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

A human cytomegalovirus prefusion-like glycoprotein B subunit vaccine elicits humoral immunity similar to that of postfusion gB in mice

Human cytomegalovirus (HCMV) is the leading infectious cause of birth defects. Despite the global disease burden, there is no Food and Drug Administration (FDA)-approved HCMV vaccine. The most efficacious HCMV vaccine candidates to date have used glycoprotein B (gB), a class III viral fusion protein, in its postfusion form. While some viral fusion proteins have been shown to elicit stronger neutralizing responses in their prefusion conformation, HCMV prefusion-like and postfusion gB were recently shown to elicit antibodies with similar fibroblast neutralization titers in mice. We aimed to define and compare the specificity and functionality of plasma IgG elicited by distinct prefusion-like and postfusion gB constructs. Prefusion-like and postfusion gB elicited comparable IgG responses that predominantly mapped to the AD-5 antigenic domain known to elicit neutralizing antibodies. Interestingly, postfusion gB elicited significantly higher plasma IgG binding to cell-associated gB and antibody-dependent cellular phagocytosis than that of prefusion-like gB. The vaccines elicited comparable neutralization titers of heterologous HCMV strain AD169r in fibroblasts; however, neither elicited neutralizing titers against the vaccine-matched strain Towne in fibroblasts. Our data indicate that gB in this prefusion-like conformation elicits similar specificity and functional humoral immunity to that of postfusion gB, unlike certain class I viral fusion proteins that have been used as vaccine antigens. These findings deepen our understanding of the immune response elicited by class III fusion proteins and may inform further design and testing of conformationally dependent herpesvirus glycoprotein vaccine candidates.IMPORTANCEVaccines against human cytomegalovirus (HCMV) still remain elusive in spite of the high disease burden of the virus, especially in pre-term infants and immunocompromised individuals. While vaccine efforts have focused on vaccine-induced antibodies to neutralize the virus, studies have increasingly shown the importance of other antibody functions in protection against cytomegalovirus (CMV) transmission. In this study, we comprehensively evaluated immune responses elicited by the prefusion state of an important HCMV protein called glycoprotein B (gB) in mice. Our results indicate that prefusion gB elicits immune responses similar to that of postfusion gB in mice and reveals areas for further redesign and testing for prefusion vaccine antigens against CMV and other herpesviruses, which could help in furthering vaccine development against HCMV.

Development of Maternal Antibodies Post ZIKV in Pregnancy is Associated with Lower Risk of Microcephaly and Structural Brain Abnormalities in Exposed Infants

BACKGROUND

We investigated the association between maternal neutralizing antibodies (nAb) to Zika virus (ZIKV) in pregnancy and neonatal outcomes.

METHODS

In pregnant participants with confirmed ZIKV infection, we determined trimester of infection, collected sera longitudinally, and measured nAbs via plaque reduction. In neonates, adverse outcomes included microcephaly (MC), structural brain abnormalities (SBA), hearing, and eye abnormalities. Associations between trimester of infection, nAbs, and neonatal outcomes were analyzed with Cox regression.

RESULTS

In total, 137 ZIKV-positive pregnant participants had neutralization assays performed during pregnancy and postdelivery. Infection rates were 29% in the first, 50% in the second, and 21% in the third trimester. Mean ZIKV nAb titer >2 weeks postinfection was 64 258 (SD 213 288). Ten percent of 90% plaque reduction neutralization assays (PRNT90) titers were <500, 10% 500-1000, 73% > 1000, and 7% did not have serologic follow-up; 15%. of infants had adverse findings. Protective factors against MC in 88 mothers with nAb titers available during pregnancy included infection later in gestation (adjusted hazard ratio [aHR], 0.06; P = .036) and adequate nAb titers (aHR, 0.17; P = .014). No SBA was associated with later infection in pregnancy (aHR, 0.16; P = .017) and adequate nAb titers (aHR, 0.34; P = .012). Adjusting for trimester, higher maternal nAb titers were associated with lower risk of MC and SBA. Seven of 137 participants (5.1%) had positive serum ZIKV polymerase chain reaction (PCR) results beyond 14 days (range, 35-269 days). Participants with ZIKV PCR positivity >60 days (n = 2) had infants with MC/SBA.

