Scientific Publications

Germinal centers (GCs) are a complex and important aspect of humoral immunity. How GCs deal with changing antigens remains unclear, yet this biology could be central to next-generation vaccine strategies such as germline targeting. Here we demonstrate, in a mouse model with human immunodeficiency virus envelope surface protein immunogens, that rapid delivery of homologous or heterologous boosts results in highly positive outcomes. Rapid reimmunization expands on-target GC B cell (BGC) populations, which emerge almost exclusively from existing BGC cells. Early homologous boosting avoids prohibitive antibody titers and utilizes off-target antibodies to maximize the BGC response. Heterologous rapid boosting shifts affinity maturation towards the new antigen. The 'refueled' GCs are sustained, developing large affinity gains and evolving rapidly to bind wildtype HIV Env trimer within 56 days, even when using as few as two distinct antigens. These findings provide insights into GC biology and translatable paths to leveraging accelerated GC function.

The high antigenic diversity of HIV has been a major obstacle to development of a broadly protective vaccine. Nevertheless, protective HIV broadly neutralizing antibodies (bnAbs) exist and have been proposed as templates for vaccine development1-6. Germline-targeting is a conceptually radical vaccine design approach to elicit bnAbs, aiming to prime rare bnAb-precursor B cells possessing pre-determined human genetic and structural features shared with template bnAbs, and then guide B cell affinity maturation to potent bnAb evolution with heterologous boosters7-11. Although the approach has shown promise in clinical12-17 and pre-clinical18-34 studies, it faces many immunological challenges and, to date, has not succeeded in generating bnAbs in humans or nontransgenic animals. Here, we report an adjuvanted protein germline-targeting vaccine tested in outbred nonhuman primates that generated bnAb-class memory B cells and sera capable of neutralizing diverse HIV clinical isolates. bnAb lineages were generated in ≥50% of animals, achieving up to 67% neutralization breadth compared to the reference bnAb. Vaccine-induced bnAbs exhibited precise structural mimicry of human bnAb interactions with HIV envelope (Env), matching the germline-targeting predictions. Furthermore, serum bnAb activity developed in 44% of animals and in the most striking instance reached titers expected to confer protection against diverse HIV isolates. These results demonstrate proof of principle that germline-targeting vaccines can reproducibly elicit prespecified classes of bnAbs to prespecified epitopes under endogenous conditions, supporting further optimization of this approach for HIV vaccine development.

In 2025, Uganda had Africa's ninth outbreak of disease caused by Sudan virus (SUDV), a filovirus similar to Ebola virus (EBOV) that causes severe febrile disease in humans. In this Review, we summarise the evidence on the epidemiology, natural history, and immunology of Sudan virus disease (SVD) from outbreaks since 1976. Following an incubation period averaging about 1 week, SVD typically presents with an influenza-like illness followed by a severe diarrhoeal disease, often accompanied by cardiorespiratory symptoms and dehydration. Clinical findings can include kidney and liver injury, acute inflammation, and coagulopathy. Severe cases can progress rapidly to shock, multiorgan failure, and death. The pooled case-fatality rate until 2022 was 49% (95% CI 39-58), although a lower case-fatality rate of 29% was recorded during the 2025 outbreak. The virus is detectable in blood from symptom onset, peaking during acute illness. Transmission occurs mainly through close contact with acutely symptomatic individuals and their body fluids, driving household and nosocomial spread. Early T-cell responses and SUDV-specific antibodies might be important for survival, and suppressed immunity and uncontrolled inflammation might predict fatal outcomes. Survivors present durable humoral and cellular immunity for up to 15 years after infection. Although outbreaks to date offer valuable insights into SVD, substantial evidence gaps and limitations exist. Future outbreak preparedness should include prospective planning for high-quality research that can be rapidly implemented to address key evidence gaps. Strengthening these data, together with advancing the development and evaluation of vaccines and therapeutics, will be essential for timely and effective outbreak response.

The first workshop dedicated to Lassa virus–specific correlates of protection (CoP) was held in 2024 and was convened by the Coalition for Epidemic Preparedness Innovations (CEPI). Experts from multiple disciplines reviewed existing knowledge and identified gaps in understanding Lassa virus- and vaccine-induced immune responses. Discussions covered key areas including epidemiology, immunogenicity, preclinical and clinical research, data science, and regulatory considerations, with the goal of pinpointing opportunities to discover CoP.

