Reactive oxygen species play a central role in the activity of cationic liposome based cancer vaccine

Potential applications of nanoparticles in cancer immunotherapy

In recent years considerable progress has been made in the field of cancer immunotherapy whereby treatments that modulate the body's own immune system are used to combat cancer. This has the potential to not only elicit strong anti-cancer immune responses which can break pre-existing tolerance and help promote tumor regression, but could also induce immunological memory which may help prevent tumor recurrence. In order to ensure effective delivery of immunotherapeutic agents, such as vaccines, checkpoint inhibitors, chemotherapeutic agents and nucleic acids, a safe and effective delivery system is often required. One such approach is the use of multifunctional nanoparticles (NPs), such as liposomes, polymers, micelles, dendrimers, inorganic NPs, and hybrid NPs, which have the potential to combine the delivery of a diverse range of therapeutic immunomodulators thereby increasing the efficacy of tumor cell killing. This review focuses on recent progress in NP-mediated immunotherapy for the treatment of cancer.

Mucosal Vaccine Development Based on Liposome Technology

Immune protection against infectious diseases is most effective if located at the portal of entry of the pathogen. Hence, there is an increasing demand for vaccine formulations that can induce strong protective immunity following oral, respiratory, or genital tract administration. At present, only few mucosal vaccines are found on the market, but recent technological advancements and a better understanding of the principles that govern priming of mucosal immune responses have contributed to a more optimistic view on the future of mucosal vaccines. Compared to live attenuated vaccines, subcomponent vaccines, most often protein-based, are considered safer, more stable, and less complicated to manufacture, but they require the addition of nontoxic and clinically safe adjuvants to be effective. In addition, another limiting factor is the large antigen dose that usually is required for mucosal vaccines. Therefore, the combination of mucosal adjuvants with the recent progress in nanoparticle technology provides an attractive solution to these problems. In particular, the liposome technology is ideal for combining protein antigen and adjuvant into an effective mucosal vaccine. Here, we describe and discuss recent progress in nanoparticle formulations using various types of liposomes that convey strong promise for the successful development of the next generation of mucosal vaccines.

Surfactin inducing mitochondria-dependent ROS to activate MAPKs, NF-κB and inflammasomes in macrophages for adjuvant activity

Surfactin, a natural lipopeptide, can be used both as parenteral and non-parenteral adjuvant for eliciting immune response. However, the mechanisms that confer its adjuvant properties have not been fully explored. By staining with NHS-Rhodamine B labeled surfactin and Mito-Tracker Green, we found surfactin could penetrate into macrophages to bind with mitochondria, following induce ROS that could be inhibited by mitochondria-dependent ROS inhibitor. ROS enhanced p38 MAPK and JNK expression, as well their phorsphorylation, following activated NF-κB nuclear translocation in macrophages that was obviously inhibited by mitochondria-dependent ROS inhibitor. However, inhibition of ROS production only weakened p38 MAPK and JNK expression, but not their phosphorylation in macrophages. As a result, surfaction could activate NF-κB to release TNF-α by the mitochondria-dependent ROS signalling pathway. ROS also induced macrophages apoptosis to release endogenous danger signals, following activated inflammasomes of NLRP1, NLRP3, IPAF and AIM2 in vitro and only NLRP1 in vivo, as well caspase-1 and IL-1 in macrophages, which were significantly inhibited by pre-treatment with ROS inhibitors. Collectively, surfactin as a kind of non-pathogen-associated molecular patterns, modulates host innate immunity by multiple signalling pathways, including induction of mitochondria-dependent ROS, activating MAPKs and NF-κB, and inducing cell apoptosis to realease endogenous danger signals for activation of inflammasomes.

Combining different types of multifunctional liposomes loaded with ammonium bicarbonate to fabricate microneedle arrays as a vaginal mucosal vaccine adjuvant-dual delivery system (VADDS)

To develop effective mucosal vaccines, two types of multifunctional liposomes, the mannosylated lipid A-liposomes (MLLs) with a size of 200nm and the stealth lipid A-liposomes (SLLs) of 50nm, both loaded with a model antigen and NH₄HCO₃, were fabricated together into microneedles, forming the proSLL/MLL-constituted microneedle array (proSMMA), which upon rehydration dissolved rapidly recovering the initial MLLs and SLLs. Mice vaccinated with proSMMAs by vaginal mucosa patching other than conventional intradermal administration established robust antigen-specific humoral and cellular immunity at both systemic and mucosal levels, especially, in the reproductive and intestinal ducts. Further exploration demonstrated that the MLLs reconstituted from the administered proSMMAs were mostly taken up by vaginal mucosal dendritic cells, whereas the recovered SLLs trafficked directly to draining lymph nodes wherein to be picked up by macrophages. Moreover, the antigens delivered by either liposomes were also cross-presented for MHC-I displaying by APCs thanks to lysosome escape and ROS (reactive oxygen species) stimulation, both of which occurred when lysosomal acidifying the liposome-released NH₄HCO₃ into CO₂ and NH₄⁺/NH₃ to rupture lysosomes by gas expansion and to cause ROS production by excessive ammonia induction, resulting in a mixed Th1/Th2 type response which was also promoted by liposomal lipid A via activation of TLR4. In addition, vaginal vaccination of the engineered HSV2 antigen gD-loaded proSMMAs successfully protected mice from the virus challenge. Thus, the proSMMAs are in fact a vaccine adjuvant-dual delivery system capable of eliciting robust humoral and cellular immunity against the invading pathogens, especially, the sexually transmitted ones.

Improved Antitumor Activity of a Therapeutic Melanoma Vaccine through the Use of the Dual COX-2/5-LO Inhibitor Licofelone

Immune-suppressive cell populations impair antitumor immunity and can contribute to the failure of immune therapeutic approaches. We hypothesized that the non-steroidal anti-inflammatory drug licofelone, a dual cyclooxygenase-2/5-LO inhibitor, would improve therapeutic melanoma vaccination by reducing immune-suppressive cell populations. Therefore, licofelone was administered after tumor implantation, either alone or in combination with a peptide vaccine containing a long tyrosinase-related protein 2-peptide and the adjuvant α-galactosylceramide, all formulated into cationic liposomes. Mice immunized with the long-peptide vaccine and licofelone showed delayed tumor growth compared to mice given the vaccine alone. This protection was associated with a lower frequency of immature myeloid cells (IMCs) in the bone marrow (BM) and spleen of tumor-inoculated mice. When investigating the effect of licofelone on IMCs in vitro, we found that the prostaglandin E₂-induced generation of IMCs was decreased in the presence of licofelone. Furthermore, pre-incubation of BM cells differentiated under IMC-inducing conditions with licofelone reduced the secretion of cytokines interleukin (IL)-10 and -6 upon lipopolysaccharides (LPS) stimulation as compared to untreated cells. Interestingly, licofelone increased IL-6 and IL-10 secretion when administered after the LPS stimulus, demonstrating an environment-dependent effect of licofelone. Our findings support the use of licofelone to reduce tumor-promoting cell populations.

