Safety and immunogenicity of a defined vaccine for the prevention of cutaneous leishmaniasis

Treatment of leishmaniasis with chemotherapy and vaccine: a mathematical model

Leishmaniasis, an infectious disease, manifests itself mostly in two forms, cutaneous leishmaniasis (CL) and, a more severe and potentially deadly form, visceral leishmaniasis (VL). The current control strategy for leishmaniasis relies on chemotherapy drugs such as sodium antimony gluconate (SAG) and meglumine antimoniate (MA). However, all these chemotherapy compounds have poor efficacy, and they are associated with toxicity and other adverse effects, as well as drug resistance. While research in vaccine development for leishmaniasis is continuously progressing, no vaccine is currently available. However, some experimental vaccines such as LEISH-F1+MPL-SE (V) have demonstrated some efficacy when used as drugs for CL patients. In this paper we use a mathematical model to address the following question: To what extent vaccine shots can enhance the efficacy of standard chemotherapy treatment of leishmaniasis? Starting with standard MA treatment of leishmaniasis and combining it with three injections of V , we find, by Day 84, that efficacy increased from 29% to 65-91% depending on the amount of the vaccine. With two or just one injection of V , efficacy is still very high, but there is a definite resurgence of the disease by end-time.

Cutaneous Leishmaniasis: Associated Risk Factors and Prevention in Hubuna, Najran, Saudi Arabia

Background

Many countries are currently affected by leishmaniasis, and cutaneous leishmaniasis is ranked among the ten most neglected diseases. The aim of this study was to determine the risk factors related to cutaneous leishmaniasis and preventive measures among people living in Hubuna, Najran, Saudi Arabia.

Methods

A community-based cross-sectional survey was conducted from January to October 2022. A convenience sampling technique was used, with 396 individuals invited to participate in the current study and 391 included. A self-administered questionnaire was utilized for collecting data. Descriptive analysis was used for risk factors and preventive measures, while χ² tests were used for determining associations with risk factors.

Results

Among participants, 38.1% (n=149) reported having cutaneous leishmaniasis clinically diagnosed and under treatment. Age 0-10 years was found to be associated significantly with cutaneous leishmaniasis infection (AOR 3.08, 95% CI 1.6-6.4; P=0.002) compared to other groups. A significant association was noted too for those residing in/around planted areas versus those who were not (AOR 1.18, 95% CI 0.13-2.24; P<0.001). In terms of occupation, farming was significantly associated with cutaneous leishmaniasis (AOR 2.54, 95% CI 1.15-3.76; P=0.010). No significant associations were observed in regard to sex (AOR 1.4, 95% CI 0.7-1.6; P=0.11), education (P=0.072), or preventive measures used (P>0.05).

Conclusion

The cutaneous leishmaniasis endemicity level in Hubuna was high. Several socioeconomic and environmental factors contribute enormously to the spread of the disease in the area. Further investigation of risk factors of cutaneous leishmaniasis all over the country and setting up appropriate interventions to prevent its spread are recommended.

MPLA and AddaVax® Adjuvants Fail to Promote Intramuscular LaAg Vaccine Protectiveness against Experimental Cutaneous Leishmaniasis

There is so far no vaccine approved for human leishmaniasis, mainly because of the lack of appropriate adjuvants. This study aimed to evaluate in mice the capacity of a mixture of monophosphoryl lipid A (MPLA) and AddaVax^® adjuvants in enhancing the efficacy of a Leishvacin^®-like vaccine comprised of Leishmania amazonensis whole antigens (LaAg). For that, mice were immunized with LaAg plus MPLA/AddaVax^® by the intramuscular route (i.m.) prior to challenge with 2 × 10⁵ and 2 × 10⁶ living parasites. Immunization with LaAg alone reduced the lesion growth of the 2 × 10⁵-challenged mice only in the peak of infection, but that was not accompanied by reduced parasite load, and thus not considered protective. Mice given a 2 × 10⁶ -challenge were not protected by LaAg. The association of LaAg with MPLA/AddaVax^® was able to enhance the cutaneous hypersensitivity response compared with LaAg alone. Despite this, there was no difference in proliferative cell response to antigen ex vivo. Moreover, regardless of the parasite challenge, association of LaAg with MPL/AddaVax^® did not significantly enhance protection in comparison with LaAg alone. This work demonstrated that MPL/AddaVax^® is not effective in improving the efficacy of i.m. LaAg vaccine against cutaneous leishmaniasis.

Three decades of clinical trials on immunotherapy for human leishmaniases: a systematic review and meta-analysis

Aim: Current treatments for leishmaniases are not satisfactory, thus alternatives are needed. We searched for clinical trials with immunotherapeutic approaches for patients with leishmaniasis. Materials & methods: Out of 205 articles, 24 clinical trials were selected, and eight submitted to meta-analysis. Results: A reduction in healing time was observed in patients with tegumentary leishmaniasis treated with pentavalent antimony plus granulocyte-macrophage colony-stimulating factor, and therapeutic vaccines. Overall meta-analysis indicated that immunotherapy associated with the standard chemotherapy generated a significantly reduced risk of treatment failure than the pentavalent antimony alone (p = 0.03). Conclusion: Our review confirmed the efficacy of immunotherapies for the treatment of cutaneous and visceral leishmaniasis and highlighted the importance of clinical trials using immunotherapies for leishmaniases.

Vaccines for leishmaniasis and the implications of their development for American tegumentary leishmaniasis

The leishmaniases are a collection of vector-borne parasitic diseases caused by a number of different Leishmania species that are distributed worldwide. Clinical and laboratory research have together revealed several important immune components that control Leishmania infection and indicate the potential of immunization to prevent leishmaniasis. In this review we introduce previous and ongoing experimental research efforts to develop vaccines against Leishmania species. First, second and third generation vaccine strategies that have been proposed to counter cutaneous and visceral leishmaniasis (CL and VL, respectively) are summarized. One of the major bottlenecks in development is the transition from results in animal model studies to humans, and we highlight that although American tegumentary leishmaniasis (ATL; New World CL) can progress to destructive and disfiguring mucosal lesions, most research has been conducted using mouse models and Old World Leishmania species. We conclude that assessment of vaccine candidates in ATL settings therefore appears merited.

