Receptor-mediated Gene Transfer Research Articles

Oversized liposomes boost macrophage-targeted RNA delivery to regulate macrophage polarity

Oversized liposomes boost macrophage-targeted RNA delivery to regulate macrophage polarity

Development of non-viral vehicles for targeted gene transfer into microglia via the integrin receptor CD11b.

Microglial activation is a central event in neurodegeneration. Novel technologies are sought for that specifically manipulate microglial function in order to delineate their role in onset and progression of neuropathologies. We investigated for the first time whether non-viral gene delivery based on polyethyleneglycol–polyethyleneimine conjugated to the monoclonal anti-CD11b antibody OX42 (“OX42-immunogene”) could be used to specifically target microglia. We first conducted immunofluorescence studies with the OX42 antibody and identified its microglial integrin receptor CD11b as a potential target for receptor-mediated gene transfer based on its cellular specificity in mixed glia culture and in vivo and found that the OX42 antibody is rapidly internalized and trafficked to acidic organelles in absence of activation of the respiratory burst. We then performed transfection experiments with the OX42-immunogene in vitro and in rat brain showing that the OX42-immunogene although internalized was degraded intracellularly and did not cause substantial gene expression in microglia. Investigation of specific barriers to microglial gene transfer revealed that aggregated OX42-immunogene polyplexes stimulated the respiratory burst that likely involved Fcγ-receptors. Transfections in the presence of the endosomolytic agent chloroquine improved transfection efficiency indicating that endosomal escape may be limited. This study identifies CD11b as an entry point for antibody-mediated gene transfer into microglia and takes important steps toward the further development of OX42-immunogenes.

Inhibition of hepatic scavenger receptor-class B type I by RNA interference decreases atherosclerosis in rabbits

ObjectiveScavenger receptor-class B type I (SR-BI), the receptor for HDL-cholesterol, plays a key role in HDL metabolism, whole body cholesterol homeostasis, and reverse cholesterol transport. We investigated the in vivo impact of hepatic SR-BI inhibition on lipoprotein metabolism and the development of atherosclerosis employing RNA interference. MethodsSmall hairpin RNA plasmid specific for rabbit SR-BI was complexed with galactosylated poly-l-lysine, allowing an organ-selective, receptor-mediated gene transfer. Rabbits were fed a cholesterol-rich diet, and were injected with plasmid-complexes once a week. ResultsAfter 2 weeks of treatment hepatic SR-BI mRNA levels were reduced by 80% accompanied by reduced SR-BI protein levels and a modulation of the lipoprotein profile. Rabbits treated with SR-BI-specific plasmid-complexes displayed higher cholesteryl ester transfer from HDL to apoB-containing lipoproteins, lower HDL-cholesterol, and higher VLDL-cholesterol levels, when compared to controls. In a long-term study, this gene therapeutic intervention led to a similar modulation of the lipoprotein profile, to lower total cholesterol levels, and most importantly to a 50% reduction of the relative atherosclerotic lesion area. ConclusionOur results are another indication that the role of SR-BI in lipoprotein metabolism and atherogenesis in rabbits – a CETP-expressing animal model displaying a manlike lipoprotein profile may be different from the one found in rodents.

Study on Galactose–Poly(Ethylene Glycol)–Poly(L-Lysine) as Novel Gene Vector for Targeting Hepatocytes In Vitro

A non-viral gene-delivery system has been used to deliver plasmid DNA into specific cell types because of its safety and ease of manufacture. Receptor-mediated gene transfer is currently a promising gene-delivery technique. To specifically target genes to asialoglycoprotein receptor of hepatocytes, a galactose moiety was combined into the poly(ethylene glycol) (PEG)-terminal end by reductive coupling using lactose and sodium cyanoborohydride. A synthesis method of conjugating poly(L-lysine) (PLL) derivatives with terminally galactose-graft-PEG was developed using ring-opening polymerization of N ε -benzyloxycarbonyl-L-lysine-N α -carboxyan-hydride (Z-Lys-NCA) initiated onto galactose graft amine-terminated PEG (galactose–PEG–NH2) as a macro-initiator. The synthesis was characterized with 1H-, 13C-NMR, IR and UV spectroscopy, and all of them successfully verified the formation of the co-polymers. The gel-retardation assay of the complexes between galactose–PEG–PLL and plasmid DNA indicated that these polymeric gene carriers demonstrated the potent ability to condense plasmid DNA electrostatically as well as PLL. The particle size and zeta potential of polymer/DNA complexes were measured, and their cytotoxicity and transfection efficiency in different cells were evaluated. The results indicate that galactose–PEG–PLL can form a complex with plasmid DNA and serve as an effective gene-delivery carrier with lower cytotoxicity compared to that of PLL. Transfection experiments clearly showed that galactose–PEG–PLL effectively delivered DNA into hepatoma cells in vitro. Such data demonstrates that galactose and its complex with plasmid DNA may serve as a safe and effective gene-transfer system targeting hepatocytes.

