Recovery of antigen-specific T cell responses from dogs infected with Leishmania (L.) infantum by use of vaccine associated TLR-agonist adjuvant

PLGA nanoparticle-delivered Leishmania antigen and TLR agonists as a therapeutic vaccine against cutaneous leishmaniasis in BALB/c mice

Leishmaniasis, caused by Leishmania (L.) species, remains a neglected infection. Therapeutic vaccination presents a promising strategy for its treatment. In this study, we aimed to develop a therapeutic vaccine candidate using Leishmaniaantigens (SLA) and Toll-like receptor (TLR) 7/8 agonist (R848) encapsulated into the poly (lactic-co-glycolic acid) (PLGA) nanoparticles (NPs). Moreover, TLR1/2 agonist (Pam3CSK4) was loaded onto the NPs. The therapeutic effects of these NPs were evaluated in L. major-infected BALB/c mice. Footpad swelling, parasite load, cellular and humoral immune responses, and nitric oxide (NO) production were analyzed. The results demonstrated that the PLGA NPs (SLA-R848-Pam3CSK4) therapeutic vaccine effectively stimulated Th1 cell responses, induced humoral responses, promoted NO production, and restricted parasite burden and lesion size.Our findings suggest that vaccination with SLA combined with TLR1/2 and TLR7/8 agonists in PLGA NPs as a therapeutic vaccine confers strong protection againstL. majorinfection. These results represent a novel particulate therapeutic vaccine against Old World cutaneous leishmaniasis.

Enhancing Control of Leishmania infantum Infection: A Multi-Epitope Nanovaccine for Durable T-Cell Immunity

Canine leishmaniosis (CanL) is a growing health problem for which vaccination is a crucial tool for the control of disease. The successful development of an effective vaccine against this disease relies on eliciting a robust and enduring T-cell immune response involving the activation of CD4+ Th1 and CD8+ T-cells. This study aimed to evaluate the immunogenicity and prophylactic efficacy of a novel nanovaccine comprising a multi-epitope peptide, known as HisDTC, encapsulated in PLGA nanoparticles against Leishmania infantum infection in the murine model. The encapsulation strategy was designed to enhance antigen loading and sustain release, ensuring prolonged exposure to the immune system. Our results showed that mice immunized with PLGA-encapsulated HisDTC exhibited a significant reduction in the parasite load in the liver and spleen over both short and long-term duration. This reduction was associated with a cellular immune profile marked by elevated levels of pro-inflammatory cytokines, such as IFN-γ, and the generation of memory T cells. In conclusion, the current study establishes that PLGA-encapsulated HisDTC can promote effective and long-lasting T-cell responses against L. infantum in the murine model. These findings underscore the potential utility of multi-epitope vaccines, in conjunction with appropriate delivery systems, as an alternative strategy for CanL control.

Within-host bayesian joint modeling of longitudinal and time-to-event data of Leishmania infection

The host immune system plays a significant role in managing and clearing pathogen material during an infection, but this complex process presents numerous challenges from a modeling perspective. There are many mathematical and statistical models for these kinds of processes that take into account a wide range of events that happen within the host. In this work, we present a Bayesian joint model of longitudinal and time-to-event data of Leishmania infection that considers the interplay between key drivers of the disease process: pathogen load, antibody level, and disease. The longitudinal model also considers approximate inflammatory and regulatory immune factors. In addition to measuring antibody levels produced by the immune system, we adapt data from CD4+ and CD8+ T cell proliferation, and expression of interleukin 10, interferon-gamma, and programmed cell death 1 as inflammatory or regulatory factors mediating the disease process. The model is developed using data collected from a cohort of dogs naturally exposed to Leishmania infantum. The cohort was chosen to start with healthy infected animals, and this is the majority of the data. The model also characterizes the relationship features of the longitudinal outcomes and time-to-death due to progressive Leishmania infection. In addition to describing the mechanisms causing disease progression and impacting the risk of death, we also present the model's ability to predict individual trajectories of Canine Leishmaniosis (CanL) progression. The within-host model structure we present here provides a way forward to address vital research questions regarding the understanding of the progression of complex chronic diseases such as Visceral Leishmaniasis, a parasitic disease causing significant morbidity worldwide.

