To assess the effect of galectin-9 in protecting breast cancer cells against cytotoxic cell-dependent killing we co-cultured MCF-7 cells (adherent) with cytotoxic ALL-derived TALL-104 CD8-positive T lymphocytes (we used these rather than NK cells since mainly T cells infiltrate solid tumors; as NK cells, TALL-104 cells express Tim-3, and not galectin-9) for 16 h at a ratio of 4 MCF-7 cells: 1 TALL-104 cells (Figure 5A—this ratio was selected experimentally to achieve moderate effects in order to be able to trace biochemical mechanisms). This evidence concerns the gene HAVCR2 and acute lymphoblastic leukemia.