A clinical trial to evaluate the safety and immunogenicity of the LEISH-F1+MPL-SE vaccine when used in combination with meglumine antimoniate for the treatment of cutaneous leishmaniasis

Immunotherapeutic Strategies as Potential Treatment Options for Cutaneous Leishmaniasis

Cutaneous leishmaniasis (CL), caused by protozoan parasites of the Leishmania genus, is prevalent in tropical and subtropical regions, with important morbidity, particularly in low- to middle-income countries. Current systemic treatments, including pentavalent antimonials and miltefosine, are associated with significant toxicity, reduced efficacy, and are frequently ineffective in cases of severe or chronic CL. Immunotherapies leverage the immune system to combat microbial infection and offer a promising adjunct or alternative approach to the current standard of care for CL. However, the heterogeneous clinical presentation of CL, which is dependent on parasite species and host immunity, may require informed clinical intervention with immunotherapies. This review explores the clinical and immunological characteristics of CL, emphasising the current landscape of immunotherapies in in vivo models and clinical studies. Such immune-based interventions aim to modulate immune responses against Leishmania, with additive therapeutic effects enabling the efficacy of lower drug doses and decreasing the associated toxicity. Understanding the mechanisms that underlie immunotherapy for CL provides critical insights into developing safer and more effective treatments for this neglected tropical disease. Identifying suitable therapeutic candidates and establishing their safety and efficacy are essential steps in this process. However, the feasibility and utility of these treatments in resource-limited settings must also be considered, taking into account factors such as cost of production, temperature stability, and overall patient access.

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.

Leishmania Vesicle-Depleted Exoproteome: What, Why, and How?

Leishmaniasis, a vector-borne parasitic protozoan disease, is among the most important neglected tropical diseases. In the absence of vaccines, disease management is challenging. The available chemotherapy is suboptimal, and there are growing concerns about the emergence of drug resistance. Thus, a better understanding of parasite biology is essential to generate new strategies for disease control. In this context, in vitro parasite exoproteome characterization enabled the identification of proteins involved in parasite survival, pathogenesis, and other biologically relevant processes. After 2005, with the availability of genomic information, these studies became increasingly feasible and revealed the true complexity of the parasite exoproteome. After the discovery of Leishmania extracellular vesicles (EVs), most exoproteome studies shifted to the characterization of EVs. The non-EV portion of the exoproteome, named the vesicle-depleted exoproteome (VDE), has been mostly ignored even if it accounts for a significant portion of the total exoproteome proteins. Herein, we summarize the importance of total exoproteome studies followed by a special emphasis on the available information and the biological relevance of the VDE. Finally, we report on how VDE can be studied and disclose how it might contribute to providing biologically relevant targets for diagnosis, drug, and vaccine development.

Comparative assessment of interventions for treating cutaneous leishmaniasis: A network meta-analysis of randomized clinical trials

INTRODUCTION

Various interventions including laser therapy, heat therapy, and several drugs have been trialed in patients with cutaneous leishmaniasis. Due to the lack of an evidence-based comparison of all these interventions, we carried out the present network meta-analysis.

METHODS

Electronic databases were searched for randomized clinical trials evaluating the efficacy and safety of any interventions in patients with cutaneous leishmaniasis. The proportion of patients with complete cure was the primary outcome. The proportion of lesions cured at the end of treatment, the proportion of lesions with minimal/no response to treatment, and proportion of wounds with minimal/no change were the secondary outcomes. Random-effects modeling was used for generating pooled estimates. Rankogram plot was used for identifying the 'best intervention'. For interventions containing a combination of treatments, backslash (/) has been used for depicting the same.

RESULTS

One-hundred and thirty-one studies were included. Intralesional meglumine, topical paromomycin/gentamicin, topical paromomycin, parenteral sodium stibogluconate, topical honey/intralesional meglumine, topical liposomal amphotericin B, oral zinc sulphate, oral miltefosine, parenteral meglumine, heat therapy, topical liposomal azithromycin, intralesional meglumine/silver dressing, intralesional sodium stibogluconate, parenteral meglumine/intralesional meglumine, oral allopurinol/parenteral meglumine, topical trichloroacetic acid/heat therapy, oral zinc sulphate/oral ketoconazole, topical imiquimod/cryotherapy, intralesional meglumine/cryotherapy, topical herbal extract of Z-HE, parenteral pentamidine, topical trichloroacetic acid/intralesional meglumine, carbon-dioxide laser, topical recombinant granulocyte-macrophage colony-stimulating factor/parenteral meglumine, intralesional dapsone, carbon-dioxide laser/intralesional meglumine, moist wet dressing with sodium hypochlorite, parenteral sodium stibogluconate/intralesional recombinant granulocyte-macrophage colony-stimulating factor, oral dapsone, intralesional sodium stibogluconate/oral ketoconazole, intralesional sodium stibogluconate/parenteral sodium stibogluconate and electrocautery/moist wet dressing with sodium hypochlorite were observed with significantly greater proportion of patients with complete cure compared to placebo/untreated controls. Rankogram analysis revealed that parenteral pentamidine has the highest statistical probability of being the best in the pool.

CONCLUSION

We observed several interventions to be effective for treating cutaneous leishmaniasis. However, greater caution is required in interpreting the results as the estimates are likely to change with the advent of results from future studies.

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.