CONCLUSIONS

MC and SBA were less frequent in infants of mothers with higher ZIKV nAb titers during pregnancy.

An insect cell-derived extracellular vesicle-based gB vaccine elicits robust adaptive immune responses against Epstein-Barr virus

Epstein-Barr virus (EBV), the first identified human tumor virus, is implicated in various human malignancies, infectious mononucleosis, and more recently, multiple sclerosis. Prophylactic vaccines have the potential to effectively prevent EBV infection. Glycoprotein B (gB) serves as the fusogen and plays a pivotal role in the virus entry process, making it a critical target for EBV vaccine development. Surface membrane proteins of enveloped viruses serve as native conformational antigens, making them susceptible to immune recognition. Utilizing lipid membrane-bound viral antigens is a promising strategy for effective vaccine presentation in this context. In this study, we employed a truncated design for gB proteins, observing that these truncated gB proteins prompted a substantial release of extracellular vesicles (EVs) in insect cells. We verified that EVs exhibited abundant gB proteins, displaying the typical virus particle morphology and extracellular vesicle characteristics. gB EVs demonstrated a more efficient humoral and cellular immune response compared with the gB ectodomain trimer vaccine in mice. Moreover, the antisera induced by the gB EVs vaccine exhibited robust antibody-dependent cytotoxicity. Consequently, gB EVs-based vaccines hold significant potential for preventing EBV infection and offer valuable insights for vaccine design.

Influence of Distinct Maternal Cytomegalovirus-Specific Neutralizing and Fc Receptor-Binding Responses on Congenital Cytomegalovirus Transmission in HIV-Exposed Neonates

Congenital cytomegalovirus (cCMV) is the most common infectious cause of birth defects worldwide, affecting approximately 1 in every 200 live-born infants globally. Recent work has identified potential immune correlates of protection against cCMV transmission including maternal and placentally transferred antibody levels and their function, which may inform the development of maternal active (vaccine) and passive (mono/polyclonal antibody) immunizations. However, these correlates need to also be assessed in diverse cohorts, including women living with HIV who have increased risk of cCMV transmission. Using a case-control design, we investigated whether the magnitude, specificity, function and placental transfer of maternal IgG responses are associated with protection against and/or risk of cCMV transmission in HIV/HCMV co-infection. Within 3 historical cohorts of pregnant women with HIV/HCMV co-infection, we identified 16 cCMV transmitting cases that were matched to 29 cCMV non-transmitting controls. Using a systems serology approach, we found that normalized HCMV-specific IgG binding to FcγR1α was higher in non-transmitting dyads, whereas HCMV-neutralizing antibody responses were higher in transmitting dyads. These findings suggest that engagement of FcγR1α by HCMV-specific IgG may help confer protection against cCMV transmission. Building upon previous research, our study reinforces the critical role of validating maternal humoral immune correlates of cCMV transmission risk across diverse seropositive cohorts, providing essential insights to inform and accelerate the development of effective HCMV vaccines.

Rhesus Cytomegalovirus-encoded Fcγ-binding glycoproteins facilitate viral evasion from IgG-mediated humoral immunity

Human cytomegalovirus (HCMV) encodes four viral Fc-gamma receptors (vFcγRs) that counteract antibody-mediated activation in vitro, but their role in infection and pathogenesis is unknown. To examine their in vivo function in an animal model evolutionarily closely related to humans, we identified and characterized Rh05, Rh152/151 and Rh173 as the complete set of vFcγRs encoded by rhesus CMV (RhCMV). Each one of these proteins displays functional similarities to their prospective HCMV orthologs with respect to antagonizing host FcγR activation in vitro. When RhCMV-naïve male rhesus macaques were infected with vFcγR-deleted RhCMV, peak plasma DNAemia levels and anti-RhCMV antibody responses were comparable to wildtype infections of both male and female animals. However, the duration of plasma DNAemia was significantly shortened in immunocompetent, but not in CD4 + T cell-depleted animals. Since vFcγRs were not required for superinfection of rhesus macaques, we conclude that these proteins can prolong lytic replication during primary infection by evading virus-specific adaptive immune responses, particularly antibodies.

A vaccine against cytomegalovirus: how close are we?

