Antibody Feedback Limits the Expansion of B Cell Responses to Malaria Vaccination but Drives Diversification of the Humoral Response

Long-lasting antibody B-cell responses to SARS-CoV-2 three years after the onset of the pandemic

Immune memory is essential for the effectiveness of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) vaccination. In the current context of the pandemic, with a diminished vaccine efficacy against emerging variants, it remains crucial to perform long-term studies to evaluate the durability and quality of immune responses. Here, we examined the antibody and memory B-cell responses in a cohort of 113 healthcare workers with distinct exposure histories over a 3-year period. Previously infected and naive participants developed comparable humoral responses by 17 months after receiving a full three-dose mRNA vaccination. In addition, both maintained a substantial SARS-CoV-2-reactive memory B-cell pool, associated with a lower incidence of breakthrough infections in naive participants. Of note, previously infected participants developed an expanded SARS-CoV-2-reactive CD27-CD21- atypical B-cell population that remained stable throughout the follow-up period. Thus, previous SARS-CoV-2 infection differentially imprints the memory B-cell compartment without compromising the development of long-lasting humoral responses.

Diverse priming outcomes under conditions of very rare precursor B cells

Rare naive B cells have special pathogen-recognition features that enable outsized contributions to protective immunity but infrequently participate in immune responses. We investigatee how germline-targeting vaccine delivery and adjuvant selection affect priming of exceptionally rare BG18-like HIV broadly neutralizing antibody-precursor B cells (<1-in-50 million) in non-human primates. Only escalating dose (ED) priming immunization using the saponin adjuvant SMNP elicited detectable BG18-like cells in germinal centers (GCs) compared with other conditions. All groups had strong GC responses, but only ED+SMNP and bolus+SMNP induced BG18-like memory B cells in >50% of animals. One group had vaccine-specific GC responses equivalent to ED+SMNP but scarce BG18-like B cells. Following homologous boosting, BG18-like memory B cells were present in a bolus priming group but with lower somatic hypermutation and affinities than ED+SMNP. This outcome inversely associated with post-prime antibody titers, suggesting antibody feedback significantly influences rare precursor B cell responses. Thus, antigen and inflammatory stimuli extensively impact priming and affinity maturation of rare B cells.

Having your cake and eating it too - a new target for sporozoite-neutralising mAbs

Current malaria vaccines provide suboptimal, waning protection. Dacon et al. identify a protective post-translationally modified epitope on Plasmodium sporozoites that is absent from current vaccines. This discovery deepens our understanding of Plasmodium biology and may inform the development of improved vaccines and complementary prophylactic monoclonal antibodies.

A rapid approach for linear epitope vaccine profiling reveals unexpected epitope tag immunogenicity

Antibody epitope profiling is essential for assessing the robustness of vaccine-induced immune responses, particularly while in development. Despite advancements in computational tools, high throughput experimental epitope validation remains an important step. Here, we describe a readily accessible method for rapid linear epitope profiling using phage-displayed oligo pools in combination with Nanopore deep sequencing. We applied this approach to TeeVax3, a Group A Streptococcus vaccine candidate, to investigate the antibody response generated in a pre-clinical rabbit model and assess antigen immunogenicity. Surprisingly, we found a strong bias in antibody binding response towards the N-terminal epitope tag used for purification. These tags are widely reported to have low immunogenicity and are frequently left uncleaved in pre-clinical studies. We further confirmed that the observed immune response against the epitope tag dominated even the conformational binding response and, using synthetic peptides, narrowed the epitope down to a set of 10 residues inclusive of the Histidine residues. Our findings highlight the importance of epitope-tag removal in pre-clinical studies and demonstrate the utility of rapid Nanopore sequencing for early-stage vaccine evaluation.

Early influenza virus exposure shapes the B cell response to influenza vaccination in individuals 50 years later

Pre-existing immunity impacts vaccine responses to influenza, but directly connecting influenza infections early in life with immune responses decades later is difficult. However, H2N2 stopped circulating in the human population in 1968, creating the opportunity to directly evaluate the impact of early H2N2 exposure on vaccine responses 50 years later. Here, we vaccinated individuals born before (H2 exposed) or after (H2 naive) 1968 with an H2 hemagglutinin (HA) DNA plasmid and/or a ferritin nanoparticle vaccine. H2-exposed individuals generated a rapid B cell recall response that was more potent, targeted more conserved epitopes, and differed phenotypically from the de novo response in H2-naive individuals. Furthermore, vaccinating with a DNA versus a protein nanoparticle vaccine altered the response in H2-naive but not H2-exposed individuals. This study establishes and describes the lifelong impact of influenza HA-specific memory B cells formed early in life on vaccine responses decades later.

Broadly neutralizing antibodies targeting pandemic GII.4 variants or seven GII genotypes of human norovirus

Human norovirus causes more than 700 million illnesses annually. Extensive genetic diversity and a paucity of information on conserved neutralizing epitopes pose major obstacles to the design of broadly protective norovirus immunogens. Here, we used high-resolution liquid chromatography-tandem mass spectrometry (LC-MS/MS)-driven proteomics to quantitatively characterize the circulating serum IgG repertoire before and after immunization with an experimental monovalent norovirus GII.4 VP1 capsid-encoding adenoviral vaccine. Two participants were specifically selected on the basis of the breadth of serum neutralization responses either across GII.4 variants (participant A) or across GII genotypes (participant B). In participant A, vaccination back-boosted highly abundant serum antibody clonotypes targeting epitopes conserved among rapidly evolving GII.4 variants spanning from a strain identified in 1987 to a strain identified in 2019. In participant B, we identified a recall response consisting of broadly neutralizing monoclonal antibodies with remarkable cross-GII ligand-binding blockade (blocking ≥ seven GII genotypes) and virus neutralization breadth. The cocrystal structure of one of these antibodies, VX22, in complex with the VP1 capsid protruding (P) domain revealed a highly conserved epitope (residues 479 to 484 and 509 to 513) within two lateral loops of the P1 subdomain. Antibody evolutionary trajectory analysis further revealed that VX22 had originally evolved from an early heterologous infection, likely by a GII.12 strain. Together, our study demonstrates that norovirus human monoclonal antibodies with broad GII.4 potency and cross-GII breadth can be boosted in serum after immunization with an adenoviral vector-based vaccine, findings that may guide the design of immunogens for broadly protective norovirus vaccines.

The effect of Plasmodium falciparum exposure and maternal anti-circumsporozoite protein antibodies on responses to RTS,S/AS01E vaccination in infants and children: an ancillary observational immunological study to a phase 3, randomised clinical trial

BACKGROUND

The RTS,S/AS01E malaria vaccine showed lower antibody response and protective efficacy in infants aged 6-12 weeks compared with children aged 5-17 months (for whom this vaccine is recommended). We aimed to study the effect of previous Plasmodium falciparum exposure on the antibody responses to RTS,S/AS01E vaccination in infants and children, and the mediating effect of baseline (including maternal) anti-circumsporozoite protein (CSP) antibodies.

METHODS

In this observational study, we included children and infants from six African countries (Burkina Faso, Gabon, Ghana, Kenya, Mozambique, and Tanzania) enrolled in the MAL067 immunology ancillary study of the RTS,S/AS01E phase 3 clinical trial from March 27, 2009, to Jan 21, 2011. We used comparator-vaccinated infants and children to identify antibody-based signatures of previous P falciparum exposure, which were later applied to RTS,S/AS01E-vaccinated infants and children. In these participants, we explored the relationship between vaccine antibody immunoglobulin G (IgG) responses measured by ELISA and pre-vaccination serological markers of malaria exposure by assessing the IgG levels against 1000 P falciparum antigens using partial proteome microarrays.