Biomaterials-Based Vaccination Strategies for the Induction of CD8+T Cell Responses

Natural and synthetic biomaterials are increasingly being used for the development of vaccines and immunotherapies as alternatives to traditional live-attenuated formulations due to their improved safety profiles and no risk of reversion to virulence. Polymeric materials in particular enjoy attention due to the ease of fabrication, control over physicochemical properties, and their wide range of immunogenicity. While the majority of studies focus on inducing protective antibody responses, in recent years, materials-based strategies for the delivery of antigens and immunomodulators to improve CD8⁺T cell immunity against infectious and non-infectious diseases have gained momentum. Notably, platforms based on polymeric nanoparticles, liposomes, micelles, virus-like particles, self-assembling peptides and peptidomimetics, and multilayer thin films show considerable promise in preclinical studies. In this Review, we first introduce the concepts of CD8⁺T cell activation, effector and memory functions, and cytotoxic activity, followed by vaccine design for eliciting robust and protective long-lived CD8⁺T cell immunity. We then discuss different materials-based vaccines developed in the past decade to elicit CD8⁺T cell responses based on molecular composition or fabrication methods and conclude with a summary and glimpse at the future trends in this area.

Mitochondrion: A Promising Target for Nanoparticle-Based Vaccine Delivery Systems

Vaccination is one of the most popular technologies in disease prevention and eradication. It is promising to improve immunization efficiency by using vectors and/or adjuvant delivery systems. Nanoparticle (NP)-based delivery systems have attracted increasing interest due to enhancement of antigen uptake via prevention of vaccine degradation in the biological environment and the intrinsic immune-stimulatory properties of the materials. Mitochondria play paramount roles in cell life and death and are promising targets for vaccine delivery systems to effectively induce immune responses. In this review, we focus on NPs-based delivery systems with surfaces that can be manipulated by using mitochondria targeting moieties for intervention in health and disease.

Application of nanostructured drug delivery systems in immunotherapy of cancer: a review

The cancer immunotherapy method uses the specificity of the immune system to provide a more effective than more conventional treatments, such as chemotherapy and radiotherapy. Immunotherapy has two main strategies (passive or active) to organize the immune system. Passive strategies use advantage of tumor-hyperpermeable cells, which have enhanced permeability and retention effects. Nanoparticles due to their better accumulation within tissues and cells of the immune system are well suitable for delivery of immune therapies such as vaccines or adjuvants. In this review, we explained application of nanotechnology in immunotherapy of cancer.

Hyaluronic Acid-Modified Cationic Lipid-PLGA Hybrid Nanoparticles as a Nanovaccine Induce Robust Humoral and Cellular Immune Responses

Here, we investigated the use of hyaluronic acid (HA)-decorated cationic lipid-poly(lactide-co-glycolide) acid (PLGA) hybrid nanoparticles (HA-DOTAP-PLGA NPs) as vaccine delivery vehicles, which were originally developed for the cytosolic delivery of genes. Our results demonstrated that after the NPs uptake by dendritic cells (DCs), some of the antigens that were encapsulated in HA-DOTAP-PLGA NPs escaped to the cytosolic compartment, and whereas some of the antigens remained in the endosomal/lysosomal compartment, where both MHC-I and MHC-II antigen presentation occurred. Moreover, HA-DOTAP-PLGA NPs led to the up-regulation of MHC, costimulatory molecules, and cytokines. In vivo experiments further revealed that more powerful immune responses were induced from mice immunized with HA-DOTAP-PLGA NPs when compared with cationic lipid-PLGA nanoparticles and free ovalbumin (OVA); the responses included antigen-specific CD4(+) and CD8(+) T-cell responses, the production of antigen-specific IgG antibodies and the generation of memory CD4(+) and CD8(+) T cells. Overall, these data demonstrate the high potential of HA-DOTAP-PLGA NPs for use as vaccine delivery vehicles to elevate cellular and humoral immune responses.

Nanotechnology: Future of Oncotherapy

Recent advances in nanotechnology have established its importance in several areas including medicine. The myriad of applications in oncology range from detection and diagnosis to drug delivery and treatment. Although nanotechnology has attracted a lot of attention, the practical application of nanotechnology to clinical cancer care is still in its infancy. This review summarizes the role that nanotechnology has played in improving cancer therapy, its potential for affecting all aspects of cancer care, and the challenges that must be overcome to realize its full promise.

A novel liposomal recombinant lipoimmunogen enhances anti-tumor immunity

Synthetic liposomes provide a biocompatible and biodegradable approach for delivering drugs and antigens. In addition, self-adjuvanting recombinant lipoproteins (rlipoproteins) can enhance Th1 anti-tumor immune responses via the TLR2 signaling pathway. To generate a liposomal rlipoprotein for a cancer immunotherapeutic vaccine, we assessed 3 types of synthetic liposomes for use with the rlipoproteins rlipoE7m and rlipoOVA. We determined that the cationic liposome DOTAP could stabilize anionic rlipoproteins and delay rlipoprotein release. Surprisingly, rlipoproteins and DOTAP could synergistically up-regulate CD83 expression in bone marrow-derived dendritic cells (BMDCs). Compared with other liposome formulations, the rlipoprotein/DOTAP formulation elicited higher cytotoxic T-lymphocyte (CTL) responses. To explore the mechanism of BMDC activation by rlipoprotein/DOTAP, we assessed the production of reactive oxygen species (ROS) and the TNF-α secretion of BMDCs. We observed that rlipoprotein/DOTAP induced ROS to the same extent as DOTAP did. In addition, TLR2 signaling was also required for the TNF-α secretion of rlipoprotein/DOTAP-treated BMDCs. Moreover, compared with rlipoOVA-treated BMDCs, rlipoOVA/DOTAP-treated BMDCs increased the levels of IFN-γ produced by OVA-specific T cells. We also observed that rlipoE7m/DOTAP treatment but not rlipoE7m treatment delayed tumor growth. These results indicate that the rlipoprotein/DOTAP formulation can synergistically activate BMDCs via ROS and the TLR2 signaling pathway. In summary, rlipoprotein/DOTAP is a novel and stable formulation for cancer immunotherapy.

