Surveillance Role of Various Leukocytes in Preventing the Outgrowth of Potentially Malignant Cells

Abstract

Several different types of leukocytes can destroy cancer cells in vitro (Klein et al., 1960; Hibbs et al., 1972; Herberman et al., 1975; Kiessling et al., 1975). Rather little, however, is known about the relative importance of these different leukocytes in the normal host, where they may exert a surveillance function and prevent the outgrowth of potentially malignant cells. We have studied the relative efficiency of the different leukocytes in restraining malignant growth in vivo by comparing the effects of the leukocytes on regressor tumors and on progressively growing tumor variants that have escaped the immunity of the host. This type of approach is based on the premise that if a leukocyte operates effectively in vivo in restraining the growth of a tumor, a tumor cell must become resistant to it before it can grow progressively. A study of such phenotypic changes in tumor variants should therefore give insight into the relative importance and hierarchy of the different naturally occurring immune defense cells. This type of analysis is analogous to that performed by the microbiologist who deduces the mechanism of action of an antibiotic from the type of change found in a bacterium that has become resistant to the drug.