Illenberger, A. | Search bioRxiv

bioRxiv2026

Improving the immunogenicity of E. coli FimH via multivalent display on I53-50 nanoparticles

Urinary tract infections, caused primarily by uropathogenic E. coli, are a significant public health burden, affecting approximately 50% of women worldwide. The adhesin FimH is responsible for host receptor binding and is therefore a promising vaccine candidate, but prior studies showed that recombinant monomeric FimH is poorly immunogenic. Here we displayed FimH antigens on the two-component protein nanoparticle I53-50 to generate nanoparticle immunogens that elicit robust levels of receptor-blocking antibodies in mice and non-human primates. We produced nanoparticle immunogens displaying either the FimH lectin domain or a recently reported conformationally stabilized antigen, FimH-DSG, comprising both the lectin and pilin domains. When formulated on aluminum hydroxide, both nanoparticle immunogens elicited similar levels of receptor-blocking activity as a ten-fold higher dose of monomeric FimH-DSG formulated with a potent adjuvant. The improved manufacturability of the stabilized antigen, combined with the ability of nanoparticle display to obviate the need for complex adjuvants, provides important preclinical data for FimH-based vaccines intended to prevent urinary tract infections. More broadly, our data extend the applicability of the I53-50 nanoparticle platform, which to date has been mainly used for displaying viral and protozoan antigens, to bacterial indications.

immunology↗

bioRxiv2024

Structure-Based Design of a Highly Immunogenic, Conformationally Stabilized FimH Antigen for a Urinary Tract Infection Vaccine

Adhesion of E. coli to the urinary tract epithelium is a critical step in establishing urinary tract infections. FimH is an adhesin positioned on the fimbrial tip which binds to mannosylated proteins on the urinary tract epithelium via its lectin domain (FimHLD). FimH is of interest as a target of vaccines to prevent urinary tract infections (UTI). Previously, difficulties in obtaining purified recombinant FimH from E. coli along with the poor inherent immunogenicity of FimH have hindered the development of effective FimH vaccine candidates. To overcome these challenges, we have devised a novel production method using mammalian cells to produce high yields of homogeneous FimH protein with comparable biochemical and immunogenic properties to FimH produced in E. coli. Next, to optimize conformational stability and immunogenicity of FimH, we used a computational approach to design improved FimH mutants and evaluated their biophysical and biochemical properties, and murine immunogenicity. This approach identified a highly immunogenic FimH variant (FimH-DSG TM) that is produced at high yields in mammalian cells. By x-ray crystallography, we confirmed that the stabilized structure of the FimHLD in FimH-DSG TM is similar to native FimH on the fimbrial tip. Characterization of monoclonal antibodies elicited by FimH-DSG TM that can block bacterial binding to mannosylated surfaces identified 4 non-overlapping binding sites whose epitopes were mapped via a combinatorial cryogenic electron microscopy approach. Novel inhibitory epitopes in the lectin binding FimH were identified, revealing diverse functional mechanisms of FimH-directed antibodies with relevance to FimH-targeted UTI vaccines. Author summaryEscherichia coli is the primary cause of urinary tract infections. Adherence to uroepithelial surfaces is mediated by the pilus adhesin protein FimH, which is of interest as a vaccine candidate. We developed a method for producing recombinant FimH at bioprocess scale, previously a barrier to commercial development. Structure-based design and screening was used to identify a novel FimH vaccine candidate with improved stability and immunogenicity in mice. Structure of this full-length protein was determined by X-ray crystallography and shown to closely resemble the pilus adhesin present in its native form on the bacterial surface. Binding sites of biologically active FimH monoclonal antibodies were determined by X-ray crystallography or by cryo-electron microscopy, providing insights into mechanisms by which antibodies block binding of the bacteria to urinary tract receptors. One sentence summaryStructure-based design of a conformationally stabilized E. coli FimH vaccine candidate capable of eliciting antibodies to diverse epitopes with the ability to block bacterial binding to bladder epithelial cells.

microbiology↗