Fusogenic Reactive Oxygen Species Triggered Charge-Reversal Vector for Effective Gene Delivery

A novel fusogenic lipidic polyplex (FLPP) vector is designed to fuse with cell membranes, mimicking viropexis, and eject the polyplex into the cytosol, where the cationic polymer is subsequently oxidized by intracellular reactive oxygen species and converts to being negatively charged, efficiently releasing the DNA. The vector delivering suicide gene achieves significantly better inhibition of tumor growth than doxorubicin.

Effect of Quercetin-loaded liposomes on induced oxidative stress in human spermatozoa

A strategy to circumvent the poor polyphenols bioavailability is to load these compounds into liposomes. We evaluated the in vitro effects of quercetin (Q) and Q-loaded liposomes (QLL, 30, 50, 100μM) on motility, viability and chromatin integrity of swim-up selected human sperm. Antioxidant power was assayed against tert-butylhydroperoxide induced lipid peroxidation (LPO) using C11-BODIPY581/591 fluorescent probe and transmission electron microscopy. QLL showed decreased toxicity for sperm motility and viability and increased DNA damage compared to Q. The percentage of sperm with fluorescence, marker of LPO, was decreased in samples incubated with Q vs QLL (P<0.001). The ultrastructure of acrosomes and membranes was preserved with Q 30/100μM, whereas QLL did not prevent membrane injury. Q alone appeared more effective than Q incorporated into liposomes; however liposomes could be considered as carriers that may convey different compounds inside sperm; they may therefore represent a field of research rich of many applications.

Synthetic TRP2 long-peptide and α-galactosylceramide formulated into cationic liposomes elicit CD8+ T-cell responses and prevent tumour progression

The lipid antigen α-galactosylceramide (α-GalCer) is a potent activator of invariant natural killer T-cells (iNKT cells) and can stimulate cytotoxic and anti-tumour immune responses. However optimal responses appear to be induced by α-GalCer when cell-based vaccines are delivered intravenously. Here we investigated if co-delivery of protein and peptide antigens along with α-GalCer in a liposomal formulation could stimulate therapeutic anti-tumour immune responses. Cationic liposomes were inherently immune-stimulatory and induced cytotoxic immune responses when delivered both by intravenous and subcutaneous injection. However, only vaccine delivered intravenously stimulated therapeutic anti-tumour immune responses to a peptide antigen. Surface modification with polyethylene glycol (PEG) did not improve immune responses to either intravenously or subcutaneously delivered vaccines. Immune responses to short and long peptide sequences (CD8 and CD4 epitopes) of the self-antigen tyrosinase-related protein 2 (TRP2) as a vaccine antigen, co-delivered with α-GalCer in either cationic liposomes or PBS were further examined. Enhanced production of IFN-γ, increased cytotoxic T-cell responses and tumour survival were observed when a long TRP2-peptide was delivered with α-GalCer in cationic liposomes.

Cationic liposome-hyaluronic acid hybrid nanoparticles for intranasal vaccination with subunit antigens

Here we report the development of a new cationic liposome-hyaluronic acid (HA) hybrid nanoparticle (NP) system and present our characterization of these NPs as an intranasal vaccine platform using a model antigen and F1-V, a candidate recombinant antigen for Yersinia pestis, the causative agent of plague. Incubation of cationic liposomes composed of DOTAP and DOPE with anionic HA biopolymer led to efficient ionic complexation and formation of homogenous liposome-polymer hybrid NPs, as evidenced by fluorescence resonance energy transfer, dynamic light scattering, and nanoparticle tracking analyses. Incorporation of cationic liposomes with thiolated HA allowed for facile surface decoration of NPs with thiol-PEG, resulting in the formation of DOTAP/HA core-PEG shell nanostructures. These NPs, termed DOTAP-HA NPs, exhibited improved colloidal stability and prolonged antigen release. In addition, cytotoxicity associated with DOTAP liposomes (LC50~0.2mg/ml) was significantly reduced by at least 20-fold with DOTAP-HA NPs (LC50>4mg/ml), as measured with bone marrow derived dendritic cells (BMDCs). Furthermore, NPs co-loaded with ovalbumin (OVA) and a molecular adjuvant, monophosphoryl lipid A (MPLA) promoted BMDC maturation and upregulation of co-stimulatory markers, including CD40, CD86, and MHC-II, and C57BL/6 mice vaccinated with NPs via intranasal route generated robust OVA-specific CD8(+) T cell and antibody responses. Importantly, intranasal vaccination with NPs co-loaded with F1-V and MPLA induced potent humoral immune responses with 11-, 23-, and 15-fold increases in F1-V-specific total IgG, IgG1, and IgG2c titers in immune sera by day 77, respectively, and induced balanced Th1/Th2 humoral immune responses, whereas mice immunized with the equivalent doses of soluble F1-V vaccine failed to achieve sero-conversion. Overall, these results suggest that liposome-polymer hybrid NPs may serve as a promising vaccine delivery platform for intranasal vaccination against Y. pestis and other infectious pathogens.

Phagocyte NADPH oxidase and specific immunity

The phagocyte NADPH oxidase NOX2 produces reactive oxygen species (ROS) and is a well-known player in host defence. However, there is also increasing evidence for a regulatory role of NOX2 in adaptive immunity. Deficiency in phagocyte NADPH oxidase causes chronic granulomatous disease (CGD) in humans, a condition that can also be studied in CGD mice. Clinical observations in CGD patients suggest a higher susceptibility to autoimmune diseases, in particular lupus, idiopathic thrombocytopenic purpura and rheumatoid arthritis. In mice, a strong correlation exists between a polymorphism in a NOX2 subunit and the development of autoimmune arthritis. NOX2 deficiency in mice also favours lupus development. Both CGD patients and CGD mice exhibit increased levels of immunoglobulins, including autoantibodies. Despite these phenotypes suggesting a role for NOX2 in specific immunity, mechanistic explanations for the typical increase of CGD in autoimmune disease and antibody levels are still preliminary. NOX2-dependent ROS generation is well documented for dendritic cells and B-lymphocytes. It is unclear whether T-lymphocytes produce ROS themselves or whether they are exposed to ROS derived from dendritic cells during the process of antigen presentation. ROS are signalling molecules in virtually any cell type, including T- and B-lymphocytes. However, knowledge about the impact of ROS-dependent signalling on T- and B-lymphocyte phenotype and response is still limited. ROS might contribute to Th1/Th2/Th17 cell fate decisions during T-lymphocyte activation and might enhance immunoglobulin production by B-lymphocytes. In dendritic cells, NOX2-derived ROS might be important for antigen processing and cell activation.

