Non PC liposome entrapped promastigote antigens elicit parasite specific CD8+ and CD4+ T-cell immune response and protect hamsters against visceral leishmaniasis

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.

Immunoinformatics Approach to Design a Novel Subunit Vaccine Against Visceral Leishmaniasis

Visceral leishmaniasis (VL) infection is mostly caused by Leishmania donovani and affects countries worldwide. Despite the need for a safe and effective vaccine against leishmaniasis due to the increased drug resistance, however, no vaccine has yet been licensed for clinical use. This study revolves around the immunoinformatics approach to design a multi-epitope vaccine against VL infection. In this case, the proteome of L. donovani has been investigated, and three host non-homologous and antigenic extracellular secretory proteins have been identified as potential vaccine candidates with low transmembrane helices (≤ 1). The multi-epitope subunit vaccine construct consists of T-cell (cytotoxic T-lymphocyte (CTL) and helper T-lymphocyte (HTL)) epitopes accompanied by appropriate adjuvant and linkers. A 372-amino acid vaccine construct has been established with specific characteristics, such as soluble, stable, antigenic, non-allergenic, non-toxic, and non-host homologous. Besides, the tertiary structure of the designed vaccine was modeled and validated. Also, the stability and affinity of the vaccine- TLR4 complex were confirmed by using molecular docking and molecular dynamics (MD) simulation. In addition, in silico immunization assay showed the efficiency of this candidate vaccine to stimulate an effective immune response. Furthermore, the refined vaccine was optimized and cloned in the pET28a (+) vector, and its successful expression was confirmed virtually. However, the experimental validation is required to verify the multi-epitope vaccine efficacy against VL infection.

Current status of nanoscale drug delivery and the future of nano-vaccine development for leishmaniasis - A review

The study of tropical diseases like leishmaniasis, a parasitic disease, has not received much attention even though it is the second-largest infectious disease after malaria. As per the WHO report, a total of 0.7-1.0 million new leishmaniasis cases, which are spread by 23 Leishmania species in more than 98 countries, are estimated with an alarming 26,000-65,000 death toll every year. Lack of potential vaccines along with the cost and toxicity of amphotericin B (AmB), the most common drug for the treatment of leishmaniasis, has raised the interest significantly for new formulations and drug delivery systems including nanoparticle-based delivery as anti-leishmanial agents. The size, shape, and high surface area to volume ratio of different NPs make them ideal for many biological applications. The delivery of drugs through liposome, polymeric, and solid-lipid NPs provides the advantage of high biocomatibilty of the carrier with reduced toxicity. Importantly, NP-based delivery has shown improved efficacy due to targeted delivery of the payload and synergistic action of NP and payload on the target. This review analyses the advantage of NP-based delivery over standard chemotherapy and natural product-based delivery system. The role of different physicochemical properties of a nanoscale delivery system is discussed. Further, different ways of nanoformulation delivery ranging from liposome, niosomes, polymeric, metallic, solid-lipid NPs were updated along with the possible mechanisms of action against the parasite. The status of current nano-vaccines and the future potential of NP-based vaccine are elaborated here.

Hypothesis: Designation of Liposomal Scavenger System for Fighting against 2019-nCoV

2019 novel coronavirus (2019-nCoV), also known as severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) or COVID-19 virus, is a member of the family Coronaviridae, which is responsible for the current pandemic of disease COVID-19. It is the seventh member of the family Coronaviridae, which infects humans, after 229E, OC43, NL63, HKU1, SARS-CoV and Middle East respiratory syndrome coronavirus (MERS-CoV). Fever, dry cough and severe pneumonia are seen as common symptoms at the early stages of COVID-19. Some cases progress to acute respiratory stress syndrome, septic shock, organ failure, and death. The development of an effective treatment or vaccination for treating or preventing this lethal condition is an urgent need in order to fight this crisis. Up to now, some effective vaccines with different efficacy profiles have been introduced. Herein, we have theoretically designed a scavenger system for gathering 2019-nCoVs, breaking them, and re-introducing them to the immune system.

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.

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.

