Cationic liposomes are a strong adjuvant for a DNA vaccine of human immunodeficiency virus type 1

A brief review on DNA vaccines in the era of COVID-19

This article provides a brief overview of DNA vaccines. First, the basic DNA vaccine design strategies are described, then specific issues related to the industrial production of DNA vaccines are discussed, including the production and purification of DNA products such as plasmid DNA, minicircle DNA, minimalistic, immunologically defined gene expression (MIDGE) and Doggybone™. The use of adjuvants to enhance the immunogenicity of DNA vaccines is then discussed. In addition, different delivery routes and several physical and chemical methods to increase the efficacy of DNA delivery into cells are explained. Recent preclinical and clinical trials of DNA vaccines for COVID-19 are then summarized. Lastly, the advantages and obstacles of DNA vaccines are discussed.

The Use of Nanobiotechnology in Immunology and Vaccination

Nanotechnology uses the unique properties of nanostructures with a size of 1 to 200 nanometers. Different nanoparticles have shown great promise for the production of new vaccines and drugs. Nanostructures can be used to deliver immunological compounds more effectively than microstructures to target sites. Different nanostructures can be applied to form a new generation of vaccines, adjuvants, and immune system drugs. The goal of nanotechnology is to better respond to a wide range of infectious and non-infectious diseases.

Three-dimensional DNA nanostructures for dual-color microRNA imaging in living cells via hybridization chain reaction

A well-defined 3D DNA nanostructure was developed by combination of DNA tetrahedron and Y-shaped DNA, which allowed multiplexed, signal amplified fluorescent imaging of miRNAs in living cells via hybridization chain reaction.

Aluminum (oxy) Hydroxide Nanorods Activate an Early Immune Response in Pseudomonas aeruginosa Vaccine

Bacterial vaccines have been widely used to prevent infectious diseases, especially in veterinary medicine. Although there are many reports on bacterin adjuvants, only a few contain innovations in bacterin adjuvants. Taking this into consideration, in this study we designed and synthesized a new aluminum (oxy) hydroxide (AlOOH) nanorod (Al-NR) with a diameter of 200 ± 80 nm and a length of 1.1 ± 0.6 μm. Using whole- Pseudomonas aeruginosa PAO1 as antigens, we showed that the bacterial antigens of P. aeruginosa PAO1 adsorbed on the Al-NRs induced a quick and stronger antigen-specific antibody response than those of the other control groups, especially in the early stage of immunization. Furthermore, the level of antigen-specific IgG was approximately 4-fold higher than that of the no adjuvant group and 2.5-fold higher than those of other adjuvant groups in the first week after the initial immunization. The potent adjuvant activity of the Al-NRs was attributed to the rapid presentation of antigen adsorbed on them by APCs. Additionally, Al-NRs induced a milder local inflammation than the other adjuvants. In short, we confirmed that Al-NRs, enhancing both humoral and cellular immune responses, are a potentially promising vaccine adjuvant delivery system for inhibiting the whole- Pseudomonas aeruginosa infection.

Nanomedicine Strategies to Target Tumor-Associated Macrophages

In recent years, the influence of the tumor microenvironment (TME) on cancer progression has been better understood. Macrophages, one of the most important cell types in the TME, exist in different subtypes, each of which has a different function. While classically activated M1 macrophages are involved in inflammatory and malignant processes, activated M2 macrophages are more involved in the wound-healing processes occurring in tumors. Tumor-associated macrophages (TAM) display M2 macrophage characteristics and support tumor growth and metastasis by matrix remodeling, neo-angiogenesis, and suppressing local immunity. Due to their detrimental role in tumor growth and metastasis, selective targeting of TAM for the treatment of cancer may prove to be beneficial in the treatment of cancer. Due to the plastic nature of macrophages, their activities may be altered to inhibit tumor growth. In this review, we will discuss the therapeutic options for the modulation and targeting of TAM. Different therapeutic strategies to deplete, inhibit recruitment of, or re-educate TAM will be discussed. Current strategies for the targeting of TAM using nanomedicine are reviewed. Passive targeting using different nanoparticle systems is described. Since TAM display a number of upregulated surface proteins compared to non-TAM, specific targeting using targeting ligands coupled to nanoparticles is discussed in detail.

Recent Developments in Preclinical DNA Vaccination

The advantages of genetic immunization of the new vaccine using plasmid DNAs are multifold. For example, it is easy to generate plasmid DNAs, increase their dose during the manufacturing process, and sterilize them. Furthermore, they can be stored for a long period of time upon stabilization, and their protein encoding sequences can be easily modified by employing various DNA-manipulation techniques. Although DNA vaccinations strongly increase Th1-mediated immune responses in animals, several problems persist. One is about their weak immunogenicity in humans. To overcome this problem, various genetic adjuvants, electroporation, and prime-boost methods have been developed preclinically, which are reviewed here.

Engineering an effective immune adjuvant by designed control of shape and crystallinity of aluminum oxyhydroxide nanoparticles

Adjuvants based on aluminum salts (Alum) are commonly used in vaccines to boost the immune response against infectious agents. However, the detailed mechanism of how Alum enhances adaptive immunity and exerts its adjuvant immune effect remains unclear. Other than being comprised of micrometer-sized aggregates that include nanoscale particulates, Alum lacks specific physicochemical properties to explain activation of the innate immune system, including the mechanism by which aluminum-based adjuvants engage the NLRP3 inflammasome and IL-1β production. This is putatively one of the major mechanisms required for an adjuvant effect. Because we know that long aspect ratio nanomaterials trigger the NLRP3 inflammasome, we synthesized a library of aluminum oxyhydroxide (AlOOH) nanorods to determine whether control of the material shape and crystalline properties could be used to quantitatively assess NLRP3 inflammasome activation and linkage of the cellular response to the material's adjuvant activities in vivo. Using comparison to commercial Alum, we demonstrate that the crystallinity and surface hydroxyl group display of AlOOH nanoparticles quantitatively impact the activation of the NLRP3 inflammasome in human THP-1 myeloid cells or murine bone marrow-derived dendritic cells (BMDCs). Moreover, these in vitro effects were correlated with the immunopotentiation capabilities of the AlOOH nanorods in a murine OVA immunization model. These results demonstrate that shape, crystallinity, and hydroxyl content play an important role in NLRP3 inflammasome activation and are therefore useful for quantitative boosting of antigen-specific immune responses. These results show that the engineered design of aluminum-based adjuvants in combination with dendritic cell property-activity analysis can be used to design more potent aluminum-based adjuvants.

