This HIV-1 PI was found to have anti-leukemic activity against ATLL cells ex vivo [54], but the inhibitory effect was considered to be a consequence of a ritonavir-dependent inhibition of NF-κB transcriptional activation in ATLL cells rather than impaired activity of HTLV-1 PR [55]. This evidence concerns the gene NFKB1 and adult T-cell leukemia/lymphoma.