Impact of Poxvirus Vector Priming, Protein Coadministration, and Vaccine Intervals on HIV gp120 Vaccine-Elicited Antibody Magnitude and Function in Infant Macaques

ABSTRACT Despite success in reducing vertical HIV transmission by maternal antiretroviral therapy, several obstacles limit its efficacy during breastfeeding, and breast-milk transmission is now the dominant mode of mother-to-child transmission (MTCT) of HIV in infants. Thus, a pediatric vaccine is needed to eradicate oral HIV infections in newborns and infants. Utilizing the infant rhesus macaque model, we compared 3 different vaccine regimens: (i) HIV envelope (Env) protein only, (ii) poxvirus vector (modified vaccinia virus Ankara [MVA])-HIV Env prime and HIV Env boost, and (iii) coadministration of HIV Env and MVA-HIV Env at all time points. The vaccines were administered with an accelerated, 3-week-interval regimen starting at birth for early induction of highly functional HIV Env-specific antibodies. We also tested whether an extended, 6-week immunization interval using the same vaccine regimen as in the coadministration group would enhance the quality of antibody responses. We found that pediatric HIV vaccines administered at birth are effective in inducing HIV Env-specific plasma IgG. The vaccine regimen consisting of only HIV Env protein induced the highest levels of variable region 1 and 2 (V1V2)-specific antibodies and tier 1 neutralizing antibodies, whereas the extended-interval regimen induced both persistent Env-specific systemic IgG and mucosal IgA responses. Antibody-dependent cell-mediated cytotoxicity (ADCC) antibodies in plasma were elicited by all vaccine regimens. These data suggest that infant immunizations beginning at birth are effective for the induction of functional HIV Env-specific antibodies that could potentially protect against breast milk transmission of HIV and set the stage for immunity prior to sexual debut

Association of HIV-1 Envelope-Specific Breast Milk IgA Responses with Reduced Risk of Postnatal Mother-to-Child Transmission of HIV-1

ABSTRACT Infants born to HIV-1-infected mothers in resource-limited areas where replacement feeding is unsafe and impractical are repeatedly exposed to HIV-1 throughout breastfeeding. Despite this, the majority of infants do not contract HIV-1 postnatally, even in the absence of maternal antiretroviral therapy. This suggests that immune factors in breast milk of HIV-1-infected mothers help to limit vertical transmission. We compared the HIV-1 envelope-specific breast milk and plasma antibody responses of clade C HIV-1-infected postnatally transmitting and nontransmitting mothers in the control arm of the Malawi-based Breastfeeding Antiretrovirals and Nutrition Study using multivariable logistic regression modeling. We found no association between milk or plasma neutralization activity, antibody-dependent cell-mediated cytotoxicity, or HIV-1 envelope-specific IgG responses and postnatal transmission risk. While the envelope-specific breast milk and plasma IgA responses also did not reach significance in predicting postnatal transmission risk in the primary model after correction for multiple comparisons, subsequent exploratory analysis using two distinct assay methodologies demonstrated that the magnitudes of breast milk total and secretory IgA responses against a consensus HIV-1 envelope gp140 (B.con env03) were associated with reduced postnatal transmission risk. These results suggest a protective role for mucosal HIV-1 envelope-specific IgA responses in the context of postnatal virus transmission. This finding supports further investigations into the mechanisms by which mucosal IgA reduces risk of HIV-1 transmission via breast milk and into immune interventions aimed at enhancing this response. IMPORTANCE Infants born to HIV-1-infected mothers are repeatedly exposed to the virus in breast milk. Remarkably, the transmission rate is low, suggesting that immune factors in the breast milk of HIV-1-infected mothers help to limit transmission. We compared the antibody responses in plasma and breast milk of HIV-1-transmitting and -nontransmitting mothers to identify responses that correlated with reduced risk of postnatal HIV-1 transmission. We found that neither plasma nor breast milk IgG antibody responses were associated with risk of HIV-1 transmission. In contrast, the magnitudes of the breast milk IgA and secretory IgA responses against HIV-1 envelope proteins were associated with reduced risk of postnatal HIV-1 transmission. The results of this study support further investigations of the mechanisms by which mucosal IgA may reduce the risk of HIV-1 transmission via breastfeeding and the development of strategies to enhance milk envelope-specific IgA responses to reduce mother-to-child HIV transmission and promote an HIV-free generation

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

ABSTRACTImmunodominant 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.IMPORTANCEThe 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

Impact of immune escape mutations on HIV-1 fitness in the context of the cognate transmitted/founder genome