Modulating polyplex-mediated gene transfection by small-molecule regulators of autophagy

Nonviral gene transfection mediated by cationic polymer/DNA polyplexes often imposes stress and toxicity to cells. To better understand the relationship between cellular stress responses and polyplex-mediated transfection, polyplex-induced early autophagy in mouse fibroblasts was characterized and the impact of autophagy modulation on transgene expression evaluated. Transmission electron microscopy revealed the formation of double-membraned autophagosome in the cytoplasm of polyplex-transfected cells. Immunofluorescence staining and microscopy revealed intracellular LC3 punctation that was characteristic of early autophagy activation. Elevated expression of autophagosome-associated LC3 II protein was also detected by Western blot. When cells were treated with small-molecule modulators of autophagy, polyplex-mediated gene transfection efficiency was significantly affected. 3-Methyladenine (3-MA), an early autophagy inhibitor, reduced transfection efficiency, whereas rapamycin, an autophagy inducer, enhanced transgene expression. Importantly, the observed functional impact on gene transfection by autophagy modulation was decoupled from that of other modes of cellular stress response (apoptosis/necrosis). Treatment of cells by 3-MA or rapamycin did not affect the level of intracellular reactive oxygen species (ROS) but did decrease or increase, respectively, nuclear localization of polyplex-delivered plasmid DNA. These findings suggest new possibilities of enhancing polyplex-mediated gene delivery by codelivery of small-molecule regulators of autophagy.

Cationic liposomes loaded with a synthetic long peptide and poly(I:C): a defined adjuvanted vaccine for induction of antigen-specific T cell cytotoxicity

For effective cancer immunotherapy by vaccination, co-delivery of tumour antigens and adjuvants to dendritic cells and subsequent activation of antigen-specific cytotoxic T cells (CTLs) is crucial. In this study, a synthetic long peptide (SLP) harbouring the model CTL epitope SIINFEKL was encapsulated with the TLR3 ligand poly(inosinic-polycytidylic acid) (poly(I:C)) in cationic liposomes consisting of DOTAP and DOPC. The obtained particles were down-sized to about 140 nm (measured by dynamic light scattering) and had a positive zeta-potential of about 26 mV (according to laser Doppler electrophoresis). SLP loading efficiency was about 40% as determined by HPLC. Poly(I:C) loading efficiency was about 50%, as assessed from the fluorescence intensity of fluorescently labelled poly(I:C). Immunogenicity of the liposomal SLP vaccine was evaluated in vitro by its capacity to activate dendritic cells (DCs) and present the processed SLP to SIINFEKL-specific T cells. The effectiveness of the vaccine to activate CD8(+) T cells was analysed in vivo after intradermal and subcutaneous immunisation in mice, by measuring antigen-specific T cells in blood and spleens and assessing their functionality by cytokine production and in vivo cytotoxicity. The liposomal formulation efficiently delivered the SLP to DCs in vitro and induced a functional CD8(+) T cell immune response in vivo to the CTL epitope present in the SLP. The SLP-specific CD8(+) T cell frequency induced by the poly(I:C)-adjuvanted liposomal SLP formulation showed an at least 25 fold increase over the T cell frequency induced by the poly(I:C)-adjuvanted soluble SLP. In conclusion, cationic liposomes loaded with SLP and poly(I:C) have potential as a powerful therapeutic cancer vaccine formulation.

A new adjuvant delivery system 'cyclic di-GMP/YSK05 liposome' for cancer immunotherapy

Cyclic dinucleotides are of importance in the field of microbiology and immunology. They function as second messengers and are thought to participate in the signal transduction of cytosolic DNA immune responses. One such dinucleotide, cyclic di-GMP (c-di-GMP), stimulates the immune system. It is thought that c-di-GMP is recognized by ATP dependent RNA helicase (DDX41) in the cytosol, forms a complex with the Stimulator of interferon genes protein (STING), triggers a signal via the tank binding kinase 1-interferon regulatory factor 3 (TBK1-IRF3) pathway and induces the production of type I interferons. Therefore c-di-GMP can be thought of as a new class of adjuvant. However, because c-di-GMP contains two phosphate groups, this prevents its use as an adjuvant because it cannot pass through the cell membrane, even though the target molecule of c-di-GMP is located in the cytoplasm. Our group has been developing a series of liposomal drug delivery systems and recently investigated YSK05 which is a synthetic, pH sensitive lipid that has a high fusogenicity. We utilized this lipid as a carrier to transport c-di-GMP into the cytosol to then use c-di-GMP as an adjuvant. Based on screening experiments, YSK05/POPE/cholesterol=40/25/35 was found to induce IFN-β in Raw264.7 cells. The induction of IFN-β from c-di-GMP liposomes was inhibited by adding BX795, a TBK1 inhibitor, indicating that the production of IFN-β caused the activation of the STING-TBK1 pathway. C-di-GMP liposomes also showed significantly higher levels of expression of CD80, CD86 and MHC class I. The c-di-GMP/YSK05 liposome facilitated antigen specific cytotoxic T cell activity and the inhibition of tumor growth in a mouse model. These findings indicate that c-di-GMP/YSK05 liposomes could be used, not only to transfer c-di-GMP to the cytosol and induce an innate immune system but also as a platform for investigating the mechanism of immune sensing with cyclic dinucleotides in vitro and in vivo.

Induction of protection against leishmaniasis in susceptible BALB/c mice using simple DOTAP cationic nanoliposomes containing soluble Leishmania antigen (SLA)

A suitable adjuvant and delivery system are needed to develop an effective vaccine against leishmaniasis. To induce a Th1 type of response and protection in BALB/c mice against Leishmania major infection, 1,2-dioleoyl-3-trimethylammonium-propane (DOTAP) nanoliposomes bearing an intrinsic adjuvanticity, were used as an antigen delivery system and immunoadjuvant for soluble Leishmania antigens (SLA). DOTAP liposomes containing different concentrations of SLA were prepared by using lipid film method followed by sonication. The prepared vesicles showed a diameter of about 100nm, a positive zeta potential and approximately 70% encapsulation efficiency of SLA. BALB/c mice were immunized subcutaneously (SC), three times in a 3-week interval with different concentrations of liposomal SLA (12.5, 25, and 50μg of SLA/50μl/mice), free SLA and as well as free liposome. The group of mice received 50μg of SLA in DOTAP-nanoliposomes showed a significantly (p<0.001) smaller footpad swelling and the lowest spleen and footpad parasite burden after the challenge. This group also showed the highest IFN-γ production compared to the other groups, lower IL-4 level and higher IgG2a antibody titer. Taken together, the results indicated that simple DOTAP nanoliposome containing 1μg/μl SLA are appropriate delivery systems to induce a Th1 type of immune response and protection against L. major infection in BALB/c mice.

