Abstract 1333: REST represses neuroendocrine transcriptional programs and enables anti-tumor immunity in SCLC.

Abstract Small-cell lung cancer (SCLC) is a devastating neuroendocrine carcinoma in critical need of new therapeutic approaches. While a small subset of patients responds well to standard of care chemo-immunotherapy, durable responses are rare. Recent studies have revealed substantial transcriptional and functional heterogeneity, including the identification of multiple low-neuroendocrine SCLC subtypes, which we and others have linked to increased inflammation and response to immunotherapy. A major mediator of neuroendocrine state in SCLC is the transcription factor REST, which is a repressor of neuronal/neuroendocrine genes. While REST is typically silenced in SCLC, it is active in inflamed, low-neuroendocrine SCLC. However, links between REST and immune phenotypes in SCLC have been understudied. To explore the interplay between REST/neuroendocrine status, immune infiltration and response to clinically relevant therapies, we first generated an autochthonous mouse model of SCLC in the Rb/p53-null (RP) background with conditional REST expression (RP-REST). Transcriptionally, REST expression promoted a low-neuroendocrine SCLC phenotype with decreased expression of ASCL1 target genes compared to RP controls. In contrast, RP-REST tumors displayed a striking enrichment of antigen presentation and inflammatory response gene signatures, which correlated with increased infiltration of CD8+ T cells and F4/80+ macrophages, confirming that REST expression generates inflamed, low-neuroendocrine SCLC. We then overexpressed REST in a panel of murine SCLC cell lines derived from the RP mouse model and confirmed REST-driven repression of a neuroendocrine gene signature. Moreover, REST overexpression potentiated responses to interferon-γ resulting in increased MHC-I antigen presentation and phospho-STAT1. Using murine cell lines to generate syngeneic allografts in immunocompetent mice, we found that REST overexpression sensitized tumors to PD1 checkpoint blockade in vivo. Multiparameter flow cytometry reveals that these responses were associated with increased infiltration of activated CD8+ T cells, in addition to an expansion of M1 macrophages. Further, scRNAseq of the tumor compartment identifies a subset of cells in REST-expressing tumors with exceptionally high levels of inflammatory signaling, including secreted cytokines that may serve to recruit the abundant immune cells found in these tumors. Tumor heterogeneity is a critical variable in determining patient outcomes clinically. Here, we show that REST drives a low-neuroendocrine, inflamed SCLC phenotype in an autochthonous mouse model, which is corroborated by isogenic models showing reduced neuroendocrine markers, increased antigen presentation and sensitivity to immunotherapy. Citation Format: Jackson P. Fatherree, Kelly Heard, Alex Doan, Joseph Hiatt, Daniel S. Hippe, Feinan Wu, Shivani Srivastava, David MacPherson, . REST represses neuroendocrine transcriptional programs and enables anti-tumor immunity in SCLC [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2026; Part 1 (Regular Abstracts); 2026 Apr 17-22; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2026;86(7 Suppl):Abstract nr 1333.