<p>Abstract</p> <p>Background</p> <p>A modest change in HIV-1 fitness can have a significant impact on viral quasispecies evolution and viral pathogenesis, transmission and disease progression. To determine the impact of immune escape mutations selected by cytotoxic T lymphocytes (CTL) on viral fitness in the context of the cognate transmitted/founder (T/F) genome, we developed a new competitive fitness assay using molecular clones of T/F genomes lacking exogenous genetic markers and a highly sensitive and precise parallel allele-specific sequencing (PASS) method.</p> <p>Results</p> <p>The T/F and mutant viruses were competed in CD4⁺ T-cell enriched cultures, relative proportions of viruses were assayed after repeated cell-free passage, and fitness costs were estimated by mathematical modeling. Naturally occurring HLA B57-restricted mutations involving the TW10 epitope in Gag and two epitopes in Tat/Rev and Env were assessed independently and together. Compensatory mutations which restored viral replication fitness were also assessed. A principal TW10 escape mutation, T242N, led to a 42% reduction in replication fitness but V247I and G248A mutations in the same epitope restored fitness to wild-type levels. No fitness difference was observed between the T/F and a naturally selected variant carrying the early CTL escape mutation (R355K) in Env and a reversion mutation in the Tat/Rev overlapping region.</p> <p>Conclusions</p> <p>These findings reveal a broad spectrum of fitness costs to CTL escape mutations in T/F viral genomes, similar to recent findings reported for neutralizing antibody escape mutations, and highlight the extraordinary plasticity and adaptive potential of the HIV-1 genome. Analysis of T/F genomes and their evolved progeny is a powerful approach for assessing the impact of composite mutational events on viral fitness.</p

Heterologous Protection against Asian Zika Virus Challenge in Rhesus Macaques.

BACKGROUND:Zika virus (ZIKV; Flaviviridae, Flavivirus) was declared a public health emergency of international concern by the World Health Organization (WHO) in February 2016, because of the evidence linking infection with ZIKV to neurological complications, such as Guillain-Barre Syndrome in adults and congenital birth defects including microcephaly in the developing fetus. Because development of a ZIKV vaccine is a top research priority and because the genetic and antigenic variability of many RNA viruses limits the effectiveness of vaccines, assessing whether immunity elicited against one ZIKV strain is sufficient to confer broad protection against all ZIKV strains is critical. Recently, in vitro studies demonstrated that ZIKV likely circulates as a single serotype. Here, we demonstrate that immunity elicited by African lineage ZIKV protects rhesus macaques against subsequent infection with Asian lineage ZIKV. METHODOLOGY/PRINCIPAL FINDINGS:Using our recently developed rhesus macaque model of ZIKV infection, we report that the prototypical ZIKV strain MR766 productively infects macaques, and that immunity elicited by MR766 protects macaques against heterologous Asian ZIKV. Furthermore, using next generation deep sequencing, we found in vivo restoration of a putative N-linked glycosylation site upon replication in macaques that is absent in numerous MR766 strains that are widely being used by the research community. This reversion highlights the importance of carefully examining the sequence composition of all viral stocks as well as understanding how passage history may alter a virus from its original form. CONCLUSIONS/SIGNIFICANCE:An effective ZIKV vaccine is needed to prevent infection-associated fetal abnormalities. Macaques whose immune responses were primed by infection with East African ZIKV were completely protected from detectable viremia when subsequently rechallenged with heterologous Asian ZIKV. Therefore, these data suggest that immunogen selection is unlikely to adversely affect the breadth of vaccine protection, i.e., any Asian ZIKV immunogen that protects against homologous challenge will likely confer protection against all other Asian ZIKV strains

An N-linked glycosylation site in envelope is rapidly selected in vivo.

<p>Envelope sequences from the three animals were sequenced at three days post infection, and from two of the animals at day six post infection. A Muscle alignment of the translated sequences was generated in Geneious. Dots represent identity to the consensus sequence. Dashes represent deletions. Capital letters represent amino acids. Only regions of the E protein with sequence variants are depicted. <b>A.</b> E protein amino acid positions 136–178. The frequencies of the deletion and the restored deletion are shown below each of the stock sequences, with the indicated site boxed. Amino acid variant frequencies matching the variant sites in <a href="http://www.plosntds.org/article/info:doi/10.1371/journal.pntd.0005168#pntd.0005168.g001" target="_blank">Fig 1A</a> are shown. The gray ellipse above the sequence alignment represents the 150 loop of the E protein [<a href="http://www.plosntds.org/article/info:doi/10.1371/journal.pntd.0005168#pntd.0005168.ref020" target="_blank">20</a>]. <b>B.</b> E protein amino acid positions 271–313. <b>C.</b> E protein amino acid positions 361–450. There were two additional nonsynonymous variants at greater than 5% in animal 562876 at day three, and the frequency of the amino acid variants from the other animals and time points are shown below each sample.</p

ZIKV-002 macaques challenged with ZIKV MR766 are protected from heterologous reinfection with ZIKV-FP.

