Scientific Publications

Durability of T follicular helper (Tfh) cell responses is pivotal for generating high affinity antibodies. We characterized Tfh cell responses to HIV Env immunization longitudinally in non-human primates, analyzing >500,000 CD4+ T cells from 192 lymph node (LN) samples collected over 60 weeks, including >36,000 vaccine-specific Tfh cells. An escalating-dose priming regimen elicited higher and more sustained Tfh cell responses in LNs, compared with conventional bolus immunization. Multiple vaccine-specific germinal center (GC)-Tfh subpopulations, including interleukin (IL)4hi and IL21hi GC-Tfh cells, were continually present. Antigen-specific Tfh clones persisted within GCs for over 6 months, maintaining stable gene expression profiles and showing no signs of exhaustion. Vaccine-specific Tfh proliferation signatures were detectable for 27+ weeks after priming. Tfh subpopulations correlated with HIV Env-specific antibody and neutralization titers. Additionally, substantial Tfh clonal migration occurred between LNs. Thus, complex populations of GC-Tfh can enhance antibody responses and survive for 48 weeks in GC responses without new antigen delivery, with implications for immunization regimens.

Background: A lack of general vaccine confidence has been identified as a potential barrier to the introduction of new tuberculosis (TB) vaccines. In the absence of TB-specific vaccine confidence surveys, analysis of general national vaccine confidence data can provide a useful proxy to determine where demand generation strategies may need to be focused ahead of future TB vaccine introductions. Methods: We analysed 2023 Vaccine Confidence Index (VCI) data from 18 of the 49 countries present on at least one of the three World Health Organisation (WHO) high TB burden lists, and together containing 65% of the global TB burden, to explore overall confidence in vaccines in high TB burden countries. Based on collected answers to three different statements, we categorised responses 1-2 as 'positive' (vaccine confident) and 3-4 as 'negative' (vaccine hesitant) and calculated a total vaccine confidence score using the mean proportion of positive responses across the three statements. Results: In 2023, over 80% of respondents in 14 of the 18 countries analysed, and over 60% of respondents in all 18 countries, believed that 'vaccines are important for people of all ages'. India, accounting for around 30% of global TB cases, demonstrated confidence levels exceeding 90%, as did Vietnam, Ethiopia and Sierra Leone. South Africa, the country with the seventh highest TB burden (280,000 incident cases in 2023), Russia and Cameroon exhibited a relatively low vaccine confidence score of 75.5% or lower, signalling a potential area for concern. These countries may require focused awareness-raising and advocacy efforts prior to the rollout of new TB vaccines, though additional research on TB-specific confidence indicators is needed. Conclusions: This analysis underscores the importance of monitoring vaccine confidence levels to address emerging challenges to maintaining or bolstering the public's trust in vaccination. Our findings could help determine which countries to prioritise for social mobilisation and demand generation efforts to boost vaccine confidence, and thus improve readiness for new TB vaccines.

Background: No vaccine is currently available for Lassa fever, a viral hemorrhagic disease that is estimated to cause thousands of deaths each year in western Africa. A replication-competent recombinant vesicular stomatitis virus-vectored vaccine encoding a Lassa virus (LASV) glycoprotein complex, rVSVΔG-LASV-GPC, has been developed, but data on its safety and immunogenicity are limited. Methods: In this phase 1, double-blind trial conducted in the United States and Liberia, we randomly assigned healthy adults (18 to 50 years of age) to receive rVSVΔG-LASV-GPC or placebo intramuscularly. Participants received a single vaccine dose of 2×104 plaque-forming units (PFU), 2×105 PFU, 2×106 PFU, or 2×107 PFU or placebo or received two vaccine doses of 2×107 PFU or placebo, within a window of 6 to 20 weeks. The side-effect profile was assessed according to the incidence of solicited and unsolicited adverse events (primary end point). Because Lassa fever can cause sensorineural hearing loss, hearing acuity was measured before and after the injection. Secondary end points were levels of binding antibodies against LASV glycoprotein, neutralizing antibodies, and vaccine vector-derived viral RNA and PFU in plasma, urine, and saliva. Results: A total of 114 adults were enrolled. No serious vaccine-related adverse events were reported. The vaccine caused minimal local reactions and dose-dependent, mild-to-severe early-onset systemic reactogenicity events that were transient. No hearing loss was detected. All doses induced robust long-lasting cellular and humoral (binding and neutralizing) responses that cross-reacted against common LASV lineages. No infectious vaccine virus particles were found in plasma, urine, or saliva. Conclusions: The rVSVΔG-LASV-GPC vaccine resulted in transient local and systemic reactogenicity events but no hearing loss or serious adverse events. The vaccine had immunogenicity over a wide dose range in healthy adults in the United States and Liberia. (Funded by the Coalition for Epidemic Preparedness Innovations and the National Institute of Allergy and Infectious Diseases; ClinicalTrials.gov number, NCT04794218; Pan African Clinical Trials Registry number, PACTR2021106625781067.).