FINDINGS

We included 718 comparator-vaccinated infants (348 [48%]) and children (370 [52%]) and 606 RTS,S/AS01E-vaccinated infants (329 [54%]) and children (277 [46%]). Anti-CSP IgG responses to primary vaccination did not correlate with a baseline signature of previous exposure in children, suggesting that prior P falciparum exposure does not significantly affect antibody immunogenicity in children (Pearson's r=-0·02 [95% CI -0·13 to 0·10]). By contrast, high P falciparum exposure signature levels at the time of vaccination in infants, presumably driven by maternally transferred antibodies and declining within the initial 6-12 months of life, correlated with reduced RTS,S/AS01E responses (r=-0·17 [-0·27 to -0·06]). This negative correlation was stronger for anti-CSP IgG than for the exposure signature or any other more immunogenic blood stage P falciparum antigens (r=-0·42 [-0·50 to -0·33]), persisted after adjustment by baseline levels of the exposure signature (semi-partial correlation r=-0·44 [-0·55 to -0·33]), and involved antibodies to the central NANP region (r=-0·39 [-0·49 to -0·28]) but not the C-terminal region (r=0·02 [-0·10 to 0·15]) of CSP. The negative effect of maternal anti-CSP IgG in infants did not appear to be confounded by other malaria transmission-dependent variables.

INTERPRETATION

Interference between passive immunity and vaccine response is clinically significant and might affect the implementation of next-generation CSP-based vaccines for young infants and mothers as well as passive immunisation with human monoclonal antibodies.

FUNDING

US National Institutes of Health, National Institute of Allergy and Infectious Diseases; PATH-Malaria Vaccine Initiative; Spanish Ministerio de Economía y Competitividad (Instituto de Salud Carlos III), European Regional Development Fund and European Social Fund; Fundación Ramón Areces; Spanish Ministry of Science and Innovation; and Generalitat de Catalunya (CERCA Program).

Targeting Bottlenecks in Malaria Transmission: Antibody-Epitope Descriptions Guide the Design of Next-Generation Biomedical Interventions

Malaria continues to pose a significant burden to global health. Thus, a strong need exists for the development of a diverse panel of intervention strategies and modalities to combat malaria and achieve elimination and eradication goals. Deploying interventions that target bottlenecks in the transmission life cycle of the causative agent of malaria, Plasmodium parasites, is an attractive strategy. The development of highly potent antibody-based biologics, including vaccines, can be greatly facilitated by an in-depth molecular understanding of antibody-epitope interactions. Here, we provide an overview of structurally characterized antibodies targeting lead vaccine candidates expressed during the bottlenecks of the Plasmodium life cycle which include the pre-erythrocytic and sexual stages. The repeat region of the circumsporozoite protein (CSP), domain 1 of Pfs230 and domains 1 and 3 of Pfs48/45 are critical Plasmodium regions targeted by the most potent antibodies at the two bottlenecks of transmission, with other promising targets emerging and requiring further characterization.

Designed mosaic nanoparticles enhance cross-reactive immune responses in mice

Nanoparticle vaccines displaying combinations of SARS-like betacoronavirus (sarbecovirus) receptor-binding domains (RBDs) could protect against SARS-CoV-2 variants and spillover of zoonotic sarbecoviruses into humans. Using a computational approach, we designed variants of SARS-CoV-2 RBDs and selected 7 natural sarbecovirus RBDs, each predicted to fold properly and abrogate antibody responses to variable epitopes. RBDs were attached to 60-mer nanoparticles to make immunogens displaying two (mosaic-2COMs), five (mosaic-5COM), or seven (mosaic-7COM) different RBDs for comparisons with mosaic-8b, which elicited cross-reactive antibodies and protected animals from sarbecovirus challenges. Naive and COVID-19 pre-vaccinated mice immunized with mosaic-7COM elicited antibodies targeting conserved RBD epitopes, and their sera exhibited higher binding and neutralization titers against sarbecoviruses than mosaic-8b. Mosaic-2COMs and mosaic-5COM elicited higher antibody potencies against some SARS-CoV-2 variants than mosaic-7COM. However, mosaic-7COM elicited more potent responses against zoonotic sarbecoviruses and highly mutated Omicrons, supporting its use to protect against SARS-CoV-2 variants and zoonotic sarbecoviruses.

Modelling antibody dynamics in humans after different Ad26.COV2.S vaccination schemes

AIMS

To develop a semimechanistic model that describes the kinetic profile and variability of antibody (Ab) concentrations following vaccination with Ad26.COV2.S at different doses and dosing intervals.

METHODS

Data were collected from participants randomized into 5 clinical trials receiving the Ad26.COV2.S vaccine. The model considered key elements of humoral immune response, dose proportionality and the evolutionary processes of the immune response. Interindividual variability and covariates were explored.

RESULTS

Fast and slow kinetic phases of Ab and their evolution over time were differentiated. After first and second administrations, Ab concentrations of both phases increased less than dose proportionally, indicating a saturation of B-cell production processes. Ab concentrations produced during the fast kinetic phase increased significantly after the second administration, indicating an underlying evolutive process after antigen exposures. For the slow kinetic phase, a less pronounced increase occurred after the second and third administrations but was relatively higher in subjects who had low concentrations after the first administration. Ab concentrations of the slow phase were higher in females and decreased with age. After multiple administrations, the fast phase had Ab maximum concentrations about 5 times higher than the slow phase. The limiting kinetic factors in the fast and slow phases were the elimination rates of Ab itself and Ab producing cells, respectively.

CONCLUSION

The model appears suitable to quantitatively describe the inter- and intraindividual kinetics of the immune response and the impact of covariates after multiple administrations of a vaccine.

Antigen affinity and site of immunization dictate B cell recall responses

Protective antibodies against HIV-1 require unusually high levels of somatic mutations introduced in germinal centers (GCs). To achieve this, a sequential vaccination approach was proposed. Using HIV-1 antibody knockin mice with fate-mapping genes, we examined if antigen affinity affects the outcome of B cell recall responses. Compared to a high-affinity boost, a low-affinity boost resulted in decreased numbers of memory-derived B cells in secondary GCs but with higher average levels of somatic mutations, indicating an affinity threshold for memory B cells to enter GCs. Furthermore, upon boosting local lymph nodes (LNs), the composition of primary GCs was modified in an antigen-affinity-dependent manner to constitute less somatically mutated B cells. Our results demonstrate that antigen affinity and location of the boost affect the outcome of the B cell recall response. These results can help guide the design of vaccine immunogens aiming to selectively engage specific B cell clones for further diversification.

Target-agnostic identification of human antibodies to Plasmodium falciparum sexual forms reveals cross-stage recognition of glutamate-rich repeats

Circulating sexual stages of Plasmodium falciparum (Pf) can be transmitted from humans to mosquitoes, thereby furthering the spread of malaria in the population. It is well established that antibodies can efficiently block parasite transmission. In search for naturally acquired antibodies targets on sexual stages, we established an efficient method for target-agnostic single B cell activation followed by high-throughput selection of human monoclonal antibodies (mAbs) reactive to sexual stages of Pf in the form of gametes and gametocyte extracts. We isolated mAbs reactive against a range of Pf proteins including well-established targets Pfs48/45 and Pfs230. One mAb, B1E11K, was cross-reactive to various proteins containing glutamate-rich repetitive elements expressed at different stages of the parasite life cycle. A crystal structure of two B1E11K Fab domains in complex with its main antigen, RESA, expressed on asexual blood stages, showed binding of B1E11K to a repeating epitope motif in a head-to-head conformation engaging in affinity-matured homotypic interactions. Thus, this mode of recognition of Pf proteins, previously described only for Pf circumsporozoite protein (PfCSP), extends to other repeats expressed across various stages. The findings augment our understanding of immune-pathogen interactions to repeating elements of the Plasmodium parasite proteome and underscore the potential of the novel mAb identification method used to provide new insights into the natural humoral immune response against Pf.

