Comparison of liposome based antigen delivery systems for protection against Leishmania donovani

Preparation of DRV Liposomes

Dried reconstituted vesicle (DRV) liposomes are formulated under mild conditions. The method has the capability to entrap substantially higher amounts of hydrophilic solutes, compared to other passive-loading liposome preparation methods. These characteristics make this liposome type ideal for entrapment of labile substances, such as peptides, proteins, or DNA's (or other nucleotides or oligonucleotides), or in general biopharmaceuticals and sensitive drugs. In this chapter, all possible types of DRV liposomes (in respect to the encapsulated molecule characteristics and/or their applications in therapeutics) are introduced, and preparation methodologies (for each type) are described in detail.

Nanoparticle-Based Delivery Systems for Vaccines

Vaccination is still the most cost-effective way to combat infectious illnesses. Conventional vaccinations may have low immunogenicity and, in most situations, only provide partial protection. A new class of nanoparticle-based vaccinations has shown considerable promise in addressing the majority of the shortcomings of traditional and subunit vaccines. This is due to recent breakthroughs in chemical and biological engineering, which allow for the exact regulation of nanoparticle size, shape, functionality, and surface characteristics, resulting in improved antigen presentation and robust immunogenicity. A blend of physicochemical, immunological, and toxicological experiments can be used to accurately characterize nanovaccines. This narrative review will provide an overview of the current scenario of the nanovaccine.

Nanomedicine in leishmaniasis: A promising tool for diagnosis, treatment and prevention of disease - An update overview

Leishmaniasis is a neglected tropical disease that has a wide spectrum of clinical manifestations, ranging from visceral to cutaneous, with millions of new cases and thousands of deaths notified every year. The severity of the disease and its various clinical forms are determined by the species of the causative agent, Leishmania, as well as the host's immune response. Major challenges still exist in the diagnosis and treatment of leishmaniasis, and there is no vaccine available to prevent this disease in humans. Nanotechnology has emerged as a promising tool in a variety of fields. In this review, we highlight the main and most recent advances in nanomedicine to improve the diagnosis and treatment, as well as for the development of vaccines, for leishmaniasis. Nanomaterials are nanometric in size and can be produced by a variety of materials, including lipids, polymers, ceramics, and metals, with varying structures and morphologies. Nanotechnology can be used as biosensors to detect antibodies or antigens, thus improving the sensitivity and specificity of such immunological and molecular diagnostic tests. While in treatment, nanomaterials can act as drug carriers or, be used directly, to reduce any toxic effects of drug compounds to the host and to be more selective towards the parasite. Furthermore, preclinical studies show that different nanomaterials can carry different Leishmania antigens, or even act as adjuvants to improve a Th1 immune response in an attempt to produce an effective vaccine.

Nanovaccine: an emerging strategy

INTRODUCTION

Vaccination is so far the most effective way of eradicating infections. Rapidly emerging drug resistance against infectious diseases and chemotherapy-related toxicities in cancer warrant immediate vaccine development to save mankind. Subunit vaccines alone, however, fail to elicit sufficiently strong and long-lasting protective immunity against deadly pathogens. Nanoparticle (NP)-based delivery vehicles like microemulsions, liposomes, virosomes, nanogels, micelles and dendrimers offer promising strategies to overcome limitations of traditional vaccine adjuvants. Nanovaccines can improve targeted delivery, antigen presentation, stimulation of body's innate immunity, strong T cell response combined with safety to combat infectious diseases and cancers. Further, nanovaccines can be highly beneficial to generate effective immutherapeutic formulations against cancer.

AREAS COVERED

This review summarizes the emerging nanoparticle strategies highlighting their success and challenges in preclinical and clinical trials in infectious diseases and cancer. It provides a concise overview of current nanoparticle-based vaccines, their adjuvant potential and their cellular delivery mechanisms.

EXPERT OPINION

The nanovaccines (50-250 nm in size) are most efficient in terms of tissue targeting, prolonged circulation and preferential uptake by the professional APCs chiefly due to their small size. More rational designing, improved antigen loading, extensive functionalization and targeted delivery are some of the future goals of ideal nanovaccines.

Nanotechnology-aided diagnosis, treatment and prevention of leishmaniasis

Leishmaniasis is a prevalent parasitic infection belonging to neglected tropical diseases. It is caused by Leishmania protozoan parasites transmitted by sandflies and it is responsible for increased morbidity/mortality especially in low- and middle-income countries. The lack of cheap, portable, easy to use diagnostic tools exhibiting high efficiency and specificity impede the early diagnosis of the disease. Furthermore, the typical anti-leishmanial agents are cytotoxic, characterized by low patient compliance and require long-term regimen and usually hospitalization. In addition, due to the intracellular nature of the disease, the existing treatments exhibit low bioavailability resulting in low therapeutic efficacy. The above, combined with the common development of resistance against the anti-leishmanial agents, denote the urgent need for novel therapeutic strategies. Furthermore, the lack of effective prophylactic vaccines hinders the control of the disease. The development of nanoparticle-based biosensors and nanocarrier-aided treatment and vaccination strategies could advance the diagnosis, therapy and prevention of leishmaniasis. The present review intends to highlight the various nanotechnology-based approaches pursued until now to improve the detection of Leishmania species in biological samples, decrease the side effects and increase the efficacy of anti-leishmanial drugs, and induce enhanced immune responses, specifically focusing on the outcome of their preclinical and clinical evaluation.

Total Phenolic Fraction (TPF) from Extra Virgin Olive Oil: Induction of apoptotic-like cell death in Leishmania spp. promastigotes and in vivo potential of therapeutic immunomodulation

BACKGROUND

Leishmaniasis is a serious multifactorial parasitic disease with limited treatment options. Current chemotherapy is mainly consisted of drugs with serious drawbacks such as toxicity, variable efficacy and resistance. Alternative bioactive phytocompounds may provide a promising source for discovering new anti-leishmanial drugs. Extra Virgin Olive Oil (EVOO), a key-product in the Mediterranean diet, is rich in phenols which are associated with anti-inflammatory, anti-cancer and anti-microbial effects. In this study, we investigate the anti-leishmanial effect of Total Phenolic Fraction (TPF) derived from EVOO in both in vitro and in vivo systems by investigating the contributing mechanism of action.