Novos adjuvantes vacinais: importante ferramenta para imunoterapia da leishmaniose visceral

Atualmente, muitas das vacinas em desenvolvimento são aquelas compostas de proteínas antigênicas individuais de parasitas ou uma combinação de vários antígenos individuais que são produzidos como produtos recombinantes obtidos por técnicas de biologia molecular. Dentre elas a Leish-111f e sua variação Leish-110f tem ganhado destaque na proteção contra a LV e LC e alcançaram estudos de fase II em seres humanos. A eficácia de uma vacina é otimizada pela adição de adjuvantes imunológicos. No entanto, embora os adjuvantes tenham sido usados por mais de um século, até o momento, apenas alguns adjuvantes são aprovados para o uso em humanos, a maioria destinada a melhorar a eficácia da vacina e a produção de anticorpos protetores específicos do antígeno. Os mecanismos de ação dos adjuvantes imunológicos são diversos, dependendo da sua natureza química e molecular sendo capazes de ativar células imunes especificas que conduzem a respostas imunes inatas e adaptativas melhoradas. Embora o mecanismo de ação molecular detalhado de muitos adjuvantes ainda seja desconhecido, a descoberta de receptores Toll-like (TLRs) forneceu informações críticas sobre o efeito imunoestimulador de numerosos componentes bacterianos que envolvem interação com receptores TLRs, mostrando que estes ligantes melhoram tanto a qualidade como a quantidade de respostas imunes adaptativas do hospedeiro quando utilizadas em formulações de vacinais direcionadas para doenças. O potencial desses adjuvantes de TLR em melhorar o design e os resultados de várias vacinas está em constante evolução, à medida que novos agonistas são descobertos e testados em modelos experimentais e estudos clínicos de vacinação. Nesta revisão, é apresentado um resumo do progresso recente no desenvolvimento de proteínas recombinantes de segunda geração e adjuvantes de TLR, sendo o foco principal nos TLR4 e suas melhorias.

New Insights on the Adjuvant Properties of the Leishmania infantum Eukaryotic Initiation Factor

Vaccination is the most effective tool against infectious diseases. Subunit vaccines are safer compared to live-attenuated vaccines but are less immunogenic and need to be delivered with an adjuvant. Adjuvants are essential for enhancing vaccine potency by improving humoral and cell-mediated immune responses. Only a limited number of adjuvants are licensed for human vaccines, and their mode of action is still not clear. Leishmania eukaryotic initiation factor (LeIF) has been described having a dual role, as a natural adjuvant and as an antigen that possesses advantageous immunomodulatory properties. In this study, we assessed the adjuvant properties of recombinant Leishmania infantum eukaryotic initiation factor (LieIF) through in vitro and in vivo assays. LieIF was intraperitoneally administered in combination with the protein antigen ovalbumin (OVA), and the widely used alum was used as a reference adjuvant. Our in vitro studies using J774A.1 macrophages showed that LieIF induced stimulatory effects as demonstrated by the enhanced surface expression of CD80 and CD86 co-stimulatory molecules and the induced production of the immune mediators NO and MIP-1α. Additionally, LieIF co-administration with OVA in an in vivo murine model induced a proinflammatory environment as demonstrated by the elevated expression of TNF-α, IL-1β, and NF-κB2 genes in peritoneal exudate cells (PEC). Furthermore, PEC derived from OVA-LieIF-immunized mice exhibited elevated expression of CD80 molecule and production of NO and MIP-1α in culture supernatants. Moreover, LieIF administration in the peritoneum of mice resulted in the recruitment of neutrophils and monocytes at 24 h post-injection. Also, we showed that this immunopotentiating effect of LieIF did not depend on the induction of uric acid danger signal. These findings suggest the potential use of LieIF as adjuvant in new vaccine formulations against different infectious diseases.

Cloning and molecular characterization of thiol-specific antioxidant gene of Leishmania tropica Turkey isolate

Background/aim

Thiol-specific antioxidant (TSA) protein is one of the most promising molecules among candidates for vaccine against cutaneous leishmaniasis. It was found to be significantly protective against different Leishmania species. In this study, cloning and molecular characterization of thiol-specific antioxidant gene of L. tropica Turkey isolate (LtTSA) were aimed.

Materials and methods

LtTSA was amplified by PCR using the specific primers of TSA gene and cloned into the pcDNA3.1 vector. The cloning was confirmed by PCR screening, restriction enzyme reactions, and DNA sequence analysis. Finally, three-dimensional structure and antigenic properties of the protein encoded by the LtTSA were determined

Results

Six hundred base pair bands belonging to LtTSA were shown with electrophoresis. It was found that LtTSA and its encoded protein have high similarity with different Leishmania species. LtTSA protein consisting of 199 amino acids was found to have 7 different antigenic regions.

Conclusion

LtTSA and its encoded TSA protein were found to be highly immunogenic and similar to TSA proteins previously tested as a vaccine candidate.

Pentavalent Antimonials Combined with Other Therapeutic Alternatives for the Treatment of Cutaneous and Mucocutaneous Leishmaniasis: A Systematic Review

The first choice drugs for the treatment of cutaneous and mucocutaneous leishmaniasis are pentavalent antimonials, sodium stibogluconate, or meglumine antimoniate. However, the treatment with these drugs is expensive, can cause serious adverse effects, and is not always effective. The combination of two drugs by different routes or the combination of an alternative therapy with systemic therapy can increase the efficacy and decrease the collateral effects caused by the reference drugs. In this systematic review we investigated publications that described a combination of nonconventional treatment for cutaneous and mucocutaneous with pentavalent antimonials. A literature review was performed in the databases Web of Knowledge and PubMed in the period from 01st of December 2004 to 01st of June 2017, according to Prisma statement. Only clinical trials involving the treatment for cutaneous or mucocutaneous leishmaniasis, in English, and with available abstract were added. Other types of publications, such as reviews, case reports, comments to the editor, letters, interviews, guidelines, and errata, were excluded. Sixteen articles were selected and the pentavalent antimonials were administered in combination with pentoxifylline, granulocyte macrophage colony-stimulating factor, imiquimod, intralesional sodium stibogluconate, ketoconazole, silver-containing polyester dressing, lyophilized LEISH-F1 protein, cryotherapy, topical honey, and omeprazole. In general, the combined therapy resulted in high rates of clinical cure and when relapse or recurrence was reported, it was higher in the groups treated with pentavalent antimonials alone. The majority of the articles included in this review showed that cure rate ranged from 70 to 100% in patients treated with the combinations. Serious adverse effects were not observed in patients treated with drugs combination. The combination of other drugs or treatment modalities with pentavalent antimonials has proved to be effective for cutaneous and mucocutaneous leishmaniasis and for most seemed to be safe. However, new randomized, controlled, and multicentric clinical trials with more robust samples should be performed, especially the combination with immunomodulators.