Bayesian multivariate longitudinal model for immune responses to Leishmania: A tick-borne co-infection study

While many Bayesian state-space models for infectious disease processes focus on population infection dynamics (eg, compartmental models), in this work we examine the evolution of infection processes and the complexities of the immune responses within the host using these techniques. We present a joint Bayesian state-space model to better understand how the immune system contributes to the control of Leishmania infantum infections over the disease course. We use longitudinal molecular diagnostic and clinical data of a cohort of dogs to describe population progression rates and present evidence for important drivers of clinical disease. Among these results, we find evidence for the importance of co-infection in disease progression. We also show that as dogs progress through the infection, parasite load is influenced by their age, ectoparasiticide treatment status, and serology. Furthermore, we present evidence that pathogen load information from an earlier point in time influences its future value and that the size of this effect varies depending on the clinical stage of the dog. In addition to characterizing the processes driving disease progression, we predict individual and aggregate patterns of Canine Leishmaniasis progression. Both our findings and the application to individual-level predictions are of direct clinical relevance, presenting possible opportunities for application in veterinary practice and motivating lines of additional investigation to better understand and predict disease progression. Finally, as an important zoonotic human pathogen, these results may support future efforts to prevent and treat human Leishmaniosis.

Within-Host Bayesian Joint Modeling of Longitudinal and Time-to-Event Data of Leishmania Infection

The host immune system plays a significant role in managing and clearing pathogen material during an infection, but this complex process presents numerous challenges from a modeling perspective. There are many mathematical and statistical models for these kinds of processes that take into account a wide range of events that happen within the host. In this work, we present a Bayesian joint model of longitudinal and time-to-event data of Leishmania infection that considers the interplay between key drivers of the disease process: pathogen load, antibody level, and disease. The longitudinal model also considers approximate inflammatory and regulatory immune factors. In addition to measuring antibody levels produced by the immune system, we adapt data from CD4+ and CD8+ T cell proliferation, and expression of interleukin 10, interferon-gamma, and programmed cell death 1 as inflammatory or regulatory factors mediating the disease process. The model is developed using data collected from a cohort of dogs naturally exposed to Leishmania infantum. The cohort was chosen to start with healthy infected animals, and this is the majority of the data. The model also characterizes the relationship features of the longitudinal outcomes and time of death due to progressive Leishmania infection. In addition to describing the mechanisms causing disease progression and impacting the risk of death, we also present the model's ability to predict individual trajectories of Canine Leishmaniosis (CanL) progression. The within-host model structure we present here provides a way forward to address vital research questions regarding the understanding progression of complex chronic diseases such as Visceral Leishmaniasis, a parasitic disease causing significant morbidity worldwide.

Investigation of comorbidities in dogs with leishmaniosis due to Leishmania infantum

In endemic areas, dogs with leishmaniosis due to Leishmania infantum frequently have comorbidities, including mostly neoplastic, infectious, and parasitic diseases. The aim of this study was to compare the prevalence of comorbidities among dogs that are not infected by L. infantum, dogs that are infected but do not present leishmaniosis, and dogs with leishmaniosis, and to examine if certain comorbidities are independent risk factors for the infection by L. infantum and/or for the development of canine leishmaniosis (CanL). A total of 111 dogs, older than 1-year and non-vaccinated against CanL, were allocated into three groups: group A (n = 18) included dogs that were not infected by L. infantum, group B (n = 52) included dogs that were infected by L. infantum but did not present CanL, and group C (n = 41) included dogs with CanL. Signalment and historical data were obtained using a structured questionnaire. Laboratory examinations included complete blood count, serum biochemistry, urinalysis, fecal parasitology, modified Knott's test, microscopic examination of capillary blood, buffy coat, lymph node, bone marrow and conjunctival smears, qualitative serology for Dirofilaria immitis, Anaplasma phagocytophilum/A. platys, Borrelia burgdorferi and E. canis, IFAT for L. infantum, ELISA for Babesia spp. and Neospora caninum, and real-time PCR for L. infantum in bone marrow, skin biopsies and conjunctival swabs. A variety of comorbidities were found in all three groups. No independent risk factors for infection by L. infantum were found. On the contrary, among dogs infected by L. infantum, being a mongrel [odds ratio (OR): 11.2], not receiving prevention for dirofilariosis (OR: 26.5) and being seropositive to N. caninum (OR: 17.1) or to Babesia spp. (OR: 37.6), were independent risk factors for presenting CanL. Although no comorbidities influence the probability of canine infection by L. infantum, certain comorbidities may be precipitating factors for the transition from the subclinical infection by L. infantum to the overt CanL.