Inhibitory effects of a cationic liposome on allergic reaction mediated by mast cell activation

Several studies have shown that cationic liposomes exert immunomodulatory effects with low immunogenicity and toxicity, and offer advantages such as easy preparation and targeting. Cationic liposomes not only transport DNA to immune cells but also enhance the function of antigen presenting cells such as dendritic cells and macrophages. Here, we investigated the effect of a particular cationic liposome on mast cell function during allergic reaction. We found that the cationic liposomes bound to the mast cell surface suppressed degranulation induced by cross-linking of high affinity immunoglobulin E receptors in a time- and dose-dependent manner. The suppression of degranulation was mediated by impairment of the sustained level of intracellular Ca(2+) concentration ([Ca(2+)]i) derived from the inhibition of store-operated Ca(2+) entry. The decrease in sustained elevation of [Ca(2+)]i led to the suppression of phosphorylation of soluble N-ethylmaleimide-sensitive factor attachment protein receptor proteins such as SNAP-23, syntaxin-4, which are necessary for membrane fusion between secretory granules and the plasma membrane during degranulation. Furthermore, the cationic liposomes suppressed vascular permeability elevation induced by mast cell activation in mice. These results showed that cationic liposomes possess the novel property of inhibiting mast cell activation, suggesting the possibility of developing cationic liposomes as anti-allergic effectors.

Nanoparticle-based vaccine delivery for cancer immunotherapy

Development of nano-sized carriers including nanoparticles, nanoemulsions or liposomes holds great potential for advanced delivery systems for cancer immunotherapy, as such nanostructures can be used to more effectively manipulate or deliver immunologically active components to specific target sites. Successful development of nanotechnology based platform in the field of immunotherapy will allow the application of vaccines, adjuvants and immunomodulatory drugs that improve clinical outcomes for immunological diseases. Here, we review current nanoparticle-based platforms in the efficacious delivery of vaccines in cancer immunotherapy.

VLPs and particle strategies for cancer vaccines

Effective delivery of tumor antigens to APCs is one of the key steps for eliciting a strong and durable immune response to tumors. Several cancer vaccines have been evaluated in clinical trials, based on soluble peptides, but results have not been fully satisfactory. To improve immunogenicity particles provide a valid strategy to display and/or incorporate epitopes which can be efficiently targeted to APCs for effective induction of adaptive immunity. In the present review, we report some leading technologies for developing particulate vaccines employed in cancer immunotherapy, highlighting the key parameters for a rational design to elicit both humoral and cellular responses.

Particle platforms for cancer immunotherapy

Elevated understanding and respect for the relevance of the immune system in cancer development and therapy has led to increased development of immunotherapeutic regimens that target existing cancer cells and provide long-term immune surveillance and protection from cancer recurrence. This review discusses using particles as immune adjuvants to create vaccines and to augment the anticancer effects of conventional chemotherapeutics. Several particle prototypes are presented, including liposomes, polymer nanoparticles, and porous silicon microparticles, the latter existing as either single- or multiparticle platforms. The benefits of using particles include immune-cell targeting, codelivery of antigens and immunomodulatory agents, and sustained release of the therapeutic payload. Nanotherapeutic-based activation of the immune system is dependent on both intrinsic particle characteristics and on the immunomodulatory cargo, which may include danger signals known as pathogen-associated molecular patterns and cytokines for effector-cell activation.

Biodegradable microparticles covalently linked to surface antigens of the scuticociliate parasite P. dicentrarchi promote innate immune responses in vitro

The histiophagous scuticociliate endoparasite Philasterides dicentrarchi is an emerging pathogen that infects the turbot Scophthalmus maximus and thus causes important economic losses in turbot aquaculture. This in vitro study investigated the adjuvant capacity of biodegradable microspheres (MS) composed of two polymers (chitosan and Gantrez(®)) covalently coupled to surface antigens (Ag) of P. dicentrarchi. The coupled MS-Ag significantly stimulated the phagocytic response of both murine macrophages (RAW 264.7 cells) and leukocytes from the anterior kidney of turbot (HLK), at a level similar to that induced by zymosan A. The MS-Ag also significantly increased production of reactive oxygen and nitrogen species, as shown by the increased O(2) consumption and stimulation of the respiratory burst and nitric oxide production by murine and in particular by turbot HLK. The MS-Ag stimulated the production of the proinflammatory cytokine tumour necrosis factor alpha (TNFα) by murine and turbot HLK. The results confirm the high adjuvant capacity of biodegradable MS covalently bound to Ag as regards stimulating the innate immune response, and they justify the use of MS in the production of safe and effective vaccines against fish pathogens.

Liposome-based delivery system for vaccine candidates: constructing an effective formulation

The discovery of liposomes in 1965 by Bangham and coworkers changed the prospects of drug delivery systems. Since then, the application of liposomes as vaccine delivery systems has been studied extensively. Liposomal vaccine delivery systems are made up of nano- or micro-sized vesicles consisting of phospholipid bilayers, in which the bioactive molecule is encapsulated/entrapped, adsorbed or surface coupled. In general, liposomes are not immunogenic on their own; thus, liposomes combined with immunostimulating ligands (adjuvants) or various other formulations have been used as vaccine delivery systems. A thorough understanding of formulation parameters allows the design of effective liposomal vaccine delivery systems. This article provides an overview of various factors that influence liposomal immunogenicity. In particular, the effects of vesicle size, surface charge, bilayer composition, lamellarity, pegylation and targeting of liposomes are described.

Cationic lipids activate intracellular signaling pathways

Cationic liposomes are commonly used as a transfection reagent for DNA, RNA or proteins and as a co-adjuvant of antigens for vaccination trials. A high density of positive charges close to cell surface is likely to be recognized as a signal of danger by cells or contribute to trigger cascades that are classically activated by endogenous cationic compounds. The present review provides evidence that cationic liposomes activate several cellular pathways like pro-apoptotic and pro-inflammatory cascades. An improved knowledge of the relationship between the cationic lipid properties (nature of the lipid hydrophilic moieties, hydrocarbon tail, mode of organization) and the activation of these pathways opens the way to the use and design of cationic tailored for a specific application (e.g. for gene transport or as adjuvants).

