Vaccination with heat-killed leishmania antigen or recombinant leishmanial protein and CpG oligodeoxynucleotides induces long-term memory CD4+ and CD8+ T cell responses and protection against leishmania major infection

Unleashing the role of potential adjuvants in leishmaniasis

Leishmaniasis is amongst one of the most neglected tropical disease, caused by an intracellular protozoan of genus Leishmania. Currently, the most promising strategy to combat leishmaniasis, relies on chemotherapy but the toxicity and increasing resistance of the standard drugs, presses the demand for new alternatives. Immunization is arguably the best strategy for cure because an individual once infected becomes immune to the disease. Yet, there is no efficient vaccine capable of providing enduring immunity against the parasite. Achieving the goal of developing highly efficacious and durable vaccine is limited due to lack of an appropriate adjuvant. Adjuvants are recognized as 'immune potentiators' which redirect or amplify the immune response. A number of adjuvants like alum, MPL-A, CpG ODN, GLA-SE, imiquimod, saponins etc. have been used in combination with various classes of Leishmania antigens. However, only few have reached clinical trials. Thus, the choice of an adjuvant is critically dependent on many factors such as the route of administration, the nature of antigen, formulation, the type of required immune response, their mode of action and the immunization schedule. This review provides an updated status on the types of adjuvants used in leishmaniasis so far and their mechanism of action if known.

Comparison of the long-term and short-term protection in mouse model of Leishmania major infection following vaccination with Live Iranian Lizard Leishmania mixed with chitin microparticles

Inducing long-term immunity is the primary goal of vaccination. Leishmanisation using non-pathogenic to human Leishmania spp. could be considered a reliable approach to immunising subjects against Leishmania infection. Here, we evaluated the long-term immune responses (14 weeks) after immunisation with either live- or killed-Iranian Lizard Leishmania (ILL) mixed with chitin microparticles (CMPs) against L. major infection in BALB/c mice. In total, nine groups of mice were included in the study. To evaluate short-term immunity, mice were immunised with live-ILL and CMPs and 3 weeks later were challenged with L. majorEGFP . To evaluate the long-term immunity, mice were immunised with either live- or killed-ILL both mixed with CMPs, and 14 weeks after immunisation, mice were challenged with L. majorEGFP . A group of healthy mice who received no injection was also included in the study. Eight weeks after the challenge with L. majorEGFP , all subjects were sacrificed and the parasite burden (quantitative real-time PCR and in vivo imaging), cytokines levels (IFN-γ, IL-4 and IL-10), Leishmania-specific antibody concentration, and total levels of IgG1 and IgG2a were measured. In addition, nitric oxide concentration and arginase activity were evaluated. Results showed that in mice that were immunised using live-ILL+CMP, the induced protective immune response lasted at least 14 weeks; since they were challenged with L. majorEGFP at the 14th -week post-immunisation, no open lesion was formed during the 8-week follow-up, and the footpad swelling was significantly lower than controls. They also showed a significant reduction in the parasite burden in splenocytes, compared to the control groups including the group that received killed-ILL+CMP. The observed protection was associated with a higher IFN-γ and a lower IL-10 production by splenocytes. Additionally, the results demonstrated that arginase activity was decreased in the ILL+CMP group compared to other groups. Immunisation with ILL alone reduced the parasite burden compared to non-immunised control; however, it was still significantly higher than the parasite burden in the ILL+CMP groups. In conclusion, the long-term immune response against L. major infection induced by Live-ILL+CMP was more competent than the response elicited by killed-ILL+CMP to protect mice against infection with L. majorEGFP .

Deletion of MIF gene from live attenuated LdCen-/- parasites enhances protective CD4+ T cell immunity

Vaccination with live attenuated Leishmania parasites such as centrin deleted Leishmania donovani (LdCen^-/-) against visceral leishmaniasis has been reported extensively. The protection induced by LdCen^-/- parasites was mediated by both CD4⁺ and CD8⁺ T cells. While the host immune mediators of protection are known, parasite determinants that affect the CD4⁺ and CD8⁺ T cell populations remain unknown. Parasite encoded inflammatory cytokine MIF has been shown to modulate the T cell differentiation characteristics by altering the inflammation induced apoptosis during contraction phase in experimental infections with Leishmania or Plasmodium. Neutralization of parasite encoded MIF either by antibodies or gene deletion conferred protection in Plasmodium and Leishmania studies. We investigated if the immunogenicity and protection induced by LdCen^-/- parasites is affected by deleting MIF genes from this vaccine strain. Our results showed that LdCen^-/-MIF^-/- immunized group presented higher percentage of CD4⁺ and CD8⁺ central memory T cells, increased CD8⁺ T cell proliferation after challenge compared to LdCen^-/- immunization. LdCen^-/-MIF^-/- immunized group presented elevated production of IFN-γ⁺ and TNF-α⁺ CD4⁺ T cells concomitant with a reduced parasite load in spleen and liver compared to LdCen^-/-group following challenge with L. infantum. Our results demonstrate the role of parasite induced factors involved in protection and long-term immunity of vaccines against VL.

Toll-like Receptor-9 (TLR-9) Signaling Is Crucial for Inducing Protective Immunity following Immunization with Genetically Modified Live Attenuated Leishmania Parasites

No human vaccine is available for visceral leishmaniasis (VL). Live attenuated centrin gene-deleted L. donovani (LdCen−/−) parasite vaccine has been shown to induce robust innate immunity and provide protection in animal models. Toll-like receptors (TLRs) are expressed in innate immune cells and are essential for the early stages of Leishmania infection. Among TLRs, TLR-9 signaling has been reported to induce host protection during Leishmania infection. Importantly, TLR-9 ligands have been used as immune enhancers for non-live vaccination strategies against leishmaniasis. However, the function of TLR-9 in the generation of a protective immune response in live attenuated Leishmania vaccines remains unknown. In this study, we investigated the function of TLR-9 during LdCen−/− infection and found that it increased the expression of TLR-9 on DCs and macrophages from ear-draining lymph nodes and spleen. The increase in TLR-9 expression resulted in changes in downstream signaling in DCs mediated through signaling protein myeloid differentiation primary response 88 (MyD88), resulting in activation and nuclear translocation of nuclear factor-κB (NF-κB). This process resulted in an increase in the DC’s proinflammatory response, activation, and DC-mediated CD4+T cell proliferation. Further, LdCen−/− immunization in TLR-9−/− mice resulted in a significant loss of protective immunity. Thus, LdCen−/− vaccine naturally activates the TLR-9 signaling pathway to elicit protective immunity against virulent L. donovani challenge.

Leishmania donovani induces CD300a expression to dampen effector properties of CD11c+ dendritic and antigen activated CD8+ T cells

CD8⁺ T cells are an important regiment of adaptive immunity that play a decisive role in elimination of many species of Leishmania parasite from the host. In visceral leishmaniasis, caused by L. donovani, the loss of CD8⁺ T cells function has been found associated with augmented pathogenesis. The factors determining CD8⁺ T cells activation and function against Leishmania antigens are largely unknown. In this study, we investigated the role of an immune inhibitory receptor, CD300a, on the effector properties of dendritic cells and CD8⁺ T cells. We observed that the Leishmania regulates the effectors function of CD8⁺ T cells by increasing CD300a expression on CD11c⁺ dendritic cells. The abrogation of CD300a signaling in parasites infected animals induced CD8⁺ T cell abilities to produce IFN-γ, TNF-α and also helped them to acquire desired multifunctionality. The CD300a receptor blocking also enhanced the number of CD8⁺ T cells memory phenotypes at the early days of infection, suggesting its potential beneficial role in vaccine induced immunity. We also observed significantly enhanced levels of pro-inflammatory cytokines in the spleen of CD300a blocked infected animals with concomitant reduced spleen parasite load. Additionally, the abrogation of CD300a signals in the infected animals helped in establishing Th1 type protective humoral immunity with significantly elevated levels of IgG2a antibodies. Since CD8⁺ T cells are an important determinant of vaccine induced immunity against leishmaniasis, the findings corroborate the potential of CD300a in vaccine induced immunity and thus require further attention.