Comparison of immune response generated against Japanese encephalitis virus envelope protein expressed by DNA vaccines under macrophage associated versus ubiquitous expression promoters

Background

Japanese encephalitis virus (JEV) is the leading cause of viral encephalitis, with ~50,000 cases reported annually worldwide. Vaccination is the only measure for prevention. Recombinant vaccines are an efficient and safe alternative for formalin inactivated or live attenuated vaccines. Nowadays, incorporation of molecular adjuvants has been the main strategy for melioration of vaccines. Our attempt of immunomodulation is based on targeting antigen presenting cells (APC) "majorly macrophages" by using macrosialin promoter. We have compared the immune response of the constructed plasmids expressing JEV envelope (E) protein under the control of aforesaid promoter and cytomegalovirus (CMV) immediate early promoter in mouse model. Protection of immunized mice from lethal challenge with JEV was also studied.

Results

The E protein was successfully expressed in the macrophage cell line and was detected using immunofluorescence assay (IFA) and Western blotting. APC expressing promoter showed comparable expression to CMV promoter. Immunization of mice with either of the plasmids exhibited induction of variable JEV neutralizing antibody titres and provided protection from challenge with a lethal dose of JEV. Immune splenocytes showed proliferative response after stimulation with the JEV antigen (Ag), however, it was higher for CMV promoter. The magnitude of immunity provided by APC dominant promoter was non-significantly lower in comparison to CMV promoter. More importantly, immune response directed by APC promoter was skewed towards Th1 type in comparison to CMV promoter, this was evaluated by cytokine secretion profile of immune splenocytes stimulated with JEV Ag.

Conclusions

Thus, our APC-expressing DNA vaccination approach induces comparable immunity in comparison to ubiquitous promoter construct. The predominant Th1 type immune responses provide opportunities to further test its potency suitable for response in antiviral or anticancer vaccines.

Comparative analysis of macrophage associated vectors for use in genetic vaccine

Background

Antigen presentation by non professional antigen presenting cells (APC) can lead to anergy. In genetic vaccines, targeting the macrophages and APC for efficient antigen presentation might lead to balanced immune response. One such approach is to incorporate APC specific promoter in the vector to be used.

Methods

Three promoters known to be active in macrophage were selected and cloned in mammalian expressing vector (pAcGFP1-N1) to reconstruct (pAcGFP-MS), (pAcGFP-EMR) and (pAcGFP-B5I) with macrosialin, EmrI and Beta-5 Integrin promoters respectively. As a positive control (pAcGFP-CMV) was used with CMV promoter and promoterless vector (pAcGFP-NIX) which served as a negative control. GFP gene was used as readout under the control of each of the promoter. The expression of GFP was analyzed on macrophage and non-macrophage cell lines using Flow cytometry and qRT-PCR with TaqMan probe chemistries.

Results

All the promoters in question were dominant to macrophage lineage cell lines as observed by fluorescence, Western blot and quantitative RT-PCR. The activity of macrosialin was significantly higher than other macrophage promoters. CMV promoter showed 1.83 times higher activity in macrophage cell lines. The expression of GFP driven by macrosialin promoter after 24 hours was 4.40 times higher in macrophage derived cell lines in comparison with non macrophage cell lines.

Conclusions

Based on this study, macrosialin promoter can be utilized for targeting macrophage dominant expression. In vivo study needs to be carried out for its utility as a vaccine candidate.

Liposomal delivery of p-ialB and p-omp25 DNA vaccines improves immunogenicity but fails to provide full protection against B. melitensis challenge

Background

We have previously demonstrated protective efficacy against B. melitensis using formulations of naked DNA vaccines encoding genes ialB and omp25. The present study was undertaken to further understand the immune response generated by the protective vaccination regimens and to evaluate cationic liposome adsorption as a delivery method to improve vaccine utility.

Methods

The protective efficacy and immunogenicity of vaccines delivered as four doses of naked DNA, a single dose of naked DNA or a single dose of DNA surface adsorbed to cationic liposomes were compared using the BALB/c murine infection model of B. melitensis. Antigen-specific T cells and antibody responses were compared between the various formulations.

Results

The four dose vaccination strategy was confirmed to be protective against B. melitensis challenge. The immune response elicited by the various vaccines was found to be dependent upon both the antigen and the delivery strategy, with the IalB antigen favouring CD4+ T cell priming and Omp25 antigen favouring CD8+. Delivery of the p-ialB construct as a lipoplex improved antibody generation in comparison to the equivalent quantity of naked DNA. Delivery of p-omp25 as a lipoplex altered the profile of responsive T cells from CD8+ to CD4+ dominated. Under these conditions neither candidate delivered by single dose naked DNA or lipoplex vaccination methods was able to produce a robust protective effect.

Conclusions

Delivery of the p-omp25 and p-ialB DNA vaccine candidates as a lipoplex was able to enhance antibody production and effect CD4+ T cell priming, but was insufficient to promote protection from a single dose of either vaccine. The enhancement of immunogenicity by lipoplex delivery is a promising step toward improving the practicality of these two candidate vaccines, and suggests that this lipoplex formulation may be of value in situations where improvements to CD4+ responses are required. However, in the case of Brucella vaccine development it is suggested that further modifications to the candidate vaccines and delivery strategies will be required in order to deliver sustained protection.

Nanotechnology-based systems for the treatment and prevention of HIV/AIDS

The HIV/AIDS pandemic is an increasing global burden with devastating health-related and socioeconomic effects. The widespread use of antiretroviral therapy has dramatically improved life quality and expectancy of infected individuals, but limitations of currently available drug regimens and dosage forms, alongside with the extraordinary adapting capacity of the virus, have impaired further success. Alongside, circumventing the escalating number of new infections can only be attained with effective and practical preventative strategies. Recent advances in the field of drug delivery are providing evidence that engineered nanosystems may contribute importantly for the enhancement of current antiretroviral therapy. Additionally, groundwork is also being carried out in the field nanotechnology-based systems for developing preventative solutions for HIV transmission. This manuscript reviews recent advances in the field of nanotechnology-based systems for the treatment and prevention of HIV/AIDS. Particular attention is given to antiretroviral drug targeting to HIV reservoirs and the usefulness of nanosystems for developing topical microbicides and vaccines.