METHODOLOGY/PRINCIPAL FINDINGS

We tested the ability of TPF to cause apoptotic-like programmed cell death in L. infantum and L. major exponential-phase promastigotes by evaluating several apoptotic indices, such as reduction of proliferation rate, sub-G0/G1 phase cell cycle arrest, phosphatidylserine externalization, mitochondrial transmembrane potential disruption and increased ROS production, by using flow cytometry and microscopy techniques. Moreover, we assessed the therapeutic effect of TPF in L. major-infected BALB/c mice by determining skin lesions, parasite burden in popliteal lymph nodes, Leishmania-specific antibodies and biomarkers of tissue site cellular immune response, five weeks post-treatment termination. Our results show that TPF triggers cell-cycle arrest and apoptotic-like changes in Leishmania spp. promastigotes. Moreover, TPF treatment induces significant reduction of parasite burden in draining lymph nodes together with an antibody profile indicative of the polarization of Th1/Th2 immune balance towards the protective Th1-type response, characterized by the presence of IFN-γ-producing CD4+ T-cells and increased Tbx21/GATA-3 gene expression ratio in splenocytes.

CONCLUSIONS/SIGNIFICANCE

TPF exhibits chemotherapeutic anti-leishmanial activity by inducing programmed cell death on cell-free promastigotes and immunomodulatory properties that induce in vivo T cell-mediated responses towards the protective Th1 response in experimental cutaneous leishmaniasis. These findings enable deeper understanding of TPF's dual mode of action that encourages further studies.

A Phospholipase-A Activity in Soluble Leishmania Antigens Causes Instability of Liposomes

Aim:

This study aimed to investigate the existence of phospholipase-A (PLA) activity in Soluble L. major Antigens (SLA) because of no reports for it so far. Liposomes were used as sensors to evaluate PLA activity.

Objective:

Liposomal SLA consisting of Egg Phosphatidylcholine (EPC) or Sphingomyelin (SM) were prepared by two different methods in different pH or temperatures and characterized by Dynamic Light Scattering (DLS) and Thin Layer Chromatography (TLC).

Methods:

Lipid hydrolysis led to the disruption of EPC liposomal SLA in both methods but the Film Method (FM) produced more stable liposomes than the Detergent Removal Method (DRM).

Results:

The preparation of EPC liposomal SLA at pH 6 via FM protected liposomes from hydrolysis to some extent for a short time. EPC liposomes but not SM liposomes were disrupted in the presence of SLA.

Conclusion:

Therefore, a phospholipid without ester bond such as SM should be utilized in liposome formulations containing PLA as an encapsulating protein.

Mimetic Heat Shock Protein Mediated Immune Process to Enhance Cancer Immunotherapy

Inspired by heat shock proteins (HSPs), a self-assembly nanochaperone (nChap) is developed as a novel nanovaccine for boosting antitumor immune responses. Taking advantage of HSP-like microdomains and surface-decorated mannose, this nChap can efficiently capture antigens and ferry them into the dendritic cells (DCs). Subsequently, the nChap can blast lysosomes by transforming the structure and property of surface microdomains, thereby promoting antigen escape and enhancing their cross-presentation in cytoplasm. As a result, the nChap-based nanovaccine can elicit both CD4+ and CD8+ T cell-based immune responses and shows an excellent preventive effect on melanoma. Further combination of the nanovaccine with antiprogrammed death-1 (anti-PD-1) checkpoint blockade offers effective inhibition on the growth of already-established melanoma. Therefore, this nC ap-based nanovaccine provides a simple and robust strategy in mimicking HSPs to realize structure-assisted antigen capture, surface-receptor-mediated DC internalization, and both activation of humoral immunity and cellular immunity, promising for efficient cancer immunotherapy.

Investigation of the antigenicity and protective efficacy of Leishmania promastigote membrane antigens in search of potential diagnostic and vaccine candidates against visceral leishmaniasis

BACKGROUND

Visceral leishmaniasis (VL), is a parasitic disease that causes serious medical consequences if treatment is delayed. Despite a decline in the number of VL cases in the Indian subcontinent, the commencement of the disease in newer areas continues to be a major concern. Although serological diagnosis mainly by immunochromatographic tests has been found to be effective, a test of cure in different phases of treatment is still desired. Even though a good prophylactic response has been obtained in murine models by a number of vaccine candidates, few have been proposed for human use.

METHODS

In this study, nine antigenic components (31, 34, 36, 45, 51, 63, 72, 91 and 97 kDa) of Leishmania promastigote membrane antigens (LAg), were electroeluted and evaluated through ELISA to diagnose and distinguish active VL from one month cured and six months post-treatment patients. Further, to investigate the immunogenicity of electroeluted proteins, human PBMCs of cured VL patients were stimulated with 31, 34, 51, 63, 72 and 91 kDa proteins.

RESULTS

We found that 34 and 51 kDa proteins show 100% sensitivity and specificity with healthy controls and other diseases. After six months post-treatment, antibodies to 72 and 91 kDa antigens show a significant decline to almost normal levels. This suggests that 34 and 51 kDa proteins are efficient in diagnosis, whereas 72 and 91 kDa proteins may be used to monitor treatment outcome. In another assay, 51 and 63 kDa proteins demonstrated maximum ability to upregulate IFN-γ and IL-12 with minimum induction of IL-10 and TGF-β. The results indicating that 51 and 63 kDa proteins could be strong candidates for human immunization against VL. In contrast, 34 and 91 kDa proteins demonstrated a reverse profile and may not be a good vaccine candidate.

CONCLUSIONS

The preliminary data obtained in this study proposes the potential of some of the antigens in Leishmania diagnosis and for test of cure. Additionally, some antigens demonstrated good immunoprophylactic cytokine production through T cell-mediated immune response, suggesting future vaccine candidates for VL. However, further studies are necessary to explore these antigens in diagnosis and to access the long-term immune response.