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

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

Immortalised canine buccal epithelial cells' CXCL8 secretion is affected by allergen extracts, Toll-like receptor ligands, IL-17A and calcitriol

Epithelial cells are known to produce mediators which can influence the behaviour of neighbouring immune cells. Although the oral mucosa has gained increased interest as a route to induce allergy desensitisation and mucosal pathogen immunisation in dogs, there is only limited knowledge on the factors which impact mediator secretion by canine oral epithelial cells. The study’s objective was to enlarge the knowledge on the stimuli that can influence the secretion of some pro- and anti-inflammatory cytokines and the chemokine CXCL8 by canine buccal epithelial cells. To investigate this, buccal epithelial cells were isolated from a biopsy of a dog and immortalised by lentiviral transduction of the SV40 large T antigen. The cells were stained with a CD49f and cytokeratin 3 antibody to confirm their epithelial origin. Cells were incubated with allergen extracts, Toll-like receptor ligands (TLRL), recombinant cytokines and vitamin A and D metabolites. Subsequently, the secretion of the cytokines interleukin (IL)-4, IL-6, IL-10, IL-17A, IFN-γ, TGF-β1 and the chemokine CXCL8 was assayed by ELISA. Immortalised canine buccal epithelial cells stained positive for CD49f but not for cytokeratin 3. The cells produced detectable amounts of CXCL8 and TGF-β1. A Dermatophagoides farinae extract, an Alternaria alternata extract, Pam3CSK4, heat-killed Listeria monocytogenes, FSL-1, flagellin and canine recombinant IL-17A significantly increased CXCL8 secretion, while the vitamin D metabolite calcitriol significantly suppressed the production of this chemokine. This study showed that certain allergens, TLRL, IL-17A and calcitriol modulate CXCL8 secretion in a cell line of canine buccal epithelial cells.

Prevalence of antinuclear antibodies and rheumatoid factor titers in dogs with arthritis secondary to leishmaniosis (Leishmania infantum)

Dogs with infectious arthritis may occasionally exhibit positive serum antinuclear antibody (ANA) and rheumatoid factor (RF) titers; however, relevant data are sparse for arthritis secondary to canine leishmaniosis (CanL) caused by Leishmania infantum. We determined the prevalence of positive serum ANA and RF titers in dogs with arthritis secondary to CanL. Blood samples from adult, client-owned dogs with purulent arthritis secondary to CanL, without any comorbidities, were collected for diagnostic purposes. Serum ANA titers were measured by immunoperoxidase test and RF titers by the Rose-Waaler latex test. Twelve of 23 dogs enrolled prospectively in our study had clinical arthritis, and 11 of 23 had subclinical arthritis. Based on LeishVet clinical staging, 7 dogs had clinical stage II disease, 11 had clinical stage III disease, and 5 had stage IV. None of the 23 dogs was seropositive for ANA; 3 of 23 were positive for RF. ANA and/or RF seropositivity, in dogs with CanL-associated arthritis, appears to be weak, if present at all. Based on our results, positive serum ANA and RF titers should not be expected in dogs with arthritis secondary to CanL.

