Macrophages, NK-cells, NK-like cells, and tumor surveillance in man

Although every second patient with leukemia or a solid tumor has lymphocytes which can recognize or can be induced to recognize autologous tumor cells, it has been difficult to demonstrate that this recognition is, in man, due to tumor specific antigens. Other immunological abnormalities, such as lineage infidelity or maturation asynchrony, are more likely explanations. Moreover, immunological heterogeneity is pronounced among human tumor cells. For these reasons, antibody independent tumor surveillance is receiving increased attention. It is mediated by cytotoxic macrophages, NK-cells and the so called NK-like, pre-induced cytotoxic T-cells. NK-cells, probably a T-cell subpopulation sharing a marker with macrophages, have a cytotoxic effect mainly on certain cell-lines, but hardly on viable human tumor cells. In contrast, different degrees of pre-stimulation with allogeneic lymphocytes, lectins or interleukin 2 can induce, in human T-cells, both HLA-restricted and non-restricted cytotoxicity against viable human tumor cells. This indication is active even in T-cell populations that are either monoclonal or pre-depleted of NK cells.