Current licensure trials of new vaccines to prevent tuberculosis disease use bacteriologically confirmed symptomatic tuberculosis disease as the primary endpoint. Globally, the incidence of symptomatic tuberculosis disease is low, making licensure trials large, long, and expensive. New data suggest that bacteriologically confirmed asymptomatic tuberculosis disease might occur more frequently than symptomatic tuberculosis disease. Therefore, if vaccines have efficacy against asymptomatic disease, tuberculosis vaccine licensure trials could include it in the primary endpoint, potentially leading to smaller or shorter trials. We describe the potential benefits and risks of this inclusion in the primary endpoint of tuberculosis vaccine licensure trials. We also simulate licensure trial endpoint accrual and summarise feedback from anonymous regulators and policy makers on the knowledge needed to consider this proposal and research studies needed to fill these evidence gaps. If bacteriologically confirmed asymptomatic tuberculosis disease could be included in the primary endpoint of tuberculosis disease licensure trials, it could lead to cheaper and more rapid tuberculosis vaccine development.

mRNA vaccines have emerged as an important platform for vaccine development. Unlike protein subunit vaccines, mRNA-expressed antigens can be expressed in either secreted or transmembrane (TM) forms mimicking a viral envelope (Env) protein. Here, we investigated the impact of antigen expression format on the antigenicity profile, glycosylation, and immunogenicity of stabilized HIV Env trimer immunogens expressed from self-replicating RNA (replicon) vaccines. Replicon-encoded trimers in both forms exhibited proper folding, and replicon-expressed secreted trimers exhibited glycosylation patterns largely consistent with recombinant trimer protein, although with enrichment of complex glycans over high mannose at some sites. Both formats were highly immunogenic in mice, eliciting comparable serum antibody and T cell responses. Interestingly, the TM format initiated smaller germinal center (GC) responses, but these GCs were enriched for trimer-binding B cells compared to secreted trimer vaccines. In a B cell receptor knockin adoptive transfer model for assessing germline targeting, the replicon-encoded TM trimer elicited a greater frequency of epitope-targeting antibodies and recruited broadly neutralizing antibody precursor B cells to the GC response more efficiently compared to the replicon-encoded secreted trimer or protein trimer combined with adjuvant. These results indicate that the form of immunogen expression can impact key elements of immune responses to RNA vaccines.

People with HIV (PWH) are understudied in COVID-19 vaccine trials, leaving knowledge gaps on whether the identified immune correlates of protection also hold in PWH. CoVPN 3008 (NCT05168813) enrolled predominantly PWH and reported lower COVID-19 incidence for a Hybrid vs. Vaccine Group (baseline SARS-CoV-2-positive and one mRNA-1273 dose vs. negative and two doses). Using case-cohort sampling, antibody markers at enrolment (M0) and four weeks post-final vaccination (Peak) are assessed as immune correlates of COVID-19. For the Hybrid Group [n = 287 (195 PWH)], all M0 markers inversely correlate with COVID-19 through 230 days post-Peak, with 50% inhibitory dilution BA.4/5 neutralizing antibody titer (nAb-ID50 BA.4/5) the strongest and only independent correlate (HR per 10-fold increase=0.46, 95% CI 0.28, 0.75; P = 0.002). For the Vaccine Group [n = 115 (86 PWH)], Peak nAb-ID50 BA.4/5 correlates with reduced COVID-19 risk (1.9%, 1.1%, and 0.3% at titers 10, 100, and 1000 AU/ml) through 92, but not 165, days post-Peak. Using multivariable Cox analysis of binding and nAb, nAb titers predict COVID-19 in PWH. Two doses of a 100-µg Ancestral strain mRNA vaccine in baseline-SARS-CoV-2-negative individuals elicit sufficient cross-reacting Omicron antibodies to reduce COVID-19 incidence for 90 days post-Peak, but viral evolution and waning antibodies abrogate this protection thereafter.

