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

Leishmania vaccine development: A comprehensive review

Infectious diseases like leishmaniasis, malaria, HIV, tuberculosis, leprosy and filariasis are responsible for an immense burden on public health systems. Among these, leishmaniasis is under the category I diseases as it is selected by WHO (World Health Organization) on the ground of diversity and complexity. High cost, resistance and toxic effects of Leishmania traditional drugs entail identification and development of therapeutic alternative. Since the natural infection elicits robust immunity, consistence efforts are going on to develop a successful vaccine. Clinical trials have been conducted on vaccines like Leish-F1, F2, and F3 formulated using specific Leishmania antigen epitopes. Current strategies utilize individual or combined antigens from the parasite or its insect vector's salivary gland extract, with or without adjuvant formulation for enhanced efficacy. Promising animal data supports multiple vaccine candidates (Lmcen-/-, LmexCen-/-), with some already in or heading for clinical trials. The crucial challenge in Leishmania vaccine development is to translate the research knowledge into affordable and accessible control tools that refines the outcome for those who are susceptible to infection. This review focuses on recent findings in Leishmania vaccines and highlights difficulties facing vaccine development and implementation.

Artificial Feeding Systems for Vector-Borne Disease Studies

This review examines the advancements and methodologies of artificial feeding systems for the study of vector-borne diseases, offering a critical assessment of their development, advantages, and limitations relative to traditional live host models. It underscores the ethical considerations and practical benefits of such systems, including minimizing the use of live animals and enhancing experimental consistency. Various artificial feeding techniques are detailed, including membrane feeding, capillary feeding, and the utilization of engineered biocompatible materials, with their respective applications, efficacy, and the challenges encountered with their use also being outlined. This review also forecasts the integration of cutting-edge technologies like biomimicry, microfluidics, nanotechnology, and artificial intelligence to refine and expand the capabilities of artificial feeding systems. These innovations aim to more accurately simulate natural feeding conditions, thereby improving the reliability of studies on the transmission dynamics of vector-borne diseases. This comprehensive review serves as a foundational reference for researchers in the field, proposing a forward-looking perspective on the potential of artificial feeding systems to revolutionize vector-borne disease research.

Memory T cells: promising biomarkers for evaluating protection and vaccine efficacy against leishmaniasis

Understanding the immune response to Leishmania infection and identifying biomarkers that correlate with protection are crucial for developing effective vaccines. One intriguing aspect of Leishmania infection is the persistence of parasites, even after apparent lesion healing. Various host cells, including dendritic cells, fibroblasts, and Langerhans cells, may serve as safe sites for latent infection. Memory T cells, especially tissue-resident memory T cells (TRM), play a crucial role in concomitant immunity against cutaneous Leishmania infections. These TRM cells are long-lasting and can protect against reinfection in the absence of persistent parasites. CD4+ TRM cells, in particular, have been implicated in protection against Leishmania infections. These cells are characterized by their ability to reside in the skin and rapidly respond to secondary infections by producing cytokines such as IFN-γ, which activates macrophages to kill parasites. The induction of CD4+ TRM cells has shown promise in experimental immunization, leading to protection against Leishmania challenge infections. Identifying biomarkers of protection is a critical step in vaccine development and CD4+ TRM cells hold potential as biomarkers, as their presence and functions may correlate with protection. While recent studies have shown that Leishmania-specific memory CD4+ T-cell subsets are present in individuals with a history of cutaneous leishmaniasis, further studies are needed to characterize CD4+ TRM cell populations. Overall, this review highlights the importance of memory T cells, particularly skin-resident CD4+ TRM cells, as promising targets for developing effective vaccines against leishmaniasis and as biomarkers of immune protection to assess the efficacy of candidate vaccines against human leishmaniasis.

IgG Subclass Switch in Volunteers Repeatedly Immunized with the Full-Length Plasmodium falciparum Merozoite Surface Protein 1 (MSP1)

Vaccines are highly effective tools against infectious diseases and are also considered necessary in the fight against malaria. Vaccine-induced immunity is frequently mediated by antibodies. We have recently conducted a first-in-human clinical trial featuring SumayaVac-1, a malaria vaccine based on the recombinant, full-length merozoite surface protein 1 (MSP1FL) formulated with GLA-SE as an adjuvant. Vaccination with MSP1FL was safe and elicited sustainable IgG antibody titers that exceeded those observed in semi-immune populations from Africa. Moreover, IgG antibodies stimulated various Fc-mediated effector mechanisms associated with protection against malaria. However, these functionalities gradually waned. Here, we show that the initial two doses of SumayaVac-1 primarily induced the cytophilic subclasses IgG1 and IgG3. Unexpectedly, a shift in the IgG subclass composition occurred following the third and fourth vaccinations. Specifically, there was a progressive transition to IgG4 antibodies, which displayed a reduced capacity to engage in Fc-mediated effector functions and also exhibited increased avidity. In summary, our analysis of antibody responses to MSP1FL vaccination unveils a temporal shift towards noninflammatory IgG4 antibodies. These findings underscore the importance of considering the impact of IgG subclass composition on vaccine-induced immunity, particularly concerning Fc-mediated effector functions. This knowledge is pivotal in guiding the design of optimal vaccination strategies against malaria, informing decision making for future endeavors in this critical field.

Development of a multi-epitope vaccine candidate for leishmanial parasites applying immunoinformatics and in vitro approaches

Leishmaniasis is a neglected tropical disease, and its severity necessitates the development of a potent and efficient vaccine for the disease; however, no human vaccine has yet been approved for clinical use. This study aims to design and evaluate a multi-epitope vaccine against the leishmanial parasite by utilizing helper T-lymphocyte (HTL), cytotoxic T-lymphocyte (CTL), and linear B-lymphocyte (LBL) epitopes from membrane-bound acid phosphatase of Leishmania donovani (LdMAcP). The designed multi-epitope vaccine (LdMAPV) was highly antigenic, non-allergenic, and non-toxic, with suitable physicochemical properties. The three-dimensional structure of LdMAPV was modeled and validated, succeeded by molecular docking and molecular dynamics simulation (MDS) studies that confirmed the high binding affinity and stable interactions between human toll-like receptors and LdMAPV. In silico disulfide engineering provided improved stability to LdMAPV, whereas immune simulation displayed the induction of both immune responses, i.e., antibody and cell-mediated immune responses, with a rise in cytokines. Furthermore, LdMAPV sequence was codon optimized and cloned into the pET-28a vector, followed by its expression in a bacterial host. The recombinant protein was purified using affinity chromatography and subjected to determine its effect on cytotoxicity, cytokines, and nitric oxide generation by mammalian macrophages. Altogether, this report provides a multi-epitope vaccine candidate from a leishmanial protein participating in parasitic virulence that has shown its potency to be a promising vaccine candidate against leishmanial parasites.

Vaccine value profile for leishmaniasis

Leishmania infections are global, occurring in 98 countries and all World Health Organization (WHO) regions with 600 million to 1 billion people at risk of infection. Visceral leishmaniasis is associated with almost 20,000 reported deaths annually, with children under 5 years of age being at the greatest risk of mortality. Amongst WHO-recognised Neglected Tropical Diseases (NTDs), leishmaniasis is one of the most important in terms of mortality and morbidity. With an increasing global burden of disease and a growing threat from climate change, urbanisation and drug resistance, there remains an imperative to develop leishmaniasis vaccines. New tools to understand correlates of protection and to assess vaccine efficacy are being developed to ease the transition into larger scale efficacy trials or provide alternate routes to licensure. Early indications suggest a diverse portfolio of manufacturers exists in endemic countries with an appetite to develop leishmaniasis vaccines. This Vaccine Value Profile (VVP) provides a high-level, comprehensive assessment of the currently available data to inform the potential public health, economic, and societal value of leishmaniasis vaccines. The leishmaniasis VVP was developed by a working group of subject matter experts from academia, public health groups, policy organizations, and non-profit organizations. All contributors have extensive expertise on various elements of the leishmaniasis VVP and have collectively described the state of knowledge and identified the current gaps. The VVP was developed using only existing and publicly available information.

