Enhanced host resistance to transplantable murine lymphosarcoma in Swiss mice by combined immunostimulation with BCG and polyinosinic-polycytidylic acid.

Combined immunostimulation with BCG and double-stranded polyinosinic-polycytidylic acid (poly I . poly C) was more effective than single-modality immunostimulation in suppressing tumor growth in inbred Swiss mice. BCG sensitization followed by administration of poly I . poly C on the day of tumor cell injection significantly prolonged the survival period against parental lymphosarcoma (LS) and its ascites variant (LS-A). BCG and poly I . poly C given together on the day of tumor cell injection suppressed only LS-A and not LS. BCG or poly I . poly C given alone did not result in tumor cures. Silica injection given 2 days before poly I . poly C injection completely abrogated the antitumor effect of sequential treatment with BCG and poly I . poly C. Silica treatment given on and beyond the day of poly I . poly C injection did not abrogate the antitumor effect. This observation indicated that intact macrophage effector function was essential at the time of tumor cell inoculation to obtain an effective antitumor action.