The S2 subunit of the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) spike is highly conserved across coronavirus strains and therefore is a potential pan-coronavirus vaccine target. However, antibodies targeting this region are typically non-neutralizing. We report herein that S2-targeting antibodies from patients who recovered from SARS-CoV-2 infection bound only closely related sarbecovirus subgenus strains and, like most known S2 antibodies, none of these were neutralizing. In contrast, first-exposure, severe acutely infected COVID-19 patients predominantly induced back-boosted antibody-secreting cells imprinted against past common cold coronavirus strain OC43 that were cross-reactive to as many as five subgenera of betacoronavirus strains and gave rise to antibodies that were neutralizing and protective. The antibodies targeted two different sites: one defined by competition with stem helix antibodies, and the second to an underdescribed epitope at the apex of S2. These findings suggest that S2-targeted vaccines could strategically exploit controlled OC43 priming followed by SARS-CoV-2 boosting to enhance the breadth and quality of protective antibody responses.

Germline-targeting is a promising approach to HIV vaccine development that begins with the elicitation of precursors to broadly neutralizing antibodies (bnAbs), but it remains unclear whether simultaneous elicitation of precursors to multiple epitopes on the HIV envelope (Env) would be inhibited by competition. This study used preclinical mouse models with physiologically relevant frequencies of bnAb precursor-bearing B cells to compare precursor elicitation by coadministration of multiple protein or mRNA lipid nanoparticle (mRNA-LNP) germline-targeting immunogens. These immunogens activate multiple bnAb precursor classes targeting distinct epitopes on Env but with evidence of potential competition. Simultaneous delivery of immunogens encoded by mRNA-LNPs, however, drove maturation across different precursor frequencies and immunogen doses. Furthermore, administration of a cocktail of mRNA-LNP immunogens (N332-GT5 gp151, ApexGT5 gp151, eOD-GT8 60mer, and 10E8-GT12 24mer) led to balanced activation of four distinct bnAb precursor classes, indicating that multiepitope HIV bnAb precursor priming might be successfully implemented in humans but might be immunogen dependent.

Inducing broadly neutralizing antibodies (bnAbs) against HIV remains a key challenge in vaccine development. Germline-targeting immunogens have effectively primed bnAb B cell lineages to individual HIV envelope epitopes in humans and nonhuman primates. However, eliciting consistent bnAb breadth requires the induction of multiple bnAb classes. We investigated whether immunization with a combination of germline-targeting immunogens could concurrently prime multiple bnAb lineages in nonhuman primates. Animals were immunized with three immunogens, targeting distinct epitopes: the V3-glycan/N332 supersite, the V2 Apex region, and the membrane-proximal external region (MPER), either individually or in combinations of two or all three. Triple combination immunization transiently reduced V2 Apex and V3-glycan responses, but by 8 weeks postboost, bnAb precursor lineages were observed to all three epitopes. Similar somatic hypermutation was observed across groups, indicative of permissive germinal center responses. These findings support combination germline-targeting immunization as a viable strategy to prime multiple bnAb lineages simultaneously.

An effective prophylactic HIV vaccine will likely need to induce broadly neutralizing antibodies (bnAbs). bnAbs to the Apex region of the HIV envelope glycoprotein (Env) are promising targets for vaccination because of their relatively low somatic hypermutation compared with other bnAbs. Most Apex bnAbs engage Env using an exceptionally long heavy-chain complementarity-determining region 3 (HCDR3) containing specific binding motifs, which reduces bnAb precursor frequency and makes priming of rare bnAb precursors a likely limiting step in the path to Apex bnAb induction. We found that adjuvanted protein or mRNA lipid nanoparticle (LNP) immunization of rhesus macaques with ApexGT6, an Env trimer engineered to bind Apex bnAb precursors, consistently induced Apex bnAb-related precursors with long HCDR3s bearing bnAb-like sequence motifs. Cryo-electron microscopy revealed that elicited Apex bnAb-related HCDR3s had structures combining elements of several prototype Apex bnAbs. These results achieve a critical HIV vaccine development milestone in outbred primates.