T Lymphocyte Exhaustion During Human and Experimental Visceral Leishmaniasis

A key point of immunity against protozoan Leishmania parasites is the development of an optimal T cell response, which includes a low apoptotic rate, high proliferative activity and polyfunctionality. During acute infection, antigen-specific T cells recognize the pathogen resulting in pathogen control but not elimination, promoting the development and the maintenance of a population of circulating effector cells that mount rapid response quickly after re-exposure to the parasite. However, in the case of visceral disease, the functionality of specific T cells is lost during chronic infection, resulting in inferior effector functions, poor response to specific restimulation, and suboptimal homeostatic proliferation, a term referred to as T cell exhaustion. Multiple factors, including parasite load, infection duration and host immunity, affect T lymphocyte exhaustion. These factors contribute to antigen persistence by promoting inhibitory receptor expression and sustained production of soluble mediators, influencing suppressive cell function and the release of endogenous molecules into chronically inflamed tissue. Together, these signals encourage several changes, reprogramming cells into a quiescent state, which reflects disease progression to more severe forms, and development of acquired resistance to conventional drugs to treat the disease. These points are discussed in this review.

Bayesian latent class models for identifying canine visceral leishmaniosis using diagnostic tests in the absence of a gold standard

Background

Like many infectious diseases, there is no practical gold standard for diagnosing clinical visceral leishmaniasis (VL). Latent class modeling has been proposed to estimate a latent gold standard for identifying disease. These proposed models for VL have leveraged information from diagnostic tests with dichotomous serological and PCR assays, but have not employed continuous diagnostic test information.

Methods/Principal findings

In this paper, we employ Bayesian latent class models to improve the identification of canine visceral leishmaniasis using the dichotomous PCR assay and the Dual Path Platform (DPP) serology test. The DPP test has historically been used as a dichotomous assay, but can also yield numerical information via the DPP reader. Using data collected from a cohort of hunting dogs across the United States, which were identified as having either negative or symptomatic disease, we evaluate the impact of including numerical DPP reader information as a proxy for immune response. We find that inclusion of DPP reader information allows us to illustrate changes in immune response as a function of age.

Conclusions/Significance

Utilization of continuous DPP reader information can improve the correct discrimination between individuals that are negative for disease and those with clinical VL. These models provide a promising avenue for diagnostic testing in contexts with multiple, imperfect diagnostic tests. Specifically, they can easily be applied to human visceral leishmaniasis when diagnostic test results are available. Also, appropriate diagnosis of canine visceral leishmaniasis has important consequences for curtailing spread of disease to humans.

Leishmania infantum xenodiagnosis from vertically infected dogs reveals significant skin tropism

BACKGROUND

Dogs are the primary reservoir for human visceral leishmaniasis due to Leishmania infantum. Phlebotomine sand flies maintain zoonotic transmission of parasites between dogs and humans. A subset of dogs is infected transplacentally during gestation, but at what stage of the clinical spectrum vertically infected dogs contribute to the infected sand fly pool is unknown.

METHODOLOGY/PRINCIPAL FINDINGS

We examined infectiousness of dogs vertically infected with L. infantum from multiple clinical states to the vector Lutzomyia longipalpis using xenodiagnosis and found that vertically infected dogs were infectious to sand flies at differing rates. Dogs with mild to moderate disease showed significantly higher transmission to the vector than dogs with subclinical or severe disease. We documented a substantial parasite burden in the skin of vertically infected dogs by RT-qPCR, despite these dogs not having received intradermal parasites via sand flies. There was a highly significant correlation between skin parasite burden at the feeding site and sand fly parasite uptake. This suggests dogs with high skin parasite burden contribute the most to the infected sand fly pool. Although skin parasite load and parasitemia correlated with one another, the average parasite number detected in skin was significantly higher compared to blood in matched subjects. Thus, dermal resident parasites were infectious to sand flies from dogs without detectable parasitemia.

CONCLUSIONS/SIGNIFICANCE

Together, our data implicate skin parasite burden and earlier clinical status as stronger indicators of outward transmission potential than blood parasite burden. Our studies of a population of dogs without vector transmission highlights the need to consider canine vertical transmission in surveillance and prevention strategies.

