Novel TCR gene rearrangements and expression in radiation-induced thymic lymphomas.

Using the intrathymic (i.t.) injection assay with a B10.Thy 1 congenic donor-host combination, we previously demonstrated that the pre-neoplastic cells (thymic prelymphoma cells) exist in immature T cell subpopulations; mainly in CD4-CD8- double negative (DN) and CD4-CD8+ single positive (SP) thymocytes and to some extent in CD4+CD8+ double positive (DP) thymocytes. Most thymic lymphomas that developed from these prelymphoma cells showed concomitant TCR alpha, beta and gamma gene rearrangements and expression. In this lymphomas, two lymphomas also showed TCR delta gene rearrangements. This represents the intermediate stages of TCR gene rearrangement. Every lymphoma, however, expressed CD3-associated alpha beta TCR on the cell surface, but not gamma delta TCR. Novel rearrangements of V gamma 4 and J gamma 4-C gamma 4 segments with non-gamma elements were found respectively in a concerted and symmetrical fashion. Recombinase-mediated inter-chromosomal exchanges characteristic of thymic lymphomas may function in radiation-induced lymphomagenesis.