Carcinogen-Induced Tumors of the Thymus. I. Restoration of Neonatally Thymectomized Mice With a Functional Thymoma2

Abstract

Direct intrathymic application of 0.1 mg of 7,12-dimethylbenz[a]anthracene into newborn mice induced a variety of thymic tumors both lymphoid and nonlymphoid. A nonlymphoid thymoma of strain A origin showed biological activity when grafted into neonatally thymectomized syngeneic or allogeneic mice. Tumor grafts prevented early mortality, induced immunological restoration (measured as allograft immunity and graft-versus-host reactivity), and produced variable degrees of lymphoid recuperation. Immunological recuperation could occur in absence of complete morphological recovery of the lymphoid tissues. Biological function was lost after repeated transplantation of the strain A thymoma. The capacity to induce restoration was specific for the functional thymoma, since other thymic and nonthymic tumors proved ineffective. Discriminant graft-versus-host analysis in the allogeneic combination indicated that all demonstrable immunocompetent cells in the spleen of animals restored by the thymic tumor were of host origin. No cells of donor origin could be detected with this test. Tolerance to the thymoma was observed in allogeneic combinations which varied according to the age at grafting of the tumor. Acceptance of the strain A thymoma induced some degree of tolerance to strain A skin. Restoration of immunological capacities by the functional thymoma seemed to require only a relatively limited period of function. Lymphoid elements within the thymoma were observed in the syngeneic combination. These cells seemed most likely to reflect an immunological reaction elicited by the antigenicity of the chemically induced tumor.