Two-component spike nanoparticle vaccine protects macaques from SARS-CoV-2 infection.

The severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) pandemic is continuing to disrupt personal lives, global healthcare systems, and economies. Hence, there is an urgent need for a vaccine that prevents viral infection, transmission, and disease. Here, we present a two-component protein-based nanoparticle vaccine that displays multiple copies of the SARS-CoV-2 spike protein. Immunization studies show that this vaccine induces potent neutralizing antibody responses in mice, rabbits, and cynomolgus macaques. The vaccine-induced immunity protects macaques against a high-dose challenge, resulting in strongly reduced viral infection and replication in the upper and lower airways. These nanoparticles are a promising vaccine candidate to curtail the SARS-CoV-2 pandemic.

Antigenic cartography using sera from sequence-confirmed SARS-CoV-2 variants of concern infections reveals antigenic divergence of Omicron.

Large-scale vaccination campaigns have prevented countless hospitalizations and deaths due to COVID-19. However, the emergence of SARS-CoV-2 variants that escape from immunity challenges the effectiveness of current vaccines. Given this continuing evolution, an important question is when and how to update SARS-CoV-2 vaccines to antigenically match circulating variants, similarly to seasonal influenza viruses where antigenic drift necessitates periodic vaccine updates. Here, we studied SARS-CoV-2 antigenic drift by assessing neutralizing activity against variants of concern (VOCs) in a set of sera from patients infected with viral sequence-confirmed VOCs. Infections with D614G or Alpha strains induced the broadest immunity, whereas individuals infected with other VOCs had more strain-specific responses. Omicron BA.1 and BA.2 were substantially resistant to neutralization by sera elicited by all other variants. Antigenic cartography revealed that Omicron BA.1 and BA.2 were antigenically most distinct from D614G, associated with immune escape, and possibly will require vaccine updates to ensure vaccine effectiveness.

Immunogenicity of Stabilized HIV-1 Envelope Trimers with Reduced Exposure of Non-neutralizing Epitopes.

The envelope glycoprotein trimer mediates HIV-1 entry into cells. The trimer is flexible, fluctuating between closed and more open conformations and sometimes sampling the fully open, CD4-bound form. We hypothesized that conformational flexibility and transient exposure of non-neutralizing, immunodominant epitopes could hinder the induction of broadly neutralizing antibodies (bNAbs). We therefore modified soluble Env trimers to stabilize their closed, ground states. The trimer variants were indeed stabilized in the closed conformation, with a reduced ability to undergo receptor-induced conformational changes and a decreased exposure of non-neutralizing V3-directed antibody epitopes. In rabbits, the stabilized trimers induced similar autologous Tier-1B or Tier-2 NAb titers to those elicited by the corresponding wild-type trimers but lower levels of V3-directed Tier-1A NAbs. Stabilized, closed trimers might therefore be useful components of vaccines aimed at inducing bNAbs.

Potent Induction of Envelope-Specific Antibody Responses by Virus-Like Particle Immunogens Based on HIV-1 Envelopes from Patients with Early Broadly Neutralizing Responses.