Development of nano-carriers for Leishmania vaccine delivery

Introduction: Leishmaniasis is a neglected tropical infection caused by several species of intracellular protozoan parasites of the genus Leishmania. It is strongly believed that the development of vaccines is the most appropriate approach to control leishmaniasis. However, there is no vaccine available yet and the lack of an appropriate adjuvant delivery system is the main reason.Areas covered: Adjuvants are the utmost important part of a vaccine, to induce the immune response in the right direction. Limitations and drawbacks of conventional adjuvants have been necessitated the development of novel particulate delivery systems as adjuvants to obtain desirable protection against infectious diseases such as leishmaniasis. This review focused on particulate adjuvants especially nanoparticles that are in use to develop vaccines against leishmaniasis. The list of adjuvants includes generally lipids-, polymers-, or mineral-based delivery systems that target antigens specifically to the site of action within the host's body and enhance immune responses.Expert opinion: Over the past few years, there has been an increasing interest in developing particulate adjuvants as alternatives to immunostimulatory types. The composition of nano-carriers and particularly the physicochemical properties of nanoparticles have great potential to overcome challenges posed to leishmaniasis vaccine developments.

Ascorbic acid encapsulated into negatively charged liposomes exhibits increased skin permeation, retention and enhances collagen synthesis by fibroblasts

Ascorbic acid (AA) is widely used in cosmetic formulations due to its antioxidant property and ability to increase collagen synthesis. Here, we encapsulated AA in vesicles with different lipid compositions. Negative liposome charge favored AA skin retention, with accumulation of 37 ± 12 and 74 ± 23 μg/cm² in the epidermis and dermis, respectively, after 6 hours. Drug flux was influenced by the formulation composition, and both the presence of cholesterol and the liposomes surface charge were able to increase the amount of AA crossing the skin. The formulation was stable for at least 30 days and promoted a 7-fold increase in flux compared to free AA. Additionally, liposomes were able to interact better with keratinocytes and fibroblasts membranes. In vitro efficacy studies demonstrated that associating AA to these liposomes resulted in increased effectiveness of type I collagen synthesis by fibroblasts and regeneration of UVA-induced damage in keratinocytes. Our results demonstrate the applicability of AA-negatively charged liposomes in promoting AA cutaneous permeation and increasing the retention and flux of this molecule in the skin. This formulation also increased AA stability and effectiveness, opening new perspectives for its application in view of reducing certain skin ageing outcomes.

Genome Plasticity in Cultured Leishmania donovani: Comparison of Early and Late Passages

Leishmania donovani possesses a complex heteroxenic life cycle where infective metacyclic promastigotes are pre-adapted to infect their host and cope up with intracellular stress. Exploiting the similarities between cultured and sandfly derived promastigotes, we used early and late passage cultured promastigotes to show specific changes at genome level which compromise pathogen fitness reflected in gene expression and infection studies. The pathogen loses virulence mostly via transcriptional and translational regulations and long-time cultivation makes them struggle to convert to virulent metacyclics. At the genomic level very subtle plasticity was observed between the early and the late passages mostly in defense-related, nutrient acquisition and signal transduction genes. Chromosome Copy number variation is seen in the early and late passages involving several genes that may be playing a role in pathogenicity. Our study highlights the importance of ABC transporters and calpain like cysteine proteases in parasite virulence in cultured promastigotes. Interestingly, these proteins are emerging as important patho-adaptive factors in clinical isolates of Leishmania. We found that the currently available genome of Leishmania in the NCBI database are from late passages. Our early passage genome can act as a reference for future studies on virulent isolates of Leishmania. The annotated leads from this study can be used for virulence surveillance and therapeutic studies in the Indian subcontinent.

Suppression of T lymphocyte activation by 3-chloro-1,2-propanediol mono- and di-palmitate esters in vitro

This study investigated whether and how 3-chloro-1,2-propanediol (3-MCPD) fatty acid esters, a group of food contaminants formed during processing, might inhibit the immune system through suppressing T lymphocyte activation for the first time. Three 3-MCPD esters including 1-palmitoyl-3-chloropropanediol (1-pal), 2-palmitoyl-3-chloropropanediol (2-pal), and1,2-dipalmitoyl-3-chloropropanediol (dipal) were selected as the probe compounds to test the possible effects of fatty acid structure on their potential immune inhibitory effect. The results showed that 1-pal and 2-pal, but not dipal, significantly suppressed ConA-induced T lymphocyte proliferation, cell cycle activity, Th1 and Th2 cytokine secretion, CD4⁺ T cell populations, and the ratio of CD4⁺/CD8⁺ T cells under the experimental conditions. Moreover, Western blotting and immunofluorescence analyses revealed that 1-pal and 2-pal could inhibit the activation of ConA-stimulated mitogen-activated protein kinase (MAPK) and nuclear factor-kappa B (NF-κB) signaling pathways. In addition, 1-pal significantly suppressed DNFB-induced delayed-type hyper sensitivity (DTH) reaction characterized by the increased ear thickness and IFN-γ production in mice. These observations indicated that 3-MCPD esters exerted a negative effect on T lymphocyte-mediated immunity, and the immunosuppressive activities of 3-MCPD monopalmitates were stronger than 3-MCPD dipalmitate.

Liposomal adjuvant development for leishmaniasis vaccines

Leishmaniasis is a parasitic disease that ranges in severity from skin lesions to fatality. Since long-lasting protection is induced upon recovery from cutaneous leishmaniasis, development of an effective vaccine is promising. However, there is no vaccine for use in humans yet. It seems limited efficacy in leishmaniasis vaccines is due to lack of an appropriate adjuvant or delivery system. Hence, the use of particulate adjuvants such as liposomes for effective delivery to the antigen presenting cells (APCs) is a valuable strategy to enhance leishmaniasis vaccine efficacy. The extraordinary versatility of liposomes because of their unique amphiphilic and biphasic nature allows for using antigens or immunostimulators within the core, on the surface or within the bilayer, and modulates both the magnitude and the T-helper bias of the immune response. In this review article, we attempt to summarize the role of liposomal adjuvants in the development of Leishmania vaccines and describe the main physicochemical properties of liposomes like phospholipid composition, surface charge, and particle size during formulation design. We also suggest potentially useful formulation strategies in order for future experiments to have a chance to succeed as liposomal vaccines against leishmaniasis.