Combinatorial delivery of antigen and TLR agonists via PLGA nanoparticles modulates Leishmania major-infected-macrophages activation

Appropriate activation of macrophages is critical for the elimination of Leishmania parasites, which resides in this cell. Some species of Leishmania (L.) fails to stimulate macrophages and establish a chronic infection. To overcome this suppression and induce an innate immune response, the effect of PLGA-encapsulated soluble antigens of Leishmania (SLA) along with agonists of TLR1/2 (Pam3CSK4) and TLR7/8 (R848) nanoparticles (NPs) on activation of L. major-infected-macrophages were investigated and were compared with those of soluble formulations. SLA and R848 were encapsulated into the PLGA, while Pam3CSK4 adsorbed onto the surface of nanoparticles. The kinetics of pro-inflammatory cytokines (IL-1β, IL-6, and TNF-α) and iNOS genes expression were investigated by qPCR over 72 h. The parasite load was also quantified by qPCR. The results indicated that engulfment of L. major promastigotes does not induce any pro-inflammatory cytokines expression by macrophages; however, the infected-cells are capable of responding to the TLRs agonists, and a lesser extent, to the SLA stimulation. Encapsulation resulted in increased strength of the IL-1β, IL-6, TNF-α, and increased and prolonged time of iNOS expression. Also, encapsulation showed the leishmanicidal activity by decreasing parasite load in treated NPs formulations. Among the different combinations of the components, the triple (SLA-R848-Pam3CSK4) forms promoted the highest activation of macrophages, followed by dual SLA-Pam3CSK4 and SLA-R848 NPs. In conclusion, the findings of this study indicate that the addition of SLA in combination with TLR1/2 and TLR7/8 agonists either in NPs or in soluble forms overcome the suppression of L. major-infected macrophages. Moreover, encapsulation increases the strength and duration of the cytokines and iNOS expression, in parallel with decreasing parasite load, suggesting a longer availability or delivery of the NPs into the macrophages. These findings highlight the advantages of particulate therapeutic vaccine formulations.

Immunoprophylactic Potential of a New Recombinant Leishmania infantum Antigen for Canine Visceral Leishmaniasis: An In Vitro Finding

The development and application of safe and effective immunoprophylactic/immunotherapeutic agents against canine visceral leishmaniasis (CanL) have been pointed out as the only means for the real control of the disease. Thus, this study aimed to evaluate the in vitro cellular immune response of dogs, elicited by the new recombinant proteins of Leishmania infantum, Lci10 and Lci13, in order to investigate their potential for vaccinology. Twenty-four dogs were submitted to clinical, parasitological, serological and molecular tests, and then separated into two study groups: 12 infected (InD) and 12 non-infected dogs (NInD), and six of each group were directed for Lci10 and Lci13 evaluation. Peripheral blood mononuclear cells (PBMC) were cultured and stimulated with Lci10 (10 μg/ml) or Lci13 (5 μg/ml), and with L. infantum soluble antigen (LSA) (25 μg/ml) or no stimulus (NS) as controls. Afterwards, the mRNA levels of different cytokines were quantified through qPCR, and Nitric Oxide (NO) production was assessed in the culture supernatants. Significant differences were considered when p ≤ 0.05. The comparative analysis revealed that, in the NInD group, Lci13 promoted a significant increase in the expression of IFN-γ in relation to LSA (p = 0.0362), and the expression of this cytokine in NInD was significantly higher than that presented in the InD (p = 0.0028). A negative expression for TGF-β was obtained in both groups. Lci13 also induced a greater production of NO in relation to the NS sample in the NInD group. No significant differences were observed after stimulation with Lci10. In conclusion, the results suggest a protective role of Lci13 for uninfected animals, thus with a potential for immunoprophylaxis. The results will help to direct the antigen Lci13 for further studies (pre-clinical trials), in order to determine its immunogenicity and reactogenicity effects, as a way to consolidate its real applicability for vaccinology against CanL.