A review of cutaneous leishmaniasis in Morocco: A vertical analysisto determine appropriate interventions for control and prevention

Leishmaniasis is considered one of the most neglected diseases worldwide. In Morocco, cutaneous leishmaniasis is an important public health problem. Leishmania major and Leishmania tropica are the two major species in this country. Despite all efforts, monitoring and control of the cutaneous leishmaniasis is still challenging. We used for the first time a vertical analysis of the control of cutaneous leishmaniasis in Morocco from the document review and publications. This analysis allowed us to develop an epidemiological model that emphasized key possible interventions. No evaluation studies of these interventions in Morocco were done. Global Evidence underline the effectiveness of preventive interventions produced in integrate inter-sectorial strategy framework (e.g use of insecticide-treated bednets, indoor residual spraying and rodents' control) rather than treatments such as based thermotherapy, cryotherapy, photodynamic therapy, CO2 laser and paromomycin. Therefore, integrated vector management control (IVMC) with communityc participation is recommended as effective strategy. Strengthening of the IVMC with community involvement are necessary conditions to improve the program of cutaneous leishmaniasis and prevent epidemic foci appearance.

The potential HLA Class I-restricted epitopes derived from LeIF and TSA of Leishmania donovani evoke anti-leishmania CD8+ T lymphocyte response

To explore new protective measure against visceral leishmaniasis, reverse vaccinology approach was employed to identify key immunogenic regions which can mediate long-term immunity. In-depth computational analysis revealed nine promiscuous epitopes which can possibly be presented by 46 human leukocyte antigen, thereby broadening the worldwide population up to 94.16%. This is of reasonable significance that most of the epitopes shared 100% sequence homology with other Leishmania species and could evoke a common pattern of protective immune response. Transporter associated with antigen processing binding affinity, molecular docking approach followed by dynamics simulation and human leukocyte antigen stabilization assay suggested that the best five optimal set of epitopes bind in between α1 and α2 binding groove with sufficient affinity and stability which allows the translocation of intact epitope to the cell surface. Fascinatingly, the human leukocyte antigen stabilization assay exhibited a modest correlation with the positive immunogenicity score predicted by class I pMHC immunogenicity predictor. A support for this notion came from ELISA and FACS analysis where the epitopes as a cocktail induced CD8+ IFN-γ and Granzyme B levels significantly in treated visceral leishmaniasis subject which suggests the immunogenic ability of the selected epitopes.

The TLR-4 agonist adjuvant, GLA-SE, improves magnitude and quality of immune responses elicited by the ID93 tuberculosis vaccine: first-in-human trial

Tuberculosis (TB) is the leading cause of infectious death worldwide. Development of improved TB vaccines that boost or replace BCG is a major global health goal. ID93 + GLA-SE is a fusion protein TB vaccine candidate combined with the Toll-like Receptor 4 agonist adjuvant, GLA-SE. We conducted a phase 1, randomized, double-blind, dose-escalation clinical trial to evaluate two dose levels of the ID93 antigen, administered intramuscularly alone or in combination with two dose levels of the GLA-SE adjuvant, in 60 BCG-naive, QuantiFERON-negative, healthy adults in the US (ClinicalTrials.gov identifier: NCT01599897). When administered as 3 injections, 28 days apart, all dose levels of ID93 alone and ID93 + GLA-SE demonstrated an acceptable safety profile. All regimens elicited vaccine-specific humoral and cellular responses. Compared with ID93 alone, vaccination with ID93 + GLA-SE elicited higher titers of ID93-specific antibodies, a preferential increase in IgG1 and IgG3 subclasses, and a multifaceted Fc-mediated effector function response. The addition of GLA-SE also enhanced the magnitude and polyfunctional cytokine profile of CD4⁺ T cells. The data demonstrate an acceptable safety profile and indicate that the GLA-SE adjuvant drives a functional humoral and T-helper 1 type cellular response.

A tuberculosis vaccine containing an immunity-potentiating agent stimulated strong immune responses in a first-in-human trial. Tuberculosis (TB) is the world’s foremost cause of infectious disease deaths, yet lacks an effective vaccine for adult humans. Rhea Coler, of the Infectious Disease Research Institute, Seattle, and a team from the United States and South Africa, tested their prophylactic on 60 healthy US adults. The vaccine consisted of ID93, a fusion of TB therapeutic target proteins, and GLA-SE—a supplement to boost immune responses. The candidate proved safe in all participants, with mild-to-moderate adverse effects, and provoked promising immune responses. The formulation was significantly more effective with GLA-SE than without. Further studies will elucidate the therapeutic benefit of this formulation and its ability to combat the pathogenicity of TB.

Overview of dendritic cell-based vaccine development for leishmaniasis

Leishmaniasis is one of the most serious vector-borne diseases in the world and is distributed over 98 countries. It is estimated that 350 million people are at risk for leishmaniasis. There are three different generation of vaccines that have been developed to provide immunity and protection against leishmaniasis. However, their use has been limited due to undesired side effects. These vaccines have also failed to provide effective and reliable protection and, as such, currently, there is no safe and effective vaccine for leishmaniasis. Dendritic cells (DCs) are a unique population of cells that come from bone marrow and become specialized to take up, process and present antigens to helper T cells in a mechanism similar to macrophages. By considering these significant features, DCs stimulated with different kinds of Leishmania antigens have been used in recent vaccine studies for leishmaniasis with promising results so far. In this review, we aim to review and combine the latest studies about this issue after defining potential problems in vaccine development for leishmaniasis and considering the importance of DCs in the immunopathogenesis of the disease.

Not All Antigens Are Created Equally: Progress, Challenges, and Lessons Associated with Developing a Vaccine for Leishmaniasis

From experimental models and the analyses of patients, it is well documented that antigen-specific T cells are critical for protection against Leishmania infection. Effective vaccines require both targeting to the pathogen and an immune stimulant to induce maturation of appropriate immune responses. While a great number of antigens have been examined as vaccine candidates against various Leishmania species, few have advanced to human or canine clinical trials. With emphasis on antigen expression, in this minireview we discuss some of the vaccine platforms that are currently being explored for the development of Leishmania vaccines. It is clear that the vaccine platform of choice can have a significant impact upon the level of protection induced by particular antigens, and we provide and highlight some examples for which the vaccine system used has impacted the protective efficacy imparted.

Synthetic Peptides as Potential Antigens for Cutaneous Leishmaniosis Diagnosis

This work's goal was to research new candidate antigens for cutaneous leishmaniosis (CL). In order to reach the goal, we used random peptide phage display libraries screened using antibodies from Leishmania braziliensis patients. After selection, three peptides (P1, P2, and P3) were synthesized using Fmoc chemistry. The peptides individually or a mixture of them (MIX) was subsequently emulsified in complete and incomplete Freund's adjuvant and injected subcutaneously in golden hamsters. Sera from the hamsters administered with P1 presented antibodies that recognized proteins between 76 and 150 kDa from L. braziliensis. Sera from hamsters which had peptides P2 and P3, as well as the MIX, administered presented antibodies that recognized proteins between 52 and 76 kDa of L. braziliensis. The research on the similarity of the peptides' sequences in protein databases showed that they match a 63 kDa glycoprotein. The three peptides and the MIX were recognized by the sera from CL patients by immunoassay approach (ELISA). The peptides' MIX showed the best performance (79% sensitivity) followed by the P1 (72% sensitivity), and the AS presented 91% sensitivity. These results show a new route for discovering molecules for diagnosis or for immunoprotection against leishmaniosis.