A Chimera of Th1 Stimulatory Proteins of Leishmania donovani Offers Moderate Immunotherapeutic Efficacy with a Th1-Inclined Immune Response against Visceral Leishmaniasis

Immunotherapy, a treatment based on host immune system activation, has been shown to provide a substitute for marginally effective conventional chemotherapy in controlling visceral leishmaniasis (VL), the deadliest form of leishmaniasis. As the majority of endemic inhabitants exhibit either subclinical or asymptomatic infection which often develops into the active disease state, therapeutic intervention seems to be an important avenue for combating infections by stimulating the natural defense system of infected individuals. With this perspective, the present study focuses on two immunodominant Leishmania (L.) donovani antigens (triosephosphate isomerase and enolase) previously proved to be potent prophylactic VL vaccine candidates, for generating a recombinant chimeric antigen. This is based on the premise that in a heterogeneous population, a multivalent antigen vaccine would be required for an effective response against leishmaniasis (a complex parasitic disease). The resulting molecule rLdT-E chimeric protein was evaluated for its immunogenicity and immunotherapeutic efficacy. A Th1 stimulating adjuvant BCG was employed with the protein which showed a remarkable 70% inhibition of splenic parasitic multiplication positively correlated with boosted Th1 dominant immune response against lethal L. donovani challenge in hamsters as evidenced by high IFN-γ and TNF-α and low IL-10. In addition, immunological analysis of antibody subclass presented IgG2-based humoral response besides considerable delayed-type hypersensitivity and lymphocyte proliferative responses in rLdT-E/BCG-treated animals. Our observations indicate the potential of the chimera towards its candidature for an effective vaccine against Leishmania donovani infection.

Harnessing the Complete Repertoire of Conventional Dendritic Cell Functions for Cancer Immunotherapy

The onset of checkpoint inhibition revolutionized the treatment of cancer. However, studies from the last decade suggested that the sole enhancement of T cell functionality might not suffice to fight malignancies in all individuals. Dendritic cells (DCs) are not only part of the innate immune system, but also generals of adaptive immunity and they orchestrate the de novo induction of tolerogenic and immunogenic T cell responses. Thus, combinatorial approaches addressing DCs and T cells in parallel represent an attractive strategy to achieve higher response rates across patients. However, this requires profound knowledge about the dynamic interplay of DCs, T cells, other immune and tumor cells. Here, we summarize the DC subsets present in mice and men and highlight conserved and divergent characteristics between different subsets and species. Thereby, we supply a resource of the molecular players involved in key functional features of DCs ranging from their sentinel function, the translation of the sensed environment at the DC:T cell interface to the resulting specialized T cell effector modules, as well as the influence of the tumor microenvironment on the DC function. As of today, mostly monocyte derived dendritic cells (moDCs) are used in autologous cell therapies after tumor antigen loading. While showing encouraging results in a fraction of patients, the overall clinical response rate is still not optimal. By disentangling the general aspects of DC biology, we provide rationales for the design of next generation DC vaccines enabling to exploit and manipulate the described pathways for the purpose of cancer immunotherapy in vivo. Finally, we discuss how DC-based vaccines might synergize with checkpoint inhibition in the treatment of malignant diseases.

A Canine-Directed Chimeric Multi-Epitope Vaccine Induced Protective Immune Responses in BALB/c Mice Infected with Leishmania infantum

Leishmaniases are complex vector-borne diseases caused by intracellular parasites of the genus Leishmania. The visceral form of the disease affects both humans and canids in tropical, subtropical, and Mediterranean regions. One health approach has suggested that controlling zoonotic visceral leishmaniasis (ZVL) could have an impact on the reduction of the human incidence of visceral leishmaniasis (VL). Despite the fact that a preventive vaccination could help with leishmaniasis elimination, effective vaccines that are able to elicit protective immune responses are currently lacking. In the present study, we designed a chimeric multi-epitope protein composed of multiple CD8⁺ and CD4⁺ T cell epitopes which were obtained from six highly immunogenic proteins previously identified by an immunoproteomics approach, and the N-termini of the heparin-binding hemagglutinin (HBHA) of Mycobacterium tuberculosis served as an adjuvant. A preclinical evaluation of the candidate vaccine in BALB/c mice showed that when it was given along with the adjuvant Addavax it was able to induce strong immune responses. Cellular responses were dominated by the presence of central and effector multifunctional CD4⁺ and CD8⁺ T memory cells. Importantly, the vaccination reduced the parasite burden in both short-term and long-term vaccinated mice challenged with Leishmania infantum. Protection was characterized by the continuing presence of IFN-γ⁺TNFα⁺-producing CD8⁺ and CD4⁺ T cells and increased NO levels. The depletion of CD8⁺ T cells in short-term vaccinated mice conferred a significant loss of protection in both target organs of the parasite, indicating a significant involvement of this population in the protection against L. infantum challenge. Thus, the overall data could be considered to be a proof-of-concept that the design of efficacious T cell vaccines with the help of reverse vaccinology approaches is possible.

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.

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.

Alternative to Chemotherapy-The Unmet Demand against Leishmaniasis

Leishmaniasis is a neglected protozoan disease that mainly affects the tropical as well as subtropical countries of the world. The primary option to control the disease still relies on chemotherapy. However, a hindrance to treatments owing to the emergence of drug-resistant parasites, enormous side effects of the drugs, their high cost, and requirement of long course hospitalization has added to the existing problems of leishmaniasis containment program. This review highlights the prospects of immunotherapy and/or immunochemotherapy to address the limitations for current treatment measures for leishmaniasis. In addition to the progress in alternate therapeutic strategies, the possibility and advances in developing preventive measures against the disease have been pointed. The review highlights our recent understandings of the protective immunology that can be exploited to develop an effective vaccine against leishmaniasis. Moreover, an update on the approaches that have evolved over the recent years are predominantly focused to overcome the current challenges in developing immunotherapeutic as well as prophylactic antileishmanial vaccines is discussed.

