Coinjection with CpG-containing immunostimulatory oligodeoxynucleotides reduces the pathogenicity of a live vaccine against cutaneous Leishmaniasis but maintains its potency and durability

Adjuvants in cutaneous vaccination: A comprehensive analysis

Skin is the body's largest organ and serves as a protective barrier from physical, thermal, and mechanical environmental challenges. Alongside, the skin hosts key immune system players, such as the professional antigen-presenting cells (APCs) like the Langerhans cells in the epidermis and circulating macrophages in the blood. Further, the literature supports that the APCs can be activated by antigen or vaccine delivery via multiple routes of administration through the skin. Once activated, the stimulated APCs drain to the associated lymph nodes and gain access to the lymphatic system. This further allows the APCs to engage with the adaptive immune system and activate cellular and humoral immune responses. Thus, vaccine delivery via skin offers advantages such as reliable antigen delivery, superior immunogenicity, and convenient delivery. Several preclinical and clinical studies have demonstrated the significance of vaccine delivery using various routes of administration via skin. However, such vaccines often employ adjuvant/(s), along with the antigen of interest. Adjuvants augment the immune response to a vaccine antigen and improve the therapeutic efficacy. Due to these reasons, adjuvants have been successfully used with infectious disease vaccines, cancer immunotherapy, and immune-mediated diseases. To capture these developments, this review will summarize preclinical and clinical study results of vaccine delivery via skin in the presence of adjuvants. A focused discussion regarding the FDA-approved adjuvants will address the experiences of using such adjuvant-containing vaccines. In addition, the challenges and regulatory concerns with these adjuvants will be discussed. Finally, the review will share the prospects of adjuvant-containing vaccines delivered via skin.

Flublok Quadrivalent Vaccine Adjuvanted with R-DOTAP Elicits a Robust and Multifunctional CD4 T Cell Response That Is of Greater Magnitude and Functional Diversity Than Conventional Adjuvant Systems

It is clear that new approaches are needed to promote broadly protective immunity to viral pathogens, particularly those that are prone to mutation and escape from antibody-mediated immunity. CD4+ T cells, known to target many viral proteins and highly conserved peptide epitopes, can contribute greatly to protective immunity through multiple mechanisms. Despite this potential, CD4+ T cells are often poorly recruited by current vaccine strategies. Here, we have analyzed a promising new adjuvant (R-DOTAP), as well as conventional adjuvant systems AddaVax with or without an added TLR9 agonist CpG, to promote CD4+ T cell responses to the licensed vaccine Flublok containing H1, H3, and HA-B proteins. Our studies, using a preclinical mouse model of vaccination, revealed that the addition of R-DOTAP to Flublok dramatically enhances the magnitude and functionality of CD4+ T cells specific for HA-derived CD4+ T cell epitopes, far outperforming conventional adjuvant systems based on cytokine EliSpot assays and multiparameter flow cytometry. The elicited CD4+ T cells specific for HA-derived epitopes produce IL-2, IFN-γ, IL-4/5, and granzyme B and have multifunctional potential. Hence, R-DOTAP, which has been verified safe by human studies, can offer exciting opportunities as an immune stimulant for next-generation prophylactic recombinant protein-based vaccines.

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 .

Using Adjuvants to Drive T Cell Responses for Next-Generation Infectious Disease Vaccines

Using adjuvants to drive features of T cell responses to vaccine antigens is an important technological challenge in the design of new and improved vaccines against infections. Properties such as T helper cell function, T cell memory, and CD8+ T cell cytotoxicity may play critical roles in optimal and long-lived immunity through vaccination. Directly manipulating specific immune activation or antigen delivery pathways with adjuvants may selectively augment desired T cell responses in vaccination and may improve the effectiveness and durability of vaccine responses in humans. In this review we outline recently studied adjuvants in their potential for antigen presenting cell and T cell programming during vaccination, with an emphasis on what has been observed in studies in humans as available.

CpG Oligonucleotides as Vaccine Adjuvants

CpG Oligonucleotides (ODN) are immunomodulatory synthetic oligonucleotides specifically designed to stimulate Toll-like receptor 9. TLR9 is expressed on human plasmacytoid dendritic cells and B cells and triggers an innate immune response characterized by the production of Th1 and pro-inflammatory cytokines. This chapter reviews recent progress in understanding the mechanism of action of CpG ODN and provides an overview of human clinical trial results using CpG ODN to improve vaccines for the prevention/treatment of cancer, allergy, and infectious disease.

Evaluation of Leishmanization Using Iranian Lizard Leishmania Mixed With CpG-ODN as a Candidate Vaccine Against Experimental Murine Leishmaniasis

Background and Objectives: The live non-pathogenic Leishmania tarantolae has recently provided a promising approach as an effective vaccine candidate against experimental leishmaniasis (ILL). Here, we evaluated the immunoprotective potential of the live Iranian Lizard Leishmania mixed with CpG adjuvant against L. major infection in BALB/c mice.

Methods: Four groups of female BALB/c mice were included in the study. The first and second groups received PBS and CpG, respectively. The immunized groups received 2 × 10⁵ ILL promastigotes and the CpG-mixed ILL (ILL+CpG). Injections were performed subcutaneously in the right footpad. Three weeks later, all mice were challenged with 2 × 10⁵ metacyclic promastigotes of Leishmania major^EGFP; inoculation was done in the left footpad. The measurement of footpad swelling and in vivo fluorescent imaging were used to evaluate disease progress during infection course. Eight weeks after challenge, all mice were sacrificed and the cytokines levels (IFN-γ, IL-4, and IL-10) and sera antibodies concentrations (IgG2a and IgG1) using ELISA assay, nitric oxide production using Griess assay, and arginase activity in cultured splenocytes, were measured. In addition, direct fluorescent microscopy analysis and qPCR assay were used to quantify the splenic parasite burden.

Result: The results showed that mice immunized with ILL+CpG were protected against the development of the dermal lesion. Moreover, they showed a significant reduction in the parasite load, in comparison to the control groups. The observed protection was associated with higher production of IFN-γ, as well as a reduction in IL-4 level. Additionally, the results demonstrated that arginase activity was decreased in ILL+CpG group compared to other groups.

Conclusion: Immunization using ILL+CpG induces a protective immunity; indicating that ILL with an appropriate adjuvant would be a suitable choice for vaccination against leishmaniasis.

Simultaneous formulation of influenza vaccine and chitosan nanoparticles within CpG oligodesoxi nucleotides leads to dose-sparing and protects against lethal challenge in the mouse model

Lack of efficient delivery systems for transporting antigenic molecules to the cytosol of antigen-presenting cells presents a major obstacle for antigen uptake by immune cells. To this end, influenza whole inactivated virus vaccines were formulated with chitosan nanoparticles and CpG oligonucleotide as a biodegradable delivery system and a Th1-specific adjuvant, respectively. Intradermal injections of a single high dose and low dose of formulated candidate vaccines were carried out. Thirty days after injection, cell proliferation assay (MTT), IFN-gamma and IL-4 ELISpot assays were conducted. Sera samples were collected 21 days after immunization to measure IgG1 and IgG2a levels. In addition, the mice challenged with mouse-adopted virus were monitored for weight loss. The results show a significant stimulation of both humoral and cellular immunities; also, weight gain and a decrease in mortality in the mice receiving both dosages of inactivated influenza virus vaccines with CpG and Chitosan coating were observed. Based on the results, it can be concluded that formulation of inactivated influenza virus with CpG and its delivery by chitosan as low-dose can return the same results as with high-dose balanced between cellular and humeral immune responses. This formulation could potentially lead to a significant saving in vaccine production.

