Diverse array of neutralizing antibodies elicited upon Spike Ferritin Nanoparticle vaccination in rhesus macaques.

The repeat emergence of SARS-CoV-2 variants of concern (VoC) with decreased susceptibility to vaccine-elicited antibodies highlights the need to develop next-generation vaccine candidates that confer broad protection. Here we describe the antibody response induced by the SARS-CoV-2 Spike Ferritin Nanoparticle (SpFN) vaccine candidate adjuvanted with the Army Liposomal Formulation including QS21 (ALFQ) in non-human primates. By isolating and characterizing several monoclonal antibodies directed against the Spike Receptor Binding Domain (RBD), N-Terminal Domain (NTD), or the S2 Domain, we define the molecular recognition of vaccine-elicited cross-reactive monoclonal antibodies (mAbs) elicited by SpFN. We identify six neutralizing antibodies with broad sarbecovirus cross-reactivity that recapitulate serum polyclonal antibody responses. In particular, RBD mAb WRAIR-5001 binds to the conserved cryptic region with high affinity to sarbecovirus clades 1 and 2, including Omicron variants, while mAb WRAIR-5021 offers complete protection from B.1.617.2 (Delta) in a murine challenge study. Our data further highlight the ability of SpFN vaccination to stimulate cross-reactive B cells targeting conserved regions of the Spike with activity against SARS CoV-1 and SARS-CoV-2 variants.

Antibody targeting of conserved sites of vulnerability on the SARS-CoV-2 spike receptor-binding domain.

Given the continuous emergence of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) variants of concern (VoCs), immunotherapeutics that target conserved epitopes on the spike (S) glycoprotein have therapeutic advantages. Here, we report the crystal structure of the SARS-CoV-2 S receptor-binding domain (RBD) at 1.95 Å and describe flexibility and distinct conformations of the angiotensin-converting enzyme 2 (ACE2)-binding site. We identify a set of SARS-CoV-2-reactive monoclonal antibodies (mAbs) with broad RBD cross-reactivity including SARS-CoV-2 Omicron subvariants, SARS-CoV-1, and other sarbecoviruses and determine the crystal structures of mAb-RBD complexes with Ab246 and CR3022 mAbs targeting the class IV site, WRAIR-2134, which binds the recently designated class V epitope, and WRAIR-2123, the class I ACE2-binding site. The broad reactivity of class IV and V mAbs to conserved regions of SARS-CoV-2 VoCs and other sarbecovirus provides a framework for long-term immunotherapeutic development strategies.

Zika-specific neutralizing antibodies targeting inter-dimer envelope epitopes.

Zika virus (ZIKV) is an emerging pathogen that causes devastating congenital defects. The overlapping epidemiology and immunologic cross-reactivity between ZIKV and dengue virus (DENV) pose complex challenges to vaccine design, given the potential for antibody-dependent enhancement of disease. Therefore, classification of ZIKV-specific antibody targets is of notable value. From a ZIKV-infected rhesus macaque, we identify ZIKV-reactive B cells and isolate potent neutralizing monoclonal antibodies (mAbs) with no cross-reactivity to DENV. We group these mAbs into four distinct antigenic groups targeting ZIKV-specific cross-protomer epitopes on the envelope glycoprotein. Co-crystal structures of representative mAbs in complex with ZIKV envelope glycoprotein reveal envelope-dimer epitope and unique dimer-dimer epitope targeting. All four specificities are serologically identified in convalescent humans following ZIKV infection, and representative mAbs from all four groups protect against ZIKV replication in mice. These results provide key insights into ZIKV-specific antigenicity and have implications for ZIKV vaccine, diagnostic, and therapeutic development.

Convalescent human IgG, but not IgM, from COVID-19 survivors confers dose-dependent protection against SARS-CoV-2 replication and disease in hamsters.

Introduction: Antibody therapeutic strategies have served an important role during the COVID-19 pandemic, even as their effectiveness has waned with the emergence of escape variants. Here we sought to determine the concentration of convalescent immunoglobulin required to protect against disease from SARS-CoV-2 in a Syrian golden hamster model. Methods: Total IgG and IgM were isolated from plasma of SARS-CoV-2 convalescent donors. Dose titrations of IgG and IgM were infused into hamsters 1 day prior to challenge with SARS-CoV-2 Wuhan-1. Results: The IgM preparation was found to have ~25-fold greater neutralization potency than IgG. IgG infusion protected hamsters from disease in a dose-dependent manner, with detectable serum neutralizing titers correlating with protection. Despite a higher in vitro neutralizing potency, IgM failed to protect against disease when transferred into hamsters. Discussion: This study adds to the growing body of literature that demonstrates neutralizing IgG antibodies are important for protection from SARS-CoV-2 disease, and confirms that polyclonal IgG in sera can be an effective preventative strategy if the neutralizing titers are sufficiently high. In the context of new variants, against which existing vaccines or monoclonal antibodies have reduced efficacy, sera from individuals who have recovered from infection with the emerging variant may potentially remain an efficacious tool.