The development of germline-targeting vaccines represents a potentially transformative strategy to elicit broadly neutralizing antibodies (bnAbs) against HIV and other antigenically diverse pathogens. Here, we report on structural characterization of vaccine-elicited VRC01-class bnAb precursors in the IAVI G001 Phase 1 clinical trial with the eOD-GT8 60mer nanoparticle as immunogen. High-resolution X-ray structures of eOD-GT8 monomer complexed with Fabs of five VRC01-class bnAb precursors with >90% germline identity revealed a conserved mode of binding to the HIV CD4-binding site via IGHV1-2-encoded heavy chains, mirroring mature bnAb interactions. The light-chain V-gene diversity emulated VRC01 bnAbs and stabilized antigen engagement, while their conserved five-residue LCDR3 motifs prevented steric clashes. Notably, the VRC01-class bnAb precursors accommodated the N276 glycan, a key barrier in HIV Env recognition, through structural rearrangements in HCDR3 or LCDR1, despite its absence in the immunogen. Surface plasmon resonance analysis showed that 87% of elicited antibodies retained glycan binding capacity, albeit with reduced affinity. These findings validate the ability of eOD-GT8 60mer nanoparticles to prime VRC01-class bnAb precursors with native-like paratopes but with intrinsic glycan adaptability. Structural mimicry of mature bnAbs was observed even with limited somatic hypermutation, indicating that critical features are encoded in the germline repertoire. The structures highlight how germline-encoded features drive bnAb-like recognition at early stages. This work provides molecular evidence supporting germline targeting in humans and provides guidance for designing booster immunogens to shepherd affinity maturation toward broad neutralization.

A protective HIV vaccine will need to induce broadly neutralizing antibodies (bnAbs) in humans, but priming rare bnAb precursor B cells has been challenging. In a double-blinded, placebo-controlled phase 1 human clinical trial, the recombinant, germline-targeting envelope glycoprotein (Env) trimer BG505 SOSIP.v4.1-GT1.1, adjuvanted with AS01B, induced bnAb precursors of the VRC01-class at a high frequency in the majority of vaccine recipients. These bnAb precursors, which target the CD4 receptor binding site, had undergone somatic hypermutation characteristic of the VRC01-class. A subset of isolated VRC01-class monoclonal antibodies neutralized wild-type pseudoviruses and was structurally extremely similar to bnAb VRC01. These results further support germline-targeting approaches for human HIV vaccine design and demonstrate atomic-level manipulation of B cell responses with rational vaccine design.

A protective vaccine against human immunodeficiency virus (HIV) will likely need to induce broadly neutralizing antibodies (bnAbs) that engage relatively conserved epitopes on the HIV envelope glycoprotein (Env) trimer. Nearly all vaccine strategies to induce bnAbs require the use of complex immunization regimens involving a series of different immunogens, most of which are Env trimers. Producing protein-based clinical material to evaluate such relatively complex regimens in humans presents major challenges in cost and time. Furthermore, immunization with HIV trimers as soluble proteins induces strong nonneutralizing responses to the trimer base, which is normally occluded on the virion. These base responses could potentially detract from the elicitation of nAbs and the eventual induction of bnAbs. mRNA vaccine platforms offer potential advantages over protein delivery for HIV vaccine development, including increased production speed, reduced cost, and the ability to deliver membrane-bound trimers that might facilitate improved immuno-focusing to nonbase epitopes. We report the design of mRNA-delivered soluble and membrane-bound forms of a stabilized native-like Env trimer (BG505 MD39.3); initial immunogenicity evaluation in rabbits that triggered clinical evaluation; and more comprehensive evaluation of B cell, T cell, and antibody responses in nonhuman primates. mRNA-encoded membrane-bound Env immunization elicited reduced off-target base-directed Env responses and stronger nAb responses compared with mRNA-encoded soluble Env. Overall, mRNA delivery of membrane-bound Env appears promising for enhancing B cell responses to subdominant epitopes and facilitating rapid translation to clinical testing, which should assist HIV vaccine development.