VRC-01

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.

Human immunodeficiency virus type 1 remains a major public health burden with 39 million people living with human immunodeficiency virus type 1 and 1.3 million new diagnoses in 2023, despite the recent approval of multiple antiretroviral-based prevention products. While the development of a safe and effective human immunodeficiency virus type 1 vaccine remains the ultimate goal for controlling the worldwide pandemic, progress has been hindered by unprecedented challenges, including the extraordinary genetic diversity of human immunodeficiency virus type 1, the inability of current vaccines to induce broadly reactive antibody responses, and the lack of clear immune correlates of protection to serve as benchmarks for vaccine development. Passive administration of broadly neutralizing monoclonal antibodies that are engineered versions of naturally occurring antibodies has emerged as a potential complement to current human immunodeficiency virus type 1 prevention modalities. These antibodies are isolated from people with human immunodeficiency virus type 1 and can neutralize a broad range of human immunodeficiency virus type 1 viruses. Importantly, advances in antibody engineering have improved the pharmacokinetics of these monoclonal antibodies, offering potential for lower levels and/or less frequent monoclonal antibody dosing with greater feasibility and accessibility for human immunodeficiency virus type 1 prevention. Evaluating monoclonal antibody candidates in human immunodeficiency virus type 1 prevention trials, dose-finding and optimization requires a careful balance between virus-neutralization coverage, cost considerations, and practical constraints. To achieve this, pharmacokinetic modeling of antibody concentrations over time, combined with pharmacodynamics modeling of the relationship between neuralization titers and prevention efficacy, serves as a core of the statistical framework. In addition, for human immunodeficiency virus type 1 monoclonal antibodies administered to individuals without human immunodeficiency virus type, neutralization titers can be reliably predicted from antibody concentrations, owning to the preservation of neutralization function post-administration of these monoclonal antibodies. Within this framework, the antibody-mediated prevention efficacy trials of VRC01, an human immunodeficiency virus type 1 monoclonal antibody, and a meta-analysis of 16 different monoclonal antibodies in non-human primates provided consistent evidence that neutralization titer is a potential pharmacodynamics biomarker of monoclonal antibody prevention efficacy. These findings support the use of integrated pharmacokinetics/pharmacodynamics modeling as a foundation for dose finding of human immunodeficiency virus type 1 monoclonal antibodies. However, in the context of combination monoclonal antibody regimens, additional challenges arise. The total dose cost, operational feasibility, and the influence of dosing ratios on neutralization breadth and potency across diverse human immunodeficiency virus type 1 viral strains are important areas for further research. While monoclonal antibody clinical trials share some common design features with therapeutic small molecule drug trials, monoclonal antibodies possess unique safety, pharmacokinetics and pharmacodynamics profiles that require dedicated statistical and clinical considerations, particularly when used for prevention of viral infections. In this article, we highlight dose-finding efforts particularly for combination monoclonal antibodies regimens, including the selection of optimal dosing ratio and total dose amount in the context of human immunodeficiency virus type 1 prevention. Looking ahead, future directions in monoclonal antibody-based human immunodeficiency virus type 1 prevention include efforts to enhance dose-associated cost-effectiveness, and the identification and validation of robust pharmacokinetic and pharmacodynamic markers that are predictive of the prevention efficacy of combination monoclonal antibodies.