Immune Response and Protective Efficacy of a Heterologous DNA-Protein Immunization with Leishmania Superoxide Dismutase B1

Growing evidence shows that antioxidant proteins of Leishmania could be used as vaccine candidates. In this study, we report the efficacy of Leishmania donovani iron superoxide dismutase B1 (LdFeSODB1) as a vaccine antigen in BALB/c mice in a DNA-protein prime-boost immunization regimen in the presence or absence of murine granulocyte macrophage colony stimulating factor (mGMCSF) DNA adjuvant. The expression study confirmed that LdFeSODB1 is expressed in mammalian cells and mGMCSF fusion mediates the secretion of the recombinant protein. Heterologous immunization with LdFeSODB1 induced a strong antibody- and cell-mediated immune response in mice. Immunization triggered a mixed Th1/Th2 response as evidenced by the ratio of IgG2a to IgG1. Antigen-stimulated spleen cells from the immunized mice produced high level IFN-γ. Multiparametric flow cytometry data showed that immunization with LdFeSODB1 induced significantly higher expression of TNF-α or IL-2 by antigen-stimulated T cells. Eight weeks after L. major infection, immunization with the antigen shifted the immune response to a more Th1 type than the controls as demonstrated by IgG2a/IgG1 ratio. Moreover, IFN-γ production by antigen-stimulated spleen cells from immunized mice remained high. The footpad swelling experiment showed that immunization with LdFeSODB1 resulted in partial protection of mice from a high dose L. major infection.

A new approach for development of vaccine against visceral leishmaniasis: Lipophosphoglycan and polyacrylic acid conjugates

OBJECTIVE

To determine the antileishmanial vaccine effectiveness of lipophosphoglycan (LPG) and polyacrylic acids (PAA) conjugates on in vivo mice models.

METHODS

LPG molecule was isolated and purified from large-scale Leishmania donovani parasite culture. Protection efficacies of LPG alone, in combination with Freund's adjuvant, in a physical mixture and in conjugate (consisting of various LPG concentrations) with PAA, were comparatively determined by various techniques, such as cultivation with the micro-culture method, assessment of in vitro infection rates of peritoneal macrophages, determination of parasite load in liver with Leishman-Donovan Units, and detection of cytokine responses.

RESULTS

Obtained results demonstrated that the highest vaccine-mediated immune protection was provided by LPG-PAA conjugate due to all parameters investigated. According to the Leishman-Donovan Units results, the sharpest decline in parasite load was seen with a ratio of 81.17% when 35 μg LPG containing conjugate was applied. This value was 44.93% for the control group immunized only with LPG. Moreover, decreases in parasite load were 53.37%, 55.2% and 65.8% for the groups immunized with 10 μg LPG containing LPG-PAA conjugate, a physical mixture of the LPG-PAA, and a mixture of LPG + Freund's adjuvant, respectively. Furthermore, cytokine results supported that Th1 mediated protection occurred when mice were immunized with LPG-PAA conjugate.

CONCLUSIONS

It has been demonstrated in this study that conjugate of LPG and PAA has an antileishmanial vaccine effect against visceral leishmaniasis. In this respect, the present study may lead to new vaccine approaches based on high immunogenic LPG molecule and adjuvant polymers in fighting against Leishmania infection.

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.

A third generation vaccine for human visceral leishmaniasis and post kala azar dermal leishmaniasis: First-in-human trial of ChAd63-KH

BACKGROUND

Visceral leishmaniasis (VL or kala azar) is the most serious form of human leishmaniasis, responsible for over 20,000 deaths annually, and post kala azar dermal leishmaniasis (PKDL) is a stigmatizing skin condition that often occurs in patients after successful treatment for VL. Lack of effective or appropriately targeted cell mediated immunity, including CD8+ T cell responses, underlies the progression of VL and progression to PKDL, and can limit the therapeutic efficacy of anti-leishmanial drugs. Hence, in addition to the need for prophylactic vaccines against leishmaniasis, the development of therapeutic vaccines for use alone or in combined immuno-chemotherapy has been identified as an unmet clinical need. Here, we report the first clinical trial of a third-generation leishmaniasis vaccine, developed intentionally to induce Leishmania-specific CD8+ T cells.

METHODS

We conducted a first-in-human dose escalation Phase I trial in 20 healthy volunteers to assess the safety, tolerability and immunogenicity of a prime-only adenoviral vaccine for human VL and PKDL. ChAd63-KH is a replication defective simian adenovirus expressing a novel synthetic gene (KH) encoding two Leishmania proteins KMP-11 and HASPB. Uniquely, the latter was engineered to reflect repeat domain polymorphisms and arrangements identified from clinical isolates. We monitored innate immune responses by whole blood RNA-Seq and antigen specific CD8+ T cell responses by IFNγ ELISPOT and intracellular flow cytometry.

FINDINGS

ChAd63-KH was safe at intramuscular doses of 1x1010 and 7.5x1010 vp. Whole blood transcriptomic profiling indicated that ChAd63-KH induced innate immune responses characterized by an interferon signature and the presence of activated dendritic cells. Broad and quantitatively robust CD8+ T cell responses were induced by vaccination in 100% (20/20) of vaccinated subjects.

CONCLUSION

The results of this study support the further development of ChAd63-KH as a novel third generation vaccine for VL and PKDL.

TRIAL REGISTRATION

This clinical trial (LEISH1) was registered at EudraCT (2012-005596-14) and ISRCTN (07766359).