Longitudinal studies in HIV-1-infected individuals have indicated that 2 to 3 years of infection are required to develop broadly neutralizing antibodies. However, we have previously identified individuals with broadly neutralizing activity (bNA) in early HIV-1 infection, indicating that a vaccine may be capable of bNA induction after short periods of antigen exposure. Here, we describe 5 HIV-1 envelope sequences from individuals who have developed bNA within the first 100 days of infection (early neutralizers) and selected two of them to design immunogens based on HIV-1-Gag virus-like particles (VLPs). These VLPs were homogeneous and incorporated the corresponding envelopes (7 to 9 µg of gp120 in 1010 VLPs). Both envelopes (Envs) bound to well-characterized broadly neutralizing antibodies (bNAbs), including trimer-specific antibodies (PGT145, VRC01, and 35022). For immunogenicity testing, we immunized rabbits with the Env-VLPs or with the corresponding stabilized soluble envelope trimers. A short immunization protocol (105 days) was used to recapitulate the early nAb induction observed after HIV-1 infection in these two individuals. All VLP and trimeric envelope immunogens induced a comparably strong anti-gp120 response despite having immunized rabbits with 30 times less gp120 in the case of the Env-VLPs. In addition, animals immunized with VLP-formulated Envs induced antibodies that cross-recognized the corresponding soluble stabilized trimer and vice versa, even though no neutralizing activity was observed. Nevertheless, our data may provide a new platform of immunogens, based on HIV-1 envelopes from patients with early broadly neutralizing responses, with the potential to generate protective immune responses using vaccination protocols similar to those used in classical preventive vaccines. IMPORTANCE It is generally accepted that an effective HIV-1 vaccine should be able to induce broad-spectrum neutralizing antibodies. Since most of these antibodies require long periods of somatic maturation in vivo, several groups are developing immunogens, based on the HIV envelope protein, that require complex and lengthy immunization protocols that would be difficult to implement in the general population. Here, we show that rabbits immunized with new envelopes (VLP formulated) from two individuals who demonstrated broadly neutralizing activity very early after infection induced specific HIV-1 antibodies after a short immunization protocol. This evidence provides the basis for generating protective immune responses with classic vaccination protocols with vaccine prototypes based on HIV envelope sequences from individuals who have developed early broadly neutralizing responses.

Antibody responses against SARS-CoV-2 variants induced by four different SARS-CoV-2 vaccines in health care workers in the Netherlands: A prospective cohort study.

BACKGROUND: Emerging and future SARS-CoV-2 variants may jeopardize the effectiveness of vaccination campaigns. Therefore, it is important to know how the different vaccines perform against diverse SARS-CoV-2 variants. METHODS AND FINDINGS: In a prospective cohort of 165 SARS-CoV-2 naive health care workers in the Netherlands, vaccinated with either one of four vaccines (BNT162b2, mRNA-1273, AZD1222 or Ad26.COV2.S), we performed a head-to-head comparison of the ability of sera to recognize and neutralize SARS-CoV-2 variants of concern (VOCs; Alpha, Beta, Gamma, Delta and Omicron). Repeated serum sampling was performed 5 times during a year (from January 2021 till January 2022), including before and after booster vaccination with BNT162b2. Four weeks after completing the initial vaccination series, SARS-CoV-2 wild-type neutralizing antibody titers were highest in recipients of mRNA-1273, followed by recipients of BNT162b2 (geometric mean titers (GMT) of 358 [95% CI 231-556] and 214 [95% CI 153-299], respectively; p<0.05), and substantially lower in those vaccinated with the adenovirus vector-based vaccines AZD1222 and Ad26.COV2.S (GMT of 18 [95% CI 11-30] and 14 [95% CI 8-25] IU/ml, respectively; p<0.001). VOCs neutralization was reduced in all vaccine groups, with the greatest reduction in neutralization GMT observed against the Omicron variant (fold change 0.03 [95% CI 0.02-0.04], p<0.001). The booster BNT162b2 vaccination increased neutralizing antibody titers for all groups with substantial improvement against the VOCs including the Omicron variant. We used linear regression and linear mixed model analysis. All results were adjusted for possible confounding of age and sex. Study limitations include the lack of cellular immunity data. CONCLUSIONS: Overall, this study shows that the mRNA vaccines appear superior to adenovirus vector-based vaccines in inducing neutralizing antibodies against VOCs four weeks after initial vaccination and after booster vaccination, which implies the use of mRNA vaccines for both initial and booster vaccination.

Convergent HIV-1 Evolution upon Targeted Destabilization of the gp120-gp41 Interface.

