Immunization with Live Attenuated Leishmania donovani Centrin-/- Parasites Is Efficacious in Asymptomatic Infection

Manufacturing and preclinical toxicity of GLP grade gene deleted attenuated Leishmania donovani parasite vaccine

Centrin1 gene deleted Leishmania donovani parasite (LdCen1-/-) was developed and extensively tested experimentally as an intracellular stage-specific attenuated and immunoprotective live parasite vaccine candidate ex vivo using human PBMCs and in vivo in animals. Here we report manufacturing and pre-clinical evaluation of current Good-Laboratory Practice (cGLP) grade LdCen1-/- parasites, as a prerequisite before proceeding with clinical trials. We screened three batches of LdCen1-/- parasites manufactured in bioreactors under cGLP conditions, for their consistency in genetic stability, attenuation, and safety. One such batch was preclinically tested using human PBMCs and animals (hamsters and dogs) for its safety and protective immunogenicity. The immunogenicity of the CGLP grade LdCen1-/- parasites was similar to one grown under laboratory conditions. The cGLP grade LdCen1-/- parasites were found to be safe and non-toxic in hamsters and dogs even at 3 times the anticipated vaccine dose. When PBMCs from healed visceral leishmaniasis (VL) cases were infected with cGLP LdCen1-/-, there was a significant increase in the stimulation of cytokines that contribute to protective responses against VL. This effect, measured by multiplex ELISA, was greater than that observed in PBMCs from healthy individuals. These results suggest that cGLP grade LdCen1-/- manufactured under cGMP complaint conditions can be suitable for future clinical trials.

Intranasal delivery of LaAg vaccine improves immunity of aged mice against visceral Leishmaniasis

There are no approved vaccines yet for human visceral leishmaniasis (VL), the most severe form of the leishmaniasis clinical manifestations that is fatal in over 95 % of untreated cases. It is well-accepted that immunological changes during aging have deleterious impact on the efficacy of vaccines and response to infections. In this work, we compared the response of young and aged mice to intranasal vaccination with killed Leishmania amazonensis promastigote antigens (LaAg) that were then challenged with L. infantum infection, a species that causes visceral leishmaniasis. Intranasal vaccination with LaAg induced a similar reduction in parasitism and hepatosplenomegaly in both young and aged mice compared to their unvaccinated counterparts. Following infection, there was also a less prominent inflammatory profile particularly in the vaccinated aged group, with lower production of TNF-α and nitrite compared to the respective unvaccinated group. Interestingly, the LaAg intranasal vaccination promoted increased production of IFN-γ that was observed in both young- and aged vaccinated groups. Additionally, CD4+ and CD8+T cells from both vaccinated groups presented decreased expression of the inhibitory receptors PD-1 and KLRG1 compared to their unvaccinated controls. Interestingly, a strong positive correlation was observed between the expression of both inhibitory receptors PD-1 and KLRG1 and parasitism, which was more conspicuous in the unvaccinated-aged mice than in the others. Overall, this study helps define new strategies to improve vaccine effectiveness and provides a perspective for prophylactic alternatives against leishmaniasis.

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.

Live attenuated Leishmania infantum centrin deleted mutant (LiCen-/-) as a novel vaccine candidate: A field study on safety, immunogenicity, and efficacy against canine leishmaniasis

This study was designed to evaluate the safety, immunogenicity, and efficacy of a single dose of L. infantum (LiCen^-/-) live attenuated candidate vaccine against canine leishmaniasis (CanL). Eighteen healthy domestic dogs with no anti-Leishmania antibodies and negative leishmanin skin test (LST) were randomly inoculated intravenously with either L. infantum (LiCen^-/-) vaccine candidate in 10 dogs or phosphate-buffered saline (PBS) in 8 dogs. The safety, immunogenicity, and efficacy rate of L. infantum (LiCen^-/-) vaccine candidate against CanL were evaluated by different criteria, including clinical manifestations, injection-site lesion, hematology and biochemistry values, anti-Leishmania antibodies using direct agglutination test (DAT), delayed-type hypersensitivity (DTH) using LST, and CD4⁺ and CD8⁺ T-cells subsets, as well as by measuring interferon (IFN-γ), interleukin (IL-23), IL-17, and IL-10 cytokines. Spleen aspiration and detection of Leishmania parasite using parasitological examinations (microscopy and culture) were performed in both vaccinated and control groups. Two months after intervention, each dog was challenged intraperitoneally (IP) with wide type (WT) L. infantum. Two-month follow-up post vaccination showed no clinical signs and serious side effects associated with the vaccination. A significant increase was found in the expression of IL-17, CD4⁺, and CD8⁺ gene transcripts in PBMCs, as well as increased levels of Th1 cytokines, and reduction of Th2 cytokine. The efficacy of the vaccine candidate was calculated to be 42.85%. While the time window for assessing the vaccine's effectiveness was too limited to draw any real conclusions but the preliminary results showed a moderate efficacy rate due to inoculation a single dose of L. infantum (LiCen^-/-) vaccine candidate. Further investigations with more sample sizes and multiple doses of the vaccine candidate using natural challenges in the endemic areas of CanL are recommended.

