Primary infection with dengue or Zika virus does not affect the severity of heterologous secondary infection in macaques.

Zika virus (ZIKV) and dengue virus (DENV) are genetically and antigenically related flaviviruses that now co-circulate in much of the tropical and subtropical world. The rapid emergence of ZIKV in the Americas in 2015 and 2016, and its recent associations with Guillain-Barré syndrome, birth defects, and fetal loss have led to the hypothesis that DENV infection induces cross-reactive antibodies that influence the severity of secondary ZIKV infections. It has also been proposed that pre-existing ZIKV immunity could affect DENV pathogenesis. We examined outcomes of secondary ZIKV infections in three rhesus and fifteen cynomolgus macaques, as well as secondary DENV-2 infections in three additional rhesus macaques up to a year post-primary ZIKV infection. Although cross-binding antibodies were detected prior to secondary infection for all animals and cross-neutralizing antibodies were detected for some animals, previous DENV or ZIKV infection had no apparent effect on the clinical course of heterotypic secondary infections in these animals. All animals had asymptomatic infections and, when compared to controls, did not have significantly perturbed hematological parameters. Rhesus macaques infected with DENV-2 approximately one year after primary ZIKV infection had higher vRNA loads in plasma when compared with serum vRNA loads from ZIKV-naive animals infected with DENV-2, but a differential effect of sample type could not be ruled out. In cynomolgus macaques, the serotype of primary DENV infection did not affect the outcome of secondary ZIKV infection.

Development of Envelope Protein Antigens To Serologically Differentiate Zika Virus Infection from Dengue Virus Infection.

Zika virus (ZIKV) is an emerging flavivirus that can cause birth defects and neurologic complications. Molecular tests are effective for diagnosing acute ZIKV infection, although the majority of infections produce no symptoms at all or present after the narrow window in which molecular diagnostics are dependable. Serology is a reliable method for detecting infections after the viremic period; however, most serological assays have limited specificity due to cross-reactive antibodies elicited by flavivirus infections. Since ZIKV and dengue virus (DENV) widely cocirculate, distinguishing ZIKV infection from DENV infection is particularly important for diagnosing individual cases or for surveillance to coordinate public health responses. Flaviviruses also elicit type-specific antibodies directed to non-cross-reactive epitopes of the infecting virus; such epitopes are attractive targets for the design of antigens for development of serological tests with greater specificity. Guided by comparative epitope modeling of the ZIKV envelope protein, we designed two recombinant antigens displaying unique antigenic regions on domain I (Z-EDI) and domain III (Z-EDIII) of the ZIKV envelope protein. Both the Z-EDI and Z-EDIII antigens consistently detected ZIKV-specific IgG in ZIKV-immune sera but not cross-reactive IgG in DENV-immune sera in late convalescence (>12 weeks postinfection). In contrast, during early convalescence (2 to 12 weeks postinfection), secondary DENV-immune sera and some primary DENV-immune sera cross-reacted with the Z-EDI and Z-EDIII antigens. Analysis of sequential samples from DENV-immune individuals demonstrated that Z-EDIII cross-reactivity peaked in early convalescence and declined steeply over time. The Z-EDIII antigen has much potential as a diagnostic antigen for population-level surveillance and for detecting past infections in patients.

Prior dengue virus serotype 3 infection modulates subsequent plasmablast responses to Zika virus infection in rhesus macaques.

