Abstract
The reactivity of peripheral blood lymphocytes from patients with advanced malignancy was assessed by mitogenβinduced stimulation of protein synthesis as measured by ^3^Hβleucine incorporation. It was confirmed that the lymphocyte response of patients was depressed. Furthermore, the lymphocytes of 15 out of 27 cancer patients, selected because of their low responses, inhibited the reactivity of normal lymphocytes in coβcultures. The lymphocytes from one patient with Hodgkin's disease were also inhibitory. In contrast, lymphocytes from healthy subjects, patients with chronic lymphocytic leukaemia, lymphosarcoma or multiple myeloma caused no suppression. Experiments with purified cell populations from patients with carcinoma indicated that purified T cells responded to mitogens while unseparated lymphocytes failed to respond and that the inhibitory activity was due to adherent cells, presumably monocytes. There was no evidence for Bβcellβmediated suppression. However, in two cases inhibition was caused by isolated T cells of the patients and not by adherent cells. These experiments suggested that one mechanism for the depression of cellβmediated immunity seen in patients with advanced cancer may be the nonspecific suppression of certain Tβcell functions by circulating monocytes.