Visceral leishmaniasis: An overview of vaccine adjuvants and their applications

Although there has been an extensive research on vaccine development over the last decade and some vaccines have been commercialized for canine visceral leishmaniasis (CVL), but as yet no effective vaccine is available for anthroponotic VL which may partly be due to the absence of an appropriate adjuvant system. Vaccines alone yield poor immunity hence requiring an adjuvant which can boost the immunosuppressed state of VL infected individuals by eliciting adaptive immune responses to achieve required immunological enhancement. Recent studies have documented the continuous efforts that are being made in the field of adjuvants research in an attempt to render vaccines more effective. This review article focuses on adjuvants, particularly particulate and non-particulate ones, which have been assessed with VL vaccine candidates in several preclinical and clinical trials outlining the induction of immune responses obtained from these studies. Moreover, we have emphasized the applicability of multiple adjuvants combination for an improvement in the potential of a VL vaccine.

Vaccination with poly(D,L-lactide-co-glycolide) nanoparticles loaded with soluble Leishmania antigens and modified with a TNFα-mimicking peptide or monophosphoryl lipid A confers protection against experimental visceral leishmaniasis

Visceral leishmaniasis (VL) persists as a major public health problem, and since the existing chemotherapy is far from satisfactory, development of an effective vaccine emerges as the most appropriate strategy for confronting VL. The development of an effective vaccine relies on the selection of the appropriate antigen and also the right adjuvant and/or delivery vehicle. In the present study, the protective efficacy of poly(D,L-lactide-co-glycolide) (PLGA) nanoparticles (NPs), which were surface-modified with a TNFα-mimicking eight-amino-acid peptide (p8) and further functionalized by encapsulating soluble Leishmania infantum antigens (sLiAg) and monophosphoryl lipid A (MPLA), a TLR4 ligand, was evaluated against challenge with L. infantum parasites in BALB/c mice. Vaccination with these multifunctionalized PLGA nanoformulations conferred significant protection against parasite infection in vaccinated mice. In particular, vaccination with PLGA-sLiAg-MPLA or p8-PLGA-sLiAg NPs resulted in almost complete elimination of the parasite in the spleen for up to 4 months post-challenge. Parasite burden reduction was accompanied by antigen-specific humoral and cellular immune responses. Specifically, injection with PLGA-sLiAg-MPLA raised exclusively anti-sLiAg IgG1 antibodies post-vaccination, while in p8-PLGA-sLiAg-vaccinated mice, no antibody production was detected. However, 4 months post-challenge, in mice vaccinated with all the multifunctionalized NPs, antibody class switching towards IgG2a subtype was observed. The study of cellular immune responses revealed the increased proliferation capacity of spleen cells against sLiAg, consisting of IFNγ-producing CD4⁺ and CD8⁺ T cells. Importantly, the activation of CD8⁺ T cells was exclusively attributed to vaccination with PLGA NPs surface-modified with the p8 peptide. Moreover, characterization of cytokine production in vaccinated-infected mice revealed that protection was accompanied by significant increase of IFNγ and lower levels of IL-4 and IL-10 in protected mice when compared to control infected group. Conclusively, the above nanoformulations hold promise for future vaccination strategies against VL.

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.

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.

Escheriosome-mediated cytosolic delivery of PLK1-specific siRNA: potential in treatment of liver cancer in BALB/c mice

AIM

In the present study, the anticancer efficacy of a novel escheriosome-based formulation of PLK1-specific siRNA was evaluated against liver cancer in BALB/c mice.

MATERIALS & METHODS

The escheriosome-based siRNA nanoparticles were prepared using lipids isolated from Escherichia coli. The escheriosomes were characterized for size, surface charge and stability. The anticancer potential of PLK1-specific siRNA formulation was ascertained on the basis of expression of pro-/anti-apoptotic factors and histopathological studies.

RESULTS

The escheriosome-entrapped siRNA was found to be released in surrounding milieu in a sustained manner. The nanoformulation was successful in modulating proapoptotic factors and eventually helped in better survival of the treated animals.

CONCLUSION

Our data demonstrate the efficacy of systemically administered siRNA in the treatment of experimental liver cancer. This novel therapeutic strategy may be applicable to a broad range of cancers in patients with the obstinate form of the disease.

Vaccines to prevent leishmaniasis

Leishmaniasis is a parasitic disease that encompasses a range of clinical manifestations affecting people in tropical and subtropical regions of the world. Epidemiological and experimental data indicate that protection from disease can be achieved in most people. In addition, we know how the host immune system must respond to infection in order to control parasite growth. However, there is still no vaccine for use in humans. Here, we review our understanding of host immunity following Leishmania infection and also discuss recent advances in the development of vaccines to prevent leishmaniasis, highlighting a new promising approach that targets the parasite hemoglobin receptor.

