CREBBP loss drives immune evasion by epigenetically silencing STING and MHC-I in small cell lung cancer

Abstract

Most small cell lung cancers (SCLCs) exhibit low immunogenicity and intrinsic resistance to immunotherapy, yet the underlying mechanisms remain poorly understood. Here, we identify CREBBP loss, a frequent genetic alteration in SCLC, as a key suppressor of tumor cell-intrinsic immune responses that drives an immune-cold tumor microenvironment in Rb1/Trp53-driven autochthonous mouse models. Consistently, Crebbp deletion promotes immune escape in syngeneic SCLC models. Mechanistically, Crebbp loss suppresses Sting and major histocompatibility complex class-I expression by reducing histone H3 acetylation. Notably, HDAC inhibition restores histone acetylation, reactivates these silenced genes, and induces tumor cell-intrinsic immune responses. Moreover, pharmacological HDAC inhibition synergizes with immune checkpoint blockade to suppress tumor growth in both Crebbp-mutant and Crebbp-wild-type SCLCs, with a more prominent effect in Crebbp-mutant tumors. Collectively, these findings establish CREBBP loss as a key mechanism of immune evasion and immunotherapy resistance in SCLC, highlighting HDAC inhibition as a promising strategy to enhance immunotherapy efficacy.