Evaluation of humoral and cellular immune responses induced by a novel YidRv subunit vaccine from hypervirulent Klebsiella pneumoniae

Background: Klebsiella pneumoniae (KP) has re-emerged as a prominent etiological agent of pneumonia and systemic infection, with extended-spectrum β-lactamase (ESBL)-producing strains posing considerable therapeutic challenges. Moreover, vaccines may have limited efficacy because of the emergence of variant strains. The yidRv gene encodes a protein linked to excessive adherence and is conserved in over 99% of KP isolates. The present study aimed to explore the ability of a rec-YidRv protein to stimulate humoral and cellular immune response in vitro and in vivo. Materials and methods: The capability of the purified rec-YidRv protein to induce antibody synthesis was tested using a mice model. We also assessed whether rec-YidRv could successfully trigger the proliferation of splenocytes and the synthesis of their cytokines. Furthermore, the capacity of antigen to protect mice from ESBL-producing KP strain infection was investigated. Results: In vitro and in vivo analyses revealed that mice immunized with rec-YidRv generated a strong antibody and memory response. Compared to non-stimulated controls, immunized mice showed an increase in measurable KP-directed immunoglobulin G (IgG) levels, with elevated IgG1 and IgG2b fractions; additionally, splenocyte proliferation expanded by 5-fold. Infection of mice with a lethal dose of KP following immunization markedly extended ani mal survival and decreased the pathogen’s ability to form ventricular biofilms. Conclusions: The rec-YidRv elicited robust antibody responses and a moderate expansion of cellular activity. Rec-YidRv is an effective protein-only platform for inhibiting infection by antibiotic-resistant KP. Future studies should incorporate refined adjuvants and improved administration methods to enhance protective responses.