Adjuvantation of whole-killed Leishmania vaccine with anti-CD200 and anti-CD300a antibodies potentiates its efficacy and provides protection against wild-type parasites

One of the major reasons behind the limited success of vaccine candidates against all forms of leishmaniasis is the inability of parasitic antigens to induce robust cell-mediated immunity and immunological memory. Here we find, for the first time, that the adjuvantation of whole-killed Leishmania vaccine (Leishvacc) with anti-CD200 and anti-CD300a antibodies enhances CD4+ T cells mediated immunity in vaccinated mice and provides protection against wild-type parasites. The antibody adjuvantation, either alone or with a TLR4 agonist monophosphoryl A (MPL-A), induced the production of pro-inflammatory cytokines viz., IFN-γ, TNF-α, and IL-2 by antigen experienced CD4+ T cells, and also enhanced their rate of conversion into their memory phenotypes against Leishvacc antigens. The antibody adjuvanted vaccine also promoted the generation of IgG2a-mediated protective humoral immunity in vaccinated mice. Further, the mice vaccinated with antibodies adjuvanted vaccine showed strong resilience against metacyclic forms of L. donovani parasites as we observed reduced clinical features such as splenomegaly, hepatomegaly, granulomatous tissues in the liver, and parasitic load in their spleen. The findings of this study demonstrate that the anti-CD200 and anti-CD300a antibodies have potential to increase the protective efficacy of the whole-killed Leishmania vaccine, and opens up a new gateway to diversify the roles of immune checkpoints in vaccine development against leishmaniasis.

CD4+ T Cell Responses to Toxoplasma gondii Are a Double-Edged Sword

CD4+ T cells have been found to play critical roles in the control of both acute and chronic Toxoplasma infection. Previous studies identified a protective role for the Toxoplasma CD4+ T cell-eliciting peptide AS15 (AVEIHRPVPGTAPPS) in C57BL/6J mice. Herein, we found that immunizing mice with AS15 combined with GLA-SE, a TLR-4 agonist in emulsion adjuvant, can be either helpful in protecting male and female mice at early stages against Type I and Type II Toxoplasma parasites or harmful (lethal with intestinal, hepatic, and spleen pathology associated with a storm of IL6). Introducing the universal CD4+ T cell epitope PADRE abrogates the harmful phenotype of AS15. Our findings demonstrate quantitative and qualitative features of an effective Toxoplasma-specific CD4+ T cell response that should be considered in testing next-generation vaccines against toxoplasmosis. Our results also are cautionary that individual vaccine constituents can cause severe harm depending on the company they keep.

Development of chimeric protein as a multivalent vaccine for human Kinetoplastid infections: Chagas disease and leishmaniasis

Leishmania spp. and Trypanosoma cruzi are parasitic kinetoplastids of great medical and epidemiological importance since they are responsible for thousands of deaths and disability-adjusted life-years annually, especially in low- and middle-income countries. Despite efforts to minimize their impact, current prevention measures have failed to fully control their spread. There are still no vaccines available. Taking into account the genetic similarity within the Class Kinetoplastida, we selected CD8+ T cell epitopes preserved among Leishmania spp. and T. cruzi to construct a multivalent and broad-spectrum chimeric polyprotein vaccine. In addition to inducing specific IgG production, immunization with the vaccine was able to significantly reduce parasite burden in the colon, liver and skin lesions from T. cruzi, L. infantum and L. mexicana challenged mice, respectively. These findings were supported by histopathological analysis, which revealed decreased inflammation in the colon, a reduced number of degenerated hepatocytes and an increased proliferation of connective tissue in the skin lesions of the corresponding T. cruzi, L. infantum and L. mexicana vaccinated and challenged mice. Collectively, our results support the protective effect of a polyprotein vaccine approach and further studies will elucidate the immune profile associated with this protection. Noteworthy, our results act as conceptual proof that a single multi-kinetoplastida vaccine can be used effectively to control different infectious etiologies, which in turn can have a profound impact on the development of a new generation of vaccines.

Adjuvant physiochemistry and advanced nanotechnology for vaccine development

Vaccines comprising innovative adjuvants are rapidly reaching advanced translational stages, such as the authorized nanotechnology adjuvants in mRNA vaccines against COVID-19 worldwide, offering new strategies to effectively combat diseases threatening human health. Adjuvants are vital ingredients in vaccines, which can augment the degree, extensiveness, and longevity of antigen specific immune response. The advances in the modulation of physicochemical properties of nanoplatforms elevate the capability of adjuvants in initiating the innate immune system and adaptive immunity, offering immense potential for developing vaccines against hard-to-target infectious diseases and cancer. In this review, we provide an essential introduction of the basic principles of prophylactic and therapeutic vaccination, key roles of adjuvants in augmenting and shaping immunity to achieve desired outcomes and effectiveness, and the physiochemical properties and action mechanisms of clinically approved adjuvants for humans. We particularly focus on the preclinical and clinical progress of highly immunogenic emerging nanotechnology adjuvants formulated in vaccines for cancer treatment or infectious disease prevention. We deliberate on how the immune system can sense and respond to the physicochemical cues (e.g., chirality, deformability, solubility, topology, and chemical structures) of nanotechnology adjuvants incorporated in the vaccines. Finally, we propose possible strategies to accelerate the clinical implementation of nanotechnology adjuvanted vaccines, such as in-depth elucidation of nano-immuno interactions, antigen identification and optimization by the deployment of high-dimensional multiomics analysis approaches, encouraging close collaborations among scientists from different scientific disciplines and aggressive exploration of novel nanotechnologies.

Immunotherapy and immunochemotherapy in combating visceral leishmaniasis

Visceral leishmaniasis (VL), a vector-borne disease, is caused by an obligate intramacrophage, kinetoplastid protozoan parasite of the genus Leishmania. Globally, VL is construed of diversity and complexity concerned with high fatality in tropics, subtropics, and Mediterranean regions with ~50,000-90,000 new cases annually. Factors such as the unavailability of licensed vaccine(s), insubstantial measures to control vectors, and unrestrained surge of drug-resistant parasites and HIV-VL co-infections lead to difficulty in VL treatment and control. Furthermore, VL treatment, which encompasses several problems including limited efficacy, emanation of drug-resistant parasites, exorbitant therapy, and exigency of hospitalization until the completion of treatment, further exacerbates disease severity. Therefore, there is an urgent need for the development of safe and efficacious therapies to control and eliminate this devastating disease. In such a scenario, biotherapy/immunotherapy against VL can become an alternative strategy with limited side effects and no or nominal chance of drug resistance. An extensive understanding of pathogenesis and immunological events that ensue during VL infection is vital for the development of immunotherapeutic strategies against VL. Immunotherapy alone or in combination with standard anti-leishmanial chemotherapeutic agents (immunochemotherapy) has shown better therapeutic outcomes in preclinical studies. This review extensively addresses VL treatment with an emphasis on immunotherapy or immunochemotherapeutic strategies to improve therapeutic outcomes as an alternative to conventional chemotherapy.