Immunodominant and highly conserved flavivirus envelope proteins can trigger cross-reactive IgG antibodies against related flaviviruses, which shapes subsequent protection or disease severity. This study examined how prior dengue serotype 3 (DENV-3) infection affects subsequent Zika virus (ZIKV) plasmablast responses in rhesus macaques (n = 4). We found that prior DENV-3 infection was not associated with diminished ZIKV-neutralizing antibodies or magnitude of plasmablast activation. Rather, characterization of 363 plasmablasts and their derivative 177 monoclonal antibody supernatants from acute ZIKV infection revealed that prior DENV-3 infection was associated with a differential isotype distribution toward IgG, lower somatic hypermutation, and lesser B cell receptor variable gene diversity as compared with repeat ZIKV challenge. We did not find long-lasting DENV-3 cross-reactive IgG after a ZIKV infection but did find persistent ZIKV-binding cross-reactive IgG after a DENV-3 infection, suggesting non-reciprocal cross-reactive immunity. Infection with ZIKV after DENV-3 boosted pre-existing DENV-3-neutralizing antibodies by two- to threefold, demonstrating immune imprinting. These findings suggest that the order of DENV and ZIKV infections has impact on the quality of early B cell immunity which has implications for optimal immunization strategies. IMPORTANCE: The Zika virus epidemic of 2015-2016 in the Americas revealed that this mosquito-transmitted virus could be congenitally transmitted during pregnancy and cause birth defects in newborns. Currently, there are no interventions to mitigate this disease and Zika virus is likely to re-emerge. Understanding how protective antibody responses are generated against Zika virus can help in the development of a safe and effective vaccine. One main challenge is that Zika virus co-circulates with related viruses like dengue, such that prior exposure to one can generate cross-reactive antibodies against the other which may enhance infection and disease from the second virus. In this study, we sought to understand how prior dengue virus infection impacts subsequent immunity to Zika virus by single-cell sequencing of antibody producing cells in a second Zika virus infection. Identifying specific qualities of Zika virus immunity that are modulated by prior dengue virus immunity will enable optimal immunization strategies.

Sutterella and its metabolic pathways positively correlate with vaccine-elicited antibody responses in infant rhesus macaques.

Introduction: It is becoming clearer that the microbiota helps drive responses to vaccines; however, little is known about the underlying mechanism. In this study, we aimed to identify microbial features that are associated with vaccine immunogenicity in infant rhesus macaques. Methods: We analyzed 16S rRNA gene sequencing data of 215 fecal samples collected at multiple timepoints from 64 nursery-reared infant macaques that received various HIV vaccine regimens. PERMANOVA tests were performed to determine factors affecting composition of the gut microbiota throughout the first eight months of life in these monkeys. We used DESeq2 to identify differentially abundant bacterial taxa, PICRUSt2 to impute metagenomic information, and mass spectrophotometry to determine levels of fecal short-chain fatty acids and bile acids. Results: Composition of the early-life gut microbial communities in nursery-reared rhesus macaques from the same animal care facility was driven by age, birth year, and vaccination status. We identified a Sutterella and a Rodentibacter species that positively correlated with vaccine-elicited antibody responses, with the Sutterella species exhibiting more robust findings. Analysis of Sutterella-related metagenomic data revealed five metabolic pathways that significantly correlated with improved antibody responses following HIV vaccination. Given these pathways have been associated with short-chain fatty acids and bile acids, we quantified the fecal concentration of these metabolites and found several that correlated with higher levels of HIV immunogen-elicited plasma IgG. Discussion: Our findings highlight an intricate bidirectional relationship between the microbiota and vaccines, where multiple aspects of the vaccination regimen modulate the microbiota and specific microbial features facilitate vaccine responses. An improved understanding of this microbiota-vaccine interplay will help develop more effective vaccines, particularly those that are tailored for early life.

Different adjuvanted pediatric HIV envelope vaccines induced distinct plasma antibody responses despite similar B cell receptor repertoires in infant rhesus macaques.

Different HIV vaccine regimens elicit distinct plasma antibody responses in both human and nonhuman primate models. Previous studies in human and non-human primate infants showed that adjuvants influenced the quality of plasma antibody responses induced by pediatric HIV envelope vaccine regimens. We recently reported that use of the 3M052-SE adjuvant and longer intervals between vaccinations are associated with higher magnitude of antibody responses in infant rhesus macaques. However, the impact of different adjuvants in HIV vaccine regimens on the developing infant B cell receptor (BCR) repertoire has not been studied. This study evaluated whether pediatric HIV envelope vaccine regimens with different adjuvants induced distinct antigen-specific memory B cell repertoires and whether specific immunoglobulin (Ig) immunogenetic characteristics are associated with higher magnitude of plasma antibody responses in vaccinated infant rhesus macaques. We utilized archived preclinical pediatric HIV vaccine studies PBMCs and tissue samples from 19 infant rhesus macaques immunized either with (i) HIV Env protein with a squalene adjuvant, (ii) MVA-HIV and Env protein co-administered using a 3-week interval, (iii) MVA-HIV prime/ protein boost with an extended 6-week interval between immunizations, or (iv) with HIV Env administered with 3M-052-SE adjuvant. Frequencies of vaccine-elicited HIV Env-specific memory B cells from PBMCs and tissues were similar across vaccination groups (frequency range of 0.06-1.72%). There was no association between vaccine-elicited antigen-specific memory B cell frequencies and plasma antibody titer or avidity. Moreover, the epitope specificity and Ig immunogenetic features of vaccine-elicited monoclonal antibodies did not differ between the different vaccine regimens. These data suggest that pediatric HIV envelope vaccine candidates with different adjuvants that previously induced higher magnitude and quality of plasma antibody responses in infant rhesus macaques were not driven by distinct antigen-specific memory BCR repertoires.

