Germline-targeting HIV vaccination induces neutralizing antibodies to the CD4 binding site

Precise targeting of HIV broadly neutralizing antibody precursors in humans

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, that 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.

Progress and Challenges in HIV-1 Vaccine Research: A Comprehensive Overview

The development of an effective HIV-1 vaccine remains a formidable challenge in biomedical research. Despite significant advancements in our understanding of HIV biology and pathogenesis, progress has been impeded by factors such as the virus's genetic diversity, high mutation rates, and its ability to establish latent reservoirs. Recent innovative approaches, including mosaic vaccines and mRNA technology to induce broadly neutralizing antibodies, have shown promise. However, the efficacy of these vaccines has been modest, with the best results achieving approximately 30% effectiveness. Ongoing research emphasizes the necessity of a multifaceted strategy to overcome these obstacles and achieve a breakthrough in HIV-1 vaccine development. This review summarizes current approaches utilized to further understand HIV-1 biology and to create a global vaccine. We discuss the impact of these approaches on vaccine development for other diseases, including COVID-19, influenza, and Zika virus. Additionally, we highlight the specific limitations faced with each approach and present the methods researchers employ to overcome these challenges. These innovative techniques, which have demonstrated preclinical and clinical success, have advanced the field closer to the ultimate goal of developing a global HIV-1 vaccine. Leveraging these advancements will enable significant strides in combating HIV-1 and other infectious diseases, ultimately improving global health outcomes.

Vaccination with mRNA-encoded membrane-bound HIV Envelope trimer induces neutralizing antibodies in animal models

A protective vaccine against 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 relatively 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 non-neutralizing responses to the trimer base, which is normally occluded on the virion. These base responses could potentially detract from the induction 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 non-base 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 non-human primates. mRNA-encoded membrane-bound Env immunization elicited reduced off-target base-directed Env responses and stronger neutralizing antibody 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.

Mosaic and mixed HIV-1 glycoprotein nanoparticles elicit antibody responses to broadly neutralizing epitopes

An effective human immunodeficiency virus 1 (HIV-1) vaccine will most likely have to elicit broadly neutralizing antibodies (bNAbs) to overcome the sequence diversity of the envelope glycoprotein (Env). So far, stabilized versions of Env, such as SOSIP trimers, have been able to induce neutralizing antibody (NAb) responses, but those responses are mainly strain-specific. Here we attempted to broaden NAb responses by using a multivalent vaccine and applying a number of design improvements. First, we used highly stabilized SOSIP.v9 trimers. Second, we removed any holes in the glycan shields and optimized glycan occupancy to avoid strain-specific glycan hole responses. Third, we selected five sequences from the same clade (B), as we observed previously that combining Env trimers from clade A, B and C did not improve cross-reactive responses, as they might have been too diverse. Fourth, to improve antibody (Ab) responses, the Env trimers were displayed on two-component I53-50 nanoparticles (NPs). Fifth, to favor activation of cross-reactive B cells, the five Env trimers were co-displayed on mosaic NPs. Sixth, we immunized rabbits four times with long intervals between vaccinations. These efforts led to the induction of cross-reactive B cells and cross-reactive binding Ab responses, but we only sporadically detected cross-neutralizing responses. We conclude that stabilized HIV-1 Env trimers that are not modified specifically for priming naive B cells are unable to elicit strong bNAb responses, and infer that sequential immunization regimens, most likely starting with specific germline-targeting immunogens, will be necessary to overcome Env's defenses against the induction of NAbs. The antigens described here could be excellent boosting immunogens in a sequential immunization regimen, as responses to bNAb epitopes were induced.

The promise of priming precursors: Advances in inducing CD4 binding site-directed HIV broadly neutralizing antibodies

HIV envelope immunogen designed to activate germline B cell precursors of CD4 binding site-specific neutralizing antibodies shows promise in monkeys.