Safety and Immunogenicity of the ID93 + GLA-SE Tuberculosis Vaccine in BCG-Vaccinated Healthy Adults: A Randomized, Double-Blind, Placebo-Controlled Phase 2 Trial

INTRODUCTION

This randomized, double-blind, placebo-controlled, phase 2a trial was conducted to evaluate the safety and immunogenicity of the ID93 + glucopyranosyl lipid adjuvant (GLA)-stable emulsion (SE) vaccine in human immunodeficiency virus (HIV)-negative, previously Bacillus Calmette-Guérin (BCG)-vaccinated, and QuantiFERON-TB-negative healthy adults in South Korea.

METHODS

Adults (n = 107) with no signs or symptoms of tuberculosis were randomly assigned to receive three intramuscular injections of 2 μg ID93 + 5 μg GLA-SE, 10 μg ID93 + 5 μg GLA-SE, or 0.9% normal saline placebo on days 0, 28, and 56. For safety assessment, data on solicited adverse events (AEs), unsolicited AEs, serious AEs (SAEs), and special interest AEs were collected. Antigen-specific antibody responses were measured using serum enzyme-linked immunosorbent assay. T-cell immune responses were measured using enzyme-linked immunospot and intracellular cytokine staining.

RESULTS

No SAEs, deaths, or AEs leading to treatment discontinuation were found. The solicited local and systemic AEs observed were consistent with those previously reported. Compared with adults administered with the placebo, those administered with three intramuscular vaccine injections exhibited significantly higher antigen-specific antibody levels and Type 1 T-helper cellular immune responses.

CONCLUSION

The ID93 + GLA-SE vaccine induced antigen-specific cellular and humoral immune responses, with an acceptable safety profile in previously healthy, BCG-vaccinated, Mycobacterium tuberculosis-uninfected adult healthcare workers.

TRIAL REGISTRATION

This clinical trial was retrospectively registered on 16 January 2019 at Clinicaltrials.gov (NCT03806686).

Alpha-galactosylceramide as adjuvant induces protective cell-mediated immunity against Leishmania mexicana infection in vaccinated BALB/c mice

Adjuvants represent a promising strategy to improve vaccine effectiveness against infectious diseases such as leishmaniasis. Vaccination with the invariant natural killer T cell ligand α-galactosylceramide (αGalCer) has been used successfully as adjuvant, generating a Th1-biased immunomodulation. This glycolipid enhances experimental vaccination platforms against intracellular parasites including Plasmodium yoelii and Mycobacterium tuberculosis. In the present study, we assessed the protective immunity induced by a single-dose intraperitoneal injection of αGalCer (2 μg) co-administrated with a lysate antigen of amastigotes (100 μg) against Leishmania mexicana infection in BALB/c mice. The prophylactic vaccination led to 5.0-fold reduction of parasite load at the infection site, compared to non-vaccinated mice. A predominant pro-inflammatory response was observed in challenged vaccinated mice, represented by a 1.9 and 2.8-fold-increase of IL-1β and IFN-γ producing cells, respectively, in the lesions, and by 23.7-fold-increase of IFN-γ production in supernatants of restimulated splenocytes, all compared to control groups. The co-administration of αGalCer also stimulated the maturation of splenic dendritic cells and modulated a Th1-skewed immune response, with high amounts of IFN-γ production in serum. Furthermore, peritoneal cells of αGalCer-immunized mice exhibited an elevated expression of Ly6G and MHCII. These findings indicate that αGalCer improves protection against cutaneous leishmaniasis, supporting evidence for its potential use as adjuvant in Leishmania-vaccines.

Leishmania Vaccines: the Current Situation with Its Promising Aspect for the Future

Leishmaniasis is a serious parasitic disease caused by Leishmania spp. transmitted through sandfly bites. This disease is a major public health concern worldwide. It can occur in 3 different clinical forms: cutaneous, mucocutaneous, and visceral Leishmaniasis (CL, MCL, and VL, respectively), caused by different Leishmania spp. Currently, licensed vaccines are unavailable for the treatment of human Leishmaniasis. The treatment and prevention of this disease rely mainly on chemotherapeutics, which are highly toxic and have an increasing resistance problem. The development of a safe, effective, and affordable vaccine for all forms of vector-borne disease is urgently needed to block transmission of the parasite between the host and vector. Immunological mechanisms in the pathogenesis of Leishmaniasis are complex. IL-12-driven Th1-type immune response plays a crucial role in host protection. The essential purpose of vaccination is to establish a protective immune response. To date, numerous vaccine studies have been conducted using live/attenuated/killed parasites, fractionated parasites, subunits, recombinant or DNA technology, delivery systems, and chimeric peptides. Most of these studies were limited to animals. In addition, standardization has not been achieved in these studies due to the differences in the virulence dynamics of the Leishmania spp. and the feasibility of the adjuvants. More studies are needed to develop a safe and effective vaccine, which is the most promising approach against Leishmania infection.

Leishmaniasis Vaccines: Applications of RNA Technology and Targeted Clinical Trial Designs

Leishmania parasites cause a variety of discrete clinical diseases that present in regions where their specific sand fly vectors sustain transmission. Clinical and laboratory research indicate the potential of immunization to prevent leishmaniasis and a wide array of vaccine candidates have been proposed. Unfortunately, multiple factors have precluded advancement of more than a few Leishmania targeting vaccines to clinical trial. The recent maturation of RNA vaccines into licensed products in the context of COVID-19 indicates the likelihood of broader use of the technology. Herein, we discuss the potential benefits provided by RNA technology as an approach to address the bottlenecks encountered for Leishmania vaccines. Further, we outline a variety of strategies that could be used to more efficiently evaluate Leishmania vaccine efficacy, including controlled human infection models and initial use in a therapeutic setting, that could prioritize candidates before evaluation in larger, longer and more complicated field trials.

Bioinformatics analysis for the purpose of designing a novel multi-epitope DNA vaccine against Leishmania major

Leishmaniasis is one of the main infectious diseases worldwide. In the midst of all the different forms of the disease, Cutaneous Leishmania (CL) has the highest incidence in the world. Many trial vaccines have been developed with the purpose of generating long-term cell-mediated immunity to Leishmania(L) major. As there is not any multi-epitope DNA vaccine with high efficacy against L.major, the aim of this study is to design a new multi-epitope DNA vaccine in order to have effective control upon this infectious disease through the immune bioinformatics. The L.major antigens: Gp63, LACK, TSA, LmSTI1and KMP11 were selected to design a multi-epitope DNA vaccine. The initial structure of the DNA vaccine was designed, benefiting from Gen Bank's website information. Epitopes of MHC-I antigens were predicted through the Immune Epitope Database (IEDB), and the selected epitopes were used to make vaccines construct along with linkers. New multi-epitope vaccine including 459 nucleic acids designed, and inserted between BamH1 and HindIII restriction sites of pCDNA3.1 mammalian expression vector. 12 epitopes among the chosen antigens were selected by two servers (IEDB and ANTIGEN). They had high stability and high antigenic power. Physicochemical features of vaccine measured by ProtParam server, and this structure was thermostable and hydrophilic. it's a suitable model to study on the animal and human phases. The designed vaccine is expected to be an effective candidate through development of (CL) vaccines. However, the effectiveness of this vaccine should also evaluate in vivo model.

