and risk ratio (RR) was as the effect indicator.

Results

A total of 13 studies, including 4,262 congenital CMV infection neonates, were enrolled in this study. Our results showed that the rate of hearing impairment (RR: 2.105, 95% CI: (1.115, 3.971), P = 0.002), sensorineural hearing loss (SNHL) (RR: 17.051, 95% CI: (6.201, 46.886), P < 0.001), and microcephaly (RR: 2.283, 95% CI: (1.325, 3.935), P =0.003) in neonates infected congenital CMV was higher than that in control group.

Conclusion

The risks of hearing impairment, SNHL, and microcephaly in neonates during childhood may be associated with congenital CMV infection. It is necessary to establish neonatal screening programs and comprehensive diagnostic tests for patients to reduce the risk of adverse brain damage to the congenital CMV infection as early as possible and to improve the prognosis of the newborn.

A Fully Protective Congenital CMV Vaccine Requires Neutralizing Antibodies to Viral Pentamer and gB Glycoprotein Complexes but a pp65 T-Cell Response Is Not Necessary

A vaccine against congenital cytomegalovirus infection is a high priority. Guinea pig cytomegalovirus (GPCMV) is the only congenital CMV small animal model. GPCMV encodes essential glycoprotein complexes for virus entry (gB, gH/gL/gO, gM/gN) including a pentamer complex (gH/gL/GP129/GP131/GP133 or PC) for endocytic cell entry. The cohorts for protection against congenital CMV are poorly defined. Neutralizing antibodies to the viral glycoprotein complexes are potentially more important than an immunodominant T-cell response to the pp65 protein. In GPCMV, GP83 (pp65 homolog) is an evasion factor, and the GP83 mutant GPCMV has increased sensitivity to type I interferon. Although GP83 induces a cell-mediated response, a GP83-only-based vaccine strategy has limited efficacy. GPCMV attenuation via GP83 null deletion mutant in glycoprotein PC positive or negative virus was evaluated as live-attenuated vaccine strains (GP83dPC+/PC-). Vaccinated animals induced antibodies to viral glycoprotein complexes, and PC+ vaccinated animals had sterilizing immunity against wtGPCMV challenge. In a pre-conception vaccine (GP83dPC+) study, dams challenged mid-2nd trimester with wtGPCMV had complete protection against congenital CMV infection without detectable virus in pups. An unvaccinated control group had 80% pup transmission rate. Overall, gB and PC antibodies are key for protection against congenital CMV infection, but a response to pp65 is not strictly necessary.

Human cytomegalovirus-induced host protein citrullination is crucial for viral replication

Citrullination is the conversion of arginine-to-citrulline by protein arginine deiminases (PADs), whose dysregulation is implicated in the pathogenesis of various types of cancers and autoimmune diseases. Consistent with the ability of human cytomegalovirus (HCMV) to induce post-translational modifications of cellular proteins to gain a survival advantage, we show that HCMV infection of primary human fibroblasts triggers PAD-mediated citrullination of several host proteins, and that this activity promotes viral fitness. Citrullinome analysis reveals significant changes in deimination levels of both cellular and viral proteins, with interferon (IFN)-inducible protein IFIT1 being among the most heavily deiminated one. As genetic depletion of IFIT1 strongly enhances HCMV growth, and in vitro IFIT1 citrullination impairs its ability to bind to 5’-ppp-RNA, we propose that viral-induced IFIT1 citrullination is a mechanism of HCMV evasion from host antiviral resistance. Overall, our findings point to a crucial role of citrullination in subverting cellular responses to viral infection.

Citrullination is a posttranslational modification of arginines. Here, the authors show that HCMV infection increases citrullination of host and virus proteins to promote infection and that citrullinated interferon-inducible protein IFIT1 is impaired in RNA binding, as a potential mechanism of evasion.

The three-component helicase/primase complex of herpes simplex virus-1

Herpes simplex virus type 1 (HSV-1) is one of the nine herpesviruses that infect humans. HSV-1 encodes seven proteins to replicate its genome in the hijacked human cell. Among these are the herpes virus DNA helicase and primase that are essential components of its replication machinery. In the HSV-1 replisome, the helicase-primase complex is composed of three components including UL5 (helicase), UL52 (primase) and UL8 (non-catalytic subunit). UL5 and UL52 subunits are functionally interdependent, and the UL8 component is required for the coordination of UL5 and UL52 activities proceeding in opposite directions with respect to the viral replication fork. Anti-viral compounds currently under development target the functions of UL5 and UL52. Here, we review the structural and functional properties of the UL5/UL8/UL52 complex and highlight the gaps in knowledge to be filled to facilitate molecular characterization of the structure and function of the helicase-primase complex for development of alternative anti-viral treatments.

