PROPHYLACTIC INTERVENTION IN RADIATION-LEUKEMIA-VIRUS-INDUCED MURINE LYMPHOMA BY THE BIOLOGICAL RESPONSE MODIFIER POLYSACCHARIDE-K

Polysaccharide K (PSK) is a biological response modifier used for adju vant immunotherapy of malignant diseases. We studied the potential app licability of PSK for preventing tumor progression using an experiment al model of murine lymphoma. Mice inoculated with the radiation leukem ia virus (RadLV) develop thymic lymphomas after a latency of 3-6 month s. However, 2 weeks after virus inoculation, prelymphoma cells can alr eady be detected in the thymus. We found that PSK treatment induced hy perresponsiveness to concanavalin A and heightened production of inter leukin-2 (IL-2) and IL-4 in spleen cells of both control and prelympho ma mice. The response was transient and was accompanied with a dominan t usage of T cells expressing V beta 8, but other T cell subsets were also stimulated by PSK. T lymphoma cells expressing V beta 8.2 underwe nt apoptosis when incubated with PSK. Treatment of RadLV-inoculated mi ce with PSK delayed the onset of overt lymphoma (and mortality) but co uld not protect the mice from the disease. Combined treatment with PSK and a RadLV-specific immunotoxin prevented synergistically the progre ssion of the prelymphoma cells to frank lymphoma. The results suggest that PSK contains a superantigen-like component that selectively activ ates V beta 8+ T cells. Its administration prelymphoma mice interfered with the process of lymphoma progression.