Evaluation of cytotoxic activity of live toxoplasma gondii tachyzoites and toxoplasma antigen on MCF-7 human breast cancer cell line

The aim of this study was to investigate the cytotoxic potency of live Toxoplasma gondii tachyzoites as well as Toxoplasma antigen on MCF-7 human breast cancer cell line. Cancer cell lines are considered an essential preliminary step towards in-vitro investigation of the potential antineoplastic impact of novel chemotherapeutic agents. Pathogens, including viruses, bacteria, and parasites are noticeably under investigation, considering their potential antineoplastic activity. Some have attained a steady position in the clinical field as hepatitis B virus, human papilloma virus and BCG immunization. Toxoplasma gondii is an apicomplexan parasite with promising antineoplastic activity. In this study, live Toxoplasma tachyzoites provoked a direct cytotoxic effect on MCF-7 in a dose dependent manner, while Toxoplasma antigen didn’t induce such impact. Skipping the direct cytotoxic effect of Toxoplasma antigen doesn’t totally divert the possible antineoplastic activity of Toxoplasma antigen. Potential alternative immune mediated mechanisms could be an alternative. Further in-vivo studies in different cancer models are mandatory to investigate the underlying mechanisms of antineoplastic activity of Toxoplasma gondii

Potential of TLR agonist as an adjuvant in Leishmania vaccine against visceral leishmaniasis in BALB/c mice

Morbid infection of leishmaniasis is posing threat to humankind due to its exacerbating prevalence in newer emerging areas. Moreover, the availability of limited drugs, their toxicity, limited efficacy, the emergence of drug resistance, and unavailability of vaccines are the major obstacles in its elimination. This implies the demand for a prophylactic vaccine candidate to prevent this infection and resulting fatal disease. We evaluated gardiquimod (a toll-like receptor-7 agonist) for its action as an adjuvant with the heat-killed antigen of Leishmania donovani. BALB/c mice were immunized with a vaccine either with or without adjuvant and given challenge infection. The results depicted the low parasite burden, higher delayed-type hypersensitivity response, and higher levels of IgG2a, Th1 cytokines, and NO in immunized mice in contrast to infected control mice. Low levels of Th2 cytokines and IgG1 were also noticed in the vaccinated mice than in infected mice. The mice immunized with a combination of gardiquimod and heat-killed antigen showed maximum efficacy. The results from the present study reflect the potential of tested vaccine candidate with gardiquimod as an adjuvant.

Immune induction by adjuvanted Leishmania donovani vaccines against the visceral leishmaniasis in BALB/c mice

Visceral leishmaniasis (VL) is a neglected tropical disease caused by Leishmania donovani or Leishmania infantum. Currently, the patients are treated with chemotherapeutic drugs; however, their toxicity limits their use. It would be desirable to develop a vaccine against this infection. In this study, we assessed the efficacy of different vaccine formulations at variable time points. Heat-killed (HK) antigen of Leishmania donovani was adjuvanted with two adjuvants (AddaVax and Montanide ISA 201) and three immunizations at a gap of 2 weeks (wk) were given to BALB/c mice. After 2 weeks of the last booster, mice were given challenge infection and sacrificed before challenge and after 4wk, 8wk, and 12 wk post-challenge. Significant protective immunity was observed in all the immunized animals and it was indicated by the notable rise in delayed-type hypersensitivity (DTH) response, remarkably declined parasite burden, a significant increase in the levels of interferon-gamma (IFN-γ), interleukin-12, interleukin-17 (Th1 cytokines), and IgG2a in contrast to infected control mice. Montanide ISA 201 with HK antigen provided maximum protection followed by AddaVax with HK and then HK alone. These findings elaborate on the importance of the tested adjuvants in the vaccine formulations against murine visceral leishmaniasis.

Adjuvanted vaccines driven protection against visceral infection in BALB/c mice by Leishmania donovani

Kinteoplastid protozoan parasite of genus Leishmania is the pathogen that causes leishmaniasis. Its prevalence is highest after malaria and visceral leishmaniasis is the most dreaded form of infection. No vaccine is available for the disease management and it relies wholly on a few chemotherapeutic agents which are toxic and besides drug resistance their costs are the limitations. Therefore, development of an effective vaccine is urgently required. In this study, Montanide ISA 201 and AddaVax were assessed for their adjuvant potential along with formalin-inactivated or killed vaccine for the immune induction. Immunological and parasitological studies were conducted to evaluate the efficacy of different vaccine formulations in BALB/c mice before challenge infection as well as 4, 8, and 12 weeks after challenge. The efficacy of vaccines was evidenced with reduced parasite burden, the higher DTH response, Th1 cytokines, and IgG2a isotype antibody in immunized mice. All the vaccines showed their potential against Leishmania donovani infection and vaccine formulated with Montanide ISA 201 exhibited maximum efficacy. Our results suggest the potential of these vaccine formulations in controlling Leishmania infection.

Optimization of Immunization Procedure for Eimeria tenella DNA Vaccine pVAX1-pEtK2-IL-2 and Its Stability

PURPOSE

To seek for the optimal immunization procedure of DNA vaccine pVAX1-pEtK2-IL-2 which was produced via cloning pEtK2 antigen gene of Eimeria tenella (E. tenella) and chicken IL-2 (chIL-2) gene into expression vector pVAX1.

METHODS

The doses, routes, times of inoculation and ages of the first inoculation of chickens were optimized. The stability of the vaccine, including store temperature and time, was also explored. The effects of the protective immunity against challenge infection were assessed according to average body weight gain, survival rate, oocyst output, lesion score and the anti-coccidial index (ACI).

RESULTS

The results suggested that intramuscular inoculation was the most efficient route to elicit immune response and 80 μg was the optimal immune dose. Two time injections induced more effective protection compared to single injection, the effect of the first injection at 14 days old was optimal. The immune efficacy of the vaccine stored at different time and temperature was very stable.

CONCLUSIONS

The optimal immunization procedure for Eimeria tenella DNA vaccine pVAX1-pEtK2-IL-2 is 80 μg DNA, two time injections at 14 and 21 days old, respectively, by intramuscular inoculation.

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.

Protection induced by Leishmania Major antigens and the imiquimod adjuvant encapsulated on liposomes in experimental cutaneous leishmaniasis

There is a need for new, effective, and less expensive and toxic treatment for Leishmaniasis. It seems that the use of a suitable adjuvant and a delivery system is effective in inducing immune reactions for protection. Liposomes can be applied as immunoadjuvants to trigger immune reactions to different antigens. The adjuvant effects of imiquimod using DSPC liposomes containing SLA (soluble Leishmania antigens) were studied on the type and intensity of the produced immune reaction to the challenge of Leishmania major in BALB/c mice. Liposomes were produced by the lipid film procedure. BALB/C mice were immunized subcutaneously, three times at 2-week intervals and with various formulations. Lesion development and the parasite burden in the spleens and feet after the challenge with Leishmania major, Th1 cytokine (IFN-γ), and the IgG isotype titration were assessed to evaluate the induced immune reaction and the protection level. The group of mice immunized with Liposome DSPC +Imiquimod +SLA revealed less severe footpad swelling, being significantly different (P < .05) from other groups. A higher level of IgG2a and IFN-γ secretion was observed in the mice immunized with Liposome DSPC +Imiquimod +SLA than the control group. These observations imply that the DSPC liposome containing imiquimod induces the Th1 immune response that is protective against the challenge of Leishmania major.

