Rationally designed FimH variants with enhanced functional immunogenicity as vaccine candidates for ExPEC urinary tract infections

Extraintestinal pathogenic Escherichia coli (ExPEC) is a major cause of urinary tract infections (UTIs) and invasive disease. Rising antimicrobial resistance highlights the need for preventive strategies such as vaccination. The conserved D-mannose-specific adhesin FimH is essential during early UTI pathogenesis, making it an attractive vaccine target. We rationally designed a FimH lectin domain antigen stabilized in a low-affinity, tense conformation by two amino-acid substitutions ( LA FimH LD ), thereby exposing epitopes within the mannose-binding pocket relevant for functional immunity. Multiple vaccine formats incorporating LA FimH LD were generated, including fimbrial tip constructs, carrier protein fusions or conjugates and a nanoparticle. In rats, monomeric LA FimH LD induced functional antibody responses comparable to a clinically tested FimCH reference, while four LA FimH LD variants elicited superior inhibition of ExPEC binding to human bladder cells. A multimeric LA FimH LD –CRM 197 conjugate further demonstrated robust functional immunogenicity in minipigs. These data show enhanced FimH vaccine potency and identify candidates for UTI prevention.