Devyani Joshi

The longitudinal effects of initial influenza exposure on the magnitude, persistence, and antigen specificity of antibody responses during infancy remain incompletely understood. We investigated humoral antibody responses following primary influenza infection or seasonal vaccination in a prospective US birth cohort with weekly respiratory surveillance for influenza infection. Influenza-specific serum IgG binding to H1 and H3 haemagglutinin (HA) antigens, HA inhibition (HAI), and live-virus neutralizing antibody responses were assessed longitudinally. To minimize the influence of maternally derived antibodies, analyses of primary exposure responses were restricted to infants for whom influenza-specific maternal antibodies had declined below the assay detection limit before exposure. Antibody responses were compared following primary infection and vaccination and examined after subsequent annual vaccination. We found that maternal influenza-specific IgG declined rapidly during early infancy. Among infants without detectable pre-exposure influenza-specific antibodies, primary influenza infection was associated with greater post-exposure antibody responses and less measurable decline over follow-up than primary vaccination. These groups differed in age, calendar season, and exposure characteristics, limiting direct attribution of these differences to the route of exposure. In infants with previous influenza infection followed by vaccination, responses after subsequent vaccination initially showed greater binding to the previously infecting subtype among the tested HA antigens. With repeated vaccination, responses became more distributed across the tested antigens. Our findings reveal differences in the magnitude, persistence, and antigen specificity of antibody responses according to the nature and sequence of influenza exposure. By prospectively capturing early-life exposures, this study provides longitudinal evidence linking exposure history to subsequent humoral antibody responses.

As Guest Editors for the Special Issue “Advances in Vaccine Adjuvants,” we are pleased to offer this closing editorial

Therapeutic antibodies have transformed the management of infectious diseases, autoimmune disorders, and cancer, yet most approved agents continue to rely on a limited range of IgG-based Fc scaffolds. Consequently, the broader therapeutic potential of antibody isotypes, subclasses, allotypes, and host Fc receptor (FcR) genetics remains incompletely integrated into antibody design and clinical development. Emerging evidence indicates that these determinants profoundly influence effector function, pharmacokinetics, tissue distribution, immunogenicity, and therapeutic efficacy. This review provides a comprehensive, translational perspective on how antibody isotype selection, IgG subclass biology, allotypic variation, Fcγ receptor (FcγR) and neonatal Fc receptor (FcRn) genetics, and Fc engineering collectively shape therapeutic outcomes. Distinct from previous reviews that examine these factors individually, we integrate their roles across infectious diseases, autoimmunity, and cancer to identify common principles governing Fc-dependent immunity and therapeutic response. We further describe the clinical implications of Fc-mediated mechanisms, Fc glycoengineering, FcRn-targeted therapies, systems serology, and emerging non-IgG antibody platforms, highlighting both established applications and unresolved challenges. By unifying structural immunology, Fc pharmacology, host genetics, and disease biology, this review advances the concept of precision Fc pharmacology, in which antibody scaffold selection and Fc optimization are tailored to specific disease contexts and patient immune profiles. This framework provides a roadmap for the rational development of next-generation antibody therapeutics with improved efficacy, safety, and clinical precision.

Vaccination remains one of the most effective strategies for preventing infectious diseases. Yet, the success of modern vaccines increasingly depends on the rational design of adjuvants that enhance and shape immune responses. In this review, we examine current and emerging adjuvant strategies for viral vaccines across the human lifespan. Traditional adjuvants, particularly aluminum salts, have long served as the foundation of vaccine formulations. Still, their limitations have driven the exploration of novel platforms, including emulsions, nucleic acid-based adjuvants, and advanced particulate delivery platforms with intrinsic immunostimulatory properties. These newer approaches act through diverse mechanisms, such as activating innate immune pathways via pattern recognition receptors (PRRs) and stimulating antigen-presenting cells (APCs), thereby improving both humoral and cellular immunity. Recent advances in molecular biology, nanotechnology, and systems vaccinology have deepened mechanistic understanding and enabled more precise modulation of immune responses. However, significant challenges remain, including incomplete knowledge of adjuvant mechanisms, limited diversity among licensed adjuvants, safety concerns, and inconsistent efficacy across age groups. In particular, immune immaturity in infants and immunosenescence in older adults highlight the need for age-specific adjuvant strategies. The review identifies critical gaps in comparative studies, long-term safety data, and the development of adjuvants capable of inducing broad and durable immunity. Further, this article integrates licensed and emerging viral vaccine adjuvants through a lifespan framework. Addressing these limitations through interdisciplinary research and precision-based approaches will be essential for advancing next-generation vaccines and improving global preparedness for emerging infectious diseases.