Clinical Effects of CpG-Based Treatment on the Efficacy of Hepatocellular Carcinoma by Skewing Polarization Toward M1 Macrophage from M2

OBJECTIVE

This study aims to explore the clinical efficacy of CpG-based therapy for treating hepatocellular carcinoma (HCC) by skewing polarization toward M1 macrophage from M2.

METHODS

Pulmonary metastasis rate, overall survival time, and remission rate of 10 patients with HCC treated with transcatheter arterial chemoembolization (TACE) combined with CpG therapy and 10 age-, gender-, and TNM₀-matched patients treated with TACE (control group) were compared.

RESULTS

No pulmonary metastasis rate was 70% in the combined treatment group and 40% in the control group, respectively; and the differences between the two groups were statistically significant (p < 0.05). Median overall survival time was 22 months in the combined treatment group, compared with 6.65 months in the control group (p < 0.05). Remission rate in the combined treatment group (70%) was higher than in the control group (30%), but the differences between these two groups were not statistically significant (p > 0.05).

CONCLUSION

Compared with TACE, CpG combined with TACE can decrease the pulmonary metastasis rate. This combined therapy can also improve the overall survival time of patients.

The role of LPD-nanoparticles containing recombinant major surface glycoprotein of Leishmania (rgp63) in protection against leishmaniasis in murine model

CONTEXT

Leishmaniasis is a major public health problem. Despite numerous attempts, yet there is no effective vaccine against human leishmaniasis, mainly due to a lack of an effective vaccine delivery system as well as adjuvant.

OBJECTIVE(S)

The aim of this study was to evaluate the ability of recombinant glycoprotein 63 (rgp63) as a model of Leishmania antigen, entrapped in liposome-polycation-DNA (LPD) complexes nanoparticles in inducing cell mediated immune (CMI) response and protecting against L. major in BALB/c mice.

MATERIALS AND METHODS

To this end, the abundant leishmania promastigote cell surface glycoprotein, gp63, was entrapped in nano-sized LPD (CpG) particles, (LPD (CpG)-rgp63), and BALB/c mice were immunized three times with either (LPD (CpG)-rgp63) or rgp63-CpG DNA or LPD (CpG) or free rgp63 and dextrose 5%. Various parameters including footpad thickness, splenic load of L. major parasites, rgp63-binding IgGs and also cytokine levels of rgp63-reactive T lymphocytes were then compared among different vaccinated animals.

RESULTS

The lowest number of parasites in spleen, the higher levels of IgG2a after challenge infection, the minimal footpad swelling and high level of IFN-γ secretion, all indicated that adjuvants and antigen-delivery systems are essential in modifying immune responses; as mice received LPD (CpG)-rgp63 induced immune response stronger than the other groups.

CONCLUSIONS

This study demonstrates that LPD nanoparticle is a promising and adaptable delivery system which could be modified towards specific vaccine targets to induce a more potent immune response in combination with rgp63.

Concomitant Immunity Induced by Persistent Leishmania major Does Not Preclude Secondary Re-Infection: Implications for Genetic Exchange, Diversity and Vaccination

BACKGROUND

Many microbes have evolved the ability to co-exist for long periods of time within other species in the absence of overt pathology. Evolutionary biologists have proposed benefits to the microbe from 'asymptomatic persistent infections', most commonly invoking increased likelihood of transmission by longer-lived hosts. Typically asymptomatic persistent infections arise from strong containment by the immune system, accompanied by protective immunity; such 'vaccination' from overt disease in the presence of a non-sterilizing immune response is termed premunition or concomitant immunity. Here we consider another potential benefit of persistence and concomitant immunity to the parasite: the 'exclusion' of competing super-infecting strains, which would favor transmission of the original infecting organism.

METHODOLOGY / PRINCIPLE FINDINGS

To investigate this in the protozoan parasite Leishmania major, a superb model for the study of asymptomatic persistence, we used isogenic lines of comparable virulence bearing independent selectable markers. One was then used to infect genetically resistant mice, yielding infections which healed and progressed to asymptomatic persistent infection; these mice were then super-infected with the second marked line. As anticipated, super-infection yielded minimal pathology, showing that protective immunity against disease pathology had been established. The relative abundance of the primary and super-infecting secondary parasites was then assessed by plating on selective media. The data show clearly that super-infecting parasites were able to colonize the immune host effectively, achieving numbers comparable to and sometimes greater than that of the primary parasite.

CONCLUSIONS / SIGNIFICANCE

We conclude that induction of protective immunity does not guarantee the Leishmania parasite exclusive occupation of the infected host. This finding has important consequences to the maintenance and generation of parasite diversity in the natural Leishmania infectious cycle alternating between mammalian and sand fly hosts.

Synthetic innate defense regulator peptide combination using CpG ODN as a novel adjuvant induces long‑lasting and balanced immune responses

Vaccines are critical tools for the prevention and treatment of several diseases. Adjuvants have been traditionally used to enhance immunity to vaccines and experimental antigens. In the present study, the adjuvant combination of CpG oligodeoxynucleotides (CpG ODN) and the innate defense regulator (IDR) peptide, IDR‑HH2, was evaluated for its ability to enhance and modulate the immune response when formulated with alum and the recombinant hepatitis B surface antigen (HBsAg). The CpG‑HH2 complex enhanced the secretions of tumor necrosis factor‑α, monocyte chemotactic protein 1 and interferon‑γ by human peripheral blood mononuclear cells and promoted murine bone marrow dentritic cell maturation. In addition, the present study demonstrated that IDR‑HH2 was chemotactic for human neutrophils, THP‑1 cells and RAW264.7 cells at concentrations between 2.5 and 40 µg/ml. The present study also observed that significantly higher anti‑HBs antibody titers, which were sustained at high levels for as long as 35 weeks following the boost immunization, were induced by the combination adjuvant, even when co‑administered with a commercial hepatitis B vaccine at a low antigen dose (0.1 µg HBsAg). Notably, the level of IgG2a was almost equal to the level of IgG1, indicating that a balanced T helper (Th)1/Th2 immune response was elicited by the novel vaccine, which was consistent with the ELISpot results. These data suggest that the CpG‑HH2 complex may be a potential effective adjuvant, which facilitates a reduction in the dose of antigen and induces long‑lasting, balanced immune responses.