Current leishmaniasis drug discovery

Leishmaniasis is a complex protozoan infectious disease and, associated with malnutrition, poor health services and unavailability of prophylactic control measures, neglected populations are particularly affected. Current drug regimens are outdated and associated with some drawbacks, such as cytotoxicity and resistance, and the development of novel, efficacious and less toxic drug regimens is urgently required. In addition, leishmanial pathogenesis is not well established or understood, and a prophylactic vaccine is an unfulfilled goal. Human kinetoplastid protozoan infections, including leishmaniasis, have been neglected for many years, and in an attempt to overcome this situation, some new drug targets were recently identified, enabling the development of new drugs and vaccines. Compounds from new drug classes have also shown excellent antileishmanial activities, some of the most promising ones included in clinical trials, and could be a hope to control the disease burden of this endemic disease in the near future. In this review, we discuss the limitations of current control methods, explore the wide range of compounds that are being screened and identified as antileishmanial drug prototypes, summarize the advances in identifying new drug targets aiming at innovative treatments and explore the state-of-art vaccine development field, including immunomodulation strategies.

Immunotherapy for visceral leishmaniasis: A trapeze of balancing counteractive forces

The protozoan parasite Leishmania donovani, residing and replicating within the cells of the monocyte-macrophage (mono-mac) lineage, causes visceral leishmaniasis (VL) in humans. While, Leishmania infantum, is the main causative agent for zoonotic VL, where dogs are the main reservoirs of the disease. The chemotherapy is a serious problem because of restricted repertoire of drugs, drug-resistant parasites, drug-toxicity and the requirement for parenteral administration, which is a problem in resource-starved countries. Moreover, immunocompromised individuals, particularly HIV-1 infected are at higher risk of VL due to impairment in T-helper cell and regulatory cell responses. Furthermore, HIV-VL co-infected patients report poor response to conventional chemotherapy. Recent efforts are therefore directed towards devising both prophylactic and therapeutic immunomodulation. As far as prophylaxis is concerned, although canine vaccines for the disease caused by Leishmania infantum or Leishmania chagasi are available, no vaccine is available for use in humans till date. Therefore, anti-leishmanial immunotherapy triggering or manipulating the host's immune response is gaining momentum during the last two decades. Immunomodulators comprised of small molecules, anti-leishmanial peptides, complex ligands for host receptors, cytokines or their agonists and antibodies have been given trials both in experimental models and in humans. However, the success of immunotherapy in humans remains a far-off target. We, therefore, propose that devising a successful immunotherapy is an act of balancing enhanced beneficial Leishmania-specific responses and deleterious immune activation/hyperinflammation just as the swings in a trapeze.

The History of Live Attenuated Centrin Gene-Deleted Leishmania Vaccine Candidates

Leishmaniasis, caused by an infection of the Leishmania protozoa, is a neglected tropical disease and a major health problem in tropical and subtropical regions of the world, with approximately 350 million people worldwide at risk and 2 million new cases occurring annually. Current treatments for leishmaniasis are not highly efficacious and are associated with high costs, especially in low- and middle-income endemic countries, and high toxicity. Due to a surge in the incidence of leishmaniases worldwide, the development of new strategies such as a prophylactic vaccine has become a high priority. However, the ability of Leishmania to undermine immune recognition has limited our efforts to design safe and efficacious vaccines against leishmaniasis. Numerous antileishmanial vaccine preparations based on DNA, subunit, and heat-killed parasites with or without adjuvants have been tried in several animal models but very few have progressed beyond the experimental stage. However, it is known that people who recover from Leishmania infection can be protected lifelong against future infection, suggesting that a successful vaccine requires a controlled infection to develop immunologic memory and subsequent long-term immunity. Live attenuated Leishmania parasites that are non-pathogenic and provide a complete range of antigens similarly to their wild-type counterparts could evoke such memory and, thus, would be effective vaccine candidates. Our laboratory has developed several live attenuated Leishmania vaccines by targeted centrin gene disruptions either by homologous recombination or, more recently, by using genome editing technologies involving CRISPR-Cas9. In this review, we focused on the sequential history of centrin gene-deleted Leishmania vaccine development, along with the characterization of its safety and efficacy. Further, we discussed other major considerations regarding the transition of dermotropic live attenuated centrin gene-deleted parasites from the laboratory to human clinical trials.

Overcoming roadblocks in the development of vaccines for leishmaniasis

INTRODUCTION

The leishmaniases represent a group of parasitic diseases caused by infection with one of several species of Leishmania parasites. Disease presentation varies because of differences in parasite and host genetics and may be influenced by additional factors such as host nutritional status or co-infection. Studies in experimental models of Leishmania infection, vaccination of companion animals and human epidemiological data suggest that many forms of leishmaniasis could be prevented by vaccination, but no vaccines are currently available for human use.

AREAS COVERED

We describe some of the existing roadblocks to the development and implementation of an effective leishmaniasis vaccine, based on a review of recent literature found on PubMed, BioRxiv and MedRxiv. In addition to discussing scientific unknowns that hinder vaccine candidate identification and selection, we explore gaps in knowledge regarding the commercial and public health value propositions underpinning vaccine development and provide a route map for future research and advocacy.

EXPERT OPINION

Despite significant progress, leishmaniasis vaccine development remains hindered by significant gaps in understanding that span the vaccine development pipeline. Increased coordination and adoption of a more holistic view to vaccine development will be required to ensure more rapid progress in the years ahead.

Protective Efficacy in a Hamster Model of a Multivalent Vaccine for Human Visceral Leishmaniasis (MuLeVaClin) Consisting of the KMP11, LEISH-F3+, and LJL143 Antigens in Virosomes, Plus GLA-SE Adjuvant

Visceral leishmaniasis (VL) is the most severe clinical form of leishmaniasis, fatal if untreated. Vaccination is the most cost-effective approach to disease control; however, to date, no vaccines against human VL have been made available. This work examines the efficacy of a novel vaccine consisting of the Leishmania membrane protein KMP11, LEISH-F3+ (a recombinant fusion protein, composed of epitopes of the parasite proteins nucleoside hydrolase, sterol-24-c-methyltransferase, and cysteine protease B), and the sand fly salivary protein LJL143, in two dose ratios. The inclusion of the TLR4 agonist GLA-SE as an adjuvant, and the use of virosomes (VS) as a delivery system, are also examined. In a hamster model of VL, the vaccine elicited antigen-specific immune responses prior to infection with Leishmania infantum. Of note, the responses were greater when higher doses of KMP11 and LEISH-F3+ proteins were administered along with the GLA-SE adjuvant and/or when delivered within VS. Remarkably, hamsters immunized with the complete combination (i.e., all antigens in VS + GLA-SE) showed significantly lower parasite burdens in the spleen compared to those in control animals. This protection was underpinned by a more intense, specific humoral response against the KMP11, LEISH-F3+, and LJL143 antigens in vaccinated animals, but a significantly less intense antibody response to the pool of soluble Leishmania antigens (SLA). Overall, these results indicate that this innovative vaccine formulation confers protection against L. infantum infection, supporting the advancement of the vaccine formulation into process development and manufacturing and the conduction of toxicity studies towards future phase I human clinical trials.

