Natural killer T (NKT) lymphocytes express an invariant T cell antigen receptor (TCR) encoded by the Valpha14 and Jalpha281 gene segments. A glycosylceramide-containing alpha-anomeric sugar with a longer fatty acyl chain (C26) and sphingosine base (C18) was identified as a ligand for this TCR. Glycosylceramide-mediated proliferative responses of Valpha14 NKT cells were abrogated by treatment with chloroquine-concanamycin A or by monoclonal antibodies against CD1d/Vbeta8, CD40/CD40L, or B7/CTLA-4/CD28, but not by interference with the function of a transporter-associated protein. Thus, this lymphocyte shares distinct recognition systems with either T or NK cells.

Agelasphin-9b, (2S,3S,4R)-1-O-(alpha-D-galactopyranosyl)-16-methyl-2- [N-((R)-2- hydroxytetracosanoyl)-amino]- 1,3,4-heptadecanetriol, is a potent antitumor agent isolated from the marine sponge Agelas mauritianus. Various analogues of agelasphin-9b (a lead compound) were synthesized, and the relationship between their structures and biological activities was examined using several assay systems. From the results, KRN7000, (2S,3S,4R)-1-O-(alpha-D- galactopyranosyl)-2-(N-hexacosanoylamino)-1,3,4-octadecanetriol , was selected as a candidate for clinical application.

The role of mouse liver NK1.1 Ag+ T (NKT) cells in the antitumor effect of α-galactosylceramide (α-GalCer) has been unclear. We now show that, whereas α-GalCer increased the serum IFN-γ concentration and alanine aminotransferase activity in NK cell-depleted C57BL/6 (B6) mice and B6-beige/beige mice similarly to its effects in control B6 mice, its enhancement of the antitumor cytotoxicity of liver mononuclear cells (MNCs) was abrogated. Depletion of both NK and NKT cells in B6 mice reduced all these effects of α-GalCer. Injection of Abs to IFN-γ also inhibited the α-GalCer-induced increase in antitumor cytotoxicity of MNCs. α-GalCer induced the expression of Fas ligand on NKT cells in the liver of B6 mice. Whereas α-GalCer did not increase serum alanine aminotransferase activity in B6-lpr/lpr mice and B6-gld/gld mice, it increased the antitumor cytotoxicity of liver MNCs. The α-GalCer-induced increase in survival rate apparent in B6 mice injected intrasplenically with B16 tumor cells was abrogated in beige/beige mice, NK cell-depleted B6 mice, and B6 mice treated with Abs to IFN-γ. Depletion of CD8+ T cells did not affect the α-GalCer-induced antitumor cytotoxicity of liver MNCs but reduced the effect of α-GalCer on the survival of B6 mice. Thus, IFN-γ produced by α-GalCer-activated NKT cells increases both the innate antitumor cytotoxicity of NK cells and the adaptive antitumor response of CD8+ T cells, with consequent inhibition of tumor metastasis to the liver. Moreover, NKT cells mediate α-GalCer-induced hepatocyte injury through Fas-Fas ligand signaling.