The HIV-1 envelope glycoprotein (Env) trimer is responsible for viral entry into target cells and is the sole target of neutralizing antibodies. The Env protein is therefore the focus of HIV-1 vaccine design. Env consists of two noncovalently linked subunits (gp120 and gp41) that form a trimer of heterodimers and this 6-subunit complex is metastable and conformationally flexible. Several approaches have been pursued to stabilize the Env trimer for vaccine purposes, which include structure-based design, high-throughput screening, and selection by mammalian cell display. Here, we employed directed virus evolution to improve Env trimer stability. Accordingly, we deliberately destabilized the Env gp120-gp41 interface by mutagenesis in the context of replicating HIV-1 LAI virus and virus evolution over time. We identified compensatory changes that pointed at convergent evolution, as they were largely restricted to specific Env regions, namely, the V1V2 domain of gp120 and the HR1 and HR2 domain of gp41. Specifically, S614G in V1V2 and Q567R in HR1 were frequently identified. Interestingly, the majority of the compensatory mutations were at distant locations from the original mutations and most likely strengthen intersubunit interactions. These results show how the virus can overcome Env instability and illuminate the regions that play a dominant role in Env stability. IMPORTANCE A successful HIV-1 vaccine most likely requires an envelope glycoprotein (Env) component, as Env is the only viral protein on the surface of the virus and the target for neutralizing antibodies. However, HIV Env is metastable and flexible because of the weak interactions between the Env subunits, complicating the generation of recombinant mimics of native Env. Here, we used directed viral evolution to study Env stability. We deliberately destabilized the interface between Env subunits and explored the capacity of the virus to repair trimer instability by evolution. We identified compensatory mutations that converged in specific Env locations: the apex and the trimer interface. Selected mutations enhanced the stability of recombinant soluble Env trimer proteins. These results provided clues on understanding the structural mechanisms involved in Env trimer stability, which can guide future immunogen design.

Structural and functional evaluation of de novo-designed, two-component nanoparticle carriers for HIV Env trimer immunogens.

Two-component, self-assembling nanoparticles represent a versatile platform for multivalent presentation of viral antigens. Computational design of protein nanoparticles with differing sizes and geometries enables combination with antigens of choice to test novel multimerization concepts in immunization strategies where the goal is to improve the induction and maturation of neutralizing antibody lineages. Here, we describe detailed antigenic, structural, and functional characterization of computationally designed tetrahedral, octahedral, and icosahedral nanoparticle immunogens displaying trimeric HIV envelope glycoprotein (Env) ectodomains. Env trimers, based on subtype A (BG505) or consensus group M (ConM) sequences and engineered with SOSIP stabilizing mutations, were fused to an underlying trimeric building block of each nanoparticle. Initial screening yielded one icosahedral and two tetrahedral nanoparticle candidates, capable of presenting twenty or four copies of the Env trimer. A number of analyses, including detailed structural characterization by cryo-EM, demonstrated that the nanoparticle immunogens possessed the intended structural and antigenic properties. When the immunogenicity of ConM-SOSIP trimers presented on a two-component tetrahedral nanoparticle or as soluble proteins were compared in rabbits, the two immunogens elicited similar serum antibody binding titers against the trimer component. Neutralizing antibody titers were slightly elevated in the animals given the nanoparticle immunogen and were initially more focused to the trimer apex. Altogether, our findings indicate that tetrahedral nanoparticles can be successfully applied for presentation of HIV Env trimer immunogens; however, the optimal implementation to different immunization strategies remains to be determined.

Neutralizing Antibody Responses Induced by HIV-1 Envelope Glycoprotein SOSIP Trimers Derived from Elite Neutralizers.