Next-Generation Leishmanization: Revisiting Molecular Targets for Selecting Genetically Engineered Live-Attenuated Leishmania

Despite decades of research devoted to finding a vaccine against leishmaniasis, we are still lacking a safe and effective vaccine for humans. Given this scenario, the search for a new prophylaxis alternative for controlling leishmaniasis should be a global priority. Inspired by leishmanization-a first generation vaccine strategy where live L. major parasites are inoculated in the skin to protect against reinfection-live-attenuated Leishmania vaccine candidates are promising alternatives due to their robust elicited protective immune response. In addition, they do not cause disease and could provide long-term protection upon challenge with a virulent strain. The discovery of a precise and easy way to perform CRISPR/Cas-based gene editing allowed the selection of safer null mutant live-attenuated Leishmania parasites obtained by gene disruption. Here, we revisited molecular targets associated with the selection of live-attenuated vaccinal strains, discussing their function, their limiting factors and the ideal candidate for the next generation of genetically engineered live-attenuated Leishmania vaccines to control leishmaniasis.

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.

Host–Pathogen Interaction in Leishmaniasis: Immune Response and Vaccination Strategies

Leishmaniasis is a zoonotic and vector-borne infectious disease that is caused by the genus Leishmania belonging to the trypanosomatid family. The protozoan parasite has a digenetic life cycle involving a mammalian host and an insect vector. Leishmaniasisis is a worldwide public health problem falling under the neglected tropical disease category, with over 90 endemic countries, and approximately 1 million new cases and 20,000 deaths annually. Leishmania infection can progress toward the development of species–specific pathologic disorders, ranging in severity from self-healing cutaneous lesions to disseminating muco-cutaneous and fatal visceral manifestations. The severity and the outcome of leishmaniasis is determined by the parasite’s antigenic epitope characteristics, the vector physiology, and most importantly, the immune response and immune status of the host. This review examines the nature of host–pathogen interaction in leishmaniasis, innate and adaptive immune responses, and various strategies that have been employed for vaccine development.

Live attenuated Leishmania major p27 gene knockout as a novel vaccine candidate: A study on safety, protective immunity and efficacy against canine leishmaniasis caused by Leishmania infantum

Canine leishmaniasis (CanL) is an important parasitic e disease caused by Leishmania infantum and is transmitted by female phlebotomine sand flies primarily between canines and secondarily to humans. Recently, we showed that immunization with Leishmania major p27 gene knockout (Lmp27^-/-) as a live attenuated vaccine was safe, induced immunogenicity, and protected against the development cutaneous and visceral leishmaniasis in mice. The p27 protein is a component of the COX protein complex which is responsible for ATP production. In this study, we analyzed the Lmp27^-/- candidate vaccine potential with this regard to the safety and induction of immunogenicity and protection against CanL. Variables such a clinical manifestation, anti-Leishmania antibodies using direct agglutination test (DAT), lymphocyte proliferation, delayed-type hypersensitivity (DTH), bone marrow aspiration (BMA) and parasite burden using parasitological and molecular examinations were measured. The results demonstrated that the Lmp27^-/- vaccinated group showed no clinical signs after inoculation with Lmp27^-/- mutant during a 12-month follow-up, and had significantly higher T-cell responses (Lymphocyte proliferation and DTH), lower seroconversion and parasite burdens following a challenge inoculation with L. infantum after 6-mounth. In conclusion, vaccination with Lmp27^-/- parasites would be safe and provide significant immunoprotectivity and efficacy against infection with wild type (WT) L. infantum.