Preparation of DRV Liposomes

Dried reconstituted vesicles (DRV) are liposomes that are formulated under mild conditions and have the capability to entrap substantially high amounts of hydrophilic solutes (compared to other types of liposomes). These characteristics make this liposome type ideal for entrapment of labile substances, as peptide, protein, or DNA vaccines, or in general biopharmaceuticals and sensitive drugs. In this chapter, all possible types of DRV liposomes (with respect to the encapsulated molecule characteristics and/or their applications in therapeutics) are introduced, and preparation methodologies (for each type) are described in detail.

Lipid based delivery and immuno-stimulatory systems: Master tools to combat leishmaniasis

Disease management of leishmaniasis is appalling due to lack of a human vaccine and the toxicity and resistance concerns with limited therapeutic drugs. The challenges in development of a safe vaccine for generation and maintenance of robust antileishmanial protective immunity through a human administrable route of immunization can be addressed through immunomodulation and targeted delivery. The versatility of lipid based particulate system for deliberate delivery of diverse range of molecules including immunomodulators, antigens and drugs have essentially found pivotal role in design of proficient vaccination and therapeutic strategies against leishmaniasis. The prospects of lipid based preventive and curative formulations for leishmaniasis have been highlighted in this review.

Protective effect of antigen delivery using monoolein-based liposomes in experimental hematogenously disseminated candidiasis

We evaluated the potential of a liposomal antigen delivery system (ADS) containing Candida albicans cell wall surface proteins (CWSP) in mediating protection against systemic candidiasis. Treatment of bone-marrow-derived dendritic cells with CWSP-loaded dioctadecyldimethylammonium bromide:monoolein (DODAB:MO) liposomes enhanced and prolonged their activation comparatively to free antigen, indicating that liposome-entrapped CWSP were released more sustainable. Therefore, we immunized mice with CWSP either in a free form or loaded into two different DODAB:MO liposome formulations, respectively designated as ADS1 and ADS2, prior to intravenous C. albicans infection. Immunization with ADS1, but not with ADS2, conferred significant protection to infected mice, comparatively to immunization with CWSP or empty liposomes as control. ADS1-immunized mice presented significantly higher serum levels of C. albicans-specific antibodies that enhanced phagocytosis of this fungus. In these mice, a mixed cytokine production profile was observed encompassing IFN-γ, IL-4, IL-17A and IL-10. Nevertheless, only production of IL-4, IL-17 and IL-10 was higher than in controls. In this study we demonstrated that DODAB:MO liposomes enhance the immunogenicity of C. albicans antigens and host protection in a murine model of systemic candidiasis. Therefore, this liposomal adjuvant could be a promising candidate to assess in vaccination against this pathogenic fungus.

STATEMENT OF SIGNIFICANCE

This work describes the immunomodulation capacity of the previously validated antigen delivery system (ADS) composed by dioctadecyldimethylammonium bromide (DODAB) and monoolein (MO) lipids incorporating the cell wall surface proteins (CWSP) from C. albicans. Here, we not only present the ability of this system in facilitating antigen uptake by DCs in vitro, but also that this system induces higher levels of pro-inflammatory cytokines and opsonizing specific IgG antibodies in serum of mice immunized subcutaneously. We show that the ADS are efficient nanocarrier and modulate the immune response against intravenous C. albicans infection favoring mouse protection. In sum, we show that the incorporation of C. albicans antigens in DODAB:MO nanocarries are a promising vaccine strategy against C. albicans fungal infection.

Social and Economic Burden of Human Leishmaniasis

Leishmaniasis continues to pose a major public health problem worldwide. With new epidemics occurring in endemic areas and the spread of the disease to previously free areas because of migration, tourism, and military activities, there is a great need for the development of an effective vaccine. Leishmaniasis is a disease of the poor, occurring mostly in remote rural villages with poor housing and little or no access to modern health-care facilities. In endemic areas, diagnosis of any form of leishmaniasis puts a huge financial strain on an already meagre financial resource at both the individual and community levels. Most often families need to sell their assets (land and livestock) or take loans from informal financial outfits with heavy interest rates to pay for the diagnosis and treatment of leishmaniasis. Here, we discuss the disease with special emphasis on its socioeconomic impact on the affected individual and community. In addition, we highlight the reasons why continued research aimed at developing an effective Leishmania vaccine is necessary.

Perspective of Peptide Vaccine Composed of Epitope Peptide, CpG-DNA, and Liposome Complex Without Carriers

The magnitude and specificity of cell-mediated and humoral immunity are critically determined by peptide sequences; peptides corresponding to the B- or T-cell receptor epitopes are sufficient to induce an effective immune response if delivered properly. Therefore, studies on the screening and application of peptide-based epitopes have been done extensively for the development of therapeutic antibodies and prophylactic vaccines. However, the efficacy of immune response and antibody production by peptide-based immunization is too limited for human application at the present. To improve the efficacy of vaccines, researchers formulated adjuvants such as alum, water-in-oil emulsion, and Toll-like receptor agonists. They also employed liposomes as delivering vehicles to stimulate immune responses. Here, we review our recent studies providing a potent method of epitope screening and antibody production without conventional carriers. We adopted Lipoplex(O), comprising a natural phosphodiester bond CpG-DNA and a specific liposome complex, as an adjuvant. Lipoplex(O) induces potent stimulatory activity in humans as well as in mice, and immunization of mice with several peptides along with Lipoplex(O) without general carriers induces significant production of each peptide-specific IgG2a. Immunization of peptide vaccines against virus-associated antigens in mice has protective effects against the viral infection. A peptide vaccine against carcinoma-associated antigen and the peptide-specific monoclonal antibody has functional effects against cancer cells in mouse models. In conclusion, we improved the efficacy of peptide vaccines in mice. Our strategy can be applied in development of therapeutic antibodies or in defense against pandemic infectious diseases through rapid screening of potent B-cell epitopes.