Recovery of antigen-specific T cell responses from dogs infected with Leishmania (L.) infantum by use of vaccine associated TLR-agonist adjuvant

Visceral leishmaniasis (VL), caused by infection with the obligate intracellular protozoan parasite Leishmania infantum, is a fatal disease of dogs and humans. Protection against VL requires a T helper 1 (Th1) skewed CD4⁺ T response, but despite this knowledge, there are currently no approved-to-market vaccines for humans and only three veterinary-use vaccines globally. As VL progresses from asymptomatic to symptomatic, L. infantum-specific interferon gamma (IFNγ) driven-Th1 responses become dampened and a state of immune exhaustion established. T cell exhaustion and other immunoregulatory processes, starting during asymptomatic disease, are likely to hinder vaccine-induced responses if vaccine is administered to infected, but asymptomatic and seronegative, individuals. In this study we evaluated how immune exhaustion, shown previously by our group to worsen in concert with VL progression, effected the capacity of vaccine candidate antigen/toll-like receptor (TLR) agonist combinations to promote protective CD4⁺ T cell responses during progressive VL. In conjunction with Th1 responses, we also evaluated concomitant stimulation of immune-balanced IL-10 regulatory cytokine production by these vaccine products in progressive VL canine T cells. Vaccine antigen L111f in combination with TLR agonists significantly recovered CD4⁺ T cell IFNγ intracellular production in T cells from asymptomatic VL dogs. Vaccine antigen NS with TLR agonists significantly recovered CD4⁺ T cell production in both endemic control and VL dogs. Combinations of TLR agonists and vaccine antigens overcame L. infantum induced cellular exhaustion, allowing robust Th1 CD4⁺ T cell responses from symptomatic dogs that previously had dampened responses to antigen alone. Antigen-agonist adjuvants can be utilized to promote more robust vaccine responses from infected hosts in endemic areas where vaccination of asymptomatic, L. infantum-infected animals is likely.

Enhanced humoral response to influenza vaccine in aged mice with a novel adjuvant, rOv-ASP-1

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Influenza-specific antibody levels were significantly increased after immunization with TIV + rOv-ASP-1 in aged mice.

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rOv-ASP-1 was superior to the conventional adjuvant alum in inducing specific IgG after TIV immunization in aged mice.

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Co-administration of rOv-ASP-1 induced cross-reactive antibody and enhanced cross-protection.

Immunization is the best way to prevent seasonal epidemics and pandemics of influenza. There are two kinds of influenza vaccines available in the United States: an inactivated vaccine (TIV) and an attenuated vaccine; however, only TIV is approved for immunization of the elderly population. While the aged population has the highest rate of influenza vaccination, the protective efficacy is low as evidenced by elderly individuals having the highest mortality associated with influenza. Recently, we reported that an adjuvant derived from the helminth parasite Onchocerca volvulus, named O. volvulus activation-associated secreted protein-1 (Ov-ASP-1), can significantly enhance the protective efficacy of an inactivated vaccine (TIV) in young adult mice. In the current study, we examined whether this recombinant Ov-ASP-1 (rOv-ASP-1) can enhance the efficacy of TIV in aged mice as well. While primary immunization with TIV alone produced only a low level of influenza-specific antibodies (total IgG, IgG1, and IgG2c) in aged mice, the antibody levels were significantly increased after immunization with TIV + rOv-ASP-1. More importantly, the level of the total IgG in aged mice administered TIV + rOv-ASP-1 was comparable to that of young adult mice immunized with TIV alone. Co-administration of rOv-ASP-1 induced a low level of cross-reactive antibody and enhanced the protective efficacy of TIV in aged mice, reflected by significantly increased survival after challenge with a heterologous influenza virus. rOv-ASP-1 was also superior to the conventional adjuvant alum in inducing specific IgG after TIV immunization in aged mice, and in conferring protection after challenge. These results demonstrate that rOv-ASP-1 may serve as a potential adjuvant for influenza vaccine to improve the efficacy of protection in the elderly.

From mouse to man: safety, immunogenicity and efficacy of a candidate leishmaniasis vaccine LEISH-F3+GLA-SE

Key antigens of Leishmania species identified in the context of host responses in Leishmania-exposed individuals from disease-endemic areas were prioritized for the development of a subunit vaccine against visceral leishmaniasis (VL), the most deadly form of leishmaniasis. Two Leishmania proteins-nucleoside hydrolase and a sterol 24-c-methyltransferase, each of which are protective in animal models of VL when properly adjuvanted- were produced as a single recombinant fusion protein NS (LEISH-F3) for ease of antigen production and broad coverage of a heterogeneous major histocompatibility complex population. When formulated with glucopyranosyl lipid A-stable oil-in-water nanoemulsion (GLA-SE), a Toll-like receptor 4 TH1 (T helper 1) promoting nanoemulsion adjuvant, the LEISH-F3 polyprotein induced potent protection against both L. donovani and L. infantum in mice, measured as significant reductions in liver parasite burdens. A robust immune response to each component of the vaccine with polyfunctional CD4 TH1 cell responses characterized by production of antigen-specific interferon-γ, tumor necrosis factor and interleukin-2 (IL-2), and low levels of IL-5 and IL-10 was induced in immunized mice. We also demonstrate that CD4 T cells, but not CD8 T cells, are sufficient for protection against L. donovani infection in immunized mice. Based on the sum of preclinical data, we prepared GMP materials and performed a phase 1 clinical study with LEISH-F3+GLA-SE in healthy, uninfected adults in the United States. The vaccine candidate was shown to be safe and induced a strong antigen-specific immune response, as evidenced by cytokine and immunoglobulin subclass data. These data provide a strong rationale for additional trials in Leishmania-endemic countries in populations vulnerable to VL.

Intranasal vaccination with leishmanial antigens protects golden hamsters (Mesocricetus auratus) against Leishmania (Viannia) Braziliensis infection

Background

Previous results have shown that oral and intranasal administration of particulate Leishmania (Leishmania) amazonensis antigens (LaAg) partially protects mice against L. amazonensis infection. However, vaccination studies on species of the subgenus Viannia, the main causative agent of cutaneous and mucosal leishmaniasis in the Americas, have been hampered by the lack of easy-to-handle bio-models that accurately mimic the human disease. Recently, we demonstrated that the golden hamster is an appropriate model for studying the immunopathogenesis of cutaneous leishmaniasis caused by L. (Viannia) braziliensis. Using the golden hamster model, our current study investigated whether the protective effect of intranasal immunisation with LaAg can be extended to L. braziliensis infection.