As rates of antimicrobial resistance (AMR) among bacterial pathogens continue to rise, the discovery and development of novel classes of therapeutics that can serve as alternatives or adjuncts to traditional small-molecule antibiotics, such as monoclonal antibodies (mAbs), is a public health priority. Some of the most promising antigen targets for antibacterial mAbs are surface polysaccharides such as O-antigen (O-Ag), a component of the lipopolysaccharide found on the outer membrane of gram-negative bacteria. However, developing mAbs against bacterial surface polysaccharides with sufficient breadth and potency to be clinically viable is difficult in part because antibodies against polysaccharides are generally low affinity, and the challenging biochemistry of polysaccharides often precludes further affinity maturation of mAbs against these targets in vitro. Here, we use a phage display library and a whole-cell in-solution panning strategy to successfully improve the affinity of a mAb against Shigella flexneri 3a O-Ag in vitro without requiring the purification of the target antigen. We demonstrate that a single mutation can improve apparent affinity as measured by ELISA by approximately 10-fold without detectably increasing polyreactivity, and increased apparent affinity correlates with enhanced potency in antibacterial effector function and anti-virulence assays. In addition, the most potent variants also gained increased breadth, successfully coordinating complement deposition and complement-independent opsonophagocytosis against S. flexneri 3b, a serotype weakly recognized by the parent mAb. Altogether, this work represents an important first step towards expanding the antibody engineering toolkit for bacterial surface polysaccharides, which will aid the development of novel mAb therapeutics against AMR bacterial pathogens.

HIV broadly neutralizing antibodies (bnAbs) are promising reagents for prevention and therapy of disease; however, their elicitation is constrained by genetic limitations of the human B cell antigen-receptor (BCR) repertoire. Precision genome-editing offers a potential solution by enabling bnAb genes to be programmed into the BCR repertoire as IgH-modified B cells. Such cells can be vaccinated to elicit durable bnAb memory responses in mice; however, extending this success to non-human primates (NHPs) would be a major advance towards clinical translation. Here, we show that ex vivo reprogrammed NHP B cells can survive autologous infusion and respond to immunization, differentiating into antibody-secreting cells (ASCs) that can produce up to 1 µg/ml of a bnAb in serum following vaccination prime. Although durable transgenic memory responses were not generated, vaccination of engineered cells in secondary lymphoid organoid (SLO) cultures recapitulated transient ASC responses in vitro. These findings suggest that NHP-derived SLOs could provide a platform to optimize engineering and vaccination conditions that drive germinal center maturation of IgH-reprogrammed B cells in a clinically relevant NHP model, supporting the development of engineered B-cell vaccines that generate durable bnAb responses as a potential functional cure for HIV.

Malaria is a leading cause of disease in developing countries. The licensed malaria vaccine RTS,S/AS01 confers partial protection in part due to the elicitation of circumsporozoite protein (CSP) antibodies, of which those to the CSP repeat and junctional regions offer the most potent protection. Anti-repeat region antibodies, including the protective antibody L9, frequently develop mutations that promote inter-Fab contacts when bound to CSP in "spiral" quaternary structures. As a first step toward the design of immunogens that elicit L9-like antibodies, we utilized generative deep learning models to design epitope scaffolds that incorporated up to three junctional repeat epitopes with structural conformations and relative spatial orientations matching those of the multivalent complex of CSP bound to three copies of L9. Affinity and structural studies demonstrated accurate scaffolding of two epitopes with the intended relative orientation, and displacement of the third epitope, while maintaining inter-Fab contacts between L9 antibodies. In a mouse model of malaria liver invasion, immunization with nanoparticles displaying these scaffold immunogens inhibited liver invasion as potently as matched nanoparticles displaying a short junctional peptide but less potently than the same nanoparticles displaying longer junctional peptides. This study demonstrates a substantial advance for design of multiepitope scaffolds with predetermined relative epitope spatial positioning. The study also represents an initial step toward development of multiepitope immunogens to elicit antibodies that utilize homotypic interactions to bind pathogens in multivalent clusters.

Germline targeting (GT) is a promising strategy to activate rare broadly neutralizing antibody (bnAb)-producing B cells against HIV, but induction of such responses in outbred animals has not been achieved. Using antibody-guided structure-based design, we engineered a GT HIV trimer immunogen, Q23-APEX-GT2, which primes diverse V2-apex bnAb precursors. Q23-APEX-GT2 efficiently activated rare V2-apex-specific B cells in humanized knockin mice and consistently elicited immunofocused antibody responses in outbred rhesus macaques, priming multiple long heavy-chain complementarity-determining region 3 (CDRH3)-loop bnAb-B cell lineages. Monoclonal antibodies isolated from immunized macaques showed broad heterologous HIV trimer recognition and modest cross-neutralization of diverse tier-2 viruses. Cryoelectron microscopy (cryo-EM) structural studies confirmed precise epitope targeting and revealed CDRH3-mediated binding modes that mirrored those of human V2-apex bnAbs. Together, these findings establish proof of principle for priming and early maturation of authentic V2-apex bnAb precursors in outbred macaques and highlight the promise of V2-apex-targeted HIV vaccines.

HIV vaccine strategies include aims to elicit broadly neutralizing antibodies (bnAbs) targeting the CD4-binding site, that are derived from immunoglobulin heavy-chain variable genes 1-2 (VH1-2) and 1-46 (VH1-46). Here, we present an integrated analysis of VH1-46 bnAbs, including in vitro functional studies, cryo-electron microscopy structures of two VH1-46 bnAbs (1-23 and 9-71) complexed with envelope trimers, and comprehensive structural and immunogenetic analyses, to help guide vaccine design. We show that VH1-46-derived bnAbs use diverse light-chain variable (VK/VL) genes and LCDR3 lengths commonly found in human antibody repertoires, which generate unique LCDR3 signatures that influence both the antibody paratope and approach angle. We identify three VH1-46 bnAb classes, 1B2530 (VL1-47), CH235 (VK3-15), and 561 (VK3-20), with the 561 class further subdivided into types I and II. Our findings indicate that VH1-46 priming immunogens should be tailored to each bnAb class, with 561-class bnAbs presenting optimal targets for germline-targeting vaccine design.

