Delivering all in one: Antigen-nanocapsule loaded with dual adjuvant yields superadditive effects by DC-directed T cell stimulation

Therapeutic vaccination is and remains a major challenge, particularly in cancer treatment. In this process, the effective activation of dendritic cells by a combination of distinctly acting adjuvants and an antigen is crucial for success. While most common vaccine formulations lack the efficiency to trigger sufficient T cell responses in a therapeutic tumor treatment, nanovaccines offer unique properties to tackle that challenge. Here, we report the stepwise development of a nanocapsule for vaccination approaches, comprising a shell consisting of antigen and loaded with a superadditive adjuvant combination. In a first initial step, we identified the combination of resiquimod (R848) and muramyl dipeptide (MDP) to have a superadditive stimulatory potential. Particulated in Spermine-modified dextran-nanoparticles, the dual-adjuvant maintains its superadditive character and stimulates murine dendritic cells (DC) stronger than the soluble equivalents. The second step was to evaluate a protein-based nanocapsule as suitable antigen source for the induction of antigen-specific T cell responses. Therefore, the DC-mediated antigen-specific T cell proliferation upon treatment with nanocapsules, whose shell consists of ovalbumin (OVA), was assessed. At least, the superadditive adjuvant combination was encapsulated into OVA-nanocapsules to create the final nanovaccine. Its immunostimulatory potential for DC was extensively tested by measuring the expression of co-stimulatory surface markers, the secretion of pro-inflammatory cytokines and the capability to mediate OVA-specific T cell responses. The developed nanovaccine triggers strong superadditive dendritic cell stimulation and potent antigen-specific CD4(+) and CD8(+) T cell proliferation. Combined with a high modifiability, an excellent biocompatibility, low cytotoxicity and an enormous loading capacity, the introduced antigen-nanocapsule provides an enormous potential for the effective delivery of superadditive adjuvant combinations, particularly when they target intracellular receptors.