killer cell

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun Any of various lymphocytes that recognize and lyse target cells bearing a specific foreign antigen, usually by infection with a virus, and that also function in defense against cancer cells.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun T cell with CD8 receptor that recognizes antigens on the surface of a virus-infected cell and binds to the infected cell and kill it