PDCD1 and neoplasm: Indeed, knockout or small hairpin RNA (shRNA)-mediated knockdown of PDCD1 enhanced the anti-tumor efficacy of C-type lectin-like molecule-1 (CLL-1)-, mesothelin-, epidermal growth factor receptor (EGFR)-, CD19-, and Glypican-3 (GPC3)- CAR-Ts [95,96,97,98].