Polymeric nanocapsules as versatile platform for the development of new dendritic cell-directed nanovaccines
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Abstract
Therapeutic vaccination against tumor diseases remains a major challenge in immune therapy. The effective activation of dendritic cells by a combination of distinctly acting adjuvants and antigens is essential for success. While conventional vaccine formulations lack the efficiency to trigger sufficient T cell responses in a therapeutic tumor treatment, nanovaccines may offer unique properties to tackle that challenge.
In this doctoral thesis, we report the use of polymeric nanocapsules as a versatile platform for the development of new dendritic cell-directed nanovaccines. Those nanocarriers are characterized by a high biocompatibility and modifiability, low cytotoxicity as well as by a large loading capacity for active substances. The resulting nanovaccine comprises a shell consisting of protein antigen and allows an efficient loading with superadditively acting combinations of adjuvants, even when their corresponding receptors are located intracellularly. Furthermore, the capsule surface can be modified with stealth components to increase blood circulation time, allows the functional encapsulation of small interfering RNA and can also be equipped with specific antibodies to substantially increase dendritic cell targeting.
Initially, we identified the combination of resiquimod and muramyl dipeptide to exert a superadditive stimulatory potential on dendritic cells. This adjuvant combination maintains its superadditive character and stimulates murine dendritic cells more effective when encapsulated in dextran nanoparticles than when applied directly. At the same time, nanocapsules, consisting of the model antigen ovalbumin, were evaluated as a suitable antigen source for the induction of antigen-specific T cell responses. Subsequently, the aforementioned adjuvant combination was encapsulated in these ovalbumin-based nanocapsules to generate a nanocarrier comprising antigen and superadditive adjuvant combination. Its immunostimulatory potential for dendritic cell stimulation was extensively tested by i) measuring the expression of co-stimulatory markers, ii) the secretion of pro-inflammatory cytokines, iii) the upregulation of immunologically relevant genes on RNA level by transcriptome sequencing, and iv) the capability of accordingly pre-treated dendritic cells to mediate antigen-specific T cell responses. The created nanocapsule, including antigen and adjuvants, triggered strong dendritic cell stimulation and potent antigen-specific T cell proliferation. Moreover, numerous relevant genes were massively upregulated upon treatment.
The second step was to equip the protein-based nanocapsule with stealth components to increase its blood circulation time and to reduce unspecific cell interaction. Thereby, a special focus was set on the influence of the molecular weight of the used components as well as on the shielding density and the mass density of the modification. It turned out that such a modification can significantly reduce cellular interaction but is highly dependent on molecular weight, shielding and mass density of the used stealth component as well as on the protein environment.
To establish small interfering RNA and targeting moieties in our portfolio of available modifications for polymeric nanocapsules, we switched to a similar, antigen-independent polymeric nanocapsule made of hydroxyethyl starch. Regarding small interfering RNA, we showed that the synthesized nanocapsules were capable of transporting them into dendritic cells and to release them resulting in a functional activity. In terms of targeting, a surface modification with targeting antibodies significantly increased the nanocapsule binding by dendritic cells.
Since the introduced protein-based type of nanocapsule provides the option to replace ovalbumin, for instance, by a tumor-related antigen, it also allows a further optimization for personalized tumor treatment by employing a patient’s tumor-specific antigen. In combination with the demonstrated advantages and available modifications, polymeric nanocapsules as presented here constitute a promising platform for the design and generation of new, innovative nanovaccines for tumor treatment.