Role of lymphocytes in dogs experimentally re-challenged with canine transmissible sarcoma

The role of lymphocytes in dogs re-challenged with canine transmissible sarcoma (CTS) was investigated histologically and immunologically. Tumors were detected on the 3rd day, began to regress on the 9th day and disappeared on approximately the 15th day after the secondary transplantation (AST). The CTS cells were surrounded by lymphocytes which had infiltrated from the early stage, degenerated and ultimately disappeared. Most of the lymphocytes expressed thymocyte antigen (Ta) on the cell membrane surface. The numbers of lymphocytes and Ta-positive lymphocytes in peripheral blood increased gradually AST. The blastogenic responses of peripheral blood lymphocytes (PBL) induced by 3 kinds of mitogens were elevated strikingly from the early stage AST. These results suggest that Ta-positive lymphocytes play an important role in vivo in the regression of tumors and that the immunological activity of PBL is stimulated immediately AST.