Maternal Broadly Neutralizing Antibodies Can Select for Neutralization-Resistant, Infant-Transmitted/Founder HIV Variants.

Each year, >180,000 infants become infected via mother-to-child transmission (MTCT) of HIV despite the availability of effective maternal antiretroviral treatments, underlining the need for a maternal HIV vaccine. We characterized 224 maternal HIV envelope (Env)-specific IgG monoclonal antibodies (MAbs) from seven nontransmitting and transmitting HIV-infected U.S. and Malawian mothers and examined their neutralization activities against nontransmitted autologous circulating viruses and infant-transmitted founder (infant-T/F) viruses. Only a small subset of maternal viruses, 3 of 72 (4%), were weakly neutralized by maternal linear V3 epitope-specific IgG MAbs, whereas 6 out of 6 (100%) infant-T/F viruses were neutralization resistant to these V3-specific IgG MAbs. We also show that maternal-plasma broadly neutralizing antibody (bNAb) responses targeting the V3 glycan supersite in a transmitting woman may have selected for an N332 V3 glycan neutralization-resistant infant-T/F virus. These data have important implications for bNAb-eliciting vaccines and passively administered bNAbs in the setting of MTCT.IMPORTANCE Efforts to eliminate MTCT of HIV with antiretroviral therapy (ART) have met little success, with >180,000 infant infections each year worldwide. It is therefore likely that additional immunologic strategies that can synergize with ART will be required to eliminate MTCT of HIV. To this end, understanding the role of maternal HIV Env-specific IgG antibodies in the setting of MTCT is crucial. In this study, we found that maternal-plasma broadly neutralizing antibody (bNAb) responses can select for T/F viruses that initiate infection in infants. We propose that clinical trials testing the efficacy of single bNAb specificities should not include HIV-infected pregnant women, as a single bNAb might select for neutralization-resistant infant-T/F viruses.

Efficient transplacental IgG transfer in women infected with Zika virus during pregnancy.

Zika virus (ZIKV) is a newly-identified infectious cause of congenital disease. Transplacental transfer of maternal IgG to the fetus plays an important role in preventing many neonatal infections. However, antibody transfer may also have negative consequences, such as mediating enhancement of flavivirus infections in early life, or trafficking of virus immune complexes to the fetal compartment. ZIKV infection produces placental pathology which could lead to impaired IgG transfer efficiency as occurs in other maternal infections, such as HIV-1 and malaria. In this study, we asked whether ZIKV infection during pregnancy impairs transplacental transfer of IgG. We enrolled pregnant women with fever or rash in a prospective cohort in Vitoria, Brazil during the recent ZIKV epidemic. ZIKV and dengue virus (DENV)-specific IgG, ZIKV and DENV neutralizing antibodies, and routine vaccine antigen-specific IgG were measured in maternal samples collected around delivery and 20 paired cord blood samples. We concluded that 8 of these mothers were infected with ZIKV during pregnancy and 12 were ZIKV-uninfected. The magnitude of flavivirus-specific IgG, neutralizing antibody, and vaccine-elicited IgG were highly correlated between maternal plasma and infant cord blood in both ZIKV-infected and -uninfected mother-infant pairs. Moreover, there was no difference in the magnitude of plasma flavivirus-specific IgG levels between mothers and infants regardless of ZIKV infection status. Our data suggests that maternal ZIKV infection during pregnancy does not impair the efficiency of placental transfer of flavivirus-specific, functional, and vaccine-elicited IgG. These findings have implications for the neonatal outomes of maternal ZIKV infection and optimal administration of antibody-based ZIKV vaccines and therapeutics.