Introduction Screening for acute and early HIV infections (AEHI) among men who have sex with men (MSM) remains uncommon in sub-Saharan Africa (SSA). Yet, undiagnosed AEHI among MSM and subsequent failure to link to care are important drivers of the HIV epidemic. We conducted a systematic review and meta-analysis of AEHI yield among MSM mobilized for AEHI testing; and assessed which risk factors and/or symptoms could increase AEHI yield in MSM. Methods We systematically searched four databases from their inception through May 2020 for studies reporting strategies of mobilizing MSM for testing and their AEHI yield, or risk and/or symptom scores targeting AEHI screening. AEHI yield was defined as the proportion of AEHI cases among the total number of visits. Study estimates for AEHI yield were pooled using random effects models. Predictive ability of risk and/or symptom scores was expressed as the area under the receiver operator curve (AUC). Results Twenty-two studies were identified and included a variety of mobilization strategies (eight studies) and risk and/or symptom scores (fourteen studies). The overall pooled AEHI yield was 6.3% (95% CI, 2.1 to 12.4; I2 = 94.9%; five studies); yield varied between studies using targeted strategies (11.1%; 95% CI, 5.9 to 17.6; I2 = 83.8%; three studies) versus universal testing (1.6%; 95% CI, 0.8 to 2.4; two studies). The AUC of risk and/or symptom scores ranged from 0.69 to 0.89 in development study samples, and from 0.51 to 0.88 in validation study samples. AUC was the highest for scores including symptoms, such as diarrhoea, fever and fatigue. Key risk score variables were age, number of sexual partners, condomless receptive anal intercourse, sexual intercourse with a person living with HIV, a sexually transmitted infection, and illicit drug use. No studies were identified that assessed AEHI yield among MSM in SSA and risk and/or symptom scores developed among MSM in SSA lacked validation. Conclusions Strategies mobilizing MSM for targeted AEHI testing resulted in substantially higher AEHI yields than universal AEHI testing. Targeted AEHI testing may be optimized using risk and/or symptom scores, especially if scores include symptoms. Studies assessing AEHI yield and validation of risk and/or symptom scores among MSM in SSA are urgently needed.

Combination vaccine formulations contain distinct components targeting multiple strains of a single pathogen or multiple pathogens. By minimizing the number of separate vaccine administrations required, combination vaccines have been critical in allowing the broad expansion of the number and range of diseases that can now be prevented by immunization. Recent advances in vaccine development and our understanding of the immune system now make it possible to envision how new combination vaccines could play a major role in helping immunization programs address a much wider range of emerging or still problematic pathogens. However, few combinations are currently in the pipeline, in part due to their inherently increased complexity and cost of development compared to standalone formulations. This complexity, in turn, is partly driven by the regulatory requirements surrounding the clinical study program for the combination vaccine, especially the primary clinical endpoints and the required degree of precision around those endpoints, as these ultimately determine the sample size, cost, and duration of the study. As part of a larger effort to facilitate combination vaccine development, vaccine experts at the World Health Organization and PATH coordinated a one-day meeting in March 2025 gathering current and former national regulatory agency staff from a dozen countries, together with vaccine developers, representatives from funding and procurement agencies, and public health and policy officials. The convened participants held spirited discussions on how multiple immune markers and controlled human infection models (CHIM) might contribute to the demonstration of vaccine efficacy. In addition, participants considered the possibility of relying on clinical endpoints when the vaccine components are directed against pathogens causing the same disease syndrome but etiological determination of each component's contribution is not feasible. Regulators welcomed scientifically sound, creative proposals for demonstration of efficacy, and agreed that the benefit-risk of the combination vaccine as a whole should be the primary focus.

Circulating antibodies from previous immune encounters impact subsequent humoral responses. Here, we investigated how local epitope-specific competition shapes ongoing germinal center (GC) responses by delivering an mRNA-LNP-encoded membrane-bound immunogen displaying three conserved HIV-1 envelope (Env) epitopes to mouse models bearing B cell receptors (BCRs) of defined affinities. High-affinity B cells exhibited shorter GC residency than lower-affinity counterparts. B cells engaged GC reactions at equivalent rates in the presence or absence of clonal lineages binding the same epitope with similar affinities; however, higher-affinity clones suppressed lower-affinity counterparts targeting the same epitope. Spatial transcriptomics revealed plasma-like cells within and adjacent to the GC, and early immunoglobulin G (IgG) was detectable in draining lymph nodes. Our findings suggest that a self-modulating local antibody feedback loop limits epitope-specific recognition-dampening selection for higher-affinity B cells and facilitating epitope spreading by redirecting the response toward alternative epitopes.