Immunity Against Leishmania major Infection: Parasite-Specific Granzyme B Induction as a Correlate of Protection

Zoonotic cutaneous leishmaniasis (ZCL) caused by Leishmania (L.) major infection is characterized by different clinical presentations which depend in part on the host factors. In attempt to investigate the impact of the host's immune response in the outcome of the disease, we conducted a prospective study of 453 individuals living in endemic foci of L. major transmission in Central Tunisia. Several factors were assessed at the baseline including (i) the presence of typical scars of ZCL, (ii) in vivo hypersensitivity reaction to leishmanin, and (iii) the in vitro release of granzyme B (Grz B) by peripheral blood mononuclear cells (PBMC) in response to stimulation with live L. major promastigotes. After one season of parasite's transmission, repeated clinical examinations allowed us to diagnose the new emerging ZCL cases. Heterogeneity was observed in terms of number of lesions developed by each individual as well as their size and spontaneous outcome, which led us to establish the parameter “severity of the disease.” The efficacy of the presence of typical ZCL scar, the leishmanin skin test (LST) positive reactivity and the high levels of Grz B (≥2 ng/ml), in the protection against the development of ZCL were 29, 15, and 22%, respectively. However, these factors were more efficient against development of intermediate or severe forms of ZCL. Levels of Grz B >2 ng/ml showed the best efficacy of protection (equals to 72.8%) against development of these forms of ZCL. The association of such parameter with the positivity of the LST exhibited a better efficacy (equals to 83.6%). In conclusion, our results support the involvement of Leishmania-specific cytotoxic cellular immune response in host protection against Leishmania-infection. This factor could be of great interest in monitoring the success of vaccination against human leishmaniasis.

Leishmania Hijacks Myeloid Cells for Immune Escape

Protozoan parasites of the Leishmania genus are the causative agents of leishmaniasis, a group of neglected tropical diseases whose clinical manifestations vary depending on the infectious Leishmania species but also on host factors. Recognition of the parasite by host myeloid immune cells is a key to trigger an effective Leishmania-specific immunity. However, the parasite is able to persist in host myeloid cells by evading, delaying and manipulating host immunity in order to escape host resistance and ensure its transmission. Neutrophils are first in infiltrating infection sites and could act either favoring or protecting against infection, depending on factors such as the genetic background of the host or the parasite species. Macrophages are the main host cells where the parasites grow and divide. However, macrophages are also the main effector population involved in parasite clearance. Parasite elimination by macrophages requires the priming and development of an effector Th1 adaptive immunity driven by specific subtypes of dendritic cells. Herein, we will provide a comprehensive outline of how myeloid cells regulate innate and adaptive immunity against Leishmania, and the mechanisms used by the parasites to promote their evasion and sabotage. Understanding the interactions between Leishmania and the host myeloid cells may lead to the development of new therapeutic approaches and improved vaccination to leishmaniases, an important worldwide health problem in which current therapeutic or preventive approaches are limited.

The role of MPL and imiquimod adjuvants in enhancement of immune response and protection in BALB/c mice immunized with soluble Leishmania antigen (SLA) encapsulated in nanoliposome

Adjuvants play an essential role in the induction of immunity against leishmaniasis. In this study, monophosphoryl lipid A (MPL) and imiquimod (IMQ) were used as TLR ligands adjuvants to enhance immunogenicity and rate of protection against leishmaniasis. Nanoliposomes containing soluble Leishmania antigens (SLA) and adjuvants were consisted of DSPC, DSPG and Chol prepared by using lipid film method followed by bath sonication. The size of nanoliposomes was around 95 nm and their zeta potential was negative. BALB/c mice were immunized by liposomal formulations of lip/SLA, lip/MPL/SLA, lip/IMQ/SLA, lip/MPL/IMQ/SLA, lip/SLA + lip/IMQ, lip/SLA + lip/MPL, lip/SLA + lip/MPL/IMQ and five controls of SLA, lip/MPL, lip/IMQ, lip/MPL/IMQ and buffer by subcutaneously (SC) injections, three times in 2 weeks intervals. The synergic effect of two adjuvants when they are used in one formulation showed significantly (p < .001) smaller footpad swelling and the lowest parasite burden in lymph node and foot after the challenge. IgG2a in these groups showed the higher titre compared to control groups, which is compatible with the high IFN-γ production and lowest IL-4. Taken together the results indicated that co-delivery of MPL and IMQ adjuvants and antigen in nanoliposome carrier could be an appropriate delivery system to induce cellular immunity pathway against leishmaniasis.

CD8+ T Cells Lack Local Signals To Produce IFN-γ in the Skin during Leishmania Infection

Resolution of leishmaniasis depends upon parasite control and limiting inflammation. CD4⁺ Th1 cells are required to control parasites, whereas CD8⁺ T cells play a dual role: they promote Th1 cell differentiation but can also increase inflammation at the site of infection as a consequence of cytolysis. Although CD8⁺ T cells taken from leishmanial lesions are cytolytic, in this study, we showed that only a few CD8⁺ T cells produced IFN-γ. Correspondingly, only low levels of IL-12 and/or IL-12 mRNA were present in lesions from infected mice, as well as patients. Addition of IL-12 increased IFN-γ production by CD8⁺ T cells isolated from leishmanial lesions, suggesting that a lack of IL-12 at the site of infection limits IFN-γ production by CD8⁺ T cells. To determine whether CD8⁺ T cells could promote resistance in vivo if IL-12 was present, we administered IL-12 to Leishmania-infected RAG mice reconstituted with CD8⁺ T cells. IL-12 treatment increased the ability of CD8⁺ T cells to make IFN-γ, but CD8⁺ T cells still failed to control the parasites. Furthermore, despite the ability of CD8⁺ T cells to promote immunity to secondary infections, we also found that CD8⁺ T cells from immune mice were unable to control Leishmania in RAG mice. Taken together, these results indicate that lesional CD8⁺ T cells fail to make IFN-γ because of a deficit in IL-12 but that, even with IL-12, CD8⁺ T cells are unable to control Leishmania in the absence of CD4⁺ T cells.

An α-Gal-containing neoglycoprotein-based vaccine partially protects against murine cutaneous leishmaniasis caused by Leishmania major

Background

Protozoan parasites from the genus Leishmania cause broad clinical manifestations known as leishmaniases, which affect millions of people worldwide. Cutaneous leishmaniasis (CL), caused by L. major, is one the most common forms of the disease in the Old World. There is no preventive or therapeutic human vaccine available for L. major CL, and existing drug treatments are expensive, have toxic side effects, and resistant parasite strains have been reported. Hence, further therapeutic interventions against the disease are necessary. Terminal, non-reducing, and linear α-galactopyranosyl (α-Gal) epitopes are abundantly found on the plasma membrane glycolipids of L. major known as glycoinositolphospholipids. The absence of these α-Gal epitopes in human cells makes these glycans highly immunogenic and thus potential targets for vaccine development against CL.

Methodology/Principal findings

Here, we evaluated three neoglycoproteins (NGPs), containing synthetic α-Gal epitopes covalently attached to bovine serum albumin (BSA), as vaccine candidates against L. major, using α1,3-galactosyltransferase-knockout (α1,3GalT-KO) mice. These transgenic mice, similarly to humans, do not express nonreducing, linear α-Gal epitopes in their cells and are, therefore, capable of producing high levels of anti-α-Gal antibodies. We observed that Galα(1,6)Galβ-BSA (NGP5B), but not Galα(1,4)Galβ-BSA (NGP12B) or Galα(1,3)Galα-BSA (NGP17B), was able to significantly reduce the size of footpad lesions by 96% in comparison to control groups. Furthermore, we observed a robust humoral and cellular immune response with production of high levels of protective lytic anti-α-Gal antibodies and induction of Th1 cytokines.

Conclusions/Significance

We propose that NGP5B is an attractive candidate for the study of potential synthetic α-Gal-neoglycoprotein-based vaccines against L. major infection.

