Evaluation of the impact of chitosan/DNA nanoparticles on the differentiation of human naive CD4⁺ T cells

Chitosan (CS) is one of the most widely studied polymers in non-viral gene delivery since it is a cationic polysaccharide that forms nanoparticles with DNA and hence protects the DNA against digestion by DNase. However, the impact of CS/DNA nanoparticle on the immune system still remains poorly understood. Previous investigations did not found CS/DNA nanoparticles had any significant impact on the function of human and murine macrophages. To date, little is known about the interaction between CS/DNA nanoparticles and naive CD4⁺ T cells. This study was designed to investigate whether CS/DNA nanoparticles affect the initial differentiation direction of human naive CD4⁺ T cells. The indirect impact of CS/DNA nanoparticles on naive CD4⁺ T cell differentiation was investigated by incubating the nanoparticles with human macrophage THP-1 cells in one chamber of a transwell co-incubation system, with the enriched human naive CD4⁺ T cells being placed in the other chamber of the transwell. The nanoparticles were also co-incubated with the naive CD4⁺ T cells to explore their direct impact on naive CD4⁺ T cell differentiation by measuring the release of IL-4 and IFN-γ from the cells. It was demonstrated that CS/DNA nanoparticles induced slightly elevated production of IL-12 by THP-1 cells, possibly owing to the presence of CpG motifs in the plasmid. However, this macrophage stimulating activity was much less significant as compared with lipopolysaccharide and did not impact on the differentiation of the naive CD4⁺ T cells. It was also demonstrated that, when directly exposed to the naive CD4⁺ T cells, the nanoparticles induced neither the activation of the naive CD4⁺ T cells in the absence of recombinant cytokines (recombinant human IL-4 or IFN-γ) that induce naive CD4⁺ T cell polarization, nor any changes in the differentiation direction of naive CD4⁺ T cells in the presence of the corresponding cytokines.