Scientific Publications

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.

We urgently need novel, effective, and accessible vaccines to end tuberculosis (TB) as a public health crisis. The 7th Global Forum on TB Vaccines was convened from 8-10 October 2024 in Rio de Janeiro, Brazil. Under the theme of "Driving innovation from discovery to access," the program covered the breadth of TB vaccine research and development (R&D) through implementation, while underscoring the need for greater innovation and investments to advance development and ensure rapid, affordable, and equitable access. Participants shared the latest research on: approaches to diversify the TB vaccine pipeline, candidates advancing through late-stage trials toward licensure, and efforts to ensure new TB vaccines reach the populations that most need them. The forum provided a platform to learn from diverse experts across the field, including researchers, industry, funders, civil society, and affected communities. Participants examined cross-cutting enablers throughout, including opportunities to establish novel partnership and financing models, enhance open science, optimize R&D practices, and strengthen leadership and engagement with community members and high burden countries alike. In this report, we synthesize key themes and findings from the meeting, highlighting progress and priorities in the TB vaccine field.

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.

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.

Advances in HIV vaccine development focus on eliciting broadly neutralizing antibodies (bNAbs) through next-generation immunogens. Human trials are testing these candidates for their ability to initiate B cell maturation. This workshop report reviews emerging data and methods for analyzing B cell repertoires, highlighting strategies to streamline these labor-intensive processes. The goal is to enable timely, cost-effective design of sequential immunization regimens that induce potent, protective bNAbs against HIV.