Methodology/Principal Findings

Golden hamsters vaccinated with either two intranasal (IN) doses of LaAg (10 µg) or two intramuscular doses of LaAg (20 µg) were challenged 2 weeks post-vaccination with L. braziliensis. The results showed that IN immunisation with LaAg significantly reduced lesion growth and parasitic load as well as serum IgG and IgG2 levels. At the experimental endpoint on day 114 post-infection, IN-immunised hamsters that were considered protected expressed IFN-γ and IL10 mRNA levels that returned to uninfected skin levels. In contrast to the nasal route, intramuscular (IM) immunisation failed to provide protection.

Conclusions/Significance

These results demonstrate for the first time that the nasal route of immunisation can induce cross protection against L. braziliensis infection.

Leishmaniasis is a disease that is common in most tropical countries. In Brazil, the cutaneous form of the disease is highly prevalent, with approximately 28,000 new cases reported annually. L. (Viannia) braziliensis is the main causative agent of cutaneous leishmaniasis; however, vaccine studies against protozoans of the subgenus Viannia have been largely neglected, mainly due to the high resistance of most mouse strains to the infection. Here, the authors used the golden hamster, which is highly susceptible to dermotropic Leishmania spp infection. It was previously shown that oral and intranasal vaccination with whole L. (Leishmania) amazonensis antigens (LaAg) protected mice against L. amazonensis infection. In the present study, the authors investigated whether the protective effect of intranasal immunisation with LaAg can be extended to L. braziliensis infection using the golden hamster model. The results showed that intranasal immunisation with LaAg significantly reduced lesion growth and parasitic load as well as IgG and IgG2 serum levels. At the endpoint of the experiment, intranasally immunised hamsters that were considered protected expressed IFN-γ and IL10 mRNA at levels similar to those in uninfected skin. These data show that the use of a proper animal model and/or different vaccination strategies may facilitate the development of an effective vaccine against L. braziliensis.

Vaccines for canine leishmaniasis

Leishmania infantum is the obligatory intracellular parasite of mammalian macrophages and causes zoonotic visceral leishmaniasis (ZVL). The presence of infected dogs as the main reservoir host of ZVL is regarded as the most important potential risk for human infection. Thus the prevention of canine visceral leishmaniasis (CVL) is essential to stop the current increase of the Mediterranean visceral leishmaniasis. Recently considerable advances in achieving protective immunization of dogs and several important attempts for achieving an effective vaccine against CVL lead to attracting the scientists trust in its important role for eradication of ZVL. This paper highlights the recent advances in vaccination against canine visceral leishmaniasis from 2007 until now.

Immunogenicity evaluation of a rationally designed polytope construct encoding HLA-A*0201 restricted epitopes derived from Leishmania major related proteins in HLA-A2/DR1 transgenic mice: steps toward polytope vaccine

Background

There are several reports demonstrating the role of CD8 T cells against Leishmania species. Therefore peptide vaccine might represent an effective approach to control the infection. We developed a rational polytope-DNA construct encoding immunogenic HLA-A2 restricted peptides and validated the processing and presentation of encoded epitopes in a preclinical mouse model humanized for the MHC-class-I and II.

Methods and Findings

HLA-A*0201 restricted epitopes from LPG-3, LmSTI-1, CPB and CPC along with H-2Kd restricted peptides, were lined-up together as a polytope string in a DNA construct. Polytope string was rationally designed by harnessing advantages of ubiquitin, spacers and HLA-DR restricted Th1 epitope. Endotoxin free pcDNA plasmid expressing the polytope was inoculated into humanized HLA-DRB1*0101/HLA-A*0201 transgenic mice intramuscularly 4 days after Cardiotoxin priming followed by 2 boosters at one week interval. Mice were sacrificed 10 days after the last booster, and splenocytes were subjected to ex-vivo and in-vitro evaluation of specific IFN-γ production and in-vitro cytotoxicity against individual peptides by ELISpot and standard chromium-51(⁵¹Cr) release assay respectively. 4 H-2Kd and 5 HLA-A*0201 restricted peptides were able to induce specific CD8 T cell responses in BALB/C and HLA-A2/DR1 mice respectively. IFN-γ and cytolytic activity together discriminated LPG-3-P1 as dominant, LmSTI-1-P3 and LmSTI-1-P6 as subdominant with both cytolytic activity and IFN-γ production, LmSTI-1-P4 and LPG-3-P5 as subdominant with only IFN-γ production potential.

Conclusions

Here we described a new DNA-polytope construct for Leishmania vaccination encompassing immunogenic HLA-A2 restricted peptides. Immunogenicity evaluation in HLA-transgenic model confirmed CD8 T cell induction with expected affinities and avidities showing almost efficient processing and presentation of the peptides in relevant preclinical model. Further evaluation will determine the efficacy of this polytope construct protecting against infectious challenge of Leishmania. Fortunately HLA transgenic mice are promising preclinical models helping to speed up immunogenicity analysis in a human related mouse model.

Immune regulation during chronic visceral leishmaniasis

Visceral leishmaniasis is a chronic parasitic disease associated with severe immune dysfunction. Treatment options are limited to relatively toxic drugs, and there is no vaccine for humans available. Hence, there is an urgent need to better understand immune responses following infection with Leishmania species by studying animal models of disease and clinical samples from patients. Here, we review recent discoveries in these areas and highlight shortcomings in our knowledge that need to be addressed if better treatment options are to be developed and effective vaccines designed.

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.

Novel vaccine approaches for protection against intracellular pathogens

Vaccination against intracellular pathogens requires generation of a pool of memory T cells able to respond upon infection and mediate either killing of the infected cell or induce killing mechanisms in the infected cell. T cell-inducing vaccines must aim to target the antigen to antigen-presenting cells (APCs) so that it can be presented on MHC molecules on the cell surface. Methods to do this include making use of vectors such as plasmid DNA or viruses, live attenuated pathogens or subunit vaccines targeted and enhanced using adjuvants. The choice of approach should be guided by the phenotype and localization of the desired T cell response. This review will discuss current approaches in the pipeline for the development of T cell-inducing vaccines, including vectored, live attenuated, and subunit vaccines.

Adjuvants containing natural and synthetic Toll-like receptor 4 ligands

The last decade has seen an increased focus on the development of adjuvants for vaccines, and several novel adjuvants are now in licensed products or in late-stage clinical development. These advancements have been aided by the discovery of receptors and signaling pathways of the innate immune system and an increased understanding of how these innate responses influence the adaptive immune response. Successful vaccine development relies on knowledge of which adjuvants to use and the proper formulation of adjuvants and antigens to achieve safe, stable and immunogenic vaccines. In this review, the authors focus on the current use of natural and synthetic lipopolysaccharide analogues that retain their adjuvant properties with reduced toxicity compared with the parent compound for use in emerging vaccines. The authors review how these compounds initiate signal transduction through Toll-like receptor 4, insights from structure-function studies and how formulation parameters can influence their effectiveness as vaccine adjuvants.

