Structural and functional evaluation of de novo-designed, two-component nanoparticle carriers for HIV Env trimer immunogens

Summary

Protein constructs based on soluble ectodomains of HIV glycoprotein (Env) trimers are the basis of many current HIV vaccine platforms. Multivalent antigen display is one strategy applied to improve the immunogenicity of various subunit vaccine candidates. Here, we describe and comprehensively evaluate a library of de novo designed protein nanoparticles of different geometries for their ability to present trimeric Env antigens. We found three nanoparticle candidates that can stably incorporate model Env trimers on their surfaces while maintaining structure and antigenicity. The designed nanoparticle immunogens had an increased capacity to stimulate B-cells expressing antigen-specific receptors. The immunogenicity of one nanoparticle candidate was assessed in rabbits. Nanoparticle presentation geometry appeared to alter the distribution of antibody responses against different epitopes while inducing similar serum binding titers and only slightly elevated neutralizing titers. In addition to introducing a novel set of reagents for multivalent display of Env trimers, this work provides both guiding principles and a detailed experimental roadmap for the generation, characterization, and optimization of Env-presenting, self-assembling nanoparticle immunogens.

Highlights

• Two-component, self-assembling nanoparticles represent a versatile platform for multivalent presentation of viral antigens.
• Computational design of protein nanoparticles with differing sizes and geometries enables combination with antigens of choice to test novel multimerization concepts in immunization strategies where the goal is to improve the induction and maturation of neutralizing antibody lineages.
• Env trimers, based on subtype A (BG505) or consensus group M (ConM) sequences and engineered with SOSIP stabilizing mutations, were fused to an underlying trimeric building block of each nanoparticle.
• A number of analyses, including detailed structural characterization by cryo EM, demonstrated that the nanoparticle immunogens possessed the intended structural and antigenic properties.
• Our findings indicate that tetrahedral nanoparticles can be successfully applied for presentation of HIV Env trimer immunogens; however, the optimal implementation to different immunization strategies remains to be determined.