The immunogenicity of HIV-1 envelope (Env) trimers is generally poor. We used the clinically relevant ConM SOSIP trimer to compare the ability of different adjuvants (squalene emulsion, ISCOMATRIX, GLA-LSQ, and MPLA liposomes) to support neutralizing antibody (NAb) responses in rabbits. The trimers were administered as free proteins or on nanoparticles. The rank order for the adjuvants was ISCOMATRIX > SE > GLA-LSQ ~ MPLA liposomes > no adjuvant. Stronger NAb responses were elicited when the ConM SOSIP trimers were presented on ferritin nanoparticles. We also found that the GLA-LSQ adjuvant induced an unexpectedly strong antibody response to the ferritin core of the nanoparticles. This “off-target” effect may have compromised its ability to induce the more desired antitrimer antibodies. In summary, both adjuvants and nanoparticle display can improve the magnitude of the antibody response to SOSIP trimers but the best combination of trimer presentation and adjuvant can only be identified experimentally.

The HIV-1 envelope glycoprotein (Env) trimer is the key target for vaccines aimed at inducing neutralizing antibodies (NAbs) against HIV-1. The clinical candidate immunogen ConM SOSIP.v7 is a stabilized native-like HIV-1 Env trimer based on an artificial consensus sequence of all HIV-1 isolates in group M. In preclinical studies ConM SOSIP.v7 trimers induced strong autologous NAb responses in non-human primates (NHPs). To fine-map these responses, we isolated monoclonal antibodies (mAbs) from six cynomolgus macaques that were immunized three times with ConM SOSIP.v7 protein and boosted twice with the closely related ConSOSL.UFO.664 immunogen. A total of 40 ConM and/or ConS-specific mAbs were isolated, of which 18 were retrieved after the three ConM SOSIP.v7 immunizations and 22 after the two immunizations with ConSOSL.UFO.664. 22 mAbs (55%) neutralized the ConM and/or ConS virus. Cross-neutralization of ConS virus by approximately one-third of the mAbs was seen prior to ConSOSL.UFO.664 immunization, albeit with modest potency. Neutralizing antibodies predominantly targeted the V1 and V2 regions of the immunogens, with an apparent extension towards the V3 region. Thus, the V1V2V3 region is immunodominant in the potent NAb response elicited by two consensus sequence native-like HIV-1 Env immunogens. Immunization with these soluble consensus Env proteins also elicited non-neutralizing mAbs targeting the trimer base. These results inform the use and improvement of consensus-based trimer immunogens in combinatorial vaccine strategies.

A protective vaccine will be the most powerful instrument to reduce HIV-1 infections worldwide and help bring about a lasting end to the AIDS epidemic. The single centre, randomised, open-label, uncontrolled, phase 1 ACTHIVE-001 clinical trial (NCT03961438) aims to assess the safety and immunogenicity of the ConM SOSIP.v7 native-like trimer protein vaccine, based on an HIV-1 group M consensus sequence, in HIV-negative adults. Twenty-four individuals were enrolled to receive three dosages of ConM SOSIP.v7 protein vaccine in a liposome formulation containing a high dose of the TLR4-agonist MPLA. The primary outcome is vaccine reactogenicity, whereas the main secondary outcome is binding and neutralising antibody responses. Overall, the vaccine is safe and well-tolerated. Furthermore, the vaccine elicits robust strain-specific binding and neutralising antibody responses in nearly all vaccinees. Post-hoc exploratory analyses demonstrate that female-born participants have 22- and 6-fold higher neutralisation titres after the second and third vaccination, respectively. The vaccine adjuvant induces higher levels of IL-6 secretion from in vitro cultured monocytes from female compared to male participants, providing a possible mechanistic explanation for the sex-based differences. Our study highlights the need to take sex-based differences into consideration when assessing HIV-1 vaccine candidates and adjuvants.

Chemical cross-linking is used to stabilize protein structures with additional benefits of pathogen and toxin inactivation for vaccine use, but its use has been restricted by the potential for local or global structural distortion. This is of particular importance when the protein in question requires a high degree of structural conservation for inducing a biological outcome such as the elicitation of antibodies to conformationally sensitive epitopes. The HIV-1 envelope glycoprotein (Env) trimer is metastable and shifts between different conformational states, complicating its use as a vaccine antigen. Here we have used the hetero-bifunctional zero-length reagent 1-Ethyl-3-(3-Dimethylaminopropyl)-Carbodiimide (EDC) to cross-link two soluble Env trimers, selected well-folded trimer species using antibody affinity, and transferred this process to good manufacturing practice (GMP) for experimental medicine use. Cross-linking enhanced trimer stability to biophysical and enzyme attack. Cryo-EM analysis revealed that cross-linking retained the overall structure with root-mean-square deviations (RMSDs) between unmodified and cross-linked Env trimers of 0.4–0.5 Å. Despite this negligible distortion of global trimer structure, we identified individual inter-subunit, intra-subunit, and intra-protomer cross-links. Antigenicity and immunogenicity of the trimers were selectively modified by cross-linking, with cross-linked ConS retaining bnAb binding more consistently than ConM. Thus, the EDC cross-linking process improves trimer stability whilst maintaining protein folding, and is readily transferred to GMP, consistent with the more general use of this approach in protein-based vaccine design.

Background/Objectives: Despite progress in antiretroviral therapy, HIV remains a major global health challenge with over one million new infections annually. An effective vaccine is urgently needed. Germline-targeting immunogens show promise in initiating broadly neutralizing antibody (bNAb) precursors. This study developed a scalable, cGMP-compliant process to manufacture the HIV vaccine booster immunogen HxB2.WT.Core-C4b, a nanoparticle designed to direct bNAb precursor maturation after priming. Methods: A CHO cell platform was established through single-cell cloning from a high-producing stable pool. Upstream and downstream processes were optimized for scalability and yield. Three scales were tested 10 L, 40 L, and 400 L. Key parameters (pH, temperature, feeding, metabolite profiles) were systematically refined. Analytical characterization included glycosylation profiling, electron microscopy, and antigenicity testing. Viral clearance was evaluated per ICH Q5A guidelines. Results: Optimization ensured consistent yields above 130 mg/L, with titers up to 250 mg/L. The selected clone (4E22) demonstrated strong growth, viability, and reproducibility. Glycan occupancy at 18 N-linked sites, including bNAb epitopes (N276, N332), was stable across scales. Over 70% of self-assembling nanoparticle were fully assembled at the GMP level. Antigenicity and purity met cGMP release criteria. Viral clearance achieved >13-log reduction for enveloped and >7-log for non-enveloped viruses. Conclusions: This work establishes a robust, scalable platform for HIV nanoparticle immunogens. Consistent quality and yield across scales support clinical development of HxB2.WT.Core-C4b and provide a model for other glycosylated nanoparticle vaccines. The immunogen is being evaluated in clinical study HVTN 320 (NCT06796686), enabling early testing of next-generation vaccines designed to elicit broadly neutralizing antibodies.