Targeting Leishmania major Antigens to Dendritic Cells In Vivo Induces Protective Immunity

Efficient vaccination against the parasite Leishmania major, the causative agent of human cutaneous leishmaniasis, requires development of type 1 T-helper (Th1) CD4⁺ T cell immunity. Because of their unique capacity to initiate and modulate immune responses, dendritic cells (DCs) are attractive targets for development of novel vaccines. In this study, for the first time, we investigated the capacity of a DC-targeted vaccine to induce protective responses against L. major. To this end, we genetically engineered the N-terminal portion of the stress-inducible 1 protein of L. major (LmSTI1a) into anti-DEC205/CD205 (DEC) monoclonal antibody (mAb) and thereby delivered the conjugated protein to DEC⁺ DCs in situ in the intact animal. Delivery of LmSTI1a to adjuvant-matured DCs increased the frequency of antigen-specific CD4⁺ T cells producing IFN-γ⁺, IL-2⁺, and TNF-α⁺ in two different strains of mice (C57BL/6 and Balb/c), while such responses were not observed with the same doses of a control Ig-LmSTI1a mAb without receptor affinity or with non-targeted LmSTI1a protein. Using a peptide library for LmSTI1a, we identified at least two distinct CD4⁺ T cell mimetopes in each MHC class II haplotype, consistent with the induction of broad immunity. When we compared T cell immune responses generated after targeting DCs with LmSTI1a or other L. major antigens, including LACK (Leishmania receptor for activated C kinase) and LeIF (Leishmania eukaryotic ribosomal elongation and initiation factor 4a), we found that LmSTI1a was superior for generation of IFN-γ-producing CD4⁺ T cells, which correlated with higher protection of susceptible Balb/c mice to a challenge with L. major. For the first time, this study demonstrates the potential of a DC-targeted vaccine as a novel approach for cutaneous leishmaniasis, an increasing public health concern that has no currently available effective treatment.

Case study for a vaccine against leishmaniasis

Leishmaniasis in many ways offers a unique vaccine case study. Two reasons for this are that leishmaniasis is a disease complex caused by several different species of parasite that are highly related, thus raising the possibility of developing a single vaccine to protect against multiple diseases. Another reason is the demonstration that a leishmaniasis vaccine may be used therapeutically as well as prophylactically. Although there is no registered human leishmaniasis vaccine today, immunization approaches using live or killed organisms, as well as defined vaccine candidates, have demonstrated at least some degree of efficacy in humans to prevent and to treat some forms of leishmaniasis, and there is a vigorous pipeline of candidates in development. Current approaches include using individual or combined antigens of the parasite or of salivary gland extract of the parasites' insect vector, administered with or without formulation in adjuvant. Animal data obtained with several vaccine candidates are promising and some have been or will be entered into clinical testing in the near future. There is sufficient scientific and epidemiological justification to continue to invest in the development of vaccines against leishmaniasis.

Leishmania donovani triose phosphate isomerase: a potential vaccine target against visceral leishmaniasis

Visceral leishmaniasis (VL) is one of the most important parasitic diseases with approximately 350 million people at risk. Due to the non availability of an ideal drug, development of a safe, effective, and affordable vaccine could be a solution for control and prevention of this disease. In this study, a potential Th1 stimulatory protein- Triose phosphate isomerase (TPI), a glycolytic enzyme, identified through proteomics from a fraction of Leishmania donovani soluble antigen ranging from 89.9–97.1 kDa, was assessed for its potential as a suitable vaccine candidate. The protein- L. donovani TPI (LdTPI) was cloned, expressed and purified which exhibited the homology of 99% with L. infantum TPI. The rLdTPI was further evaluated for its immunogenicity by lymphoproliferative response (LTT), nitric oxide (NO) production and estimation of cytokines in cured Leishmania patients/hamster. It elicited strong LTT response in cured patients as well as NO production in cured hamsters and stimulated remarkable Th1-type cellular responses including IFN-ã and IL-12 with extremely lower level of IL-10 in Leishmania-infected cured/exposed patients PBMCs in vitro. Vaccination with LdTPI-DNA construct protected naive golden hamsters from virulent L. donovani challenge unambiguously (∼90%). The vaccinated hamsters demonstrated a surge in IFN-ã, TNF-á and IL-12 levels but extreme down-regulation of IL-10 and IL-4 along with profound delayed type hypersensitivity and increased levels of Leishmania-specific IgG2 antibody. Thus, the results are suggestive of the protein having the potential of a strong candidate vaccine.

An epidemic outbreak of canine cutaneous leishmaniasis in Colombia caused by Leishmania braziliensis and Leishmania panamensis

The largest recorded outbreak of cutaneous leishmaniasis in Colombia's history occurred during 2005-2009 in soldiers of the Colombian Army, with ~40,000 cases. This outbreak was caused by the influx of military personnel into the jungle with the mission of combat illicit crops and the guerrilla. The soldiers remain for long periods within the rainforest and are exposed to the bite of infected sand flies. During the military activities, soldiers work with dogs specially trained to detect landmines, and therefore, dogs are also exposed to the infected sand flies and show high incidence of cutaneous leishmaniasis (CL). This work describes an epidemic outbreak of canine CL caused by Leishmania braziliensis and Leishmania panamensis in Colombia, South America. The clinical features of the disease and the response to treatment with pentavalent antimonials observed in 72 guard dogs from the Colombian Army are described. A program for prevention and control of canine CL is also discussed.

Adjuvants for Leishmania vaccines: from models to clinical application

Two million new cases of leishmaniasis occur every year, with the cutaneous leishmaniasis (CL) presentation accounting for approximately two-thirds of all cases. Despite the high incidence rates and geographic expansion of the disease, CL remains a neglected tropical disease without effective intervention strategies. Efforts to address this deficit have given rise to the experimental murine model of CL. By virtue of its simplicity and pliability, the CL model has been used to provide substantial information regarding cellular immunity, as well as in the discovery and evaluation of various vaccine adjuvants. The CL model has facilitated in vivo studies of the mechanism of action of many adjuvants, including the TLR4 agonist monophosphoryl lipid A, the TLR7/8 agonist imiquimod, the TLR9 agonist CpG, adenoviral vectors, and the immunostimulatory complexes. Together, these studies have helped to unveil the requirement for certain types of immune responses at specific stages of CL disease and provide a basis to aid the design of effective second-generation vaccines for human CL. This review focuses on adjuvants that have been tested in experimental CL, outlining how they have helped advance our understanding of the disease and ultimately, how they have performed when applied within clinical trials against human CL.