Safety and efficacy of current alternatives in the topical treatment of cutaneous leishmaniasis: a systematic review

Studies of topical treatments for leishmaniasis were systematically reviewed, to evaluate the therapeutic efficacy, safety and any adverse effects of these treatments. The papers identified in the databases PubMed and Web of Knowledge involved eight studies with a total of 1744 patients. The majority of trials was from Iran (4/8), covered a period of 8 years (2003–2011), and included patients 4–85 years of age. The most frequent Leishmania species in the studies were L. tropica (4/8) and L. major (2/8). The treatments administered were thermotherapy, paromomycin and combinations, CO2 laser, 5-aminolevulinic acid hydrochloride (10%) plus visible red light (633 nm) and cryotherapy. Six articles reported cure rates over 80·0%. Six studies reported on failure rates, three of them reporting rates lower than 10%. Four studies did not report relapses or recurrences, while the other studies reported low rates (1·8–6·3%). The most common adverse effects of the topical treatments were redness/erythema, pain, pruritus burning, oedema, vesicles and hyper- or hypopigmentation. The results provide strong evidence that the treatments topical evaluated showed high cure rates, safety and effectiveness, with low side-effects, relapse and recurrence rates, except for cryotherapy, which showed a moderate cure rate.

Local Delivery of the Toll-Like Receptor 9 Ligand CpG Downregulates Host Immune and Inflammatory Responses, Ameliorating Established Leishmania (Viannia) panamensis Chronic Infection

Infection by Leishmania (Viannia) panamensis, the predominant etiologic agent for cutaneous leishmaniasis in Colombia, is characterized by a chronic mixed inflammatory response. Current treatment options are plagued by toxicity, lengthy treatment regimens, and growing evidence of drug resistance. Immunotherapy, modulating the immune system to mount a protective response, may provide an alternate therapeutic approach. We investigated the ability of the Toll-like receptor 9 (TLR9) ligand CpG to modulate established disease in the L (V) panamensis mouse model. Treatment of established infection with a high dose (50 μg) of CpG ameliorated disease and lowered parasite burden. Interestingly, immediately after treatment there was a significant increase in transforming growth factor β (TGF-β) and concomitantly an increase in T regulatory cell (Treg) function. Although a general reduction in cell-mediated immune cytokine and chemokine (gamma interferon [IFN-γ], interleukin 10 [IL-10], IL-13, IL-6, granulocyte-macrophage colony-stimulating factor [GM-CSF], IL-4, and MIP-1α) responses of the treated mice was observed, certain chemokines (RANTES, monocyte chemoattractant protein 1[MCP-1], and IP-10) were increased. Further, in peripheral blood mononuclear cells (PBMCs) from patients with cutaneous leishmaniasis, CpG treatment similarly exhibited a dose-response effect on the production of IFN-γ, IL-17, IL-10, and IL-13, with reductions observed at higher doses. To further understand the underlying mechanisms and cell populations driving the CpG mediated response, we examined the ex vivo dose effects mediated by the TLR9⁺ cell populations (dendritic cells, macrophages, and B cells) found to accumulate labeled CpG in vivo Notably, B cells altered the production of IL-17, IL-13, and IFN-γ, supporting a role for B cells functioning as antigen-presenting cells (APCs) and/or regulatory cells during infection. Interestingly, B cells have been previously demonstrated as a primary type of APC in patients infected with L (V) panamensis and thus may be useful targets of immunotherapy. Collectively, our results show that CpG-induced immune regulation leads to a dampening of the host immune response and healing in the mouse model, and it may provide an alternate approach to treatment of cutaneous leishmaniasis caused by L (V) panamensis.

Status of vaccine research and development of vaccines for leishmaniasis

A number of leishmaniasis vaccine candidates are at various stages of pre-clinical and clinical development. Leishmaniasis is a vector-borne neglected tropical disease (NTD) caused by a protozoan parasite of the genus Leishmania and transmitted to humans by the bite of a sand fly. Visceral leishmaniasis (VL, kala-azar) is a high mortality NTD found mostly in South Asia and East Africa, while cutaneous leishmaniasis (CL) is a disfiguring NTD highly endemic in the Middle East, Central Asia, North Africa, and the Americas. Estimates attribute 50,000 annual deaths and 3.3 million disability-adjusted life years to leishmaniasis. There are only a few approved drug treatments, no prophylactic drug and no vaccine. Ideally, an effective vaccine against leishmaniasis will elicit long-lasting immunity and protect broadly against VL and CL. Vaccines such as Leish-F1, F2 and F3, developed at IDRI and designed based on selected Leishmania antigen epitopes, have been in clinical trials. Other groups, including the Sabin Vaccine Institute in collaboration with the National Institutes of Health are investigating recombinant Leishmania antigens in combination with selected sand fly salivary gland antigens in order to augment host immunity. To date, both VL and CL vaccines have been shown to be cost-effective in economic modeling studies.

