Murine dendritic cells pulsed with an anti-idiotype antibody induce antigen-specific protective antitumor immunity

In this study, using the carcinoembryonic antigen (CEA)-expressing C15 murine colon carcinoma system in syngeneic C57BL/6 mice, we have evaluated the efficacy of bone marrow-derived dendritic cells (DCs) pulsed with the murine anti-idiotype antibody 3H1 as a tumor vaccine. Anti-idiotype 3H1 mimics a distinct and specific epitope of CEA and can generate anti-CEA immunity in mice, rabbits, monkeys, and humans when used with a conventional immune adjuvant. Our goal was to determine whether the use of DC as direct antigen-presenting cells would improve the potency of 3H1 as vaccine. Bone marrow-DC pulsed with 3H1 and injected into naïve mice induced both humoral and cellular anti-3H1, as well as anti-CEA immunity. Specific killing of C15 cells in in vitro antibody-dependent cellular cytotoxicity has been observed by immune sera. Immune-splenic lymphocytes when stimulated in vitro with 3H1 or CEA, showed increased proliferative CD4⁺ Th1 type T-cell response and secreted significantly high levels of Th1 cytokines [IFN-γ, interleukin (IL)-2] and low levels of Th2 cytokines (IL-4, IL-10). This vaccine also induced MHC class I antigen-restricted CD8⁺ T-cell responses. The upregulation of activation markers CD69 and CD25 on CD8⁺ CTLs correlated with antigen-specific strong CTL responses in vitro. The immunity induced in mice resulted in a complete rejection of CEA-expressing C15 tumor cells in 100% of experimental mice, whereas no protection was observed when 3H1-pulsed DC-vaccinated mice were challenged with CEA-negative MC-38 cells. The tumor rejection in 3H1-pulsed DC-treated mice was associated with the induction of a memory response that helped those mice to survive a second challenge with a lethal dose of C15 cells.