Interactions between malignant tumor growth and allogeneic graft rejection in an experimental rat model

We describe a combined tumor and simultaneous transplant model in rats in tended to investigate interactions between tumor growth and graft rejection. To study the influence of tumor growth on graft rejection. Novikoff hepatoma cells were injected subcutaneously into the back of Lewis rats. Eight days later, the grown solid tumor was resected, and allogeneic heart transplantation was performed. Four groups were formed, receiving 5-fluorouracil (5-FU), cyclosporin A (CsA), 5-FU + CsA, and placebo, respectively. In the corresponding groups, tumor injection was omitted. Graft survival was significantly prolonged when CsA was given 5-FU did not abrogate or augment CsA efficiency nor influence graft survival when given alone. In the corresponding control groups, graft survival was similar, thus excluding an immunomodulating effect of the prior tumor growth on graft survival. To study the reverse interaction of allogeneic graft on tumor growth, heart grafting and tumor cell injection were performed on the same day. In different groups, 5-FU, CsA, 5-FU + CsA, and placebo was given. For the control, no transplantation was carried out. The tumor was resected on the 8th postoperative day and examined by immunohistology. A slight decrease of tumor growth by 5-FU, but a marked increase by CsA were found, whereas the graft alone showed no immunomodulation.