The induction of broadly neutralizing antibodies (bNAbs) is a major goal in vaccine research. HIV-1-infected individuals that develop exceptionally strong bNAb responses, termed elite neutralizers, can inform vaccine design by providing blueprints for the induction of similar bNAb responses. We describe a new recombinant native-like envelope glycoprotein (Env) SOSIP trimer, termed AMC009, based on the viral founder sequences of an elite neutralizer. The subtype B AMC009 SOSIP protein formed stable native-like trimers that displayed multiple bNAb epitopes. Overall, its structure at 4.3-Å resolution was similar to that of BG505 SOSIP.664. The AMC009 trimer resembled one from a second elite neutralizer, AMC011, in having a dense and complete glycan shield. When tested as immunogens in rabbits, the AMC009 trimers did not induce autologous neutralizing antibody (NAb) responses efficiently while the AMC011 trimers did so very weakly, outcomes that may reflect the completeness of their glycan shields. The AMC011 trimer induced antibodies that occasionally cross-neutralized heterologous tier 2 viruses, sometimes at high titer. Cross-neutralizing antibodies were more frequently elicited by a trivalent combination of AMC008, AMC009, and AMC011 trimers, all derived from subtype B viruses. Each of these three individual trimers could deplete the NAb activity from the rabbit sera. Mapping the polyclonal sera by electron microscopy revealed that antibodies of multiple specificities could bind to sites on both autologous and heterologous trimers. These results advance our understanding of how to use Env trimers in multivalent vaccination regimens and the immunogenicity of trimers derived from elite neutralizers.IMPORTANCE Elite neutralizers, i.e., individuals who developed unusually broad and potent neutralizing antibody responses, might serve as blueprints for HIV-1 vaccine design. Here, we studied the immunogenicity of native-like recombinant envelope glycoprotein (Env) trimers based on viral sequences from elite neutralizers. While immunization with single trimers from elite neutralization did not recapitulate the breadth and potency of neutralization observed in these infected individuals, a combination of three subtype B Env trimers from elite neutralizers resulted in some neutralization breadth within subtype B viruses. These results should guide future efforts to design vaccines to induce broadly neutralizing antibodies.

HIV-1 anchor inhibitors and membrane fusion inhibitors target distinct but overlapping steps in virus entry.

HIV-1 entry into cells is mediated by the envelope glycoprotein (Env) and represents an attractive target for therapeutic intervention. Two drugs that inhibit HIV entry are approved for clinical use: the membrane fusion-inhibitor T20 (Fuzeon, enfuvirtide) and the C-C chemokine receptor type 5 (CCR5) blocker maraviroc (Selzentry). Another class of entry inhibitors supposedly target the fusion peptide (FP) and are termed anchor inhibitors. These include the VIRIP peptide and VIRIP derivatives such as VIR165, VIR353, and VIR576. Here, we investigated the mechanism of inhibition by VIR165. We show that substitutions within the FP modulate sensitivity to VIR165, consistent with the FP being the drug target. Our results also revealed that VIR165 acts during an intermediate post-CD4-binding entry step that is overlapping but not identical to the step inhibited by fusion inhibitors such as T20. We found that some but not all resistance mutations to heptad repeat 2 (HR2)-targeting fusion inhibitors can provide cross-resistance to VIR165. In contrast, resistance mutations in the HR1-binding site for the fusion inhibitors did not cause cross-resistance to VIR165. However, Env with mutations located outside this binding site and thought to affect fusion kinetics, exhibited decreased sensitivity to VIR165. Although we found a strong correlation between Env stability and resistance to HR2-based fusion inhibitors, such correlation was not observed for Env stability and VIR165 resistance. We conclude that VIRIP analogs target the FP during an intermediate, post-CD4-binding entry step that overlaps with but is distinct from the step(s) inhibited by HR2-based fusion inhibitors.

HIV-1 Escape from a Peptidic Anchor Inhibitor through Stabilization of the Envelope Glycoprotein Spike.

