Suchan, M. | bioRxiv Science

bioRxiv2023

An mRNA-encoded, long-lasting Interleukin-2 restores CD8+ T cell neoantigen immunity in MHC class I-deficient cancers

MHC class I antigen presentation deficiency is considered to be the most prevalent cancer immune escape mechanism. Despite its increasing occurrence, the mechanistic implications, and potential strategies to address this challenge, remain poorly understood. Studying {beta}2-microglobulin (B2M) deficient mouse tumor models, we found that MHC class I loss leads to a substantial immune desertification of the tumor microenvironment (TME) and broad therapeutic resistance to immune-, chemo- and radiotherapy. We show that treatment with long-lasting mRNA-encoded interleukin-2 (IL2) restores an immune cell infiltrated, IFN{gamma}-promoted, highly proinflammatory TME signa-ture, and when combined with a tumor-targeting monoclonal antibody (mAb), can overcome ther-apeutic resistance. Surprisingly, we identified that effectiveness of this treatment is driven by ne-oantigen-specific IFN{gamma}-releasing CD8+ T cells that recognize neoantigens cross-presented by TME-resident activated macrophages that under IL2 treatment acquire augmented antigen presen-tation proficiency along with other M1-phenotype-associated features. Our findings highlight the unexpected importance of restoring neoantigen-specific immune responses in the treatment of cancers with MHC class I deficiencies.

immunology↗

bioRxiv2023

Prediction of tumor-specific splicing from somatic mutations as a source of neoantigen candidates

Splicing is dysregulated in many tumors and may result in tumor-specific transcripts that can encode neoantigens, which are promising targets for cancer immunotherapy. Detecting tumor-specific splicing is challenging because many non-canonical splice junctions identified in tumor transcriptomes also appear in healthy tissues. Here, we developed splice2neo to integrate the predicted splice effects from somatic mutations with splice junctions detected in tumor RNA-seq for individual cancer patients. Splice2neo excludes splice junctions from healthy tissue samples, annotates resulting transcript and peptide sequences, and provides targeted re-quantification of supporting RNA-seq reads. We developed a stringent detection rule to predict splice junctions as mutation-derived targets and identified 1.7 target splice junctions per tumor with a false discovery rate below 5% in a melanoma cohort. We confirmed tumor-specificity using independent, healthy tissue samples. Furthermore, using tumor-derived RNA, we confirmed individual exon skipping events experimentally. Most target splice junctions encoded neoepitope candidates with predicted MHC-I or MHC-II binding. Compared to neoepitope candidates derived from non-synonymous point mutations, the splicing-derived MHC-I neoepitope candidates had a lower self-similarity to corresponding wild-type peptides. In conclusion, we demonstrate that identifying mutation-derived and tumor-specific splice junctions can lead to additional neoantigen candidates to expand the target repertoire for cancer immunotherapies. Key PointsO_LIsplice2neo is a versatile tool for identifying and analyzing of splice junctions as a source of neoantigen candidates C_LIO_LIWe identified mutation-retrieved splice junctions supported by RNA-seq in melanoma samples C_LIO_LIThe predicted target splice junctions exhibited a strong tumor-specificity as they were absent in healthy tissues. C_LIO_LITarget splice junctions often lead to frame-shift peptides and encode promising neoantigen candidates C_LI

bioinformatics↗