Treatment of Cutaneous Leishmaniasis Caused by Leishmania aethiopica: A Systematic Review

Leishmania aethiopica is the etiological agent of cutaneous leishmaniasis (CL) in Ethiopia and can cause severe and complicated cases such as diffuse CL (DCL), mucocutaneous leishmaniasis or extensive CL, requiring systemic treatment. Despite the substantial burden, evidence-based treatment guidelines are lacking. We conducted a systematic review of clinical studies reporting on treatment outcomes of CL due to L aethiopica in order to help identify potentially efficacious medications on CL that can be taken forward for clinical trials. We identified a total of 24 records reporting on 506 treatment episodes of CL presumably due to L aethiopica. The most commonly used drugs were antimonials (n = 201), pentamidine (n = 150) and cryotherapy (n = 103). There were 20 case reports/series, with an overall poor study quality. We only identified two small and/or poor quality randomized controlled trials conducted a long time ago. There were two prospective non-randomized studies reporting on cryotherapy, antimonials and pentamidine. With cryotherapy, cure rates were 60-80%, and 69-85% with antimonials. Pentamidine appeared effective against complicated CL, also in cases non-responsive to antimonials. However, all studies suffered from methodological limitations. Data on miltefosine, paromomycin and liposomal amphotericin B are extremely scarce. Only a few studies are available on DCL. The only potentially effective treatment options for DCL seem to be antimonials with paromomycin in combination or pentamidine, but none have been properly evaluated. In conclusion, the evidence-base for treatment of complicated CL due to L aethiopica is extremely limited. While antimonials remain the most available CL treatment in Ethiopia, their efficacy and safety in CL should be better defined. Most importantly, alternative first line treatments (such as miltefosine or paromomycin) should be explored. High quality trials on CL due to L aethiopica are urgently needed, exploring group sequential methods to evaluate several options in parallel.

Sequential chemoimmunotherapy of experimental visceral leishmaniasis using a single low dose of liposomal amphotericin B and a novel DNA vaccine candidate

Combination therapies for leishmaniasis, including drugs and immunomodulators, are one approach to shorten treatment courses and to improve the treatment of complex manifestations of the disease. We evaluated a novel T-cell-epitope-enriched DNA vaccine candidate (LEISHDNAVAX) as host-directed immunotherapy in combination with a standard antileishmanial drug in experimental visceral leishmaniasis. Here we show that the DNA vaccine candidate can boost the efficacy of a single suboptimal dose of liposomal amphotericin B in C57BL/6 mice.

Immunity to visceral leishmaniasis: implications for immunotherapy

Visceral leishmaniasis, caused by Leishmania donovani, L. infantum (syn. Leishmania chagasi), is a globally widespread disease with a burden of about 400,000 new infections reported annually. It is the most dangerous form of human leishmaniasis in terms of mortality and morbidity and is spreading to several nonendemic areas because of migration, global traveling and military conflicts. The emergence of Leishmania-HIV co-infection and increased prevalence of drug-resistant strains have worsened the impact of the disease. The traditional low-cost drugs are often toxic with several adverse effects, highlighting the need for development of new therapeutic and prophylactic strategies. Therefore, a detailed understanding of mechanisms of protective immunity is extremely important in order to develop new therapeutics in the form of vaccines or immunotherapies. This review gives an overview of visceral leishmaniasis, with particular emphasis on the innate and adaptive immune responses, vaccine and vaccination strategies and their potentials for immunotherapy against the disease.

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.

Historical review of clinical vaccine studies at Oswaldo Cruz Institute and Oswaldo Cruz Foundation--technological development issues

This paper presents, from the perspective of technological development and production, the results of an investigation examining 61 clinical studies with vaccines conducted in Brazil between 1938-2013, with the participation of the Oswaldo Cruz Institute (IOC) and the Oswaldo Cruz Foundation (Fiocruz). These studies have been identified and reviewed according to criteria, such as the kind of vaccine (viral, bacterial, parasitic), their rationale, design and methodological strategies. The results indicate that IOC and Fiocruz have accumulated along this time significant knowledge and experience for the performance of studies in all clinical phases and are prepared for the development of new vaccines products and processes. We recommend national policy strategies to overcome existing regulatory and financing constraints.

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 Adjuvant Effect of Molecularly-defined Toll-Like Receptor Ligands

Vaccine efficacy is optimized by addition of immune adjuvants. However, although adjuvants have been used for over a century, to date, only few adjuvants are approved for human use, mostly aimed at improving vaccine efficacy and antigen-specific protective antibody production. The mechanism of action of immune adjuvants is diverse, depending on their chemical and molecular nature, ranging from non-specific effects (i.e., antigen depot at the immunization site) to specific activation of immune cells leading to improved host innate and adaptive responses. Although the detailed molecular mechanism of action of many adjuvants is still elusive, the discovery of Toll-like receptors (TLRs) has provided new critical information on immunostimulatory effect of numerous bacterial components that engage TLRs. These ligands have been shown to improve both the quality and the quantity of host adaptive immune responses when used in vaccine formulations targeted to infectious diseases and cancer that require both humoral and cell-mediated immunity. The potential of such TLR adjuvants in improving the design and the outcomes of several vaccines is continuously evolving, as new agonists are discovered and tested in experimental and clinical models of vaccination. In this review, a summary of the recent progress in development of TLR adjuvants is presented.

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.

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.

Interventions for American cutaneous and mucocutaneous leishmaniasis: a systematic review update

Introduction

Leishmaniasis is an important public health problem in the Americas. A Cochrane review published in 2009 analyzed 38 randomized controlled trials (RCT). We conducted a systematic review to evaluate the effects of therapeutic interventions for American cutaneous and mucocutaneous leishmaniasis.

Methods

All studies were extracted from PubMed, Embase, Lilacs (2009 to July, 2012 respectively), the Cochrane Central Register of Controlled Trials (6-2012) and references of identified publications. RCTs’ risk of bias was assessed.