The generation of CD8+ T-cell population specific for vaccinia virus epitope involved in the antiviral protection against ectromelia virus challenge

Eradication of smallpox has led to cessation of vaccination programs. This has rendered the human population increasingly susceptible not only to variola virus infection but also to infections with other representatives of Poxviridae family that cause zoonotic variola-like diseases. Thus, new approaches for designing improved vaccine against smallpox are required. Discovering that orthopoxviruses, e.g. variola virus, vaccinia virus, ectromelia virus, share common immunodominant antigen, may result in the development of such a vaccine. In our study, the generation of antigen-specific CD8(+) T cells in mice during the acute and memory phase of the immune response was induced using the vaccinia virus immunodominant TSYKFESV epitope and CpG oligodeoxynucleotides as adjuvants. The role of the generated TSYKFESV-specific CD8(+) T cells was evaluated in mice during ectromelia virus infection using systemic and mucosal model. Moreover, the involvement of dendritic cells subsets in the adaptive immune response stimulation was assessed. Our results indicate that the TSYKFESV epitope/TLR9 agonist approach, delivered systemically or mucosally, generated strong CD8(+) T-cell response when measured 10 days after immunization. Furthermore, the TSYKFESV-specific cell population remained functionally active 2 months post-immunization, and gave cross-protection in virally challenged mice, even though the numbers of detectable antigen-specific T cells decreased.

Cutaneous Infection with Leishmania major Mediates Heterologous Protection against Visceral Infection with Leishmania infantum

Visceral leishmaniasis (VL) is a fatal disease of the internal organs caused by the eukaryotic parasite Leishmania. Control of VL would best be achieved through vaccination. However, this has proven to be difficult partly because the correlates of protective immunity are not fully understood. In contrast, protective immunity against nonfatal cutaneous leishmaniasis (CL) is well defined and mediated by rapidly recruited, IFN-γ-producing Ly6C(+)CD4(+) T cells at the dermal challenge site. Protection against CL is best achieved by prior infection or live vaccination with Leishmania major, termed leishmanization. A long-standing question is whether prior CL or leishmanization can protect against VL. Employing an intradermal challenge model in mice, we report that cutaneous infection with Leishmania major provides heterologous protection against visceral infection with Leishmania infantum. Protection was associated with a robust CD4(+) T cell response at the dermal challenge site and in the viscera. In vivo labeling of circulating cells revealed that increased frequencies of IFN-γ(+)CD4(+) T cells at sites of infection are due to recruitment or retention of cells in the tissue, rather than increased numbers of cells trapped in the vasculature. Shortly after challenge, IFN-γ-producing cells were highly enriched for Ly6C(+)T-bet(+) cells in the viscera. Surprisingly, this heterologous immunity was superior to homologous immunity mediated by prior infection with L. infantum. Our observations demonstrate a common mechanism of protection against different clinical forms of leishmaniasis. The efficacy of leishmanization against VL may warrant the introduction of the practice in VL endemic areas or during outbreaks of disease.

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.

Evidence for induction of humoral and cytotoxic immune responses against devil facial tumor disease cells in Tasmanian devils (Sarcophilus harrisii) immunized with killed cell preparations

Tasmanian devils (Sarcophilus harrisii) risk extinction from a contagious cancer, devil facial tumour disease (DFTD) in which the infectious agent is the tumor cell itself. Because devils are unable to produce an immune response against the tumor cells no devil has survived 'infection'. To promote an immune response we immunized healthy devils with killed DFTD tumor cells in the presence of adjuvants. Immune responses, including cytotoxicity and antibody production, were detected in five of the six devils. The incorporation of adjuvants that act via toll like receptors may provide additional signals to break 'immunological ignorance'. One of these devils was protected against a challenge with viable DFTD cells. This was a short-term protection as re-challenge one year later resulted in tumor growth. These results suggest that Tasmanian devils can generate immune responses against DFTD cells. With further optimization of immune stimulation it should be possible to protect Tasmanian devils against DFTD with an injectable vaccine.

A dual drug sensitive L. major induces protection without lesion in C57BL/6 mice

Leishmaniasis is a major health problem in some endemic areas and yet, no vaccine is available against any form of the disease. Historically, leishmanization (LZ) which is an inoculation of individual with live Leishmania, is the most effective control measure at least against cutaneous leishmaniasis (CL). Due to various reasons, LZ is not used today. Several live attenuated Leishmania have been developed but their use is limited. Previously, we developed a transgenic strain of L. major that harbors two suicide genes tk and cd genes (lmtkcd+/+) for use as a challenge strain in vaccine studies. These genes render the parasite susceptible to Ganciclovir (GCV) and 5-flurocytosine (5-FC). The dual drug sensitive strain of L. major was developed using gene targeting technology using a modified Herpes Simplex Virus thymidine kinase gene (hsv-tk) sensitive to Ganciclovir antibiotic and Saccharomyces cerevisae cytosine deaminase gene (cd sensitive to 5-flurocytosine) that were stably introduced into L. major chromosome. BALB/c mice inoculated with lmtkcd+/+ developed lesions which upon treatment with GCV and 5-FC completely healed. In the current study, the transgenic lmtkcd+/+strain was assessed as a live vaccine model to determine the time necessary to develop a protective immune response. C57BL/6 mice were inoculated with the transgenic lmtkcd+/+strain, and treated at the time of inoculation (day 0) or at day 8 after inoculation. Immunized animals were challenged with wild-type L. major, and complete protection was induced in mice that were treated at day 8. The results show that in contrast to leishmanization, in group of mice inoculated with a dual sensitive L. major development and persistence of lesion is not necessary to induce Th1 response and protection.

Detection and chronology of parasitic kinetoplast DNA presence in hair of experimental Leishmania major infected BALB/c mice by Real Time PCR

Hair can accumulate foreign chemical or biological substances. Recently, it has been reported that parasite DNA can also be detected in the hair of Leishmania infantum infected dogs. The aim of this work has been to find out whether parasite DNA incorporates in the hair of Leishmania major experimentally infected animals. For this purpose, a group of 4 BALB/c mice, intradermally inoculated in both ears with 1000 L. major V1 strain promastigote forms, was monitored for parameters associated to the infection during 35 days. Weekly, ear swelling was measured, and hair samples from ears and leg were collected. Blood samples were obtained before challenge and at day 35 post infection, when parasite load was measured in ear, lymph node and spleen by limit dilution. Ear swelling and other parameters observed in the infected mice were consistent with those described for this model. The presence of parasite kinetoplast DNA (kDNA) was detected by Real Time PCR in all ear and leg hair samples at the final timepoint. These data suggests that hair is a specialized tissue in the sequestration and removal of foreign DNA. Detection of DNA in hair could be, therefore, a useful tool to chronologically record the infection process during experimental mice assays.

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.

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.

