Stimulation of immune mechanisms against mammary tumors by incomplete T cell depletion.

When BALB/cfC3H females are subjected to continous suction thymectomy, a procedure that results in retention of thymic remnants, the latent period before tumor development is significantly prolonged. However, when BALB/cfC3H females are thymectomized by control suction, a procedure which removes thymic lobes completely, there is no effect on mammary tumorigenesis. Our results show that incomplete T cell depletion causes premature onset of non-T cell cytotoxicity, an augmentation of T cell cytotoxicity, and an alteration in a serum-blocking activity to mammary tumor target cells as tested in microcytotoxicity assay. On the other hand, complete neonatal thymectomy effectively and completely abrogates immune response to mammary tumor target cells. The inability of completely thymectomized mice to generate an immune response to MTV suggests (but does not prove) that MTV-induced mammary tumor target cell surface antigens are thymus-dependent.