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

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

The balancing act: Immunology of leishmaniosis

Immune control of Leishmania infantum, the causative agent of most canine leishmaniosis (CanL), requires a balancing act between inflammatory and regulatory responses. This balance is specifically between the proinflammatory T helper 1 type (Th1) CD4+ T cells that are responsible for controlling parasite replication and T regulatory 1 cells which mediate an immunosuppressive, regulatory, response needed to dampen overabundant inflammation but if predominant, result in CanL progression. How this delicate immune cell interaction occurs in the dog will be highlighted in this review, focusing on the progressive changes observed within myeloid lineage cells (predominantly macrophages), B cells and T cells. After exposure to parasites, macrophages should become activated, eliminating L. infantum through release of reactive oxygen species. Unfortunately, multiple parasite and host factors can prevent macrophage activation allowing parasites to persist within them. T cells balance between a productive T_H1 type CD4+ response capable of producing IFN-γ which aids macrophage activation versus T cell exhaustion which reduces T cell proliferation, IFN-γ production and allows parasite expansion within macrophages. Neutrophils and Th17 cells add to the inflammatory state, aiding in parasite removal, but also leading to pathology. A regulatory B cell population increases IL-10 production and down regulates the T_H1 response allowing parasite growth. All of these immune challenges affect the balance between progression to clinical disease and maintaining sub-clinical disease. Vaccines and immunotherapies targeted at recovering or maintaining T and B cell function can be important factors in mending the immune balance required to survive CanL.

Toll-like receptors 2, 4 and 7, interferon-gamma and interleukin 10, and programmed death ligand 1 transcripts in skin from dogs of different clinical stages of leishmaniosis

Background

Canine leishmaniosis (CanL) caused by Leishmania infantum can have several dermatological manifestations. The type of immune response elicited against the parasite appears to be at the basis for such clinical variability. Much of the work in CanL has focused on adaptive immune response and there are scarce data on the importance of the innate immune responses. Moreover, few studies have evaluated the immunological response in the cutaneous lesions in dogs naturally infected with L. infantum and with different degrees of disease severity, and no study has compared clinically-lesioned with normal-looking skin.

Methods

We determined and compared the transcription of toll like receptors (TLRs) 2, 4 and 7, interferon gamma (IFN-γ), interleukin (IL) 10 and programmed cell death protein ligand (PD-L) 1 by real-time PCR in paired clinically-lesioned and normal-looking skin from 25 diseased dogs (mild disease-stage I (n = 11) and moderate to severe disease-stages II and III (n = 14) as well as in normal-looking skin from healthy dogs (n = 10) from a non-endemic area. We also assessed the association between the transcripts in clinically-lesioned and normal-looking skin of dogs with leishmaniosis with clinicopathological, immunological and parasitological findings.

Results

Clinically-lesioned skin from mildly affected dogs was characterized by a significant upregulation of TLR2 (P < 0.0001) and IL-10 (P = 0.021) and downregulation of TLR7 (P = 0.004) when compared with more severely affected dogs. Normal-looking skin of mildly affected dogs was characterized by a significant lower expression of TLR7 (P = 0.003), IFN-γ (P < 0.0001) and PD-L1 (P = 0.001) when compared with more severely affected dogs. TLR2, TLR4, IL-10 and IFN-γ upregulation in clinically-lesioned skin was correlated with lower disease severity while TLR7 upregulation was correlated with markers of disease severity. Upregulation of TLR7, IL-10, IFN-γ and PD-L1 in normal-looking skin was correlated with disease severity.

Conclusions

This study demonstrated different expression profiles of immune genes in clinically-lesioned and normal-looking skin among mildly and more severely affected dogs. These immunological conditions might favor the maintenance and replication of the parasite in the skin of more severely affected dogs.

Allopurinol therapy provides long term clinical improvement, but additional immunotherapy is required for sustained parasite clearance, in L. infantum-infected dogs

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L. infantum-infected dogs were treated with allopurinol alone or plus Leish-F2 + SLA-SE.

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Both treatment regimen generated long term clinical improvement.

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Immunochemotherapy, but not chemotherapy alone, generated sustained parasite control.