Effect of genetic adjuvants on immune respondance, growth and hormone levels in somatostatin DNA vaccination-induced Hu lambs

The aim of current study was to evaluate the prospects of adjuvants against DNA vaccination (pES/2SS) encoding somatostatin (SS) and hepatitis B surface antigen fusion gene. A total of 60 female Hu lambs were divided into 6 groups and vaccinated in the context of various adjuvants (and controls): pE-CpG, Escherichia coli DH5alpha DNA, crude liposomes or GM-CSF in combination with the pES/2SS plasmid. Controls included pES/2SS only vaccinated and physiological saline groups. The antibody against SS level in the E. coli DH5alpha DNA group was significantly increased compared to that in the pES/2SS vaccine alone. Vaccination with pES/2SS/pE-CpG or pES/2SS/E. coli DH5alpha resulted in elevated weight gains that were 33.0 and 31.6% higher, respectively, than in saline group and pES/2SS only vaccinated controls. The concentrations of GH and IGF-I in the DNA vaccine groups were remarkably higher than those in the saline group, and those with positive antibody higher than negative antibody. These results suggested that different adjuvant/pES/2SS combinations can enhance the immune effect and had significant positive effects on growth.

Gene delivery systems for gene therapy in tissue engineering and central nervous system applications

The present review aims to describe the potential applications of gene delivery systems to tissue engineering and central nervous system diseases. Some key experimental work has been done with interesting results, but the subject is far from being fully explored. The combined approach of gene therapy and material science has a huge potential to improve the therapeutic approaches now available for a wide range of medical applications. Focus is given to this multidisciplinary strategy in neurodegenerative pathologies, where the use of polymeric matrices as gene carriers might make a crucial difference.

Potent adjuvant activity of cationic liposome-DNA complexes for genital herpes vaccines

Development of a herpes simplex virus (HSV) vaccine is a priority because these infections are common. It appears that potent adjuvants will be required to augment the immune response to subunit HSV vaccines. Therefore, we evaluated cationic liposome-DNA complexes (CLDC) as an adjuvant in a mouse model of genital herpes. Using a whole-virus vaccine (HVAC), we showed that the addition of CLDC improved antibody responses compared to vaccine alone. Most important, CLDC increased survival, reduced symptoms, and decreased vaginal virus replication compared to vaccine alone or vaccine administered with monophosphoryl lipid A (MPL) plus trehalose dicorynomycolate (TDM) following intravaginal challenge of mice. When CLDC was added to an HSV gD2 vaccine, it increased the amount of gamma interferon that was produced from splenocytes stimulated with gD2 compared to the amount produced with gD2 alone or with MPL-alum. The addition of CLDC to the gD2 vaccine also improved the outcome following vaginal HSV type 2 challenge compared to vaccine alone and was equivalent to vaccination with an MPL-alum adjuvant. CLDC appears to be a potent adjuvant for HSV vaccines and should be evaluated further.

Poly(propyleneimine) dendrimer and dendrosome mediated genetic immunization against hepatitis B

The purpose of the present research work is to explore the potential of dendrosomes in genetic immunization against hepatitis B. Plasmid DNA encoding pRc/CMV-HBs[S] (5.6 kb), encoding the small region of the hepatitis B surface antigen, was complexed with 5th generation poly(propyleneimine) dendrimer (PPI) in different ratios. Transfection of CHO cells revealed that a ratio of 1:50 for pDNA:PPI was optimum for transfection. Results of cytotoxicity studies showed that the toxicity of PPI-DNA complex was significantly (p<0.05) higher for PPI 75 and PPI 100 as compared to the other PPI-DNA complexes. PPI 50 was employed for preparation of dendrosomes by reverse phase evaporation method. The dendrosomal formulation DF3 was found to possess optimum vesicle size, zeta potential and entrapment efficiency. In vitro production of HBsAg in CHO cells showed that DF3 possess maximum transfection efficiency. In vivo immunization studies were carried out by giving a single intramuscular injection of 10 microg of plasmid DNA (pDNA) or its dendrimeric or dendrosomal formulation to female Balb/c mice, followed by estimation of total IgG, IgG(1), IgG(2a), IgG(2b), biweekly. DF3 was found to elicit maximum immune response in terms of total IgG and its subclasses under study as compared to PPI 50 and pDNA at all time points. Animals immunized with DF3 developed very high cytokine level. Higher level of IFN-gamma suggests that the immune response was strictly Th1 mediated. Our observations clearly prove the superiority of dendrosomes over PPI-DNA complex and pDNA for genetic immunization against hepatitis B.

Cationic liposomal lipids: from gene carriers to cell signaling

Cationic lipids are positively charged amphiphilic molecules which, for most of them, form positively charged liposomes, sometimes in combination with a neutral helper lipid. Such liposomes are mainly used as efficient DNA, RNA or protein carriers for gene therapy or immunization trials. Over the past decade, significant progress has been made in the understanding of the cellular pathways and mechanisms involved in lipoplex-mediated gene transfection but the interaction of cationic lipids with cell components and the consequences of such an interaction on cell physiology remains poorly described. The data reported in the present review provide evidence that cationic lipids are not just carriers for molecular delivery into cells but do modify cellular pathways and stimulate immune or anti-inflammatory responses. Considering the wide number of cationic lipids currently available and the variety of cellular components that could be involved, it is likely that only a few cationic lipid-dependent functions have been identified so far.

Inorganic nanoparticles as carriers of nucleic acids into cells

The transfer of nucleic acids (DNA or RNA) into living cells, that is, transfection, is a major technique in current biochemistry and molecular biology. This process permits the selective introduction of genetic material for protein synthesis as well as the selective inhibition of protein synthesis (antisense or gene silencing). As nucleic acids alone are not able to penetrate the cell wall, efficient carriers are needed. Besides viral, polymeric, and liposomal agents, inorganic nanoparticles are especially suitable for this purpose because they can be prepared and surface-functionalized in many different ways. Herein, the current state of the art is discussed from a chemical viewpoint. Advantages and disadvantages of the available methods are compared.

Particle-based vaccines for transcutaneous vaccination

Immunization concepts evolve with increasing knowledge of how the immune system works and the development of new vaccination methods. Traditional vaccines are made of live, attenuated, killed or fragmented pathogens. New vaccine strategies can take advantage of particulate compounds--microspheres or nanoparticles--to target antigen-presenting cells better, which must subsequently reach the secondary lymphoid organs, which are the sites of the immune response. The use of the skin as a target organ for vaccine delivery stems from the fact that immature dendritic cells (DCs), which are professional antigen-presenting cells can be found at high density in the epidermis and dermis of human or animal skin. This has led to design various methods of dermal or transcutaneous vaccination. The quality and duration of the humoral and cellular responses to vaccination depend on the appropriate targeting of antigen-presenting cells, of the vaccine dose, route of administration and use of adjuvant. In this review, we will focus on the use of micro- and nano-particles to target the skin antigen-presenting cells and will discuss recent advances in the field of transcutaneous vaccination in animal models and humans.