Fc receptor engagement of HIV-1 Env-specific antibodies in mothers and infants predicts reduced vertical transmission.

Introduction: Infants acquire maternal antibodies by Fc receptor transcytosis across the placenta during pregnancy. Fc receptors are expressed on immune cells and are important for activation of effector cell functions. Methods: In this study, we evaluated Fc receptor engagement and ADCC activity of plasma binding antibodies from human immunodeficiency virus-1 (HIV) -infected mothers and to identify factors that may contribute to protection from HIV vertical transmission. Results: HIV-specific binding and Fc receptor engagement of plasma antibodies varied between mothers by transmission status and infants by infection status. Non-transmitting (NT) mothers and HIV-uninfected infants had antibodies with higher neonatal Fc receptor (FcRn) and FcγR engagement, as compared to transmitting (T) mothers and HIV+ infants, respectively. A significant inverse correlation between plasma antibody FcRn and FcγR engagement was observed for T mothers, but not NT mothers. Conversely, a significant direct correlation was observed between plasma antibody FcRn and FcγR engagement for HIV- infants, but not for HIV+ infants. Consequently, we observed significantly higher plasma antibody ADCC potency and breadth in HIV- infants, as compared to HIV+ infants. However, no differences in overall ADCC potency and breadth were observed between mothers. FcRn-engagement of HIV-specific antibodies in both mothers and infants predicted a lack of vertical transmission of HIV. Discussion: This study indicates that HIV-uninfected infants acquire HIV-specific antibodies with greater Fc receptor engagement and thus, greater ADCC capacity.

SARS-CoV-2 ferritin nanoparticle vaccines elicit broad SARS coronavirus immunogenicity.

The need for severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) next-generation vaccines has been highlighted by the rise of variants of concern (VoCs) and the long-term threat of emerging coronaviruses. Here, we design and characterize four categories of engineered nanoparticle immunogens that recapitulate the structural and antigenic properties of the prefusion SARS-CoV-2 spike (S), S1, and receptor-binding domain (RBD). These immunogens induce robust S binding, ACE2 inhibition, and authentic and pseudovirus neutralizing antibodies against SARS-CoV-2. A spike-ferritin nanoparticle (SpFN) vaccine elicits neutralizing titers (ID50 > 10,000) following a single immunization, whereas RBD-ferritin nanoparticle (RFN) immunogens elicit similar responses after two immunizations and also show durable and potent neutralization against circulating VoCs. Passive transfer of immunoglobulin G (IgG) purified from SpFN- or RFN-immunized mice protects K18-hACE2 transgenic mice from a lethal SARS-CoV-2 challenge. Furthermore, S-domain nanoparticle immunization elicits ACE2-blocking activity and ID50 neutralizing antibody titers >2,000 against SARS-CoV-1, highlighting the broad response elicited by these immunogens.

Low-dose in vivo protection and neutralization across SARS-CoV-2 variants by monoclonal antibody combinations.

Prevention of viral escape and increased coverage against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) variants of concern require therapeutic monoclonal antibodies (mAbs) targeting multiple sites of vulnerability on the coronavirus spike glycoprotein. Here we identify several potent neutralizing antibodies directed against either the N-terminal domain (NTD) or the receptor-binding domain (RBD) of the spike protein. Administered in combinations, these mAbs provided low-dose protection against SARS-CoV-2 infection in the K18-human angiotensin-converting enzyme 2 mouse model, using both neutralization and Fc effector antibody functions. The RBD mAb WRAIR-2125, which targets residue F486 through a unique heavy-chain and light-chain pairing, demonstrated potent neutralizing activity against all major SARS-CoV-2 variants of concern. In combination with NTD and other RBD mAbs, WRAIR-2125 also prevented viral escape. These data demonstrate that NTD/RBD mAb combinations confer potent protection, likely leveraging complementary mechanisms of viral inactivation and clearance.

RV144 vaccine imprinting constrained HIV-1 evolution following breakthrough infection.

The scale of the HIV-1 epidemic underscores the need for a vaccine. The multitude of circulating HIV-1 strains together with HIV-1's high evolvability hints that HIV-1 could adapt to a future vaccine. Here, we wanted to investigate the effect of vaccination on the evolution of the virus post-breakthrough infection. We analyzed 2,635 HIV-1 env sequences sampled up to a year post-diagnosis from 110 vaccine and placebo participants who became infected in the RV144 vaccine efficacy trial. We showed that the Env signature sites that were previously identified to distinguish vaccine and placebo participants were maintained over time. In addition, fewer sites were under diversifying selection in the vaccine group than in the placebo group. These results indicate that HIV-1 would possibly adapt to a vaccine upon its roll-out.

SARS-CoV-2 ferritin nanoparticle vaccines elicit broad SARS coronavirus immunogenicity.