Oligomannose-coated liposome as a novel adjuvant for the induction of cellular immune responses to control disease status

Professional phagocytic cells, such as dendritic cells, are mainly responsible for phagocytosis, antigen presentation, and cytokine secretion, which induce subsequent activation of T cell-mediated immunity. Thus, strategies that deliver antigens and stimulatory signals to the cells have significant implications for vaccine design. In this paper, we summarize the potential for liposomes coated with the neoglycolipids containing oligomannose residues (OMLs) as a novel adjuvant for induction of Th1 immune responses and CTLs specific for the encased antigen. OMLs preferentially take up peripheral phagocytic cells. In response to OML uptake, the cells secrete IL-12 selectively, enhance the expression of costimulatory molecules, and migrate into lymphoid tissues from peripheral tissues. OMLs also have the ability to deliver encapsulated protein antigens to the MHC class I and class II pathways to generate antigen-specific CTLs and Th1 cells, respectively, and lipid antigen to CD1d to activate NKT cells. Since administration of OML-based vaccines can eliminate an established tumor, inhibit elevation of the serum IgE level, and prevent progression of protozoan infections in several murine, human, and bovine models, OML-based vaccines have revealed their potential for clinical use in vaccination for a variety of diseases in which CTLs and/or Th1 cells act as effector cells.

Heat shock proteins enriched-promastigotes of Leishmania major inducing Th2 immune response in BALB/c mice

BACKGROUND

Heat shock proteins (HSP) are highly conserved molecules with many immunological functions. They are highly immunogenic with important role in cancer immunotherapy and in vaccine development against infectious diseases. As adjuvant, HSP can augment the immunogenicity of weak antigens and can stimulate antigen presenting cells. Although vaccines have been successful for many infectious diseases, progress in leishmaniasis has not been achieved. In this report, the protective effect of HSP-enriched soluble leishmania antigen (SLA) was determined.

METHODS

BALB/c mice were immunized 3× with HSP-enriched SLA and SLA alone and 10 days after final boost. They were infected with 106 stationary phase promastigote of Leishmania major and immunological responses were followed until nine weeks.

RESULTS

No significant differences were observed in lymphocyte proliferation, footpad swelling, parasite burden, nitric oxide or IL-12 cytokine between HSP-enriched or SLA groups. Although the levels of IFN-γ, IL-4, TGF-β, IgG1 and IgG2b were increased in both groups, IFN-γ was significantly higher in SLA group and IgG2a in HSP-enriched SLA.

CONCLUSION

These results indicate that HSP direct the immune system towards Th2 pattern and does not have protective role in L. major infection.

Development of Leishmania vaccines: predicting the future from past and present experience

Leishmaniasis is a disease that ranges in severity from skin lesions to serious disfigurement and fatal systemic infection. Resistance to infection is associated with a T-helper-1 immune response that activates macrophages to kill the intracellular parasite in a nitric oxide-dependent manner. Conversely, disease progression is generally associated with a T-helper-2 response that activates humoral immunity. Current control is based on chemotherapeutic treatments which are expensive, toxic and associated with high relapse and resistance rates. Vaccination remains the best hope for control of all forms of the disease, and the development of a safe, effective and affordable antileishmanial vaccine is a critical global public-health priority. Extensive evidence from studies in animal models indicates that solid protection can be achieved by immunization with defined subunit vaccines or live-attenuated strains of Leishmania. However, to date, no vaccine is available despite substantial efforts by many laboratories. Major impediments in Leishmania vaccine development include: lack of adequate funding from national and international agencies, problems related to the translation of data from animal models to human disease, and the transition from the laboratory to the field. Furthermore, a thorough understanding of protective immune responses and generation and maintenance of the immunological memory, an important but least-studied aspect of antiparasitic vaccine development, during Leishmania infection is needed. This review focuses on the progress of the search for an effective vaccine against human and canine leishmaniasis.