Treatment and Evaluation Advances in Leprosy Neuropathy

Neuropathy and related disabilities are the major medical consequences of leprosy, which remains a global medical concern. Despite major advances in understanding the mechanisms of M. leprae entry into peripheral nerves, most aspects of the pathogenesis of leprosy neuropathy remain poorly understood. Sensory loss is characteristic of leprosy, but neuropathic pain is sometimes observed. Effective anti-microbial therapy is available, but neuropathy remains a problem especially if diagnosis and treatment are delayed. Currently there is intense interest in post-exposure prophylaxis with single-dose rifampin in endemic areas, as well as with enhanced prophylactic regimens in some situations. Some degree of nerve involvement is seen in all cases and neuritis may occur in the absence of leprosy reactions, but acute neuritis commonly accompanies both Type 1 and Type 2 leprosy reactions and may be difficult to manage. A variety of established as well as new methods for the early diagnosis and assessment of leprosy neuropathy are reviewed. Corticosteroids offer the primary treatment for neuritis and for subclinical neuropathy in leprosy, but success is limited if nerve function impairment is present at the time of diagnosis. A candidate vaccine has shown apparent benefit in preventing nerve injury in the armadillo model. The development of new therapeutics for leprosy neuropathy is greatly needed.

From infection to vaccination: reviewing the global burden, history of vaccine development, and recurring challenges in global leishmaniasis protection

INTRODUCTION

Leishmaniasis is a major public health problem and the second most lethal parasitic disease in the world due to the lack of effective treatments and vaccines. Even when not lethal, leishmaniasis significantly affects individuals and communities through life-long disabilities, psycho-sociological trauma, poverty, and gender disparity in treatment.

AREAS COVERED

This review discusses the most relevant and recent research available on Pubmed and GoogleScholar highlighting leishmaniasis' global impact, pathogenesis, treatment options, and lack of effective control strategies. An effective vaccine is necessary to prevent morbidity and mortality, lower health care costs, and reduce the economic burden of leishmaniasis for endemic low- and middle-income countries. Since there are several forms of leishmaniasis, a pan-Leishmania vaccine without geographical restrictions is needed. This review also focuses on recent advances and common challenges in developing prophylactic strategies against leishmaniasis.

EXPERT OPINION

Despite advances in pre-clinical vaccine research, approval of a human leishmaniasis vaccine still faces major challenges - including manufacturing of candidate vaccines under Good Manufacturing Practices, developing well-designed clinical trials suitable in endemic countries, and defined correlates of protection. In addition, there is a need to explore Challenge Human Infection Model to avoid large trials because of fluctuating incidence and prevalence of leishmanasis.

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

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

A review of combination adjuvants for malaria vaccines: a promising approach for vaccine development

It is obvious that there is a critical need for an efficient malaria vaccine to accelerate malaria eradication. Currently, recombinant subunit vaccination against malaria using proteins and peptides is gaining attention. However, one of the major drawbacks of this approach is the lack of an efficient and durable immune response. Therefore, subunit vaccines require adjuvants to make the vaccine sufficiently immunogenic. Considering the history of the RTS,S vaccine, it seems likely that no single adjuvant is capable of eliciting all the protective immune responses required in many malarial subunit vaccines and the use of combination adjuvants will be increasingly important as the science of malaria vaccines advances. In light of this, it appears that identifying the most effective mixture of adjuvants with minimal adverse effects offers tremendous opportunities in improving the efficacy of vaccines against malaria. Owing to the importance of a multi-adjuvanted approach in subunit malaria vaccine development, this review paper outlines some of the best known combination adjuvants used in malaria subunit vaccines, focusing on their proposed mechanisms of action, their immunological properties, and their notable results. The aim of the present review is to consolidate these findings to aid the application of these combination adjuvants in experimental malaria vaccines.

Role of Virus-Specific T Cell Therapy for Cytomegalovirus and BK Infections in Kidney Transplant Recipients

Cytomegalovirus (CMV) and BK virus (BKV) are common viral infections after kidney transplant. Their negative effects on patient and graft outcomes have been well described. However, despite improvement in screening and prophylaxis strategies, CMV and BKV continue to negatively affect both short- and long-term graft survival. Adequate cell-mediated immunity is essential for the control and prevention of opportunistic viral infections, such as CMV and BKV. Therefore, immune reconstitution, in particular T cell recovery, is a key factor in antiviral control after kidney transplantation. Cell-based immunotherapy offers an attractive alternative approach to traditional interventions. Adoptive T cell transfer, via infusions of allogeneic virus-specific T lymphocytes is capable of restoring virus-specific T cell immunity, and are safe and effective in the treatment of viral infections after hematopoietic stem cell transplantation. In this article, we review the emerging role of virus-specific T cell therapy in the management of CMV and BKV after kidney transplantation. On the basis of the available data, virus-specific T cell therapy may be a promising addition to the antiviral treatment armamentarium after kidney transplantation. Future studies are needed to more clearly define the efficacy and risks of virus-specific T cell therapy in the kidney transplant population.

A Review of Leishmaniasis: Current Knowledge and Future Directions

Purpose of Review

The goal of this review is to summarize the current knowledge of the epidemiology, clinical manifestations, diagnosis, and treatment of cutaneous, mucosal, and visceral leishmaniasis. We will describe the most recent findings and suggest areas of further research in the leishmaniasis field.

Recent Findings

This article reviews newer leishmaniasis tests (including rapid diagnostic tests using rK39 antibodies), vaccine candidates, and updated treatment recommendations.

Summary

While leishmaniasis is a complex disease, learning the prominent clinical manifestations and major parasite species can guide the recommendations for diagnosis and treatment.

Revival of Leishmanization and Leishmanin

Leishmaniasis includes a spectrum of diseases ranging from debilitating cutaneous to fatal visceral infections. This disease is caused by the parasitic protozoa of the genus Leishmania that is transmitted by infected sandflies. Over 1 billion people are at risk of leishmaniasis with an annual incidence of over 2 million cases throughout tropical and subtropical regions in close to 100 countries. Leishmaniasis is the only human parasitic disease where vaccination has been successful through a procedure known as leishmanization that has been widely used for decades in the Middle East. Leishmanization involved intradermal inoculation of live Leishmania major parasites resulting in a skin lesion that following natural healing provided protective immunity to re-infection. Leishmanization is however no longer practiced due to safety and ethical concerns that the lesions at the site of inoculation that can last for months in some people. New genome editing technologies involving CRISPR has now made it possible to engineer safer attenuated strains of Leishmania, which induce protective immunity making way for a second generation leishmanization that can enter into human trials. A major consideration will be how the test the efficacy of a vaccine in the midst of the visceral leishmaniasis elimination program. One solution will be to use the leishmanin skin test (LST) that was also used for decades to determine exposure and immunity to Leishmania. The LST involves injection of antigen from Leishmania in the skin dermis resulting in a delayed type hypersensitivity (DTH) immune reaction associated with a Th1 immune response and protection against visceral leishmaniasis. Reintroduction of novel approaches for leishmanization and the leishmanin skin test can play a major role in eliminating leishmaniasis.

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.

Evolution of antigen-specific immune responses in cutaneous leishmaniasis patients

AIMS

Despite immunization appearing to be the most appropriate strategy for long-term control of the vector-borne leishmaniases, no sustainable vaccine is currently available against any form of leishmaniasis. We therefore evaluated, in the context of vaccine antigen candidates, antigen-specific immune response at various stages of cutaneous leishmaniasis (CL).

