Interactions of engineered and endogenous nanoparticles with cells in the immune system

Abstract

Nanotechnology is a fast developing area, which refers to research and technology development at the nanometer scale, ranging from 0.1-100 nm. The properties of nanomaterials offer the ability to interact with complex biological functions, implying enormous opportunities for novel applications within medicine. However, there is little information available concerning the potential toxicity of nanoparticles and what influence such particles have on the immune system, e.g. on dendritic cells (DCs). DCs are the most efficient antigen presenting cells, having a capacity to initiate and direct immune responses against foreign material. The aim of this thesis was to study effects of differently sized and shaped nanomaterials in the interaction with primary human monocyte derived DCs (MDDCs), thereby obtaining an insight on what impact these materials have on the immune system and their potential use in medical applications. In addition, we wanted to determine if endogenous nanoparticles (exosomes), produced by various cells, are natural targeting vehicles.

We show that conventionally produced gold nanoparticles had a maturing effect on human MDDCs, but this was found to be a result of lipopolysaccharide (LPS) contamination. By modification of the production process, clean particles were obtained, which had practically no effect on phenotype or cytokine production of MDDCs. These findings emphasize the importance of retaining high purity during the production of nanoparticles, since possible contaminants may interfere with the assessment of nanoparticles biological effects and result in hazardous particles.

To investigate whether various shapes of gold nanoparticles affect MDDC differently, a novel method was developed for the preparation of gold nanorods with high aspect ratios (ARs) based on a self-seeded surfactant-mediated protocol. The biocompatibility of these high AR gold nanorods, with potential use in thermal therapy, was compared with spherical gold nanoparticles. Both materials had no or minor effects on MDDC's viability and phenotype, thus shape did not seem to affect the biocompatibility of gold.

To determine whether the size of the particle is important for its biocompatibility, the impact of mesoporous silica nano- (270 nm) and microparticles (2.5 μm) was compared. Size- and concentration-dependent effects were seen where the smaller particles and lower concentrations affected MDDCs to a minor degree compared to the larger particles and higher concentrations, both in terms of viability, uptake, and immune regulatory markers. Thus, the larger particles have promising features to serve as an immune-stimulant, with possible T cell modulatory properties, while the smaller particles are more suitable for neutral drug delivery systems.

Finally, we evaluated whether exosomes of different origins are selectively targetingdifferent immune cells. Results revealed that exosomes derived from human MDDCs and breast milk preferably associated with monocytes, whereas exosomes from an Epstein-Barr virus (EBV) transformed B cell line (LCL1) selectively targeted B cells. The interaction between LCL1-derived exosomes and peripheral blood B cells was dependent on CD21 on B cells and the exosome associated EBV glycoprotein gp350. This finding suggests that exosome-based vaccines can be engineered for specific B-cell targeting by inducing gp350 expression.

To summarize, the work included in this thesis has contributed to the understanding of how particles of various materials, shapes and sizes affect and interact with human MDDCs. The knowledge gained is of importance for the further development of the studied materials within various medical applications. This thesis also highlights the potential use of endogenous nanoparticles, exosomes, as targeting delivery vehicles in medical applications.