Leveraging antigenic seniority for maternal vaccination to prevent mother-to-child transmission of HIV-1.

The development of a maternal HIV vaccine to synergize with current antiretroviral drug prophylaxis can overcome implementation challenges and further reduce mother-to-child transmission (MTCT) of HIV. Both the epitope-specificity and autologous neutralization capacity of maternal HIV envelope (Env)-specific antibodies have been implicated in decreased risk of MTCT of HIV. Our goal was to determine if heterologous HIV Env immunization of SHIV.C.CH505-infected, ART-suppressed female rhesus macaques (RMs) could boost autologous Env-specific antibodies. SHIV.C.CH505-infected female RMs (n = 12), began a daily ART regimen at 12 weeks post-infection (wpi), which was continued for 12 weeks. Starting 2 weeks after ART initiation, RMs received 3 monthly immunizations with HIV b.63521/1086.C gp120 or placebo (n = 6/group) vaccine with adjuvant STR8S-C. Compared to the placebo-immunized animals, Env-vaccinated, SHIV-infected RMs exhibited enhanced IgG binding, avidity, and ADCC responses against the vaccine immunogens and the autologous SHIV.C.CH505 Env. Notably, the Env-specific memory B cells elicited by heterologous vaccination were dominated by cells that recognized the SHIV.C.CH505 Env, the antigen of primary exposure. Thus, vaccination of SHIV-infected, ART-suppressed RMs with heterologous HIV Envs can augment multiple components of the antibody response against the Env antigen of primary exposure, suggesting antigenic seniority. Our results suggest that a universal maternal HIV vaccination regimen can be developed to leverage antigenic seniority in targeting the maternal autologous virus pool.

Broad neutralization of H1 and H3 viruses by adjuvanted influenza HA stem vaccines in nonhuman primates.

Seasonal influenza vaccines confer protection against specific viral strains but have restricted breadth that limits their protective efficacy. The H1 and H3 subtypes of influenza A virus cause most of the seasonal epidemics observed in humans and are the major drivers of influenza A virus-associated mortality. The consequences of pandemic spread of COVID-19 underscore the public health importance of prospective vaccine development. Here, we show that headless hemagglutinin (HA) stabilized-stem immunogens presented on ferritin nanoparticles elicit broadly neutralizing antibody (bnAb) responses to diverse H1 and H3 viruses in nonhuman primates (NHPs) when delivered with a squalene-based oil-in-water emulsion adjuvant, AF03. The neutralization potency and breadth of antibodies isolated from NHPs were comparable to human bnAbs and extended to mismatched heterosubtypic influenza viruses. Although NHPs lack the immunoglobulin germline VH1-69 residues associated with the most prevalent human stem-directed bnAbs, other gene families compensated to generate bnAbs. Isolation and structural analyses of vaccine-induced bnAbs revealed extensive interaction with the fusion peptide on the HA stem, which is essential for viral entry. Antibodies elicited by these headless HA stabilized-stem vaccines neutralized diverse H1 and H3 influenza viruses and shared a mode of recognition analogous to human bnAbs, suggesting that these vaccines have the potential to confer broadly protective immunity against diverse viruses responsible for seasonal and pandemic influenza infections in humans.

Immunogenicity, safety, and efficacy of sequential immunizations with an SIV-based IDLV expressing CH505 Envs.

A preventative HIV-1 vaccine is an essential intervention needed to halt the HIV-1 pandemic. Neutralizing antibodies protect against HIV-1 infection in animal models, and thus an approach toward a protective HIV-1 vaccine is to induce broadly cross-reactive neutralizing antibodies (bnAbs). One strategy to achieve this goal is to define envelope (Env) evolution that drives bnAb development in infection and to recreate those events by vaccination. In this study, we report the immunogenicity, safety, and efficacy in rhesus macaques of an SIV-based integrase defective lentiviral vector (IDLV) expressing sequential gp140 Env immunogens derived from the CH505 HIV-1-infected individual who made the CH103 and CH235 bnAb lineages. Immunization with IDLV expressing sequential CH505 Envs induced higher magnitude and more durable binding and neutralizing antibody responses compared to protein or DNA +/- protein immunizations using the same sequential envelopes. Compared to monkeys immunized with a vector expressing Envs alone, those immunized with the combination of IDLV expressing Env and CH505 Env protein demonstrated improved durability of antibody responses at six months after the last immunization as well as lower peak viremia and better virus control following autologous SHIV-CH505 challenge. There was no evidence of vector mobilization or recombination in the immunized and challenged monkeys. Although the tested vaccines failed to induce bnAbs and to mediate significant protection following SHIV-challenge, our results show that IDLV proved safe and successful at inducing higher titer and more durable immune responses compared to other vaccine platforms.

