Uracil-DNA glycosylase deficiency is associated with repressed tumor cell-intrinsic inflammatory signaling and altered sensitivity to exogenous interferons

2'-deoxyuridine (dU) is a common DNA lesion resulting from cytosine deamination and from dUMP incorporation by DNA polymerases, both of which are prevalent in cancer. The primary mechanism that repairs dU lesions in genomic DNA is base excision repair initiated by Uracil-DNA Glycosylase 2 (UNG2). We generated <i>Ung</i> knockout mouse B16 melanoma cells to investigate the consequences of UNG deficiency in a well-characterized, immunocompetent, syngeneic mouse cancer model. We show that UNG-deficient (ΔUNG) B16 tumors exhibited T cell-dependent, delayed growth <i>in vivo</i> and were more responsive to anti-PD-L1 therapy. Immune profiling revealed reduced CD8⁺ T cell infiltration but augmented IFN-γ-competent effector CD4⁺ T cells in ΔUNG tumors. <i>In vitro</i>, ΔUNG tumor cells exhibited strongly suppressed cell-intrinsic type-I interferon, type-II interferon, and inflammatory signaling gene expression signatures as well as altered cytokine and chemokine secretion. <i>In vivo</i>, ΔUNG tumors exhibited a modified inflammatory cytokine and chemokine milieu. Furthermore, ΔUNG tumor cells had altered sensitivity to exogenous interferons <i>in vitro</i>, with increased sensitivity to IFN-γ but decreased sensitivity to IFN-α/β. Collectively, our data show that tumor-cell-specific UNG deficiency results in an altered tumor microenvironment <i>in vivo</i> and provide proof of concept for the use of UNG inhibitors to modulate inflammatory pathways in tumors.