Protective antibodies target cryptic epitope unmasked by cleavage of malaria sporozoite protein

The most advanced monoclonal antibodies (mAbs) and vaccines against malaria target the central repeat region or closely related sequences within the Plasmodium falciparum circumsporozoite protein (PfCSP). Here, using an antigen-agnostic strategy to investigate human antibody responses to whole sporozoites, we identified a class of mAbs that target a cryptic PfCSP epitope that is only exposed after cleavage and subsequent pyroglutamylation (pGlu) of the newly formed N terminus. This pGlu-CSP epitope is not targeted by current anti-PfCSP mAbs and is not included in the licensed malaria vaccines. MAD21-101, the most potent mAb in this class, confers sterile protection against Pf infection in a human liver-chimeric mouse model. These findings reveal a site of vulnerability on the sporozoite surface that can be targeted by next-generation antimalarial interventions.

Malaria: Factors affecting disease severity, immune evasion mechanisms, and reversal of immune inhibition to enhance vaccine efficacy

Malaria is a complex parasitic disease caused by species of Plasmodium parasites. Infection with the parasites can lead to a spectrum of symptoms and disease severity, influenced by various parasite, host, and environmental factors. There have been some successes in developing vaccines against the disease recently, but the vaccine efficacies require improvement. Some issues associated with the difficulties in developing a sterile vaccine include high antigenic diversity, switching expression of the immune targets, and inhibition of immune pathways. Current vaccine research focuses on identifying conserved and protective epitopes, developing multivalent vaccines (including the whole parasite), and using more powerful adjuvants. However, overcoming the systematic immune inhibition and immune cell dysfunction/exhaustion may be required before high titers of protective antibodies can be achieved. Increased expression of surface molecules such as CD86 and MHC II on antigen-presenting cells and blocking immune checkpoint pathways (interactions of PD-1 and PD-L1; CTLA-4 and CD80) using small molecules could be a promising approach for enhancing vaccine efficacy. This assay reviews the factors affecting the disease severity, the genetics of host-parasite interaction, immune evasion mechanisms, and approaches potentially to improve host immune response for vaccine development.

mRNA vaccine-induced IgG mediates nasal SARS-CoV-2 clearance in mice

Coronavirus disease 2019 (COVID-19) mRNA vaccines that have contributed to controlling the SARS-CoV-2 pandemic induce specific serum antibodies, which correlate with protection. However, the neutralizing capacity of antibodies for emerging SARS-CoV-2 variants is altered. Suboptimal antibody responses are observed in patients with humoral immunodeficiency diseases, ongoing B cell depletion therapy, and aging. Common experimental mouse models with altered B cell compartments, such as B cell depletion or deficiency, do not fully recapitulate scenarios of declining or suboptimal antibody levels as observed in humans. We report on SARS-CoV-2 immunity in a transgenic mouse model with restricted virus-specific antibodies. Vaccination of C57BL/6-Tg(IghelMD4)4Ccg/J mice with unmodified or N1mΨ-modified mRNA encoding for ancestral spike (S) protein and subsequent challenge with mouse-adapted SARS-CoV-2 provided insights into antibody-independent immunity and the impact of antibody titers on mucosal immunity. Protection against fatal disease was independent of seroconversion following mRNA vaccination, suggesting that virus-specific T cells can compensate for suboptimal antibody levels. In contrast, mRNA-induced IgG in the nasal conchae limited the local viral load and disease progression. Our results indicate that parenteral mRNA immunization can elicit nasal IgG antibodies that effectively suppress local viral replication, highlighting the potential of vaccines in controlling SARS-CoV-2 transmission and epidemiology.

Booster COVID-19 mRNA vaccination ameliorates impaired B-cell but not T-cell responses in older adults

Age-associated differences in the effect of repetitive vaccination, particularly on memory T-cell and B-cell responses, remain unclear. While older adults (aged ≥65 years) exhibited enhanced IgG responses following COVID-19 mRNA booster vaccination, they produced fewer spike-specific circulating follicular helper T cells-1 than younger adults. Similarly, the cytotoxic CD8+ T-cell response remained diminished with reduced PD-1 expression even after booster vaccination compared with that in younger adults, suggesting impaired memory T-cell activation in older adults. In contrast, although B-cell responses in older adults were weaker than those in younger adults in the primary response, the responses were significantly enhanced upon booster vaccination, reaching levels comparable with that observed in younger adults. Therefore, while booster vaccination ameliorates impaired humoral immunity in older adults by efficiently stimulating memory B-cell responses, it may less effectively enhance T-cell-mediated cellular immunity. Our study provides insights for the development of effective therapeutic and vaccine strategies for the most vulnerable older population.

Neutralizing antibodies elicited in macaques recognize V3 residues on altered conformations of HIV-1 Env trimer

Eliciting broadly neutralizing antibodies that protect against diverse HIV-1 strains is a primary goal of AIDS vaccine research. We characterized Ab1456 and Ab1271, two heterologously-neutralizing antibodies elicited in non-human primates by priming with an engineered V3-targeting SOSIP Env immunogen and boosting with increasingly native-like SOSIP Envs derived from different strain backgrounds. Structures of Env trimers in complex with these antibodies revealed V3 targeting, but on conformational states of Env distinct from the typical closed, prefusion trimeric SOSIP structure. Env trimers bound by Ab1456 adopted conformations resembling CD4-bound open Env states in the absence of soluble CD4, whereas trimers bound by Ab1271 exhibited a trimer apex-altered conformation to accommodate antibody binding. The finding that elicited antibodies cross-neutralized by targeting altered, non-closed, prefusion Env trimer conformations provides important information about Env dynamics that is relevant for HIV-1 vaccine design aimed at raising antibodies to desired epitopes on closed pre-fusion Env trimers.

Streptococcus pyogenes pharyngitis elicits diverse antibody responses to key vaccine antigens influenced by the imprint of past infections

Knowledge gaps regarding human immunity to Streptococcus pyogenes have impeded vaccine development. To address these gaps and evaluate vaccine candidates, we established a human challenge model of S. pyogenes pharyngitis. Here, we analyse antibody responses in serum and saliva against 19 antigens to identify characteristics distinguishing 19 participants who developed pharyngitis and 6 who did not. We show that pharyngitis elicits serum IgG responses to key vaccine antigens and a muted mucosal IgA response, whereas IgG responses are minimal and IgA responses more pronounced in participants without pharyngitis. Serum IgG responses to pharyngitis in adult participants resemble those in children and are inversely correlated with the magnitude of pre-existing responses. While a straightforward correlate of protection is not evident, baseline antibody signatures distinguish clinical and immunological outcomes following experimental challenge. This highlights the influence of a complex humoral imprint from previous exposure, relevant for interpreting immunogenicity in forthcoming vaccine trials.