Protective immunity and vaccination against cutaneous leishmaniasis

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

Vaccine Development Against Leishmania donovani

Visceral leishmaniasis (VL) caused by Leishmania donovani and Leishmania infantum/chagasi represents the second most challenging infectious disease worldwide, leading to nearly 500,000 new cases and 60,000 deaths annually. Zoonotic VL caused by L. infantum is a re-emergent canid zoonoses which represents a complex epidemiological cycle in the New world where domestic dogs serve as a reservoir host responsible for potentially fatal human infection and where dog culling is the only measure for reservoir control. Life-long immunity to VL has motivated development of prophylactic vaccines against the disease but very few have progressed beyond the experimental stage. No licensed vaccine is available till date against any form of leishmaniasis. High toxicity and increasing resistance to the current chemotherapeutic regimens have further complicated the situation in VL endemic regions of the world. Advances in vaccinology, including recombinant proteins, novel antigen-delivery systems/adjuvants, heterologous prime-boost regimens and strategies for intracellular antigen presentation, have contributed to recent advances in vaccine development against VL. Attempts to develop an effective vaccine for use in domestic dogs in areas of canine VL should be pursued for preventing human infection. Studies in animal models and human patients have revealed the pathogenic mechanisms of disease progression and features of protective immunity. This review will summarize the accumulated knowledge of pathogenesis, immune response, and prerequisites for protective immunity against human VL. Authors will discuss promising vaccine candidates, their developmental status and future prospects in a quest for rational vaccine development against the disease. In addition, several challenges such as safety issues, renewed and coordinated commitment to basic research, preclinical studies and trial design will be addressed to overcome the problems faced in developing prophylactic strategies for protection against this lethal infection.

CpG DNA as a vaccine adjuvant

Synthetic oligodeoxynucleotides (ODNs) containing unmethylated CpG motifs trigger cells that express Toll-like receptor 9 (including human plasmacytoid dendritic cells and B cells) to mount an innate immune response characterized by the production of Th1 and proinflammatory cytokines. When used as vaccine adjuvants, CpG ODNs improve the function of professional antigen-presenting cells and boost the generation of humoral and cellular vaccine-specific immune responses. These effects are optimized by maintaining ODNs and vaccine in close proximity. The adjuvant properties of CpG ODNs are observed when administered either systemically or mucosally, and persist in immunocompromised hosts. Preclinical studies indicate that CpG ODNs improve the activity of vaccines targeting infectious diseases and cancer. Clinical trials demonstrate that CpG ODNs have a good safety profile and increase the immunogenicity of coadministered vaccines.

Alginate microspheres encapsulated with autoclaved Leishmania major (ALM) and CpG-ODN induced partial protection and enhanced immune response against murine model of leishmaniasis

A suitable adjuvant and delivery system are needed to enhance efficacy of vaccines against leishmaniasis. In this study, alginate microspheres as an antigen delivery system and CpG-ODN as an immunoadjuvant were used to enhance immune response and induce protection against an experimental autoclaved Leishmania major (ALM) vaccine. Alginate microspheres were prepared by an emulsification technique and the characteristics of the preparation such as size, encapsulation efficiency and release profile of encapsulates were studied. Mean diameter of microspheres was determined using SEM (Scanning Electron Microscopy) and particle size analyzer. The encapsulation efficiency was determined using Lowry protein assay method. The integrity of ALM antigens was assessed using SDS-PAGE. Mean diameter of microspheres was 1.8±1.0μm. BALB/c mice were immunized three times in 3-weeks intervals with ALM+CpG-ODN loaded microspheres [(ALM+CpG)(ALG)], ALM encapsulated alginate microspheres [(ALM)(ALG)], (ALM)(ALG)+CpG, ALM+CpG, ALM alone or PBS. The intensity of infection induced by L. major challenge was assessed by measuring size of footpad swelling. The strongest protection was observed in group of mice immunized with (ALM+CpG)(ALG). The groups of mice received (ALM+CpG)(ALG), (ALM)(ALG)+CpG, (ALM)(ALG) and ALM+CpG were also showed a significantly (P<0.05) smaller footpad swelling compared with the group that received either ALM alone or PBS. The mice immunized with (ALM+CpG)(ALG) or ALM+CpG showed the significantly (P<0.05) highest IgG2a/IgG1 ratio. The IFN-γ level was significantly (P<0.0001) highest in group of mice immunized with either (ALM)(ALG)+CpG or ALM+CpG. It is concluded that alginate microspheres and CpG-ODN adjuvant when are used simultaneously induced protection and enhanced immune response against ALM antigen.

H-ras and N-ras are dispensable for T-cell development and activation but critical for protective Th1 immunity

The small guanine nucleotide binding proteins of the Ras family, including in mammals the highly homologous H-ras, N-ras, and K-ras isoforms, are rapidly activated on ligation of the T-cell antigen receptor (TCR), but whether each isoform plays specific roles in T cells is largely unknown. Here, we show, with the use of mice specifically lacking H-ras or N-ras, that these isoforms are dispensable for thymocyte development and mature T-cell activation. By contrast, CD4⁺ T cells from Ras-deficient mice exhibited markedly decreased production of the Th1 signature cytokine IFN-γ early after TCR stimulation, concomitantly with impaired induction of the Th1-specific transcription factor T-bet. Accordingly, Ras-deficient mice failed to mount a protective Th1 response in vivo against the intracellular parasite Leishmania major, although they could be rendered resistant to infection if a Th1-biased milieu was provided during parasite challenge. Collectively, our data indicate that the TCR recruits distinct Ras isoforms for signal transduction in developing and mature T cells, thus providing a mechanism for differential signaling from the same surface receptor. Furthermore, we demonstrate for the first time that H-ras and N-ras act as critical controllers of Th1 responses, mostly by transmitting TCR signals for Th1 priming of CD4⁺ T cells.

Immunization against leishmaniasis by PLGA nanospheres encapsulated with autoclaved Leishmania major (ALM) and CpG-ODN

Various adjuvants and delivery systems have been evaluated for increasing the protective immune responses against leishmaniasis and mostly have been shown not to be effective enough. In this study, poly(D,L-lactide-co-glycolide) (PLGA) nanospheres as an antigen delivery system and CpG-ODN as an immunoadjuvant have been used for the first time to enhance the immune response against autoclaved Leishmania major (ALM). PLGA nanospheres were prepared by a double-emulsion (W/O/W) technique. Particulate characteristics were studied by scanning electron microscopy and particle size analysis. Mean diameter of ALM + CpG-ODN-loaded nanospheres was 300 ± 128 nm. BALB/c mice were immunized three times in 3-week intervals using ALM plus CpG-ODN-loaded nanospheres [(ALM + CpG-ODN)(PLGA)], ALM encapsulated PLGA nanospheres [(ALM)(PLGA)], (ALM)(PLGA) + CpG, ALM + CpG, ALM alone, or phosphate buffer solution (PBS). The intensity of infection induced by L. major challenge was assessed by measuring size of footpad swelling. The strongest protection, showed by significantly (P<0.05) smaller footpad, was observed in mice immunized with (ALM + CpG-ODN)(PLGA). The (ALM)(PLGA), (ALM)(PLGA) + CpG, and ALM + CpG were also showed a significantly (P<0.05) smaller footpad swelling compared to the groups received either PBS or ALM alone. The mice immunized with (ALM + CpG-ODN)(PLGA), (ALM)(PLGA) + CpG, and ALM + CpG showed the highest IgG2a/IgG1 ratio, interferon-γ production, and lowest interleukin-4 production compared to the other groups. It is concluded that when both PLGA nanospheres and CpG-ODN adjuvants were used simultaneously, it induce stronger immune response and enhance protection rate against Leishmania infection.