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.

Leishmania donovani recombinant iron superoxide dismutase B1 protein in the presence of TLR-based adjuvants induces partial protection of BALB/c mice against Leishmania major infection

In this study, we tested the protective efficacy of recombinant Leishmania donovani iron superoxide dismutase B1 (SODB1) against Leishmania major infection in BALB/c mice. Mice were challenged with L. major 3weeks after the second boost immunization with rSODB1 alone or in the presence of adjuvants. Injection of BALB/c mice with rSODB1 alone elicited both humoral and cellular immune responses. Administration of rSODB1 with CpG ODN or GLA-SE (a synthetic toll-like receptor 4 agonist) adjuvant resulted in the induction of anti-SODB1 IgG1, and more importantly of significantly high levels of IgG2a isotype. Immunization of mice with rSODB1 alone or with adjuvant induced the production of IFN-γ by splenocytes in response to stimulation with L. major soluble leishmanial antigens (SLA). Moreover, immunization protocols involving rSODB1 resulted in a significant decrease in IL-10 as compared to controls. The presence of CpG ODN or GLA-SE adjuvant in the immunization protocols resulted in a relative increase in IFN-γ in response to stimulation with rSODB1 in comparison to immunization with rSODB1 alone. Mice immunized with rSODB1 plus CpG ODN or GLA-SE, were able to partially control their Leishmania infections, as indicated by the reduction in footpad swelling and parasite numbers, compared to controls. These results suggest that immunization with recombinant SODB1 protein together with CpG ODN or GLA-SE can be potential vaccine candidate against leishmaniasis.

Intradermally administered TLR4 agonist GLA-SE enhances the capacity of human skin DCs to activate T cells and promotes emigration of Langerhans cells

The natural TLR4 agonist lipopolysaccharide (LPS) has notable adjuvant activity. However, it is not useful as a vaccine adjuvant due to its toxicity. Glucopyranosyl lipid A (GLA) is a synthetic derivative of the lipid A tail of LPS with limited cytotoxicity, but strong potential to induce immune responses in mice, guinea pigs, non-human primates, and humans. In this study we determined how this synthetic TLR4 agonist affects the function of different subsets of human skin dendritic cells (DCs). The effect of GLA in an aqueous formulation (GLA-AF) or in an oil-in-water emulsion (GLA-SE) was compared to that of LPS and TLR3 agonist poly(I:C) using a human skin explant model with intradermal injections for the administration of the agonists. Intradermal injection of GLA-SE or LPS, but not GLA-AF, enhanced the emigration of CD1a(high)/langerin(+) Langerhans cells (LCs), but not dermal DCs (DDCs). LCs and CD14(-) DDCs exhibited an enhanced mature phenotype following intradermal administration of either of the two GLA formulations tested, similar to DCs that emigrated from LPS-injected skin. However, only injection of GLA-SE resulted in a significant increase in the production of the wide range of cytokines that is observed with LPS. Moreover, DCs that emigrated from GLA-SE-injected skin induced stronger CD4(+) T-cell activation, as indicated by a more pronounced T-cell proliferation, than DCs from skin injected with GLA-AF or LPS. Altogether, our data show that GLA-SE has a notable potency to stimulate the function of skin DCs, indicating that GLA-SE may be a good candidate as adjuvant for vaccines administered via the intradermal route.

The economic value of a visceral leishmaniasis vaccine in Bihar state, India

Visceral leishmaniasis (VL) is responsible for substantial morbidity and mortality and current available treatments have many limitations. The ability of VL infection to generate life-long immunity offers promise for the development of a VL vaccine. A VL vaccine candidate has recently completed phase I clinical trials. We constructed a computer simulation model to determine the potential economic value of a VL vaccine in the endemic region of Bihar state, India. Results found a potential vaccine to be cost-effective (and in many cases economically dominant, i.e., saving costs and providing health benefits) throughout a wide range of vaccination costs and vaccine efficacies, and VL risks. Overall, our study strongly supports the continued development of a VL vaccine.

Enlarging the "Audacious Goal": elimination of the world's high prevalence neglected tropical diseases

The high prevalence neglected tropical diseases (NTDs) exhibit a global disease burden that exceeds malaria, tuberculosis, and other better known global health conditions; they also represent a potent force in trapping the world's poorest people in poverty. Through extremely low cost national programs of disease mapping and mass drug administration (MDA) for the seven most common NTDs, integrated NTD control and elimination efforts are now in place in more than 14 countries through the support of the United States Agency for International Development (USAID), the British Department for International Development (DFID), and the Global Network for NTDs and its partners. The World Health Organization (WHO) estimates that in 2008 some 670 million people in 75 countries received NTD treatments through these and other sponsored programs. With continued successes the next decade could witness the global elimination of blinding trachoma, human Africa trypanosomiasis (HAT), lymphatic filariasis (LF), onchocerciasis, trachoma, and leprosy as public health problems, in addition to the eradication of dracunculiasis. For other high prevalence NTDs, including hookworm infection, schistosomiasis, Chagas disease and leishmaniasis, new drugs and vaccines may still be required. Increasingly it is recognized that the high prevalence NTDs exhibit extensive geographic overlap and polyparasitism is commonly found throughout the world's low income countries. Therefore, global elimination will also require integrated packages of drugs together with vaccine-linked chemotherapy. Ultimately, the global elimination of the high prevalence NTDs will require continued large-scale support from the U.S. Government and selected European governments, however, the emerging market economies, such as Brazil, China, India, Mexico, and Nigeria, and wealthy countries in the Middle East will also have to substantially contribute.

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.

The development and clinical evaluation of second-generation leishmaniasis vaccines

Infection with Leishmania parasites results in a range of clinical manifestations and outcomes. Control of Leishmania parasite transmission is extremely difficult due to the large number of vectors and potential reservoirs, and none of the current treatments are ideal. Vaccination could be an effective strategy to provide sustained control. In this review, the current global situation with regard to leishmaniasis, the immunology of Leishmania infection and various efforts to identify second generation vaccine candidates are briefly discussed. The variety of clinical trials conducted using the only current second generation vaccine approved for clinical use, LEISH-F1+MPL-SE, are described. Given that epidemiological evidence suggests that reducing the canine reservoir also positively impacts human incidence, efforts at providing a vaccine for leishmaniasis in dogs are highlighted. Finally, potential refinements and surrogate markers that could expedite the introduction of a vaccine that can limit the severity and incidence of leishmaniasis are discussed.

