Tumour regression by IL-2 mediated stagnation of blood flow

The histology of Interleukin-2 induced tumour regression is presented. DBA/2 mice were injected simultaneously ip (intraperitoneally) and sc (subcutaneously) with 2 x 10(4) and 2 x 10(5) syngeneic SL2 lymphosarcoma cells, respectively. After treatment with 20,000 U IL-2 given ip at days 10-14, 50% of these mice survive. Histological analysis of the sc tumours showed that stagnation of blood flow and an occurrence of sudden massive necrosis were indicative of tumour regression. We hypothesize that peritoneal lymphocytes, activated by the ip tumour cells and IL-2, home in the sc tumour. There these activated lymphocytes produce lymphokines and trigger off other infiltrate cells to do similarly. This causes vascular leakage which leads to an increased intratumoural interstitial hydrostatic pressure. Subsequently circulatory obstruction and tumour necrosis occurs.