There is little evidence that current control strategies for canine leishmaniosis (CanL), the veterinary disease caused by L. infantum infection, are having a positive impact. This is of critical importance because dogs are a primary reservoir for L. infantum and a significant source of parasite transmission to humans. Drugs intended primarily for human use are prohibited for the treatment of CanL because of concerns over the propagation of resistant parasites. Although allopurinol effectively decreases parasite burden in CanL the treatment needs to be maintained for life. We hypothesized that during the allopurinol-induced parasite reduction dogs may become capable of developing a more robust immune response that may permit more effective control of parasites. To test this, we investigated the clinical and parasitological impact of short-term treatment with allopurinol, either alone or in combination with a defined subunit vaccine, on dogs naturally infected with L. infantum. A total of 28 dogs were distributed as follows: untreated; oral allopurinol alone (20 mg/kg, once each day for 90 days); or allopurinol with immunization with the Leish-F2 antigen formulated with the Toll-like receptor (TLR) 4 agonist Second generation Lipid Adjuvant (SLA) in stable emulsion (SE; SLA-SE). Dogs that did not receive treatment had a progressive decline in their clinical condition and an increase in their infection levels, while treatment with allopurinol alone alleviated the clinical symptoms of CanL but did not generate sustained reduction in parasites. Concomitant immunization with Leish-F2 + SLA-SE, however, improved clinical condition while also providing long-term clearance of L. infantum from lymphoid tissues and systemic organs. These results have important implications for both the management of CanL and for limiting L. infantum transmission to humans.

Eosinophils Affect Antibody Isotype Switching and May Partially Contribute to Early Vaccine-Induced Immunity against Coxiella burnetii

Coxiella burnetii is an obligate intracellular Gram-negative bacterium which causes human Q fever. An acidified citrate cysteine medium (ACCM-2) has been developed which mimics the intracellular replicative niche of C. burnetii and allows axenic growth of the bacteria. To determine if C. burnetii cultured in ACCM-2 retains immunogenicity, we compared the protective efficacies of formalin-inactivated C. burnetii Nine Mile phase I (PIV) and phase II (PIIV) vaccines derived from axenic culture 7, 14, and 28 days postvaccination. PIV conferred significant protection against virulent C. burnetii as early as 7 days postvaccination, which suggests that ACCM-2-derived PIV retains immunogenicity and protectivity. We analyzed the cellular immune response in spleens from PIV- and PIIV-vaccinated mice by flow cytometry at 7 and 14 days postvaccination and found significantly more granulocytes in PIV-vaccinated mice than in PIIV-vaccinated mice. Interestingly, we found these infiltrating granulocytes to be SSChigh CD11b+ CD125+ Siglec-F+ (where SSChigh indicates a high side scatter phenotype) eosinophils. There was no change in the number of eosinophils in PIV-vaccinated CD4-deficient mice compared to the level in controls, which suggests that eosinophil accumulation is CD4+ T cell dependent. To evaluate the importance of eosinophils in PIV-mediated protection, we vaccinated and challenged eosinophil-deficient ΔdblGATA mice. ΔdblGATA mice had significantly worse disease than their wild-type counterparts when challenged 7 days postvaccination, while no significant difference was seen at 28 days postvaccination. Nevertheless, ΔdblGATA mice had elevated serum IgM with decreased IgG1 and IgG2a whether mice were challenged at 7 or 28 days postvaccination. These results suggest that eosinophils may play a role in early vaccine protection against C. burnetii and contribute to antibody isotype switching.

Randomized, controlled, double-blinded field trial to assess Leishmania vaccine effectiveness as immunotherapy for canine leishmaniosis

Better tools are necessary to eliminate visceral leishmaniasis (VL). Modeling studies for regional Leishmania elimination indicate that an effective vaccine is a critical tool. Dogs are the reservoir host of L. infantum in Brazil and the Mediterranean basin, and therefore are an important target for public health interventions as well as a relevant disease model for human VL. No vaccine has been efficacious as an immunotherapy to prevent progression of already diagnostically positive individuals to symptomatic leishmaniasis. We performed a double-blinded, block-randomized, placebo-controlled, vaccine immunotherapy trial testing the efficacy of a recombinant Leishmania A2 protein, saponin-adjuvanted, vaccine, LeishTec®, in owned hunting dogs infected with L. infantum. The primary outcome was reduction of clinical progression, with reduction of mortality as a secondary outcome. Vaccination as an immunotherapy reduced the risk of progression to clinically overt leishmaniasis by 25% in asymptomatic dogs (RR: 1.33 95% C.I. 1.009-1.786 p-value: 0.0450). Receiving vaccine vs. placebo reduced all-cause mortality in younger asymptomatic dogs by 70% (RR: 3.19 95% C.I.: 1.185-8.502 p-value = 0.0245). Vaccination of infected-healthy animals with an anti-Leishmania vaccine significantly reduced clinical progression and decreased all-cause mortality. Use of vaccination in infected-healthy dogs can be a tool for Leishmania control.