Non-Coding RNAs in the Etiology and Control of Major and Neglected Human Tropical Diseases

Non-coding RNAs (ncRNAs) including microRNAs (miRs) and long non-coding RNAs (lncRNAs) have emerged as key regulators of gene expression in immune cells development and function. Their expression is altered in different physiological and disease conditions, hence making them attractive targets for the understanding of disease etiology and the development of adjunctive control strategies, especially within the current context of mitigated success of control measures deployed to eradicate these diseases. In this review, we summarize our current understanding of the role of ncRNAs in the etiology and control of major human tropical diseases including tuberculosis, HIV/AIDS and malaria, as well as neglected tropical diseases including leishmaniasis, African trypanosomiasis and leprosy. We highlight that several ncRNAs are involved at different stages of development of these diseases, for example miR-26-5p, miR-132-3p, miR-155-5p, miR-29-3p, miR-21-5p, miR-27b-3p, miR-99b-5p, miR-125-5p, miR-146a-5p, miR-223-3p, miR-20b-5p, miR-142-3p, miR-27a-5p, miR-144-5p, miR-889-5p and miR-582-5p in tuberculosis; miR-873, MALAT1, HEAL, LINC01426, LINC00173, NEAT1, NRON, GAS5 and lincRNA-p21 in HIV/AIDS; miR-451a, miR-let-7b and miR-106b in malaria; miR-210, miR-30A-5P, miR-294, miR-721 and lncRNA 7SL RNA in leishmaniasis; and miR-21, miR-181a, miR-146a in leprosy. We further report that several ncRNAs were investigated as diseases biomarkers and a number of them showed good potential for disease diagnosis, including miR-769-5p, miR-320a, miR-22-3p, miR-423-5p, miR-17-5p, miR-20b-5p and lncRNA LOC152742 in tuberculosis; miR-146b-5p, miR-223, miR-150, miR-16, miR-191 and lncRNA NEAT1 in HIV/AIDS; miR-451 and miR-16 in malaria; miR-361-3p, miR-193b, miR-671, lncRNA 7SL in leishmaniasis; miR-101, miR-196b, miR-27b and miR-29c in leprosy. Furthermore, some ncRNAs have emerged as potential therapeutic targets, some of which include lncRNAs NEAT1, NEAT2 and lnr6RNA, 152742 in tuberculosis; MALAT1, HEAL, SAF, lincRNA-p21, NEAT1, GAS5, NRON, LINC00173 in HIV/AIDS; miRNA-146a in malaria. Finally, miR-135 and miR-126 were proposed as potential targets for the development of therapeutic vaccine against leishmaniasis. We also identify and discuss knowledge gaps that warrant for increased research work. These include investigation of the role of ncRNAs in the etiology of African trypanosomiasis and the assessment of the diagnostic potential of ncRNAs for malaria, and African trypanosomiasis. The potential targeting of ncRNAs for adjunctive therapy against tuberculosis, leishmaniasis, African trypanosomiasis and leprosy, as well as their targeting in vaccine development against tuberculosis, HIV/AIDS, malaria, African trypanosomiasis and leprosy are also new avenues to explore.

Expression analysis of centrin gene in promastigote and amastigote forms of leishmania infantum iranian isolates: a promising target for live attenuated vaccine development against canine leishmaniasis

Background

Leishmania parasites express various essential proteins in different growth phases (logarithmic/stationary) and forms (promastigote/amastigote). Targeting the genes encoding such proteins paves the way for controlling these parasites. Centrin is an essential gene, which its protein product seems to be vital for the proliferation of Leishmania parasites. Herein, this study was contrived to analyze the expression level of the centrin gene in different growth phases and forms of Leishmania infantum (L. infantum) parasites isolated from various endemic areas of canine leishmaniasis (CanL) in Iran.

Results

All three collected isolates were identified as L. infantum using polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP). Real-time reverse transcription (RT)-PCR revealed a statistically significant up-regulation (3.13-fold) in the logarithmic phase promastigotes compared to stationary ones (p < 0.01), whereas centrin was expressed equally in intracellular amastigotes at different time points during cell culture. Also, our finding revealed a slight up-regulation of the centrin gene (1.22-fold) in the intracellular amastigotes compared to logarithmic phase promastigotes, which was found statistically non-significant (p > 0.05).

Conclusions

Centrin gene in Iranian isolates of L. infantum is more expressed in exponential than stationary phases and seems to be considered as a promising target in the development of a genetically modified live attenuated vaccine for CanL control.

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.

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.

