Mechanisms by which whole genome doubling drives breast tumor evolution [scATAC-seq]

Whole genome doubling (WGD) is one of the most common genetic alterations in human cancer generally associated with poor clinical outcome, yet the underlying mechanisms have not been delineated. Here we developed an experimental model of WGD using murine mammary tumor cell lines in immunocompetent mice and found that WGD triggers immune evasion characterized by reduced infiltration of CD8+ T cells. Via comprehensive cellular and molecular characterization of WGD+ and WGD- tumors at the single cell level, we determined that WGD+ cancer cells have diminished antigen presentation due to muted response to IFN stimulation in part due to epigenetic silencing of transcriptional regulators of MHCI genes via the PRC2 complex. WGD+ tumors also have lower alpha-ketoglutarate/succinate ratio that might lead to the observed increase in histone H3 lysine 27 trimethyl levels associated with repressive chromatin. Lastly, WGD+ tumors are more responsive to anti-PD-L1 blockade and to EED inhibitors and this is associated with increased antigen presentation and CD8+ T cell infiltration. Our results have important implications for the treatment of patients with WGD+ breast cancer.