Initially (10–20 min following uptake) the majority of polyplexes, regardless of DNA topology, were observed to be within the periphery of DCs (Fig. 2a). However by 1 h uptake of SC-pDNA complexes was

much more efficient, with 15% (±2.5% RSE) of complexes associated with the nuclei (polyplex fluorescence overlaid with nuclear stain). In contrast no nuclear association was observed for OC- and linear-pDNA polyplexes, indicating topology dependent uptake. Uptake also showed dependence on DNA topology ATM Kinase Inhibitor clinical trial at longer periods (Fig. 2b). The optimum percentages observed were still small compared to previous studies with CHO cells [9] (61% [±1.67% RSE], 24.3[±2.72% RSE] and 3.5% [±7.12% RSE] for SC-, OC-, and linear-pDNA polyplexes). DCs are key sentinels of the immune system which engulf foreign antigens [13]. Nanoparticle

uptake by DCs has been reported previously which led researchers MLN8237 in vitro to focus on polyplexes due to similarity in size [14] and [15]. Our previous study regarding PLL/DNA polyplexes reported sizes of 139.06 nm (±0.84% RSE), 305.54 nm (±3.2% RSE) and 841.5 nm (±7.2% RSE) for SC-, OC- and linear-pDNA polyplexes respectively [9], which are clearly within the size criterion to be taken up by DCs (up to 1 μm [14]). This may account for the uptake observed in Fig. 1. Uptake of DNA does not necessarily correlate to gene expression, so reporter gene β-galactosidase expression was measured directly. In this study complexes containing 20 μg pDNA were transfected into DCs for 48 h to induce gene expression. Although 2 μg and pDNA was used for confocal image studies, there was no significant difference between uptake profiles of complexes containing 2 and 20 μg (data not shown). Gene expression (lacZ reporter gene encoding β-galactosidase) was highest for SC-pDNA polyplexes at 14% ( Fig. 3). This was significantly greater than OC- (9.59%) and linear-pDNA polyplexes (7.43%) (p < 0.05). The ability of SC-pDNA polyplexes to diffuse through cells more efficiently than the other pDNA forms may contribute towards higher gene expression. We previously

reported how polyplexes containing SC-pDNA displayed smaller sizes and greater nuclease resistance than other DNA forms [9]. This is pivotal as DCs have been found to express various nucleases [16]. Gene expression was modest compared to a similar study with CHO cells [9], which may be due to premature phagocytic clearance thereby reducing nuclear uptake [15], [17], [18] and [19]. Other researchers have attempted to improve DC gene expression with immature DCs to increase cell viability [17]. A mannosylating complex has been found to enhance interaction with DC surface receptors [20]. Block copolymer systems which shield, internalise and release DNA cargo can also improve gene expression [21]. However these systems are polydisperse (combination of polymers), are prone to aggregation and can be cytotoxic at high polymer concentrations [21].