Trade-off between the antiviral and vaccinal effects of antibody therapy in the humoral response to HIV

Antibody therapy for HIV-1 infection exerts two broad effects: a drug-like, antiviral effect, which rapidly lowers the viral load, and a vaccinal effect, which may control the viral load long-term by improving the immune response. Here, we elucidate a trade-off between these two effects as they pertain to the humoral response, which may compromise antibody therapy aimed at eliciting long-term HIV-1 remission. We developed a multi-scale computational model that combined within-host viral dynamics and stochastic simulations of the germinal centre (GC) reaction, enabling simultaneous quantification of the antiviral and vaccinal effects of antibody therapy. The model predicted that increasing antibody dosage or antibody-antigen affinity increased immune complex formation and enhanced GC output. Beyond a point, however, a strong antiviral effect reduced antigen levels substantially, extinguishing GCs and limiting the humoral response. We found signatures of this trade-off in clinical studies. Accounting for the trade-off could be important in optimizing antibody therapy for HIV-1 remission.

Longitudinal Immunological Analysis of Portuguese Healthcare Workers Across the COVID-19 Pandemic Reveals Differences in the Humoral Immune Response to Vaccines

Background: A vaccination programme against severe acute respiratory syndrome coronavirus 2 was initiated in Portugal in December 2020. In this study, we report the findings of a prospective cohort study implemented with the objective of monitoring antibody production in response to COVID-19 vaccination. Methods: The humoral immune response to vaccination was followed up using blood samples collected from 191 healthcare workers. Participants were split into three groups: the Oxford-AstraZeneca (Vaxzevria) vaccine group (n = 68), the Pfizer-BioNTech COVID-19 (Comirnaty) vaccine group (n = 51), and the Post-COVID group (n = 72). The kinetics of anti-spike antibody production were evaluated until 56 days on average after the third dose (booster). Results: We observed that antibody titres peaked approximately one month after full vaccination and declined steadily thereafter. We also found that mRNA vaccination induces higher titres of antibodies than viral vector vaccination, and both generate greater antibody responses than mild or moderate COVID-19. Additionally, whilst the booster for the Oxford-AstraZeneca and Pfizer-BioNTech groups led to antibody levels higher than those at any previous sample collection point, the booster for the Post-COVID group (persons with a history of COVID-19 prior to vaccination) led to antibody levels lower than those attained one month after the second dose. Interpretation: Our results indicate that there are different kinetics of antibody production between individuals who received the Pfizer-BioNtech mRNA vaccine and those who received the Oxford-AstraZeneca vector vaccine, or individuals who had COVID-19 before being vaccinated. Additionally, we observed that exposure to either natural infection or vaccination modulates the response to subsequent vaccination. This is particularly evident after administration of the third dose to the Post-COVID group, where our findings point to a hindrance in vaccine boosting, probably due to unwanted feedback by high titres of pre-existing antibodies.

Immunofocusing on the conserved fusion peptide of HIV envelope glycoprotein in rhesus macaques

During infection, the fusion peptide (FP) of HIV envelope glycoprotein (Env) serves a central role in viral fusion with the host cell. As such, the FP is highly conserved and therefore an attractive epitope for vaccine design. Here, we describe a vaccination study in non-human primates (NHPs) where glycan deletions were made on soluble HIV Env to increase FP epitope exposure. When delivered via implantable osmotic pumps, this immunogen primed immune responses against the FP, which were then boosted with heterologous trimers resulting in a focused immune response targeting the conserved FP epitope. Although autologous immunizations did not elicit high affinity FP-targeting antibodies, the conserved FP epitope on a heterologous trimer further matured the lower affinity, FP-targeting B cells. This study suggests using epitope conservation strategies on distinct Env trimer immunogens can focus humoral responses on desired neutralizing epitopes and suppress immune-distracting antibody responses against non-neutralizing epitopes.

Diverse priming outcomes under conditions of very rare precursor B cells

Rare B cells can have special pathogen-recognition features giving them the potential to make outsized contributions to protective immunity. However, rare naive B cells infrequently participate in immune responses. We investigated how germline-targeting vaccine antigen delivery and adjuvant selection affect priming of exceptionally rare BG18-like HIV broadly neutralizing antibody-precursor B cells (~1 in 50 million) in non-human primates. Only escalating dose (ED) priming immunization using the saponin adjuvant SMNP elicited detectable BG18-like cells in germinal centers (GCs). All groups had strong GC responses, but only ED+SMNP and bolus+SMNP induced BG18-like memory B cells in >50% of animals. One group had vaccine-specific GC responses equivalent to ED+SMNP, but BG18-like memory B cells were rarely detected. Following homologous boosting, BG18-like memory B cells were more frequent in a bolus priming group, but had lower somatic hypermutation and affinities. This outcome was inversely associated with post-prime antibody titers, suggesting antibody feedback can significantly influence rare precursor B cell responses.

Modulation of B cell receptor activation by antibody competition

During repeated virus exposure, pre-existing antibodies can mask viral epitopes by competing with B cell receptors for antigen. Although this phenomenon has the potential to steer B cell responses away from conserved epitopes, the factors that influence epitope masking by competing antibodies remain unclear. Using engineered, influenza-reactive B cells, we investigate how antibodies influence the accessibility of epitopes on the viral surface. We find that membrane-proximal epitopes on influenza hemagglutinin are fundamentally at a disadvantage for B cell recognition because they can be blocked by both directly and indirectly competing antibodies. While many influenza-specific antibodies can inhibit B cell activation, the potency of masking depends on proximity of the targeted epitopes as well as antibody affinity, kinetics, and valency. Although most antibodies are inhibitory, we identify one that can enhance accessibility of hidden viral epitopes. Together, these findings establish rules for epitope masking that could help advance immunogen design.

Antibody feedback regulation

Antibodies are able to up- or downregulate antibody responses to the antigen they bind. Two major mechanisms can be distinguished. Suppression is most likely caused by epitope masking and can be induced by all isotypes tested (IgG1, IgG2a, IgG2b, IgG3, IgM, and IgE). Enhancement is often caused by the redistribution of antigen in a favorable way, either for presentation to B cells via follicular dendritic cells (IgM and IgG3) or to CD4+ T cells via dendritic cells (IgE, IgG1, IgG2a, and IgG2b). IgM and IgG3 complexes activate complement and are transported from the marginal zone to follicles by marginal zone B cells expressing complement receptors. IgE-antigen complexes are captured by CD23+ B cells in the blood and transported to follicles, delivered to CD8α+ conventional dendritic cells, and presented to CD4+ T cells. Enhancement of antibody responses by IgG1, IgG2a, and IgG2b in complex with proteins requires activating FcγRs. These immune complexes are captured by dendritic cells and presented to CD4+ T cells, subsequently helping cognate B cells. Endogenous feedback regulation influences the response to booster doses of vaccines and passive administration of anti-RhD antibodies is used to prevent alloimmunization of RhD-negative women carrying RhD-positive fetuses.

Conversion of vaccines from low to high immunogenicity by antibodies with epitope complementarity

Existing antibodies (Abs) have varied effects on humoral immunity during subsequent infections. Here, we leveraged in vivo systems that allow precise control of antigen-specific Abs and B cells to examine the impact of Ab dose, affinity, and specificity in directing B cell activation and differentiation. Abs competing with the B cell receptor (BCR) epitope showed affinity-dependent suppression. By contrast, Abs targeting a complementary epitope, not overlapping with the BCR, shifted B cell differentiation toward Ab-secreting cells. Such Abs allowed for potent germinal center (GC) responses to otherwise poorly immunogenic sites by promoting antigen capture and presentation by low-affinity B cells. These mechanisms jointly diversified the B cell repertoire by facilitating the recruitment of high- and low-affinity B cells into Ab-secreting cell, GC, and memory B cell fates. Incorporation of small amounts of monoclonal Abs into protein- or mRNA-based vaccines enhanced immunogenicity and facilitated sustained immune responses, with implications for vaccine design and our understanding of protective immunity.