Mannan‐mediated gene delivery for cancer immunotherapy

Recent years have seen a resurgence in interest in the development of efficient non-viral delivery systems for DNA vaccines and gene therapy. We have previously used oxidized and reduced mannan as carriers for protein delivery to antigen-presenting cells by targeting the receptors that bind mannose, resulting in efficient induction of cellular responses. In the present study, oxidized mannan and reduced mannan were used as receptor-mediated gene transfer ligands for cancer immunotherapy. In vivo studies in C57BL/6 mice showed that injection of DNA encoding ovalbumin (OVA) complexed to oxidized or reduced mannan-poly-L-lysine induced CD8 and CD4 T-cell responses as well as antibody responses leading to protection of mice from OVA+ tumours. Both oxidized and reduced mannan delivery was superior to DNA alone or DNA-poly-L-lysine. These studies demonstrate the potential of oxidized and reduced mannan for efficient receptor-mediated gene delivery in vivo, particularly as DNA vaccines for cancer immunotherapy.

Gene Transfer by DNA/mannosylated Chitosan Complexes into Mouse Peritoneal Macrophages

Chitosan is a biodegradable and biocompatible polymer and is useful as a non-viral vector for gene delivery. In order to deliver pDNA/chitosan complex into macrophages expressing a mannose receptor, mannose-modified chitosan (man-chitosan) was employed. The cellular uptake of pDNA/man-chitosan complexes through mannose recognition was then observed. The pDNA/man-chitosan complexes showed no significant cytotoxicity in mouse peritoneal macrophages, while pDNA/man-PEI complexes showed strong cytotoxicity. The pDNA/man-chitosan complexes showed much higher transfection efficiency than pDNA/chitosan complexes in mouse peritoneal macrophages. Observation with a confocal laser microscope suggested differences in the cellular uptake mechanism between pDNA/chitosan complexes and pDNA/man-chitosan complexes. Mannose receptor-mediated gene transfer thus enhances the transfection efficiency of pDNA/chitosan complexes.

Developments on receptor-mediated gene transfer

Receptor-mediated gene transfer has many advantages such as cell and tissue targeting, high efficiency, high safety, low immunogenicity and easy-to-produce. This article briefly reviews the recent developments on receptor-mediated gene transfer technology, including its main types, effect factors and tactics to augment gene transfer efficiency.

Interaction with Blood Components Plays a Crucial Role in Asialoglycoprotein Receptor-Mediated in Vivo Gene Transfer by Galactosylated Lipoplex

In this study, we evaluated the effect of blood components (whole blood and serum) on asialoglycoprotein receptor-mediated in vivo gene transfer. The hepatic transfection activity of galactosylated lipoplex preincubated with serum was approximately 10 times higher than that without incubation after intraportal injection in mice. However, preincubation with whole blood significantly reduced hepatic transfection activity. Fluorescent resonance energy transfer analysis and agarose gel electrophoresis revealed that preincubation with serum reduced the degree of destabilization of the galactosylated lipoplex in blood, partially supporting enhanced hepatic transfection activity by preincubation with serum. Inhibition of hepatic transfection activity by predosing galactosylated bovine serum albumin indicated that the galactosylated lipoplex exposed to serum is recognized by asialoglycoprotein-receptors on hepatocytes. Inactivation of serum prior to mixing with galactosylated lipoplex reduced liver accumulation and completely abolished enhancement of hepatic transfection activity by preincubation with active serum, suggesting that not only the stability of the lipoplex in blood but also the serum opsonin activity plays important roles. Alternatively, preincubation with inactivated serum reduced the lung accumulation and inflammatory cytokine production of galactosylated lipoplex. The information provided by this study will be valuable for the future use, design, and development of galactosylated lipoplex for in vivo asialoglycoprotein receptor-mediated gene transfer.