Despite a worldwide prevalence, cutaneous leishmaniasis (CL) remains largely neglected, with no prophylactic or therapeutic vaccine available. In the Old World, CL is mainly caused by either Leishmania major or L. tropica parasites, which produce localized cutaneous ulcers, often leading to scarring and social stigma. Currently, the disease has reached hyperendemicity levels in the Middle East due to conflict and human displacement. Furthermore, the first choice of treatment in that region continues to be pentavalent antimonials, which are costly and highly toxic, and current vector control measures alone are not sufficient to stop disease transmission. Hence, a vaccine against CL would be very beneficial. Previous studies have demonstrated that sugars are promising vaccine candidates against leishmaniasis, since most parasite species have a cell surface coat composed of immunogenic sugars, including linear α-galactopyranosyl (α-Gal) epitopes, which are absent in humans. Here, we have developed an α-Gal-based vaccine candidate, named NGP5B. When tested in transgenic mice which like humans lack α-Gal epitopes in their cells, NGP5B was able to induce a significant partial protection against L. major infection, by significantly reducing mouse footpad lesions and parasite burden. Altogether, we propose NGP5B as a promising preventive vaccine for CL caused by L. major.

Cutaneous leishmaniasis: immune responses in protection and pathogenesis

Cutaneous leishmaniasis is a major public health problem and causes a range of diseases from self-healing infections to chronic disfiguring disease. Currently, there is no vaccine for leishmaniasis, and drug therapy is often ineffective. Since the discovery of CD4(+) T helper 1 (TH1) cells and TH2 cells 30 years ago, studies of cutaneous leishmaniasis in mice have answered basic immunological questions concerning the development and maintenance of CD4(+) T cell subsets. However, new strategies for controlling the human disease have not been forthcoming. Nevertheless, advances in our knowledge of the cells that participate in protection against Leishmania infection and the cells that mediate increased pathology have highlighted new approaches for vaccine development and immunotherapy. In this Review, we discuss the early events associated with infection, the CD4(+) T cells that mediate protective immunity and the pathological role that CD8(+) T cells can have in cutaneous leishmaniasis.

Expression and purification of an engineered, yeast-expressed Leishmania donovani nucleoside hydrolase with immunogenic properties

Leishmania donovani is the major cause of visceral leishmaniasis (kala-azar), now recognized as the parasitic disease with the highest level of mortality second only to malaria. No human vaccine is currently available. A 36 kDa L. donovani nucleoside hydrolase (LdNH36) surface protein has been previously identified as a potential vaccine candidate antigen. Here we present data on the expression of LdNH36 in Pichia pastoris and its purification at the 20 L scale to establish suitability for future pilot scale manufacturing. To improve efficiency of process development and ensure reproducibility, 4 N-linked glycosylation sites shown to contribute to heterogeneous high-mannose glycosylation were mutated to glutamine residues. The mutant LdNH36 (LdNH36-dg2) was expressed and purified to homogeneity. Size exclusion chromatography and light scattering demonstrated that LdNH36-dg2 existed as a tetramer in solution, similar to the wild-type recombinant L. major nucleoside hydrolase. The amino acid mutations do not affect the tetrameric interface as confirmed by theoretical modeling, and the mutated amino acids are located outside the major immunogenic domain. Immunogenic properties of the LdNH36-dg2 recombinant protein were evaluated in BALB/c mice using formulations that included a synthetic CpG oligodeoxynucleotide, together with a microparticle delivery platform (poly(lactic-co-glycolic acid)). Mice exhibited high levels of IgG1, IgG2a, and IgG2b antibodies that were reactive to both LdNH36-dg2 and LdNH36 wild-type. While the point mutations did affect the hydrolase activity of the enzyme, the IgG antibodies elicited by LdNH36-dg2 were shown to inhibit the hydrolase activity of the wild-type LdNH36. The results indicate that LdNH36-dg2 as expressed in and purified from P. pastoris is suitable for further scale-up, manufacturing, and testing in support of future first-in-humans phase 1 clinical trials.

Coadminstration of L. major amastigote class I nuclease (rLmaCIN) with LPD nanoparticles delays the progression of skin lesion and the L. major dissemination to the spleen in BALB/c mice-based experimental setting

Human cutaneous leishmaniasis is a disease caused by eukaryotic single-celled Leishmania species, the developmental program of which relies upon blood-feeding adult female sand flies and their dominant mammal blood sources, namely wild rodents in area where human beings exert more or less transient activities. The recourse to model rodents - namely laboratory mice such as C57BL/6 mice - has allowed extracted the immune signatures that account for the healing of the transient cutaneous lesion that develops at the site where Leishmania major promastigotes were delivered. Indeed, if the latter mice are exposed to a second inoculum of L. major promastigotes, no lesion will develop in the secondary skin site remodeled as a niche for a low size intracellular L. major amastigote population. Moreover, IFN-γ dominates over IL-10 in the supernatant of cultures of PBMCs -prepared from blood sampled from human beings who healed from a cutaneous lesion- and incubated with L. major class I Nuclease LmaCIN, a protein highly expressed in the cell-cycling amastigote population which is dominant by macrophages. Altogether, these datasets were strong incentive to promote research aimed to design and monitor efficacy of L. major amastigote protein-based vaccines in pre-clinical settings. Using L. major enzyme class I nuclease (LmaCIN) expressed in the L. major cell-cycling amastigote population hosted by macrophages, BALB/c mice were immunized three times with either rLmaCIN plus LPD nanoparticles (LPD-rLmaCIN), or rLmaCIN-CpG DNA or free rLmaCIN and dextrose. The following parameters: footpad swelling, splenic L. major load, L. major binding IgGs and cytokine profiles of rLmaCIN- reactive T lymphocytes were then compared. Once coadminstered with LPD, rLmaCIN allow BALB/c mice to display delayed onset of skin lesion at the challenge inoculation site and delayed L. major dissemination from the challenged site to the spleen. Thus, the LPD-rLmaCIN is shown to display some promising features out of three formulations inoculated to the BALB/c mouse immunization.

Immunity, immunopathology, and human vaccine development against sexually transmitted Chlamydia trachomatis

This review examines the immunity, immunopathology, and contemporary problems of vaccine development against sexually transmitted Chlamydia trachomatis. Despite improved surveillance and treatment initiatives, the incidence of C. trachomatis infection has increased dramatically over the past 30 years in both the developed and developing world. Studies in animal models have shown that protective immunity to C. trachomatis is largely mediated by Th1 T cells producing IFN-γ which is needed to prevent dissemination of infection. Similar protection appears to develop in humans but in contrast to mice, immunity in humans may take years to develop. Animal studies and evidence from human infection indicate that immunity to C. trachomatis is accompanied by significant pathology in the upper genital tract. Although no credible evidence is currently available to indicate that autoimmunity plays a role, nevertheless, this underscores the necessity to design vaccines strictly based on chlamydial-specific antigens and to avoid those displaying even minimal sequence homologies with host molecules. Current advances in C. trachomatis vaccine development as well as alternatives for designing new vaccines for this disease are discussed. A novel approach for chlamydia vaccine development, based on targeting endogenous dendritic cells, is described.

The TLR2/6 ligand PAM2CSK4 is a Th2 polarizing adjuvant in Leishmania major and Brugia malayi murine vaccine models

Background

Toll-like receptors (TLRs) play an important role in the innate and adaptive immune responses to pathogens, and are the target of new vaccine adjuvants. TLR2 plays a role in parasite recognition and activation of immune responses during cutaneous leishmaniasis infection, suggesting that TLR2 could be targeted by adjuvants for use in Leishmania vaccines. We therefore explored using Pam₂CSK₄ (Pam2) and Pam₃CSK₄ (Pam3) lipopeptide adjuvants, which activate TLR2/6 and TLR2/1 heterodimers respectively, in vaccine models for parasitic infections.

Methods

The use of lipopeptide adjuvants was explored using two vaccine models. For cutaneous leishmaniasis, the lipopeptide adjuvants Pam2 and Pam3 were compared to that of the Th1-driving double-stranded DNA TLR9 agonist CpG for their ability to improve the efficacy of the autoclaved Leishmania major (ALM) vaccine to protect against L. major infection. The ability of Pam2 to enhance the efficacy of a soluble Brugia malayi microfilariae extract (BmMfE) vaccine to protect against filarial infection was also assessed in a peritoneal infection model of B. malayi filariasis. Parasite antigen-specific cellular and humoral immune responses were assessed post-challenge.

