P1.074. SNORD33-Driven 18S rRNA 2′-O-Methylation Licenses TNFSF9–4-1BB Signaling and Sensitizes ESCC to PD-1 Blockade

Abstract

Abstract Topic Esophageal Cancer: Adjuvant and Neo-Adjuvant Therapies Background Neoadjuvant PD-1/PD-L1 based immunotherapy improve outcomes for resectable esophageal squamous cell carcinoma (ESCC), but patient outcome are heterogeneous and robust pretreatment blood biomarkers are lacking. Methods We performed an unbiased plasma snoRNA screen (359 snoRNAs) and quantified SNORD33 in two independent neoadjuvant immunotherapy cohorts (training N = 62; validation N =33). Mechanistic studies integrated scRNA-seq of post-treatment specimens (N = 6), tumor-cell SNORD33 perturbation in syngeneic models under anti–PD-1, paired RNA-seq/TMT proteomics, RNA-FISH, RTL-P, polysome profiling, and 4-1BB agonism; multiplex RNA-FISH/IF assessed human tissues. Results SNORD33 was prioritized in discovery screening and, clinically, baseline plasma SNORD33 was higher in ypCR, inversely correlated with tumor regression grade, and predicted ypCR (AUC 0.815 and 0.767 in training and validation). SNORD33 high tumors showed increased NK cells/neutrophils and an activated NK program. Tumor-cell SNORD33 loss blunted anti–PD-1 efficacy, reduced intratumoral NK accumulation, and impaired NK effector features with increased inhibitory receptors. Multi-omics prioritized TNFSF9 (4-1BBL) as a SNORD33-dependent output with transcript–protein discordance; SNORD33 localized to nucleoli, modulated 18S rRNA U1326 2′-O-methylation, and promoted TNFSF9 translation. Agonistic 4-1BB restored anti–PD-1 tumor control, and human multiplex RNA-FISH/IF showed SNORD33–TNFSF9 proximity with effective NK enrichment. Conclusion Plasma SNORD33 is a clinically tractable pretreatment biomarker and defines a ribosome-centered SNORD33–TNFSF9–4-1BB axis linking rRNA modification to NK-dependent checkpoint sensitivity, supporting biomarker-guided 4-1BB–based combinations in ESCC.