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.