Role of thymic selection in the development of thymic lymphomas in TCR transgenic mice.

To investigate the role of antigen receptor-mediated interactions in lymphomagenesis we have analyzed the influence of alpha beta TCR-mediated selection on the development of spontaneous thymic lymphomas, which appear with a high (up to 50%) frequency in mice expressing a transgenic TCR specific for the male antigen (HY) in the context of H-2Db molecules. To this end we compared the kinetics and the incidence of thymic lymphomas developing in females and males with selecting (H-2b) and non-selecting (H-2k) MHC molecules. The kinetics of development of thymic lymphomas was similar in positively selecting (H-2b females) and non-selecting (H-2k females and males) environments but significantly slower (P < 0.01) in the negatively selecting environment (H-2b male). Injection of lymphoma cells derived from a H-2b female into the thymus of a H-2b male resulted in strong, antigen-specific inhibition of growth, indicating that the slower kinetics of lymphomagenesis in H-2b males could be due, at least partially, to the sensitivity of oncogenically transformed thymocytes to TCR-mediated negative selection. Phenotypic and functional analysis of lymphoma cells indicated that they originated from the stage of pre-TCR-dependent transition of immature CD4-CD8- to CD4+ CD8+ thymocytes, which in H-2b females and males developed into tumors under different environmental pressures. These results failed to provide convincing evidence for the role of positive selection but provided a strong indication that self antigen-induced negative selection, in addition to its well established role in self tolerance, can occasionally act as a tumor surveillance mechanism by eliminating or suppressing growth of thymocytes undergoing oncogenic transformation.