Importance of divalent cations in nanolipoplex gene delivery

Gene therapy is a promising therapeutic strategy to combat genetic or acquired diseases at their root cause rather than just treating symptoms. It is well recognised that there is an urgent need for non-toxic and efficient gene delivery vectors to fully exploit the current potential of gene therapy in molecular medicine. Cell-specific targeting of bioactive nucleotides is a prerequisite to attain the concentration of nucleic acids required for therapeutic efficacy in the target tissue. Many metal ions such as Mg2+, Mn2+, Ba2+ and, most importantly, Ca2+ have been demonstrated to have significant roles in gene delivery. These inorganic cations show low toxicity, good biocompatibility and promise for controlled delivery properties, thus presenting a new alternative to toxic and immunogenic carriers. Recently, inorganic nanoparticles alone, or in combination with a colloidal particulate system such as nanoliposome, an advanced approach to gene delivery, were found to exert a positive effect on gene transfer. In this report, the role of the divalent cations in nucleic acid delivery, particularly with respect to the potential improvement of transfection efficiency of nanolipoplexes, is reviewed.

Nanotechnology-based delivery systems in HIV/AIDS therapy

The therapeutic efficacy of anti-HIV agents is often hampered by poor bioavailability and lack of drug penetration in infected target tissues and cells. Using different types of nanotechnology-based delivery systems, it is possible to engineer strategies that can improve the therapeutic efficacy in HIV/AIDS by delivering drugs to cellular and anatomical viral reservoirs. The rationale for the use of nanocarrier systems relies on the fact that different types of therapeutic payloads can be encapsulated and the systemic pharmacokinetics and distribution are dictated by the properties of the nanocarriers rather than the drugs. The versatility of nanoplatforms can be further exploited in a formulation that has enhanced oral bioavailability, protects against degradation upon oral or systemic administration and prolongs the residence time at the target site. Nanocarriers can facilitate lymphatic transport, delivery across the blood–brain barrier, and efficient internalization in cells by nonspecific or receptor-mediated endocytosis. In this review, we will address the role of nanotechnology-based delivery systems in improving the delivery efficiency of anti-HIV drugs to cellular and anatomical sites of interest. Specific published examples will be highlighted with emphasis on the role of polymeric nanoparticle micelles, liposomes and nanoemulsions in improving delivery efficiency.

Oral vaccination with modified vaccinia virus Ankara attached covalently to TMPEG-modified cationic liposomes overcomes pre-existing poxvirus immunity from recombinant vaccinia immunization

Development of a safe and effective vaccine for induction of mucosal immunity to the human immunodeficiency virus (HIV) envelope glycoprotein (Env, gp160) represents the best hope for containing the spread of an HIV epidemic worldwide. The highly attenuated modified vaccinia virus Ankara (MVA) is a laboratory virus well suited as a safe vaccine vector. However, the presence of pre-existing immunity to Vaccinia virus in the adult population represents a hindrance that limits the application of the MVA vector for inducing immunity to HIV antigens. Here, cationic liposomes were covalently attached to the surface of recombinant MVA expressing the HIV-1 strain IIIB Env glycoprotein and beta-galactosidase (MVA(IIIB/beta-gal)) using tresylmonomethoxypolyethylene glycol (TMPEG) grafted into a lipid membrane without compromising viral infectivity in vitro and in vivo. The orally administered MVA(IIIB/beta-gal)-TMPEG/liposome complexes were capable of delivering the transgenes to mucosal tissues in mice with pre-existing poxvirus immunity based on beta-galactosidase gene expression in intestinal tissues measured 18 h after infection. Importantly, the MVA(IIIB/beta-gal)-TMPEG/liposome complexes enhanced Env-specific cellular and humoral immune responses in the mucosal and systemic tissues after repeated oral immunization of BALB/c mice. This approach may prove useful for induction of protective immunity against infectious diseases and cancer in populations with pre-existing immunity to vaccinia from smallpox vaccination.

Enhanced DNA vaccine potency by mannosylated lipoplex after intraperitoneal administration

BACKGROUND

Here we describe a novel DNA vaccine formulation that can enhance cytotoxic T lymphocyte (CTL) activity through efficient gene delivery to dendritic cells (DCs) by mannose receptor-mediated endocytosis.

METHODS

Ovalbumin (OVA) was selected as a model antigen for vaccination; accordingly, OVA-encoding pDNA (pCMV-OVA) was constructed to evaluate DNA vaccination. Mannosylated cationic liposomes (Man-liposomes) were prepared using cholesten-5-yloxy-N-{4-[(1-imino-2-D-thiomannosylethyl)amino]butyl}formamide (Man-C4-Chol) with cationic lipid. The potency of the mannosylated liposome/pCMV-OVA complex (Man-lipoplex) was evaluated by measuring OVA mRNA in CD11c+ cells, CTL activity, and the OVA-specific anti-tumor effect after in vivo administration.

RESULTS

An in vitro study using DC2.4 cells demonstrated that Man-liposomes could transfect pCMV-OVA more efficiently than cationic liposomes via mannose receptor-mediated endocytosis. In vivo studies revealed that the Man-lipoplex exhibited higher OVA mRNA expression in CD11c+ cells in the spleen and peritoneal cavity and provided a stronger OVA-specific CTL response than intraperitoneal (i.p.) administration of the conventional lipoplex and intramuscular (i.m.) administration of naked pCMV-OVA, the standard protocol for DNA vaccination. Pre-immunization with the Man-lipoplex provided much better OVA-specific anti-tumor effect than naked pCMV-OVA via the i.m. route.

CONCLUSIONS

These results suggested that in vivo active targeting of DNA vaccine to DCs with Man-lipoplex might prove useful for the rational design of DNA vaccine.

Efficient Immunization and Cross-Priming by Vaccine Adjuvants Containing TLR3 or TLR9 Agonists Complexed to Cationic Liposomes

Complexing TLR9 agonists such as plasmid DNA to cationic liposomes markedly potentiates their ability to activate innate immunity. We therefore reasoned that liposomes complexed with DNA or other TLR agonists could be used as effective vaccine adjuvants. To test this hypothesis, the vaccine adjuvant effects of liposomes complexed to TLR agonists were assessed in mice. We found that liposomes complexed to nucleic acids (liposome-Ag-nucleic acid complexes; LANAC) were particularly effective adjuvants for eliciting CD4(+) and CD8(+) T cell responses against peptide and protein Ags. Notably, LANAC containing TLR3 or TLR9 agonists effectively cross-primed CD8(+) T cell responses against even low doses of protein Ags, and this effect was independent of CD4(+) T cell help. Ag-specific CD8(+) T cells elicited by LANAC adjuvants were functionally active and persisted for long periods of time in tissues. In a therapeutic tumor vaccine model, immunization with the melanoma peptide trp2 and LANAC adjuvant controlled the growth of established B16 melanoma tumors. In a prophylactic vaccine model, immunization with the Mycobacterium tuberculosis protein ESAT-6 with LANAC adjuvant elicited significant protective immunity against aerosol challenge with virulent M. tuberculosis. These results suggest that certain TLR agonists can be combined with cationic liposomes to produce uniquely effective vaccine adjuvants capable of eliciting strong T cell responses against protein and peptide Ags.

