Vaccine Ligand Binding Assay Development.

This white paper (Part 2 of a series on vaccine immunogenicity assay validation) addresses the development of Ligand Binding Assays (LBAs) to support vaccine immunogenicity studies. Developed through a collaborative effort by a working group of experts from 16 global vaccine manufacturers, national regulatory authorities, and a nonprofit global-health foundation convened under the Workshop on Recent Issues in Bioanalysis (WRIB), this manuscript provides practical guidance to complement existing regulatory frameworks for bioanalytical method validation.Part 2 details the iterative process of LBA development, with emphasis on defining the Analytical Target Profile (ATP) as a foundational tool for guiding decision-making across the assay life cycle. Key topics include assay purpose and analyte specificity, regulatory expectations, the use of statistical Design of Experiments (DOE) to systematically optimize assay conditions, and the selection of appropriate reagents, controls, and sample matrices. The paper also addresses the unique challenges posed by the structural diversity of vaccine antigens and the need for representative reference materials.The manuscript further highlights the importance of ongoing performance assessment and the adaptability of assays as they transition from early exploratory phases to pivotal clinical studies. Collectively, the recommendations presented aim to supplement existing regulatory guidance with vaccine-specific considerations, ultimately supporting the development of safe and effective vaccines. This paper is complemented by Part 1 (LBA Validation) and Part 3 (Assay Lifecycle Management, including Maintenance, Monitoring, and Transfers).