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Broadly neutralizing antibodies (bNAbs) protect against HIV infection in non-human primates and their efficacy may be enhanced through interaction with Fc receptors on immune cells. Antibody isotype is a modulator of this binding with the IgG3 subclass mediating potent Fc effector function and is associated with HIV vaccine efficacy and HIV control. BNAb functions are typically assessed independently of the constant region with which they are naturally expressed. To examine the role of natural isotype in the context of a bNAb lineage we studied CAP256, an HIV-infected individual that mounted a potent V2-specific bNAb response. CAP256 expressed persistently high levels of plasma IgG3 which we found mediated both broad neutralizing activity and potent Fc function. Sequencing of germline DNA and the constant regions of V2-directed bNAbs from this donor revealed the expression of a novel IGHG3 allele as well as IGHG3*17, an allele that produces IgG3 antibodies with increased plasma half-life. Both allelic variants were used to generate CAP256-VRC26.25 and CAP256-VRC26.29 IgG3 bNAbs and these were compared to IgG1 versions. IgG3 variants were shown to have significantly higher phagocytosis and trogocytosis compared to IgG1 versions, which corresponded to increased affinity for FcγRIIa. Neutralization potency was also significantly higher for IgG3 bNAbs, particularly against viruses lacking the N160 glycan. By exchanging hinge regions between subclass variants, we showed that hinge length modulated both neutralization potency and Fc function. This study showed that co-operation between the variable and natural IgG3 constant regions enhanced the polyfunctionality of antibodies, indicating the value of leveraging genetic variation which could be exploited for passive immunity.

About the Authors: Lynn Morris * E-mail: lynnm@nicd.ac.za Affiliations National Institute for Communicable Diseases of the National Health Laboratory Service and the University of the Witwatersrand, Johannesburg, South Africa, Center for the AIDS Programme of Research in South Africa (CAPRISA), Durban, South Africa ORCID http://orcid.org/0000-0003-3961-7828 Nonhlanhla N. Mkhize Affiliation: National Institute for Communicable Diseases of the National Health Laboratory Service and the University of the Witwatersrand, Johannesburg, South AfricaCitation: Morris L, Mkhize NN (2017) Prospects for passive immunity to prevent HIV infection. Competing interests: I have read the journal's policy and the authors of this manuscript have the following competing interests: LM and NM are responsible for the VRC01 sensitivity testing on the AMP trial funded through the HIV Vaccines Trials Network (HVTN). Effective methods to prevent HIV infection include condom use and pre-exposure prophylaxis (PrEP) with antiretroviral drugs; however, owing to barriers such as adherence, an effective vaccine would be the most definitive solution to the ongoing burden of HIV infection. Since natural resistance to VRC01 exists, it will be important to establish whether breakthrough HIV infections are due to preexisting viral resistance or early adaptive escape from VRC01.

While the induction of broadly neutralizing antibodies (bNAbs) is a major goal of HIV vaccination strategies, there is mounting evidence to suggest that antibodies with Fc effector function also contribute to protection against HIV infection. Here we investigated Fc effector functionality of HIV-specific IgG plasma antibodies over 3 years of infection in 23 individuals, 13 of whom developed bNAbs. Antibody-dependent cellular phagocytosis (ADCP), complement deposition (ADCD), cellular cytotoxicity (ADCC) and cellular trogocytosis (ADCT) were detected in almost all individuals with levels of activity increasing over time. At 6 months post-infection, individuals with bNAbs had significantly higher levels of ADCD and ADCT that correlated with antibody binding to C1q and FcγRIIa respectively. In addition, antibodies from individuals with bNAbs showed more IgG subclass diversity to multiple HIV antigens which also correlated with Fc polyfunctionality. Germinal center activity represented by CXCL13 levels and expression of activation-induced cytidine deaminase (AID) was found to be associated with neutralization breadth, Fc polyfunctionality and IgG subclass diversity. Overall, multivariate analysis by random forest classification was able to group bNAb individuals with 85% sensitivity and 80% specificity based on the properties of their antibody Fc early in HIV infection. Thus, the Fc effector function profile predicted the development of neutralization breadth in this cohort, suggesting that intrinsic immune factors within the germinal center provide a mechanistic link between the Fc and Fab of HIV-specific antibodies.