Vaccination with mRNAs encoding tumor-associated antigens and granulocyte-macrophage colony-stimulating factor efficiently primes CTL responses, but is insufficient to overcome tolerance to a model tumor/self antigen

Immunization of mice with dendritic cells transfected ex vivo with tumor-associated antigen (TAA)-encoding mRNA primes cytotoxic T lymphocytes (CTL) that mediate tumor rejection. Here we investigated whether direct injection of TAA mRNA, encapsulated in cationic liposomes, could function similarly as cancer immunotherapy. Intradermal and intravenous injection of ovalbumin (OVA) mRNA generated specific CTL activity and inhibited the growth of OVA-expressing tumors. Vaccination studies with DNA have demonstrated that co-administration of antigen (Ag)- and cytokine-encoding plasmids potentiate the T cell response; in analogous fashion, the inclusion of granulocyte-macrophage colony-stimulating factor (GM-CSF) mRNA enhanced OVA-specific cytotoxicity. The ability of this GM-CSF-augmented mRNA vaccine to treat an established spontaneous tumor was evaluated in the Transgenic Adenocarcinoma of Mouse Prostate (TRAMP) mouse, using the SV40 large T Ag (TAg) as a model tumor/self Ag. Repeated vaccination elicited vigorous TAg-specific CTL activity in nontransgenic mice, but tumor-bearing TRAMP mice remained tolerant. Adoptive transfer of naïve splenocytes into TRAMP mice prior to the first vaccination restored TAg reactivity, and slowed tumor progression. The data from this study suggests that vaccination with TAA mRNA is a simple and effective means of priming antitumor CTL, and that immunogenicity of the vaccine can be augmented by co-delivery of GM-CSF mRNA. Nonetheless, limitations of such vaccines in overcoming tolerance to tumor/self Ag may mandate prior or simultaneous reconstitution of the autoreactive T cell repertoire for this form of immunization to be effective.

Effective transfection of cells with multi-shell calcium phosphate-DNA nanoparticles

Coated calcium phosphate nanoparticles were prepared for cell transfection. A calcium phosphate nanoparticle served as core which was then coated with DNA for colloidal stabilisation. The efficiency of transfection could be considerably increased by adding another layer of calcium phosphate on the surface, thereby incorporating DNA into the particle and preventing its degradation within the cell by lysosomes. A subsequent outermost layer of DNA on the calcium phosphate gave a colloidal stabilisation. The efficiency of such multi-shell particles was significantly higher than that of simple DNA-coated calcium phosphate nanoparticles. The transfection efficiency of EGFP-encoding DNA was tested with different cell lines (T-HUVEC, HeLa, and LTK). The dispersions were stable and could be used for transfection after 2 weeks of storage at 4 degrees C without loss of efficiency.

Efficient Gene Transfer into Macrophages and Dendritic Cells by in Vivo Gene Delivery with Mannosylated Lipoplex via the Intraperitoneal Route

In this study, we developed an antigen-presenting cell (APC)-selective intraperitoneal (i.p.) gene delivery system with mannosylated cationic liposomes (Man-liposomes)/plasmid DNA complex (Man-lipoplex). An in vitro study using cultured peritoneal macrophages demonstrated that Man-liposomes could transfect luciferase-encoding plasmid DNA (pCMV-Luc) more efficiently than cationic liposomes via a mannose receptor-mediated mechanism. In vivo gene transfection studies revealed that Man-lipoplex showed a higher gene expression in the liver, spleen, peritoneal exuded cells, and mesenteric lymph nodes than cationic liposomes/plasmid DNA complex (lipoplex) or naked pCMV-Luc after i.p. administration, and this gene expression lasted for at least 24 h. The transfection activity of Man-lipoplex after i.p. administration was significantly higher than that after i.v. gene delivery with the Man-liposomes we developed previously, indicating that gene delivery via the i.p. route seems to be an efficient approach for in vivo gene delivery to APCs. Furthermore, it was demonstrated that Man-lipoplex could enhance gene expression in both F4/80+ and CD11c+ cells in the spleen. These results show that gene delivery with Man-liposomes via the i.p. route could be an effective approach for APC-selective gene transfection.

An interferon gamma-gp120 fusion delivered as a DNA vaccine induces enhanced priming

Nucleic acid vaccination has many potential advantages over traditional methods, but suffers from the fact that DNA vaccines tend to be relatively poorly immunogenic. Attempts to enhance DNA vaccine immunogenicity have included the addition of cytokine-encoding plasmids into the formulation, as well as the use of heterologous prime-boost regimes and the addition of conventional adjuvants, such as alum. We have previously shown that interferon gamma fusions have enhanced immunogenicity as recombinant protein vaccines. We have assessed here the immunogenicity of an interferon gamma-gp120 fusion delivered as a DNA vaccine, in the context of a prime-boost strategy and in the presence of absence of aluminium phosphate. Fusion of gp120 DNA to interferon gamma-encoding DNA resulted in strongly enhanced priming, especially of Th1 responses, including IgG2a responses to a protein boost.

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.

Plasmid vaccines and therapeutics: from design to applications

In the late 1980s, Vical and collaborators discovered that the injection into tissues of unformulated plasmid encoding various proteins resulted in the uptake of the plasmid by cells and expression of the encoded proteins. After this discovery, a period of technological improvements in plasmid delivery and expression and in pharmaceutical and manufacturing development was quickly followed by a plethora of human clinical trials testing the ability of injected plasmid to provide therapeutic benefits. In this chapter, we summarize in detail the technologies used in the most recent company-sponsored clinical trials and discuss the potential for future improvements in plasmid design, manufacturing, delivery, formulation and administration. A generic path for the clinical development of plasmid-based products is outlined and then exemplified using a case study on the development of a plasmid vaccine from concept to clinical trial.

