To assess the possible role of granzyme B, a pro-apoptotic proteolytic enzyme produced mainly by cytotoxic T cells and NK cells, in galectin-9-induced killing of T cells, we co-cultured THP-1 human AML cells and Jurkat T cells (at a ratio 1:1; Jurkat T cells express high amounts of VISTA and can express granzyme B and release this enzyme upon stimulation with PMA (28, 29), which activates granzyme B expression through NF-kB (29)). This evidence concerns the gene VSIR and acute myeloid leukemia.