Coordinated Fc-effector and neutralization functions in HIV-infected children define a window of opportunity for HIV vaccination

Influenza antibody breadth and effector functions are immune correlates from acquisition of pandemic infection of children

Cross-reactive antibodies with Fc receptor (FcR) effector functions may mitigate pandemic virus impact in the absence of neutralizing antibodies. In this exploratory study, we use serum from a randomized placebo-controlled trial of seasonal trivalent influenza vaccination in children (NCT00792051) conducted at the onset of the 2009 H1N1 pandemic (pH1N1) and monitored for infection. We found that seasonal vaccination increases pH1N1 specific antibodies and FcR effector functions. Furthermore, prospective baseline antibody profiles after seasonal vaccination, prior to pH1N1 infection, show that unvaccinated uninfected children have elevated ADCC effector function, FcγR3a and FcγR2a binding antibodies to multiple pH1N1 proteins, past seasonal and avian (H5, H7 and H9) strains. Whereas, children that became pH1N1 infected after seasonal vaccination have antibodies focussed to seasonal strains without FcR functions, and greater aggregated HA-specific profiles for IgM and IgG3. Modeling to predict infection susceptibility, ranked baseline hemagglutination antibody inhibition as the highest contributor to lack of pH1N1 infection, in combination with features that include pH1-IgG1, H1-stem responses and FcR binding to seasonal vaccine and pH1 proteins. Thus, seasonal vaccination can have benefits against pandemic influenza viruses, and some children already have broadly reactive antibodies with Fc potential without vaccination and may be considered 'elite influenza controllers'.

Characterization of antibody-dependent cellular phagocytosis in patients infected with hepatitis C virus with different clinical outcomes

Early neutralizing antibodies against hepatitis C virus (HCV) and CD8 + T cell effector responses can lead to viral clearance. However, these functions alone are not sufficient to protect patients against HCV infection, thus undefined additional antiviral immune mechanisms are required. In recent years, Fc-receptor-dependent antibody effector functions, particularly, antibody-dependent cellular phagocytosis (ADCP) were shown to offer immune protection against several RNA viruses. However, its development and clinical role in patients with HCV infection remain unknown. In this study, we found that patients with chronic GT1a or GT3a HCV infection had significantly higher concentrations of anti-envelope 2 (E2) antibodies, predominantly IgG1 subclass, than patients that cleared the viruses while the latter had antibodies with higher affinities. 97% of the patients with HCV had measurable ADCP of whom patients with chronic disease showed significantly higher ADCP than those who naturally cleared the virus. Epitope mapping studies showed that patients with antibodies that target antigenic domains on the HCV E2 protein that are known to associate with neutralization function are also strongly associated with ADCP, suggesting antibodies with overlapping/dual functions. Correlation studies showed that ADCP significantly correlated with plasma anti-E2 antibody levels and neutralization function regardless of clinical outcome and genotype of infecting virus, while a significant correlation between ADCP and affinity was only evident in patients that cleared the virus. These results suggest ADCP was mostly driven by antibody titer in patients with chronic disease while maintained in clearers due to the quality (affinity) of their anti-E2 antibodies despite having lower antibody titers.

Polyfunctional antibodies: a path towards precision vaccines for vulnerable populations

Vaccine efficacy determined within the controlled environment of a clinical trial is usually substantially greater than real-world vaccine effectiveness. Typically, this results from reduced protection of immunologically vulnerable populations, such as children, elderly individuals and people with chronic comorbidities. Consequently, these high-risk groups are frequently recommended tailored immunisation schedules to boost responses. In addition, diverse groups of healthy adults may also be variably protected by the same vaccine regimen. Current population-based vaccination strategies that consider basic clinical parameters offer a glimpse into what may be achievable if more nuanced aspects of the immune response are considered in vaccine design. To date, vaccine development has been largely empirical. However, next-generation approaches require more rational strategies. We foresee a generation of precision vaccines that consider the mechanistic basis of vaccine response variations associated with both immunogenetic and baseline health differences. Recent efforts have highlighted the importance of balanced and diverse extra-neutralising antibody functions for vaccine-induced protection. However, in immunologically vulnerable populations, significant modulation of polyfunctional antibody responses that mediate both neutralisation and effector functions has been observed. Here, we review the current understanding of key genetic and inflammatory modulators of antibody polyfunctionality that affect vaccination outcomes and consider how this knowledge may be harnessed to tailor vaccine design for improved public health.

