Effect of combination therapy of radiation and local administration of OK-432 on a murine fibrosarcoma.

The effects of a combination therapy of radiation and local administration of OK-432, which is one of BRMs (biological response modifiers), were studied using a radioresistant murine fibrosarcoma with weak immunogenicity. Fifty percent tumor control doses were 83.5 (79.6-87.4) Gy in animals given radiation alone and 64.3 (57.9-71.0) Gy in animals given OK-432 immediately after radiation, indicating that this biological response modifier can enhance the radiation dose effectiveness by a factor of 83.5/64.3, that is, 1.30. Histological observations of treated tumors showed that the combination therapy induced a marked infiltration with lymphocytes and prominent degeneration and necrosis of the tumor cells. Examination of subsets of the infiltrating lymphocytes using the monoclonal antibodies showed that Lyt-2 positive lymphocytes were more abundant in the group given the combination therapy than in the radiation alone group on day 5 (p greater than 0.05). Two days later, Lyt-1, Lyt-2, and L3T4 positive lymphocytes increased in the group given the combination therapy, whereas these lymphocytes disappeared in the group given radiation alone.