Activation or anergy: NKT cells are stunned by alpha-galactosylceramide.

Invariant natural killer T (iNKT) cells are T lymphocytes that behave similarly to cells of the innate immune system. The glycolipid alpha-galactosylceramide (alpha-GalCer) is a potent and specific activator of mouse and human iNKT cells and has been used in cancer clinical trials to drive NKT cell-mediated immune responses. However, little is known about the dynamics of the iNKT cell response to alpha-GalCer in vivo. In this issue of the JCI, Parekh and colleagues demonstrate that administration of alpha-GalCer causes iNKT cells to become unresponsive, for at least 1 month, in mice. This leads us to ask, should sequential administration of alpha-GalCer still be used to activate iNKT cells given the anergic state it has been shown here to induce? This intriguing article raises the issue of the avoidance of anergy induction in the design of treatment regimens that use alpha-GalCer as a specific activator of iNKT cells.