The trimeric HIV-1 envelope glycoprotein spike (Env) mediates viral entry into cells by using a spring-loaded mechanism that allows for the controlled insertion of the Env fusion peptide into the target membrane, followed by membrane fusion. Env is the focus of vaccine research aimed at inducing protective immunity by antibodies as well as efforts to develop drugs that inhibit the viral entry process. The molecular factors contributing to Env stability and decay need to be understood better in order to optimally design vaccines and therapeutics. We generated viruses with resistance to VIR165, a peptidic inhibitor that binds the fusion peptide of the gp41 subunit and prevents its insertion into the target membrane. Interestingly, a number of escape viruses acquired substitutions in the C1 domain of the gp120 subunit (A60E, E64K, and H66R) that rendered these viruses dependent on the inhibitor. These viruses could infect target cells only when VIR165 was present after CD4 binding. Furthermore, the VIR165-dependent viruses were resistant to soluble CD4-induced Env destabilization and decay. These data suggest that VIR165-dependent Env proteins are kinetically trapped in the unliganded state and require the drug to negotiate CD4-induced conformational changes. These studies provide mechanistic insight into the action of the gp41 fusion peptide and its inhibitors and provide new ways to stabilize Env trimer vaccines. IMPORTANCE: Because of the rapid development of HIV-1 drug resistance, new drug targets need to be explored continuously. The fusion peptide of the envelope glycoprotein can be targeted by anchor inhibitors. Here we describe virus escape from the anchor inhibitor VIR165. Interestingly, some escape viruses became dependent on the inhibitor for cell entry. We show that the identified escape mutations stabilize the ground state of the envelope glycoprotein and should thus be useful in the design of stabilized envelope-based HIV vaccines.

Targeting HIV-1 envelope glycoprotein trimers to B cells by using APRIL improves antibody responses.

An HIV-1 vaccine remains elusive, in part because various factors limit the quantity and quality of the antibodies raised against the viral envelope glycoprotein complex (Env). We hypothesized that targeting Env vaccines directly to B cells, by fusing them to molecules that bind and activate these cells, would improve Env-specific antibody responses. Therefore, we fused trimeric Env gp140 to A PRoliferation-Inducing Ligand (APRIL), B-cell Activating Factor (BAFF), and CD40 Ligand (CD40L). The Env-APRIL, Env-BAFF, and Env-CD40L gp140 trimers all enhanced the expression of activation-induced cytidine deaminase (AID), the enzyme responsible for inducing somatic hypermutation, antibody affinity maturation, and antibody class switching. They also triggered IgM, IgG, and IgA secretion from human B cells in vitro. The Env-APRIL trimers induced higher anti-Env antibody responses in rabbits, including neutralizing antibodies against tier 1 viruses. The enhanced Env-specific responses were not associated with a general increase in total plasma antibody concentrations, indicating that the effect of APRIL was specific for Env. All the rabbit sera raised against gp140 trimers, irrespective of the presence of CD40L, BAFF, or APRIL, recognized trimeric Env efficiently, whereas sera raised against gp120 monomers did not. The levels of trimer-binding and virus-neutralizing antibodies were strongly correlated, suggesting that gp140 trimers are superior to gp120 monomers as immunogens. Targeting and activating B cells with a trimeric HIV-1 Env-APRIL fusion protein may therefore improve the induction of humoral immunity against HIV-1.

Bispecific antibodies combine breadth, potency, and avidity of parental antibodies to neutralize sarbecoviruses.

SARS-CoV-2 variants evade current monoclonal antibody therapies. Bispecific antibodies (bsAbs) combine the specificities of two distinct antibodies taking advantage of the avidity and synergy provided by targeting different epitopes. Here we used controlled Fab-arm exchange to produce bsAbs that neutralize SARS-CoV and SARS-CoV-2 variants, including Omicron and its subvariants, by combining potent SARS-CoV-2-specific neutralizing antibodies with broader antibodies that also neutralize SARS-CoV. We demonstrated that the parental antibodies rely on avidity for neutralization using bsAbs containing one irrelevant Fab arm. Using mass photometry to measure the formation of antibody:spike complexes, we determined that bsAbs increase binding stoichiometry compared to corresponding cocktails, without a loss of binding affinity. The heterogeneous binding pattern of bsAbs to spike, observed by negative-stain electron microscopy and mass photometry provided evidence for both intra- and inter-spike crosslinking. This study highlights the utility of cross-neutralizing antibodies for designing bivalent agents to combat circulating and future SARS-like coronaviruses.

Broad SARS-CoV-2 neutralization by monoclonal and bispecific antibodies derived from a Gamma-infected individual.