The need for SARS-CoV-2 next-generation vaccines has been highlighted by the rise of variants of concern (VoC) and the long-term threat of other coronaviruses. Here, we designed and characterized four categories of engineered nanoparticle immunogens that recapitulate the structural and antigenic properties of prefusion Spike (S), S1 and RBD. These immunogens induced robust S-binding, ACE2-inhibition, and authentic and pseudovirus neutralizing antibodies against SARS-CoV-2 in mice. A Spike-ferritin nanoparticle (SpFN) vaccine elicited neutralizing titers more than 20-fold higher than convalescent donor serum, following a single immunization, while RBD-Ferritin nanoparticle (RFN) immunogens elicited similar responses after two immunizations. Passive transfer of IgG purified from SpFN- or RFN-immunized mice protected K18-hACE2 transgenic mice from a lethal SARS-CoV-2 virus challenge. Furthermore, SpFN- and RFN-immunization elicited ACE2 blocking activity and neutralizing ID50 antibody titers >2,000 against SARS-CoV-1, along with high magnitude neutralizing titers against major VoC. These results provide design strategies for pan-coronavirus vaccine development. HIGHLIGHTS: Iterative structure-based design of four Spike-domain Ferritin nanoparticle classes of immunogensSpFN-ALFQ and RFN-ALFQ immunization elicits potent neutralizing activity against SARS-CoV-2, variants of concern, and SARS-CoV-1Passively transferred IgG from immunized C57BL/6 mice protects K18-hACE2 mice from lethal SARS-CoV-2 challenge.

B cell engagement with HIV-1 founder virus envelope predicts development of broadly neutralizing antibodies.

Determining which immunological mechanisms contribute to the development of broad neutralizing antibodies (bNAbs) during HIV-1 infection is a major goal to inform vaccine design. Using samples from a longitudinal HIV-1 acute infection cohort, we found key B cell determinants within the first 14-43 days of viremia that predict the development of bNAbs years later. Individuals who develop neutralization breadth had significantly higher B cell engagement with the autologous founder HIV envelope (Env) within 1 month of initial viremia. A higher frequency of founder-Env-specific naive B cells was associated with increased B cell activation and differentiation and predictive of bNAb development. These data demonstrate that the initial B cell interaction with the founder HIV Env is important for the development of broadly neutralizing antibodies and provide evidence that events within HIV acute infection lead to downstream functional outcomes.

Correction: RV144 HIV-1 vaccination impacts post-infection antibody responses.

[This corrects the article DOI: 10.1371/journal.ppat.1009101.].

RV144 HIV-1 vaccination impacts post-infection antibody responses.

The RV144 vaccine efficacy clinical trial showed a reduction in HIV-1 infections by 31%. Vaccine efficacy was associated with stronger binding antibody responses to the HIV Envelope (Env) V1V2 region, with decreased efficacy as responses wane. High levels of Ab-dependent cellular cytotoxicity (ADCC) together with low plasma levels of Env-specific IgA also correlated with decreased infection risk. We investigated whether B cell priming from RV144 vaccination impacted functional antibody responses to HIV-1 following infection. Antibody responses were assessed in 37 vaccine and 63 placebo recipients at 6, 12, and 36 months following HIV diagnosis. The magnitude, specificity, dynamics, subclass recognition and distribution of the binding antibody response following infection were different in RV144 vaccine recipients compared to placebo recipients. Vaccine recipients demonstrated increased IgG1 binding specifically to V1V2, as well as increased IgG2 and IgG4 but decreased IgG3 to HIV-1 Env. No difference in IgA binding to HIV-1 Env was detected between the vaccine and placebo recipients following infection. RV144 vaccination limited the development of broadly neutralizing antibodies post-infection, but enhanced Fc-mediated effector functions indicating B cell priming by RV144 vaccination impacted downstream antibody function. However, these functional responses were not associated with clinical markers of disease progression. These data reveal that RV144 vaccination primed B cells towards specific binding and functional antibody responses following HIV-1 infection.

Potent Zika and dengue cross-neutralizing antibodies induced by Zika vaccination in a dengue-experienced donor.

Zika virus (ZIKV) has caused significant disease, with widespread cases of neurological pathology and congenital neurologic defects. Rapid vaccine development has led to a number of candidates capable of eliciting potent ZIKV-neutralizing antibodies (reviewed in refs. 1-3). Despite advances in vaccine development, it remains unclear how ZIKV vaccination affects immune responses in humans with prior flavivirus immunity. Here we show that a single-dose immunization of ZIKV purified inactivated vaccine (ZPIV)4-7 in a dengue virus (DENV)-experienced human elicited potent cross-neutralizing antibodies to both ZIKV and DENV. Using a unique ZIKV virion-based sorting strategy, we isolated and characterized multiple antibodies, including one termed MZ4, which targets a novel site of vulnerability centered on the Envelope (E) domain I/III linker region and protects mice from viremia and viral dissemination following ZIKV or DENV-2 challenge. These data demonstrate that Zika vaccination in a DENV-experienced individual can boost pre-existing flavivirus immunity and elicit protective responses against both ZIKV and DENV. ZPIV vaccination in Puerto Rican individuals with prior flavivirus experience yielded similar cross-neutralizing potency after a single vaccination, highlighting the potential benefit of ZIKV vaccination in flavivirus-endemic areas.