Chronic viral mimicry induction following p53 loss promotes immune evasion [CUTandRUN]

Epigenetic therapies that alter DNA- and/or histone modifications facilitate transcription of immunogenic repetitive elements that cull cancer cells through ‘viral mimicry’ responses. Paradoxically, cancer-initiating events that include functional inactivation of canonical tumor suppressor proteins also facilitate transcription of repetitive elements. Contributions of repetitive element transcription towards cancer initiation, and the mechanisms by which cancer cells evade lethal viral mimicry responses during tumor initiation remain poorly understood. In this report, we characterize patient-derived premalignant lesions of the fallopian tube along with syngeneic mouse models of epithelial ovarian cancer to explore the earliest events of tumorigenesis following loss of the p53 tumor suppressor protein. We report that p53 loss disrupts constitutive heterochromatin to permit transcription of immunogenic repetitive elements capable of activating viral mimicry responses. While acute viral mimicry activation diminishes cell fitness, chronic viral mimicry activation following p53 loss promotes epigenetic reprogramming that increases tolerance of cytosolic nucleic acids and diminishes cellular immunogenicity as a pro-survival adaptation. This selection process we describe as ‘viral mimicry conditioning’ can be partially attenuated by the reverse transcriptase inhibitor 3TC to delay spontaneous tumorigenesis. Altogether, these results reveal that viral mimicry conditioning following p53 loss selects for diminished cell immunogenicity to promote immune evasion upon cancer initiation. Disruption of viral mimicry conditioning during cancer initiation may represent a pharmacological target for early cancer interception.