Transgene vaccination using Ulex europaeus agglutinin I (UEA-1) for targeted mucosal immunization against HIV-1 envelope

Receptor-mediated gene transfer using an M cell ligand has been shown to be an efficient method for mucosal DNA immunization. To investigate further into alternative M cell ligands, the plant lectin, Ulex europaeus agglutinin I (UEA-1), was tested. UEA-1 binds to human intestinal Caco-2 cells, and these cells can be transfected with poly- l-lysine (PL)-conjugated UEA-1 for expression of reporter cDNAs. When tested in vivo, mice nasally immunized with UEA-1-PL complexed to plasmid encoding HIV-1 envelope showed elevated systemic and mucosal antibody responses, and these were supported by tissue antibody-forming cells. Likewise, elevated envelope-specific CTLs were induced. Thus, UEA-1 mediated DNA delivery represents an alternative mucosal formulation for inducing humoral and cellular immunity against HIV-1.

Specific interaction of mannosylated glycopolymers with macrophage cells mediated by mannose receptor

Poly[N-p-vinylbenzyl-O-beta-mannopyranosyl-(1-4)-D-gluconamide] (PV-Man) is a polystyrene derivative that contains mannose moieties and interacts with the mannose-receptor-carrying macrophage cell line. To clarify the specific interaction between the PV-Man and the macrophage cell line J774A1, PV-Man polymer labeled with fluorescent fluorescein isothiocyanate (FITC) was used to amonitor the specific interaction, which was visualized by confocal laser microscopy. We found that PV-Man strongly binds to macrophage cells, probably due to a specific interaction mediated by the presence of mannose receptors on the cell membrane. The fluorescence intensity of PV-Man and macrophage cells was up to 7-fold that of any other glycopolymers bound to macrophage cells. Moreover, cellular fluorescence intensity increased significantly with increasing incubation time and polymer concentration. Many macrophage cells strongly express mannose and mannose receptor-related receptors, and receptor-mediated gene transfer via the mannose receptor using a PV-Man glycopolymer is a versatile means of targeted gene delivery into these cells.

Potential of Transferrin and Transferrin Conjugates of Liposomes in Drug Delivery and Targeting

Targeted drug delivery has gained recognition in modern therapeutics and attempts are being made to explore the potential of cell biology-related bioevents in the development of specific and target-oriented systems. In connection to modern therapeutic systems, most of the emphasis has been laid upon the bioconjugated drug delivery systems. Bioconjugates involve the linking of two or more molecules to form a novel complex having the combined properties of its individual components. The nature of the linking agent between the pharmacologic agent and the delivery-augmenting moiety dictates the degree of successful delivery and its outcome. The component for the bioconjugated drug delivery includes receptors and ligands, where the receptors act as molecular targets or portals whereas ligands with receptors provide selective and specific trafficking towards the targeting site. Recently, a number of bioconjugated systems have been discovered for the site-specific presentation and delivery of various bioactive substances using biorelevant ligands, including antibodies, glycoprotein, viral proteins, and molecules of endogenous origin. In this review, the potential of transferrin (Tf) and Tf conjugates of liposomes in site-specific drug delivery systems are discussed. Tf is an abundant component of serum with the capacity to bind and transport iron, while Tf receptor (TfR), a dimeric transmembrane glycoprotein, is present on the surface of the most proliferating, higher eukaryotic cells. Tf expression is also found in nonproliferating tissues, such as hepatocytes, tissue macrophages, pituitary cells, pancreatic islet cells, and the endothelium of brain capillaries. Tumor cells frequently carry elevated numbers of TfRs compared with corresponding normal cells, and reduced serum levels of Tf are often observed in patients with tumors. In the past, various strategies have been developed, which include coupling of the liposomal surface with Tf by using various linking agents. Low-molecular weight drugs and proteins as well as liposomes can be linked with Tf. The Tf-coupled vesicular system is physicochemically stable in the bioenvironment and is site-specific. The aim of coupling liposomes with Tf is to improve the physical and biochemical stability of liposomes and make them appropriate for targeting specific organs and cells. Tf may be widely applied either as a carrier or targeting ligand in the active targeting of anticancer agents, proteins, and genes to primarily proliferating malignant cells that overexpress TfRs. Tf has been used as a molecular conjugate to deliver DNA to erythroleukemic, lung, and liver cell lines. Tf can also be modified with the positive charge N-acylurea groups to make them suitable for electrostatic binding of DNA, in order to achieve a well defined DNA-binding ligand for receptor-mediated gene transfer. Association of Tf with lipoplexes, in particular the negatively charged ternary complexes, significantly overcomes the inhibitory effect of serum and facilitates efficient transfection in many cell lines, including HeLa, K-562 cells, and lung carcinoma cells Calu-3 and H-292 cells. Tf-lipoplex has demonstrated high efficiency in tumor-targeted gene delivery and long-term therapeutic accuracy in systemic p53 gene therapy for both human head and neck cancer and prostate cancer. Tf and Tf-coupled liposomal drug delivery systems may prove particularly valuable to enable the use of a drug that seems to be ineffective or toxic if delivered systematically. The delivery of drugs to the brain has been particularly challenging because of the presence of the blood-brain barrier, which restricts the passage of most therapeutic agents into the brain. Therefore, active targeting of the brain is crucial for effective treatment of brain diseases. The anti-TfR antibody, such as OX26, when coupled with therapeutic agents, has shown potential in drug and gene delivery to the brain.

