Objective: An anti-idiotypic minibody with optimal antigenicity which mimicking ovarian cancer antigen was used for therapeutic research in mice model bearing ovarian cancer.
Methods: Using gene engineering technique, prokaryotic expression vector was constructed by genetic fusion of 6B11scFv to human IgG1 hinge and CH3 region. The fusion protein named minibody was induced with IPTG in E. coli and analyzed with Western blot and inhibition ELISA tests respectively. Twenty human-PBL-SCID mice bearing i.p. Skov3.ip1 cells were divided into two groups (10 per-group), 10 mice were immunized repeatedly by minibody every two weeks for three times. Indirect ELISA test was employed for analyzing the characterization of anti-anti-idiotypic scFv (Ab3). The latent period of ascites growth and the mean survival time were observed respectively. CD4+ and CD8+ T cells from the spleen of immunized mice were assayed by flow cytometry.
Results: SDS-PAGE gel electrophoresis showed that a protein band with molecular weight of 50,000 appeared as the expected size after transformation and induction the host bacteria BL21 (DE3). The expressed minibody could be reacted with COC166-9 (Ab1 of 6B11) and binding goat anti-human IgG1 antibody in Western blot. Inhibition ELISA showed minibody had the capacity of binding ovarian cancer monoclonal antibody COC166-9 instead of primal antigen. Ab3 could be detected in the sera of immunized mice with minibody by ELISA test. Ab3 reached the highest at the 14th day after last vaccination and lasted for 6 weeks. The ratio of CD4+/CD8+ was the highest at the 13th day after last vaccination. The latent period of ascites growth were (37.7 +/- 5.5) days and (48.6 +/- 14.3) days (P = 0.04) respectively; while the mean survival time were (42.5 +/- 1.8) days and (59.4 +/- 16.8) days (P = 0.011) in the control and minibody group respectively.
Conclusions: These results demonstrate the successful construction and expression minibody with good immune activities of 6B11scFv and human IgG1 molecules function. Antigenicity is increased without adjuvants and partial humanization is realized. Minibody can induce humoral anti-idiotypic immunity responses against ovarian carcinoma in vivo. When ascites formation was delayed or prevented and the survival was prolonged in minibody group. We expect that minibody may be used as tumor vaccine to ovarian carcinoma in the future clinical trails.