Results

The use of lipopeptides in ALM-containing vaccines did not provide any protection upon infection with L. major, and Pam2 exacerbated the disease severity in vaccinated mice post-challenge. Pam2, and to a lesser extent Pam3, were able to elevate antigen-specific immune responses post-challenge in this model, but these responses displayed a skewed Th2 phenotype as characterised by elevated levels of IgG1. In the B. malayi vaccine model, the use of Pam2 as an adjuvant with BmMfE induced significant protective immunity to the same level as inclusion of an Alum adjuvant. Here, both Pam2 and Alum were found to enhance antigen-specific antibody production post-challenge, and Pam2 significantly elevated levels of antigen-specific IL-4, IL-5 and IL-13 produced by splenocytes.

Conclusions

These data indicate that TLR2/6-targeting ligands could be considered as adjuvants for vaccines that require robust Th2 and/or antibody-dependent immunity.

Antigenic profile of heat-killed versus thimerosal-treated Leishmania major using sodium dodecyl sulfate-polyacrylamide gel electrophoresis

BACKGROUND

Leishmania is a parasitic protozoan of trypanosomatidae family which causes a wide spectrum of diseases ranging from self-healing cutaneous lesions to deadly visceral forms. In endemic areas, field trials of different preparations of Leishmania total antigen were tested as leishmaniasis vaccine. Two preparations of killed Leishmania major were produced In Iran, which were heat-killed vaccine called autoclaved L. major (ALM) and thimerosal-treated freeze-thawed vaccine called killed L. major (KLM). In this study, the protein content of both ALM and KLM were compared with that of freshly harvested intact L. major promastigotes using sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE).

MATERIALS AND METHODS

L. major (MRHO/IR/75/ER) from pre-infected Balb/c mice was isolated with modified Novy-MacNeal-Nicolle (NNN) medium and then subcultured in liquid RPMI 1640 medium supplemented with fetal calf serum (FCS) 20% for mass production. Two preparations of KLM and ALM were produced by Razi Vaccine and Serum Research Institute, Iran, under WHO/TDR supervision. Electrophoresis was performed by SDS-PAGE method and the gel was stained by Coomassie brilliant blue dye. The resultant unit bands were compared using standard molecular proteins.

RESULTS

Electrophoresis of the two preparations produced many bands from 10 kDa to 100 kDa. KLM bands were much like those of freshly harvested intact L. major.

CONCLUSION

It is concluded that although there are similar bands in the three forms of Leishmania antigens, there are some variations which might be considered for identification and purification of protective immunogens in a total crude antigen, and detection of their stability is essential for the production and marketing of a putative vaccine.

CD8+ T cells in cutaneous leishmaniasis: the good, the bad, and the ugly

CD8(+) T lymphocytes are components of the adaptive immune response and play an important role in protection against many viral and bacterial infections. However, their role in parasitic infections is less well understood. In leishmaniasis, a disease caused by intracellular protozoan parasites of the genus Leishmania, CD8(+) T cells have been shown to be protective. However, increasing evidence indicates that CD8(+) T cells may also exacerbate disease. In this review, we will describe the situations where CD8(+) T cells are either good or bad for the outcome of the infection and attempt to reconcile the dual role played by CD8(+) T cells in cutaneous leishmaniasis.

Coinjection with TLR2 agonist Pam3CSK4 reduces the pathology of leishmanization in mice

Cutaneous leishmaniasis caused by Leishmania major is an emergent, uncontrolled public health problem and there is no vaccine. A promising prophylactic approach has been immunotherapy with Toll-like receptor (TLR) agonists to enhance parasite-specific immune responses. We have previously reported that vaccination of C57BL/6 mice with live L. major plus the TLR9 agonist CpG DNA prevents lesion development and confers immunity to reinfection. Our current study aims to investigate whether other TLR agonists can be used in leishmanization without induction of lesion formation. We found that live L. major plus the TLR2 agonist Pam3CSK4 reduced the pathology in both genetically resistant (C57BL/6) and susceptible (BALB/c) mouse strains. The addition of Pam3CSK4 activated dermal dendritic cells and macrophages to produce greater amounts of proinflammatory cytokines in both mouse strains. Both Th1 and Th17 responses were enhanced by leishmanization with L. major plus Pam3CSK4 in C57BL/6 mice; however, Th17 cells were unchanged in BALB/c mice. The production of IL-17 from neutrophils was enhanced in both strains infected with L. major plus Pam3CSK4. However, the sustained influx of neutrophils in sites of infection was only observed in BALB/c mice. Our data demonstrate that the mechanism behind leishmanization with TLR agonists may be very different depending upon the immunological background of the host. This needs to be taken into account for the rational development of successful vaccines against the disease.

Cutaneous leishmaniasis is a skin infection caused by a protozoan parasite Leishmania major (L. major). The only available treatment option is chemotherapy, which is toxic and expensive. Currently, there is no vaccine. Although inoculation of virulent L. major (leishmanization) that provides effective protection in humans was widely applied, it was discontinued due to safety concerns. To improve the safety of leishmanization, we applied agonists of Toll-like receptor in the leishmanization to induce parasite-specific immune responses. In particular, we show here that inoculation with live L. major plus a TLR2 agonist Pam3CSK4 in both resistant (C57BL/6) and susceptible (BALB/c) mouse strains completely prevents the development of lesion and decreases parasite burden. The improved pathology is associated with enhanced production of IL-6 and IL-12 from dermal dendritic cells and macrophages. Both Th1 and Th17 responses are enhanced in C57BL/6 mice. Although only the Th1 response was enhanced in BALB/c mice in the presence of Pam3CSK4, there is an enhanced and sustained neutrophil influx at sites of infection. Overall, our study reveals the clinical significance of TLR2 agonist in treating cutaneous leishmaniasis. However, the protective mechanism may be quite different depending upon the genetic background of the host.

Identifying vaccine targets for anti-leishmanial vaccine development

Leishmaniasis is a neglected tropical disease spread by an arthropod vector. It remains a significant health problem with an incidence of 0.2–0.4 million visceral leishmaniasis and 0.7–1.2 million cutaneous leishmaniasis cases each year. There are limitations associated with the current therapeutic regimens for leishmaniasis and the fact that after recovery from infection the host becomes immune to subsequent infection therefore, these factors force the feasibility of a vaccine for leishmaniasis. Publication of the genome sequence of Leishmania has paved a new way to understand the pathogenesis and host immunological status therefore providing a deep insight in the field of vaccine research. This review is an effort to study the antigenic targets in Leishmania to develop an anti-leishmanial vaccine.

Evaluation of the immunoprophylactic potential of a killed vaccine candidate in combination with different adjuvants against murine visceral leishmaniasis

Despite a large number of field trials, till date no prophylactic antileishmanial vaccine exists for human use. Killed antigen formulations offer the advantage of being safe but they have limited immunogenicity. Recent research has documented that efforts to develop effective Leishmania vaccine have been limited due to the lack of an appropriate adjuvant. Addition of adjuvants to vaccines boosts and directs the immunogenicity of antigens. So, the present study was done to evaluate the effectiveness of four adjuvants i.e. alum, saponin, cationic liposomes and monophosphoryl lipid-A in combination with Autoclaved Leishmania donovani (ALD) antigen against murine visceral leishmaniasis (VL). BALB/c mice were immunized thrice with respective vaccine formulation. Two weeks after last booster, challenge infection was given. Mice were sacrificed 15 days after last immunization and on 30, 60 and 90 post infection/challenge days. A considerable protective efficacy was shown by all vaccine formulations. It was evident from significant reduction in parasite load, profound delayed type hypersensitivity responses (DTH), increased IgG2a titres and high levels of Th1 cytokines (IFN-γ, IL-12) as compared to the infected controls. However, level of protection varied with the type of adjuvant used. Maximum protection was achieved with the use of liposome encapsulated ALD antigen and it was closely followed by group immunized with ALD+MPL-A. Significant results were also obtained with ALD+saponin, ALD+alum and ALD antigen (alone) but the protective efficacy was reduced as compared to other immunized groups. The present study reveals greater efficacy of two vaccine formulations i.e. ALD+liposome and ALD+MPL-A against murine VL.