Copolymers of poly- l-lysine with serine and tryptophan form stable DNA vectors: implications for receptor-mediated gene transfer

Inefficient gene transfer and poor stability in physiological medium are important shortcomings for receptor-mediated gene transfer vectors. Here, we evaluate vectors formulated with random copolymers of l-lysine/ l-serine (3:1) and l-lysine/ l-tryptophan (4:1), focusing on both their biophysical and functional characterization. By means of dynamic light scattering (DLS) and transmission electron microscopy (TEM), we demonstrate that poly- l-lysine (pK), poly- l-lysine- l-tryptophan (pKW) and poly- l-lysine- l-serine (pKS) are able to form compacted, small particles when mixed with plasmid DNA in the absence of salt. Upon dilution in physiological medium, copolymers of both lys/ser and lys/trp do not aggregate, in contrast with poly- l-lysine DNA complexes as determined by scattering, DLS and TEM measurements. Tight packing, as demonstrated by resistance to heparin, SDS and trypsin treatments, is also featured in tryptophan-containing complexes. Successful receptor-mediated endocytosis gene transfer using galactosylated copolymers into cells expressing the asiagloglycoprotein receptor correlated with lack of aggregation. Particles obtained using galactosylated poly- l-lysine- l-tryptophan (Gal-pKW) copolymer demonstrated specific receptor-mediated gene transfer since reporter gene activity dropped in the presence of an excess ligand in the culture medium during transfection. Although copolymers of galactosylated poly- l-lysine- l-serine (Gal-pKS) do not aggregate in the presence of salt, they are not able to internalize in a specific receptor-mediated endocytosis fashion. The introduction of bulky aromatic/hydrophobic (tryptophan) or hydrophillic (serine) moieties into the positively charged vectors allows the compacted particles to disperse into salt-containing medium avoiding salt-induced aggregation. Moreover, tryptophan-containing particles are able to mediate specific gene transfer via receptor-mediated endocytosis.

Nerve Growth Factor Receptor-Mediated Gene Transfer

One obstacle to effective gene therapies for neurological disorders lies in the cell-type diversity of the nervous system, making it difficult to direct gene delivery vectors to specific types of cells. To meet this challenge, we have developed a recombinant peptide-based gene delivery vector that targets nerve growth factor (NGF) receptors. The peptide comprises a cell-targeting domain derived from the NGF hairpin motif containing loops 1 and 2 linked to a DNA-binding domain composed of SPKR repeats. In PC12 cells, it activated the high-affinity NGF receptor, TrkA, and displayed NGF-like bioactivity by promoting neurite outgrowth and cell survival after serum deprivation. When combined with a low molecular weight of polyethylenimine (PEI), the peptide condensed plasmid DNA into nanoparticles that efficiently transferred exogenous genes into PC12 cells, enhancing reporter gene expression 5600-fold over peptide-free DNA/PEI complexes. Co-incubation with free NGF inhibited this effect. Furthermore, the peptide enhanced gene expression in NGF-receptor-rich rat primary cortex neurons but not glial cells. An in vivo experiment targeting TrkA-expressing dorsal root ganglia demonstrated that the peptide-containing complexes were 9- to 14-fold more efficient in transfection than controls. These properties make the chimeric peptide a promising gene delivery vector for targeting specific subtypes of neurons.

Receptor-mediated gene transfer vectors: progress towards genetic pharmaceuticals.

