ATLL clones that rapidly expanded after PD-1 blockade carry mutations commonly found in ATLL. Mutations present in patient PBMCs before (A) and after (B) nivolumab therapy. Percentage of reads is for mutant over total number of reads for each gene segment. Mutations that increased in abundance after nivolumab are shaded green, the mutation that decreased after nivolumab is shaded pink, and the mutation present only after nivolumab is shaded red in the table. The schematic diagram below the table shows the role of each gene product in T-lymphocyte signaling pathways (green, mutations in patient 1; red, mutations in patient 3).