Results

We identified 1865 references of interest; we finally included 10 new RCTs. The risk of bias scored low or unclear for most domains. Miltefosine was not significantly different from meglumine antimoniate in the complete cure rate at 6 months (4 RCT; 584 participants; ITT; RR: 1.12; 95%CI: 0.85 to 1.47; I2 78%). However a significant difference in the rate of complete cure favoring miltefosine at 6 months was found in L. panamensis and L. guyanensis (2 RCTs, 206 participants; ITT; RR: 1.22; 95%CI: 1.02 to 1.46; I2 0%). One RCT found that meglumine antimoniate was superior to pentamidine in the rate of complete cure for L. braziliensis (80 participants, ITT; RR: 2.21; 95%CI: 1.41 to 3.49), while another RCT assessing L. guyanensis did not find any significant difference. Although meta-analysis of three studies found a significant difference in the rate of complete cure at 3 months favoring imiquimod versus placebo (134 participants; ITT; RR: 1.45; 95%CI: 1.12 to 1.88; I2 0%), no significant differences were found at 6 and 12 months. Thermotherapy and nitric oxide were not superior to meglumine antimoniate.

Conclusion

Therapeutic interventions for American cutaneous and mucocutaneous leishmaniasis are varied and should be decided according to the context. Since mucosal disease is the more neglected form of leishmaniasis a multicentric trial should be urgently considered.

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.

Evaluation of recombinant Leishmania polyprotein plus glucopyranosyl lipid A stable emulsion vaccines against sand fly-transmitted Leishmania major in C57BL/6 mice

Numerous experimental Leishmania vaccines have been developed to prevent the visceral and cutaneous forms of Leishmaniasis, which occur after exposure to the bite of an infected sand fly, yet only one is under evaluation in humans. KSAC and L110f, recombinant Leishmania polyproteins delivered in a stable emulsion (SE) with the TLR4 agonists monophosphoryl lipid A or glucopyranosyl lipid A (GLA) have shown protection in animal models. KSAC+GLA-SE protected against cutaneous disease following sand fly transmission of Leishmania major in susceptible BALB/c mice. Similar polyprotein adjuvant combinations are the vaccine candidates most likely to see clinical evaluation. We assessed immunity generated by KSAC or L110f vaccination with GLA-SE following challenge with L. major by needle or infected sand fly bite in resistant C57BL/6 mice. Polyprotein-vaccinated mice had a 60-fold increase in CD4(+)IFN-γ(+) T cell numbers versus control animals at 2 wk post-needle inoculation of L. major, and this correlated with a 100-fold reduction in parasite load. Immunity did not, however, reach levels observed in mice with a healed primary infection. Following challenge by infected sand fly bite, polyprotein-vaccinated animals had comparable parasite loads, greater numbers of neutrophils at the challenge site, and reduced CD4(+)IFN-γ(+)/IL-17(+) ratios versus nonvaccinated controls. In contrast, healed animals had significantly reduced parasite loads and higher CD4(+)IFN-γ(+)/IL-17(+) ratios. These observations demonstrate that vaccine-induced protection against needle challenge does not necessarily translate to protection following challenge by infected sand fly bite.

Identification of Leishmania infantum chagasi proteins in urine of patients with visceral leishmaniasis: a promising antigen discovery approach of vaccine candidates

Visceral leishmaniasis (VL) is a serious lethal parasitic disease caused by Leishmania donovani in Asia and by Leishmania infantum chagasi in southern Europe and South America. VL is endemic in 47 countries with an annual incidence estimated to be 500,000 cases. This high incidence is due in part to the lack of an efficacious vaccine. Here, we introduce an innovative approach to directly identify parasite vaccine candidate antigens that are abundantly produced in vivo in humans with VL. We combined RP-HPLC and mass spectrometry and categorized three L. infantum chagasi proteins, presumably produced in spleen, liver and bone marrow lesions and excreted in the patients' urine. Specifically, these proteins were the following: Li-isd1 (XP_001467866.1), Li-txn1 (XP_001466642.1) and Li-ntf2 (XP_001463738.1). Initial vaccine validation studies were performed with the rLi-ntf2 protein produced in Escherichia coli mixed with the adjuvant BpMPLA-SE. This formulation stimulated potent Th1 response in BALB/c mice. Compared to control animals, mice immunized with Li-ntf2+ BpMPLA-SE had a marked parasite burden reduction in spleens at 40 days post-challenge with virulent L. infantum chagasi. These results strongly support the proposed antigen discovery strategy of vaccine candidates to VL and opens novel possibilities for vaccine development to other serious infectious diseases.

Therapeutic immunization against Mycobacterium tuberculosis is an effective adjunct to antibiotic treatment

BACKGROUND

Recent advances in rational adjuvant design and antigen selection have enabled a new generation of vaccines with potential to treat and prevent infectious disease. The aim of this study was to assess whether therapeutic immunization could impact the course of Mycobacterium tuberculosis infection with use of a candidate tuberculosis vaccine antigen, ID93, formulated in a synthetic nanoemulsion adjuvant, GLA-SE, administered in combination with existing first-line chemotherapeutics rifampicin and isoniazid.

METHODS

We used a mouse model of fatal tuberculosis and the established cynomolgus monkey model to design an immuno-chemotherapeutic strategy to increase long-term survival and reduce bacterial burden, compared with standard antibiotic chemotherapy alone.

RESULTS

This combined approach induced robust and durable pluripotent antigen-specific T helper-1-type immune responses, decreased bacterial burden, reduced the duration of conventional chemotherapy required for survival, and decreased M. tuberculosis-induced lung pathology, compared with chemotherapy alone.

CONCLUSIONS

These results demonstrate the ability of therapeutic immunization to significantly enhance the efficacy of chemotherapy against tuberculosis and other infectious diseases, with implications for treatment duration, patient compliance, and more optimal resource allocation.