Mosaic sarbecovirus nanoparticles elicit cross-reactive responses in pre-vaccinated animals

Immunization with mosaic-8b (nanoparticles presenting 8 SARS-like betacoronavirus [sarbecovirus] receptor-binding domains [RBDs]) elicits more broadly cross-reactive antibodies than homotypic SARS-CoV-2 RBD-only nanoparticles and protects against sarbecoviruses. To investigate original antigenic sin (OAS) effects on mosaic-8b efficacy, we evaluated the effects of prior COVID-19 vaccinations in non-human primates and mice on anti-sarbecovirus responses elicited by mosaic-8b, admix-8b (8 homotypics), or homotypic SARS-CoV-2 immunizations, finding the greatest cross-reactivity for mosaic-8b. As demonstrated by molecular fate mapping, in which antibodies from specific cohorts of B cells are differentially detected, B cells primed by WA1 spike mRNA-LNP dominated antibody responses after RBD-nanoparticle boosting. While mosaic-8b- and homotypic-nanoparticles boosted cross-reactive antibodies, de novo antibodies were predominantly induced by mosaic-8b, and these were specific for variant RBDs with increased identity to RBDs on mosaic-8b. These results inform OAS mechanisms and support using mosaic-8b to protect COVID-19-vaccinated/infected humans against as-yet-unknown SARS-CoV-2 variants and animal sarbecoviruses with human spillover potential.

Rational structure-guided design of a blood stage malaria vaccine immunogen presenting a single epitope from PfRH5

There is an urgent need for improved malaria vaccine immunogens. Invasion of erythrocytes by Plasmodium falciparum is essential for its life cycle, preceding symptoms of disease and parasite transmission. Antibodies which target PfRH5 are highly effective at preventing erythrocyte invasion and the most potent growth-inhibitory antibodies bind a single epitope. Here we use structure-guided approaches to design a small synthetic immunogen, RH5-34EM which recapitulates this epitope. Structural biology and biophysics demonstrate that RH5-34EM is correctly folded and binds neutralising monoclonal antibodies with nanomolar affinity. In immunised rats, RH5-34EM induces PfRH5-targeting antibodies that inhibit parasite growth. While PfRH5-specific antibodies were induced at a lower concentration by RH5-34EM than by PfRH5, RH5-34EM induced antibodies that were a thousand-fold more growth-inhibitory as a factor of PfRH5-specific antibody concentration. Finally, we show that priming with RH5-34EM and boosting with PfRH5 achieves the best balance between antibody quality and quantity and induces the most effective growth-inhibitory response. This rationally designed vaccine immunogen is now available for use as part of future malaria vaccines, alone or in combination with other immunogens.

Blood-stage malaria vaccine candidate RH5.1/Matrix-M in healthy Tanzanian adults and children; an open-label, non-randomised, first-in-human, single-centre, phase 1b trial

BACKGROUND

A blood-stage Plasmodium falciparum malaria vaccine would provide a second line of defence to complement partially effective or waning immunity conferred by the approved pre-erythrocytic vaccines. RH5.1 is a soluble protein vaccine candidate for blood-stage P falciparum, formulated with Matrix-M adjuvant to assess safety and immunogenicity in a malaria-endemic adult and paediatric population for the first time.

METHODS

We did a non-randomised, phase 1b, single-centre, dose-escalation, age de-escalation, first-in-human trial of RH5.1/Matrix-M in Bagamoyo, Tanzania. We recruited healthy adults (aged 18-45 years) and children (aged 5-17 months) to receive the RH5.1/Matrix-M vaccine candidate in the following three-dose regimens: 10 μg RH5.1 at 0, 1, and 2 months (Adults 10M), and the higher dose of 50 μg RH5.1 at 0 and 1 month and 10 μg RH5.1 at 6 months (delayed-fractional third dose regimen; Adults DFx). Children received either 10 μg RH5.1 at 0, 1, and 2 months (Children 10M) or 10 μg RH5.1 at 0, 1, and 6 months (delayed third dose regimen; Children 10D), and were recruited in parallel, followed by children who received the dose-escalation regimen (Children DFx) and children with higher malaria pre-exposure who also received the dose-escalation regimen (High Children DFx). All RH5.1 doses were formulated with 50 μg Matrix-M adjuvant. Primary outcomes for vaccine safety were solicited and unsolicited adverse events after each vaccination, along with any serious adverse events during the study period. The secondary outcome measures for immunogenicity were the concentration and avidity of anti-RH5.1 serum IgG antibodies and their percentage growth inhibition activity (GIA) in vitro, as well as cellular immunogenicity to RH5.1. All participants receiving at least one dose of vaccine were included in the primary analyses. This trial is registered at ClinicalTrials.gov, NCT04318002, and is now complete.

FINDINGS

Between Jan 25, 2021, and April 15, 2021, we recruited 12 adults (six [50%] in the Adults 10M group and six [50%] in the Adults DFx group) and 48 children (12 each in the Children 10M, Children 10D, Children DFx, and High Children DFx groups). 57 (95%) of 60 participants completed the vaccination series and 55 (92%) completed 22 months of follow-up following the third vaccination. Vaccinations were well-tolerated across both age groups. There were five serious adverse events involving four child participants during the trial, none of which were deemed related to vaccination. RH5-specific T cell and serum IgG antibody responses were induced by vaccination and purified total IgG showed in vitro GIA against P falciparum. We found similar functional quality (ie, GIA per μg RH5-specific IgG) across all age groups and dosing regimens at 14 days after the final vaccination; the concentration of RH5.1-specific polyclonal IgG required to give 50% GIA was 14·3 μg/mL (95% CI 13·4-15·2). 11 children were vaccinated with the delayed third dose regimen and showed the highest median anti-RH5 serum IgG concentration 14 days following the third vaccination (723 μg/mL [IQR 511-1000]), resulting in all 11 who received the full series showing greater than 60% GIA following dilution of total IgG to 2·5 mg/mL (median 88% [IQR 81-94]).

INTERPRETATION

The RH5.1/Matrix-M vaccine candidate shows an acceptable safety and reactogenicity profile in both adults and 5-17-month-old children residing in a malaria-endemic area, with all children in the delayed third dose regimen reaching a level of GIA previously associated with protective outcome against blood-stage P falciparum challenge in non-human primates. These data support onward efficacy assessment of this vaccine candidate against clinical malaria in young African children.

FUNDING

The European and Developing Countries Clinical Trials Partnership; the UK Medical Research Council; the UK Department for International Development; the National Institute for Health and Care Research Oxford Biomedical Research Centre; the Division of Intramural Research, National Institute of Allergy and Infectious Diseases; the US Agency for International Development; and the Wellcome Trust.

Influenza virus antibodies inhibit antigen-specific de novo B cell responses in mice

Antibody responses to influenza vaccines tend to be focused on epitopes encountered during prior influenza exposures, with little production of de novo responses to novel epitopes. To examine the contribution of circulating antibodies to this phenomenon, we passively transferred a hemagglutinin (HA)-specific monoclonal antibody (mAb) into mice before immunizing with whole inactivated virions. The HA mAb inhibited de novo HA-specific antibodies, plasmablasts, germinal center B cells, and memory B cells, while responses to a second antigen in the vaccine, neuraminidase (NA), were uninhibited. The HA mAb potently inhibited de novo antibody responses against epitopes near the HA mAb binding site. The HA mAb also promoted IgG1 class switching, an effect that, unlike the inhibition of HA responses, relied on signaling through Fc-gamma receptors. These studies suggest that circulating antibodies inhibit de novo B cell responses in an antigen-specific manner, which likely contributes to differences in antibody specificities elicited during primary and secondary influenza virus exposures.IMPORTANCEMost humans are exposed to influenza viruses in childhood and then subsequently exposed to antigenically drifted influenza variants later in life. It is unclear if antibodies elicited by earlier influenza virus exposures impact immunity against new influenza virus strains. Here, we used a mouse model to investigate how an anti-hemagglutinin (HA) monoclonal antibody (mAb) affects de novo B cell and antibody responses to the protein targeted by the monoclonal antibody (HA) and a second protein not targeted by the monoclonal antibody [neuraminidase (NA)]. Collectively, our studies suggest that circulating anti-influenza virus antibodies can potently modulate the magnitude and specificity of antibody responses elicited by secondary influenza virus exposures.

