Cbx3/HP1γ deficiency leads to augmented transcription initiation and chromatin remodeling that results in increased transcriptional activity at Lef1 and Il21r. Genetic ablation of Lef1 and Il21r in Cbx3/HP1γ-deficient mice causes a loss of tumor CD8+ effector T cells accompanied by the reduction of Ifng, Gzmb and Prf1 expression, which results in uncontrolled ovarian, melanoma and neuroblastoma growth. The gene discussed is PRF1; the disease is neoplasm.