A further comprehensive immunostaining study of ATLL biopsy samples (n = 69) for immune checkpoint molecules has shown that expression of PD-1, OX40, galectin-9, and PD-L1 on neoplastic cells is nearly mutually exclusive, suggesting the use of distinct immune checkpoint pathways in individual ATLL cases [217]. This evidence concerns the gene LGALS9 and adult T-cell leukemia/lymphoma.