Regression of transplantable immunoglobulin-secreting rat tumors by irradiation and chemotherapy and induction of transplantation resistance.

from the Fonds Médical de la Recherche Scientifique (Belgium). 'Chargéde Recherches at the Fonds National de la Recherche Sci entifique (Belgium). 3Head: Professor H. Maisin. 'Originally of Wistar origin, inbred at the Cancer Institute; more than 40 brother-sister matings in this line. Skin grafts are accepted between rats of this strain. Only inbred animals were used in this work. The name LOU/c is proposed in the new edition of the International index of Laboratory Animals. Received January 15, 1973; accepted June II, 1973. served in our rat strain in 1955 and was described previously as a leukosarcoma (11). The animals developed these spon taneous tumors of the ileocecal lymph node between 7 and 20 months of age (age of animals at appearance of tumors). At present, the incidence of immunoglobulin-secreting im munocytomas has increased to 10% (2). The primary tumor grows rapidly in the peritoneal cavity, invades the mesenterial lymph nodes and the peritoneum, and provokes ascitic fluid containing isolated cancer cells. Metastatic in volvement of mediastinal, axillary, and cervical lymph nodes and pleural effusion, as well as anemia and peripheral blood disorders, are seen in the terminal stage of the dis ease^, 11). Microscopically, the immunoglobulin-secreting immuno cytoma structure is that of an undifferentiated reticulosarcoma (2, 11). (Dr. Dunn and Dr. Snell examined our tumor and described it as an undifferentiated lymphoreticular cell tumor.) The primary tumors secrete complete or in complete immunoglobulins which can be detected in the serum, in the ascitic fluid, and in the pleural effusion by electrophoresis or immunoelectrophoresis (24). Different strains of transplantable tumors were estab lished from these immunoglobulin-secreting immunocy tomas. From the 1st passage on, the paraprotein secretion that was observed in the host serum remained in some cases after more than 100 passages. In exceptional cases paraproteinemia diminished to very low levels during subse quent grafts (2). In this work, we used the IgG-secreting immunocytoma ISIS130 which originated from the inbred strain and which is easily transplanted (2). The primary tumor was an ileocecal lymph node isolated from a male rat in 1965. The tumor is transplanted by s.c. administration of IO6 viable cells or of small tumor frag ments. These tumor fragments are given by s.c. injection in the flank (0.25 ml of a suspension of l g minced tumor tis sue per 1 ml 0.9% NaCl solution). Under these conditions, nearly 100% of the untreated animals develop a palpable tumor within 1 week which kills the animal in 2 to 4 weeks. All challenge injections con sisted of IO6isolated viable cells. Local Irradiation of the Tumor. The graft was irradiated by a narrow beam (about 2x2 cm) covering only the tumor. The animals were restrained on a special table during ir radiation, which was given by a Maxitron unit (250 kV; 80-cm focus-to-target distance; filter, Cu 0.25/A1 1 mm).