A BIT of sugar and fat can send an unusual type of immune cell on a
tumour-killing spree, say Japanese researchers. The discovery may open up a new
avenue for finding anticancer drugs.
All immune cells attack in their own style. Natural killer (NK) cells are
born ready to attack any tumour or virally infected cell. T cells learn by
experience to attack a particular enemy: they grow a specific binding protein,
known as the T-cell receptor, on their surfaces.
For years, immunulogists have scratched their heads at the purpose of cells
dubbed NKT cells, which possess NK proteins as well as a T-cell receptor. 鈥淲e
knew they all have the same T-cell receptor,鈥� says Masaru Taniguchi of Chiba
University in Japan. 鈥淏ut what was this very specific protein binding to?鈥�
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One possibility was that NKT cells look for the sugars and fats that sit on
some cells. When Taniguchi鈥檚 team tested sugar-fat compounds for their ability
to stimulate the cells, they found that two closely related compounds made NKT
cells start their engines: a-galactosylceramide and a-glucosylceramide.
The researchers also discovered that if the NKT cell鈥檚 T-cell receptor is
knocked out in genetically engineered mice, the animals are unable to fight off
liver tumours even though they have both NK cells and T cells. In contrast, mice
that have only NKT cells can eliminate the tumours, as long as they are first
primed with one of its favourite sugar-and-fat combinations (Science,
vol 278, pp 1623 and 1626).
This suggests that the cells play a major role in tumour rejection, says
Taniguchi. His team is now trying to find the best compounds to activate NKT
cells, in the hope that they will act as anticancer drugs. 鈥淭hese new compounds
look promising because they excite NKT cells but seem to leave the rest of the
immune system alone.鈥