Inhibition of growth and metastases in mice by immunization with cholesterol hemisuccinate-enriched tumor cells.

Incorporation of cholesterol hemisuccinate (CHS) into the membrane of tumor cell rigidifies the lipid layer, exposes cryptic antigens, and enhances immunogenicity. The local growth and metastatic spread of the 3LL Lewis lung carcinoma were studied in conjunction with immunizations by CHS-enriched 3LL cells. C57BL/6J mice received 2 consecutive immunizations with 10(7) CHS-treated, irradiated (10,000 rad) 3LL cells. Two control groups were immunized with MCA-102 sarcoma cells or CHS-enriched syngeneic spleen cells. All groups were challenged with viable 3LL cells after immunizations. Mice pre-immunized with CHS-enriched 3LL cells showed a delayed tumor growth after subsequent challenge with 3LL. Effect of immunization on the growth of established tumors was examined in 3LL-bearing mice which were treated with 10(7) CHS-enriched tumor cells on days 1-12 after initial tumor implantation. A second identical immunotherapy was given 6 days after the first immunization. Tumor growth was significantly inhibited in mice which received the first immunization 1 day after tumor implantation, while immunization on day 3 or after inhibited the growth rate to a lesser extent. Suppression of pulmonary metastases was assessed after excision of a primary 3LL tumor growing in the foot pad which had reached 8 mm in diameter. Immunization consisted of intraperitoneal injection of 10(7) irradiated CHS-enriched tumor cells following excision and repeated after 6 days. This immunization resulted in a significant decrease in pulmonary metastasis as scored by direct counts of metastatic nodules, by [125I]iododeoxyuridine (125IUdR) incorporation, and by lung weight. Metastatic 3LL cells from nodules which survived immune elimination were isolated and implanted into mice which were pre-immunized with primary 3LL cells enriched with CHS. For comparison, a group of mice was immunized and challenged with primary 3LL cells. Inhibition of tumor growth and pulmonary metastasis formation was observed only in the mice which were challenged with the primary tumor.