<p><b>A.</b> Study timeline with dates of primary and secondary, heterologous ZIKV challenges. Samples were collected daily from 0 to 10 dpi, and then weekly thereafter until secondary challenge (denoted by ticks along the timeline). Challenge stocks were derived from the East African and French Polynesian virus strains detailed above the timeline. <b>B.</b> Plasma viral loads, shown as vRNA copies/mL for each of the macaques challenged with 1 x 10⁶ (solid green line), 1x 10⁵ (solid orange line), or 1 x 10⁴ (solid blue line) PFU/mL of ZIKV MR766 challenge stock from the date of primary challenge through 10 days post heterologous challenge with ZIKV-FP. For comparison of plasma viral loads between ZIKV strains, solid light grey lines depict the plasma viral load trajectories for animals that were challenged with the same dose of ZIKV-FP and then rechallenged with homologous ZIKV-FP [<a href="http://www.plosntds.org/article/info:doi/10.1371/journal.pntd.0005168#pntd.0005168.ref022" target="_blank">22</a>]. <b>C.</b> Oral swab and <b>D.</b> pan urine viral loads.</p

Summary of virus stocks and culture history.

<p>All Zika virus strains are the MR 766 prototype strain derived from the virus that was isolated from a sentinel rhesus monkey in Zika Forest, Entebbe, Uganda in April 1947[<a href="http://www.plosntds.org/article/info:doi/10.1371/journal.pntd.0005168#pntd.0005168.ref006" target="_blank">6</a>]. All have undergone extensive mouse brain passage. The MR766 challenge stock was created for nonhuman primate natural history studies and was derived from the CDC virus. Challenge virus was prepared by inoculation of CDC virus onto a confluent monolayer of C6/36 mosquito cells and a clarified harvest of the culture medium was collected nine days post infection.</p

East African ZIKV MR766 envelope sequences often contain an in-frame deletion of an N-linked glycosylation site and are heterologous with respect to Asian ZIKV.

<p>The amino acid sequences of the Envelope protein for six ZIKV MR766 Genbank sequences were aligned to the consensus amino acid sequences of the three ZIKV MR766 stock viruses (Chal Stck, CDC Stock, and WRCEVA stock) using a Muscle alignment in Geneious. Dots represent identity to the consensus sequence. Dashes represent deletions. Only sections of the E protein with variations are shown, all other parts of the E protein showed no variation. Capital letters represent amino acids. The frequencies of the deletion and the restored deletion are shown below each of the stock sequences. Genbank reference sequence AY632535 had two amino acids that were different from the other reference sequences. The frequency of reads with these amino acid variants as determined by deep sequencing are shown below each of the stock sequences. <b>A.</b> Envelope protein amino acid region 136–178. The gray ellipse above the sequences represent the 150 loop of the E protein [<a href="http://www.plosntds.org/article/info:doi/10.1371/journal.pntd.0005168#pntd.0005168.ref020" target="_blank">20</a>]. <b>B.</b> Envelope protein amino acid region 271–313.</p

Highly efficient maternal-fetal Zika virus transmission in pregnant rhesus macaques

<div><p>Infection with Zika virus (ZIKV) is associated with human congenital fetal anomalies. To model fetal outcomes in nonhuman primates, we administered Asian-lineage ZIKV subcutaneously to four pregnant rhesus macaques. While non-pregnant animals in a previous study contemporary with the current report clear viremia within 10–12 days, maternal viremia was prolonged in 3 of 4 pregnancies. Fetal head growth velocity in the last month of gestation determined by ultrasound assessment of head circumference was decreased in comparison with biparietal diameter and femur length within each fetus, both within normal range. ZIKV RNA was detected in tissues from all four fetuses at term cesarean section. In all pregnancies, neutrophilic infiltration was present at the maternal-fetal interface (decidua, placenta, fetal membranes), in various fetal tissues, and in fetal retina, choroid, and optic nerve (first trimester infection only). Consistent vertical transmission in this primate model may provide a platform to assess risk factors and test therapeutic interventions for interruption of fetal infection. The results may also suggest that maternal-fetal ZIKV transmission in human pregnancy may be more frequent than currently appreciated.</p></div