Results

We show that intravenous administration of MVA-MUC1 is therapeutically superior to subcutaneous injection. Therapeutic efficacy of MVA-MUC1 can be further enhanced by intravenous administration of a TLR9 ligand (ODN1826). Substantial and necessary infiltration of tumor-bearing kidneys by CD8⁺ lymphocytes is associated with therapeutic protection. We observe that infiltration of CD8⁺ lymphocytes is not limited to tumor-bearing kidneys and is also detected in naive kidneys, liver and lungs. Kidney infiltrating lymphocytes are characterized by an effector memory phenotype and express PD-1 and Tim3 immune checkpoints molecules. Biodistribution experiments indicate that MVA encoded antigens quickly reach deep organs and in particular APC from the spleen upon i.v. injection of MVA in comparison to s.c. injection, resulting in a faster generation of MUC1 specific CD8⁺ T cells. Unexpectedly, addition of ODN1826 to MVA-MUC1 immunization does not result in an increase in the frequency of MUC1 specific T cells detected in the spleen. Instead, ODN1826 was associated with a more pronounced modification of the tumor microenvironment towards a T_H1 type inflammatory response and a recruitment of activated lymphocytes.