Abstract
Mounting an immune response sufficient to eradicate a tumor is the goal of modern immunotherapy. Single agent therapies with checkpoint inhibitors or costimulatory molecule agonists are effective only for a small portion of all treated patients. Combined therapy, e.g., CTLA-4 and PD-1 checkpoint blockade, is a more effective treatment modality, but in preclinical studies OX40 agonism with CTLA-4 blockade using monoclonal antibodies (aOX40/aCTLA-4) failed to induce tumor regression of larger, more established tumors. We hypothesized that administration of a vaccine with a tumor-associated antigen targeted to the appropriate antigen presenting cell could make combined aOX40/aCTLA-4 therapy more effective. We administered an antibody-based vaccine targeting HER2 to the DEC-205 endocytic receptor on cross-presenting dendritic cells (anti-DEC-205/HER2; aDEC-205/HER2) and a potent adjuvant (poly (I:C)) to assist with maturation, along with aOX40/aCTLA-4 therapy. This therapy induced complete regression of established tumors and a pronounced infiltration of effector CD8 and CD4 T cells, with no effect on regulatory T cell infiltration compared to aOX40/aCTLA-4 alone. To be maximally effective, this therapy required expression of both OX40 and CTLA-4 on CD8 T cells. These data indicate that vaccination targeting cross-presenting dendritic cells with a tumor-associated antigen is a highly effective immunization strategy that can overcome some of the limitations of current systemic immunotherapeutic approaches that lack defined tumor-directed antigenic targets.