The pandemic caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has remained a medical threat due to the evolution of multiple variants that acquire resistance to vaccines and prior infection. Therefore, it is imperative to discover monoclonal antibodies (mAbs) that neutralize a broad range of SARS-CoV-2 variants. A stabilized spike glycoprotein was used to enrich antigen-specific B cells from an individual with a primary Gamma variant infection. Five mAbs selected from those B cells showed considerable neutralizing potency against multiple variants, with COVA309-35 being the most potent against the autologous virus, as well as Omicron BA.1 and BA.2, and COVA309-22 having binding and neutralization activity against Omicron BA.4/5, BQ.1.1, and XBB.1. When combining the COVA309 mAbs as cocktails or bispecific antibodies, the breadth and potency were improved. In addition, the mechanism of cross-neutralization of the COVA309 mAbs was elucidated by structural analysis. Altogether these data indicate that a Gamma-infected individual can develop broadly neutralizing antibodies.

Resistance of human immunodeficiency virus type 1 to a third-generation fusion inhibitor requires multiple mutations in gp41 and is accompanied by a dramatic loss of gp41 function.

HIV-1 entry into target cells requires the fusion of viral and cellular membranes. This process is an attractive target for therapeutic intervention, and a first-generation fusion inhibitor, T20 (Enfuvirtide; Fuzeon), was approved for clinical use in 2003. Second-generation (T1249) and third-generation (T2635) fusion inhibitors with improved stability and potency were developed. Resistance to T20 and T1249 usually requires one or two amino acid changes within the binding site. We studied the in vitro evolution of resistance against T2635. After 6 months of culturing, a multitude of resistance mutations was identified in all gp41 subdomains, but no single mutation provided meaningful T2635 resistance. In contrast, multiple mutations within gp41 were required for resistance, and this was accompanied by a dramatic loss of viral infectivity. Because most of the escape mutations were situated outside the T2635 binding site, a decrease in drug target affinity cannot account for most of the resistance. T2635 resistance is likely to depend on altered kinetics of six-helix bundle formation, thus limiting the time window for T2635 to interfere with membrane fusion. Interestingly, the loss of virus infectivity caused by T2635 resistance mutations in gp41 was partially compensated for by a mutation at the base of the V3 domain in gp120. Thus, escape from the third-generation HIV-1 fusion inhibitor T2635 is mechanistically distinct from resistance against its predecessors T20 and T1249. It requires the accumulation of multiple mutations in gp41, is accompanied with a dramatic loss of gp41 function, and induces compensatory mutations in gp120.

Innate cell markers that predict anti-HIV neutralizing antibody titers in vaccinated macaques.

Given the time and resources invested in clinical trials, innovative prediction methods are needed to decrease late-stage failure in vaccine development. We identify combinations of early innate responses that predict neutralizing antibody (nAb) responses induced in HIV-Env SOSIP immunized cynomolgus macaques using various routes of vaccine injection and adjuvants. We analyze blood myeloid cells before and 24 h after each immunization by mass cytometry using a three-step clustering, and we discriminate unique vaccine signatures based on HLA-DR, CD39, CD86, CD11b, CD45, CD64, CD14, CD32, CD11c, CD123, CD4, CD16, and CADM1 surface expression. Various combinations of these markers characterize cell families positively associated with nAb production, whereas CADM1-expressing cells are negatively associated (p < 0.05). Our results demonstrate that monitoring immune signatures during early vaccine development could assist in identifying biomarkers that predict vaccine immunogenicity.

Co-display of diverse spike proteins on nanoparticles broadens sarbecovirus neutralizing antibody responses.

The emergence of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) variants poses continuous challenges in combating the virus. Here, we describe vaccination strategies to broaden SARS-CoV-2 and sarbecovirus immunity by combining spike proteins based on different viruses or viral strains displayed on two-component protein nanoparticles. First, we combined spike proteins based on ancestral and Beta SARS-CoV-2 strains to broaden SARS-CoV-2 immune responses. Inclusion of Beta spike improved neutralizing antibody responses against SARS-CoV-2 Beta, Gamma, and Omicron BA.1 and BA.4/5. A third vaccination with ancestral SARS-CoV-2 spike also improved cross-neutralizing antibody responses against SARS-CoV-2 variants, in particular against the Omicron sublineages. Second, we combined SARS-CoV and SARS-CoV-2 spike proteins to broaden sarbecovirus immune responses. Adding SARS-CoV spike to a SARS-CoV-2 spike vaccine improved neutralizing responses against SARS-CoV and SARS-like bat sarbecoviruses SHC014 and WIV1. These results should inform the development of broadly active SARS-CoV-2 and pan-sarbecovirus vaccines and highlight the versatility of two-component nanoparticles for displaying diverse antigens.

