Inducing and Optimizing VRC01-like Broadly Neutralizing Antibodies in Mouse Models with mRNA-LNP

Background Introduction

In recent years, the importance of acquiring broadly neutralizing antibodies (bnAbs) has been increasingly recognized in vaccine development, particularly in the field of HIV (Human Immunodeficiency Virus) vaccine research. The HIV envelope glycoprotein (Env) is critical for the virus to enter host cells and is considered a target for bnAbs in research. Although bnAbs isolated from patients exhibit high affinity against HIV, their precursors usually do not possess the high affinity seen in mature antibodies. Therefore, inducing the evolution of these precursor antibodies into mature bnAbs remains a significant challenge in vaccine development.

One promising method is the germline-targeting (GT) vaccination strategy, which aims to activate bnAb precursor antibodies during the initial vaccination and recruit these precursor antibodies into the germinal centers (GCs) for somatic hypermutation (SHM), gradually enhancing affinity for the HIV Env.

Source of Research

The research paper titled “mRNA-LNP Prime Boost Evolves Precursors Toward VRC01-like Broadly Neutralizing Antibodies in Preclinical Humanized Mouse Models” was published on May 16, 2024, in the journal Science Immunology. The primary authors include Xuesong Wang, Christopher A. Cottrell, Xiaozhen Hu, and others from institutions such as the Ragon Institute of Massachusetts General, MIT and Harvard University, the Scripps Research Institute, and Moderna Inc. This paper provides a detailed discussion of preclinical validation of HIV immunogens in humanized mouse models.

Research Process

Experimental Design

The study first validated the effectiveness of lipid nanoparticle-encapsulated nucleoside-modified mRNA (mRNA-LNP) encoding a self-assembling nanoparticle (EOD-GT8 60mer) in a mouse model. The study involved three humanized B cell lineages, with mice carrying B cells equipped with different VRC01 precursor B cell receptors (BCR).

1. Transfer and Immunization of B Cells

   • Mice were immunized with high-dose (10 μg) and low-dose (0.6 μg) EOD-GT8 60mer protein and EOD-GT8 mRNA-LNP.
   • Immunized mice were analyzed on days 14, 42, and 72 post-vaccination.

2. Secondary Immunization (Boost)

   • On day 42 post-primary immunization, secondary immunizations with three different mRNA-LNP-encoding nanoparticles were performed.
   • The effects of various combinations of primary and secondary immunizations on germinal centers were evaluated.

Data Analysis and Results

1. Germinal Center Responses

   • The study found that EOD-GT8 60mer mRNA-LNP induced and maintained strong B cell responses in the lymph nodes and spleen of immunized mice. The formation of antigen-specific B cells in GCs was similar in both low-dose and high-dose mRNA-LNP groups, peaking on day 14 and remaining significant on day 42.
   • Compared to the protein immunization group, EOD-GT8 60mer mRNA-LNP was more effective at generating memory B cells (MBC).

2. Somatic Hypermutation (SHM) and Affinity Maturation

   • Single-cell sequencing results showed that EOD-GT8 60mer mRNA-LNP induced diverse SHM across different B cell lineages, with significant mutation frequencies observed on days 14 and 36. Notable mutations in the complementarity-determining regions (CDRs) peaked on day 36.
   • Affinity measurements indicated that antibodies from mRNA-LNP immunized mice enhanced their affinity for the EOD-GT8 antigen by 40 to 900 times and showed significant increases in affinity for secondary immunization antigens (G5 and G28).

3. Secondary Immunization Effects

   • The use of G5 or G28 mRNA-LNP for secondary immunization further enhanced GC responses and promoted higher levels of SHM. The secondary immunizations led to mutations in clk19 and clk09 lineages’ antibodies similar to those in mature VRC01, including key residue mutations.
   • Following secondary immunization, the overall affinity of antibodies continued to improve substantially, particularly showing significant affinity enhancement toward antigens containing the N276 glycosylation site.

Key Findings and Value

1. Multi-lineage Induction

   • mRNA-LNP successfully induced preliminary immune responses from multiple precursor lineages in the same host and guided these lineages to further evolve during secondary immunization, demonstrating the feasibility of multi-lineage immune induction.

2. Somatic Hypermutation and Affinity Maturation

   • The research validated that mRNA-LNP immunization could effectively induce diverse SHM and gradually increase the affinity of antibodies to primary and secondary antigens, laying the groundwork for subsequent vaccine development.

3. Importance of Secondary Immunization

   • The secondary immunization strategy significantly enhanced immune responses, especially improving antibody affinity for highly conserved sites (e.g., N276), thereby increasing the breadth of neutralizing capacity.

Outlook

This study achieved significant progress in the preclinical stage of HIV vaccine development, verifying the effectiveness of mRNA-LNP immunization and the feasibility of multi-lineage induction, providing a solid scientific basis for future clinical trials. Furthermore, the mRNA-LNP immunization strategy employed in this study offers new insights and technological support for the development of vaccines for other infectious diseases.

Summary

This paper comprehensively and meticulously validated the potential of mRNA-LNP to induce and optimize broadly neutralizing antibodies in preclinical mouse models. The research not only revealed the feasibility of multi-lineage immune induction but also highlighted the crucial role of secondary immunization in affinity maturation of antibodies. In the future, this study is expected to provide important references for the development of HIV vaccines and other infectious disease vaccines.