Although Tim-3-expressing NK cells are highly functional in terms of their cytotoxicity and cytokine-secretion capabilities (30), the engagement of Tim-3 by one of its ligands (e.g., Galectin-9) or the overexpression of Tim-3 in cancer or during persistent infection, as in hepatitis B virus (31) and HIV (32) infections, can restrict NK cell function. Here, HAVCR2 is linked to cancer.