2 11 newly generated MCC lines through genomic and proteomic analysis. We then interrogated MCC lines through genome-scale gain-and loss-of-function screens for the restoration of HLA-I. These screens identified MYCL and the non-canonical Polycomb repressive complex 1.1 (PRC1.1) as regulators of HLA-I. We further demonstrate that pharmacologic inhibition of the PRC1.1 component USP7 can restore HLA-I expression.