The emergence of the SARS-CoV-2 Omicron BA.2.86 subvariant, a lineage derived from the BA.2 strain, led to the 2024-2025 COVID-19 vaccine update to include KP.2 or related JN.1-lineage spike antigens. We evaluated the magnitude, breadth, and durability of humoral immune responses following a single KP.2 vaccine dose in a longitudinal cohort of 21 individuals up to six months. KP.2 vaccination increased spike-specific binding and neutralizing antibodies against the ancestral WA1 strain, alongside the BA.5, XBB.1.5, and KP.2 variants. Power law modeling estimated half-lives for WA1- and KP.2-specific IgG responses at 770 and 248 days, respectively. Additionally, the KP.2 dose increased IgG1 and IgG4 subclasses more than IgG2 and IgG3 responses to both spike proteins. Serum depletion experiments using WA1 or KP.2 proteins demonstrated most vaccine-elicited antibodies were cross-reactive. Consequently, KP.2 vaccine-induced antibodies retained broad neutralizing activity against recently circulating Omicron subvariants (BA.2.86, KP.3.1.1, XEC, LP.8.1, LF.7, XFG.3.12, PQ.1, BA.3.2.1, and RE.2). Using a live virus neutralization assay, XFG.3.12 showed the greatest reduction in neutralizing titers relative to KP.2 (4.2-fold). In a small subset, an LP.8.1 vaccine dose increased neutralizing activity against the matched variant while maintaining WA1 and KP.2 cross-reactivity, but only modestly increased antibodies to divergent variants BA.3.2.1 and RE.2. Ultimately, these data indicate the KP.2 mRNA vaccine generates durable, cross-reactive responses against current Omicron subvariants. However, ongoing spike evolution impacts neutralization of emerging lineages, highlighting the need for continued viral monitoring and timely vaccine updates. IMPORTANCE: SARS-CoV-2 continues to evolve, raising ongoing concerns about how well updated vaccines protect against emerging variants. This study evaluates antibody responses after KP.2 spike mRNA vaccine dose and shows that a single dose induces durable and broadly cross-reactive immunity against both earlier strains and recently circulating Omicron subvariants. Despite this breadth, reduced neutralizing activity against certain emerging variants indicates that ongoing antigenic changes can impact vaccine induced antibody effectiveness. These findings provide insight into how current vaccines perform over time and highlight the need to track viral evolution and update vaccine antigens to maintain broad protection against severe disease, hospitalization, and death.

The rapid emergence of divergent SARS-CoV-2 variants led to a 2023–2024 update of the COVID-19 mRNA vaccine to a monovalent version containing the XBB.1.5 SARS-CoV-2 spike antigen. To determine the durability and breadth of the antibody responses after immunization, we analyzed antibodies and memory B cells from 24 individuals before and after a single XBB.1.5 mRNA vaccine dose for up to 6 months. Using a live virus neutralization assay, we found that the XBB.1.5 vaccine improved the magnitude and breadth of antibody neutralizing activity against the ancestral SARS-CoV-2 strain (WA1), BA.5 strain, and XBB.1.5 Omicron variants. Durable WA1 and XBB.1.5 IgG spike protein binding antibodies were induced with an estimated half-life of 703 and 531 days (at day 120), respectively. There was a greater increase of IgG1 and IgG4 binding antibodies against the XBB.1.5 spike protein compared with the WA1 spike protein postvaccination. A high proportion of antibodies were cross-reactive against both WA1 and XBB.1.5 strains, as determined by serum depletion and memory B cell analysis, and this cross-reactivity was durable. Last, we evaluated the neutralizing activity of these antibodies against more contemporary circulating Omicron strains and observed reduced cross-reactivity to KP.2 and KP.3 compared with XBB.1.5 6 months after vaccination. These data show that the XBB.1.5 COVID-19 vaccine promotes more durable binding and neutralizing antibodies than prior ancestral WA1 or bivalent vaccines. However, divergent Omicron variants with mutations in the spike protein were able to evade these neutralizing antibodies, emphasizing the need for periodic consideration of COVID-19 vaccine reformulation.