The impact of Plasmodium-driven immunoregulatory networks on immunity to malaria

Malaria, caused by infection with Plasmodium parasites, drives multiple regulatory responses across the immune landscape. These regulatory responses help to protect against inflammatory disease but may in some situations hamper the acquisition of adaptive immune responses that clear parasites. In addition, the regulatory responses that occur during Plasmodium infection may negatively affect malaria vaccine efficacy in the most at-risk populations. Here, we discuss the specific cellular mechanisms of immunoregulatory networks that develop during malaria, with a focus on knowledge gained from human studies and studies that involve the main malaria parasite to affect humans, Plasmodium falciparum. Leveraging this knowledge may lead to the development of new therapeutic approaches to increase protective immunity to malaria during infection or after vaccination.

Antibody gene features associated with binding and functional activity in malaria vaccine-derived human mAbs

The impact of adjuvants on malaria vaccine-induced antibody repertoire is poorly understood. Here, we characterize the impact of two adjuvants, Alhydrogel® and AS01, on antibody clonotype diversity, binding and function, post malaria vaccination. We expressed 132 recombinant anti-Pfs230D1 human monoclonal antibodies (mAbs) from participants immunized with malaria transmission-blocking vaccine Pfs230D1, formulated with either Alhydrogel® or AS01. Anti-Pfs230D1 mAbs generated by Alhydrogel® formulation showed higher binding frequency to Pfs230D1 compared to AS01 formulation, although the frequency of functional mAbs was similar between adjuvant groups. Overall, the AS01 formulation induced anti-Pfs230D1 functional antibodies from a broader array of germline sequences versus the Alhydrogel® formulation. All mAbs using IGHV1-69 gene from the Alhydrogel® cohort bound to recombinant Pfs230D1, but did not block parasite transmission to mosquitoes, similar to the IGHV1-69 mAbs isolated from the AS01 cohort. These findings may help inform vaccine design and adjuvant selection for immunization with Plasmodium antigens.

Antibody modulation of B cell responses-Incorporating positive and negative feedback

Antibodies are powerful modulators of ongoing and future B cell responses. While the concept of antibody feedback has been appreciated for over a century, the topic has seen a surge in interest due to the evidence that the broadening of antibody responses to SARS-CoV-2 after a third mRNA vaccination is a consequence of antibody feedback. Moreover, the discovery that slow antigen delivery can lead to more robust humoral immunity has put a spotlight on the capacity for early antibodies to augment B cell responses. Here, we review the mechanisms whereby antibody feedback shapes B cell responses, integrating findings in humans and in mouse models. We consider the major influence of epitope masking and the diverse actions of complement and Fc receptors and provide a framework for conceptualizing the ways antigen-specific antibodies may influence B cell responses to any form of antigen, in conditions as diverse as infectious disease, autoimmunity, and cancer.

Opposing effects of pre-existing antibody and memory T cell help on the dynamics of recall germinal centers

Re-exposure to an antigen generates abundant antibody responses and drives the formation of secondary germinal centers (GCs). Recall GCs in mice consist almost entirely of naïve B cells, whereas recall antibodies derive overwhelmingly from memory B cells. Here, we examine this division between cellular and serum compartments. After repeated immunization with the same antigen, tetramer analyses of recall GCs revealed a marked decrease in the ability of B cells in these structures to bind the antigen. Boosting with viral variant proteins restored antigen binding in recall GCs, as did genetic ablation of primary-derived antibody-secreting cells through conditional deletion of Prdm1, demonstrating suppression of GC recall responses by pre-existing antibodies. In hapten-carrier experiments in which B and T cell specificities were uncoupled, memory T cell help allowed B cells with undetectable antigen binding to access GCs. Thus, antibody-mediated feedback steers recall GC B cells away from previously targeted epitopes and enables specific targeting of variant epitopes, with implications for vaccination protocols.

Target-agnostic identification of human antibodies to Plasmodium falciparum sexual forms reveals cross stage recognition of glutamate-rich repeats

Circulating sexual stages of Plasmodium falciparum (Pf) can be transmitted from humans to mosquitoes, thereby furthering the spread of malaria in the population. It is well established that antibodies (Abs) can efficiently block parasite transmission. In search for naturally acquired Ab targets on sexual stages, we established an efficient method for target-agnostic single B cell activation followed by high-throughput selection of human monoclonal antibodies (mAbs) reactive to sexual stages of Pf in the form of gamete and gametocyte extract. We isolated mAbs reactive against a range of Pf proteins including well-established targets Pfs48/45 and Pfs230. One mAb, B1E11K, was cross-reactive to various proteins containing glutamate-rich repetitive elements expressed at different stages of the parasite life cycle. A crystal structure of two B1E11K Fab domains in complex with its main antigen, RESA, expressed on asexual blood stages, showed binding of B1E11K to a repeating epitope motif in a head-to-head conformation engaging in affinity-matured homotypic interactions. Thus, this mode of recognition of Pf proteins, previously described only for PfCSP, extends to other repeats expressed across various stages. The findings augment our understanding of immune-pathogen interactions to repeating elements of the Plasmodium parasite proteome and underscore the potential of the novel mAb identification method used to provide new insights into the natural humoral immune response against Pf .

Impact Statement

A naturally acquired human monoclonal antibody recognizes proteins expressed at different stages of the Plasmodium falciparum lifecycle through affinity-matured homotypic interactions with glutamate-rich repeats.

mRNA-LNP HIV-1 trimer boosters elicit precursors to broad neutralizing antibodies

Germline-targeting (GT) HIV vaccine strategies are predicated on deriving broadly neutralizing antibodies (bnAbs) through multiple boost immunogens. However, as the recruitment of memory B cells (MBCs) to germinal centers (GCs) is inefficient and may be derailed by serum antibody-induced epitope masking, driving further B cell receptor (BCR) modification in GC-experienced B cells after boosting poses a challenge. Using humanized immunoglobulin knockin mice, we found that GT protein trimer immunogen N332-GT5 could prime inferred-germline precursors to the V3-glycan-targeted bnAb BG18 and that B cells primed by N332-GT5 were effectively boosted by either of two novel protein immunogens designed to have minimum cross-reactivity with the off-target V1-binding responses. The delivery of the prime and boost immunogens as messenger RNA lipid nanoparticles (mRNA-LNPs) generated long-lasting GCs, somatic hypermutation, and affinity maturation and may be an effective tool in HIV vaccine development.