Transmission of cell-associated human cytomegalovirus isolates between various cell types using polymorphonuclear leukocytes as a vehicle

Polymorphonuclear leukocytes (PMNs) are regarded as vehicles for the hematogenous dissemination of human cytomegalovirus (HCMV). In cell culture, this concept has been validated with cell-free laboratory strains but not yet with clinical HCMV isolates that grow strictly cell-associated. We, therefore, aimed to evaluate whether PMNs can also transmit such isolates from initially infected fibroblasts to other cell types, which might further clarify the role of PMNs in HCMV dissemination and provide a model to search for potential inhibitors. PMNs, which have been isolated from HCMV-seronegative individuals, were added for 3 h to fibroblasts infected with recent cell-associated HCMV isolates, then removed and transferred to various recipient cell cultures. The transfer efficiency in the recipient cultures was evaluated by immunofluorescence staining of viral immediate early antigens. Soluble derivatives of the cellular HCMV entry receptor PDGFRα were analyzed for their potential to interfere with this transfer. All of five tested HCMV isolates could be transferred to fibroblasts, endothelial and epithelial cells with transfer rates ranging from 2 to 9%, and the transferred viruses could spread focally in these recipient cells within 1 week. The PDGFRα-derived peptides IK40 and GT40 reduced transfer by 40 and 70% when added during the uptake step. However, when added during the transfer step, only IK40 was effective, inhibiting transmission by 20% on endothelial cells and 50–60% on epithelial cells and fibroblasts. These findings further corroborate the assumption of cell-associated HCMV dissemination by PMNs and demonstrate that it is possible to inhibit this transmission mode.

Assessment of HCMV-encoded microRNAs in plasma as potential biomarkers in pregnant women with adverse pregnancy outcomes

Background

Human cytomegalovirus (HCMV) is the most frequent cause of congenital infections and can lead to adverse pregnancy outcomes (APOs). HCMV encodes multiple microRNAs (miRNAs) that have been reported to be partially related to host immune responses, cell cycle regulation, viral replication, and viral latency, and can be detected in human plasma. However, the relevance for HCMV-encoded miRNAs in maternal plasma as an indicator for APOs has never been evaluated.

Methods

Expression profiles of 22 HCMV-encoded miRNAs were first measured in plasma samples from 20 pregnant women with APOs and 28 normal controls using quantitative reverse-transcription polymerase chain reaction. Next, markedly changed miRNAs were validated in another independent validation set consisting of 20 pregnant women with APOs and 27 control subjects. Markedly changed miRNAs were further assessed in the placenta tissues. HCMV DNA in peripheral blood leukocytes (PBLs) and anti-HCMV immunoglobulin M (IgM) and anti-HCMV immunoglobulin G (IgG) in plasma were also examined in both training and validation sets. Diagnostic value and risk factors were compared between APO cohorts and normal controls.

Results

Analysis of the training and validation data sets revealed that plasma concentrations of hcmv-miR-UL148D, hcmv-miR-US25-1-5p and hcmv-miR-US5-1 were significantly increased in pregnant women with APOs compared with normal controls. Hcmv-miR-US25-1-5p presented the largest area under the receiver-operating characteristic (ROC) curve (AUC) (0.735; 95% CI, 0.635–0.836), with a sensitivity of 68% and specificity of 71%. Furthermore, plasma levels of hcmv-miR-US25-1-5p and hcmv-miR-US5-1 correlated positively with APOs (P=0.029 and 0.035, respectively). Hcmv-miR-US25-1-5p in the placenta tissues were dramatically increased in APOs, and correlated with plasma hcmv-miR-US25-1-5p. Nevertheless, neither the concentration of HCMV DNA in PBLs nor the positivity rates of anti-HCMV IgM and anti-HCMV IgG in plasma showed a statistically significant correlation with APOs.

Conclusions

We identified a unique signature of HCMV-encoded miRNAs in pregnant women with APOs that may be useful as a potential noninvasive biomarker for predicting and monitoring APOs during HCMV infection.

Localization of the WD repeat-containing protein 5 to the Virion Assembly Compartment Facilitates Human Cytomegalovirus Assembly

