Improved immune-suppression techniques for the exongrafting of human tumours

The transplantability of a xenografted human adenocarcinoma has been examined in mice that had been immune-suppressed by thymectomy and whole-body irradiation and the results have been compared with transplantation into athymic (nude) mice. Two alternative techniques were used to prevent marrow failure following whole-body irradiation: reconstituting the animals with a marrow graft, or protecting them by an injection of cytosine arabinoside (Ara-C) 2 days before the irradiation. The results show that the Ara-C-prepared mice were more receptive to transplantation than marrow-grafted or nude mice, and they were the only animals that developed regional metastases from implanted xenografts. Some recovery of immunity occurred in both types of immune-suppressed mice, which was evident more than 5 weeks after immune-suppression and which was more marked in females than in males. It was concluded that the immune-suppressed mice were superior to nude mice for short-term experiments but they may be less satisfactory for long-term experiments.