METHODS AND RESULTS

Peripheral blood mononuclear cells (PBMC) isolated from healthy volunteers and CL patients (caused by either Leishmania major or L tropica) were incubated with crude Leishmania proteins (soluble Leishmania antigen; SLA), single recombinant proteins (TSA, LeIF, LmSTI1) or chimeric fusion proteins (LEISH-F2 and LEISH-F3). The concentrations of immune modulatory cytokines were then determined. While we did not detect appreciable antigen-specific IL-5 secretion, SLA induced secretion of interleukin (IL)-10 in cultures from early active lesion CL patients and even from healthy individuals. Conversely, interferon (IFN)-γ responses to SLA and recombinant proteins followed a similar pattern, developing only in the late active CL lesion phase. Once established, antigen-specific IFN-γ responses persisted in cured CL patients.

CONCLUSION

Together, our results provide further insight into the development of immune responses during CL and further validate the selection of LEISH-F2 and LEISH-F3 as vaccine antigen candidates.

Evaluation of protection induced by in vitro maturated BMDCs presenting CD8+ T cell stimulating peptides after a heterologous vaccination regimen in BALB/c model against Leishmania major

Leishmaniasis is a complex vector-borne disease mediated by Leishmania parasite and a strong and long-lasting CD4⁺ Th1 and CD8⁺-T cell immunity is required to control the infection. Thus far multivalent subunit vaccines have met this requirement more promisingly. However several full protein sequences cannot be easily arranged in one construct. Instead, new emerging immune-informatics based epitope formulations surpass this restriction. Herein, we aimed to examine the protective potential of a dendritic cell based vaccine presenting epitopes to CD8⁺ and CD4⁺-T cells in combination with DNA vaccine encoding the same epitopes against murine cutaneous leishmaniasis. Immature DCs were loaded with epitopes (selected from parasite proteome) in vitro with or without CpG oligonucleotides and were used to immunize BALB/c mice. Peptide coding DNA was used to boost the system and immunological responses were evaluated after Leishmania (L.) major infectious challenge. The pre-challenge response to included epitopes was Th1 polarized which potentially lowered the infection at early time points post-challenge but not at later weeks. Collectively, DC prime-DNA boost was found to be a promising approach for Th1 polarization however the constituent epitopes undoubtedly make a significant contribution in the protection outcome of the vaccine.

Characterization of a new Leishmania major strain for use in a controlled human infection model

Leishmaniasis is widely regarded as a vaccine-preventable disease, but the costs required to reach pivotal Phase 3 studies and uncertainty about which candidate vaccines should be progressed into human studies significantly limits progress in vaccine development for this neglected tropical disease. Controlled human infection models (CHIMs) provide a pathway for accelerating vaccine development and to more fully understand disease pathogenesis and correlates of protection. Here, we describe the isolation, characterization and GMP manufacture of a new clinical strain of Leishmania major. Two fresh strains of L. major from Israel were initially compared by genome sequencing, in vivo infectivity and drug sensitivity in mice, and development and transmission competence in sand flies, allowing one to be selected for GMP production. This study addresses a major roadblock in the development of vaccines for leishmaniasis, providing a key resource for CHIM studies of sand fly transmitted cutaneous leishmaniasis.

Long-Lived Skin-Resident Memory T Cells Contribute to Concomitant Immunity in Cutaneous Leishmaniasis

Memory T cells, which protect against reinfection in many diseases, have predominantly been characterized in models of acute viral or bacterial infection. In contrast, memory T cells are less well understood in diseases where pathogens persist following disease resolution, such as leishmaniasis, in spite of the fact that these infections often lead to immunity to reinfection, termed concomitant immunity. Defining the T cells that mediate concomitant immunity is an important step in developing vaccines for these diseases. One set of protective T cells are short-lived effector T cells requiring constant stimulation, which would be difficult to maintain by vaccination. However, parasite-independent memory T cells, including central memory T cells (Tcm) and skin-resident T cells (Trm) have recently been described in leishmaniasis. Given their location, Trm cells are particularly suited for protection, and were found to globally seed the skin following Leishmania infection or immunization. Upon challenge, Trm cells rapidly respond to reduce the parasite burden, suggesting that developing strategies to generate parasite-independent Trm cells will be an important step in the quest for a successful leishmaniasis vaccine.

The potential impact of human visceral leishmaniasis vaccines on population incidence

Human visceral leishmaniasis (VL) vaccines are currently under development and there is a need to understand their potential impact on population wide VL incidence. We implement four characteristics from different human VL vaccine candidates into two published VL transmission model variants to estimate the potential impact of these vaccine characteristics on population-wide anthroponotic VL incidence on the Indian subcontinent (ISC). The vaccines that are simulated in this study 1) reduce the infectiousness of infected individuals towards sand flies, 2) reduce risk of developing symptoms after infection, 3) reduce the risk of developing post-kala-azar dermal leishmaniasis (PKDL), or 4) lead to the development of transient immunity. We also compare and combine a vaccine strategy with current interventions to identify their potential role in elimination of VL as a public health problem. We show that the first two simulated vaccine characteristics can greatly reduce VL incidence. For these vaccines, an approximate 60% vaccine efficacy would lead to achieving the ISC elimination target (<1 VL case per 10,000 population per year) within 10 years’ time in a moderately endemic setting when vaccinating 100% of the population. Vaccinating VL cases to prevent the development of PKDL is a promising tool to sustain the low incidence elimination target after regular interventions are halted. Vaccines triggering the development of transient immunity protecting against infection lead to the biggest reduction in VL incidence, but booster doses are required to achieve perduring impact. Even though vaccines are not yet available for implementation, their development should be pursued as their potential impact on transmission can be substantial, both in decreasing incidence at the population level as well as in sustaining the ISC elimination target when other interventions are halted.

Vaccines for human visceral leishmaniasis (VL) are currently under development. In this study, we simulate VL transmission dynamics using mathematical models to explore the potential impact of vaccines on population-wide incidence. We show that some vaccines have high potential to reduce VL incidence, namely those that reduce the infectiousness of infected individuals to sand flies and those that reduce the chance of developing symptoms once infected. The effect of vaccines that lead to protection from infection is potentially the greatest, but depending on the duration of immunity, individuals would require booster doses to guarantee lifelong impact. Vaccines that prevent the development of post-kala-azar dermal leishmaniasis are a promising tool to sustain low VL incidence and prevent recrudescence of infection when regular interventions are halted. Our results strongly support the continued development of VL vaccines, as their potential impact on population incidence can be substantial.

Evaluation of the protective efficacy of a Leishmania protein associated with distinct adjuvants against visceral leishmaniasis and in vitro immunogenicity in human cells

The treatment against visceral leishmaniasis (VL) presents problems, mainly related to the toxicity and/or high cost of the drugs. In this context, a prophylactic vaccination is urgently required. In the present study, a Leishmania protein called LiHyE, which was suggested recently as an antigenic marker for canine and human VL, was evaluated regarding its immunogenicity and protective efficacy in BALB/c mice against Leishmania infantum infection. In addition, the protein was used to stimulate peripheral blood mononuclear cells (PBMCs) from VL patients before and after treatment, as well as from healthy subjects. Vaccination results showed that the recombinant (rLiHyE) protein associated with liposome or saponin induced effective protection in the mice, since significant reductions in the parasite load in spleen, liver, draining lymph nodes, and bone marrow were found. The parasitological protection was associated with Th1-type cell response, since high IFN-γ, IL-12, and GM-CSF levels, in addition to low IL-4 and IL-10 production, were found. Liposome induced a better parasitological and immunological protection than did saponin. Experiments using PBMCs showed rLiHyE-stimulated lymphoproliferation in treated patients' and healthy subjects' cells, as well as high IFN-γ levels in the cell supernatant. In conclusion, rLiHyE could be considered for future studies as a vaccine candidate against VL.