Broad SARS-CoV-2 Neutralization by Monoclonal and Bispecific Antibodies Derived from a Gamma-infected Individual.

The worldwide pandemic caused by SARS-CoV-2 has remained a human medical threat due to the continued evolution of multiple variants that acquire resistance to vaccines and prior infection. Therefore, it is imperative to discover monoclonal antibodies (mAbs) that neutralize a broad range of SARS-CoV-2 variants for therapeutic and prophylactic use. A stabilized autologous SARS-CoV-2 spike glycoprotein was used to enrich antigen-specific B cells from an individual with a primary Gamma variant infection. Five mAbs selected from those B cells showed considerable neutralizing potency against multiple variants of concern, with COVA309-35 being the most potent against the autologous virus, as well as against Omicron BA.1 and BA.2. When combining the COVA309 mAbs as cocktails or bispecific antibody formats, the breadth and potency was significantly improved against all tested variants. In addition, the mechanism of cross-neutralization of the COVA309 mAbs was elucidated by structural analysis. Altogether these data indicate that a Gamma-infected individual can develop broadly neutralizing antibodies.

A single mRNA vaccine dose in COVID-19 patients boosts neutralizing antibodies against SARS-CoV-2 and variants of concern.

The urgent need for, but limited availability of, SARS-CoV-2 vaccines worldwide has led to widespread consideration of dose-sparing strategies. Here, we evaluate the SARS-CoV-2-specific antibody responses following BNT162b2 vaccination in 150 previously SARS-CoV-2-infected individuals from a population-based cohort. One week after first vaccine dose, spike protein antibody levels are 27-fold higher and neutralizing antibody titers 12-fold higher, exceeding titers of fully vaccinated SARS-CoV-2-naive controls, with minimal additional boosting after the second dose. Neutralizing antibody titers against four variants of concern increase after vaccination; however, overall neutralization breadth does not improve. Pre-vaccination neutralizing antibody titers and time since infection have the largest positive effect on titers following vaccination. COVID-19 severity and the presence of comorbidities have no discernible impact on vaccine response. In conclusion, a single dose of BNT162b2 vaccine up to 15 months after SARS-CoV-2 infection offers higher neutralizing antibody titers than 2 vaccine doses in SARS-CoV-2-naive individuals.

A public antibody class recognizes an S2 epitope exposed on open conformations of SARS-CoV-2 spike.

Delineating the origins and properties of antibodies elicited by SARS-CoV-2 infection and vaccination is critical for understanding their benefits and potential shortcomings. Therefore, we investigate the SARS-CoV-2 spike (S)-reactive B cell repertoire in unexposed individuals by flow cytometry and single-cell sequencing. We show that ∼82% of SARS-CoV-2 S-reactive B cells harbor a naive phenotype, which represents an unusually high fraction of total human naive B cells (∼0.1%). Approximately 10% of these naive S-reactive B cells share an IGHV1-69/IGKV3-11 B cell receptor pairing, an enrichment of 18-fold compared to the complete naive repertoire. Following SARS-CoV-2 infection, we report an average 37-fold enrichment of IGHV1-69/IGKV3-11 B cell receptor pairing in the S-reactive memory B cells compared to the unselected memory repertoire. This class of B cells targets a previously undefined non-neutralizing epitope on the S2 subunit that becomes exposed on S proteins used in approved vaccines when they transition away from the native pre-fusion state because of instability. These findings can help guide the improvement of SARS-CoV-2 vaccines.