A live Leishmania major vaccine containing CpG motifs induces the de novo generation of Th17 cells in C57BL/6 mice

Cutaneous leishmaniasis produces open sores that lead to scarring and disfiguration. We have reported that vaccination of C57BL/6 mice with live Leishmania major plus CpG DNA (Lm/CpG) prevents lesion development and provides long-term immunity. Our current study aims to characterize the components of the adaptive immune response that are unique to Lm/CpG. We find that this vaccine enhances the proliferation of CD4(+) Th17 cells, which contrasts with the highly polarized Th1 response caused by L. major alone; the Th17 response is dependent upon release of vaccine-induced IL-6. Neutralization of IFN-gamma and, in particular, IL-17 caused increased parasite burdens in Lm/CpG-vaccinated mice. IL-17R-deficient Lm/CpG-vaccinated mice develop lesions, and display decreased IL-17 and IFN-gamma, despite normal IL-12, production. Neutrophil accumulation is also decreased in the IL-17R-deficient Lm/CpG-vaccinated mice but Treg numbers are augmented. Our data demonstrate that activation of immune cells through CpG DNA, in the presence of live L. major, causes the specific induction of Th17 cells, which enhances the development of a protective cellular immunity against the parasite. Our study also demonstrates that vaccines combining live pathogens with immunomodulatory molecules may strikingly modify the natural immune response to infection in an alternative manner to that induced by killed or subunit vaccines.

Cancer testis antigen vaccination affords long-term protection in a murine model of ovarian cancer

Sperm protein (Sp17) is an attractive target for ovarian cancer (OC) vaccines because of its over-expression in primary as well as in metastatic lesions, at all stages of the disease. Our studies suggest that a Sp17-based vaccine can induce an enduring defense against OC development in C57BL/6 mice with ID8 cells, following prophylactic and therapeutic treatments. This is the first time that a mouse counterpart of a cancer testis antigen (Sp17) was shown to be expressed in an OC mouse model, and that vaccination against this antigen significantly controlled tumor growth. Our study shows that the CpG-adjuvated Sp17 vaccine overcomes the issue of immunologic tolerance, the major barrier to the development of effective immunotherapy for OC. Furthermore, this study provides a better understanding of OC biology by showing that Th-17 cells activation and contemporary immunosuppressive T-reg cells inhibition is required for vaccine efficacy. Taken together, these results indicate that prophylactic and therapeutic vaccinations can induce long-standing protection against OC and delay tumor growth, suggesting that this strategy may provide additional treatments of human OC and the prevention of disease onset in women with a family history of OC.

The Role of Liposomal CpG ODN on the Course of L. major Infection in BALB/C Mice

BACKGROUND

Historically, leishmanization is the most effective protective measure against Cutaneous Leishmaniasis (CL), CL lesion induced by leishmanization sometimes takes a long time to heal. Manipulation of leishmanization inoculums needed to induce a mild and acceptable CL lesion. The aim of this study was to explore if liposomal form of CpG ODN (Cytosin phosphate Guanin Oligodeoxynucleotides) mixed with Leishmania major would induce a milder lesion size in Balb/c mice.

METHODS

This study was performed in Biotechnology Research Center, Mashhad, and Center for Research and Training in Skin Diseases and Leprosy, Tehran, Iran during 2008-2009. Different groups of BALB/c mice were subcutaneously (SC) inoculated with L. major mixed with liposomal form of CpG ODN, or L. major plus free CpG ODN, or L. major mixed with empty liposomes or L. major in PBS. The lesion onset and the size of lesion were recorded; the death rate was also monitored.

RESULT

Footpad thickness was significantly (P<0.01) smaller, death rate was also significantly (P<0.05) lower in the mice received L. major mixed with liposomal CpG ODN or free CpG ODN than control groups received L. major in PBS or L. major plus liposomes, also mice which received L. major mixed with CpG ODN in soluble form showed a significantly (P<0.001) smaller lesion size than control groups.

CONCLUSION

CpG ODN seems to be an appropriate immunopotentiator mixed with Leishmania stabilate in leishmanization.

The IL-6-deficient mouse exhibits impaired lymphocytic responses to a vaccine combining live Leishmania major and CpG oligodeoxynucleotides

We have previously reported that vaccination with CpG oligodeoxynucleotides delivered concomitantly with live Leishmania major (Lm/CpG) eliminates lesions associated with live vaccination in C57BL/6 mice. The absence of lesions is at least in part a result of the CpG DNA-mediated activation of dermal dendritic cells to produce cytokines such as interleukin (IL)-6. Wild-type C57BL/6 mice and IL-6-/- mice were immunized with the Lm/CpG vaccine and monitored for the development of lesions. IL-6-/- mice developed extensive, nonhealing lesions following live vaccination. The analysis of the inoculation site and draining lymph nodes of the IL-6-/- mice revealed a constitutive reduction in lymphocyte numbers, particularly CD4+ T cells. Live vaccination resulted in the specific expansion of CD4+Foxp3+ regulatory T cells in the knockout mice, and in a decrease of CD4+ IFN-gamma -producing cells. These results indicate that IL-6-/- mice may have collateral immune defects that could influence the development of the natural immune response to pathogens, vaccines, or other inflammatory stimuli.

Vaccination with live Leishmania major and CpG DNA promotes interleukin-2 production by dermal dendritic cells and NK cell activation

Cutaneous leishmaniasis due to Leishmania major is an emerging, chronic parasitic disease that causes disfigurement and social stigmatization. Drug therapy is inadequate, and there is no vaccine. Inoculation of virulent parasites (leishmanization) is the only intervention that has ever provided protection, because it mimics natural infection and immunity, but it was discontinued due to safety concerns (uncontrolled vaccinal lesions). In an effort to retain the benefits (immunity) while avoiding the side effects (lesions) of leishmanization, we immunized C57BL/6 mice with L. major and CpG DNA (Lm/CpG). This combination prevented lesions while inducing immunity. Also, the vaccination with live parasites and the Toll-like receptor 9 agonist enhanced innate immune responses by activating dermal dendritic cells (DCs) to produce cytokines. Here we report that the Lm/CpG vaccine induced dermal DCs, but not bone marrow-derived DCs, to produce interleukin-2 (IL-2). The release of this unusual DC-derived cytokine was concomitant with a peak in numbers of NK cells that produced gamma interferon (IFN-gamma) and also enhanced activation of proliferation of IFN-gamma+ CD4+ T cells. Parasite growth was controlled in Lm/CpG-vaccinated animals. This is the first demonstration of the ability of dermal DCs to produce IL-2 and of the activation of NK cells by vaccination in the context of leishmaniasis. Understanding how the Lm/CpG vaccine enhances innate immunity may provide new tools to develop vaccines against L. major, other chronic infectious diseases, or other conditions, such as cancer.