Innate immune activation restricts priming and protective efficacy of the radiation-attenuated PfSPZ malaria vaccine

A systems analysis was conducted to determine the potential molecular mechanisms underlying differential immunogenicity and protective efficacy results of a clinical trial of the radiation-attenuated whole-sporozoite PfSPZ vaccine in African infants. Innate immune activation and myeloid signatures at prevaccination baseline correlated with protection from P. falciparum parasitemia in placebo controls. These same signatures were associated with susceptibility to parasitemia among infants who received the highest and most protective PfSPZ vaccine dose. Machine learning identified spliceosome, proteosome, and resting DC signatures as prevaccination features predictive of protection after highest-dose PfSPZ vaccination, whereas baseline circumsporozoite protein-specific (CSP-specific) IgG predicted nonprotection. Prevaccination innate inflammatory and myeloid signatures were associated with higher sporozoite-specific IgG Ab response but undetectable PfSPZ-specific CD8+ T cell responses after vaccination. Consistent with these human data, innate stimulation in vivo conferred protection against infection by sporozoite injection in malaria-naive mice while diminishing the CD8+ T cell response to radiation-attenuated sporozoites. These data suggest a dichotomous role of innate stimulation for malaria protection and induction of protective immunity by whole-sporozoite malaria vaccines. The uncoupling of vaccine-induced protective immunity achieved by Abs from more protective CD8+ T cell responses suggests that PfSPZ vaccine efficacy in malaria-endemic settings may be constrained by opposing antigen presentation pathways.

Influenza virus antibodies inhibit antigen-specific de novo B cell responses in mice

Antibody responses to influenza vaccines tend to be focused on epitopes encountered during prior influenza exposures, with little production of de novo responses to novel epitopes. To examine the contribution of circulating antibody to this phenomenon, we passively transferred a hemagglutinin (HA)-specific monoclonal antibody (mAb) into mice before immunizing with whole inactivated virions. The HA mAb inhibited de novo HA-specific antibodies, plasmablasts, germinal center B cells, and memory B cells, while responses to a second antigen in the vaccine, neuraminidase (NA), were uninhibited. The HA mAb potently inhibited de novo antibody responses against epitopes near the HA mAb binding site. The HA mAb also promoted IgG1 class switching, an effect that, unlike the inhibition of HA responses, relied on signaling through Fc-gamma receptors. These studies suggest that circulating antibodies inhibit de novo B cell responses in an antigen-specific manner, which likely contributes to differences in antibody specificities elicited during primary and secondary influenza virus exposures.

Poly I:C elicits broader and stronger humoral and cellular responses to a Plasmodium vivax circumsporozoite protein malaria vaccine than Alhydrogel in mice

Malaria remains a global health challenge, necessitating the development of effective vaccines. The RTS,S vaccination prevents Plasmodium falciparum (Pf) malaria but is ineffective against Plasmodium vivax (Pv) disease. Herein, we evaluated the murine immunogenicity of a recombinant PvCSP incorporating prevalent polymorphisms, adjuvanted with Alhydrogel or Poly I:C. Both formulations induced prolonged IgG responses, with IgG1 dominance by the Alhydrogel group and high titers of all IgG isotypes by the Poly I:C counterpart. Poly I:C-adjuvanted vaccination increased splenic plasma cells, terminally-differentiated memory cells (MBCs), and precursors relative to the Alhydrogel-combined immunization. Splenic B-cells from Poly I:C-vaccinated mice revealed an antibody-secreting cell- and MBC-differentiating gene expression profile. Biological processes such as antibody folding and secretion were highlighted by the Poly I:C-adjuvanted vaccination. These findings underscore the potential of Poly I:C to strengthen immune responses against Pv malaria.

Immunological factors linked to geographical variation in vaccine responses

Vaccination is one of medicine's greatest achievements; however, its full potential is hampered by considerable variation in efficacy across populations and geographical regions. For example, attenuated malaria vaccines in high-income countries confer almost 100% protection, whereas in low-income regions these same vaccines achieve only 20-50% protection. This trend is also observed for other vaccines, such as bacillus Calmette-Guérin (BCG), rotavirus and yellow fever vaccines, in terms of either immunogenicity or efficacy. Multiple environmental factors affect vaccine responses, including pathogen exposure, microbiota composition and dietary nutrients. However, there has been variable success with interventions that target these individual factors, highlighting the need for a better understanding of their downstream immunological mechanisms to develop new ways of modulating vaccine responses. Here, we review the immunological factors that underlie geographical variation in vaccine responses. Through the identification of causal pathways that link environmental influences to vaccine responsiveness, it might become possible to devise modulatory compounds that can complement vaccines for better outcomes in regions where they are needed most.

Zeb2 drives the formation of CD11c+ atypical B cells to sustain germinal centers that control persistent infection

CD11c+ atypical B cells (ABCs) are an alternative memory B cell lineage associated with immunization, infection, and autoimmunity. However, the factors that drive the transcriptional program of ABCs have not been identified, and the function of this population remains incompletely understood. Here, we identified candidate transcription factors associated with the ABC population based on a human tonsillar B cell single-cell dataset. We identified CD11c+ B cells in mice with a similar transcriptomic signature to human ABCs, and using an optimized CRISPR-Cas9 knockdown screen, we observed that loss of zinc finger E-box binding homeobox 2 (Zeb2) impaired ABC formation. Furthermore, ZEB2 haplo-insufficient Mowat-Wilson syndrome (MWS) patients have decreased circulating ABCs in the blood. In Cd23Cre/+Zeb2fl/fl mice with impaired ABC formation, ABCs were dispensable for efficient humoral responses after Plasmodium sporozoite immunization but were required to control recrudescent blood-stage malaria. Immune phenotyping revealed that ABCs drive optimal T follicular helper (TFH) cell formation and germinal center (GC) responses and they reside at the red/white pulp border, likely permitting better access to pathogen antigens for presentation. Collectively, our study shows that ABC formation is dependent on Zeb2, and these cells can limit recrudescent infection by sustaining GC reactions.

Designed mosaic nanoparticles enhance cross-reactive immune responses in mice

1Using computational methods, we designed 60-mer nanoparticles displaying SARS-like betacoronavirus (sarbecovirus) receptor-binding domains (RBDs) by (i) creating RBD sequences with 6 mutations in the SARS-COV-2 WA1 RBD that were predicted to retain proper folding and abrogate antibody responses to variable epitopes (mosaic-2COMs; mosaic-5COM), and (ii) selecting 7 natural sarbecovirus RBDs (mosaic-7COM). These antigens were compared with mosaic-8b, which elicits cross-reactive antibodies and protects from sarbecovirus challenges in animals. Immunizations in naïve and COVID-19 pre-vaccinated mice revealed that mosaic-7COM elicited higher binding and neutralization titers than mosaic-8b and related antigens. Deep mutational scanning showed that mosaic-7COM targeted conserved RBD epitopes. Mosaic-2COMs and mosaic-5COM elicited higher titers than homotypic SARS-CoV-2 Beta RBD-nanoparticles and increased potencies against some SARS-CoV-2 variants than mosaic-7COM. However, mosaic-7COM elicited more potent responses against zoonotic sarbecoviruses and highly mutated Omicrons. These results support using mosaic-7COM to protect against highly mutated SARS-CoV-2 variants and zoonotic sarbecoviruses with spillover potential.

Antibody-Mediated Suppression Regulates the Humoral Immune Response to Influenza Vaccination in Humans

BACKGROUND

Preexisting immunity, including memory B cells and preexisting antibodies, can modulate antibody responses to influenza in vivo to antigenically related antigens. We investigated whether preexisting hemagglutination inhibition (HAI) antibodies targeting the K163 epitope on the hemagglutinin (K163 antibodies) could affect antibody responses following vaccination with A/California/07/2009-like A(H1N1)pdm09 influenza viruses in humans.

METHODS

Pre- and postvaccination sera collected from 300 adults (birth years, 1961-1998) in 6 seasons (2010-2016) were analyzed by HAI assays with 2 reverse genetics viruses and A(H1N1) viruses circulated from 1977 to 2018. Antibody adsorption assays were used to verify the preexisting K163 antibody-mediated suppression effect.