Protective immunity and vaccination against cutaneous leishmaniasis

Although a great deal of knowledge has been gained from studies on the immunobiology of leishmaniasis, there is still no universally acceptable, safe, and effective vaccine against the disease. This strongly suggests that we still do not completely understand the factors that control and/or regulate the development and sustenance of anti-Leishmania immunity, particularly those associated with secondary (memory) immunity. Such an understanding is critically important for designing safe, effective, and universally acceptable vaccine against the disease. Here we review the literature on the correlate of protective anti-Leishmania immunity and vaccination strategies against leishmaniasis with a bias emphasis on experimental cutaneous leishmaniasis.

Vaccines for canine leishmaniasis

Leishmaniasis is the third most important vector-borne disease worldwide. Visceral leishmaniasis (VL) is a severe and frequently lethal protozoan disease of increasing incidence and severity due to infected human and dog migration, new geographical distribution of the insect due to global warming, coinfection with immunosuppressive diseases, and poverty. The disease is an anthroponosis in India and Central Africa and a canid zoonosis (ZVL) in the Americas, the Middle East, Central Asia, China, and the Mediterranean. The ZVL epidemic has been controlled by one or more measures including the culling of infected dogs, treatment of human cases, and insecticidal treatment of homes and dogs. However, the use of vaccines is considered the most cost-effective control tool for human and canine disease. Since the severity of the disease is related to the generation of T-cell immunosuppression, effective vaccines should be capable of sustaining or enhancing the T-cell immunity. In this review we summarize the clinical and parasitological characteristics of ZVL with special focus on the cellular and humoral canine immune response and review state-of-the-art vaccine development against human and canine VL. Experimental vaccination against leishmaniasis has evolved from the practice of leishmanization with living parasites to vaccination with crude lysates, native parasite extracts to recombinant and DNA vaccination. Although more than 30 defined vaccines have been studied in laboratory models no human formulation has been licensed so far; however three second-generation canine vaccines have already been registered. As expected for a zoonotic disease, the recent preventive vaccination of dogs in Brazil has led to a reduction in the incidence of canine and human disease. The recent identification of several Leishmania proteins with T-cell epitopes anticipates development of a multiprotein vaccine that will be capable of protecting both humans and dogs against VL.

KSAC, a defined Leishmania antigen, plus adjuvant protects against the virulence of L. major transmitted by its natural vector Phlebotomus duboscqi

Background

Recombinant KSAC and L110f are promising Leishmania vaccine candidates. Both antigens formulated in stable emulsions (SE) with the natural TLR4 agonist MPL® and L110f with the synthetic TLR4 agonist GLA in SE protected BALB/c mice against L. major infection following needle challenge. Considering the virulence of vector-transmitted Leishmania infections, we vaccinated BALB/c mice with either KSAC+GLA-SE or L110f+GLA-SE to assess protection against L. major transmitted via its vector Phlebotomus duboscqi.

Methods

Mice receiving the KSAC or L110f vaccines were challenged by needle or L. major-infected sand flies. Weekly disease progression and terminal parasite loads were determined. Immunological responses to KSAC, L110f, or soluble Leishmania antigen (SLA) were assessed throughout vaccination, three and twelve weeks after immunization, and one week post-challenge.

Results

Following sand fly challenge, KSAC-vaccinated mice were protected while L110f-vaccinated animals showed partial protection. Protection correlated with the ability of SLA to induce IFN-γ-producing CD4⁺CD62L^lowCCR7^low effector memory T cells pre- and post-sand fly challenge.

Conclusions

This study demonstrates the protective efficacy of KSAC+GLA-SE against sand fly challenge; the importance of vector-transmitted challenge in evaluating vaccine candidates against Leishmania infection; and the necessity of a rapid potent Th1 response against Leishmania to attain true protection.

Leishmaniasis is a neglected disease caused by the Leishmania parasite and transmitted by the bite of an infective sand fly. Despite the importance of this disease there is no vaccine available for humans. Studies have shown that vector-transmitted infections are more virulent, promoting parasite establishment and abrogating protection observed against needle-injected parasites in vaccinated mice. KSAC and L110f, derived from Leishmania-based polyproteins, protected mice against the needle-injected parasites. Here, we tested the two molecules for their capacity to protect mice against cutaneous leishmaniasis transmitted by an infective sand fly. Our results show that KSAC, but not L110f, confers protection against Leishmania transmitted by sand fly bites where protection was correlated to a strong immune response to Leishmania antigens by memory T cells before and after sand fly transmission of the parasite. This is the first report of a Leishmania-based vaccine that confers protection against a virulent sand fly challenge. Our results support the importance of screening Leishmania vaccine candidates using infective sand flies before moving forward with the costly steps of vaccine development.

Leishmaniasis: vaccine candidates and perspectives

Leishmania is a protozoan parasite and a causative agent of the various clinical forms of leishmaniasis. High cost, resistance and toxic side effects of traditional drugs entail identification and development of therapeutic alternatives. The sound understanding of parasite biology is key for identifying novel drug targets, that can induce the cell mediated immunity (mainly CD4+ and CD8+ IFN-gamma mediated responses) polarized towards a Th1 response. These aspects are important in designing a new vaccine along with the consideration of the candidates with respect to their ability to raise memory response in order to improve the vaccine performance. This review is an effort to identify molecules according to their homology with the host and their ability to be used as potent vaccine candidates.