Comparative evaluation of two vaccine candidates against experimental leishmaniasis due to Leishmania major infection in four inbred mouse strains

Experimental leishmaniasis in BALB/c and C57BL/6 mice are the most investigated murine models that were used for the preclinical evaluation of Leishmania vaccine candidates. We have previously described two new inbred mouse strains named PWK and MAI issued from feral founders that also support the development of experimental leishmaniasis due to L. major. In this study, we sought to determine whether different mouse inbred strains generate concordant or discordant results when used to evaluate the potential of Leishmania proteins to protect against experimental leishmaniasis. To this end, two Leishmania proteins, namely, LACK (for Leishmania homolog of receptor for activated C kinase) and LmPDI (for L. major protein disulfide isomerase) were compared for their capacity to protect against experimental leishmaniasis in PWK, MAI, BALB/c, and C57BL/6 inbred mouse strains. Our data show that the capacity of Leishmania proteins to confer protection depends on the mouse strain used, stressing the important role played by the genetic background in shaping the immune response against the pathogen. These results may have important implications for the preclinical evaluation of candidate Leishmania vaccines: rather than using a single mouse strain, a panel of different inbred strains of various genetic backgrounds should be tested in parallel. The antigen that confers protection in the larger range of inbred strains may have better chances to be also protective in outbred human populations and should be selected for clinical trials.

Inoculation of killed Leishmania major into immune mice rapidly disrupts immunity to a secondary challenge via IL-10-mediated process

Recovery from natural or experimental Leishmania major infection, the causative agent of cutaneous leishmaniasis, results in development of durable immunity in mice and humans that is manifested as rapid control of parasite replication and resolution of cutaneous lesion after secondary challenge. This form of "infection-induced" immunity is thought to occur naturally in endemic areas and is generally considered the gold standard for any effective vaccine against cutaneous leishmaniasis. To determine factors that might heighten or abrogate infection-induced immunity, we investigated the impact of inoculating dead antigen in the form of killed Leishmania parasites to healed mice. We show that inoculation of killed parasites into mice that resolved their primary virulent L. major infection results in rapid and relatively sustained loss of infection-induced immunity. This loss of immunity was not due to the inability of killed parasites to induce inflammatory responses (such as delayed type hypersensitivity), but it was related to their failure to induce robust IFN-gamma response. Furthermore, inoculation of killed Leishmania parasites into healed mice led to rapid expansion of IL-10-producing CD4(+)CD25(+)Foxp3(+) T cells in lymph nodes draining the primary infection site. Treatment with anti-CD25 or anti-IL-10R mAb abolished killed parasite-induced loss of immunity. Our study suggests that vaccination with killed parasites could predispose naturally immune individuals to become susceptible to new infections and/or disease reactivation. This may account for the lack of efficacy of such vaccines in field trials in endemic regions. These findings have important implications for vaccine design and vaccination strategies against human cutaneous leishmaniasis.

CpG oligonucleotides as adjuvants for vaccines targeting infectious diseases

Synthetic oligodeoxynucleotides (ODN) containing unmethylated CpG motifs act as immune adjuvants, accelerating and boosting antigen-specific immune responses. CpG motifs promote the induction of Th1 and pro-inflammatory cytokines and support the maturation/activation of professional antigen presenting cells (particularly plasmacytoid dendritic cells). These effects are optimized by maintaining close physical contact between the CpG ODN and the immunogen. Co-administering CpG ODN with a variety of vaccines has improved the resultant humoral and/or cellular immune responses, culminating in enhanced protective immunity in rodent and primate challenge models. Ongoing clinical studies indicate that CpG ODN are safe and well-tolerated when administered as adjuvants to humans, and that they can support increased vaccine-specific immune responses.

Photodynamic vaccination of hamsters with inducible suicidal mutants of Leishmania amazonensis elicits immunity against visceral leishmaniasis

Leishmania, naturally residing in the phagolysosomes of macrophages, is a suitable carrier for vaccine delivery. Genetic complementation of these trypanosomatid protozoa to partially rectify their defective heme-biosynthesis renders them inducible with delta-aminolevulinate to develop porphyria for selective photolysis, leaving infected host cells unscathed. Delivery of released "vaccines" to antigen-presenting cells is thus expected to enhance immune response, while their self-destruction presents added advantages of safety. Such suicidal L. amazonensis was found to confer immunoprophylaxis and immunotherapy on hamsters against L. donovani. Neither heat-killed nor live parasites without suicidal induction were effective. Photodynamic vaccination of hamsters with the suicidal mutants reduced the parasite loads by 99% and suppressed the development of disease. These suppressions were accompanied by an increase in Leishmania-specific delayed-type hypersensitivity and lymphoproliferation as well as in the levels of splenic iNOS, IFN-gamma, and IL-12 expressions and of Leishmania-specific IgG2 in the serum. Moreover, a single intravenous administration of T cells from vaccinated hamsters was shown to confer on naïve animals an effective cellular immunity against L. donovani challenges. The absence of lesion development at vaccination sites and parasites in the draining lymphnodes, spleen and liver further indicates that the suicidal mutants provide a safe platform for vaccine delivery against experimental visceral leishmaniasis.

Qualitative differences in the early immune response to live and killed Leishmania major: Implications for vaccination strategies against Leishmaniasis

Recovery from natural or deliberate infection with Leishmania major leads to the development of lifelong immunity against rechallenge infections. In contrast, vaccination with killed parasites or defined leishmanial antigens generally induces only short-term protection. The reasons for this difference are currently not known but may be related to differences in the quality of the early immune responses to live and killed parasites. Here, we report that live and killed L. major parasites elicit comparable early inflammatory response as evidenced by influx and/or proliferation of cells in the draining lymph nodes (dLNs). In contrast, the early cytokine responses were qualitatively different. Cells from mice inoculated with killed parasites produced significantly more antigen-specific IL-4 and less IFN-gamma than those from mice injected with live parasites. Inclusion of CpG ODN into killed parasite preparations changed the early response to killed parasites from IL-4 to a predominantly IFN-gamma response, resulting in better protection following secondary high dose virulent L. major challenge. Interestingly, CpG-mediated enhancement of killed parasites-induced protection was short-lived and waned after 12 weeks. Taken together, these results suggest that the nature of primary immunity induced by killed and live parasites are qualitatively different and that these differences may account for the differential protection seen in mice following vaccination with live and killed parasites. They further suggest that modulating the early response with an appropriate adjuvant could enhance efficacy of killed parasite vaccines.

Recent developments in leishmaniasis vaccine delivery systems

BACKGROUND

The observation that recovery from infection with Leishmania confers immunity to reinfection suggests that control of leishmaniasis by vaccination may be possible. New generation vaccines, particularly those based on recombinant proteins and DNA, are found to be less immunogenic.

OBJECTIVE

There is an urgent need for the development of new and improved vaccine adjuvants.

METHODS

Based on their principal mechanisms of action, adjuvants can be broadly separated into two classes: immunostimulatory adjuvants and vaccine delivery systems. Vaccine delivery systems can carry both antigen and adjuvant for effective delivery to the antigen-presenting cells (APCs). In this article, we review the adjuvants, the delivery systems and their combinations used in the search of an effective vaccine against leishmaniasis.

