PDCD1 and neoplasm: We therefore performed an additional in vivo CRISPR/Cas9 screen using pmel CD8+ T cells in an MC38-gp100 tumor model found to be insensitive to treatment by Pdcd1-inactivated pmel T cells (35) The screen again performed robustly, with 82% of the sgRNAs recovered (Supplemental Data 3) and with sgRNAs targeting the Pdcd1 gene displaying no enrichment within tumors (Figure 1F).