Chromosome 9p21.3 Coordinates Cell Intrinsic and Extrinsic Tumor Suppression

Somatic chromosomal deletions are prevalent in cancer, yet their effects are poorly understood. The most prominent homozygous deletions affect chromosome 9p21.3 and eliminate the CDKN2A/B tumor suppressor genes, thus disabling a cell intrinsic barrier to tumorigenesis. However, half of 9p21.3 deletions encompass a cluster of 16 type I interferons (IFNs) whose co-deletion remains unexplored. To functionally dissect 9p21.3 and other genomic deletions, we developed MACHETE (Molecular Alteration of Chromosomes with Engineered Tandem Elements), a genome engineering strategy that enables flexible modeling of megabase-sized deletions. Applying MACHETE to a syngeneic mouse model of pancreatic cancer, we show that concomitant loss of the IFN cluster with Cdkn2a/b enhanced immune evasion, metastasis, and immunotherapy resistance compared to Cdkn2a/b deletions alone. Mechanistically, IFN co-deletion disrupted type I IFN signaling in the tumor microenvironment, leading to marked changes in infiltrating immune cells and escape from CD8+ T cell surveillance, effects largely driven by the poorly understood interferon epsilon (Ifne). These results reveal how IFN-encompassing 9p21.3 deletions disable cell intrinsic and extrinsic tumor suppression, thereby providing a pervasive route for immune evasion, metastasis, and immunotherapy resistance. Our study provides a framework for interrogating large deletion events in cancer and beyond.