Human natural killer T cells acquire a memory-activated phenotype before birth

Natural killer T (NKT) cells have recently been shown to play an important role in the rejection of malignant tumors and in the regulation of autoimmu ne diseases. Potent antitumor effects of the marine sponge-derived NKT cell ligand KRN7000 were observed in mice. Therefore, the elucidation of the na tural ligand of NKT cells, which is currently still unknown, might have imp ortant clinical consequences for the treatment of cancer and autoimmune dis eases. Analysis of cord blood mononuclear cells from healthy term infants d emonstrated that in sharp contrast with the vast majority of cord blood lym phocytes, human NKT cells have already acquired a memory-activated phenotyp e before birth. This observation indicates that NKT cells encounter a natur al ligand during fetal life and that this ligand is unlikely to be of micro bial origin.(Blood.2000;95:2440-2442) (C) 2000 by The American Society of H ematology.