Exploring the impact of persistent mutations in SARS-CoV-2 variants and reduced immunity on breakthrough infections (BTIs) is crucial, particularly in understanding how antigen-specific memory B cells (MBCs) respond to new variants. We followed 107 participants who received the ancestral inactivated vaccine and experienced one or two Omicron BTIs over six months. Using flow cytometry, SARS-CoV-2 antigen probes, single-cell RNA sequencing, and B cell receptor (BCR) profiling, we assessed MBCs and immune diversity. Our findings revealed that although neutralizing antibody levels decreased over time, the number of specific MBCs remained stable and matured progressively. Notably, pre-existing Omicron-specific MBCs played a key role in preventing secondary Omicron infections. Differential gene analysis showed enrichment in antigen processing and immune regulation pathways, while clonal lineage analysis revealed more B cell expansion and V(D)J gene-specific rearrangements in high neutralization samples. These results emphasize MBCs' critical role in long-term immunity and inform future vaccination strategies.
© 2025 The Author(s).

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.
Copyright © 2025 The Author(s). Published by Elsevier Inc. All rights reserved.

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.

A mucosal route of vaccination could prevent severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) replication at the site of infection and limit transmission. We compared protection against heterologous XBB.1.16 challenge in nonhuman primates (NHPs) ~5 months following intramuscular boosting with bivalent mRNA encoding WA1 and BA.5 spike proteins or mucosal boosting with a WA1-BA.5 bivalent chimpanzee adenoviral-vectored vaccine delivered by intranasal or aerosol device. NHPs boosted by either mucosal route had minimal virus replication in the nose and lungs, respectively. By contrast, protection by intramuscular mRNA was limited to the lower airways. The mucosally delivered vaccine elicited durable airway IgG and IgA responses and, unlike the intramuscular mRNA vaccine, induced spike-specific B cells in the lungs. IgG, IgA and T cell responses correlated with protection in the lungs, whereas mucosal IgA alone correlated with upper airway protection. This study highlights differential mucosal and serum correlates of protection and how mucosal vaccines can durably prevent infection against SARS-CoV-2.
© 2024. This is a U.S. Government work and not under copyright protection in the US; foreign copyright protection may apply.

Understanding the evolution of the B cell response to severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) variants is fundamental to design the next generation of vaccines and therapeutics. We longitudinally analyze at the single-cell level almost 900 neutralizing human monoclonal antibodies (nAbs) isolated from vaccinated people and from individuals with hybrid and super hybrid immunity (SH), developed after three mRNA vaccine doses and two breakthrough infections. The most potent neutralization and Fc functions against highly mutated variants belong to the SH cohort. Repertoire analysis shows that the original Wuhan antigenic sin drives the convergent expansion of the same B cell germlines in vaccinated and SH cohorts. Only Omicron breakthrough infections expand previously unseen germ lines and generate broadly nAbs by restoring IGHV3-53/3-66 germ lines. Our analyses find that B cells initially expanded by the original antigenic sin continue to play a fundamental role in the evolution of the immune response toward an evolving virus.
Copyright © 2024 The Author(s). Published by Elsevier Inc. All rights reserved.