Although specific delivery to tissues and unique cell types in vivo has been demonstrated for many non-viral vectors, current methods are still inadequate for human applications, mainly because of limitations on their efficiencies. All the steps required for an efficient receptor-mediated gene transfer process may in principle be exploited to enhance targeted gene delivery. These steps are: DNA/vector binding, internalization, subcellular trafficking, vesicular escape, nuclear import, and unpacking either for transcription or other functions (i.e., antisense, RNA interference, etc.). The large variety of vector designs that are currently available, usually aimed at improving the efficiency of these steps, has complicated the evaluation of data obtained from specific derivatives of such vectors. The importance of the structure of the final vector and the consequences of design decisions at specific steps on the overall efficiency of the vector will be discussed in detail. We emphasize in this review that stability in serum and thus, proper bioavailability of vectors to their specific receptors may be the single greatest limiting factor on the overall gene transfer efficiency in vivo. We discuss current approaches to overcome the intrinsic instability of synthetic vectors in the blood. In this regard, a summary of the structural features of the vectors obtained from current protocols will be presented and their functional characteristics evaluated. Dissecting information on molecular conjugates obtained by such methodologies, when carefully evaluated, should provide important guidelines for the creation of effective, targeted and safe DNA therapeutics.

Molecular weight-dependent gene transfection activity of unmodified and galactosylated polyethyleneimine on hepatoma cells and mouse liver

To optimize a receptor-mediated and cell-selective gene transfer with polyethyleneimine (PEI)-based vector, we synthesized three galactosylated PEIs (Gal-PEI) with different molecular weights (PEI(1800), PEI(10,000), and PEI(70,000)) and investigated their potential as a targetable vector to asialoglycoprotein receptor-positive cells. All PEI derivatives formed complexes with plasmid DNA (pDNA), whereas the particle size of the complex became smaller on increasing the molecular weight of PEI. Transfection efficiency in HepG2 cells with PEI was highest with PEI(1800); efficiency was next highest with PEI(10,000), although the cellular association was similar. After galactosylation, Gal(19)-PEI(10,000)/pDNA and Gal(120)-PEI(70,000)/pDNA showed considerable agglutination with a galactose-recognizing lectin, but Gal(9)-PEI(1800) did not, suggesting that galactose units on the Gal(9)-PEI(1800)-pDNA complex are not sufficiently available for recognition. Gal(19)-PEI(10,000)-pDNA and Gal(120)-PEI(70,000)-pDNA complexes showed galactose-inhibitable transgene expression in HepG2 cells. Transfection efficiency was greatest with Gal(19)-PEI(10,000)/pDNA, a result that highlights the importance of obtaining a balance between the cytotoxicity and the transfection activity, both of which are found to be a function of the molecular weight of PEI. After intraportal injection, however, Gal(153)-PEI(70,000)/pDNA having a low N/P ratio was most effective, suggesting that additional variables, such as the size of the complex, are important for in vivo gene transfer to hepatocytes.

Marked enhancement in gene expression by targeting the human insulin receptor.

Exogenous genes can be delivered to cells without viral vectors using an "artificial virus" comprised of nonviral plasmid DNA encapsulated in the interior of 85 nm pegylated immunoliposomes (PIL). The liposomes are targeted to cells with receptor-specific targeting ligands such as receptor-specific peptidomimetic monoclonal antibodies. The levels of luciferase gene expression in human or rat glioma cells are measured after targeting the PIL-encapsulated plasmid DNA via the human insulin receptor, the human epidermal growth factor receptor, or the rat transferrin receptor. The luciferase expression plasmids were either derived from pCEP4, which contains the Epstein-Barr nuclear antigen-1/oriP replication system, or from pGL2, which lacks this system for episomal replication of plasmid DNA. Depending on the plasmid construct used and the receptor targeted, the peak luciferase gene expression varied more than 200-fold from 1.8 +/- 0.1 to 419 +/- 31 pg luciferase per mg cell protein. With the same plasmid, the peak level of gene expression following delivery to the cell via the human insulin receptor was 100-200-fold higher than gene expression following delivery via either the epidermal growth factor receptor or the transferrin receptor. There was no gene expression if the targeting ligand on the PIL was replaced with a nonspecific isotype control antibody. The extent to which an exogenous gene is expressed within a cell via a nonviral, receptor-mediated gene transfer technology is determined by the receptor specificity of the targeting ligand. The highest levels of gene expression are obtained after targeting the insulin receptor, and this may derive from the nuclear targeting properties of this receptor system.