The pursuit of a vaccine against the human cytomegalovirus (HCMV) has been ongoing for more than 50 years. HCMV is the leading infectious cause of birth defects, including damage to the brain, and is a common cause of complications in organ transplantation. The complex biology of HCMV has made vaccine development difficult, but a recent meeting sponsored by the National Institute of Allergy and Infectious Diseases in September of 2023 brought together experts from academia, industry, and federal agencies to discuss progress in the field. The meeting reviewed the status of candidate HCMV vaccines under study and the challenges in clinical trial design in demonstrating efficacy against congenital CMV infection or the reduction of HCMV disease following solid organ transplantation or hematopoietic stem cell transplantation. Discussion in the meeting revealed that, with the numerous candidate vaccines that are under study, it is clear that a safe and effective HCMV vaccine is within reach. Meeting attendees achieved a consensus opinion that even a partially effective vaccine would have a major effect on the global health consequences of HCMV infection.

Human cytomegalovirus: pathogenesis, prevention, and treatment

Human cytomegalovirus (HCMV) infection remains a significant global health challenge, particularly for immunocompromised individuals and newborns. This comprehensive review synthesizes current knowledge on HCMV pathogenesis, prevention, and treatment strategies. We examine the molecular mechanisms of HCMV entry, focusing on the structure and function of key envelope glycoproteins (gB, gH/gL/gO, gH/gL/pUL128-131) and their interactions with cellular receptors such as PDGFRα, NRP2, and THBD. The review explores HCMV's sophisticated immune evasion strategies, including interference with pattern recognition receptor signaling, modulation of antigen presentation, and regulation of NK and T cell responses. We highlight recent advancements in developing neutralizing antibodies, various vaccine strategies (live-attenuated, subunit, vector-based, DNA, and mRNA), antiviral compounds (both virus-targeted and host-targeted), and emerging cellular therapies such as TCR-T cell approaches. By integrating insights from structural biology, immunology, and clinical research, we identify critical knowledge gaps and propose future research directions. This analysis aims to stimulate cross-disciplinary collaborations and accelerate the development of more effective prevention and treatment strategies for HCMV infections, addressing a significant unmet medical need.

Improving antibody-mediated protection against HSV infection by eliminating interactions with the viral Fc receptor gE/gI

Herpes simplex virus (HSV) encodes surface glycoproteins that are host defense evasion molecules, allowing the virus to escape immune clearance. In addition to their role in neuropathogenesis and cell-cell spread, glycoproteins E and I (gE/gI) form a viral Fc receptor (vFcR) for most subclasses and allotypes of human IgG and promote evasion of humoral immune responses. While monoclonal antibodies (mAbs) protect mice from neonatal HSV (nHSV) infections, the impact of the vFcR on mAb-mediated protection by binding to IgG is unknown. Using HSV-1 with intact and ablated gE-mediated IgG Fc binding, and Fc-engineered antibodies with modified ability to interact with gE/gI, we investigated the role of the vFcR in viral pathogenesis and mAb-mediated protection from nHSV. The gD-specific human mAb HSV8 modified to lack binding to gE exhibited enhanced neutralization and in vivo protection compared to its native IgG1 form. This improved protection by the engineered mAbs was dependent on the presence of the vFcR. Human IgG3 allotypes lacking vFcR binding also exhibited enhanced antiviral activity in vivo, suggesting that vaccines that robustly induce IgG3 responses could show enhanced protection. suggesting the value of vaccination strategies that robustly induce this subclass. Lastly, analysis of longitudinal responses to acute primary genital infection in humans raised the possibility that unlike most viruses, HSV may exhibited slow induction of IgG3. In summary, this study demonstrates that mAbs lacking the ability to interact with the vFcR can exhibit improved protection from HSV-offering new prospects for antibody-based interventions.