CONCLUSION

Based on current knowledge, cationic liposomes appear to have better prospects as effective delivery systems for developing a vaccine for leishmaniasis.

CpG-ODN enhances ingestion of apoptotic neutrophils by macrophages

The clearance of apoptotic neutrophils by macrophages plays an important role in the process of inflammatory response. In the present study, we examined the ability of macrophages to ingest apoptotic neutrophils after activated by synthetic oligodeoxynucleotides containing CpG motifs (CpG-ODN) in vitro. The results showed that, while CpG-ODN at the experimental concentration had no cytotoxic effect on the viability of macrophages, the percentage of macrophages with ingested apoptotic neutrophils was increased from 23.6 to 42.30% by CpG-ODN stimulation. This effect was silenced when macrophages were treated with the mutation of CpG-ODN motifs. Both the total and cell surface protein of Toll-like receptor 9 (TLR9) expression in macrophages was up-regulated after CpG-ODN stimulation. While chloroquine (CHQ) had no effect on TLR9 expression in macrophages, it abolished the enhanced uptake of apoptotic neutrophils by macrophages. Although CpG-ODN had no significant effect on the IL-6 production, it was able to induce the increase of TNF-alpha protein expression and this effect was inhibited by CHQ pretreatment. Increased TNF-alpha production from macrophages induced by CpG-ODN stimulation was down-regulated after phagocytosis of apoptotic neutrophils. In conclusion, CpG-ODN could enhance the ingestion of apoptotic neutrophils by macrophages via TLR9 accompanied with an increasing in the level of TNF-alpha. After phagocytosis of apoptotic neutrophils, the increased TNF-alpha production from macrophages induced by CpG-ODN stimulation was down-regulated which the implications in the immune response remains for the further study.

Pathogen-imposed skewing of mouse chemokine and cytokine expression at the infected tissue site

Compartmentalization of immunity ensures tight regulation of T cell activation in the LN and precise effector T cell delivery to inflamed sites. Herein we show that the tissue-specific accumulation of effector T cells can be subverted by a pathogen at the infection site. Using the Leishmania major mouse model of dermal infection, we observed a restricted chemokine profile at the infection site, i.e., the expression of Th2 cell-attracting CCL7 but not of Th1 cell-attracting chemokines. Consistent with these chemokine expression data, recruitment of cytokine-producing T cells to the infection site was also selective. Both IL-4- and IFN-gamma-producing effector T cells homed to inflamed OVA/CFA-immunized dermis, but only IL-4-producing cells homed to L. major-infected dermis. The narrowing of the cytokine repertoire at the site of infection with L. major was driven, in part, by pathogen-induced CCL7. Inflammatory signals failed to disrupt the early restrictive L. major infection site, which suggests that L. major dominantly modifies the local milieu. We have highlighted an emerging principle in pathogen-host interactions: that the cytokine repertoire at the infection site and the LN draining the infection site can be different because of the ability of the pathogen to modify the chemokine profile at the infection site. Thus, pathogens may edit the LN cytokine repertoire through differential recruitment of cytokine-producing cells.

Leishmania mexicana infection induces impaired lymph node expansion and Th1 cell differentiation despite normal T cell proliferation

Leishmania mexicana infections in C57BL/6 mice are associated with minimal immune responses and persistent cutaneous lesions. In contrast, Leishmania major elicits a robust Th1 response that promotes lesion resolution. We investigated whether the nonhealing phenotype associated with L. mexicana was due to a failure of L. mexicana to activate T cells. In vivo T cell responses to infection were assessed by tracking the behavior of labeled naive T cells following the transfer of these cells into congenic mice. Although L. mexicana infection was associated with minimal expansion of the draining lymph nodes, we observed no difference in the percentage of T cells proliferating in response to L. mexicana and L. major. Instead, differences in the size and cellularity of lymph nodes were associated with decreased recruitment of cells trafficking to the lymph node. Furthermore, we found that T cells responding to L. mexicana infection were less able to differentiate into IFN-gamma producing cells, and this deficit extended to previously activated T cells as well. Coadministration of CpG-containing oligodeoxynucleotides at the time of infection overcame this deficit and promoted disease resolution. Taken together, our results identify two distinct components that contribute to the minimal immune response associated with L. mexicana infection. First, despite ample levels of T cell proliferation, L. mexicana fails to induce substantial lymph node expansion, which limits the number of responding T cells. Second, L. mexicana infection fails to drive the differentiation of the majority of responding cells into IFN-gamma producers.

CpG oligonucleotides as adjuvant in therapeutic vaccines against parasitic infections

Immunostimulatory CpG DNA is recognized by cells of the innate immune system through Toll-like receptor 9 (TLR9). Synthetic CpG oligonucleotides (CpG-ODN) belong to the most potent vaccine adjuvants known today. This is due to their capacity not only to stimulate cells of the innate immune system but also to trigger effectively specific T- and B-lymphocyte responses. This unique quality seems to be superior in the induction of long-term effects and immunological memory. In addition to prophylactic vaccination, we showed that mice already infected with Toxoplasma gondii could be therapeutically vaccinated by the combined use of CpG-ODN and a bradyzoite antigen (BAG1 protein subunit). This treatment was effective against the infection and resulted in a long-term survival of the mice and reduced parasite burden in the brain. Different routes of CpG-ODN vaccine application including intranasal, oral or intraperitoneal delivery were compared with the classical subcutaneous application in two established experimental infection models of murine leishmaniasis and toxoplasmosis. Comparable effects were demonstrated for these modes of inoculation except for the oral uptake of uncoupled CpG-ODN, which resulted in a complete failure of treatment. Detailed studies were performed to optimize the time point of CpG-ODN application. The best results were obtained when the ODN were given within a few days around the infection, in contrast to former trials showing a time window of several weeks for significant oligonucleotide effects in non-infectious models. As CPG-ODN is a synthetic compound, it is not only available in high purity and reproducible quality, but can also be produced with different backbone modifications and sequence modifications. Combination of these possibilities resulted in new molecules that were highly effective as adjuvant in parasite infection models. Finally, our studies revealed not only that bacterial DNA is an effective vaccine adjuvants, but also that Leishmania DNA itself had immunostimulatory properties which are counteracted by a yet undefined inhibitory principle from living Leishmania.

STAT1 expression in dendritic cells, but not T cells, is required for immunity to Leishmania major

The generation of Th1 responses is important for resistance to intracellular pathogens, including the parasite, Leishmania major. Although IFN-gammaR/STAT1 signaling promotes a Th1 response via the up-regulation of T-bet, the requirement for STAT1 in Th1 cell differentiation remains controversial. Although in some cases Th1 cells develop independently of STAT1, STAT1(-/-) mice fail to develop a Th1 response during L. major infection. However, the interpretation of this result is complicated by the role STAT1 plays in Ag presentation and, more importantly, in elimination of parasites by macrophages, because both defective Ag presentation and increased parasite burden can influence Th cell development. To resolve this issue, we assessed the ability of STAT1(-/-) T cells to become Th1 cells and protect mice against L. major following adoptive transfer into STAT1-sufficient mice. We found that whereas T-bet is critical for the differentiation of protective Th1 cells during L. major infection, IFN-gammaR and STAT1 are dispensable. Given that a STAT1-independent Th1 cell response was generated by STAT1-sufficient APCs, but not by STAT1(-/-) cells, we next addressed whether dendritic cells (DCs) require STAT1 signaling to effectively present Ag. We found that STAT1(-/-) DCs had impaired up-regulation of MHC and costimulatory molecules, and, as a consequence, the absence of STAT1 resulted in reduced Th1 cell priming. Taken together, these results demonstrate that T cell expression of STAT1 is not required for the development of Th1 cells protective against L. major and instead stress the importance of STAT1 signaling in DCs for the optimal induction of Th1 responses.