Leishmaniasis diagnosis: an update on the use of parasitological, immunological and molecular methods

Diagnosis of leishmaniasis has always been a major challenge as its clinical features resemble some other commonly occurring diseases such as tuberculosis, typhoid, and malaria. Reliable laboratory methods become important for differential diagnosis. Demonstration of the parasites in stained preparations of bone marrow and splenic aspirates being risky and invasive is still the gold standard for diagnosis. Serological tests utilizing rapid immunochromatographic formats or rK39 in enzyme linked immune sorbent assay, immunoblotting, direct agglutination test have complications related to high proportions of positive asymptomatic individuals and the inability to diagnose a relapse. Among the molecular techniques, polymerase chain reaction is the most commonly used technique that is successfully implied for diagnosis. This review provides updated information on the recent developments in the field of diagnosis in leishmaniasis, various methods utilized with their advantages and limitations.

Genetically modified live attenuated vaccine: A potential strategy to combat visceral leishmaniasis

Visceral leishmaniasis (VL) is caused by a protozoan parasite Leishmania donovani mainly influencing the population of tropical and subtropical regions across the globe. The arsenal of drugs available is limited, and prolonged use of such drugs makes parasite to become resistant. Therefore, it is very imperative to develop a safe, cost-effective and inexpensive vaccine against VL. Although in recent years, many strategies have been pursued by researchers, so far only some of the vaccine candidates reached for clinical trial and more than half of them are still in pipeline. There is now a broad consent among Leishmania researchers that the perseverance of parasite is very essential for eliciting a protective immune response and may perhaps be attained by live attenuated parasite vaccination. For making a live attenuated parasite, it is very essential to ensure that the parasite is deficient of virulence and should further study genetically modified parasites to perceive the mechanism of pathogenesis. So it is believed that in the near future, a complete understanding of the Leishmania genome will explore clear strategies to discover a novel vaccine. This review describes the need for a genetically modified live attenuated vaccine against VL, and obstacles associated with its development.

Development and Characterization of an Avirulent Leishmania major Strain

Leishmania major causes cutaneous leishmaniasis. An antileishmanial vaccine for humans is unavailable. In this study, we report development of two attenuated L. major strains-5ASKH-HP and LV39-HP-by continuous culture (high passage) of the corresponding virulent strains (low passage). Both avirulent strains showed similar changes in proteome profiles when analyzed by surface-enhanced laser desorption ionization mass spectrometry. Liquid chromatography-mass spectrometry and microarray characterization of 5ASKH strains revealed substantially altered gene and protein expression profiles, respectively. Both virulent and avirulent L. major strains grew comparably in culture, but the avirulent strain survived significantly less in BALB/c-derived peritoneal macrophages. Both attenuated strains failed to infect BALB/c mice and elicited IFN-γ, but not IL-4 and IL-10, responses. 5ASKH-HP parasites failed to induce significant infection even in severely immunocompromised- SCID or inducible NO synthase-, CD40-, or IL-12-deficient mice, indicating attenuation. The avirulent strain induced less IL-10, but higher IL-12, in macrophages. The avirulent strain failed to reduce CD40 relocation to the detergent-resistant membrane domain and to inhibit CD40-induced phosphorylation of the kinases Lyn and protein kinase C-β and MAPKs MKK-3/6 and p38MAPK or to upregulate MEK-1/2 and ERK-1/2 in BALB/c-derived peritoneal macrophages. The virulent and the avirulent strains reciprocally modulated CD40-induced Ras-mediated signaling through PI-3K and Raf-1. Avirulent 5ASKH-primed BALB/c mice were protected against virulent L. major challenge infection. The loss of virulence accompanied by substantially altered proteome profiles and the elicitation of host-protective immune responses indicate plausibly irreversible attenuation of the L. major strain and its potential use as a vaccine strain.

MicroRNAs: Biological Regulators in Pathogen-Host Interactions

An inflammatory response is essential for combating invading pathogens. Several effector components, as well as immune cell populations, are involved in mounting an immune response, thereby destroying pathogenic organisms such as bacteria, fungi, viruses, and parasites. In the past decade, microRNAs (miRNAs), a group of noncoding small RNAs, have emerged as functionally significant regulatory molecules with the significant capability of fine-tuning biological processes. The important role of miRNAs in inflammation and immune responses is highlighted by studies in which the regulation of miRNAs in the host was shown to be related to infectious diseases and associated with the eradication or susceptibility of the infection. Here, we review the biological aspects of microRNAs, focusing on their roles as regulators of gene expression during pathogen-host interactions and their implications in the immune response against Leishmania, Trypanosoma, Toxoplasma, and Plasmodium infectious diseases.