DNA vaccination before conception protects Zika virus-exposed pregnant macaques against prolonged viremia and improves fetal outcomes.

Zika virus (ZIKV) infection of pregnant women is associated with congenital Zika syndrome (CZS) and no vaccine is available, although several are being tested in clinical trials. We tested the efficacy of ZIKV DNA vaccine VRC5283 in a rhesus macaque model of congenital ZIKV infection. Most animal vaccine experiments have a set pathogen exposure several weeks or months after vaccination. In the real world, people encounter pathogens years or decades after vaccination, or may be repeatedly exposed if the virus is endemic. To more accurately mimic how this vaccine would be used, we immunized macaques before conception and then exposed them repeatedly to ZIKV during early and mid-gestation. In comparison to unimmunized animals, vaccinated animals had a significant reduction in peak magnitude and duration of maternal viremia, early fetal loss, fetal infection, and placental and fetal brain pathology. Vaccine-induced neutralizing antibody titers on the day of first ZIKV exposure were negatively associated with the magnitude of maternal viremia, and the absence of prolonged viremia was associated with better fetal outcomes. These data support further clinical development of ZIKV vaccine strategies to protect against negative fetal outcomes.

Polyclonal HIV envelope-specific breast milk antibodies limit founder SHIV acquisition and cell-associated virus loads in infant rhesus monkeys.

Breast milk HIV-1 transmission is currently the predominant contributor to pediatric HIV infections. Yet, only ~10% of breastfeeding infants born to untreated HIV-infected mothers become infected. This study assessed the protective capacity of natural HIV envelope-specific antibodies isolated from the milk of HIV-infected women in an infant rhesus monkey (RM), tier 2 SHIV oral challenge model. To mimic placental and milk maternal antibody transfer, infant RMs were i.v. infused and orally treated at the time of challenge with a single weakly neutralizing milk monoclonal antibody (mAb), a tri-mAb cocktail with weakly neutralizing and ADCC functionalities, or an anti-influenza control mAb. Of these groups, the fewest tri-mAb-treated infants had SHIV detectable in plasma or tissues (2/6, 5/6, and 7/8 animals infected in tri-mAb, single-mAb, and control-mAb groups, respectively). Tri-mAb-treated infants demonstrated significantly fewer plasma transmitted/founder variants and reduced peripheral CD4+ T cell proviral loads at 8 weeks post-challenge compared to control mAb-treated infants. Abortive infection was observed as detectable CD4+ T cell provirus in non-viremic control mAb- and single mAb-, but not in tri-mAb-treated animals. These results suggest that polyfunctional milk antibodies contribute to the natural inefficiency of HIV-1 transmission through breastfeeding and infant vaccinations eliciting non-neutralizing antibody responses could reduce postnatal HIV transmission.

Intraamniotic Zika virus inoculation of pregnant rhesus macaques produces fetal neurologic disease.

Zika virus (ZIKV) infection of pregnant women can cause fetal microcephaly and other neurologic defects. We describe the development of a non-human primate model to better understand fetal pathogenesis. To reliably induce fetal infection at defined times, four pregnant rhesus macaques are inoculated intravenously and intraamniotically with ZIKV at gestational day (GD) 41, 50, 64, or 90, corresponding to first and second trimester of gestation. The GD41-inoculated animal, experiencing fetal death 7 days later, has high virus levels in fetal and placental tissues, implicating ZIKV as cause of death. The other three fetuses are carried to near term and euthanized; while none display gross microcephaly, all show ZIKV RNA in many tissues, especially in the brain, which exhibits calcifications and reduced neural precursor cells. Given that this model consistently recapitulates neurologic defects of human congenital Zika syndrome, it is highly relevant to unravel determinants of fetal neuropathogenesis and to explore interventions.

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

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