Cationic liposomal vaccine adjuvants in animal challenge models: overview and current clinical status

Cationic liposome formulations can function as efficient vaccine adjuvants. However, due to the highly diverse nature of lipids, cationic liposomes have different physical-chemical characteristics that influence their adjuvant mechanisms and their relevance for use in different vaccines. These characteristics can be further manipulated by incorporation of additional lipids or stabilizers, and inclusion of carefully selected immunostimulators is a feasible strategy when tailoring cationic liposomal adjuvants for specific disease targets. Thus, cationic liposomes present a plasticity, which makes them promising adjuvants for future vaccines. This versatility has also led to a vast amount of literature on different experimental liposomal formulations in combination with a wide range of immunostimulators. Here, we have compiled information about the animal challenge models and administration routes that have been used to study vaccine adjuvants based on cationic liposomes and provide an overview of the applicability, progress and clinical status of cationic liposomal vaccine adjuvants.

Design considerations for liposomal vaccines: influence of formulation parameters on antibody and cell-mediated immune responses to liposome associated antigens

Liposomes (phospholipid bilayer vesicles) are versatile and robust delivery systems for induction of antibody and T lymphocyte responses to associated subunit antigens. In the last 15 years, liposome vaccine technology has matured and now several vaccines containing liposome-based adjuvants have been approved for human use or have reached late stages of clinical evaluation. Given the intensifying interest in liposome-based vaccines, it is important to understand precisely how liposomes interact with the immune system and stimulate immunity. It has become clear that the physicochemical properties of liposomal vaccines - method of antigen attachment, lipid composition, bilayer fluidity, particle charge, and other properties - exert dramatic effects on the resulting immune response. Here, we present a comprehensive review of the physicochemical properties of liposomal vaccines and how they influence immune responses. A discussion of novel and emerging immunomodulators that are suitable for inclusion in liposomal vaccines is also presented. Through a comprehensive analysis of the body of liposomal vaccine literature, we enumerate a series of principles that can guide the rational design of liposomal vaccines to elicit immune responses of a desired magnitude and quality. We also identify major unanswered questions in the field, pointing the direction for future study.

Cationic liposomes as vaccine adjuvants

The application of cationic liposomes as vaccine delivery systems and adjuvants has been investigated extensively over the last few decades. However, cationic liposomes are, in general, not sufficiently immunostimulatory, which is why the combination of liposomes with immunostimulating ligands has arisen as a strategy in the development of novel adjuvant systems. Within the last 5 years, two novel adjuvant systems based on cationic liposomes incorporating Toll-like receptor or non-Toll-like receptor immunostimulating ligands have progressed from preclinical testing in smaller animal species to clinical testing in humans. The immune responses that these clinical candidates induce are primarily of the Th1 type for which there is a profound unmet need. Furthermore, a number of new cationic liposome-forming surfactants with notable immunostimulatory properties have been discovered. In this article we review the recent progress on the application of cationic liposomes as vaccine delivery systems/adjuvants.

The role of surface charge density in cationic liposome-promoted dendritic cell maturation and vaccine-induced immune responses

Cationic liposomes have emerged as a novel adjuvant and antigen delivery system to enhance vaccine efficacy. However, the role of surface charge density in cationic liposome-regulated immune responses has not yet been elucidated. In the present study, we prepared a series of DOTAP/DOPC cationic liposomes with different surface densities by incorporating varying amounts of DOPC (a neutral lipid) into DOTAP (a cationic lipid). The results showed that DOTAP/DOPC cationic liposome-regulated immune responses relied on the surface charge density, and might occur through ROS signaling. The liposomes with a relatively high charge density, such as DOTAP/DOPC 5:0 and 4:1 liposomes, potently enhanced dendritic cell maturation, ROS generaion, antigen uptake, as well as the production of OVA-specific IgG2a and IFN-γ. In contrast, low-charge liposomes, such as DOTAP/DOPC 1:4 liposome, failed to promote immune responses even at high concentrations, confirming that the immunoregulatory effect of cationic liposomes is mostly attributable to their surface charge density. Moreover, the DOTAP/DOPC 1:4 liposome suppressed anti-OVA antibody responses in vivo. Overall, maintaining an appropriate surface charge is crucial for optimizing the adjuvant effect of cationic liposomes and enhancing the efficacy of liposome-based vaccines.

Enantiospecific adjuvant activity of cationic lipid DOTAP in cancer vaccine

Commercially available DOTAP is a racemic mixture of two enantiomers. The adjuvanticity of each isomer was examined using a peptide/lipid complex as a therapeutic vaccine in an established murine cervical cancer model. This simple vaccine consists of a cationic lipid (DOTAP) and a major histocompatibility complex (MHC) class I-restricted epitope of the Human Papillomavirus (HPV) 16 protein E7. Dose-dependent tumor regression experiments have been completed for racemic DOTAP/E7, (R)-DOTAP/E7 and (S)-DOTAP/E7. Tumor-bearing mice treated with (R)-DOTAP/E7 complexes have shown tumor regression in a dose-dependent manner comparable to those mice treated with a racemic DOTAP with E7 peptide. These data are supported by IFN-γ production by CD8(+) splenocytes, in vivo cytotoxic T-lymphocytes (CTL) response, CD8(+) tumor-infiltrating lymphocytes (TIL), and IFN-γ production by CD8(+) TIL in (R)-DOTAP/E7-vaccinated mice. When (S)-DOTAP/E7 is delivered, tumor progression is delayed. While IFN-γ production is absent from CD8(+) splenocytes in mice vaccinated with (S)-DOTAP/E7, IFN-γ production by CD8(+) TIL is present, supporting our hypothesis that (S)-DOTAP has limited activity. Activation of bone marrow-derived dendritic cells by the enantiomeric formulations has also been evaluated, as well as cytokine production and toxicity with no considerable differences between the groups. The results show the DOTAP enantiomers act differently as adjuvants in vivo, with (R)-DOTAP being more effective at stimulating a CD8(+) anti-tumor response.

Improved antigen cross-presentation by polyethyleneimine-based nanoparticles

Purpose

In the development of therapeutic vaccines against cancer, it is important to design strategies for antigen cross-presentation to stimulate cell-mediated immune responses against tumor antigens.