In utero human cytomegalovirus infection expands NK-like FcγRIII+CD8+ T cells that mediate Fc antibody functions

Human cytomegalovirus (HCMV) profoundly impacts host T and NK cells across the lifespan, yet how this common congenital infection modulates developing fetal immune cell compartments remains underexplored. Using cord blood from neonates with and without congenital HCMV (cCMV) infection, we identify an expansion of Fcγ receptor III-expressing (FcγRIII-expressing) CD8+ T cells following HCMV exposure in utero. Most FcγRIII+CD8+ T cells express the canonical αβ T cell receptor (TCR), but a proportion express noncanonical γδ TCR. FcγRIII+CD8+ T cells are highly differentiated and have increased expression of NK cell markers and cytolytic molecules. Transcriptional analysis reveals FcγRIII+CD8+ T cells upregulate T-bet and downregulate BCL11B, known transcription factors that govern T/NK cell fate. We show that FcγRIII+CD8+ T cells mediate antibody-dependent IFN-γ production and degranulation against IgG-opsonized target cells, similar to NK cell antibody-dependent cellular cytotoxicity (ADCC). FcγRIII+CD8+ T cell Fc effector functions were further enhanced by IL-15, as has been observed in neonatal NK cells. Our study reveals that FcγRIII+CD8+ T cells elicited in utero by HCMV infection can execute Fc-mediated effector functions bridging cellular and humoral immunity and may be a promising target for antibody-based therapeutics and vaccination in early life.

Antibody-mediated control mechanisms of viral infections

Antibodies generated after vaccination or natural pathogen exposure are essential mediators of protection against many infections. Most studies with viruses have focused on antibody neutralization, in which protection is conferred by the fragment antigen binding region (Fab) through targeting of different steps in the viral lifecycle including attachment, internalization, fusion, and egress. Beyond neutralization, the fragment crystallizable (Fc) region of antibodies can integrate innate and adaptive immune responses by engaging complement components and distinct Fc gamma receptors (FcγR) on different host immune cells. In this review, we discuss recent advances in our understanding of antibody neutralization and Fc effector functions, and the assays used to measure them. Additionally, we describe the contexts in which these mechanisms are associated with protection against viruses and highlight how Fc-FcγR interactions can improve the potency of antibody-based therapies.

Proceedings of the Conference "CMV Vaccine Development-How Close Are We?" (27-28 September 2023)

Congenital cytomegalovirus (cCMV) is the most common infectious cause of disability in children, including sensorineural hearing loss. There is interest in developing a pre-conception vaccine that could confer protective immunity on a woman of child-bearing age, hence resulting in a reduced cCMV disease burden. Other populations, including solid organ transplant (SOT) and hematopoietic stem cell transplant (HSCT) patients, could also benefit from CMV vaccination. To review and discuss vaccines that are in clinical development, a workshop, sponsored by the National Institutes of Health (NIH) and the National Institute of Allergy and Infectious Diseases (NIAID), was empaneled. At this workshop, correlates of protective immunity against CMV, epidemiologic features of CMV transmission, and vaccine platforms in development were reviewed. Representatives from academia, pharma, and the NIH engaged in discussion on the current state-of-the-art in CMV vaccinology. A summary of the presentations from this is provided in this report.

Discrimination of primary and chronic cytomegalovirus infection based on humoral immune profiles in pregnancy

BACKGROUNDMost humans have been infected with cytomegalovirus (CMV) by midlife without clinical signs of disease. However, in settings in which the immune system is undeveloped or compromised, the virus is not adequately controlled and consequently presents a major infectious cause of both congenital disease during pregnancy as well as opportunistic infection in children and adults. With clear evidence that risk to the fetus varies with gestational age at the time of primary maternal infection, further research on humoral responses to primary CMV infection during pregnancy is needed.METHODSHere, systems serology tools were applied to characterize antibody responses to CMV infection in pregnant and nonpregnant women experiencing either primary or chronic infection.RESULTSWhereas strikingly different antibody profiles were observed depending on infection status, limited differences were associated with pregnancy status. Beyond known differences in IgM responses used clinically for identification of primary infection, distinctions observed in IgA and FcγR-binding antibodies and among antigen specificities accurately predicted infection status. Machine learning was used to define the transition from primary to chronic states and predict time since infection with high accuracy. Humoral responses diverged over time in an antigen-specific manner, with IgG3 responses toward tegument decreasing over time as typical of viral infections, while those directed to pentamer and glycoprotein B were lower during acute and greatest during chronic infection.CONCLUSIONIn sum, this work provides insights into the antibody response associated with CMV infection status in the context of pregnancy, revealing aspects of humoral immunity that have the potential to improve CMV diagnostics.FUNDINGCYMAF consortium and NIH NIAID.