Adjuvant-Dependent Enhancement of HIV Env-Specific Antibody Responses in Infant Rhesus Macaques.

Toward the goal of developing an effective HIV vaccine that can be administered in infancy to protect against postnatal and lifelong sexual HIV transmission risks, the current pilot study was designed to compare the effect of novel adjuvants on the induction of HIV Env-specific antibody responses in infant macaques. Aligning our studies with the adjuvanted proteins evaluated in a prime-boost schedule with ALVAC in the ongoing HVTN (HIV Vaccine Trials Network) 702 efficacy trial, we selected the bivalent clade C Env immunogens gp120 C.1086 and gp120 TV1 in combination with the MF59 adjuvant. However, we hypothesized that the adjuvant system AS01, that is included in the pediatric RTS,S malaria vaccine, would promote Env-specific antibody responses superior to those of the oil-in-water MF59 emulsion adjuvant. In a second study arm, we compared two emulsions, glucopyranosyl lipid adjuvant formulated in a stable emulsion (GLA-SE) and 3M-052-SE, containing Toll-like receptor 4 (TLR4) and TLR7/TLR8 (TLR7/8) ligand, respectively. The latter adjuvant had been previously demonstrated to be especially effective in activating neonatal antigen-presenting cells. Our results demonstrate that different adjuvants drive quantitatively or qualitatively distinct responses to the bivalent Env vaccine. AS01 induced higher Env-specific plasma IgG antibody levels than the antigen in MF59 and promoted improved antibody function in infants, and 3M-052-SE outperformed GLA-SE by inducing the highest breadth and functionality of antibody responses. Thus, distinct adjuvants are likely to be required for maximizing vaccine-elicited immune responses in infants, particularly when immunization in infancy aims to elicit both perinatal and lifelong immunity against challenging pathogens such as HIV.IMPORTANCE Alum remains the adjuvant of choice for pediatric vaccines. Yet the distinct nature of the developing immune system in infants likely requires novel adjuvants targeted specifically at the pediatric population to reach maximal vaccine efficacy with an acceptable safety profile. The current study supports the idea that additional adjuvants for pediatric vaccines should be, and need to be, tested in infants for their potential to enhance immune responses. Using an infant macaque model, our results suggest that both AS01 and 3M-052-SE can significantly improve and better sustain HIV Env-specific antibody responses than alum. Despite the limited number of animals, the results revealed interesting differences that warrant further testing of promising novel adjuvant candidates in larger preclinical and clinical studies to define the mechanisms leading to adjuvant-improved antibody responses and to identify targets for adjuvant and vaccine optimization.

Short Communication: Small-Molecule CD4 Mimetics Sensitize HIV-1-Infected Cells to Antibody-Dependent Cellular Cytotoxicity by Antibodies Elicited by Multiple Envelope Glycoprotein Immunogens in Nonhuman Primates.

Recent studies have linked antibody Fc-mediated effector functions with control of human immunodeficiency virus type 1 (HIV-1) and simian immunodeficiency virus infections. Interestingly, the presence of antibodies with potent antibody-dependent cellular cytotoxicity (ADCC) activity in RV144 vaccine trial participants correlated inversely with HIV-1 acquisition risk. These antibodies were recently found to recognize epitopes on the HIV-1 envelope (Env) glycoprotein exposed upon Env-CD4 binding. Accordingly, small-molecule CD4 mimetics (CD4mc) that induce Env to sample the CD4-bound conformation were shown to sensitize HIV-1-infected cells to ADCC mediated by sera from HIV-1-infected individuals. However, it remains unknown whether antibodies elicited through immunization can also mediate CD4mc-induced ADCC. In this study, we tested the capacity of CD4mc to sensitize HIV-1-infected cells to ADCC by sera from Env-vaccinated nonhuman primates using a FACS-based ADCC assay. In parallel, we evaluated the ability of CD4mc to sensitize HIV-1 viral particles to neutralization by sera from these immunized animals. We found that the vaccine-induced antibodies were able to mediate ADCC and viral neutralization in the presence, but not the absence, of CD4mc. Thus, CD4mc are capable of sensitizing HIV-1-infected cells to ADCC and infectious viral particles to neutralization by easy-to-elicit antibodies that are otherwise unable to mediate these activities.

Assessment of three new parasite lactate dehydrogenase (pan-pLDH) tests for diagnosis of uncomplicated malaria.