Methods

We developed a polyethyleneimine (PEI)-based protein antigen delivery system to promote cross-presentation through the major histocompatibility complex (MHC) I pathway using ovalbumin (OVA) as a model antigen. PEIs formed nanoparticles with OVA by electrostatic interactions, as demonstrated by electrophoresis analysis, scanning electron microscopy, and photon correlation spectroscopy analysis.

Results

The nanoparticles were used to stimulate mouse bone marrow-derived dendritic cells in vitro and resulted in significantly more OVA_257–264/MHC I complex presentation on dendritic cell surfaces. The activated dendritic cells interacted specifically with RF33.70 to stimulate interleukin-2 secretion. The cross-presentation promoting effect was more prominent in dendritic cells that had been cultured for longer periods of time (13 days). Further studies comparing the antigen presentation efficacies by other polyanionic agents, such as PLL or lysosomotropic agents, suggested that the unique “proton sponge effect” of PEI facilitated antigen escape from the endosome toward the MHC I pathway.

Conclusion

Such a PEI-based nanoparticle system may have the potential to be developed into an effective therapeutic vaccine delivery system.

Synthetic vehicles for DNA vaccination

DNA vaccination is an attractive immunization method able to induce robust cellular immune responses in pre-clinical models. However, clinical DNA vaccination trials performed thus far have resulted in marginal responses. Consequently, strategies are currently under development to improve the efficacy of DNA vaccines. A promising strategy is the use of synthetic particle formulations as carrier systems for DNA vaccines. This review discusses commonly used synthetic carriers for DNA vaccination and provides an overview of in vivo studies that use this strategy. Future recommendations on particle characteristics, target cell types and evaluation models are suggested for the potential improvement of current and novel particle delivery systems. Finally, hurdles which need to be tackled for clinical evaluation of these systems are discussed.

Comparison of the depot effect and immunogenicity of liposomes based on dimethyldioctadecylammonium (DDA), 3β-[N-(N',N'-Dimethylaminoethane)carbomyl] cholesterol (DC-Chol), and 1,2-Dioleoyl-3-trimethylammonium propane (DOTAP): prolonged liposome retention mediates stronger Th1 responses

The immunostimulatory capacities of cationic liposomes are well-documented and are attributed both to inherent immunogenicity of the cationic lipid and more physical capacities such as the formation of antigen depots and antigen delivery. Very few studies have however been conducted comparing the immunostimulatory capacities of different cationic lipids. In the present study we therefore chose to investigate three of the most well-known cationic liposome-forming lipids as potential adjuvants for protein subunit vaccines. The ability of 3β-[N-(N',N'-dimethylaminoethane)carbomyl] cholesterol (DC-Chol), 1,2-dioleoyl-3-trimethylammonium propane (DOTAP), and dimethyldioctadecylammonium (DDA) liposomes incorporating immunomodulating trehalose dibehenate (TDB) to form an antigen depot at the site of injection (SOI) and to induce immunological recall responses against coadministered tuberculosis vaccine antigen Ag85B-ESAT-6 are reported. Furthermore, physical characterization of the liposomes is presented. Our results suggest that liposome composition plays an important role in vaccine retention at the SOI and the ability to enable the immune system to induce a vaccine specific recall response. While all three cationic liposomes facilitated increased antigen presentation by antigen presenting cells, the monocyte infiltration to the SOI and the production of IFN-γ upon antigen recall was markedly higher for DDA and DC-Chol based liposomes which exhibited a longer retention profile at the SOI. A long-term retention and slow release of liposome and vaccine antigen from the injection site hence appears to favor a stronger Th1 immune response.

Comparison of lung accumulation of cationic liposomes in normal rats and LPS-treated rats

OBJECTIVE

Cationic liposomes have been shown to target angiogenic endothelial cells in lungs and joints with evidence of chronic inflammation. We sought to determine whether cationic liposomes accumulate in acutely inflamed lung tissue. SUBJECTS, TREATMENT AND METHODS: Acute lung injury was induced by intratracheal instillation of lipopolysaccharide (LPS) in Sprague Dawley rats. The controls received saline. Following instillation, the rats were ventilated for 5 h. Four hours after LPS-instillation each rat received rhodamine-labeled, cationic liposomes intravenously. The liposomes were allowed to circulate for 1 h. Thereafter, a bronchoalveolar lavage (BAL) was done and the lungs were perfused with saline and formalin. Accumulation of liposomes was assessed by quantitative confocal microscopy and determination of rhodamine-content in lung tissue.

RESULTS

LPS induced a significant increase in BAL white blood cell count (3,444 ± 1,420 vs. 1,314 ± 906*10(3)/μl) and cytokines (IL-1β: 145.57 vs. 51.94 pg/ml; TNF-α: 3,467.5 vs. 42.1 pg/ml) as compared to controls. Cationic liposomes exhibited an accumulation up to twofold in the inflamed lung tissue as compared to healthy lungs (fluorescent pixels 2.93 vs. 1.90(%)).

CONCLUSIONS

Our findings indicate that cationic liposomes accumulate in the acutely inflamed lung tissue. This uptake raises the possibility of using cationic liposomes to direct diagnostic/therapeutic agents selectively to the sites of acute inflammation in the lung.

Tresyl-based conjugation of protein antigen to lipid nanoparticles increases antigen immunogenicity

The present studies were aimed at investigating the engineering of NPs with protein-conjugated-surfactant at their surface. In order to increase the immunogenicity of a protein antigen, Brij 78 was functionalized by tresyl chloride and then further reacted with the primary amine of the model proteins ovalbumin (OVA) or horseradish peroxide (HRP). The reaction yielded Brij 78-OVA and Brij 78-HRP conjugates which were then used directly to form NP-OVA or NP-HRP using a one-step warm oil-in-water microemulsion precursor method with emulsifying wax as the oil phase, and Brij 78 and the Brij 78-OVA or Brij 78-HRP conjugate as surfactants. Similarly, Brij 700 was conjugated to HIV p24 antigen to yield Brij 700-p24 conjugate. The utility of these NPs for enhancing the immune responses to protein-based vaccines was evaluated in vivo using ovalbumin (OVA) as model protein and p24 as a relevant HIV antigen. In separate in vivo studies, female BALB/c mice were immunized by subcutaneous (s.c.) injection with NP-OVA and NP-p24 formulations along with several control formulations. These results suggested that with multiple antigens, covalent attachment of the antigen to the NP significantly enhanced antigen-specific immune responses. This facile covalent conjugation and incorporation method may be utilized to further incorporate other protein antigens, even multiple antigens, into an enhanced vaccine delivery system.