miR-21 Expression Determines the Early Vaccine Immunity Induced by LdCen -/- Immunization

No vaccine exists against visceral leishmaniasis. Toward developing vaccines against VL, we have reported previously on the immunogenicity of live attenuated LdCen ^-/- parasites in animal models. Immunization with LdCen ^-/- parasites has been shown to induce durable protective immunity in pre-clinical animal models. Although the innate immune responses favoring a Th1 type immunity are produced following LdCen ^-/- immunization, the molecular determinants of such responses remain unknown. To identify early biomarkers of immunogenicity associated with live attenuated parasitic vaccines, we infected macrophages derived from healthy human blood donors with LdCen ^-/- or LdWT parasites ex vivo and compared the early gene expression profiles. In addition to altered expression of immune related genes, we identified several microRNAs that regulate important cytokine genes, significantly altered in LdCen ^-/- infection compared to LdWT infection. Importantly, we found that LdCen ^-/- infection suppresses the expression of microRNA-21 (miR-21) in human macrophages, which negatively regulates IL12, compared to LdWT infection. In murine DC experiments, LdCen ^-/- infection showed a reduced miR-21 expression with a concomitant induction of IL12. Silencing of miR-21 using specific inhibitors resulted in an augmented induction of IL12 in LdWT infected BMDCs, illustrating the role of miR-21 in LdWT mediated suppression of IL12. Further, exosomes isolated from LdCen ^-/- infected DCs contained significantly reduced levels of miR-21 compared to LdWT infection, that promoted proliferation of CD4⁺ T cells in vitro. Similar miR-21 mediated IL12 regulation was also observed in ex vivo human macrophage infection experiments indicating that miR-21 plays a role in early IL12 mediated immunity. Our studies demonstrate that LdCen ^-/- infection suppresses miR-21 expression, enables IL12 mediated induction of adaptive immunity including proliferation of antigen experienced CD4⁺ T cells and development of a Th1 immunity, and suggest that miR-21 could be an important biomarker for LdCen ^-/- vaccine immunity in human clinical trials.

One Sentence Summary

Role of miR-21 in vaccine induced immunity.

Pam3CSK4 adjuvant given intranasally boosts anti-Leishmania immunogenicity but not protective immune responses conferred by LaAg vaccine against visceral leishmaniasis

The use of adjuvants in vaccine formulations is a well-established practice to improve immunogenicity and protective immunity against diseases. Previously, we have demonstrated the feasibility of intranasal vaccination with the antigen of killed Leishmania amazonensis promastigotes (LaAg) against experimental leishmaniasis. In this work, we sought to optimize the immunogenic effect and protective immunity against murine visceral leishmaniasis conferred by intranasal delivery of LaAg in combination with a synthetic TLR1/TLR2 agonist (Pam3CSK4). Intranasal vaccination with LaAg/PAM did not show toxicity or adverse effects, induced the increase of delayed-type hypersensitivity response and the production of inflammatory cytokines after parasite antigen recall. However, mice vaccinated with LaAg/PAM and challenged with Leishmania infantum presented significant reduction of parasite burden in both liver and spleen, similar to those vaccinated with LaAg. Although LaAg/PAM intranasal vaccination had induced higher frequencies of specific CD4⁺ and CD8⁺ T cells and increased levels of IgG2a antibody isotype in serum, both LaAg and LaAg/PAM groups presented similar levels of IL-4 and IFN-y and decreased production of IL-10 when compared to controls. Our results provide the first evidence of the feasibility of intranasal immunization with antigens of killed Leishmania in association with a TLR agonist, which may be explored for developing an effective and alternative strategy for vaccination against visceral leishmaniasis.

Using proteomics as a powerful tool to develop a vaccine against Mediterranean visceral leishmaniasis

Visceral leishmaniasis (VL) is a tropical infectious disease, which is called Mediterranean visceral leishmaniasis (MVL) in the Mediterranean area. In spite of many attempts, no effective commercial vaccine exists for MVL. To find new targets for developing antileishmanial vaccines, knowing parasite antigens that provoke the immune system are on demand. Nowadays, proteomics methods are defined as approaches for analysis of protein profiling of different cells. Within this framework, detection of new antigens is becoming more facilitated. In this review, we aimed to introduce possible targets using proteomics so; they could be used as candidates for developing vaccines against MVL. It can shed new light in the near future on the development of promising vaccines for MVL.