Structural vaccinology for infectious diseases

National Institute Of Allergy And Infectious Diseases

Investigators

Linked publications & trials

Abstract

Malaria is caused by eukaryotic parasites that display distinct surface antigens during three independent stages of the life cycle: 1) initial infection caused by the pre-erythrocytic stage, 2) clinical symptoms as a result of the blood stage, and 3) transmission by the mosquito stage. While both T-cell and B-cell responses play a role in naturally acquired immunity to malaria, focusing B-cell responses on conserved broadly-neutralizing functional epitopes significantly improves protection and may lead to sterile immunity. Four aspects of parasite biology confound malaria vaccine development: 1) antigenic variability across strains and species; 2) the presence of immunodominant but non-neutralizing epitopes in antigens; 3) the diverse, numerous, and often redundant parasite antigens required for each stage of the life cycle; and 4) poor immune response upon vaccination with designed parasite antigens. Major rapid advances in the structural definition of neutralizing epitopes on key malaria antigens, as well as in nanoparticle technology, motivate structure-guided design of immunogens for malaria vaccines targeting all stages of the Plasmodium life cycle. We propose to leverage existing structural information of malaria antigens and neutralizing antibody complexes to design improved immunogens and nanoparticles that will elicit protective immune responses. Immunogens will be improved through protein design to retain neutralizing epitopes, eliminate non-neutralizing epitopes, and present optimized immunogens on nanoparticles for efficient delivery and increased immunogenicity. Proteins will be designed via computational and human-guided approaches to stabilize protein conformations, reduce large proteins to immunogenic subdomains, and scaffold epitopes for efficient presentation. Diverse established nanoparticle platforms will be evaluated for their ability to effectively present antigens, and novel nanoparticles will be developed for delivery. All designed immunogens and nanoparticles will be structurally characterized through X-ray crystallography and cryo-electron microscopy to ensure that the correct conformational 3D structure of the antigen is retained. We developed a computational design procedure using the NIAID Skyline and NIH Biowulf high performance computer clusters and an in vitro screening platform to validate computationally designed antigens. In FY25, we published a study in npj Vaccines describing a potent multi-stage malaria vaccine that can simultaneously protect against infection and diseases transmission. Using the SPEEDesign platform that we have established in previous funding cycles, we have engineered immunogens for multiple malaria antigens, targeting various parasite species and all three stages of the parasite life cycle. The designed immunogens show higher production yields, increased thermostability, and lack unwanted immunodominant or non-neutralizing epitopes. These lead candidates retain essential neutralizing epitopes and exhibit improved biophysical properties compared to the native antigens. In the npj Vaccines study, we genetically fused a previously designed Pfs48/45 transmission-blocking antigen with a newly designed circumsporozoite (CSP) infection-blocking antigen to create a single vaccine antigen with multiple mechanisms of action. We also fused a self-assembling nanoparticle to increase immunogenicity. All combinations showed protection against infection in a mouse model of malaria, and the ability to induce antibodies that block transmission to mosquitos. The nanoparticle designs were exceptionally potent in preventing infection and transmission and the addition of the designed Pfs48/45 immunogen to CSP enhanced the protection conferred by CSP, a finding that informs the larger field of CSP-based vaccines. Our most potent design holds promise as a single vaccine to target multiple stages of malaria pathogenesis and could play a key role in control efforts. In parallel, we continue to advance the development of innovative nanoparticle platforms using Plasmodium proteins, which can self-assemble into large multimeric proteins. These native nanoparticles allow for the fusion of multiple distinct antigens thereby potentially targeting multiple stages of the parasite life cycle and elicit robust immune responses upon vaccination. These platforms are designed with a modular approach, allowing for plug-and-play screening of designed immunogens in various expression systems, which expedites the identification of optimized vaccines. We also continue to utilize three established platforms to display designed immunogens with up to 180 copies, thereby enhancing their immunogenicity and protective capabilities. Together these approaches will result in the development of vaccines with expected high potency and durability.