Strategies for HIV-1 vaccines that induce broadly neutralizing antibodies

After nearly four decades of research, a safe and effective HIV-1 vaccine remains elusive. There are many reasons why the development of a potent and durable HIV-1 vaccine is challenging, including the extraordinary genetic diversity of HIV-1 and its complex mechanisms of immune evasion. HIV-1 envelope glycoproteins are poorly recognized by the immune system, which means that potent broadly neutralizing antibodies (bnAbs) are only infrequently induced in the setting of HIV-1 infection or through vaccination. Thus, the biology of HIV-1-host interactions necessitates novel strategies for vaccine development to be designed to activate and expand rare bnAb-producing B cell lineages and to select for the acquisition of critical improbable bnAb mutations. Here we discuss strategies for the induction of potent and broad HIV-1 bnAbs and outline the steps that may be necessary for ultimate success.

Complementary Roles of Antibody Heavy and Light Chain Somatic Hypermutation in Conferring Breadth and Potency to the HIV-1-Specific CAP256-VRC26 bNAb Lineage

Some HIV-infected people develop broadly neutralizing antibodies (bNAbs) that block many diverse, unrelated strains of HIV from infecting target cells and, through passive immunization, protect animals and humans from infection. Therefore, understanding the development of bNAbs and their neutralization can inform the design of an HIV vaccine. Here, we extend our previous studies of the ontogeny of the CAP256-VRC26 V2-targeting bNAb lineage by defining the mutations that confer neutralization to the unmutated common ancestor (CAP256.UCA). Analysis of the sequence of the CAP256.UCA showed that many improbable mutations were located in the third complementarity-determining region of the heavy chain (CDRH3) and the heavy chain framework 3 (FR3). Transferring the CDRH3 from bNAb CAP256.25 (63% breadth and 0.003 μg/mL potency) into the CAP256.UCA introduced breadth and the ability to neutralize emerging viral variants. In addition, we showed that the framework and light chain contributed to potency and that the second CDR of the light chain forms part of the paratope of CAP256.25. Notably, a minimally mutated CAP256 antibody, with 41% of the mutations compared to bNAb CAP256.25, was broader (64% breadth) and more potent (0.39 μg/mL geometric potency) than many unrelated bNAbs. Together, we have identified key regions and mutations that confer breadth and potency in a V2-specific bNAb lineage. These data indicate that immunogens that target affinity maturation to key sites in CAP256-VRC26-like precursors, including the CDRHs and light chain, could rapidly elicit breadth through vaccination. IMPORTANCE A major focus in the search for an HIV vaccine is elucidating the ontogeny of broadly neutralizing antibodies (bNAbs), which prevent HIV infection in vitro and in vivo. The unmutated common ancestors (UCAs) of bNAbs are generally strain specific and acquire breadth through extensive, and sometimes redundant, somatic hypermutation during affinity maturation. We investigated which mutations in the CAP256-VRC26 bNAb lineage conferred neutralization capacity to the UCA. We found that mutations in the antibody heavy and light chains had complementary roles in neutralization breadth and potency, respectively. The heavy chain, particularly the third complementarity-determining region, was responsible for conferring breadth. In addition, previously uninvestigated mutations in the framework also contributed to breadth. Together, approximately half of the mutations in CAP256.25 were necessary for broader and more potent neutralization than many unrelated neutralizing antibodies. Vaccine approaches that promote affinity maturation at key sites could therefore more rapidly produce antibodies with neutralization breadth.