Cationic liposomal sodium stibogluconate (SSG), a potent therapeutic tool for treatment of infection by SSG-sensitive and -resistant Leishmania donovani

Pentavalent antimonials have been the first-line treatment for leishmaniasis for decades. However, the development of resistance to sodium stibogluconate (SSG) has limited its use, especially for treating visceral leishmaniasis (VL). The present work aims to optimize a cationic liposomal formulation of SSG for the treatment of both SSG-sensitive (AG83) and SSG-resistant (GE1F8R and CK1R) Leishmania donovani infections. Parasite killing was determined by the 3-(4,5-dimethylthiazol-2)-2,5-diphenyltetrazolium bromide (MTT) assay and microscopic counting of Giemsa-stained macrophages. Macrophage uptake studies were carried out by confocal microscopic imaging. Parasite-liposome interactions were visualized through transmission electron microscopy. Toxicity tests were performed using assay kits. Organ parasite burdens were determined by microscopic counting and limiting dilution assays. Cytokines were measured by enzyme-linked immunosorbent assays (ELISAs) and flow cytometry. Although all cationic liposomes studied demonstrated leishmanicidal activity, phosphatidylcholine (PC)-dimethyldioctadecylammonium bromide (DDAB) vesicles were most effective, followed by PC-stearylamine (SA) liposomes. Since entrapment of SSG in PC-DDAB liposomes demonstrated enhanced ultrastructural alterations in promastigotes, PC-DDAB-SSG vesicles were further investigated in vitro and in vivo. PC-DDAB-SSG could effectively alleviate SSG-sensitive and SSG-resistant L. donovani infections in the liver, spleen, and bone marrow of BALB/c mice at a dose of SSG (3 mg/kg body weight) not reported previously. The parasiticidal activity of these vesicles was attributed to better interactions with the parasite membranes, resulting in direct killing, and generation of a strong host-protective environment, necessitating a very low dose of SSG for effective cures.

Production of epitope-specific antibodies using peptide-CpG-ODN-liposome complex without carriers and their application as a cancer vaccine in mice

Low efficacy of peptide vaccines limits their potential application. We developed a powerful strategy to produce epitope-specific antibodies using peptides. Immunization with novel formula into mice showed target-specific prophylactic and therapeutic effects against tumors. Our strategy will be useful for rapid eiptope screening, therapeutic antibody production and cancer vaccine development.

Visceral Leishmaniasis: Advancements in Vaccine Development via Classical and Molecular Approaches

Visceral leishmaniasis (VL) or kala-azar, a vector-borne protozoan disease, shows endemicity in larger areas of the tropical, subtropical and the Mediterranean countries. WHO report suggested that an annual incidence of VL is nearly 200,000 to 400,000 cases, resulting in 20,000 to 30,000 deaths per year. Treatment with available anti-leishmanial drugs are not cost effective, with varied efficacies and higher relapse rate, which poses a major challenge to current kala-azar control program in Indian subcontinent. Therefore, a vaccine against VL is imperative and knowing the fact that recovered individuals developed lifelong immunity against re-infection, it is feasible. Vaccine development program, though time taking, has recently gained momentum with the emergence of omic era, i.e., from genomics to immunomics. Classical as well as molecular methodologies have been overtaken with alternative strategies wherein proteomics based knowledge combined with computational techniques (immunoinformatics) speed up the identification and detailed characterization of new antigens for potential vaccine candidates. This may eventually help in the designing of polyvalent synthetic and recombinant chimeric vaccines as an effective intervention measures to control the disease in endemic areas. This review focuses on such newer approaches being utilized for vaccine development against VL.

Combining cationic liposomal delivery with MPL-TDM for cysteine protease cocktail vaccination against Leishmania donovani: evidence for antigen synergy and protection

BACKGROUND

With the paucity of new drugs and HIV co-infection, vaccination remains an unmet research priority to combat visceral leishmaniasis (VL) requiring strong cellular immunity. Protein vaccination often suffers from low immunogenicity and poor generation of memory T cells for long-lasting protection. Cysteine proteases (CPs) are immunogenic proteins and key mediators of cellular functions in Leishmania. Here, we evaluated the vaccine efficacies of CPs against VL, using cationic liposomes with Toll like receptor agonists for stimulating host immunity against L. donovani in a hamster model.

METHODOLOGY/PRINCIPAL FINDINGS

Recombinant CPs type I (cpb), II (cpa) and III (cpc) of L. donovani were tested singly and in combination as a triple antigen cocktail for antileishmanial vaccination in hamsters. We found the antigens to be highly immunoreactive and persistent anti-CPA, anti-CPB and anti-CPC antibodies were detected in VL patients even after cure. The liposome-entrapped CPs with monophosphoryl lipid A-Trehalose dicorynomycolate (MPL-TDM) induced significantly high nitric oxide (up to 4 fold higher than controls) mediated antileishmanial activity in vitro, and resulted in strong in vivo protection. Among the three CPs, CPC emerged as the most potent vaccine candidate in combating the disease. Interestingly, a synergistic increase in protection was observed with liposomal CPA, CPB and CPC antigenic cocktail which reduced the organ parasite burden by 1013-1016 folds, and increased the disease-free survival of >80% animals at least up to 6 months post infection. Robust secretion of IFN-γ and IL-12, along with concomitant downregulation of Th2 cytokines, was observed in cocktail vaccinates, even after 3 months post infection.

CONCLUSION/SIGNIFICANCE

The present study is the first report of a comparative efficacy of leishmanial CPs and their cocktail using liposomal formulation with MPL-TDM against L. donovani. The level of protection attained has not been reported for any other subcutaneous single or polyprotein vaccination against VL.

Targeted immunomodulation using antigen-conjugated nanoparticles

The growing prevalence of nanotechnology in the fields of biology, medicine, and the pharmaceutical industry is confounded by the relatively small amount of data on the impact of these materials on the immune system. In addition to concerns surrounding the potential toxicity of nanoparticle (NP)-based delivery systems, there is also a demand for a better understanding of the mechanisms governing interactions of NPs with the immune system. Nanoparticles can be tailored to suppress, enhance, or subvert recognition by the immune system. This 'targeted immunomodulation' can be achieved by delivery of unmodified particles, or by modifying particles to deliver drugs, proteins/peptides, or genes to a specific site. In order to elicit the desired, beneficial immune response, considerations should be made at every step of the design process: the NP platform itself, ligands, and other modifiers, the delivery route, and the immune cells that will encounter the conjugated NPs can all impact host immune responses.