Structure-based design of a soluble human cytomegalovirus glycoprotein B antigen stabilized in a prefusion-like conformation

Human cytomegalovirus (HCMV) glycoprotein B (gB) is a class III membrane fusion protein required for viral entry. HCMV vaccine candidates containing gB have demonstrated moderate clinical efficacy, but no HCMV vaccine has been approved. Here, we used structure-based design to identify and characterize amino acid substitutions that stabilize gB in its metastable prefusion conformation. One variant containing two engineered interprotomer disulfide bonds and two cavity-filling substitutions (gB-C7), displayed increased expression and thermostability. A 2.8 Å resolution cryoelectron microscopy structure shows that gB-C7 adopts a prefusion-like conformation, revealing additional structural elements at the membrane-distal apex. Unlike previous observations for several class I viral fusion proteins, mice immunized with postfusion or prefusion-stabilized forms of soluble gB protein displayed similar neutralizing antibody titers, here specifically against an HCMV laboratory strain on fibroblasts. Collectively, these results identify initial strategies to stabilize class III viral fusion proteins and provide tools to probe gB-directed antibody responses.

Human Cytomegalovirus mRNA-1647 Vaccine Candidate Elicits Potent and Broad Neutralization and Higher Antibody-Dependent Cellular Cytotoxicity Responses Than the gB/MF59 Vaccine

BACKGROUND

MF59-adjuvanted gB subunit (gB/MF59) vaccine demonstrated approximately 50% efficacy against human cytomegalovirus (HCMV) acquisition in multiple clinical trials, suggesting that efforts to improve this vaccine design might yield a vaccine suitable for licensure.

METHODS

A messenger RNA (mRNA)-based vaccine candidate encoding HCMV gB and pentameric complex (PC), mRNA-1647, is currently in late-stage efficacy trials. However, its immunogenicity has not been compared to the partially effective gB/MF59 vaccine. We assessed neutralizing and Fc-mediated immunoglobulin G (IgG) effector antibody responses induced by mRNA-1647 in both HCMV-seropositive and -seronegative vaccinees from a first-in-human clinical trial through 1 year following third vaccination using a systems serology approach. Furthermore, we compared peak anti-gB antibody responses in seronegative mRNA-1647 vaccinees to that of seronegative gB/MF59 vaccine recipients.

RESULTS

mRNA-1647 vaccination elicited and boosted HCMV-specific IgG responses in seronegative and seropositive vaccinees, respectively, including neutralizing and Fc-mediated effector antibody responses. gB-specific IgG responses were lower than PC-specific IgG responses. gB-specific IgG and antibody-dependent cellular phagocytosis responses were lower than those elicited by gB/MF59. However, mRNA-1647 elicited higher neutralization and antibody-dependent cellular cytotoxicity (ADCC) responses.

CONCLUSIONS

Overall, mRNA-1647 vaccination induced polyfunctional and durable HCMV-specific antibody responses, with lower gB-specific IgG responses but higher neutralization and ADCC responses compared to the gB/MF59 vaccine.

CLINICAL TRIALS REGISTRATION

NCT03382405 (mRNA-1647) and NCT00133497 (gB/MF59).

Evaluation of the In Vitro Capacity of Anti-Human Cytomegalovirus Antibodies to Initiate Antibody-Dependent Cell Cytotoxicity

In the setting of infectious diseases, antibodies show different functions beyond neutralizing activity. In this study, we investigated the activation of NK cells in vitro in the presence of human cytomegalovirus (HCMV)-specific antibodies and their potential role in the control of HCMV infection through antibody-dependent cell cytotoxicity (ADCC). Retinal pigmented epithelial cells (ARPE-19) infected with the HCMV strain VR1814 were co-cultured with cytokine-activated peripheral blood mononuclear cells (PBMCs) in the presence of sera collected from 23 HCMV-seropositive and 9 HCMV-seronegative donors. Moreover, 13 pregnant women sampled 3 and 6 months after HCMV primary infection and 13 pregnant women with pre-conception immunity were tested and compared. We determined the percentage of activated NK cells via the analysis of CD107a expression as a marker of degranulation. Significantly higher levels of NK-cell activation were observed using 1/100 and 1/10 dilutions of sera from HCMV-seropositive individuals, and when cells were infected for 96 and 120 h, suggesting that NK cells are activated by antibodies directed against late antigens. In the absence of serum NK cells, activation was negligible. In seropositive subjects, the median percentages of CD107a-positive NK cells in the presence of autologous serum and pooled HCMV-positive serum were similar (14.03% [range 0.00-33.56] and 12.42% [range 1.01-46.00], respectively), while NK-cell activation was negligible using an HCMV-negative serum pool. In HCMV-seronegative subjects, the median percentage of activated NK cells was 0.90% [range 0.00-3.92] with autologous serum and 2.07% [0.00-5.76] in the presence of the HCMV-negative serum pool, while it was 8.97% [0.00-26.49] with the pool of HCMV-positive sera. NK-cell activation using hyperimmune globulin is comparable to what is obtained using autologous serum. Sera from subjects at 3 and 6 months post primary infection showed a lower capacity of NK-cell activation than sera from subjects with past infection (p < 0.001). NK activation against HCMV-infected epithelial cells is dependent on the presence of HCMV-specific antibodies. This serum activity increases with time after the onset of HCMV infection. The protective role of NK-cell activation by HCMV-specific serum antibodies should be verified in clinical settings.

