PDCD1 and neoplasm: To reduce the risk of graft rejection by the host immune system, HLA genes have been disrupted in donor T cells.108, 109, 110, 111 Notably, CRISPR-Cas9-mediated triple KO of the T cell receptor α constant (TRAC) locus, an HLA complex gene (B2M), and an immune checkpoint gene (PDCD1) was used to potentiate the anti-tumor effect of CAR-T cells against multiple targets in mouse models, for example in mice intravenously injected with a B cell ALL cell line,109 in mice intraperitoneally injected with a lymphoma cell line,110 and in mice intracerebrally injected with a glioma cell line.111