Vaccination of aged mice with adjuvanted recombinant influenza nucleoprotein enhances protective immunity

Elderly individuals are highly susceptible to influenza virus (IAV) infection and respond poorly to influenza vaccines. Although the generally accepted correlate of protection following influenza vaccination is neutralizing antibody titers, cytotoxic T cell activity has been found to be a better correlate in the elderly. This suggests that vaccines designed to protect against influenza in the elderly should induce both humoral and cellular immunity. The co-induction of T cell immunity is additionally advantageous, as virus-specific T cells are frequently cross-reactive against different strains of IAV. Here, we tested the capacity of a synthetic TLR-4 adjuvant, SLA-SE (second-generation lipid adjuvant formulated in a squalene-based oil-in-water emulsion) to elicit T cell immunity to a recombinant influenza nucleoprotein (rNP), in both young and aged mice. IAV challenge of vaccinated mice resulted in a modest increase in the numbers of NP-specific CD4 and CD8 effector T cells in the spleen, but did not increase numbers of memory phenotype CD8 T cells generated following viral clearance (compared to control vaccinated mice). Cytotoxic activity of CD8, but not CD4 T cells was increased. In addition, SLA-SE adjuvanted vaccination specifically enhanced the production of NP-specific IgG2c antibodies in both young and aged mice. Although NP-specific antibodies are not neutralizing, they can cooperate with CD8 T cells and antigen-presenting cells to enhance protective immunity. Importantly, SLA-SE adjuvanted rNP-vaccination of aged mice resulted in significantly enhanced viral clearance. In addition, vaccination of aged mice resulted in enhanced survival after lethal challenge compared to control vaccination, that approached statistical significance. These data demonstrate the potential of SLA-SE adjuvanted rNP vaccines to (i) generate both cellular and humoral immunity to relatively conserved IAV proteins and (ii) elicit protective immunity to IAV in aged mice.

An immunoinformatic approach driven by experimental proteomics: in silico design of a subunit candidate vaccine targeting secretory proteins of Leishmania donovani amastigotes

Background

Visceral leishmaniasis (VL) caused by dimorphic Leishmania species is a parasitic disease with high socioeconomic burden in endemic areas worldwide. Sustaining control of VL in terms of proper and prevailing immunity development is a global necessity amid unavailability of a prophylactic vaccine. Screening of experimental proteome of the human disease propagating form of Leishmania donovani (amastigote) can be more pragmatic for in silico mining of novel vaccine candidates.

Methods

By using an immunoinformatic approach, CD4+ and CD8+ T cell-specific epitopes from experimentally reported L. donovani proteins having secretory potential and increased abundance in amastigotes were screened. A chimera linked with a Toll-like receptor 4 (TLR4) peptide adjuvant was constructed and evaluated for physicochemical characteristics, binding interaction with TLR4 in simulated physiological condition and the trend of immune response following hypothetical immunization.

Results

Selected epitopes from physiologically important L. donovani proteins were found mostly conserved in L. infantum, covering theoretically more than 98% of the global population. The multi-epitope chimeric vaccine was predicted as stable, antigenic and non-allergenic. Structural analysis of vaccine-TLR4 receptor docked complex and its molecular dynamics simulation suggest sufficiently stable binding interface along with prospect of non-canonical receptor activation. Simulation dynamics of immune response following hypothetical immunization indicate active and memory B as well as CD4+ T cell generation potential, and likely chance of a more Th1 polarized response.

Conclusions

The methodological approach and results from this study could facilitate more informed screening and selection of candidate antigenic proteins for entry into vaccine production pipeline in future to control human VL.

Report of the Fifth Post-Kala-Azar Dermal Leishmaniasis Consortium Meeting, Colombo, Sri Lanka, 14-16 May 2018

The 5th Post-Kala-Azar Dermal Leishmaniasis (PKDL) Consortium meeting brought together PKDL experts from all endemic areas to review and discuss existing and new data on PKDL. This report summarizes the presentations and discussions and provides the overall conclusions and recommendations.

The Delay in the Licensing of Protozoal Vaccines: A Comparative History

Although viruses and bacteria have been known as agents of diseases since 1546, 250 years went by until the first vaccines against these pathogens were developed (1796 and 1800s). In contrast, Malaria, which is a protozoan-neglected disease, has been known since the 5th century BCE and, despite 2,500 years having passed since then, no human vaccine has yet been licensed for Malaria. Additionally, no modern human vaccine is currently licensed against Visceral or Cutaneous leishmaniasis. Vaccination against Malaria evolved from the inoculation of irradiated sporozoites through the bite of Anopheles mosquitoes in 1930's, which failed to give protection, to the use of controlled human Malaria infection (CHMI) provoked by live sporozoites of Plasmodium falciparum and curtailed with specific chemotherapy since 1940's. Although the use of CHMI for vaccination was relatively efficacious, it has some ethical limitations and was substituted by the use of injected recombinant vaccines expressing the main antigens of the parasite cycle, starting in 1980. Pre-erythrocytic (PEV), Blood stage (BSV), transmission-blocking (TBV), antitoxic (AT), and pregnancy-associated Malaria vaccines are under development. Currently, the RTS,S-PEV vaccine, based on the circumsporozoite protein, is the only one that has arrived at the Phase III trial stage. The "R" stands for the central repeat region of Plasmodium (P.) falciparum circumsporozoite protein (CSP); the "T" for the T-cell epitopes of the CSP; and the "S" for hepatitis B surface antigen (HBsAg). In Africa, this latter vaccine achieved only 36.7% vaccine efficacy (VE) in 5-7 years old children and was associated with an increase in clinical cases in one assay. Therefore, in spite of 35 years of research, there is no currently licensed vaccine against Malaria. In contrast, more progress has been achieved regarding prevention of leishmaniasis by vaccine, which also started with the use of live vaccines. For ethical reasons, these were substituted by second-generation subunit or recombinant DNA and protein vaccines. Currently, there is one live vaccine for humans licensed in Uzbekistan, and four licensed veterinary vaccines against visceral leishmaniasis: Leishmune® (76-80% VE) and CaniLeish® (68.4% VE), which give protection against strong endpoints (severe disease and deaths under natural conditions), and, under less severe endpoints (parasitologically and PCR-positive cases), Leishtec® developed 71.4% VE in a low infective pressure area but only 35.7% VE and transient protection in a high infective pressure area, while Letifend® promoted 72% VE. A human recombinant vaccine based on the Nucleoside hydrolase NH36 of Leishmania (L.) donovani, the main antigen of the Leishmune® vaccine, and the sterol 24-c-methyltransferase (SMT) from L. (L.) infantum has reached the Phase I clinical trial phase but has not yet been licensed against the disease. This review describes the history of vaccine development and is focused on licensed formulations that have been used in preventive medicine. Special attention has been given to the delay in the development and licensing of human vaccines against Protozoan infections, which show high incidence worldwide and still remain severe threats to Public Health.

