Nivolumab treatment resulted in rapid expansion of predominant ATLL clones. Clonal analysis of the peripheral blood of patients 1 and 3 before (A) and after (B) nivolumab therapy comparing probe-capture sequencing for HTLV-1 proviral integration sites with TCR gene rearrangement of β locus (TRB; supplemental Table 2) and γ locus (TRG; supplemental Table 1). Clones < 1% of total reads are shown in white.