HBHA vaccination may require both Th1 and Th17 immune responses to protect mice against tuberculosis

Almost one century after the discovery of the BCG vaccine, tuberculosis remains a major cause of global mortality and morbidity, emphasizing the urgent need to design more efficient vaccines. The heparin-binding haemagglutinin (HBHA) appears to be a promising vaccine candidate, as it was shown to afford protection to mice against a challenge infection with Mycobacterium tuberculosis when combined with the strong adjuvant DDA/MPL (dimethyldioctadecyl-ammonium bromide/monophosphoryl lipid A), a TLR4 ligand. In this study, we investigated the immunological response and protection of mice immunized with HBHA formulated in lipid-containing nanoparticles and adjuvanted with CpG, a TLR9 ligand. Subcutaneous immunization with this HBHA formulation led to a marked Th1 response, characterized by high IFN-γ levels, but no significant IL-17 production, both in spleen and lung, in contrast to DDA/MPL MPL-formulated HBHA, which induced both IFN-γ and IL-17. This cytokine profile was also observed in BCG-primed mice and persisted after M. tuberculosis infection. No significant protection was obtained against challenge infection after vaccination with the nanoparticle-CpG formulation, and this was associated with a failure to mount a memory immune response. These results suggest the importance of both Th1 and Th17 immune responses for vaccine-induced immunity.

Time course study of the antigen-specific immune response to a PLGA microparticle vaccine formulation

Microparticle-based vaccine delivery systems are known to promote enhanced immune responses to protein antigens and can elicit TH1-biased responses when used in combination with Toll-like receptor (TLR) agonists. It is important to understand the kinetics of the immune responses to microparticle-based protein vaccines in order to predict the duration of protective immunity and to optimize prime-boost vaccination regimens. We carried out a 10-week time course study to investigate the magnitude and kinetics of the antibody and cellular immune responses to poly(lactic-co-glycolic acid) (PLGA) microparticles containing 40 μg ovalbumin (OVA) protein and 16 μg CpG-ODN adjuvant (MP/OVA/CpG) in comparison to OVA-containing microparticles, soluble OVA plus CpG, or OVA formulated with Alhydrogel(®) aluminum adjuvant. Mice vaccinated with MP/OVA/CpG developed the highest TH1-associated IgG2b and IgG2c antibody titers, while also eliciting TH2-associated IgG1 antibody titers on par with Alhydrogel(®)-formulated OVA, with all IgG subtype titers peaking at day 56. The MP/OVA/CpG vaccine also induced the highest antigen-specific splenocyte IFN-γ responses, with high levels of IFN-γ responses persisting until day 42. Thus the MP/OVA/CpG formulation produced a sustained and heightened humoral and cellular immune response, with an overall TH1 bias, while maintaining high levels of IgG1 antibody equivalent to that seen with Alhydrogel(®) adjuvant. The time course kinetics study provides a useful baseline for designing vaccination regimens for microparticle-based protein vaccines.

MyD88 and TLR9 dependent immune responses mediate resistance to Leishmania guyanensis infections, irrespective of Leishmania RNA virus burden

Infections with Leishmania parasites of the Leishmania Viannia subgenus give rise to both localized cutaneous (CL), and metastatic leishmaniasis. Metastasizing disease forms including disseminated (DCL) and mutocutaneous (MCL) leishmaniasis result from parasitic dissemination and lesion formation at sites distal to infection and have increased inflammatory responses. The presence of Leishmania RNA virus (LRV) in L. guyanensis parasites contributes to the exacerbation of disease and impacts inflammatory responses via activation of TLR3 by the viral dsRNA. In this study we investigated other innate immune response adaptor protein modulators and demonstrated that both MyD88 and TLR9 played a crucial role in the development of Th1-dependent healing responses against L. guyanensis parasites regardless of their LRV status. The absence of MyD88- or TLR9-dependent signaling pathways resulted in increased Th2 associated cytokines (IL-4 and IL-13), which was correlated with low transcript levels of IL-12p40. The reliance of IL-12 was further confirmed in IL12AB^−/− mice, which were completely susceptible to infection. Protection to L. guyanensis infection driven by MyD88- and TLR9-dependent immune responses arises independently to those induced due to high LRV burden within the parasites.

Vaccination with Leishmania mexicana LPG induces PD-1 in CD8⁺ and PD-L2 in macrophages thereby suppressing the immune response: a model to assess vaccine efficacy

Leishmania lipophosphoglycan (LPG) is a molecule that has been used as a vaccine candidate, with contradictory results. Since unsuccessful protection could be related to suppressed T cell responses, we analyzed the expression of inhibitory receptor PD-1 in CD8(+) and CD4(+) lymphocytes and it is ligand PD-L2 in macrophages of BALB/c mice immunized with various doses of Leishmania mexicana LPG and re-stimulated in vitro with different concentrations of LPG. Vaccination with LPG enhanced the expression of PD-1 in CD8(+) cells. Activation molecules CD137 were reduced in CD8(+) cells from vaccinated mice. In vitro re-stimulation enhanced PD-L2 expression in macrophages of healthy mice in a dose-dependent fashion. The expression of PD-1, PD-L2 and CD137 is modulated according to the amount of LPG used during immunization and in vitro re-stimulation. We analyzed the expression of these molecules in mice infected with 1×10(4) or 1×10(5)L. mexicana promastigotes and re-stimulated in vitro with LPG. Infection with 1×10(5) parasites increased the PD-1 expression in CD8(+) and diminished PD-L2 in macrophages. When these CD8(+) cells were re-stimulated in vitro with LPG, simulating a second exposure to parasite antigens, PD-1 expression increased significantly more, in a dose dependent fashion. We conclude that CD8(+) T lymphocytes and macrophages express inhibition molecules according to the concentrations of Leishmania LPG and to the parasite load. Vaccination with increased amounts of LPG or infections with higher parasite numbers induces enhanced expression of PD-1 and functional inactivation of CD8(+) cells, which can have critical consequences in leishmaniasis, since these cells are crucial for disease control. These results call for pre-vaccination evaluations of potential immunogens, specifically where CD8 cells are required, since inhibiting molecules can be induced after certain thresholds of antigen concentrations. We propose that the analysis of PD-1 and PD-L2 are useful tools to monitor the optimal dose for vaccination candidates.

Cross-protective effect of a combined L5 plus L3 Leishmania major ribosomal protein based vaccine combined with a Th1 adjuvant in murine cutaneous and visceral leishmaniasis

Background

Two Leishmania major ribosomal proteins L3 (LmL3) and L5 (LmL5) have been described as protective molecules against cutaneous leishmaniasis due to infection with L. major and Leishmania braziliensis in BALB/c mice when immunized with a Th1 adjuvant (non-methylated CpG-oligodeoxynucleotides; CpG-ODN). In the present study we analyzed the cross-protective efficacy of an LmL3-LmL5-CpG ODN combined vaccine against infection with Leishmania amazonensis and Leishmania chagasi (syn. Leishmania infantum) the etiologic agents of different clinical forms of human leishmaniasis in South America.

Methods

The combined vaccine was administered subcutaneously to BALB/c mice. After immunization the cellular and humoral responses elicited were analyzed. Mice were independently challenged with L. amazonensis and L. chagasi. The size of the cutaneous lesions caused by the infection with the first species, the parasite loads and the immune response in both infection models were analyzed nine weeks after challenge.

Results

Mice vaccinated with the combined vaccine showed a Th1-like response against LmL3 and LmL5. Vaccinated mice were able to delay lesion development due to L. amazonensis infection and to control parasite loads in the site of infection. A reduction of the parasite burden in the lymph nodes draining the site of infection and in the liver and spleen was observed in the vaccinated mice after a subcutaneous infection with L. chagasi. In both models of infection, protection was correlated to parasite antigen-specific production of IFN-γ and down-regulation of parasite-mediated IL-4 and IL-10 responses.

