DC targeting DNA vaccines induce protective and therapeutic antitumor immunity in mice.

BACKGROUND Anti-CD11c antibodies target to the CD11c receptor that mediates antigen presentation to T cells by dendritic cells (DCs). To exploit these properties for immunization purposes, we obtained DC-targeting DNA vaccines by fusing tumor-associated antigen HER2/neu ectodomain to single chain antibody fragment (scFv) from N418 (scFv(N418)), a monoclonal antibody binding the mouse DC-restricted surface molecule CD11c, and explored its antitumoral efficacy and underlying mechanisms in mouse breast cancer models. METHODS Induction of humoral and cellular immune responses and antitumoral activity of the DNA vaccines were tested in transplantable HER2/neu-expressing murine tumor models and in transgenic BALB-neuT mice developing spontaneous Neu-driven mammary carcinomas. RESULTS Upon injection of the breast tumor cell line D2F2/E2 (stably expressing human wild-type HER2), scFv(N418)-HER2 immunized mice were protected against tumor growth. Even more important for clinical applications, we were able to substantially slow the growth of implanted D2F2/E2 cells by injection of scFv(N418)-HER2 conjugates into tumor bearing hosts. The existing tumors were eradicated by treatment with scFv(N418)-HER2 combined with low-dose cyclophosphamide (CTX), which can make a temporary regulatory T cells (Treg) depletion. What's more, in combination with the low-dose CTX, vaccination with scFv(N418)-neu significantly retarded the development of spontaneous mammary carcinomas in transgenic BALB-neuT mice. CONCLUSION Our results show that DNA vaccine which targeting of dendritic cells in situ by the means of antibody-antigen conjugates may be a novel way to induce long-lasting antitumor immunity.