Suitability of different multi-functionalized nanocarriers aimed to address antigen presenting cells for vaccination purposes, and parameters that regulate unwanted accumulation of nanocarriers in the liver

Abstract

The treatment of severe immune diseases such as cancer, allergy or autoimmunity demands new strategies to overcome the development of resistances or relapses. The employment of nanoparticles as carriers for the delivery of biological components targeting specific tissues or cell types might help to meet these challenges. Especially their employment for the vaccination of antigen presenting cells (APCs), a pivotal group of immune cells, has turned out to be a promising immunotherapeutic approach. In this case, nanocarriers ensure the co-delivery of antigen and adjuvant, the two components required for a vaccination. The aim of this thesis was to investigate the potential of different types of nanoparticles for an in situ vaccination of APCs to induce an effective immune response. Therefore, inorganic and organic, polymer-based non-toxic nanoparticles were synthesized, and modified with various biological components with the aim to target and activate APCs. These nanocarriers were investigated in cell cultures and mouse models regarding their biodistribution, APC targeting efficiency and their capacity to induce T cell immune responses. To achieve an active targeting of APCs their expression of C-type lectins which constitute pathogen recognizing receptors, were exploited. Natural ligands for these receptors or corresponding antibodies were attached to the nanocarriers which led to a successful targeting of dendritic cells and B cells in vitro and in vivo, as confirmed by flow cytometry and confocal microscopy. Comprehensive biodistribution experiments of sarcosine-based polymer brushes on organ and cellular level provided more insights into mechanisms leading to liver trapping of nanoparticles, which is often observed after their systemic application. This study revealed that antibody-coated polymer-brushes are cleared by Fc (fragment crystallizable) receptors of liver sinusoidal endothelial cells and indicated that a lower antibody density on nanocarriers is preferable since this largely prevented their recognition by Fc receptors compared to high antibody amounts, and thereby facilitated the intended dendritic cell (DC)-specific targeting. Functionalization of the nanocarriers with a toll-like receptor (TLR) ligand or nucleotide binding oligomerization domain (NOD)-like receptor (NLR) ligand as an adjuvant and SIINFEKL/Ovalbumin (OVA), a protein derived from the chicken egg as model antigen led to a maturation of targeted dendritic cells in vitro and induced a T cell response in vitro and in vivo. Finally, the efficiency of this approach was confirmed in tumor and allergy mouse models. To conclude, the obtained results indicate a functional activity of different nanocarriers, give new insights into the requirements for a nanoparticle-based APC vaccination and show that these can be fulfilled by several types of nanoparticles.