Natural killing activity in patients with spontaneous regression of malignant lymphoma.

Previously, we proposed a new analysis of natural killing activity, for comparison, employing an "individual effector/target cell ratio" according to the number of effector cells in blood. The activity could be measured in four patients with spontaneous regression of malignant lymphoma. Despite the absence of episodes suggesting viral infections, patients with spontaneous regression had significantly higher activities prior to their regressions than either controls or patients without regression. In one patient who had a spontaneous regression accompanied by a high level of natural killing activity, subsequent exacerbation of the disease with a reduced activity was never followed by a regression and became life-threatening. In another patient, a spontaneous regression was accelerated after greater augmentation of natural killing activity was induced by a superimposed viral infection. These facts suggest that highly elevated natural killing activity may be one of the possible mechanisms responsible for spontaneous regression of malignant lymphoma.