Novel cationic lipid that delivers siRNA and enhances therapeutic effect in lung cancer cells

We have developed lipid-polycation-DNA (LPD) nanoparticles containing DOTAP and targeted with polyethylene glycol (PEG) tethered with anisamide (AA) to specifically deliver siRNA to H460 human lung carcinoma cells which express the sigma receptor. A novel non-glycerol based cationic lipid which contains both a guanidinium and a lysine residue as the cationic headgroup, i.e. DSGLA, downregulated pERK more efficiently in H460 cells than DOTAP. As demonstrated by using fluorescently labeled siRNA, LPD-PEG-AA prepared with DSGLA efficiently delivered siRNA to the cytoplasm of the H460 cells. Although the siRNA delivered by LPD-PEG-AA containing either DOTAP or DSGLA could effectively silence EGFR expression, a synergistic cell killing effect in promoting cellular apoptosis was only observed with DSGLA. The fluorescently labeled siRNA was efficiently delivered into the cytoplasm of H460 xenograft tumor by the LPD-PEG-AA containing either DOTAP or DSGLA 4 h after intravenous injection. Three daily injections (0.6 mg/kg) of siRNA formulated in the LPD-PEG-AA containing either DOTAP or DSGLA could effectively silence the epidermal growth factor receptor (EGFR) in the tumor, but the formulation containing DSGLA could induce more cellular apoptosis. A significant improvement in tumor growth inhibition was observed after dosing with LPD-PEG-AA containing DSGLA. Thus, DSGLA served as both a formulation component as well as a therapeutic agent which synergistically enhanced the activity of siRNA.

Chitosan-based systems for the delivery of vaccine antigens

This review discusses the current status of chitosan and its derivatives as adjuvants and delivery systems in vaccine delivery, and their future possibilities and challenges. After a brief introduction to adjuvants and delivery systems, chitosan will be described in detail in regard to vaccine formulation. Applications of chitosan and its derivatives will be reviewed and their proposed mechanisms in the enhancement of immune responses will be discussed.

Lipid Nanoparticles with Accessible Nickel as a Vaccine Delivery System for Single and Multiple His-tagged HIV Antigens

Lipid-based nanoparticles (NPs) with a small amount of surface-chelated nickel (Ni-NPs) were developed to easily formulate the human immunodeficiency virus (HIV) his-tagged Tat (his-Tat) protein, as well as to formulate and co-deliver two HIV antigens (his-p24 and his-Nef) on one particle. Female BALB/c mice were immunized by subcutaneous injection with his-Tat/Ni-NP formulation (1.5 μg his-Tat/mouse) and control formulations on day 0 and 14. The day 28 anti-Tat specific immunoglobulin G titer with his-Tat/Ni-NPs was significantly greater than that with Alum/his-Tat. Furthermore, splenocytes from his-Tat/Ni-NP-immunized mice secreted significantly higher IFN-γ than those from mice immunized with Alum/his-Tat. Although Ni-NPs did not show better adjuvant activity than Tat-coated anionic NPs made with sodium dodecyl sulfate (SDS/NPs), they were less toxic than SDS/NPs. The initial results indicated that co-immunization of mice using his-p24/his-Nef/Ni-NP induced greater antibody response compared to using Alum/his-p24/his-Nef. Co-delivery of two antigens using Ni-NPs also increased the immunogenicity of individual antigens compared to delivery of a single antigen by Ni-NPs. In conclusion, Ni-NPs are an efficient delivery system for HIV vaccines including both single antigen delivery and multiple antigen co-delivery.

Addressing the problem of cationic lipid-mediated toxicity: the magnetoliposome model

The high biocompatibility and versatile nature of liposomes made these particles keystone components in many hot-topic research areas. For transfection and cell labelling purposes, synthetic cationic lipids are often added, but in most studies, little attention has been paid to their cytotoxic effects. In the present work, cationic magnetoliposomes (MLs), i.e. iron oxide cores enwrapped by a phospholipid bilayer (dimyristoylphosphatidylcholine or sphingomyelin) doped with cationic lipids (1,2-distearoyl-3-trimethylammonium propane), serve as a model to examine cationic lipid toxicity. Mechanisms of cytotoxic effects were found to be either dependent or independent of actual particle internalisation according to data obtained in the absence or presence of several endocytosis inhibitors. The former seem to be caused by the generation of reactive oxygen species (ROS) leading to a Ca2+ influx at high ROS levels. The latter are due to a destabilisation of the cell plasma membrane upon transfer of the cationic lipid from the ML bilayer into the plasma membrane. However, these adverse effects can be diminished by the use of a ROS scavenger, a Ca(2+)-channel blocker or by modulating the liposome size, lipid bilayer constitution or by stabilising the membrane by anchoring it on a solid core. Careful attention must be paid in terms of assessing cell viability as the effects are highly time dependent and the data suggest the incompatibility of using the well-known MTT assay when high levels of ROS species are generated.

The effects of salt on the physicochemical properties and immunogenicity of protein based vaccine formulated in cationic liposome

Recently, we have developed a simple and potent therapeutic cancer vaccine consisting of a cationic lipid and a peptide antigen. In this report, we expanded the utility of this formulation to protein based vaccines. First, we formulated the human papillomavirus (HPV) 16 E7 protein (E7) in different doses of DOTAP liposome. The results showed that these formulations failed to regress an established tumor. However, when sodium chloride (30 mM) was added to the DOTAP (100 nmol)/E7 (20 microg) formulation, anti-tumor activity was generated in the immunized mice. Correlatively, 30 mM NaCl in the DOTAP/E7 protein formulation increased the particle size from approximately 350 to 550 nm, decreased the protein loading capacity (from 95 to 90%), and finally increased the zeta potential (from 29 to 38 mV). Next, a model protein antigen ovalbumin (OVA) was formulated in different doses of DOTAP liposomes. Similarly, the results showed that 20 microg OVA formulated in 200 nmol DOTAP with 30 mM NaCl had the best OVA-specific antibody response, including both IgG(1) and IgG(2a), suggesting both Th1 and Th2 immune responses were generated by this formulation. In conclusion, we have expanded the application of cationic DOTAP liposome formulation to protein based vaccines and also identified that small amounts of salt could change the physicochemical properties of the vaccine formulation and enhance the activity of the DOTAP/protein based vaccine. The enhancement of immune responses by salt is possibly due to its interference of the electrostatic interaction between the cationic lipid and the protein antigen to facilitate the antigen release from the carrier and at the same time activate the antigen presenting cells.