2025 White Paper on Recent Issues in Bioanalysis: Redosing Patients with AAV Gene Therapy; CRS Immunogenicity Risk; Shedding Assays; NHP Studies Immunogenicity; CMC vs Bioanalytical Assays; Artificial Intelligence-Powered Genomic Pipelines for NGS ( <u>PART 3A</u> – Recommendations on Gene, Cell, and Vaccine Therapies Immunogenicity &amp; Technologies; Biotherapeutics &amp; Biosimilars Immunogenicity Assessment &amp; Clinical Relevance <u>PART 3B</u> – Regulatory Agencies’ Input on Immunogenicity/Technologies of Biotherapeutics, Gene, Cell &amp; Vaccine Therapies)

The 19^th Workshop on Recent Issues in Bioanalysis (19^th WRIB) took place in New Orleans, LA, USA on April 7-11, 2025. Over 1200 professionals representing pharma/biotech companies, CROs, and multiple regulatory agencies convened to actively discuss the most current topics of interest in bioanalysis. The 19^th WRIB included 3 Main Workshops and 7 Specialized Workshops that together spanned 1 week to allow an exhaustive and thorough coverage of all major issues in bioanalysis of biomarkers, immunogenicity, gene therapy, cell therapy and vaccines.Moreover, in-depth workshops on "Implementation Practice for the Newest ELN/LIMS Systems" and on "Vaccine Cell-Based/Functional & Molecular Assays as part of the harmonization of vaccine clinical assays global initiative" were the special features of the 19^th edition.As in previous years, WRIB continued to gather a wide diversity of international, industry opinion leaders and Regulatory Agency experts working on both small and large molecules as well as gene, cell therapies and vaccines to facilitate sharing and discussions focused on improving quality, increasing regulatory compliance, and achieving scientific excellence on bioanalytical issues.This 2025 White Paper encompasses recommendations emerging from the extensive discussions held during the workshop and is aimed to provide the bioanalytical community with key information and practical solutions on topics and issues addressed, in an effort to enable advances in scientific excellence, improved quality and better regulatory compliance. Due to its length, the 2025 edition of this comprehensive White Paper has been divided into three parts for editorial reasons.This publication (Part 3) covers in the Part 3A the recommendations on Gene Therapy, Cell therapy, Vaccines and Biotherapeutics Immunogenicity and in Part 3B the Regulatory Inputs on these topics. Part 1 (Mass Spectrometry Assays and Regulated Bioanalysis/BMV) and Part 2 (Biomarkers/BAV, IVD/CDx, LBA and Cell-Based Assays) are published in volume 18 of Bioanalysis, issues 3 and 2, respectively.