Cutaneous Leishmania infection: progress in pathogenesis research and experimental therapy

Studies in murine experimental Leishmania major infection have helped to understand the requirements for efficient development of T helper (Th)1/cytotoxic T (Tc)1-mediated protection against the parasite. As such they have revealed that Fc gamma receptor (Fc gamma R)I and Fc gamma RIII-mediated uptake of L. major amastigotes by dendritic cells (DC) is an important prerequisite for Th1 development. In addition, DC-derived cytokines contribute to adequate T-cell education. DC-based vaccines may thus provide an important tool for both the development of a prophylactic vaccine against leishmaniasis and - together with leishmanicidal drugs - for eliciting immune-deviating functions towards protective immunity in non-healing leishmaniasis. This review highlights recent advances in the understanding of the role of DC for the induction of Th1/Tc1-predominant immunity against L. major and how this knowledge may translate into clinical approaches.

Immunomodulatory effects associated with a live vaccine against Leishmania major containing CpG oligodeoxynucleotides

The inoculation of live Leishmania major to produce a lesion that heals (leishmanization) is to date the only vaccine against cutaneous leishmaniasis that has proven effective in humans, but it still has an unacceptable frequency of large ulcerating lesions that are slow to heal or, in rare cases, non-healing. We have previously shown that C57BL/6 mice vaccinated intradermally with 10(4) L. major/50 microg CpG oligodeoxynucleotides develop little or no dermal lesions and show early containment of parasite growth in the vaccination site, eliminating safety concerns related to the inoculation of live organisms. The addition of CpG to the live vaccine resulted in early activation of dermal dendritic cells and increased IL-6 production, as well as in a reduction in the accumulation of Foxp3(+)CD4(+)CD25(+) regulatory T (T(reg)) cells that naturally occurs in the skin following Leishmania infection. Neutralization of IL-6 caused the development of larger lesions and increased local T(reg) cell numbers. Transfer of vaccine-primed dendritic cells into IL-6-deficient mice mitigated lesion development, indicating that IL-6 reconstitution limited pathology in the vaccination site.

Adjuvant activity of CpG oligodeoxynucleotides

Synthetic oligodeoxynucleotides (ODNs) containing unmethylated CpG motifs directly stimulate human B cells and plasmacytoid dendritic cells (pDCs), thereby promoting the production of Th1 and proinflammatory cytokines and the maturation/activation of professional antigen-presenting cells. These activities enable CpG ODNs to act as immune adjuvants, accelerating and boosting antigen-specific immune responses by 5- to 500-fold. The CpG motifs present in bacterial DNA plasmids may contribute to the immunogenicity of DNA vaccines. Ongoing clinical studies indicate that CpG ODNs are safe and well tolerated when administered as adjuvants to humans and can improve vaccine-induced immune responses.

Immunization with persistent attenuated Delta lpg2 Leishmania major parasites requires adjuvant to provide protective immunity in C57BL/6 mice

Leishmania major parasites lacking the GDP-mannose transporter, termed Deltalpg2 parasites, fail to induce disease in mice but persist long-term. We previously found that Deltalpg2 organisms protect BALB/c mice from virulent L. major challenge. In contrast, we report here that Deltalpg2 parasites induce protective immunity in C57BL/6 mice only when administered with CpG-containing oligodeoxynucleotides, indicating that parasite persistence alone is not sufficient to maintain protective immunity to L. major.

Live nonpathogenic parasitic vector as a candidate vaccine against visceral leishmaniasis

To date, there are no proven vaccines against any form of leishmaniasis. The development of live attenuated vectors shows promise in the field of Leishmania vaccination because these organisms mimic more effectively the course of real infections and can elicit potent activation of the immune system. In the present study, we investigated the potential of a parasitic protozoan that is nonpathogenic to humans, Leishmania tarentolae, as a live candidate vaccine that efficiently targets dendritic cells and lymphoid organs, thus enhancing antigen presentation and consequently influencing the magnitude and quality of T-cell immune responses. We demonstrated that L. tarentolae activates the dendritic cell maturation process and induces T-cell proliferation and the production of gamma interferon, thus skewing CD4(+) T cells toward a Th1 cell phenotype. More importantly, we found that a single intraperitoneal injection of L. tarentolae could elicit a protective immune response against infectious challenge with Leishmania donovani in susceptible BALB/c mice. These results suggest that the use of L. tarentolae as a live vaccine vector may represent a promising approach for improving the effectiveness and safety of candidate live vaccines against Leishmania infections and possibly other intracellular pathogens for which T-cell mediated responses are critical for the development of protective immunity.

Vaccination with the Leishmania infantum acidic ribosomal P0 protein plus CpG oligodeoxynucleotides induces protection against cutaneous leishmaniasis in C57BL/6 mice but does not prevent progressive disease in BALB/c mice

We have examined the efficacy of the administration in mice of a molecularly defined vaccine based on the Leishmania infantum acidic ribosomal protein P0 (rLiP0). Two different challenge models of murine cutaneous leishmaniasis were used: (i) subcutaneous inoculation of L. major parasites in susceptible BALB/c mice (a model widely used for vaccination analysis) and (ii) the intradermal inoculation of a low infective dose in resistant C57BL/6 mice (a model that more accurately reproduces the L. major infection in natural reservoirs and in human hosts). First, we demonstrated that C57BL/6 mice vaccinated with LiP0-DNA or rLiP0 protein plus CpG oligodeoxynucleotides (ODN) were protected against the development of dermal pathology and showed a reduction in the parasite load. This protection was associated with production of gamma interferon (IFN-gamma) in the dermal site. Secondly, we showed that immunization with rLiP0 plus CpG ODN is able to induce only partial protection in BALB/c, since these mice finally developed a progressive disease. Further, we demonstrated that LiP0 vaccination induces a Th1 immunological response in both strains of mice. In both cases, the antibodies against LiP0 were predominantly of the immunoglobulin G2a isotype, which was correlated with an rLiP0-stimulated production of IFN-gamma in draining lymph nodes. Finally, we demonstrated that LiP0 vaccination does not prevent the Th2 response induced by L. major infection in BALB/c mice. Taken together, these data indicate that the BALB/c model of cutaneous leishmaniasis may undervalue the potential efficacy of some vaccines based on defined proteins, making C57BL/6 a suitable alternative model to test vaccine candidates.