Immunopeptidomics combined with full-length transcriptomics uncovers diverse neoantigens

Neoantigens are crucial for antitumor immunity and immune checkpoint inhibitor (ICI) efficacy by triggering strong immune responses. However, conventional methods for identifying neoantigens, such as whole-exon sequencing and short-read RNA sequencing (RNA-seq), appear to be insufficient, and the tumor mutational burden cannot sufficiently predict ICI efficacy. In this study, we employed a proteogenomic approach using long-read RNA-seq with Pacific Biosciences Single-Molecule Real-Time Sequencing technology to analyze full-length transcripts in combination with the human leukocyte antigen ligandome. As a result, many neoantigen candidates were identified, which were unregistered in a comprehensive database, including those from non-coding regions. Additionally, we validated the responses of specific T cell receptors (TCRs) to these candidates and identified several pairs of TCRs and neoantigens. These findings highlight the presence of more diverse neoantigens than expected that cannot be identified by conventional methods.