The VRC01 Antibody Mediated Prevention (AMP) efficacy trials conducted between 2016 and 2020 showed for the first time that passively administered broadly neutralizing antibodies (bnAbs) could prevent HIV-1 acquisition against bnAb-sensitive viruses. HIV-1 viruses isolated from AMP participants who acquired infection during the study in the sub-Saharan African (HVTN 703/HPTN 081) and the Americas/European (HVTN 704/HPTN 085) trials represent a panel of currently circulating strains of HIV-1 and offer a unique opportunity to investigate the sensitivity of the virus to broadly neutralizing antibodies (bnAbs) being considered for clinical development. Pseudoviruses were constructed using envelope sequences from 218 individuals. The majority of viruses identified were clade B and C; with clades A, D, F and G and recombinants AC and BF detected at lower frequencies. We tested eight bnAbs in clinical development (VRC01, VRC07-523LS, 3BNC117, CAP256.25, PGDM1400, PGT121, 10–1074 and 10E8v4) for neutralization against all AMP placebo viruses (n = 76). Compared to older clade C viruses (1998–2010), the HVTN703/HPTN081 clade C viruses showed increased resistance to VRC07-523LS and CAP256.25. At a concentration of 1μg/ml (IC80), predictive modeling identified the triple combination of V3/V2-glycan/CD4bs-targeting bnAbs (10-1074/PGDM1400/VRC07-523LS) as the best against clade C viruses and a combination of MPER/V3/CD4bs-targeting bnAbs (10E8v4/10-1074/VRC07-523LS) as the best against clade B viruses, due to low coverage of V2-glycan directed bnAbs against clade B viruses. Overall, the AMP placebo viruses represent a valuable resource for defining the sensitivity of contemporaneous circulating viral strains to bnAbs and highlight the need to update reference panels regularly. Our data also suggests that combining bnAbs in passive immunization trials would improve coverage of global viruses.

The Antibody Mediated Prevention trials showed that the broadly neutralizing antibody (bnAb) VRC01 prevented acquisition of human immunodeficiency virus-1 (HIV-1) sensitive to VRC01. Using AMP trial data, here we show that the predicted serum neutralization 80% inhibitory dilution titer (PT 80 ) biomarker—which quantifies the neutralization potency of antibodies in an individual’s serum against an HIV-1 isolate—can be used to predict HIV-1 prevention efficacy. Similar to the results of nonhuman primate studies, an average PT 80 of 200 (meaning a bnAb concentration 200-fold higher than that required to reduce infection by 80% in vitro) against a population of probable exposing viruses was estimated to be required for 90% prevention efficacy against acquisition of these viruses. Based on this result, we suggest that the goal of sustained PT 80 >200 against 90% of circulating viruses can be achieved by promising bnAb regimens engineered for long half-lives. We propose the PT 80 biomarker as a surrogate endpoint for evaluation of bnAb regimens, and as a tool for benchmarking candidate bnAb-inducing vaccines. By integrating the serum concentration of a broadly neutralizing antibody (bNAb) with its in vitro 80% inhibitory concentration, the PT 80 biomarker may be used to guide target levels of bNAbs for effective prevention of HIV-1 acquisition.

BACKGROUNDThe neonatal immune system is uniquely poised to generate broadly neutralizing antibodies (bnAbs), and thus infants are ideal for evaluating HIV vaccine candidates. We present the design and safety of a new-in-infants glucopyranosyl lipid A-stable emulsion (GLA-SE) adjuvant admixed with a first-in-infant CH505 transmitter-founder (CH505TF) gp120 immunogen designed to induce precursors for bnAbs against HIV.METHODSHIV Vaccine Trials Network 135 is a phase I randomized, placebo-controlled trial of CH505TF plus GLA-SE or placebo. Healthy infants aged ≤5 days, born to mothers living with HIV but HIV nucleic acid-negative at birth, were randomized to 5 doses of CH505TF plus GLA-SE or placebo at birth and 8, 16, 32, and 54 weeks.RESULTSThirty-eight infants (median age 4 days; interquartile range 4-4.75 days) were enrolled November 2020 to January 2022. Among 28 infants assigned to receive CH505TF plus GLA-SE and 10 assigned to receive placebo, most completed the 5-dose immunization series (32/38) and follow-up (35/38). Solicited local and systemic reactions were more frequent in vaccine (8, 28.6% local; 16, 57.1% systemic) versus placebo recipients (1, 10% local, P = 0.25; 4, 40.0% systemic, P = 0.38). All events were grade 1 except 2 grade 2 events (pain, lethargy). Serious vaccine-related adverse events were not recorded.CONCLUSIONThis study illustrates the feasibility of conducting trials of new-in-infants adjuvanted HIV vaccines in HIV-exposed infants receiving standard infant vaccinations. The safety profile of the CH505TF plus GLA-SE vaccine was reassuring.TRIAL REGISTRATIONClinicalTrials.gov NCT04607408.FUNDINGNational Institute of Allergy and Infectious Diseases of the NIH under grants UM1AI068614, UM1AI068635, and UM1AI068618.

