Cytolytic effector cells against human tumors: distinguishing phenotype and function.

Activation and expansion of lymphocytes in vitro and their adoptive transfer to animal models have helped to elucidate mechanisms of tumor rejection and to define the cytolytic effector cells involved. Several cell types that exhibit antitumor activity have been described. These include natural killer cells, lymphokine-activated killer cells, cytolytic T cells, and tumor infiltrating lymphocytes. Here we discuss our present understanding of the origins of these cells and the phenotypic and functional properties by which they can be distinguished.