Leishmaniasis

Leishmaniasis is a disease that ranges in severity from skin lesions to serious disfigurement and fatal systemic infection. WHO has classified the disease as emerging and uncontrolled and estimates that the infection results in two million new cases a year. There are 12 million people currently infected worldwide, and leishmaniasis threatens 350 million people in 88 countries. 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. However, to date, no such vaccine is available despite substantial efforts by many laboratories. Main obstacle in vaccine design is the transition from the laboratory to the field and extrapolation of data from animal models to humans. This review discusses recent findings in the antileishmania vaccine field and current difficulties hampering vaccine implementation.

Use of defined TLR ligands as adjuvants within human vaccines

Our improved understanding of how innate immune responses can be initiated and how they can shape adaptive B- and T-cell responses is having a significant impact on vaccine development by directing the development of defined adjuvants. Experience with first generation vaccines, as well as rapid advances in developing defined vaccines containing Toll-like receptor ligands (TLRLs), indicate that an expanded number of safe and effective vaccines containing such molecules will be available in the future. In this review, we outline current knowledge regarding TLRs, detailing the different cell types that express TLRs, the various signaling pathways TLRs utilize, and the currently known TLRLs. We then discuss the current status of TLRLs within vaccine development programs, including the importance of appropriate formulation, and how recent developments can be used to better define the mechanisms of action of vaccines. Finally, we introduce the possibility of using TLRLs, either in combination or with non-TLRLs, to synergistically potentiate vaccine-induced responses to provide not only prophylactic, but therapeutic protection against infectious diseases and cancer.

Vaccines to combat the neglected tropical diseases

The neglected tropical diseases (NTDs) represent a group of parasitic and related infectious diseases such as amebiasis, Chagas disease, cysticercosis, echinococcosis, hookworm, leishmaniasis, and schistosomiasis. Together, these conditions are considered the most common infections in low- and middle-income countries, where they produce a level of global disability and human suffering equivalent to better known conditions such as human immunodeficiency virus/acquired immunodeficiency syndrome and malaria. Despite their global public health importance, progress on developing vaccines for NTD pathogens has lagged because of some key technical hurdles and the fact that these infections occur almost exclusively in the world's poorest people living below the World Bank poverty line. In the absence of financial incentives for new products, the multinational pharmaceutical companies have not embarked on substantive research and development programs for the neglected tropical disease vaccines. Here, we review the current status of scientific and technical progress in the development of new neglected tropical disease vaccines, highlighting the successes that have been achieved (cysticercosis and echinococcosis) and identifying the challenges and opportunities for development of new vaccines for NTDs. Also highlighted are the contributions being made by non-profit product development partnerships that are working to overcome some of the economic challenges in vaccine manufacture, clinical testing, and global access.

New adjuvants in evolving vaccine strategies

Adjuvants are becoming the key players of vaccine formulations to enhance the immunogenicity of subunit (peptides, proteins, virus-like particles (VLPs)) and DNA vaccines, as well as to reach the current new goals of preventing and/or treating chronic infectious diseases and cancers. Induction of humoral response, in particular neutralizing antibodies able to inhibit the binding of pathogens to their cellular receptors, remains a major goal of vaccines targeted to prevent acute lytic infections; induction/modulation of cellular immunity is, however, critical to fight latently/chronically infected cells as well as cancer cells. The new adjuvants, included in vaccine preparations, are currently able to modify the presentation of epitopes to the immune system with a specific T(H)1 versus T(H)2 polarization efficacy. A paradigm of the relevance of these new adjuvants is the immunological result obtained with the inclusion of monophosphoryl lipid A in the formulation of L1-based human papillomavirus (HPV)-naked VLPs. In the May issue of this journal, Garcon and colleagues describe the highly enhanced humoral and memory B cellular immunity of the AS04-adjuvanted HPV vaccine, which results in a long-lasting and broad spectrum immunity.

TLR-based immune adjuvants

This work describes the nature and strength of the immune response induced by various Toll-like receptor ligands and their ability to act as vaccine adjuvants. It reviews the various ligands capable of triggering individual TLRs, and then focuses on the efficacy and safety of those agents for which clinical results are available.

A clinical trial to evaluate the safety and immunogenicity of the LEISH-F1+MPL-SE vaccine for use in the prevention of visceral leishmaniasis

Healthy Indian adult volunteers, with or without a history of leishmaniasis, were evaluated for evidence of previous infection with Leishmania donovani based on the direct agglutination test (DAT). Three cohorts of 6 DAT-negative and 6 DAT-positive subjects were enrolled in an open-label, dose-escalating, uncontrolled clinical trial and received three injections of the LEISH-F1+MPL-SE vaccine (consisting of 5μg, 10μg, or 20μg recombinant Leishmania polyprotein LEISH-F1 antigen+25μg MPL®-SE adjuvant). The study injections were given subcutaneously on days 0, 28, and 56, and the subjects were followed through day 168 for safety and immunological endpoints. The vaccine was safe and well-tolerated in DAT-negative and DAT-positive subjects and induced T-cell production of IFN-γ and other cytokines in response to stimulation with the LEISH-F1 antigen. This clinical trial shows that the LEISH-F1+MPL-SE vaccine is safe and immunogenic in healthy subjects with and without history of previous infection with Leishmania donovani.

A defined tuberculosis vaccine candidate boosts BCG and protects against multidrug-resistant Mycobacterium tuberculosis

Despite the widespread use of the childhood vaccine against tuberculosis (TB), Mycobacterium bovis bacillus Calmette-Guérin (BCG), the disease remains a serious global health problem. A successful vaccine against TB that replaces or boosts BCG would include antigens that induce or recall the appropriate T cell responses. Four Mycobacterium tuberculosis (Mtb) antigens--including members of the virulence factor families PE/PPE and EsX or antigens associated with latency--were produced as a single recombinant fusion protein (ID93). When administered together with the adjuvant GLA-SE, a stable oil-in-water nanoemulsion, the fusion protein was immunogenic in mice, guinea pigs, and cynomolgus monkeys. In mice, this fusion protein-adjuvant combination induced polyfunctional CD4 T helper 1 cell responses characterized by antigen-specific interferon-γ, tumor necrosis factor, and interleukin-2, as well as a reduction in the number of bacteria in the lungs of animals after they were subsequently infected with virulent or multidrug-resistant Mtb strains. Furthermore, boosting BCG-vaccinated guinea pigs with fusion peptide-adjuvant resulted in reduced pathology and fewer bacilli, and prevented the death of animals challenged with virulent Mtb. Finally, the fusion protein elicited polyfunctional effector CD4 and CD8 T cell responses in BCG-vaccinated or Mtb-exposed human peripheral blood mononuclear cells. This study establishes that the protein subunit vaccine consisting of the fusion protein and adjuvant protects against TB and drug-resistant TB in animals and is a candidate for boosting the protective efficacy of the childhood BCG vaccine in humans.