A study to assess the diagnostic capabilities of three parasite lactate dehydrogenase (pan-pLDH) tests, Vistapan), Carestart and Parabank), was conducted in Uganda. An HRP2 test, Paracheck-Pf), and a Giemsa-stained blood film were performed with the pLDH tests for outpatients with suspected malaria. In total, 460 subjects were recruited: 248 with positive blood films and 212 with negative blood films. Plasmodium falciparum was present in 95% of infections. Sensitivity above 90% was shown by two pLDH tests, Carestart (95.6%) and Vistapan (91.9%), and specificity above 90% by Parabank (94.3%) and Carestart (91.5%). Sensitivity decreased with low parasitaemia (chi(2) trend, P<0.001); however, all tests achieved sensitivity >90% with parasitaemia > or =100/microl. All tests had good inter-reader reliability (kappa>0.95). Two weeks after diagnosis, 4-10% of pLDH tests were still positive compared with 69.7% of the HRP2 tests. All tests had similar ease of use. In conclusion, two pLDH tests performed well in diagnosing P. falciparum malaria, and all pLDH tests became negative after treatment more quickly than the HRP2. Therefore the rapid test of choice for use with artemisinin-combination therapies in this area would be one of these new pLDH tests.

The heat stability of Plasmodium lactate dehydrogenase-based and histidine-rich protein 2-based malaria rapid diagnostic tests.

Malaria rapid diagnostic tests (RDTs) have performed well in a variety of studies, but recent reports have described sensitivity for Plasmodium falciparum as significantly lower than that required for operational deployment. Exposure to high temperature has been suggested as an explanation. This study assessed the temperature stability of two different Plasmodium lactate dehydrogenase (pLDH)- and three histidine-rich protein 2 (HRP2)-detecting RDTs. One HRP2 test proved insufficiently sensitive for assessment. After incubation at 35, 45 and 60 degrees C, two RDTs detecting pLDH showed a substantial fall in percentage test line positivity over time, which was not seen with the remaining two HRP-2-based RDTs. For the particular products studied, variability was high, with the pLDH-based RDTs being less sensitive than HRP2-based RDTs against the sample of P. falciparum used and more susceptible to heat-induced damage, but the reasons for this are unclear. The performance of malaria RDTs can be adversely affected at the temperatures to which they will be exposed when transported to, and used in, the rural tropics.

Rapid diagnostic tests for malaria parasites.

Malaria presents a diagnostic challenge to laboratories in most countries. Endemic malaria, population movements, and travelers all contribute to presenting the laboratory with diagnostic problems for which it may have little expertise available. Drug resistance and genetic variation has altered many accepted morphological appearances of malaria species, and new technology has given an opportunity to review available procedures. Concurrently the World Health Organization has opened a dialogue with scientists, clinicians, and manufacturers on the realistic possibilities for developing accurate, sensitive, and cost-effective rapid diagnostic tests for malaria, capable of detecting 100 parasites/microl from all species and with a semiquantitative measurement for monitoring successful drug treatment. New technology has to be compared with an accepted "gold standard" that makes comparisons of sensitivity and specificity between different methods. The majority of malaria is found in countries where cost-effectiveness is an important factor and ease of performance and training is a major consideration. Most new technology for malaria diagnosis incorporates immunochromatographic capture procedures, with conjugated monoclonal antibodies providing the indicator of infection. Preferred targeted antigens are those which are abundant in all asexual and sexual stages of the parasite and are currently centered on detection of HRP-2 from Plasmodium falciparum and parasite-specific lactate dehydrogenase or Plasmodium aldolase from the parasite glycolytic pathway found in all species. Clinical studies allow effective comparisons between different formats, and the reality of nonmicroscopic diagnoses of malaria is considered.

The intensity of interference varies with food density: support for behaviour-based models of interference.

Dolman (1995) measured the intake rates of snow buntings feeding on seed patches at difference bird densities, for each of two different seed densities. Interference occurred in the low food density treatment, with intake rate declining at high bird densities, but did not occur in the high food density treatment. Dolman states that existing models of the interference process assume that the intensity of interference is independent of food density. While this statement is true for the model of Hassell and Varley (1969), we show that behaviour-based models of interference do not assume that interference is independent of food density. We examine two simple analytic behaviour-based models of interference and show that, in agreement with Dolman's observations, intensity of interference is predicted to decrease with increasing food density. Dolman plotted log (intake rate) against log (bird density). Rather than obtaining a linear relationship predicted by the Hassell and Varley model, the results from the low seed density treatment indicated a curvilinear relationship consistent with those produced by our behaviour-based models. These results provide support for the use of behaviour-based models of interference over the model of Hassell and Varley.