In a mouse model to study tumor cell clones originating from the same mouse cell line, #2D10 tumors had high PD-1+CD8+ T-cell infiltration and responded to PD-1 blockade, whereas #1C11 tumors failed to respond to PD-1 blockade and displayed low PD-1+CD8+ T-cell infiltration. This evidence concerns the gene PDCD1 and neoplasm.