In vivo generation of dendritic cells by intramuscular codelivery of FLT3 ligand and GM-CSF plasmids

Potential Pitfalls of the Humanized Mice in Modeling Sepsis

Humanized mice are a state-of-the-art tool used to study several diseases, helping to close the gap between mice and human immunology. This review focuses on the potential obstacles in the analysis of immune system performance between humans and humanized mice in the context of severe acute inflammation as seen in sepsis or other critical care illnesses. The extent to which the reconstituted human immune system in mice adequately compares to the performance of the human immune system in human hosts is still an evolving question. Although certain viral and protozoan infections can be replicated in humanized mice, whether a highly complex and dynamic systemic inflammation like sepsis can be accurately represented by current humanized mouse models in a clinically translatable manner is unclear. Humanized mice are xenotransplant animals in the most general terms. Several organs (e.g., bone marrow mesenchymal cells, endothelium) cannot interact with the grafted human leukocytes effectively due to species specificity. Also the interaction between mice gut flora and the human immune system may be paradoxical. Often, grafting is performed utilizing an identical batch of stem cells in highly inbred animals which fails to account for human heterogeneity. Limiting factors include the substantial cost and restricting supply of animals. Finally, humanized mice offer an opportunity to gain knowledge of human-like conditions, requiring careful data interpretation just as in nonhumanized animals.

Electroporation-mediated gene therapy

Non-viral gene transfer is markedly enhanced by the application of in vivo electroporation. Electroporation is a safe and efficient system to introduce genes to a wide variety of tissues, including skeletal muscle, tumors, kidney, liver and skin. Electroporation has been demonstrated to be effective in numerous disease models. This review focuses on the principles of electroporation and the target tissues employed for gene therapy. Based on the accumulation of positive results, the first clinical study for the treatment of malignant melanoma is now underway, and preclinical studies have suggested that electroporation is useful as a gene therapy protocol.

Coexpression of Flt3 ligand and GM-CSF genes modulates immune responses induced by HER2/neu DNA vaccine

DNA vaccine and dendritic cells (DCs)-based vaccine have emerged as promising strategies for cancer immunotherapy. Fms-like tyrosine kinase 3-ligand (Flt3L) and granulocyte-macrophage-colony-stimulating factor (GM-CSF) have been exploited for the expansion of DC. It was reported previously that combination of plasmid encoding GM-CSF with HER2/neu DNA vaccine induced predominantly CD4(+) T-cell-mediated antitumor immune response. In this study, we investigated the modulation of immune responses by murine Flt3L and GM-CSF, which acted as genetic adjuvants in the forms of bicistronic (pFLAG) and monocistronic (pFL and pGM) plasmids for HER2/neu DNA vaccine (pN-neu). Coexpression of Flt3L and GM-CSF significantly enhanced maturation and antigen-presentation abilities of splenic DC. Increased numbers of infiltrating DC at the immunization site, higher interferon-gamma production, and enhanced cytolytic activities by splenocytes were prominent in mice vaccinated with pN-neu in conjunction with pFLAG. Importantly, a potent CD8(+) T-cell-mediated antitumor immunity against bladder tumors naturally overexpressing HER2/neu was induced in the vaccinated mice. Collectively, our results indicate that murine Flt3L and GM-CSF genes coexpressed by a bicistronic plasmid modulate the class of immune responses and may be superior to those codelivered by two separate monocistronic plasmids as the genetic adjuvants for HER2/neu DNA vaccine.

