The type I NKT cells are defined by the expression of a semi-invariant αβTCR, comprising an invariant TCR α-chain using the TRAV10-TRAJ18 (in humans) and TRAV11-TRAJ18 (in mice) genes that are associated with a limited array of TCR β-chains (TRBV25-1 in humans; TRBV1, TRBV13, and TRBV29 in mice) [5,6], and by their ability to be potently activated by the archetypal anti-tumor glycolipid, α-Galactosylceramide (α-GalCer). The gene discussed is TRAJ18; the disease is neoplasm.