Therapeutic vaccination with recombinant adenovirus reduces splenic parasite burden in experimental visceral leishmaniasis

Therapeutic vaccines, when used alone or in combination therapy with antileishmanial drugs, may have an important place in the control of a variety of forms of human leishmaniasis. Here, we describe the development of an adenovirus-based vaccine (Ad5-KH) comprising a synthetic haspb gene linked to a kmp11 gene via a viral 2A sequence. In nonvaccinated Leishmania donovani–infected BALB/c mice, HASPB- and KMP11-specific CD8⁺ T cell responses were undetectable, although IgG1 and IgG2a antibodies were evident. After therapeutic vaccination, antibody responses were boosted, and IFNγ⁺CD8⁺ T cell responses, particularly to HASPB, became apparent. A single vaccination with Ad5-KH inhibited splenic parasite growth by ∼66%, a level of efficacy comparable to that observed in early stage testing of clinically approved antileishmanial drugs in this model. These studies indicate the usefulness of adenoviral vectors to deliver leishmanial antigens in a potent and host protective manner to animals with existing L. donovani infection.

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.

Single dose novel Salmonella vaccine enhances resistance against visceralizing L. major and L. donovani infection in susceptible BALB/c mice

Visceral leishmaniasis is a major neglected tropical disease, with an estimated 500,000 new cases and more than 50,000 deaths attributable to this disease every year. Drug therapy is available but costly and resistance against several drug classes has evolved. Despite all efforts, no commercial, let alone affordable, vaccine is available to date. Thus, the development of cost effective, needle-independent vaccines is a high priority. Here, we have continued efforts to develop live vaccine carriers based on recombinant Salmonella. We used an in silico approach to select novel Leishmania parasite antigens from proteomic data sets, with selection criteria based on protein abundance, conservation across Leishmania species and low homology to host species. Five chosen antigens were differentially expressed on the surface or in the cytosol of Salmonella typhimurium SL3261. A two-step procedure was developed to select optimal Salmonella vaccine strains for each antigen, based on bacterial fitness and antigen expression levels. We show that vaccine strains of Salmonella expressing the novel Leishmania antigens LinJ08.1190 and LinJ23.0410 significantly reduced visceralisation of L. major and enhanced systemic resistance against L. donovani in susceptible BALB/c mice. The results show that Salmonella are valid vaccine carriers for inducing resistance against visceral leishmaniasis but that their use may not be suitable for all antigens.

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.

Visceral leishmaniasis: immunology and prospects for a vaccine

Human visceral leishmaniasis (HVL) is the most severe clinical form of a spectrum of neglected tropical diseases caused by protozoan parasites of the genus Leishmania. Caused mainly by L. donovani and L. infantum/chagasi, HVL accounts for more than 50 000 deaths every year. Drug therapy is available but costly, and resistance against several drug classes has evolved. Here, we review our current understanding of the immunology of HVL and approaches to and the status of vaccine development against this disease.

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.

Intracellular targeting specificity of novel phthalocyanines assessed in a host-parasite model for developing potential photodynamic medicine

Photodynamic therapy, unlikely to elicit drug-resistance, deserves attention as a strategy to counter this outstanding problem common to the chemotherapy of all diseases. Previously, we have broadened the applicability of this modality to photodynamic vaccination by exploiting the unusual properties of the trypanosomatid protozoa, Leishmania, i.e., their innate ability of homing to the phagolysosomes of the antigen-presenting cells and their selective photolysis therein, using transgenic mutants endogenously inducible for porphyrin accumulation. Here, we extended the utility of this host-parasite model for in vitro photodynamic therapy and vaccination by exploring exogenously supplied photosensitizers. Seventeen novel phthalocyanines (Pcs) were screened in vitro for their photolytic activity against cultured Leishmania. Pcs rendered cationic and soluble (csPcs) for cellular uptake were phototoxic to both parasite and host cells, i.e., macrophages and dendritic cells. The csPcs that targeted to mitochondria were more photolytic than those restricted to the endocytic compartments. Treatment of infected cells with endocytic csPcs resulted in their accumulation in Leishmania-containing phagolysosomes, indicative of reaching their target for photodynamic therapy, although their parasite versus host specificity is limited to a narrow range of csPc concentrations. In contrast, Leishmania pre-loaded with csPc were selectively photolyzed intracellularly, leaving host cells viable. Pre-illumination of such csPc-loaded Leishmania did not hinder their infectivity, but ensured their intracellular lysis. Ovalbumin (OVA) so delivered by photo-inactivated OVA transfectants to mouse macrophages and dendritic cells were co-presented with MHC Class I molecules by these antigen presenting cells to activate OVA epitope-specific CD8+T cells. The in vitro evidence presented here demonstrates for the first time not only the potential of endocytic csPcs for effective photodynamic therapy against Leishmania but also their utility in photo-inactivation of Leishmania to produce a safe carrier to express and deliver a defined antigen with enhanced cell-mediated immunity.

KSAC, the first defined polyprotein vaccine candidate for visceral leishmaniasis

A subunit vaccine using a defined antigen(s) may be one effective solution for controlling leishmaniasis. Because of genetic diversity in target populations, including both dogs and humans, a multiple-antigen vaccine will likely be essential. However, the cost of a vaccine to be used in developing countries must be considered. We describe herein a multiantigen vaccine candidate comprised of antigens known to be protective in animal models, including dogs, and to be recognized by humans immune to visceral leishmaniasis. The polyprotein (KSAC) formulated with monophosphoryl lipid A, a widely used adjuvant in human vaccines, was found to be immunogenic and capable of inducing protection against Leishmania infantum, responsible for human and canine visceral leishmaniasis, and against L. major, responsible for cutaneous leishmaniasis. The results demonstrate the feasibility of producing a practical, cost-effective leishmaniasis vaccine capable of protecting both humans and dogs against multiple Leishmania species.