BRCA2 and infection: To perform the screen, we introduced a Brie mouse lentiviral library with puromycin selection containing four sgRNAs per gene and 1,000 nontargeting sgRNAs (34) into organoid cultures of three Brca2-deficient genotypes (Brca2Δ/Δ Trp53Δ/Δ; Brca2Δ/Δ sgRb1; and Brca2Δ/Δ Trp53Δ/Δ PtenΔ/Δ) at a multiplicity of infection of 0.3, and screens were run in duplicate for each organoid line.