Enhancement of immune responses by DNA vaccination through targeted gene delivery using mannosylated cationic liposome formulations following intravenous administration in mice

The present study investigated the potency of the mannosylated cationic liposomes (Man liposomes) that we have developed in novel DNA vaccine carrier. Ovalbumin (OVA) was selected as a model antigen for vaccination; accordingly, OVA-encoding pDNA (pCMV-OVA) was constructed to evaluate DNA vaccination. The potency of the Man liposome/pCMV-OVA complex was compared with naked pCMV-OVA and that complexed with DC-Chol liposomes. In cultured mouse peritoneal macrophages, MHC class I-restricted antigen presentation of the Man liposome/pCMV-OVA complex was significantly higher than that of naked pCMV-OVA and that complexed with DC-Chol liposomes. After intravenous administration, OVA mRNA expression and MHC class I-restricted antigen presentation on CD11c+ cells and inflammatory cytokines, such as TNF-alpha, IL-12, and IFN-gamma, that can enhance the Th1 response of the Man liposome/pCMV-OVA complex were higher than that of naked pCMV-OVA and that complexed with DC-Chol liposomes. Also, the spleen cells from mice immunized by intravenous administration of the Man liposome/pCMV-OVA complex showed the highest proliferation response and IFN-gamma secretion. These findings suggest that the targeted delivery of DNA vaccine by Man liposomes is a potent vaccination method for DNA vaccine therapy.

Peptides containing antigenic and cationic domains have enhanced, multivalent immunogenicity when bound to DNA vaccines

We explored strategies to codeliver DNA- and peptide-based vaccines in a way that enhances the immunogenicity of both components of the combination vaccine for T cells. Specific CD8(+) T cell responses to an antigenic peptide are primed when the peptide is fused to a cationic peptide domain that is bound to plasmid DNA or oligonucleotides (ODN; with or without CpG motifs). Plasmid DNA mixed with antigenic/cationic peptides or histones forms large complexes with different biological properties depending on the molar ratios of peptide/protein and polynucleotide. Complexes containing high (but not low) molar ratios of cationic peptide to DNA facilitate transfection (DNA uptake and expression of the plasmid-encoded product) of cells. In contrast, complexes containing low (but not high) molar ratios of cationic peptide to DNA prime potent multispecific T cell responses after a single intramuscular injection of the complexes. The general validity of this observation was confirmed mixing different antigenic/cationic peptides with different DNA vaccines. In these vaccine formulations, multispecific CD8(+) T cell responses specific for epitopes of the peptide- as well as the DNA-based vaccine were efficiently coprimed, together with humoral antibody responses to conformational determinants of large viral antigens encoded by the DNA vaccine. The data indicate that mixtures of DNA vaccines with antigenic, cationic peptides are immunogenic vaccine formulations particularly suited for the induction of multispecific T cell responses.

Mechanisms of increased immunogenicity for DNA-based vaccines adsorbed onto cationic microparticles

Investigation into the mechanism of action of vaccine adjuvants provides opportunities to define basic immune principles underlying the induction of strong immune responses and insights useful for the rational development of subunit vaccines. A novel HIV vaccine composed of plasmid DNA-encoding p55 gag formulated with poly-lactide-co-glycolide microparticles (PLG) and cetyl trimethyl ammonium bromide (CTAB) elicits both serum antibody titers and cytotoxic lymphocyte activity in mice at doses two orders of magnitude lower than those required for comparable response to plasmid DNA in saline. Using this model, we demonstrated the increase in potency requires the DNA to be complexed to the PLG-CTAB microparticles. Furthermore, the PLG-CTAB-DNA formulation increased the persistence of DNA at the injection site, recruited mononuclear phagocytes to the site of injection, and activated a population of antigen presenting cells. Intramuscular immunization with the PLG-CTAB-DNA complex induced antigen expression at both the injection site and the draining lymph node. These findings demonstrate that the PLG-CTAB-DNA formulation exhibits multiple mechanisms of immunopotentiation.

A DNA vaccine containing inverted terminal repeats from adeno-associated virus increases immunity to HIV

BACKGROUND

DNA vaccines have been used to induce both humoral and cellular immune responses against infectious microorganisms. This study explores whether DNA vaccine immunogenicity can be improved by introducing inverted terminal repeats (ITRs) from adeno-associated virus (AAV) into the regulatory region of the DNA plasmid.

METHODS

CMV promoter-driven HIV Env expressing plasmid (pCMV-HIV) and the pCMV-HIV plasmid introduced ITRs (pITR/CMV-HIV) were transfected in HEK293 cells with LipofectAmine. The HIV Env expression was quantified with Western blot. Fifty micro g of pCMV-HIV or pITR/CMV-HIV plasmid with RIBI adjuvant were immunized to BALB/c mice on days 0, 14 and 28 by intramuscular route, and HIV-specific serum IgG titer was detected 2, 6, 10, 14 and 18 weeks after the first immunization. HIV-specific tetramer assay and HIV-specific IFN-gamma ELIspot assay were performed 1 week after the last immunization. The immune mice were intravenously challenged with a vaccinia virus expressing the HIV env gene 1 week after the last immunization.

RESULTS

Significantly higher level of HIV Env expression was achieved by pITR/CMV-HIV plasmid. BALB/c mice immunized with pITR/CMV-HIV plasmid generated significantly higher HIV-specific antibody, higher cellular immune responses and lower viral loading than animals immunized with pCMV-HIV plasmid.

CONCLUSIONS

AAV ITRs enhance CMV-dependent up-regulation of transgene expression and immunogenicity of DNA vaccine.

A New Potent Route of DNA Vaccine Inoculation: DNA-Liposome Complexes on Bare Skin Induce Antigen-Special Antibody Responses

Transcutaneous immunization is a novel strategy for genetic vaccine immunization to induce detectable antigen-special antibody in humor and mucosal. In this study, plasmid expressing hepatitis B surface antigen (pGFP-HBsAg) was encapsulated in liposome, then DNA-liposome complexes were glued on bare skin of mice ear in different dosage (50μg, 10μg and 1μg). As control, DNA-liposome complexes of pGFP-HBsAg and pGFP vector were inoculated intraperitoneally. The anti-HBsAg antibodies of serum were detected weekly by ELISA. It was found that the detectable antibodies of transcutaneous immunized mouse were elicited after four weeks, and reached a maximum at the sixth week. Even 1μg plasmid DNA in liposomes through immune skin can elicit the highest ELISA antibody titer (> 1:512) in test group, and corresponding percentage of positive response is up to 71% at sixth week, but higher amounts of plasmid DNA (50μg DNA per mice) on immune skin cannot induce higher antibody levels. The result showed that DNA-liposome complexes glued on bare skin appear to be a novel method for the administration of DNA vaccines.

