Effect of immunization with anti-idiotypic antibody to melanoma antigen on lung metastasis in mice

To determine whether the pulmonary metastases of melanoma cells could be inhibited, C57BL/6 mice were immunized with an anti-idiotypic antibody, 7C4, corresponding to a mouse melanoma antigen. Three groups of mice were compared: 1) 7C4-immunized group which received an injection of 100 micrograms of 7C4 in Freund's complete adjuvant (FCA) subcutaneously on day -21 followed by intraperitoneal injections of the same dose on days -14 and -7,2) adjuvant-treated control group administered with only FCA, and 3) untreated control group. On day 0, 5 x 10(5) of BL6 cells were injected into the caudal vein of all mice. Two weeks later, they were sacrificed and their lungs were removed. The number pulmonary metastatic colonies present on the lung surface were counted and compared among the groups. The length of survival days was also compared. The 7C4-immunized group showed an average of 166 +/- 44 colonies as compared to more than that of 300 colonies in each control groups, and a significant difference was observed (P0.01). The immunized group survived significantly longer than the control group (Greenwood's formulation) on day 23 (P0.01). Thus the immunization with 7C4 effectively inhibited lung metastasis of melanoma cells. These findings suggest that vaccination with anti-idiotypic antibody to tumor antigen is effective on inhibiting tumor metastasis.