Emerging research and clinical development trends of liposome and lipid nanoparticle drug delivery systems

Liposomes are spherical-enclosed membrane vesicles mainly constructed with lipids. Lipid nanoparticles are loaded with therapeutics and may not contain an enclosed bilayer. The majority of those clinically approved have diameters of 50-300 nm. The growing interest in nanomedicine has fueled lipid-drug and lipid-protein studies, which provide a foundation for developing lipid particles that improve drug potency and reduce off-target effects. Integrating advances in lipid membrane research has enabled therapeutic development. At present, about 600 clinical trials involve lipid particle drug delivery systems. Greater understanding of pharmacokinetics, biodistribution, and disposition of lipid-drug particles facilitated particle surface hydration technology (with polyethylene glycol) to reduce rapid clearance and provide sufficient blood circulation time for drug to reach target tissues and cells. Surface hydration enabled the liposome-encapsulated cancer drug doxorubicin (Doxil) to gain clinical approval in 1995. Fifteen lipidic therapeutics are now clinically approved. Although much research involves attaching lipid particles to ligands selective for occult cells and tissues, preparation procedures are often complex and pose scale-up challenges. With emerging knowledge in drug target and lipid-drug distribution in the body, a systems approach that integrates knowledge to design and scale lipid-drug particles may further advance translation of these systems to improve therapeutic safety and efficacy.

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 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.

Liposomes and nanotechnology in drug development: focus on oncotargets

Nanotechnology is the development of an engineered device at the atomic, molecular, and macromolecular level in the nanometer range. Advances in nanotechnology have proven beneficial in therapeutic fields such as drug-delivery and gene/protein delivery. Antigen delivery systems are important for inducing and modifying immune responses. In cellular immunity, cytotoxic T lymphocytes (CTLs) are important in the host defense against tumors. Key to the development of CTL-inducible vaccines is the ability to deliver antigens to antigen-presenting cells efficiently and to induce the subsequent activation of T cell-mediated immunity without adjuvants, as they can induce excessive inflammation leading to systemic febrile disease. Since expression and cloning methods for tumor-associated antigens have been reported, cancer vaccines that induce effective cell immunity may be promising therapeutic candidates, but Th2 cells are undesirable for use in cancer immunotherapy. Peptide vaccines have immunological and economic advantages as cancer vaccines because CTL epitope peptides from tumor-associated antigens have high antigen-specificity. However, cancer vaccines have had limited effectiveness in clinical responses due to the ability of cancer cells to “escape” from cancer immunity and a low efficiency of antigen-specific CTL induction due to immunogenic-free synthetic peptides. In contrast, carbohydrate-decorated particles such as carbohydrate-coated liposomes with encapsulated antigens might be more suitable as antigen delivery vehicles to antigen-presenting cells. Oligomannose-coated liposomes (OML) can eliminate established tumors in mouse cancer models. In addition, OMLs with an encased antigen can induce antigen-specific CTLs from peripheral blood mononuclear cells obtained from patients. Feasibility studies of OML-based vaccines have revealed their potential for clinical use as vaccines for diseases where CTLs act as effector cells. Furthermore, use of the hepatitis B core particle, in which tumor-antigen epitopes are set, has consistently been shown to induce strong CTL responses without the use of an adjuvant. Thus, nanoparticles may provide a new prophylactic strategy for infectious disease and therapeutic approaches for cancer via the induction of T-cell immunity.

Vaccine Development Against Leishmania donovani

Visceral leishmaniasis (VL) caused by Leishmania donovani and Leishmania infantum/chagasi represents the second most challenging infectious disease worldwide, leading to nearly 500,000 new cases and 60,000 deaths annually. Zoonotic VL caused by L. infantum is a re-emergent canid zoonoses which represents a complex epidemiological cycle in the New world where domestic dogs serve as a reservoir host responsible for potentially fatal human infection and where dog culling is the only measure for reservoir control. Life-long immunity to VL has motivated development of prophylactic vaccines against the disease but very few have progressed beyond the experimental stage. No licensed vaccine is available till date against any form of leishmaniasis. High toxicity and increasing resistance to the current chemotherapeutic regimens have further complicated the situation in VL endemic regions of the world. Advances in vaccinology, including recombinant proteins, novel antigen-delivery systems/adjuvants, heterologous prime-boost regimens and strategies for intracellular antigen presentation, have contributed to recent advances in vaccine development against VL. Attempts to develop an effective vaccine for use in domestic dogs in areas of canine VL should be pursued for preventing human infection. Studies in animal models and human patients have revealed the pathogenic mechanisms of disease progression and features of protective immunity. This review will summarize the accumulated knowledge of pathogenesis, immune response, and prerequisites for protective immunity against human VL. Authors will discuss promising vaccine candidates, their developmental status and future prospects in a quest for rational vaccine development against the disease. In addition, several challenges such as safety issues, renewed and coordinated commitment to basic research, preclinical studies and trial design will be addressed to overcome the problems faced in developing prophylactic strategies for protection against this lethal infection.

Prevention and therapy of hepatocellular carcinoma by vaccination with TM4SF5 epitope-CpG-DNA-liposome complex without carriers

Although peptide vaccines have been actively studied in various animal models, their efficacy in treatment is limited. To improve the efficacy of peptide vaccines, we previously formulated an efficacious peptide vaccine without carriers using the natural phosphodiester bond CpG-DNA and a special liposome complex (Lipoplex(O)). Here, we show that immunization of mice with a complex consisting of peptide and Lipoplex(O) without carriers significantly induces peptide-specific IgG2a production in a CD4⁺ cells- and Th1 differentiation-dependent manner. The transmembrane 4 superfamily member 5 protein (TM4SF5) has gained attention as a target for hepatocellular carcinoma (HCC) therapy because it induces uncontrolled growth of human HCC cells via the loss of contact inhibition. Monoclonal antibodies specific to an epitope of human TM4SF5 (hTM4SF5R2-3) can recognize native mouse TM4SF5 and induce functional effects on mouse cancer cells. Pre-immunization with a complex of the hTM4SF5R2-3 epitope and Lipoplex(O) had prophylactic effects against tumor formation by HCC cells implanted in an mouse tumor model. Furthermore, therapeutic effects were revealed regarding the growth of HCC when the vaccine was injected into mice after tumor formation. These results suggest that our improved peptide vaccine technology provides a novel prophylaxis measure as well as therapy for HCC patients with TM4SF5-positive tumors.

