 Natural killer T NKT cells are a unique subset of lymphocytes that present a mixed T-NK phenotype. NKT cells are expanded conventionally from peripheral blood mononuclear cells by addition of a variety of cytokines in vitro culture. Our previous studies demonstrated that the expansion of NKT cells in a clinical usage scale from peripheral blood mononuclear cells is feasible. Those expanded NKT cells exhibit antitumor effect in vitro and in vivo tumor -bearing nude mice against a variety of tumor cells. Furthermore, intravenous infusion of a single dose of 4X109 NKT cells in mice has been proved safe. 