Cytokine profiles of canine monocyte-derived dendritic cells as a function of lipopolysaccharide- or tumor necrosis factor-alpha-induced maturation

In response to exogenous as well as endogenous signals, dendritic cells (DC) undergo programmed maturation to become efficient, antigen-presenting cells and mediate innate and adaptive immune responses. Very little is known, however, about the differential maturation responses of canine DC to endogenous and exogenous stimuli, especially the concomitant events related to the specific expression of cytokine genes. Canine monocyte-derived immature DC (iDC) were treated with an exogenous signal, bacterial lipopolysaccharide (LPS), or an endogenous signal, tumor necrosis factor-alpha (TNF-alpha), to generate mature DC (mDC). The mDC generated from either stimuli were characterized by significant increases in the expression of surface molecules, including CD11c, MHC class II, CD80, CD83, and CD86. Using real-time reverse transcriptase polymerase chain reactions, the cytokine expression profiles generated by these two stimuli were studied. Compared with the iDC, the LPS-stimulated mDC exhibited a significantly increased expression of IL-1 beta, IL-10, IL-12p40, IL-13, and TNF-alpha. Using the mixed lymphocyte reaction and cytokine intracellular staining, it was shown that the array of cytokines from LPS-generated mDC contributed to T cell priming and T helper cell type 1 (Th1) polarization. TNF-alpha-generated mDC increased the expression of a distinctly different panel of cytokines, namely IL-2, IL-4, IL-12p40, IL-13, TNF-alpha, TGF-beta, IFN-gamma, and MCP-2, and shifted naïve T cell differentiation to T helper cell type 2 (Th2) polarization. IL-13 expression was dramatically increased in canine TNF-alpha-generated mDC, which does not occur in other mammalian species, including humans. Because IL-13 is functionally similar to IL-4, IL-13 may contribute to the observed Th2 polarization. Thus, canine DC maturing from different stimuli release different cytokine profiles that in turn promote different immune responses and activate innate and adaptive immune responses.

Augmenting the immunogenicity of DNA vaccines: role of plasmid-encoded Flt-3 ligand, as a molecular adjuvant in genetic vaccination

In this study, we have taken advantage of the unique property of a potent dendritic cell (DC) growth factor, Flt-3 ligand (FL), which could act as a vaccine adjuvant. Accordingly, a single injection of plasmid DNA coding for soluble FL (FLex) was shown to induce large numbers of DCs in various tissue compartments and was critical for generating high frequencies of antigen-specific (HIV gp120 and LCMV NP) immune responses in mice. Interestingly, this enhanced level of immune response is strictly dependent on the co-delivery (i.m.) of the DNA vaccines and hFLex DNA to mice harboring large numbers of DCs. The high frequencies of antigen-specific CD8(+) T cells were largely associated with the expansion phase of DCs in vivo. However, DC expansion and immune enhancement have not reciprocally maintained a linear correlation, suggesting that other factors, cytokines/chemokines, which have the potential to modulate the microenvironment of DCs, could influence immunological outcome in this vaccination modality.

Treatment with Flt3 ligand plasmid reverses allergic airway inflammation in ovalbumin-sensitized and -challenged mice

We have previously reported that fms-like tyrosine kinase 3 ligand (Flt3-L) prevents and reverses established allergic airway inflammation in an ovalbumin (OVA) induced mouse model of asthma. In this study, we investigated the effect of pUMVC3-hFLex, a plasmid, mammalian expression vector for the secretion of Flt3-L on the same mouse model as well as the duration of the effect of the treatment. Allergic airway inflammation to OVA was established in BALB/c mice. OVA-sensitized mice received three intramuscular (i.m.) injections of 200 mug pUMVC3-hFLex over 10 days. The response to pUMVC3-hFLex therapy was assessed based on airway hyperresponsiveness (AHR) to methacholine and inflammation, measured as serum cytokine and immunoglobulins (Ig) levels, and the total and differential cells in bronchoalveolar lavage fluid (BALF). pUMVC3-hFLex treatment completely reversed established AHR (P<0.01) and this effect lasted for at least 24 days after the last treatment injection (P<0.001). pUMVC3-hFLex treatment significantly increased BALF interferon-gamma (IFN-gamma) (P<0.01), serum interleukin (IL)-10 (P<0.01) and anti-OVA IgG2a levels (P<0.01). In contrast, serum IL-4 and IgE levels were significantly reduced (P<0.05). Total BALF cellularity, eosinophiles counts and BALF IL-5 levels were also reduced (P<0.01). pUMVC3-hFLex treatment can reverse established experimental asthma and might provide a novel approach for treating asthma.

