BACKGROUND: Immunotherapy in many tumors is limited by tumor heterogeneity and low mutational burden. While the vast majority of tumor-specific antigens (neoantigens) are identified through somatic mutations, recent studies indicate aberrant RNA-splicing (neojunctions) as a new source for targets. Our spatial splicing neoantigen identification platform (SNIPP) characterizes a novel class of clonally-expressed splicing-derived neoantigens that elicit a CD8+ T-cell-mediated tumor killing response. METHODS: SNIPP identified public neojunctions expressed in TCGA RNA-seq (positive sample rate (PSR) > 10%) and not in GTEx normal tissue RNA-seq data (PSR < 1%) across 12 cancer types. To characterize intratumorally-conserved neojunctions, we performed maximally-distanced multi-site biopsies (n=535) within glioma patients (n=56) and obtained RNA-seq data from each intratumoral site. This was additionally performed on publicly-available multi-site sequencing data from other cancer types. Two independent algorithms then predicted peptide processing likelihood and HLA-binding affinity of ASN candidates. Neoantigen-specific TCR sequences characterized from subsequent PBMC in vitro sensitization and 10x V(D)J scRNA-seq were transduced into CD8+ T-cells for immunogenicity and cytotoxicity assays against glioma cell lines. Differential gene expression (DESeq2) and gene set enrichment analyses (GSEA) is performed between tumor subtypes within cancers, and a Pearson correlation matrix is generated to identify correlated neojunctions with specific splicing factor expression. CRISPRi knockdown of select splicing factors followed by qPCR of their corresponding neojunctions are performed to determine the correlative mechanism for neojunction expression. RESULTS: Our pipeline identified 789 public neojunctions, with 32 neojunctions concurrently identified in transcriptomic and proteomic glioma data and predicted to be presented by HLA-A*02:01 with high confidence. IVS and subsequent 10x VDJ scRNA-seq identified TCR clonotypes reactive against neojunctions in RPL22 (n=7) and GNAS (n=1), the latter being highly intratumorally-conserved (detected in > 90% of spatially-mapped biopsies across 17/56 patients (26.78%)). TCR-transduced T-cells demonstrated recognition and immunogenic activation against endogenously processed and presented neoantigens in various pan-cancer cell lines. Furthermore, IDH1-mutant oligodendroglioma samples demonstrated significantly elevated expression of neojunctions over IDH1-mutant astrocytoma and IDH1wt subtypes. Differential gene expression (DESeq2) identified decreased expression of splicing factors due to oligodendroglioma-specific co-deletion of Chromosomes 1p/19q. siRNA knockdown of these splicing factors (e.g. SF3A3, SNRPD2) in IDH1wt glioma cells resulted in significantly increased expression of corresponding neojunctions. CONCLUSION: Our unique SNIPP neoantigen discovery platform identified novel public tumor-wide splice-derived neoantigens and reactive TCRs, and its pan-cancer application characterized candidates targetable across multiple diseases.