Diagnosis and management of human cytomegalovirus infection in the mother, fetus, and newborn infant

Human cytomegalovirus (HCMV) is the leading cause of congenital viral infection and mental retardation. HCMV infection, while causing asymptomatic infections in most immunocompetent subjects, can be transmitted during pregnancy from the mother with primary (and also recurrent) infection to the fetus. Hence, careful diagnosis of primary infection is required in the pregnant woman based on the most sensitive serologic assays (immunoglobulin M [IgM] and IgG avidity assays) and conventional virologic and molecular procedures for virus detection in blood. Maternal prognostic markers of fetal infection are still under investigation. If primary infection is diagnosed in a timely manner, prenatal diagnosis can be offered, including the search for virus and virus components in fetal blood and amniotic fluid, with fetal prognostic markers of HCMV disease still to be defined. However, the final step for definite diagnosis of congenital HCMV infection is detection of virus in the blood or urine in the first 1 to 2 weeks of life. To date, treatment of congenital infection with antiviral drugs is only palliative both prior to and after birth, whereas the only efficacious preventive measure seems to be the development of a safe and immunogenic vaccine, including recombinant, subunit, DNA, and peptide-based vaccines now under investigation. The following controversial issues are discussed in the light of the most recent advances in the field: the actual perception of the problem; universal serologic screening before pregnancy; the impact of correct counseling on decision making by the couple involved; the role of prenatal diagnosis in ascertaining transmission of virus to the fetus; the impact of preconceptional and periconceptional infections on the prevalence of congenital infection; and the prevalence of congenitally infected babies born to mothers who were immune prior to pregnancy compared to the number born to mothers undergoing primary infection during pregnancy.

Salivary gland delivery of pDNA-cationic lipoplexes elicits systemic immune responses

OBJECTIVE

To test the ability of two cationic lipoplexes, Vaxfectin and GAP-DLRIE/DOPE, to facilitate transfection and elicit immune responses from plasmid DNAs (pDNAs) after retrograde instillation into salivary glands.

METHODS

Two pDNA expression vectors encoding either the influenza NP protein or human growth hormone (hGH) were complexed with the cationic lipid transfection reagents, GAP-DLRIE/DOPE or Vaxfectin, and delivered to the submandibular glands of rats. Samples from rats receiving the influenza NP protein pDNA and cationic lipoplexes were analyzed for anti-influenza NP-specific IgG1, IgG2a, and IgG2b in serum, and IgA in saliva, by an enzyme- linked immunosorbent assay (ELISA). Cytotoxic T-cell lymphocyte (CTL) assays were also performed. Transgene protein expression (hGH) was determined from extracts of submandibular glands of rats receiving hGH lipoplexes.

RESULTS

Serum antibodies (IgG) against the NP protein developed and were highest in all rats vaccinated with GAP-DLRIE/DOPE or Vaxfectin. The major serum IgG subclass stimulated by this route of immunization was IgG2b, followed by IgG2a. CTL assay results showed statistically significantly higher percentage killing in the Vaxfectin group than controls (P < 0.05). No rats developed IgA antibodies to NP protein in saliva. Animals receiving plasmid encoding hGH and either lipoplex expressed significantly higher amounts of hGH compared with those receiving the hGH plasmid and water. Although hGH expression was higher in the animals receiving pDNA/Vaxfectin (approximately 30-fold > pDNA/water), the difference with those receiving pDNA/GAP-DLRIE/DOPE (approximately 10-fold > pDNA/water) was not significant.

CONCLUSIONS

Retrograde instillation of pDNA complexed with Vaxfectin into the salivary glands can stimulate cytotoxic and humoral responses to the influenza NP protein antigen. Optimization of the conditions required to stimulate humoral and secretory antibody formation may facilitate use of this tissue for specific clinical applications of pDNA immunization.

Enhanced immune responses after DNA vaccination with combined envelope genes from different HIV-1 subtypes

In a multisubtype approach to HIV-1 vaccination, mice were immunized with HIV-1 envelope gp160 genes from subtypes A, B, and C. Subsequently the mice were challenged with syngeneic primary splenocytes infected with a HIV-1/MuLV pseudovirus carrying a subtype B genome. HIV-specific immune responses and protection were strongest in the group of animals immunized with a combination of subtype A, B, and C specific gp160 genes as compared to subtype B only. Immunization with the combination of the cross-reactive subtypes A and C envelope genes induced HIV-specific immune responses but did not result in significant protection to challenge with subtype B infected cells. From this we conclude that immunization with the envelope genes from several HIV-1 subtypes may indeed enhance immune responses. This study shows that by using a mix of subtype envelope genes, an enhanced protective immunity can be obtained experimentally, potentially also in humans.

Diagnosis and management of human cytomegalovirus infection in the mother, fetus, and newborn infant

Human cytomegalovirus (HCMV) is the leading cause of congenital viral infection and mental retardation. HCMV infection, while causing asymptomatic infections in most immunocompetent subjects, can be transmitted during pregnancy from the mother with primary (and also recurrent) infection to the fetus. Hence, careful diagnosis of primary infection is required in the pregnant woman based on the most sensitive serologic assays (immunoglobulin M [IgM] and IgG avidity assays) and conventional virologic and molecular procedures for virus detection in blood. Maternal prognostic markers of fetal infection are still under investigation. If primary infection is diagnosed in a timely manner, prenatal diagnosis can be offered, including the search for virus and virus components in fetal blood and amniotic fluid, with fetal prognostic markers of HCMV disease still to be defined. However, the final step for definite diagnosis of congenital HCMV infection is detection of virus in the blood or urine in the first 1 to 2 weeks of life. To date, treatment of congenital infection with antiviral drugs is only palliative both prior to and after birth, whereas the only efficacious preventive measure seems to be the development of a safe and immunogenic vaccine, including recombinant, subunit, DNA, and peptide-based vaccines now under investigation. The following controversial issues are discussed in the light of the most recent advances in the field: the actual perception of the problem; universal serologic screening before pregnancy; the impact of correct counseling on decision making by the couple involved; the role of prenatal diagnosis in ascertaining transmission of virus to the fetus; the impact of preconceptional and periconceptional infections on the prevalence of congenital infection; and the prevalence of congenitally infected babies born to mothers who were immune prior to pregnancy compared to the number born to mothers undergoing primary infection during pregnancy.