HVTN 100 evaluated the safety and immunogenicity of an HIV subtype C pox-protein vaccine regimen, investigating a 12-month booster to extend vaccine-induced immune responses. A phase 1-2 randomized double-blind placebo-controlled trial enrolled 252 participants (210 vaccine/42 placebo; median age 23 years; 43% female) between 9 February 2015 and 26 May 2015. Vaccine recipients received ALVAC-HIV (vCP2438) alone at months 0 and 1 and with bivalent subtype C gp120/MF59 at months 3, 6, and 12. Antibody (IgG, IgG3 binding, and neutralizing) and CD4+ T-cell (expressing interferon-gamma, interleukin-2, and CD40 ligand) responses were evaluated at month 6.5 for all participants and at months 12, 12.5, and 18 for a randomly selected subset. The primary analysis compared IgG binding antibody (bAb) responses and CD4+ T-cell responses to 3 vaccine-matched antigens at peak (month 6.5 versus 12.5) and durability (month 12 versus 18) timepoints; IgG responses to CaseA2_gp70_V1V2.B, a primary correlate of risk in RV144, were also compared at these same timepoints. Secondary and exploratory analyses compared IgG3 bAb responses, IgG bAb breadth scores, neutralizing antibody (nAb) responses, antibody-dependent cellular phagocytosis, CD4+ polyfunctionality responses, and CD4+ memory sub-population responses at the same timepoints. Vaccines were generally safe and well tolerated. During the study, there were 2 deaths (both in the vaccine group and both unrelated to study products). Ten participants became HIV-infected during the trial, 7% (3/42) of placebo recipients and 3% (7/210) of vaccine recipients. All 8 serious adverse events were unrelated to study products. Less waning of immune responses was seen after the fifth vaccination than after the fourth, with higher antibody and cellular response rates at month 18 than at month 12: IgG bAb response rates to 1086.C V1V2, 21.0% versus 9.7% (difference = 11.3%, 95% CI = 0.6%-22.0%, P = 0.039), and ZM96.C V1V2, 21.0% versus 6.5% (difference = 14.5%, 95% CI = 4.1%-24.9%, P = 0.004). IgG bAb response rates to all 4 primary V1V2 antigens were higher 2 weeks after the fifth vaccination than 2 weeks after the fourth vaccination: 87.7% versus 75.4% (difference = 12.3%, 95% CI = 1.7%-22.9%, P = 0.022) for 1086.C V1V2, 86.0% versus 63.2% (difference = 22.8%, 95% CI = 9.1%-36.5%, P = 0.001) for TV1c8.2.C V1V2, 67.7% versus 44.6% (difference = 23.1%, 95% CI = 10.4%-35.7%, P < 0.001) for ZM96.C V1V2, and 81.5% versus 60.0% (difference = 21.5%, 95% CI = 7.6%-35.5%, P = 0.002) for CaseA2_gp70_V1V2.B. IgG bAb response rates to the 3 primary vaccine-matched gp120 antigens were all above 90% at both peak timepoints, with no significant differences seen, except a higher response rate to ZM96.C gp120 at month 18 versus month 12: 64.5% versus 1.6% (difference = 62.9%, 95% CI = 49.3%-76.5%, P < 0.001). CD4+ T-cell response rates were higher at month 18 than month 12 for all 3 primary vaccine-matched antigens: 47.3% versus 29.1% (difference = 18.2%, 95% CI = 2.9%-33.4%, P = 0.021) for 1086.C, 61.8% versus 38.2% (difference = 23.6%, 95% CI = 9.5%-37.8%, P = 0.001) for TV1.C, and 63.6% versus 41.8% (difference = 21.8%, 95% CI = 5.1%-38.5%, P = 0.007) for ZM96.C, with no significant differences seen at the peak timepoints. Limitations were that higher doses of gp120 were not evaluated, this study was not designed to investigate HIV prevention efficacy, and the clinical significance of the observed immunological effects is uncertain. In this study, a 12-month booster of subtype C pox-protein vaccines restored immune responses, and slowed response decay compared to the 6-month vaccination. ClinicalTrials.gov NCT02404311. South African National Clinical Trials Registry (SANCTR number: DOH--27-0215-4796).