Electric pulse-mediated gene delivery to various animal tissues

Electroporation designates the use of electric pulses to transiently permeabilize the cell membrane. It has been shown that DNA can be transferred to cells through a combined effect of electric pulses causing (1) permeabilization of the cell membrane and (2) an electrophoretic effect on DNA, leading the polyanionic molecule to move toward or across the destabilized membrane. This process is now referred to as DNA electrotransfer or electro gene transfer (EGT). Several studies have shown that EGT can be highly efficient, with low variability both in vitro and in vivo. Furthermore, the area transfected is restricted by the placement of the electrodes, and is thus highly controllable. This has led to an increasing use of the technology to transfer reporter or therapeutic genes to various tissues, as evidenced from the large amount of data accumulated on this new approach for non-viral gene therapy, termed electrogenetherapy (EGT as well). By transfecting cells with a long lifetime, such as muscle fibers, a very long-term expression of genes can be obtained. A great variety of tissues have been transfected successfully, from muscle as the most extensively used, to both soft (e.g., spleen) and hard tissue (e.g., cartilage). It has been shown that therapeutic levels of systemically circulating proteins can be obtained, opening possibilities for using EGT therapeutically. This chapter describes the various aspects of in vivo gene delivery by means of electric pulses, from important issues in methodology to updated results concerning the electrotransfer of reporter and therapeutic genes to different tissues.

DNA vaccination against tumors

DNA vaccines have been used to generate protective immunity against tumors in a variety of experimental models. The favorite target antigens have been those that are frequently expressed by human tumors, such as carcinoembryonic antigen (CEA), ErbB2/neu, and melanoma-associated antigens. DNA vaccines have the advantage of being simple to construct, produce and deliver. They can activate all arms of the immune system, and allow substantial flexibility in modifying the type of immune response generated through codelivery of cytokine genes. DNA vaccines can be applied by intramuscular, dermal/epidermal, oral, respiratory and other routes, and pose relatively few safety concerns. Compared to other nucleic acid vectors, they are usually devoid of viral or bacterial antigens and can be designed to deliver only the target tumor antigen(s). This is likely to be important when priming a response against weak tumor antigens. DNA vaccines have been more effective in rodents than in larger mammals or humans. However, a large number of methods that might be applied clinically have been shown to ameliorate these vaccines. This includes in vivo electroporation, and/or inclusion of various immunostimulatory molecules, xenoantigens (or their epitopes), antigen-cytokine fusion genes, agents that improve antigen uptake or presentation, and molecules that activate innate immunity mechanisms. In addition, CpG motifs carried by plasmids can overcome the negative effects of regulatory T cells. There have been few studies in humans, but recent clinical trials suggest that plasmid/virus, or plasmid/antigen-adjuvant, prime-boost strategies generate strong immune responses, and confirm the usefulness of plasmid-based vaccination.

DNA electrotransfer: its principles and an updated review of its therapeutic applications

The use of electric pulses to transfect all types of cells is well known and regularly used in vitro for bacteria and eukaryotic cells transformation. Electric pulses can also be delivered in vivo either transcutaneously or with electrodes in direct contact with the tissues. After injection of naked DNA in a tissue, appropriate local electric pulses can result in a very high expression of the transferred genes. This manuscript describes the evolution in the concepts and the various optimization steps that have led to the use of combinations of pulses that fit with the known roles of the electric pulses in DNA electrotransfer, namely cell electropermeabilization and DNA electrophoresis. A summary of the main applications published until now is also reported, restricted to the in vivo preclinical trials using therapeutic genes.