Lipoidal soft hybrid biocarriers of supramolecular construction for drug delivery

Lipid-based innovations have achieved new heights during the last few years as an essential component of drug development. The current challenge of drug delivery is liberation of drug agents at the right time in a safe and reproducible manner to a specific target site. A number of novel drug delivery systems has emerged encompassing various routes of administration, to achieve controlled and targeted drug delivery. Microparticulate lipoidal vesicular system represents a unique technology platform suitable for the oral and systemic administration of a wide variety of molecules with important therapeutic biological activities, including drugs, genes, and vaccine antigens. The success of liposomes as drug carriers has been reflected in a number of liposome-based formulations, which are commercially available or are currently undergoing clinical trials. Also, novel lipid carrier-mediated vesicular systems are originated. This paper has focused on the lipid-based supramolecular vesicular carriers that are used in various drug delivery and drug targeting systems.

Lipoidal soft hybrid biocarriers of supramolecular construction for drug delivery

Lipid-based innovations have achieved new heights during the last few years as an essential component of drug development. The current challenge of drug delivery is liberation of drug agents at the right time in a safe and reproducible manner to a specific target site. A number of novel drug delivery systems has emerged encompassing various routes of administration, to achieve controlled and targeted drug delivery. Microparticulate lipoidal vesicular system represents a unique technology platform suitable for the oral and systemic administration of a wide variety of molecules with important therapeutic biological activities, including drugs, genes, and vaccine antigens. The success of liposomes as drug carriers has been reflected in a number of liposome-based formulations, which are commercially available or are currently undergoing clinical trials. Also, novel lipid carrier-mediated vesicular systems are originated. This paper has focused on the lipid-based supramolecular vesicular carriers that are used in various drug delivery and drug targeting systems.

The pH-sensitive fusogenic 3-methyl-glutarylated hyperbranched poly(glycidol)-conjugated liposome induces antigen-specific cellular and humoral immunity

We examined the ability of a novel liposome, surface modified by 3-methyl-glutarylated hyperbranched poly(glycidol) (MGlu-HPG), to enhance antigen-specific immunity in vitro and in vivo and to function as a vaccine carrier. Murine bone marrow-derived dendritic cells took up ovalbumin (OVA) encapsulated in MGlu-HPG-modified liposomes more effectively than free OVA or OVA encapsulated in unmodified liposomes. Immunization of mice with OVA-containing MGlu-HPG-modified liposomes induced antigen-specific splenocyte proliferation and production of gamma interferon (IFN-γ) more strongly than did immunization with free OVA or OVA encapsulated in unmodified liposomes. The immune responses induced by OVA encapsulated in MGlu-HPG-modified liposomes were significantly suppressed by addition of anti-major histocompatibility complex (MHC) class I and class II monoclonal antibodies, indicating the involvement of antigen presentation via MHC class I and II. Furthermore, delayed-type hypersensitivity responses and OVA-specific antibodies were induced more effectively in mice immunized with OVA encapsulated by MGlu-HPG-modified liposomes than with unencapsulated OVA or OVA encapsulated in unmodified liposomes. These results suggested that MGlu-HPG-modified liposomes effectively induced both cell-mediated and humoral immune responses. Collectively, this study is the first to demonstrate the induction of both cell-mediated and humoral immune responses in vivo by MGlu-HPG-modified liposomes.

Liposomal SLA co-incorporated with PO CpG ODNs or PS CpG ODNs induce the same protection against the murine model of leishmaniasis

First generation Leishmania vaccines consisting of whole killed parasites with or without adjuvants have reached phase 3 trial and failed to show enough efficacy mainly due to the lack of an appropriate adjuvant. In this study, the nuclease-resistant phosphorothioate CpG oligodeoxynucleotides (PS CpG) or nuclease-sensitive phosphodiester CpG ODNs (PO CpG) were used as adjuvants to enhance immunogenicity and rate of protection against leishmaniasis. Due to the susceptibility of PO CpG to nuclease degradation, an efficient liposomal delivery system was developed to protect them from degradation. 1, 2-dioleoyl-3-trimethylammonium-propane (DOTAP) as a cationic lipid was used because of its unique adjuvanticity and electrostatic interaction with negatively charged CpG ODNs. To evaluate the role of liposomal formulation in protection rate and enhanced immune response, BALB/c mice were immunized subcutaneously with liposomal soluble Leishmania antigens (SLA) co-incorporated with PO CpG (Lip-SLA-PO CpG), Lip-SLA-PS CpG, SLA+PO CpG, SLA+PS CpG, SLA or buffer. As criteria for protection, footpad swelling at the site of challenge, parasite loads, the levels of IFN-γ and IL-4, and the IgG subtypes were evaluated. The groups of mice receiving Lip-SLA-PO CpG or Lip-SLA-PS CpG showed a high protection rate compared with the control groups. In addition, there was no significant difference in immune response generation between mice immunized with PS CpG and the group receiving PO CpG when incorporated into the liposomes. The results suggested that liposomal form of PO CpG might be used instead of PS CpG in future vaccine formulations as an efficient adjuvant.