Conclusions

The data presented here demonstrate the potential use of L. major L3 and L5 recombinant ribosomal proteins for the development of vaccines against various Leishmania species.

Whole recombinant Pichia pastoris expressing HPV16 L1 antigen is superior in inducing protection against tumor growth as compared to killed transgenic Leishmania

The development of an efficient vaccine against high-risk HPV types can reduce the incidence rates of cervical cancer by generating anti-tumor protective responses. Traditionally, the majority of prophylactic viral vaccines are composed of live, attenuated or inactivated viruses. Among them, the design of an effective and low-cost vaccine is critical. Inactivated vaccines especially heat-killed yeast cells have emerged as a promising approach for generating antigen-specific immunotherapy. Recent studies have indicated that yeast cell wall components possess adjuvant activities. Moreover, a non-pathogenic protozoan, Leishmania tarentolae (L.tar) has attracted a great attention as a live candidate vaccine. In current study, immunological and protective efficacy of whole recombinant killed Pichia pastoris and Leishmania tarentolae expressing HPV16 L1 capsid protein was evaluated in tumor mice model. We found that Pichia-L1, L.tar-L1 and Gardasil groups increase the IgG2a/IgG1 ratio, indicating a relative preference for the induction of Th1 immune responses. Furthermore, subcutaneous injection of killed Pichia-L1 generated the significant L1-specific IFN-γ immune response as well as the best protective effects in vaccinated mice as compared to killed L.tar-L1, killed Pichia pastoris, killed L.tar and PBS groups. Indeed, whole recombinant Leishmania tarentolae could not protect mice against C3 tumor mice model. These data suggest that Pichia-L1 may be a candidate for the control of HPV infections.

Leishmania expressed lipophosphoglycan interacts with Toll-like receptor (TLR)-2 to decrease TLR-9 expression and reduce anti-leishmanial responses

Two different Toll-like receptors (TLRs) have been shown to play a role in host responses to Leishmania infection. TLR-2 is involved in parasite survival in macrophages upon activation by lipophosphoglycan (LPG), a virulence factor expressed by Leishmania. In contrast, activation of TLR-9 has been shown to promote a host-protective response. However, whether there is a relationship between the interaction of LPG and TLR-2, on one hand, with the effect of TLR-9, on the other hand, remains unknown. In this study, we report that in-vitro infection of macrophages with a L. major parasite with high expression levels of LPG results in decreased TLR-9 expression compared to infection with a L. major parasite with lower expression levels of LPG. Addition of anti-LPG as well as anti-TLR-2 antibodies prevents this reduction of TLR-9 expression. Also, the addition of purified LPG to macrophages results in a decrease of TLR-9 expression, which is shown to be mediated by transforming growth factor (TGF)-β and interleukin (IL)-10. Finally, in-vitro treatment of macrophages with anti-LPG and/or anti-TLR-2 antibodies before infection reduces the number of amastigotes in macrophages and co-treatment of mice with anti-TLR-2 antibodies and cytosine-phosphate-guanosine (CpG) reduces footpad swelling and parasite load in the draining lymph nodes, accompanied by an interferon (IFN)-γ-predominant T cell response. Thus, for the first time, we show how interactions between LPG and TLR-2 reduce anti-leishmanial responses via cytokine-mediated decrease of TLR-9 expression.

Case study for a vaccine against leishmaniasis

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

Evaluation of immune responses and analysis of the effect of vaccination of the Leishmania major recombinant ribosomal proteins L3 or L5 in two different murine models of cutaneous leishmaniasis

Four new antigenic proteins located in Leishmania ribosomes have been characterized: S4, S6, L3 and L5. Recombinant versions of the four ribosomal proteins from Leishmania major were recognized by sera from human and canine patients suffering different clinical forms of leishmaniasis. The prophylactic properties of these proteins were first studied in the experimental model of cutaneous leishmaniasis caused by L. major inoculation into BALB/c mice. The administration of two of them, LmL3 or LmL5 combined with CpG-oligodeoxynucleotides (CpG-ODN) was able to protect BALB/c mice against L. major infection. Vaccinated mice showed smaller lesions and parasite burden compared to mice inoculated with vaccine diluent or vaccine adjuvant. Protection was correlated with an antigen-specific increased production of IFN-γ paralleled by a decrease of the antigen-specific IL-10 mediated response in protected mice relative to non-protected controls. Further, it was demonstrated that BALB/c mice vaccinated with recombinant LmL3 or LmL5 plus CpG-ODN were also protected against the development of cutaneous lesions following inoculation of L. braziliensis. Together, data presented here indicate that LmL3 or LmL5 ribosomal proteins combined with Th1 inducing adjuvants, may be relevant components of a vaccine against cutaneous leishmaniasis caused by distinct species.

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

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

The role of liposome-protamine-DNA nanoparticles containing CpG oligodeoxynucleotides in the course of infection induced by Leishmania major in BALB/c mice

An inoculation of virulent Leishmania major is known as leishmanization (LZ) which is proven to be the most effective control measure against cutaneous leishmaniasis (CL) and mimic natural infection. However, use of LZ is restricted due to various reasons such as development of uncontrolled lesion. In the present study, the efficacy of coadminstration of live L. major with liposome-protamine-DNA nanoparticles (LPD) containing immunostimulatory CpG oligodeoxynucleotides (CpG ODN) which is an improved adjuvant delivery system is examined to check Leishmania pathology and immune response generated. BALB/c mice were inoculated subcutaneously (SC) with L. major plus LPD (CpG), CpG ODN or PBS buffer. The results showed that group of mice received LPD nanoparticles developed a significantly smaller lesion and the mice in this group showed minimum number of L. major in the spleen and lymph nodes. In addition, using LPD (CpG) resulted in a Th1 type of immune response with a preponderance of IgG2a isotype which is concurrent with the production of LPD induced IFN-γ in the spleen of the mice. Taken together, the results suggested that immune modulation using LPD nanoparticles might be a practical approach to improve the safety of LZ.

Making an anti-amastigote vaccine for visceral leishmaniasis: rational, update and perspectives

Visceral leishmaniasis is a major health problem in Latina America, as well as the Mediterranean region of Europe and Asia. We aimed to develop a vaccine against visceral leishmaniasis targeting the intracellular amastigotes, which is the parasite stage that persists throughout infections with Leishmania parasites. With this in mind, we identified an amastigote specific antigen (A2) that contains an immunogenic epitope for CD4+ T helper (Th) cells and multiple repetitive units encoding CD8+ cytotoxic T lymphocyte (CTL) epitopes. Vaccine formulations containing the recombinant A2 associated with saponin, alum and IL-12 or expressed by attenuated adenovirus were shown to be protective in mice, dogs and nonhuman-primates. We are currently identifying novel amastigote specific immunogenic proteins that could be aggregated to A2 to further improve the level of vaccine-induced cell-mediated immunity and protection against visceral leishmaniasis.

Adjuvants for Leishmania vaccines: from models to clinical application

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

Proteins of Leishmania (Viannia) shawi confer protection associated with Th1 immune response and memory generation

BACKGROUND

Leishmania (Viannia) shawi parasite was first characterized in 1989. Recently the protective effects of soluble leishmanial antigen (SLA) from L. (V.) shawi promastigotes were demonstrated using BALB/c mice, the susceptibility model for this parasite. In order to identify protective fractions, SLA was fractionated by reverse phase HPLC and five antigenic fractions were obtained.

METHODS

F1 fraction was purified from L. (V.) shawi parasite extract by reverse phase HPLC. BALB/c mice were immunized once a week for two consecutive weeks by subcutaneous routes in the rump, using 25 μg of F1. After 1 and 16 weeks of last immunization, groups were challenged in the footpad with L. (V.) shawi promastigotes. After 2 months, those same mice were sacrificed and parasite burden, cellular and humoral immune responses were evaluated.

