Effects of Thymectomy and Antithymocyte Serum on Spontaneous Regression of Friend Virus-Induced Erythroleukemia 2

Abstract

To evaluate the role of immune response in regression of leukemia, we studied the effect of immunosuppression on the spontaneous regression of a leukemia induced by a specific strain of Friend murine leukemia virus complex (RFV). Thymectomy of newborn but not adult outbred Swiss mice markedly inhibited regression. The effect of antithymocyte serum (ATS) on regression depended on the timing of ATS treatment. Regression was markedly inhibited in leukemic mice given ATS just before the start of regression. During leukemia development, ATS treatment but not thymectomy potentiated splenomegaly and delayed the start of regression. Both ATS treatment and neonatal thymectomy increased mortality as a function of the decrease in disease regression. Treatment with normal rabbit serum also inhibited regression but, when given during leukemia development, affected neither the splenomegalic response to RFV nor the number of deaths. The data demonstrated that an intact immune system was required for leukemia regression and suggested that some thymus-dependent parameter of immune response was a major factor in regression.