Leptosome-entrapped leptospiral antigens conferred significant higher levels of protection than those entrapped with PC-liposomes in a hamster model

We prepared novel liposomes from total polar lipids of non-pathogenic Leptospira biflexa serovar Potac (designated leptosomes) and evaluated their vaccine delivery/adjuvant potential with novel protective antigens (Lp0607, Lp1118 and Lp1454) of L. interrogans serovar Pomona in a hamster model. The immune response induced by three individual antigens and protective efficacy were evaluated and compared to those induced by same antigens entrapped with PC-liposomes and E. coli lipid liposomes (escheriosomes). Four-week-old hamsters were immunized subcutaneously twice at a 3-week interval, bled at various time points to evaluate antibody response and sacrificed to isolate splenocytes for lymphocyte proliferation and cytokine profiles in response to recall antigen. For the challenge test, 10x MLD(50) (modified lethal dose 50%) of virulent L. interrogans serovar Pomona were administered intraperitoneally. Our results demonstrate that leptosome are better adjuvant than PC-liposomes as revealed by enhanced long term antibody response, lymphocyte proliferation and significant enhancement of both Th1 (IFN-gamma) and Th2 (IL-4 and IL-10) cytokines. Additionally, leptosomes and escheriosomes induced significantly higher level of memory responses than PC-liposome did. Moreover, the novel leptosomal vaccine induced significantly higher levels of protection than those prepared with PC-liposomes as revealed by enhanced survival, reduced histopathological lesions in vital organs and reduced leptospiral load in kidneys. Taken together, the results of the present study clearly reveal that both leptosomes and escheriosomes have emerged as promising delivery vehicles/adjuvants that can be widely exploited with newly discovered antigens in future leptospira vaccines.

The utility of rhesus monkey (Macaca mulatta) and other non-human primate models for preclinical testing of Leishmania candidate vaccines

Leishmaniasis causes significant morbidity and mortality, constituting an important global health problem for which there are few effective drugs. Given the urgent need to identify a safe and effective Leishmania vaccine to help prevent the two million new cases of human leishmaniasis worldwide each year, all reasonable efforts to achieve this goal should be made. This includes the use of animal models that are as close to leishmanial infection in humans as is practical and feasible. Old world monkey species (macaques, baboons, mandrills etc.) have the closest evolutionary relatedness to humans among the approachable animal models. The Asian rhesus macaques (Macaca mulatta) are quite susceptible to leishmanial infection, develop a human-like disease, exhibit antibodies to Leishmania and parasite-specific T-cell mediated immune responses both in vivo and in vitro, and can be protected effectively by vaccination. Results from macaque vaccine studies could also prove useful in guiding the design of human vaccine trials. This review summarizes our current knowledge on this topic and proposes potential approaches that may result in the more effective use of the macaque model to maximize its potential to help the development of an effective vaccine for human leishmaniasis.

Recent developments in leishmaniasis vaccine delivery systems

BACKGROUND

The observation that recovery from infection with Leishmania confers immunity to reinfection suggests that control of leishmaniasis by vaccination may be possible. New generation vaccines, particularly those based on recombinant proteins and DNA, are found to be less immunogenic.

OBJECTIVE

There is an urgent need for the development of new and improved vaccine adjuvants.

METHODS

Based on their principal mechanisms of action, adjuvants can be broadly separated into two classes: immunostimulatory adjuvants and vaccine delivery systems. Vaccine delivery systems can carry both antigen and adjuvant for effective delivery to the antigen-presenting cells (APCs). In this article, we review the adjuvants, the delivery systems and their combinations used in the search of an effective vaccine against leishmaniasis.

CONCLUSION

Based on current knowledge, cationic liposomes appear to have better prospects as effective delivery systems for developing a vaccine for leishmaniasis.