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.

Potentiating effects of MPL on DSPC bearing cationic liposomes promote recombinant GP63 vaccine efficacy: high immunogenicity and protection

Background

Vaccines that activate strong specific Th1-predominant immune responses are critically needed for many intracellular pathogens, including Leishmania. The requirement for sustained and efficient vaccination against leishmaniasis is to formulate the best combination of immunopotentiating adjuvant with the stable antigen (Ag) delivery system. The aim of the present study is to evaluate the effectiveness of an immunomodulator on liposomal Ag through subcutaneous (s.c.) route of immunization, and its usefulness during prime/boost against visceral leishmaniasis (VL) in BALB/c mice.

Methodology/Principal Findings

Towards this goal, we formulated recombinant GP63 (rGP63)-based vaccines either with monophosphoryl lipid A-trehalose dicorynomycolate (MPL-TDM) or entrapped within cationic liposomes or both. Combinatorial administration of liposomes with MPL-TDM during prime confers activation of dendritic cells, and induces an early robust T cell response. To investigate whether the combined formulation is required for optimum immune response during boost as well, we chose to evaluate the vaccine efficacy in mice primed with combined adjuvant system followed by boosting with either rGP63 alone, in association with MPL-TDM, liposomes or both. We provide evidences that the presence of either liposomal rGP63 or combined formulations during boost is necessary for effective Th1 immune responses (IFN-γ, IL-12, NO) before challenge infection. However, boosting with MPL-TDM in conjugation with liposomal rGP63 resulted in a greater number of IFN-γ producing effector T cells, significantly higher levels of splenocyte proliferation, and Th1 responses compared to mice boosted with liposomal rGP63, after virulent Leishmania donovani (L. donovani) challenge. Moreover, combined formulations offered superior protection against intracellular amastigote replication in macrophages in vitro, and hepatic and splenic parasite load in vivo.

Conclusion

Our results define the immunopotentiating effect of MPL-TDM on protein Ag encapsulated in a controlled release system against experimental VL.

Visceral leishmaniasis (VL), a vector-transmitted disease caused by Leishmania donovani, is potentially fatal if left untreated. Vaccination against VL has received limited attention compared with cutaneous leishmaniasis, although the need for an effective vaccine is pressing for the control of the disease. Earlier, we observed protective efficacy using leishmanial antigen (Ag) in the presence of either cationic liposomes or monophosphoryl lipid A-trehalose dicorynomycolate (MPL-TDM) against experimental VL through the intraperitoneal (i.p.) route of administration in the mouse model. However, this route of immunization is not adequate for human use. For this work, we developed vaccine formulations combining cationic liposomes with MPL-TDM using recombinant GP63 (rGP63) as protein Ag through the clinically relevant subcutaneous (s.c.) route. Two s.c. injections with rGP63 in association with cationic liposomes and MPL-TDM showed enhanced immune responses that further resulted in high protective levels against VL in the mouse model. This validates the combined use of MPL-TDM as an immunopotentiator and liposomes as a suitable vaccine delivery system.

Vaccination with liposomal leishmanial antigens adjuvanted with monophosphoryl lipid-trehalose dicorynomycolate (MPL-TDM) confers long-term protection against visceral leishmaniasis through a human administrable route

The development of a long-term protective subunit vaccine against visceral leishmaniasis depends on antigens and adjuvants that can induce an appropriate immune response. The immunization of leishmanial antigens alone shows limited efficacy in the absence of an appropriate adjuvant. Earlier we demonstrated sustained protection against Leishmania donovani with leishmanial antigens entrapped in cationic liposomes through an intraperitoneal route. However, this route is not applicable for human administration. Herein, we therefore evaluated the immune response and protection induced by liposomal soluble leishmanial antigen (SLA) formulated with monophosphoryl lipid-trehalose dicorynomycolate (MPL-TDM) through a subcutaneous route. Subcutaneous immunization of BALB/c mice with SLA entrapped in liposomes or with MPL-TDM elicited partial protection against experimental visceral leishmaniasis. In contrast, liposomal SLA adjuvanted with MPL-TDM induced significantly higher levels of protection in liver and spleen in BALB/c mice challenged 10 days post-vaccination. Protection conferred by this formulation was sustained up to 12 weeks of immunization, and infection was controlled for at least 4 months of the challenge, similar to liposomal SLA immunization administered intraperitoneally. An analysis of cellular immune responses of liposomal SLA + MPL-TDM immunized mice demonstrated the induction of IFN-γ and IgG2a antibody production not only 10 days or 12 weeks post-vaccination but also 4 months after the challenge infection and a down regulation of IL-4 production after infection. Moreover, long-term immunity elicited by this formulation was associated with IFN-γ production also by CD8⁺ T cells. Taken together, our results suggest that liposomal SLA + MPL-TDM represent a good vaccine formulation for the induction of durable protection against L. donovani through a human administrable route.

Hyaluronan-modified and regular multilamellar liposomes provide sub-cellular targeting to macrophages, without eliciting a pro-inflammatory response

Macrophages, pivotal cells in onset and progression of inflammation, can benefit from sub-cellular drug targeting to the molecular loci of drug action, whether cell membrane or cell interior. Postulating manipulation of liposome size and surface properties can provide sub-cellular targeting, we studied: thermodynamics of liposome-macrophage binding; liposome cellular localizations; liposome safety including pro-inflammatory cytokine production. We aimed at extending the body of knowledge on interactions of regular unilamellar (RL-ULV) and multilamellar (RL-MLV) liposomes with macrophages. We investigated, for the first time, the interactions of hyaluronan (HA) surface-modified liposomes (HA-ULV and HA-MLV) with macrophages, with respect to multiple equilibria binding combined with cellular localization. Macrophages bound all four liposome types, substantially-favoring the two MLV species over the two ULV species, and internalizing only RL-MLV. Three macrophage-internalization inhibitors (2-deoxyglucose, LY294002 and Wortmannin) reduced RL-MLV internalization but not binding affinity nor binding capacity. Both MLV types were not detrimental to cell proliferation, nor did they elicit TNF-α production in resting and in LPS-activated macrophages. Moreover, a 24-hour exposure of LPS-activated macrophages to HA-MLV reduced TNF-α production by 40%, indicating potential for anti-inflammatory activity. In conclusion RL-MLV and HA-MLV are the liposomes of choice for delivering anti-inflammatory drugs to the macrophage surface or its interior, according to the loci of drug action.