Characterization of Natural Killer Cell Profile in a Cohort of Infected Pregnant Women and Their Babies and Its Relation to CMV Transmission

Human cytomegalovirus (CMV) is a common herpesvirus causing lifelong latent infection in most people and is a primary cause of congenital infection worldwide. Given the role of NK cells in the materno-fetal barrier, we investigated peripheral blood NK cell behavior in the context of CMV infection acquired during pregnancy. We analyzed the NK phenotype and CD107a surface mobilization on PBMCs from CMV-transmitting and non-transmitting mothers and newborns with or without congenital infection. NK cells from non-transmitting mothers showed the typical phenotype of CMV-adaptive NK cells, characterized by higher levels of NKG2C, CD57, and KIRs, with reduced NKG2A, compared to transmitting ones. A significantly higher percentage of DNAM-1+, PD-1+, and KIR+NKG2A-CD57+PD-1+ CD56dim cells was found in the non-transmitting group. Accordingly, NK cells from congenital-CMV (cCMV)-infected newborns expressed higher levels of NKG2C and CD57, with reduced NKG2A, compared to non-congenital ones. Furthermore, they showed a significant expansion of CD56dim cells co-expressing NKG2C and CD57 or with a memory-like (KIR+NKG2A-CD57+NKG2C+) phenotype, as well as a significant reduction of the CD57-NKG2C- population. Degranulation assays showed a slightly higher CD107a geomean ratio in NK cells of mothers who were non-transmitting compared to those transmitting the virus. Our findings demonstrate that both CMV-transmitting mothers and cCMV newborns show a specific NK profile. These data can guide studies on predicting virus transmission from mothers and congenital infection in infants.

Characterization of humoral and cellular immunologic responses to an mRNA-based human cytomegalovirus vaccine from a phase 1 trial of healthy adults

mRNA-1647 is an investigational mRNA-based vaccine against cytomegalovirus (CMV) that contains sequences encoding the CMV proteins glycoprotein B and pentamer. Humoral and cellular immune responses were evaluated in blood samples collected from healthy CMV-seropositive and CMV-seronegative adults who participated in a phase 1 trial of a three-dose series of mRNA-1647 (NCT03382405). Neutralizing antibody (nAb) titers against fibroblast and epithelial cell infection in sera from CMV-seronegative mRNA-1647 recipients were higher than those in sera from control CMV-seropositive samples and remained elevated up to 12 months after dose 3. nAb responses elicited by mRNA-1647 were comparable across 14 human CMV (HCMV) strains. Frequencies of antigen-specific memory B cells increased in CMV-seropositive and CMV-seronegative participants after each mRNA-1647 dose and remained elevated for up to 6 months after dose 3. mRNA-1647 elicited robust increases in frequencies and polyfunctionality of CD4+ T helper type 1 and effector CD8+ T cells in samples from CMV-seronegative and CMV-seropositive participants after stimulation with HCMV-specific peptides. The administration of three doses of mRNA-1647 to healthy adults elicited high nAb titers with wide-breadth, long-lasting memory B cells, and strong polyfunctional T-cell responses. These findings support further clinical development of the mRNA-1647 vaccine against CMV.IMPORTANCECytomegalovirus (CMV), a common virus that can infect people of all ages, may lead to serious health problems in unborn babies and those with a weakened immune system. Currently, there is no approved vaccine available to prevent CMV infection; however, the investigational messenger RNA (mRNA)-based CMV vaccine, mRNA-1647, is undergoing evaluation in clinical trials. The current analysis examined samples from a phase 1 trial of mRNA-1647 in healthy adults to better understand how the immune system reacts to vaccination. Three doses of mRNA-1647 produced a long-lasting immune response, thus supporting further investigation of the vaccine in the prevention of CMV infection.CLINICAL TRIALSRegistered at ClinicalTrials.gov (NCT03382405).