We previously reported that human cytomegalovirus (HCMV) utilizes the cellular protein WD repeat-containing protein 5 (WDR5) to facilitate capsid nuclear egress. Here, we further show that HCMV infection results in WDR5 localization in a juxtanuclear region, and that its localization to this cellular site is associated with viral replication and late viral gene expression. Furthermore, WDR5 accumulated in the virion assembly compartment (vAC) and co-localized with vAC markers of gamma-tubulin (γ-tubulin), early endosomes, and viral vAC marker proteins pp65, pp28, and glycoprotein B (gB). WDR5 co-immunoprecipitated with multiple virion proteins, including MCP, pp150, pp65, pIRS1, and pTRS1, which may explain WDR5 accumulation in the vAC during infection. WDR5 fractionated with virions either in the presence or absence of Triton X-100 and was present in purified viral particles, suggesting that WDR5 was incorporated into HCMV virions. Thus, WDR5 localized to the vAC and was incorporated into virions, raising the possibility that in addition to capsid nuclear egress, WDR5 could also participate in cytoplasmic HCMV virion morphogenesis.Importance Human cytomegalovirus (HCMV) has a large (∼235-kb) genome that contains over 170 ORFs and exploits numerous cellular factors to facilitate its replication. In the late phase of HCMV infection cytoplasmic membranes are reorganized to establish the virion assembly compartment (vAC), which has been shown to necessary for efficient assembly of progeny virions. We previously reported that WDR5 facilitates HCMV nuclear egress. Here, we show that WDR5 is localized to the vAC and incorporated into virions, perhaps contributing to efficient virion maturation. Thus, findings in this study identified a potential role for WDR5 in HCMV assembly in the cytoplasmic phase of virion morphogenesis.

A trimeric capable gB CMV vaccine provides limited protection against a highly cell associated and epithelial tropic strain of cytomegalovirus in guinea pigs

Multiple strains of human cytomegalovirus (HCMV) can cause congenital cytomegalovirus (cCMV) by primary or secondary infection. The viral gB glycoprotein is a leading vaccine candidate, essential for infection of all cell-types, and immunodominant antibody target. Guinea pig cytomegalovirus (GPCMV) is the only small animal model for cCMV. Various gB vaccines have shown efficacy but studies have utilized truncated gB and protection against prototype strain 22122 with preferential tropism to fibroblasts despite encoding a gH-based pentamer complex for non-fibroblast infection. A highly cell-associated novel strain of GPCMV (TAMYC) with 99 % identity in gB sequence to 22122 exhibited preferred tropism to epithelial cells. An adenovirus vaccine encoding full-length gB (AdgB) was highly immunogenic and partially protected against 22122 strain challenge in vaccinated animals but not when challenged with TAMYC strain. GPCMV studies with AdgB vaccine sera on numerous cell-types demonstrated impaired neutralization (NA₅₀) compared to fibroblasts. GPCMV-convalescent sera including pentamer complex antibodies increased virus neutralization on non-fibroblasts and anti-gB depletion from GPCMV-convalescent sera had minimal impact on epithelial cell neutralization. GPCMV(PC+) 22122-convalescent animals challenged with TAMYC exhibited higher protection compared to AdgB vaccine. Overall, results suggest that antibody response to both gB and PC are important components of a GPCMV vaccine.

Detection of Genotype-Specific Antibody Responses to Glycoproteins B and H in Primary and Non-Primary Human Cytomegalovirus Infections by Peptide-Based ELISA

BACKGROUND

Strain-specific antibodies to human cytomegalovirus (HCMV) glycoproteins B and H (gB and gH) have been proposed as a potential diagnostic tool for identifying reinfection. We investigated genotype-specific IgG antibody responses in parallel with defining the gB and gH genotypes of the infecting viral strains.

METHODS

Subjects with primary (n = 20) or non-primary (n = 25) HCMV infection were studied. The seven gB (gB1-7) and two gH (gH1-2) genotypes were determined by real-time PCR and whole viral genome sequencing, and genotype-specific IgG antibodies were measured by a peptide-based enzyme-linked immunosorbent assay (ELISA).

RESULTS

Among subjects with primary infection, 73% (n = 8) infected by gB1-HCMV and 63% (n = 5) infected by gB2/3-HCMV had genotype-specific IgG antibodies to gB (gB2 and gB3 are similar in the region tested). Peptides from the rarer gB4-gB7 genotypes had nonspecific antibody responses. All subjects infected by gH1-HCMV and 86% (n = 6) infected by gH2-HCMV developed genotype-specific responses. Among women with non-primary infection, gB and gH genotype-specific IgG antibodies were detected in 40% (n = 10) and 80% (n = 20) of subjects, respectively.

CONCLUSIONS

Peptide-based ELISA is capable of detecting primary genotype-specific IgG responses to HCMV gB and gH, and could be adopted for identifying reinfections. However, about half of the subjects did not have genotype-specific IgG antibodies to gB.

In utero human cytomegalovirus infection is associated with increased levels of putatively protective maternal antibodies in nonprimary infection: evidence for boosting but not protection

BACKGROUND

Although primary maternal cytomegalovirus infections are associated with higher risk of in utero transmission, most fetal infections worldwide result from nonprimary maternal infections. Antibodies directed at glycoprotein B and the gH/gL/pUL128-130-131 pentamer can neutralize virus, and higher levels of antibody directed at several particular pentamer epitopes defined by monoclonal antibodies (mAbs) are associated with reduced risk of fetal cytomegalovirus transmission during primary maternal infection. This had not been explored in maternal nonprimary infection.