RESULTS

The F1 fraction induced a high degree of protection associated with an increase in IFN-γ, a decrease in IL-4, increased cell proliferation and activation of CD8+T lymphocytes. Long-term protection was acquired in F1-immunized mice, associated with increased CD4+ central memory T lymphocytes and activation of both CD4+ and CD8+ T cells. In addition, F1-immunized groups showed an increase in IgG2a levels.

CONCLUSIONS

The inductor capability of antigens to generate memory lymphocytes that can proliferate and secrete beneficial cytokines upon infection could be an important factor in the development of vaccine candidates against American Tegumentary Leishmaniasis.

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

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

Cationic liposomes containing soluble Leishmania antigens (SLA) plus CpG ODNs induce protection against murine model of leishmaniasis

Development of an effective vaccine against leishmaniasis is possible due to the fact that individuals cured from cutaneous leishmaniasis (CL) are protected from further infection. First generation Leishmania vaccines consisting of whole killed parasites reached to phase 3 clinical trials but failed to show enough efficacies mainly due to the lack of an appropriate adjuvant. In this study, an efficient liposomal protein-based vaccine against Leishmania major infection was developed using soluble Leishmania antigens (SLA) as a first generation vaccine and cytidine phosphate guanosine oligodeoxynucleotides (CpG ODNs) as an immunostimulatory adjuvant. 1, 2-Dioleoyl-3-trimethylammonium-propane was used as a cationic lipid to prepare the liposomes due to its intrinsic adjuvanticity. BALB/c mice were immunized subcutaneously (SC), three times in 2-week intervals, with Lip-SLA-CpG, Lip-SLA, SLA + CpG, SLA, or HEPES buffer. As criteria for protection, footpad swelling at the site of challenge and spleen parasite loads were assessed, and the immune responses were evaluated by determination of IFN-γ and IL-4 levels of cultured splenocytes, and IgG subtypes. The group of mice that received Lip-SLA-CpG showed a significantly smaller footpad swelling, lower spleen parasite burden, higher IgG2a antibody, and lower IL-4 level compared to the control groups. It is concluded that cationic liposomes containing SLA and CpG ODNs are appropriate to induce Th1 type of immune response and protection against leishmaniasis.

Comparison of in vivo Adjuvanticity of Liposomal PO CpG ODN with Liposomal PS CpG ODN: Soluble Leishmania Antigens as a Model

OBJECTIVES

CpG oligodeoxynucleotides (CpG ODNs) have been shown to have potent immunostimulatory adjuvant activity for a wide range of antigens. Due to susceptibility of phosphodiester CpG ODNs (PO CpG) to nuclease degradation, nuclease-resistant phosphorothioate CpG ODNs (PS CpG) were currently utilized in an in vivo model. In this study, according to some recently reported drawbacks with PS CpG, the adjuvant potential of liposomal PO CpG as a substitute for PS CpG was evaluated.

MATERIALS AND METHODS

Soluble Leishmania antigens (SLA) as a model antigen and distearoylphosphatidylcoline (DSPC) as a neutral lipid were employed to prepare liposomes. Susceptible BALB/c mice received buffer, SLA, Lip-SLA, Lip-SLA-PS CpG, Lip-SLA-PO CpG, SLA+PS CpG, or SLA+PO CpG subcutaneously 3 times with 3 weeks intervals and then were challenged with Leishmania major's live promastigotes. Blood and spleen samples were analyzed to determine the level and type of antibodies and cytokines. The number of live parasites in the spleen of immunized mice was determined. Moreover, the lesion size progress was assessed weekly by footpad swelling measurement.

RESULTS

The results showed that mice immunized with Lip-SLA-PS CpG or Lip-SLA-PO CpG developed a significantly smaller footpad swelling, higher level of anti SLA IgG antibodies before and after challenge, and lower spleen parasite burden compared with the control groups. However, there was no significant difference between mice received Lip-SLA-PS CpG and those received Lip-SLA-PO CpG.

CONCLUSION

The results demonstrated that liposomal PO CpG ODN could be used instead of PS CpG ODN to overcome the possible drawbacks.

Vaccination with liposomal leishmanial antigens adjuvanted with monophosphoryl lipid-trehalose dicorynomycolate (MPL-TDM) confers long-term protection against visceral leishmaniasis through a human administrable route

The development of a long-term protective subunit vaccine against visceral leishmaniasis depends on antigens and adjuvants that can induce an appropriate immune response. The immunization of leishmanial antigens alone shows limited efficacy in the absence of an appropriate adjuvant. Earlier we demonstrated sustained protection against Leishmania donovani with leishmanial antigens entrapped in cationic liposomes through an intraperitoneal route. However, this route is not applicable for human administration. Herein, we therefore evaluated the immune response and protection induced by liposomal soluble leishmanial antigen (SLA) formulated with monophosphoryl lipid-trehalose dicorynomycolate (MPL-TDM) through a subcutaneous route. Subcutaneous immunization of BALB/c mice with SLA entrapped in liposomes or with MPL-TDM elicited partial protection against experimental visceral leishmaniasis. In contrast, liposomal SLA adjuvanted with MPL-TDM induced significantly higher levels of protection in liver and spleen in BALB/c mice challenged 10 days post-vaccination. Protection conferred by this formulation was sustained up to 12 weeks of immunization, and infection was controlled for at least 4 months of the challenge, similar to liposomal SLA immunization administered intraperitoneally. An analysis of cellular immune responses of liposomal SLA + MPL-TDM immunized mice demonstrated the induction of IFN-γ and IgG2a antibody production not only 10 days or 12 weeks post-vaccination but also 4 months after the challenge infection and a down regulation of IL-4 production after infection. Moreover, long-term immunity elicited by this formulation was associated with IFN-γ production also by CD8⁺ T cells. Taken together, our results suggest that liposomal SLA + MPL-TDM represent a good vaccine formulation for the induction of durable protection against L. donovani through a human administrable route.

Preparation and evaluation of niosomes containing autoclaved Leishmania major: a preliminary study

In this study, different positively charged niosomal formulations containing sorbitan esters, cholesterol and cetyl trimethyl ammonium bromide were prepared by film hydration method for the entrapment of autoclaved Leishmania major (ALM). Size distribution pattern and stability of niosomes were investigated by laser light scattering method and ALM encapsulation per cent was measured by the bicinchoninic acid method. Finally, the selected formulation was used for the induction of the immune response against cutaneous leishmaniasis in BALB/c mice. Size distribution curves of all the formulations followed a log-normal pattern and the mean volume diameter was in the range 7.57-15.80 µm. The mean volume diameters were significantly increased by adding Tween to Span formulations (p < 0.05). The percentage of ALM entrapped in all formulations varied between 14.88% and 36.65%. In contrast to ALM, in vivo studies showed that the niosomes containing ALM have a moderate effect in the prevention of cutaneous leishmaniasis in BALB/c mice.

Recombinant BCG coexpressing Ag85B, CFP10, and interleukin-12 induces multifunctional Th1 and memory T cells in mice

Mycobacterium tuberculosis (MTB) continues to be a leading cause of human deaths due to an infectious agent. Current efforts are focused on making better TB vaccines. We describe the generation and immunological characterization of recombinant BCG (rBCG). This rBCG was generated by incorporating an expression plasmid encoding two mycobacterial antigens (Ag85B and CFP10) and human interleukin (IL)-12 into a BCG strain. Immunogenicity studies in mice showed that rBCG coexpressing Ag85B, CFP10, and IL-12 (rBCG::Ag85B-CFP10-IL-12) induces a robust immune response in mice. The rBCG vaccine promotes a T-cell response against MTB that is characterized by a high proportion of polyfunctional and memory T cells in spleen and lung. Our results showed strong immunogenicity and mycobacterial growth inhibition of rBCG::Ag85B-CFP10 plus IL-12 than that of BCG vaccine.