Absence of Metabolic Cross-correction in Tay-Sachs Cells: IMPLICATIONS FOR GENE THERAPY

We have investigated the ability of a receptor-mediated gene transfer strategy (cross-correction) to restore ganglioside metabolism in fibroblasts from Tay-Sachs (TS) patients in vitro. TS disease is a GM2 gangliosidosis attributed to the deficiency of the lysosomal enzyme beta-hexosaminidase A (HexA) (beta-N-acetylhexosaminidase, EC ). The hypothesis is that transduced cells overexpressing and secreting large amounts of the enzyme would lead to a measurable activity in defective cells via a secretion-recapture mechanism. We transduced NIH3T3 murine fibroblasts with the LalphaHexTN retroviral vector carrying the cDNA encoding for the human Hex alpha-subunit. The Hex activity in the medium from transduced cells was approximately 10-fold higher (up to 75 milliunits) than observed in non-transduced cells. TS cells were cultured for 72 h in the presence of the cell medium derived from the transduced NIH3T3 cells, and they were analyzed for the presence and catalytic activity of the enzyme. Although TS cells were able to efficiently uptake a large amount of the soluble enzyme, the enzyme failed to reach the lysosomes in a sufficient quantity to hydrolyze the GM2 ganglioside to GM3 ganglioside. Thus, our results showed that delivery of the therapeutic HexA was not sufficient to correct the phenotype of TS cells.

Somatic gene transfer into the lactating ovine mammary gland.

Somatic gene therapy requires safe and efficient techniques for the gene transfer procedure. The ovine mammary gland is described as a model system for the evaluation of somatic gene transfer methods. Different gene delivery formulations were retrogradely injected into the mammary gland of lactating sheep. The efficiency of the gene transfer was subsequently measured by the detection of the secreted transgene products in the milk. To counteract the milk flow in the lactating gland caused by the permanent milk production, a newly developed pretreatment of the mammary gland with hyperosmotic solutions was applied. In addition, in vivo electroporation of DNA into the mammary gland is described. Gene transfer using naked DNA or simple complexes of DNA with polycations did not result in traceable amounts of reporter gene products. However, utilizing the complex cationic lipid DOSPER, a peak expression of about 400 ng/ml was observed 6 days after transfection. Maximum expression rates of more than 1 microg/ml were obtained by combining hyperosmotic pretreatment and receptor-mediated gene transfer. For the in vivo electroporation, the proof of principle for this technique in the mammary gland is reported. The ovine mammary gland turned out to be a very well suited as a model system for evaluation and optimization of various gene transfer protocols.

Highly Compacted DNA-Polymer Complexes Obtained via New Polynorbornene Polycationic Latexes with Lactobionate Counterion

Receptor-mediated gene transfer is an attractive method for the targeting of DNA in specific tissues. Membrane lectins have been found at the surface of many cells and are good candidates for gene transfer by DNA-glycoconjugate complexes as specific carriers. However, to be useful for gene therapy, it is critical that the DNA be complexed and aggregated in very small particles. We describe here the properties of a new polycationic polynorbornene, with lactobionate counterions, that spontaneously forms small and stable latexes in water. Furthermore, because of lactobionate effect, the complexation with DNA lead to highly compacted aggregates with a diameter of around 10−20 nm. By the use of transmission electron microscopy, gel electrophoresis, and zeta potential measurements, we have studied both polymer organization and DNA-polymer complex formation.

Mannose receptor-mediated gene delivery into antigen presenting dendritic cells.

Dendritic cells are professional antigen presenting cells and are unique in their ability to prime naïve T cells. Gene modification of dendritic cells is of particular interest for immunotherapy of diseases where the immune system has failed or is aberrantly regulated, such as in cancer or autoimmune disease, respectively. Dendritic cells abundantly express mannose receptor and mannose receptor-related receptors, and receptor-mediated gene transfer via mannose receptor offers a versatile tool for targeted gene delivery into these cells. Accordingly, mannose polyethylenimine DNA transfer complexes were generated and used for gene delivery into dendritic cells. Mannose receptor belongs to the group of scavenger receptors that allow dendritic cells to take up pathogenic material, which is directed for degradation and MHC class II presentation. Therefore, a limiting step of transgene expression by mannose receptor-mediated gene delivery is endosomal degradation of DNA. Several strategies have been explored to overcome this limitation including the addition of endosomolytic components to DNA transfer complexes like adenovirus particles and influenza peptides. Here, we review the current understanding of mannose receptor-mediated gene delivery into dendritic cells and discuss strategies to identify appropriate endosomolytic agents to improve DNA transfer efficacy.