Objectives Sexually transmitted infections (STI) and bacterial vaginosis (BV) cause female genital tract inflammation. This inflammation, which is often present in the absence of symptoms, is associated with increased susceptibility to HIV infection. We aimed to evaluate genital cytokine profiles and the degree of inflammation associated with common STIs and BV. Methods HIV-uninfected women (n=227) were screened for BV, Chlamydia trachomatis, Neisseria gonorrhoeae, Herpes simplex virus type 2 (HSV-2), and Trichomonas vaginalis. Concentrations of 42 cytokines in cervicovaginal lavages and 13 cytokines in plasma were measured using Luminex. Changes in cytokine profiles were evaluated using Mann–Whitney U test, logistic regression and factor analysis. p Values were adjusted for multiple comparisons using a false discovery rate step-down procedure. Results Women with chlamydia or gonorrhoea had the highest genital cytokine concentrations, with 17/42 and 14/42 cytokines upregulated compared with women with no infection, respectively. BV was associated with elevated proinflammatory cytokine concentrations, but lower chemokine and haematopoietic cytokine concentrations. HSV-2 reactivation was associated with lower levels of inflammation, while trichomoniasis did not cause significant differences in genital cytokine concentrations. Genital infections did not influence plasma cytokine concentrations. Although certain STIs, in particular chlamydia and gonorrhoea, were associated with high genital cytokine concentrations, only 19% of women with an STI/BV had clinical signs. Conclusions Chlamydia was associated with the highest genital cytokine levels, followed by gonorrhoea, HSV-2, trichomoniasis, and BV. In regions where HIV is prevalent and STIs are managed syndromically, better STI/BV screening is urgently needed, as certain infections were found to be highly inflammatory.

Generally, individuals assigned female at birth (AFAB) develop greater immunogenicity to various vaccines than individuals assigned male at birth (AMAB). Little is known about sex-disaggregated immunogenicity to HIV-1 vaccines. We disaggregated immune responses to an experimental HIV vaccine regimen. We retrospectively analyzed data from HVTN 100, a clinical trial conducted in South Africa during which 143 adults AMAB and 109 AFAB aged 18-40 years without HIV received ALVAC-HIV vCP2438 plus bivalent subtype C gp120/MF59 or placebo at 0, 1, 3, 6, and 12 months. Eligible data were from per-protocol vaccine recipients at month 6.5. We measured IgG binding antibodies, neutralizing antibodies, antibody-dependent cell-mediated cytotoxicity (ADCC), antibody-dependent cellular phagocytosis (ADCP), and CD4+ IFNγ and/or II-2 responses. We compared sex-based differences in response rates using Barnard's test and response magnitudes using Wilcoxon Rank Sum test. P-values were Holm-adjusted for multiple comparisons. Of 185 vaccine recipients, 73 were AFAB and 112 were AMAB. Vaccine recipients AFAB had greater ADCC response rate (57.5% versus 29.5%; = 0.0003) and greater ADCC magnitude (area under the net % granzyme B activity vs log10 curve (AUC), 16.1 versus 11.2; = 0.05) to vaccine-matched antigen TV1.C gp120 compared to AMAB. Vaccine recipients AMAB had higher CD4+ T cell response rates to 2/3 vaccine-matched antigens at month 6.5 (ZM96.C gp120, [54.1% versus 36.8%; = 0.04]; 1086.C gp120, [44.1% versus 29.4%; = 0.05]) than AFAB. CD4+ T cell response magnitudes were similar by sex. IgG binding antibody response rate to B.CaseA V1V2 antigen (associated with reduced HIV acquisition risk in the RV144 trial) was 56.8% among AMAB vaccine recipients versus 38.9% among AFAB ( = 0.08). There were no sex-based differences in neutralizing antibody or ADCP responses. We identified sex-based differences in immune responses to an HIV vaccine regimen, but they varied by immunologic assay. While vaccine recipients AFAB demonstrated higher ADCC responses, AMAB exhibited higher CD4+ T cell response rates. Future analyses should investigate whether vaccine factors such as platform, dosing and adjuvants contribute to sex-based differences in immunogenicity of experimental HIV vaccines.

The Antibody Mediated Prevention (AMP) trials (NCT02716675 and NCT02568215) demonstrated that passive administration of the broadly neutralizing monoclonal antibody VRC01 could prevent some HIV-1 acquisition events. Here, we use mathematical modeling in a post hoc analysis to demonstrate that VRC01 influenced viral loads in AMP participants who acquired HIV. Instantaneous inhibitory potential (IIP), which integrates VRC01 serum concentration and VRC01 sensitivity of acquired viruses in terms of both IC50 and IC80, follows a dose-response relationship with first positive viral load ( p  = 0.03), which is particularly strong above a threshold of IIP = 1.6 ( r  = -0.6, p  = 2e-4). Mathematical modeling reveals that VRC01 activity predicted from in vitro IC80s and serum VRC01 concentrations overestimates in vivo neutralization by 600-fold (95% CI: 300–1200). The trained model projects that even if future therapeutic HIV trials of combination monoclonal antibodies do not always prevent acquisition, reductions in viremia and reservoir size could be expected. Antibody Mediated Prevention (AMP) trials showed that the broadly neutralizing antibody VRC01 could prevent some HIV-1 acquisitions. Here the authors use VRC01 levels and the sensitivity of each acquired HIV virus to predict viral loads in the AMP studies and show that VRC01 influenced viral loads, though potency was lower in vivo than expected.