Immunization with full-length Plasmodium falciparum merozoite surface protein 1 is safe and elicits functional cytophilic antibodies in a randomized first-in-human trial

A vaccine remains a priority in the global fight against malaria. Here, we report on a single-center, randomized, double-blind, placebo and adjuvant-controlled, dose escalation phase 1a safety and immunogenicity clinical trial of full-length Plasmodium falciparum merozoite surface protein 1 (MSP1) in combination with GLA-SE adjuvant. Thirty-two healthy volunteers were vaccinated at least three times with MSP1 plus adjuvant, adjuvant alone, or placebo (24:4:4) to evaluate the safety and immunogenicity. MSP1 was safe, well tolerated and immunogenic, with all vaccinees sero-converting independent of the dose. The MSP1-specific IgG and IgM titers persisted above levels found in malaria semi-immune humans for at least 6 months after the last immunization. The antibodies were variant- and strain-transcending and stimulated respiratory activity in granulocytes. Furthermore, full-length MSP1 induced memory T-cells. Our findings encourage challenge studies as the next step to evaluate the efficacy of full-length MSP1 as a vaccine candidate against falciparum malaria (EudraCT 2016-002463-33).

Development of nano-carriers for Leishmania vaccine delivery

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

Genome based screening of epitope ensemble vaccine candidates against dreadful visceral leishmaniasis using immunoinformatics approach

Visceral leishmaniasis (VL) is a dreadful protozoan disease caused by Leishmania donovani that severely affects huge populations in tropical and sub-tropical regions. The present study reports an unbiased genome based screening of 4 potent vaccine antigens against 8023 L. donovani proteins by following the criteria of presence of signal peptides, GPI-anchors and ≤1 transmembrane helix using advanced bioinformatics tools viz. SignalP4.0, PredGPI and TMHMM2.0, respectively. They are designated as genome based predicted signal peptide antigens (GBPSPA). The antigenicity/immunogenicity of chosen vaccine antigens (GBPSPA) with 4 randomly selected known leishmanial antigens (RSKLA) was compared by simulation study employing C-ImmSim software for human immune responses. This revealed better immunological responses. These antigens were further evaluated for the presence of B- and T-cell epitopes using immune epitope database (IEDB) based recommended consensus method of MHC class I and II tools. It was found to forecast CD4⁺ and CD8⁺ T-cell responses in genetically diverse human population worldwide as well as different endemic regions through IEDB based predicted population coverage (PPC) analysis tool. The worldwide percent PPC value of combined (HLA class I and II) epitope ensemble forecast was found to be 99.98, 99.96 and 50.04, respectively for GBPSPA, RSKLA and experimentally known epitopes (EKE) of L. donovani. Therefore, these potential antigens/epitope ensembles could favor the design of prospective and novel vaccine constructs like self-assembled epitopes as nano vaccine formulations against VL. Overall, the present study will serve as a model framework that might improve the effectiveness of designed vaccine against L. donovani and other related pathogens.

Immunotherapy in clinical canine leishmaniosis: a comparative update

Leishmaniosis due to Leishmania infantum is a complex infection that can affect both humans and dogs, and present a wide range of clinical signs and clinicopathological abnormalities. The conventional treatment of this disease is challenging due to the fact that complete parasitological cure commonly does not occur. Furthermore, treatment of the disease with the conventionally used drugs has several shortcomings. These include the need for long-term treatment, side effects and the formation of drug resistance. Moreover, it is important to highlight that the host immune responses play a crucial role in the outcome of this infection. For this reason, the use of immunotherapy in clinical leishmaniosis to improve the result of treatment with the conventional anti-leishmanial drugs by enhancing the immune response is imperative. The aim of this review is to provide a comparative overview of the wide range of immunotherapeutical approaches and strategies for the treatment of L. infantum infection in animals focusing on dogs.

Leishmania Vaccines Entered in Clinical Trials: A Review of Literature

Leishmaniasis is considered as a zoonotic infection and neglected tropical disease. Leishmania treatment is not totally successful and imposes high expenditures, especially in developing countries. Since the natural infection leads to the robust immunity in most of the human cases, many bodies of research have been focusing on Leishmania vaccines, being capable to control Leishmania infection. First generation vaccines (such as Leishmune^® and CaniLeish^®) have proved robust protective immunity in dogs. In human, recombinant vaccines, including Leish-F1 could confer some degrees of protective immunity against natural infection. Recently, ChAd63-KH DNA vaccine has been accomplished in providing prevention against Leishmania infection; however, this vaccine should be further evaluated in other clinical trials.

The adjuvant GLA-SE promotes human Tfh cell expansion and emergence of public TCRβ clonotypes

A rational strategy to achieve optimal vaccine responses is to potentiate Tfh cells and the germinal center response. This work shows the adjuvant GLA-SE enhances circulating Tfh cells and enduring antibody responses to a malaria vaccine in Tanzanian adults.

The generation of protective humoral immunity after vaccination relies on the productive interaction between antigen-specific B cells and T follicular helper (Tfh) cells. Despite the central role of Tfh cells in vaccine responses, there is currently no validated way to enhance their differentiation in humans. From paired human lymph node and blood samples, we identify a population of circulating Tfh cells that are transcriptionally and clonally similar to germinal center Tfh cells. In a clinical trial of vaccine formulations, circulating Tfh cells were expanded in Tanzanian volunteers when an experimental malaria vaccine was adjuvanted in GLA-SE but not when formulated in Alum. The GLA-SE–formulated peptide was associated with an increase in the extrafollicular antibody response, long-lived antibody production, and the emergence of public TCRβ clonotypes in circulating Tfh cells. We demonstrate that altering vaccine adjuvants is a rational approach for enhancing Tfh cells in humans, thereby supporting the long-lived humoral immunity that is required for effective vaccines.

Glucopyranosyl lipid adjuvant enhances immune response to Ebola virus-like particle vaccine in mice

The identification of adjuvants that promote lasting antigen-specific immunity and augment vaccine efficacy are integral to the development of new protein-based vaccines. The Ebola virus-like particle (VLP) vaccine expressing Ebola virus glycoprotein (GP) and matrix protein (VP40) was used in this study to evaluate the ability of TLR4 agonist glucopyranosyl lipid adjuvant (GLA) formulated in a stable emulsion (SE) to enhance immunogenicity and promote durable protection against mouse-adapted Ebola virus (ma-EBOV). Antibody responses and Ebola-specific T cell responses were evaluated post vaccination. Survival analysis after lethal ma-EBOV challenge was performed 4 weeks and 22 weeks following final vaccination. GLA-SE enhanced EBOV-specific immunity and resulted in long-term protection against challenge with ma-EBOV infection in a mouse model. Specifically, GLA-SE elicited Th1-skewed antibodies and promoted the generation of EBOV GP-specific polyfunctional T cells. These results provide further support for the utility of TLR4 activating GLA-SE-adjuvanted vaccines.

Visceral leishmaniasis: An overview of vaccine adjuvants and their applications

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

CD4+ T Cell-Mediated Immunity against the Phagosomal Pathogen Leishmania: Implications for Vaccination

The generation of an efficacious vaccine that elicits protective CD4⁺ T cell-mediated immunity has been elusive. The lack of a vaccine against the Leishmania parasite is particularly perplexing as infected individuals acquire life-long immunity to reinfection. Experimental observations suggest that the relationship between immunological memory and protection against Leishmania is not straightforward and that a new paradigm is required to inform vaccine design. These observations include: (i) induction of Th1 memory is a component of protective immunity, but is not sufficient; (ii) memory T cells may be protective only if they generate circulating effector cells prior to, not after, challenge; and (iii) the low-dose/high-inflammation conditions of physiological vector transmission compromises vaccine efficacy. Understanding the implications of these observations is likely key to efficacious vaccination.