Development and Characterization of a Ten-Plex Assay to Measure Klebsiella pneumoniae Antigen-Specific IgG in Human Sera

<i>Klebsiella pneumoniae</i> is a leading cause of nosocomial infections, neonatal sepsis, and childhood mortality worldwide. A drastic rise in antibiotic-resistant isolates poses an urgent threat to humanity, and the World Health Organization (WHO) has classified this as a critical-priority antimicrobial-resistant (AMR) pathogen. Recent advancements in developing vaccines against <i>Klebsiella pneumoniae</i> have highlighted the lack of standardized assays to evaluate immunogenicity, complicating comparison among different vaccines under development and the establishment of a serological threshold of risk reduction (SToRR). Here, we describe the development of a ten-plex multiplex assay to measure IgG against capsular polysaccharides (K2, K25, K102, K149), O antigens (O1v1, O1v2, O2v1, O2v2 and O5), and a conserved protein (MrkA). A standard curve was established by pooling human sera from naturally exposed subjects and then calibrated in terms of Relative Luminex Units/mL. The assay was fully characterized in terms of specificity, precision, linearity, and repeatability. This immunoassay demonstrates performance suitable for future clinical trials, as well as to perform sero-epidemiological studies to gain insights into naturally occurring immunity, potentially contributing to the establishment of a serological threshold of risk reduction against <i>Klebsiella pneumoniae</i>.