Leishmanial antigens in liposomes promote protective immunity and provide immunotherapy against visceral leishmaniasis via polarized Th1 response

Leishmaniasis affects 12 million people, and it is generally agreed that vaccination provides the best long-term strategy for its control. An ideal vaccine should be effective in both preventing and treating leishmaniasis. However, immunological correlates to predict vaccine efficacy and success of treatment in visceral leishmaniasis (VL) remain ill defined. Here, we correlated the vaccine efficacy of soluble leishmanial antigens (SLA) from Leishmania donovani promastigote membrane, entrapped in negative, neutral and positively charged liposomes with the elicited immune responses to predict vaccine success in experimental VL. Production of both IFN-gamma and IL-4 with a dominance of Th1 response following immunization was required for optimum success against L. donovani infection in BALB/c mice. The best vaccine formulation, SLA in positively charged liposomes, was then used for immunotherapy. This vaccine induced more than 90% elimination of parasites from both liver and spleen. The success of immunotherapy exhibited an immune modulation with surge in Th1 cytokines, IFN-gamma and IL-12 with extreme down regulation of disease promoting IL-4 and IL-10. These findings suggest that an immune modulation towards Th1 is effective for both successful vaccination and immunotherapy.

Enhanced desensitization efficacy by liposomal conjugation of a specific antigen

Since liposomes are known as strong adjuvants, we attempted to use liposomes in immunotherapy as adjuvants, and to achieve desensitization in pre-sensitized mice. At first, we sensitized mice with intraperitoneal injection of model antigen, 100 microg ovalbumin (OVA), with Alum and treated them with liposome composed of distearoylphosphatidylcholine (DSPC) and cholesterol (2:1 as a molar ratio), which was coupled with a small amount of OVA (10 microg OVA in 400 nmol DSPC and 200 nmol cholesterol-liposome was injected into 20 g mouse). It is well known that antigen-specific immunotherapy increases IgG blocking antibodies and decreases in IgE antibodies. The treatment with i.v. injection of OVA-liposome at days 8, 10, and 12 after sensitization strongly suppressed OVA-specific IgE production without affecting IgG level after the boost (100 microg OVA with Alum). Moreover, the treatment with high-density OVA-liposome (10 microg OVA in 80 nmol DSPC and 40 nmol cholesterol-liposome/20 g mouse) not only strongly suppressed IgE levels but also reduced IgG production after the boost of OVA-sensitized mice suggesting the importance of liposomal characteristic in desensitization immunotherapy. Next we reduced the dose of OVA-liposome and the desensitization effect was also observed at the dose of as low as 1 microg OVA on OVA-liposome/mouse. On the contrary, free OVA did not affect the production of both IgG and IgE levels. Biodistribution study indicated that OVA-liposome was highly accumulated in spleen of OVA-sensitized mice compared to control liposome at 3 h after i.v. injection. These results suggest that the liposomal OVA effectively interacts with and desensitizes immune cells, therefore, liposomes coupling with a certain antigen may be effective in allergy immunotherapy.

Prophylactic potential of liposomized integral membrane protein of Plasmodium yoelii nigeriensis against blood stage infection in BALB/c mice

Triton X-114 phase separated integral membrane proteins (IMPs) of a multidrug resistant strain of Plasmodium yoelii nigeriensis (P. yoelii) were screened for their potential to impart protection against malaria infection in BALB/c mice. As revealed by immunoblotting, antibodies present in parasite specific sera from convalescent (protected) as well as immunized (partially protected) animals recognized different membrane proteins. A thorough investigation reveals that P. yoelii specific convalescent sera recognized IMPs with molecular masses ranging from 21 to 81 kDa. Among various membrane proteins, the IMPs corresponding to 81 and 66 kDa molecular weight were highly prominent in the immunoblots probed with the sera from convalescent animals, whereas sera from immunized animals failed to produce impressive band pattern. Immunofluorescence assay revealed that the 66-kDa IMP specific antibodies reacted with fixed smears of mature schizonts and merozoites. Further immunization with 66 kDa IMP (PyIMP) purified through polyclonal IgG sepharose 4B affinity did not impart effective immune response (in its free form) and could provided partial protection only. On the other hand, animals immunized with 66 kDa PyIMP entrapped in phosphatidyl-choline/cholesterol (PC/chol) liposomes protected BALB/c mice against lethal P. yoelii challenge.