RESULTS

Preexisting K163 antibody titers ≥80 affected HAI antibody responses following influenza vaccination containing A/California/07/2009-like antigens. At high K163 antibody concentrations (HAI antibody titers ≥160), all HAI antibody responses were suppressed. However, at moderate K163 antibody concentrations (HAI antibody titer, 80), only K163 epitope-specific antibody responses were suppressed, and novel HAI antibody responses targeting the non-K163 epitopes were induced by vaccination. Novel antibodies targeting non-K163 epitopes cross-reacted with newly emerging A(H1N1)pdm09 strains with a K163Q mutation rather than historic 1977-2007 A(H1N1) viruses.

CONCLUSIONS

K163 antibody-mediated suppression shapes antibody responses to A(H1N1)pdm09 vaccination. Understanding how preexisting antibodies suppress and redirect vaccine-induced antibody responses is of great importance to improve vaccine effectiveness.

Lack of affinity signature for germinal center cells that have initiated plasma cell differentiation

Long-lived plasma cells (PCs) secrete antibodies that can provide sustained immunity against infection. High-affinity cells are proposed to preferentially select into this compartment, potentiating the immune response. We used single-cell RNA-seq to track the germinal center (GC) development of Ighg2A10 B cells, specific for the Plasmodium falciparum circumsporozoite protein (PfCSP). Following immunization with Plasmodium sporozoites, we identified 3 populations of cells in the GC light zone (LZ). One LZ population expressed a gene signature associated with the initiation of PC differentiation and readily formed PCs in vitro. The estimated affinity of these pre-PC B cells was indistinguishable from that of LZ cells that remained in the GC. This remained true when high- or low-avidity recombinant PfCSP proteins were used as immunogens. These findings suggest that the initiation of PC development occurs via an affinity-independent process.

Germinal centers are permissive to subdominant antibody responses

Introduction

A protective humoral response to pathogens requires the development of high affinity antibodies in germinal centers (GC). The combination of antigens available during immunization has a strong impact on the strength and breadth of the antibody response. Antigens can display various levels of immunogenicity, and a hierarchy of immunodominance arises when the GC response to an antigen dampens the response to other antigens. Immunodominance is a challenge for the development of vaccines to mutating viruses, and for the development of broadly neutralizing antibodies. The extent by which antigens with different levels of immunogenicity compete for the induction of high affinity antibodies and therefore contribute to immunodominance is not known.

Methods

Here, we perform in silico simulations of the GC response, using a structural representation of antigens with complex surface amino acid composition and topology. We generate antigens with complex domains of different levels of immunogenicity and perform simulations with combinations of these domains.

Results

We found that GC dynamics were driven by the most immunogenic domain and immunodominance arose as affinity maturation to less immunogenic domain was inhibited. However, this inhibition was moderate since the less immunogenic domain exhibited a weak GC response in the absence of the most immunogenic domain. Less immunogenic domains reduced the dominance of GC responses to more immunogenic domains, albeit at a later time point.

Discussion

The simulations suggest that increased vaccine valency may decrease immunodominance of the GC response to strongly immunogenic domains and therefore, act as a potential strategy for the natural induction of broadly neutralizing antibodies in GC reactions.

Memory B cells

Recent advances in studies of immune memory in mice and humans have reinforced the concept that memory B cells play a critical role in protection against repeated infections, particularly from variant viruses. Hence, insights into the development of high-quality memory B cells that can generate broadly neutralizing antibodies that bind such variants are key for successful vaccine development. Here, we review the cellular and molecular mechanisms by which memory B cells are generated and how these processes shape the antibody diversity and breadth of memory B cells. Then, we discuss the mechanisms of memory B cell reactivation in the context of established immune memory; the contribution of antibody feedback to this process has now begun to be reappreciated.

Role of affinity in plasma cell development in the germinal center light zone

Protective immune responses to many pathogens depend on the development of high-affinity antibody-producing plasma cells (PC) in germinal centers (GCs). Transgenic models suggest that there is a stringent affinity-based barrier to PC development. Whether a similar high-affinity barrier regulates PC development under physiologic circumstances and the nature of the PC fate decision has not been defined precisely. Here, we use a fate-mapping approach to examine the relationship between GC B cells selected to undergo additional rounds of affinity maturation, GC pre-PC, and PC. The data show that initial PC selection overlaps with GC B cell selection, but that the PC compartment accumulates a less diverse and higher affinity collection of antibodies over time. Thus, whereas the GC continues to diversify over time, affinity-based pre-PC selection sieves the GC to enable the accumulation of a more restricted group of high-affinity antibody-secreting PC.

A candidate antibody drug for prevention of malaria

Over 75% of malaria-attributable deaths occur in children under the age of 5 years. However, the first malaria vaccine recommended by the World Health Organization (WHO) for pediatric use, RTS,S/AS01 (Mosquirix), has modest efficacy. Complementary strategies, including monoclonal antibodies, will be important in efforts to eradicate malaria. Here we characterize the circulating B cell repertoires of 45 RTS,S/AS01 vaccinees and discover monoclonal antibodies for development as potential therapeutics. We generated >28,000 antibody sequences and tested 481 antibodies for binding activity and 125 antibodies for antimalaria activity in vivo. Through these analyses we identified correlations suggesting that sequences in Plasmodium falciparum circumsporozoite protein, the target antigen in RTS,S/AS01, may induce immunodominant antibody responses that limit more protective, but subdominant, responses. Using binding studies, mouse malaria models, biomanufacturing assessments and protein stability assays, we selected AB-000224 and AB-007088 for advancement as a clinical lead and backup. We engineered the variable domains (Fv) of both antibodies to enable low-cost manufacturing at scale for distribution to pediatric populations, in alignment with WHO's preferred product guidelines. The engineered clone with the optimal manufacturing and drug property profile, MAM01, was advanced into clinical development.

Memory B cell differentiation from germinal centers

Establishment of humoral immune memory depends on two layers of defense: pre-existing antibodies secreted by long-lived plasma cells; and the antibodies produced by antigen-reactivated memory B cells. Memory B cells can now be considered as a second layer of defense upon re-infection by variant pathogens that have not been cleared by the long-lived plasma cell-mediated defense. Affinity-matured memory B cells are derived from the germinal center (GC) reaction, but the selection mechanism of GC B cells into the memory compartment is still incompletely understood. Recent studies have revealed the critical determinants of cellular and molecular factors for memory B cell differentiation from the GC reaction. In addition, the contribution of antibody-mediated feedback regulation to B cell selection, as exemplified by the B cell response upon COVID-19 mRNA vaccination, has now garnered considerable attention, which may provide valuable implications for future vaccine design.

Opposing effects of pre-existing antibody and memory T cell help on the dynamics of recall germinal centers

Re-exposure to an antigen generates serum antibody responses that greatly exceed in magnitude those elicited by primary antigen encounter, while simultaneously driving the formation of recall germinal centers (GCs). Although recall GCs in mice are composed almost entirely of naïve B cells, recall antibody titers derive overwhelmingly from memory B cells, suggesting a division between cellular and serum compartments. Here, we show that this schism is at least partly explained by a marked decrease in the ability of recall GC B cells to detectably bind antigen. Variant priming and plasmablast ablation experiments show that this decrease is largely due to suppression by pre-existing antibody, whereas hapten-carrier experiments reveal a role for memory T cell help in allowing B cells with undetectable antigen binding to access GCs. We propose a model in which antibody-mediated feedback steers recall GC B cells away from previously targeted epitopes, thus enabling specific targeting of variant epitopes.