Development of Vaccines against Visceral Leishmaniasis

Leishmaniasis is a neglected disease resulting in a global morbidity of 2,090 thousand Disability-Adjusted Life Years and a mortality rate of approximately 60,000 per year. Among the three clinical forms of leishmaniasis (cutaneous, mucosal, and visceral), visceral leishmaniasis (VL) accounts for the majority of mortality, as if left untreated VL is almost always fatal. Caused by infection with Leishmania donovani or L. infantum, VL represents a serious public health problem in endemic regions and is rapidly emerging as an opportunistic infection in HIV patients. To date, no vaccine exists for VL or any other form of leishmaniasis. In endemic areas, the majority of those infected do not develop clinical symptoms and past infection leads to robust immunity against reinfection. Thus the development of vaccine for Leishmania is a realistic public health goal, and this paper summarizes advances in vaccination strategies against VL.

Negatively charged liposomes show potent adjuvant activity when simply admixed with protein antigens

Liposomes have been investigated extensively as a vaccine delivery system. Herein the adjuvant activities of liposomes with different net surface charges (neutral, positive, or negative) were evaluated when admixed with protein antigens, ovalbumin (OVA, pI = 4.7), Bacillus anthracis protective antigen protein (PA, pI = 5.6), or cationized OVA (cOVA). Mice immunized subcutaneously with OVA admixed with different liposomes generated different antibody responses. Interestingly, OVA admixed with net negatively charged liposomes prepared with DOPA was as immunogenic as OVA admixed with positively charged liposomes prepared with DOTAP. Immunization of mice with the anthrax PA protein admixed with the net negatively charged DOPA liposomes also induced a strong and functional anti-PA antibody response. When the cationized OVA was used as a model antigen, liposomes with net neutral, negative, or positive charges showed comparable adjuvant activities. Immunization of mice with the OVA admixed with DOPA liposomes also induced OVA-specific CD8(+) cytotoxic T lymphocyte responses and significantly delayed the growth of OVA-expressing B16-OVA tumors in mice. However, not all net negatively charged liposomes showed a strong adjuvant activity. The adjuvant activity of the negatively charged liposomes may be related to the liposome's ability (i) to upregulate the expression of molecules related to the activation and maturation of antigen-presenting cells and (ii) to slightly facilitate the uptake of the antigens by antigen-presenting cells. Simply admixing certain negatively charged liposomes with certain protein antigens of interest may represent a novel platform for vaccine development.

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.

Interbilayer-crosslinked multilamellar vesicles as synthetic vaccines for potent humoral and cellular immune responses

Vaccines based on recombinant proteins avoid the toxicity and antivector immunity associated with live vaccine (for example, viral) vectors, but their immunogenicity is poor, particularly for CD8(+) T-cell responses. Synthetic particles carrying antigens and adjuvant molecules have been developed to enhance subunit vaccines, but in general these materials have failed to elicit CD8(+) T-cell responses comparable to those for live vectors in preclinical animal models. Here, we describe interbilayer-crosslinked multilamellar vesicles formed by crosslinking headgroups of adjacent lipid bilayers within multilamellar vesicles. Interbilayer-crosslinked vesicles stably entrapped protein antigens in the vesicle core and lipid-based immunostimulatory molecules in the vesicle walls under extracellular conditions, but exhibited rapid release in the presence of endolysosomal lipases. We found that these antigen/adjuvant-carrying vesicles form an extremely potent whole-protein vaccine, eliciting endogenous T-cell and antibody responses comparable to those for the strongest vaccine vectors. These materials should enable a range of subunit vaccines and provide new possibilities for therapeutic protein delivery.

Comparison of BCG, MPL and cationic liposome adjuvant systems in leishmanial antigen vaccine formulations against murine visceral leishmaniasis

Background

The development of an effective vaccine against visceral leishmaniasis (VL) caused by Leishmania donovani is an essential aim for controlling the disease. Use of the right adjuvant is of fundamental importance in vaccine formulations for generation of effective cell-mediated immune response. Earlier we reported the protective efficacy of cationic liposome-associated L. donovani promastigote antigens (LAg) against experimental VL. The aim of the present study was to compare the effectiveness of two very promising adjuvants, Bacille Calmette-Guerin (BCG) and Monophosphoryl lipid A (MPL) plus trehalose dicorynomycolate (TDM) with cationic liposomes, in combination with LAg, to confer protection against murine VL.

Results

All the three formulations afforded significant protection against L. donovani in both the visceral organs, liver and spleen. Although comparable level of protection was observed in BCG+LAg and MPL-TDM+LAg immunized mice, highest level of protection was exhibited by the liposomal LAg immunized group. Significant increase in anti-LAg IgG levels were detected in both MPL-TDM+LAg and liposomal LAg immunized animals with higher levels of IgG2a than IgG1. But BCG+LAg failed to induce any antibody response. As an index of cell-mediated immunity DTH responses were measured and significant response was observed in mice vaccinated with all the three different formulations. However, highest responses were observed with liposomal vaccine immunization. Comparative evaluation of IFN-γ and IL-4 responses in immunized mice revealed that MPL-TDM+LAg group produced the highest level of IFN-γ but lowest IL-4 level, while BCG+LAg demonstrated generation of suboptimum levels of both IFN-γ and IL-4 response. Elicitation of moderate levels of prechallenge IFN-γ along with optimum IL-4 corresponds with successful vaccination with liposomal LAg.

Conclusion

This comparative study reveals greater effectiveness of the liposomal vaccine for protection against progressive VL in BALB/c. Again, evaluation of the immune responses by vaccination emphasizes the need of stimulation of potent cellular immunity based on both Th1 and Th2 cell responses to confer protection against VL.