METHODS

In a setting where most maternal cytomegalovirus infections are nonprimary, 42 mothers of infants with congenital CMV infections (transmitters) were compared to 75 cytomegalovirus-seropositive mothers whose infants were cytomegalovirus-uninfected (nontransmitters). Control infants were matched by sex, maternal HIV status and gestational age. We measured the ability of maternal antibodies to block three key pentameric epitopes: one in the gH subunit, another straddling UL130/UL131 and the third straddling gH/gL/UL128/UL130. We tested if levels of antibodies directed at these epitopes were higher in nontransmitters compared to transmitters.

RESULTS

Levels of all three putatively protective pentamer-directed antibodies were significantly higher in transmitters compared to nontransmitters. In contrast, antibodies targeting an epitope on glycoprotein B were not different. Total antibody specific for pentamer and for gB were also higher in transmitters.

CONCLUSIONS

We found no evidence that higher levels of any CMV-specific antibodies were associated with reduced risk of congenital CMV infection in nonprimary maternal infection. Instead, we found higher maternal antibody targeting epitopes on CMV pentamer in transmitters than nontransmitters, providing evidence for antibody boosting but not protection.

Preventing Infection by Human Cytomegalovirus

The way to a successful vaccine against human cytomegalovirus is hampered by the peculiar biology of this infection. However, some candidate vaccines have been shown to protect seronegative women and transplant recipients, and we should know soon whether they can prevent congenital infection.

Recent Approaches and Strategies in the Generation of Anti-human Cytomegalovirus Vaccines

Human cytomegalovirus is the largest human herpesvirus and shares many core features of other herpesviruses such as tightly regulated gene expression during genome replication and latency as well as the establishment of lifelong persistence following infection. In contrast to stereotypic clinical syndromes associated with alpha-herpesvirus infections, almost all primary HCMV infections are asymptomatic and acquired early in life in most populations in the world. Although asymptomatic in most individuals, HCMV is a major cause of disease in hosts with deficits in adaptive and innate immunity such as infants who are infected in utero and allograft recipients following transplantation. Congenital HCMV is a commonly acquired infection in the developing fetus that can result in a number of neurodevelopmental abnormalities. Similarly, HCMV is a major cause of disease in allograft recipients in the immediate and late posttransplant period and is thought to be a major contributor to chronic allograft rejection. Even though HCMV induces robust innate and adaptive immune responses, it also encodes a vast array of immune evasion functions that are thought aid in its persistence. Immune correlates of protective immunity that prevent or modify intrauterine HCMV infection remain incompletely defined but are thought to consist primarily of adaptive responses in the pregnant mother, thus making congenital HCMV a potentially vaccine modifiable disease. Similarly, HCMV infection in allograft recipients is often more severe in recipients without preexisting adaptive immunity to HCMV. Thus, there has been a considerable effort to modify HCMV specific immunity in transplant recipient either through active immunization or passive transfer of adaptive effector functions. Although efforts to develop an efficacious vaccine and/or passive immunotherapy to limit HCMV disease have been underway for nearly six decades, most have met with limited success at best. In contrast to previous efforts, current HCMV vaccine development has relied on observations of unique properties of HCMV in hopes of reproducing immune responses that at a minimum will be similar to that following natural infection. However, more recent findings have suggested that immunity following naturally acquired HCMV infection may have limited protective activity and almost certainly, is not sterilizing. Such observations suggest that either the induction of natural immunity must be specifically tailored to generate protective activity or alternatively, that providing targeted passive immunity to susceptible populations could be prove to be more efficacious.

Mixed cytomegalovirus genotypes in HIV-positive mothers show compartmentalization and distinct patterns of transmission to infants

Cytomegalovirus (CMV) is the commonest cause of congenital infection and particularly so among infants born to HIV-infected women. Studies of congenital CMV infection (cCMVi) pathogenesis are complicated by the presence of multiple infecting maternal CMV strains, especially in HIV-positive women, and the large, recombinant CMV genome. Using newly developed tools to reconstruct CMV haplotypes, we demonstrate anatomic CMV compartmentalization in five HIV-infected mothers and identify the possibility of congenitally transmitted genotypes in three of their infants. A single CMV strain was transmitted in each congenitally infected case, and all were closely related to those that predominate in the cognate maternal cervix. Compared to non-transmitted strains, these congenitally transmitted CMV strains showed statistically significant similarities in 19 genes associated with tissue tropism and immunomodulation. In all infants, incident superinfections with distinct strains from breast milk were captured during follow-up. The results represent potentially important new insights into the virologic determinants of early CMV infection.