Response rates to immune checkpoint blockade (ICB) in KRAS-mutant lung adenocarcinoma remain poor. In this issue of Cancer Discovery, Li and colleagues report an in vivo CRISPR screen of epigenetic regulators of the tumor immune microenvironment that uncovers Asf1a as a tumor-intrinsic suppressor of ICB through suppression of GM-CSF expression.See related article by Li et al., p. 270.