Antibodies are produced when naive B cells differentiate into plasma cells within germinal centres (GCs) of lymphoid tissues. Patients with B cell lymphoma on effective immunotherapies exhibit diminished antibody production, leading to higher infection rates and reduced vaccine efficacy, even after B cell recovery. Current ex vivo models fail to sustain long-term GC reactions and effectively test B cell responses. Here we developed synthetic hydrogels mimicking the lymphoid tissue microenvironment, enabling human GCs from tonsils and peripheral blood mononuclear cell-derived B cells. Immune organoids derived from peripheral blood mononuclear cells maintain GC B cells and plasma cells longer than tonsil-derived ones and exhibit unique B cell programming, including GC compartments, somatic hypermutation, immunoglobulin class switching and B cell clones. Chemical inhibition of transcriptional and epigenetic processes enhances plasma cell formation. While integrating polarized CXCL12 protein in a lymphoid organ-on-chip modulates GC responses in healthy donor B cells, it fails with B cells derived from patients with lymphoma. Our system allows rapid, controlled modelling of immune responses and B cell disorders.

Background: We assessed associations between binding antibody (bAb) concentration <5 days from symptom onset and testing positive for COVID-19 among patients in a test-negative study. Methods: From October 2021 to June 2022, study sites in 7 states enrolled patients aged ≥6 months presenting with acute respiratory illness. Respiratory specimens were tested for SARS-CoV-2. In blood specimens, we measured concentrations of anti-SARS-CoV-2 antibodies against the spike protein receptor binding domain (RBD) and nucleocapsid antigens from the ancestral strain in standardized bAb units (BAU). Percentage change in odds of COVID-19 by increasing anti-RBD bAb was estimated via logistic regression as (1 – adjusted odds ratio of COVID-19) × 100, adjusting for COVID-19 mRNA vaccine doses, age, site, and high-risk exposure. Results: Out of 2018 symptomatic patients, 662 (33%) tested positive for acute SARS-CoV-2 infection. Geometric mean RBD bAb levels were lower among COVID-19 cases than SARS-CoV-2 test-negative controls during the Delta-predominant period (112 vs 498 BAU/mL) and Omicron-predominant period (823 vs 1189 BAU/mL). Acute-phase ancestral spike RBD bAb levels associated with 50% lower odds of COVID-19 were 1968 BAU/mL against Delta and 3375 BAU/mL against Omicron; thresholds may differ in other laboratories. Conclusions: During acute illness, antibody concentrations against ancestral spike RBD were associated with protection against COVID-19.

The molecule (S)-4,5-dihydroxy-2,3-pentanedione (DPD) is produced by many different species of bacteria and is involved in bacterial communication. DPD is the precursor of signal molecule autoinducer-2 (AI-2) and has high potential to be used as a vaccine adjuvant. Vaccine adjuvants are compounds that enhance the stability and immunogenicity of vaccine antigens, modulate efficacy, and increase the immune response to a particular antigen. Previously, the microparticulate form of (S)-DPD was found to have an adjuvant effect with the gonorrhea vaccine. In this study, we evaluated the immunogenicity and adjuvanticity of several synthetic analogs of the (S)-DPD molecule, including ent—DPD((R)-4,5-dihydroxy-2,3-pentanedione), n-butyl—DPD ((S)-1,2-dihydroxy-3,4-octanedione), isobutyl—DPD ((S)-1,2-dihydroxy-6-methyl-3,4-heptanedione), n-hexyl—DPD ((S)-1,2-dihydroxy-3,4-decanedione), and phenyl—DPD ((S)-3,4-dihydroxy-1-phenyl-1,2-butanedione), in microparticulate formulations. The microparticulate formulations of all analogs of (S)-DPD were found to be noncytotoxic toward dendritic cells. Among these analogs, ent—DPD, n-butyl—DPD, and isobutyl—DPD were found to be immunogenic toward antigens and showed adjuvant efficacy with microparticulate gonorrhea vaccines. It was observed that n-hexyl—DPD and phenyl—DPD did not show any adjuvant effect. This study shows that synthetic analogs of (S)-DPD molecules are capable of eliciting adjuvant effects with vaccines. A future in vivo evaluation will further confirm that these analogs are promising vaccine adjuvants.