Beyond bNAbs: Uses, Risks, and Opportunities for Therapeutic Application of Non-Neutralising Antibodies in Viral Infection

The vast majority of antibodies generated against a virus will be non-neutralising. However, this does not denote an absence of protective capacity. Yet, within the field, there is typically a large focus on antibodies capable of directly blocking infection (neutralising antibodies, NAbs) of either specific viral strains or multiple viral strains (broadly-neutralising antibodies, bNAbs). More recently, a focus on non-neutralising antibodies (nNAbs), or neutralisation-independent effects of NAbs, has emerged. These can have additive effects on protection or, in some cases, be a major correlate of protection. As their name suggests, nNAbs do not directly neutralise infection but instead, through their Fc domains, may mediate interaction with other immune effectors to induce clearance of viral particles or virally infected cells. nNAbs may also interrupt viral replication within infected cells. Developing technologies of antibody modification and functionalisation may lead to innovative biologics that harness the activities of nNAbs for antiviral prophylaxis and therapeutics. In this review, we discuss specific examples of nNAb actions in viral infections where they have known importance. We also discuss the potential detrimental effects of such responses. Finally, we explore new technologies for nNAb functionalisation to increase efficacy or introduce favourable characteristics for their therapeutic applications.

g-NK cells from umbilical cord blood are phenotypically and functionally different than g-NK cells from peripheral blood

FcRγ-deficient natural killer (NK) cells, designated as g-NK cells, exhibit enhanced antibody-dependent cellular cytotoxicity (ADCC) capacity and increased IFN-γ and TNF-α production, rendering them promising for antiviral and antitumor responses. g-NK cells from peripheral blood (PB) are often associated with prior human cytomegalovirus (HCMV) infection. However, the prevalence, phenotype, and function of g-NK cells in umbilical cord blood (UCB-g-NK) remain unclear. Here, we demonstrate significant phenotypical differences between UCB-g-NK and PB-g-NK cells. Unlike PB-g-NK cells, UCB-g-NK cells did not show heightened cytokine production upon CD16 engagement, in contrast to the conventional NK (c-NK) cell counterparts. Interestingly, following in vitro activation, UCB-g-NK cells also exhibited elevated levels of IFN-γ production, particularly when co-cultured with HCMV and plasma from g-NK+ adults. Furthermore, g-NK+ plasma from PB even facilitated the in vitro expansion of UCB-g-NK cells. These findings underscore the phenotypic and functional heterogeneity of g-NK cells based on their origin and demonstrate that components within g-NK+ plasma may directly contribute to the acquisition of an adult phenotype by the "immature" UCB-g-NK cells.

Single-cell analysis of memory B cells from top neutralizers reveals multiple sites of vulnerability within HCMV Trimer and Pentamer

Human cytomegalovirus (HCMV) can cause severe diseases in fetuses, newborns, and immunocompromised individuals. Currently, no vaccines are approved, and treatment options are limited. Here, we analyzed the human B cell response of four HCMV top neutralizers from a cohort of 9,000 individuals. By single-cell analyses of memory B cells targeting the pentameric and trimeric HCMV surface complexes, we identified vulnerable sites on the shared gH/gL subunits as well as complex-specific subunits UL128/130/131A and gO. Using high-resolution cryogenic electron microscopy, we revealed the structural basis of the neutralization mechanisms of antibodies targeting various binding sites. Moreover, we identified highly potent antibodies that neutralized a broad spectrum of HCMV strains, including primary clinical isolates, that outperform known antibodies used in clinical trials. Our study provides a deep understanding of the mechanisms of HCMV neutralization and identifies promising antibody candidates to prevent and treat HCMV infection.