Vaccine development against HIV-1: current perspectives and future directions

The development of an efficacious vaccine against the human immunodeficiency virus (HIV) is of great urgency, because it is accepted that vaccination is the only means capable of controlling the AIDS pandemic. The foundation of HIV vaccine development is the analysis of immune responses during natural infection and the utilization of this knowledge for the development of protective immunization strategies. Initial vaccine development and experimentation are usually in animal models, including murine, feline, and nonhuman primates. Experimental vaccine candidates are closely studied for both efficacy and safety before proceeding to human clinical trials. There are a number of different therapeutic and prophylactic vaccine strategies currently being studied in human clinical trials. Vaccine strategies that are being tested, or have previously been tested, in humans include subunit, DNA plasmid, and viral vector, and combinations of these various strategies. Some of the results of these trials are promising, and additional research has focused on the development of appropriate chemical and genetic adjuvants as well as methods of vaccine delivery to improve the host immune response. This review summarizes the vaccine strategies that have been tested in both animal models and human clinical trials.

Synergy between cationic lipid and co-lipid determines the macroscopic structure and transfection activity of lipoplexes

The large number of cytofectin and co-lipid combinations currently used for lipoplex-mediated gene delivery reflects the fact that the optimal cytofectin/co-lipid combination varies with the application. The effects of structural changes in both cytofectin and co-lipid were systematically examined to identify structure-activity relationships. Specifically, alkyl chain length, degree of unsaturation and the head group to which the alkyl side chain was attached were examined to determine their effect on lipoplex structure and biological activity. The macroscopic lipoplex structure was assessed using a dye-binding assay and the biological activity was examined using in vitro transfection in three diverse cell lines. Lipoplexes were formulated in three different vehicles currently in use for in vivo delivery of naked plasmid DNA (pDNA) and lipoplex formulations. The changes in dye accessibility were consistent with structural changes in the lipoplex, which correlated with alterations in the formulation. In contrast, transfection activity of different lipoplexes was cell type and vehicle dependent and did not correlate with dye accessibility. Overall, the results show a correlation between transfection and enhanced membrane fluidity in both the lipoplex and cellular membranes.

Immunization strategies to augment oral vaccination with DNA and viral vectors expressing HIV envelope glycoprotein

Induction of mucosal immunity to the human immunodeficiency virus (HIV) envelope (env; gp160) glycoprotein has been demonstrated with orally administered recombinant vaccinia virus (rVV) vectors and poly(DL-lactide-co-glycolide) (PLG)-encapsulated plasmid DNA expressing gp160. In this study, we investigated the effect of an oral DNA-prime/rVV-boost vaccine regimen in conjunction with adjuvants on the level of gp160-specific cellular and humoral responses in BALB/c mice. We demonstrated that DNA priming followed by a booster with rVV expressing gp160 (vPE16) significantly augmented env-specific immunity in systemic and mucosal tissues of the immunized mice. Association of vPE16 with liposomes and coadministration of liposome-associated beta-glucan lentinan or IL-2/Ig-encoded plasmid DNA-encapsulated in PLG microparticles triggered the optimal cell-mediated immune (CMI) responses. Lentinan was found to increase env-specific type 1 cytokine production and cytotoxic T-lymphocyte (CTL) activities but had no effect on humoral responses. On the other hand, IL-2/Ig-mediated increases in both type 1 and 2 activities were associated with higher levels of env-specific CTL and antibody responses. Results of these studies demonstrated the effectiveness of oral vaccines with DNA and rVV vectors in conjunction with immunomodulators in inducing specific immune responses in systemic and mucosal tissues.

DNA vaccines: future strategies and relevance to intracellular pathogens

Increasing awareness of microbial threat has rekindled interest in the great potential of vaccines for controlling infectious diseases. The fact that diseases caused by intracellular pathogens cannot be overcome by chemotherapy alone has increased our interest in the generation of highly efficacious novel vaccines. Vaccines have proven their efficacy, as the immunoprotection they induce appears to be mediated by long-lived humoral immune responses. However, there are no consistently effective vaccines available against diseases such as tuberculosis and HIV, and other infections caused by intracellular pathogens, which are predominantly controlled by T lymphocytes. This review describes the T-cell populations and the type of immunity that should be activated by successful DNA vaccines against intracellular pathogens. It further discusses the parameters that need to be fulfilled by protective T-cell Ag. We then discuss future approaches for DNA vaccination against diseases in which cell-mediated immune responses are essential for providing protection.

Efficient delivery of Antennapedia homeodomain fused to CTL epitope with liposomes into dendritic cells results in the activation of CD8+ T cells

The in vivo induction of a CTL response using Antennapedia homeodomain (AntpHD) fused to a poorly immunogenic CTL epitope requires that the Ag is given in presence of SDS, an unacceptable adjuvant for human use. In the present report, we developed a hybrid CTL epitope delivery system consisting of AntpHD peptide vector formulated in liposomes as an alternative approach to bypass the need for SDS. It is proposed that liposomes will prevent degradation of the Ag in vivo and will deliver AntpHD recombinant peptide to the cytosol of APCs. We show in this work that dendritic cells incubated with AntpHD-fused peptide in liposomes can present MHC class I-restricted peptide and induce CTL response with a minimal amount of Ag. Intracellular processing studies have shown that encapsulated AntpHD recombinant peptide is endocytized before entering the cytosol, where it is processed by the proteasome complex. The processed liposomal peptides are then transported to the endoplasmic reticulum. The increase of the CTL response induced by AntpHD-fused peptide in liposomes correlates with this active transport to the class I-processing pathway. In vivo studies demonstrated that positively charged liposomes increase the immunogenicity of AntpHD-Cw3 when injected s.c. in mice in comparison to SDS. Moreover, addition of CpG oligodeoxynucleotide immunostimulatory sequences further increase the CD8+ T cell response. This strategy combining lipid-based carriers with AntpHD peptide to target poorly immunogenic Ags into the MHC class I processing pathway represents a novel approach for CTL vaccines that may have important applications for development of cancer vaccines.

Immunologic characterization of HIV-specific DNA vaccine

We developed a method for applying HIV-1 DNA vaccine topically in mice. Topical application of DNA vaccine to the skin is useful against infections. To find a less expensive and less cumbersome vaccination method, we administered HIV-1 DNA vaccine to the skin of mice after elimination of keratinocytes using a fast-acting adhesive. HIV-1 DNA vaccine induced high levels of both humoral and cell-mediated immune activity against HIV-1 envelope antigen. A high level of HIV-1-specific cytotoxic T lymphocyte response was also observed, and a high level of IFN-gamma and IL-4 production was induced by the improved skin application of DNA vaccine. High levels of both HIV-specific cytotoxic T lymphocyte and delayed type hypersensitivity in topical application were induced by coadministration of the DNA vaccine with IL-12 expression plasmids and granulocyte-macrophage colony-stimulating factor expression plasmids. These immune responses were inhibited by intradermal injection of anti-CD11c or anti-I-A/I-E antibody. Therefore, topical administration of DNA vaccine is an effective route, and may be very useful for the prevention of infectious diseases.