Safety Analysis of Leishmania Vaccine Used in a Randomized Canine Vaccine/Immunotherapy Trial

In Leishmania infantum-endemic countries, controlling infection within dogs, the domestic reservoir, is critical to public health. There is a need for safe vaccines that prevent canine progression with disease and transmission to others. Protective vaccination against Leishmania requires mounting a strong, inflammatory, Type 1 response. Three commercially available canine vaccines on the global veterinary market use saponin or inflammatory antigen components (Letifend) as a strong pro-inflammatory adjuvant. There is very little information detailing safety of saponin as an adjuvant in field trials. Safety analyses for the use of vaccine as an immunotherapeutic in asymptomatically infected animals are completely lacking. Leishmania infantum, the causative agent of canine leishmaniasis, is enzootic within U.S. hunting hounds. We assessed the safety of LeishTec^® after use in dogs from two different clinical states: 1) without clinical signs and tested negative on polymerase chain reaction and serology or 2) without clinical signs and positive for at least one Leishmania diagnostic test. Vaccine safety was assessed after all three vaccinations to quantify the number and severity of adverse events. Vaccinated animals had an adverse event rate of 3.09%, whereas placebo animals had 0.68%. Receiving vaccine was correlated with the occurrence of mild, site-specific, reactions. Occurrence of severe adverse events was not associated with having received vaccine. Infected, asymptomatic animals did not have a higher rate of adverse events. Use of vaccination is, therefore, likely to be safe in infected, asymptomatic animals.

Proteome-scale identification of Leishmania infantum for novel vaccine candidates: A hierarchical subtractive approach

Vaccines are one of the most significant achievements in medical science. However, vaccine design is still challenging at all stages. The selection of antigenic peptides as vaccine candidates is the first and most important step for vaccine design. Experimental selection of antigenic peptides for the design of vaccines is a time-consuming, labor-intensive and expensive procedure. More recently, in the light of computer-aided biotechnology and reverse vaccinology, the precise selection of antigenic peptides and rational vaccine design against many pathogens have developed. In this study, the whole proteome of Leishmania infantum was analyzed using a pipeline of algorithms. From the set of 8045 proteins of L. infantum, sixteen novel antigenic proteins were derived using a hierarchical proteome subtractive analysis. These novel vaccine targets can be utilized as top candidates for designing the new prophylactic or therapeutic vaccines against visceral leishmaniasis. Significantly, all the sixteen novel vaccine candidates are non-allergen antigenic proteins that have not been used for the design of vaccines against visceral leishmaniasis until now.

Recombinant small glutamine-rich tetratricopeptide repeat-containing protein of Leishmania infantum: Potential vaccine and diagnostic application against visceral leishmaniasis

Different Leishmania proteins have been evaluated in order to find a potential vaccine candidate or diagnostic marker capable of providing long lasting protection against infection or helping to identify infected mammalian hosts, respectively. However, just few molecules have fulfilled all the requirements to be evaluated. In the current study, we evaluated the prophylactic and diagnostic value against visceral leishmaniasis (VL) of a small glutamine-rich tetratricopeptide repeat-containing (SGT) protein from Leishmania infantum species. In a first step, the immune response elicited by the immunization using the recombinant protein (rSGT) plus saponin was evaluated in BALB/c mice. Immunized animals had a low parasitism in all evaluated organs. They developed a specific Th1 immune response, which was based on protein-specific production of IFN-γ, IL-12 and GM-CSF, and a humoral response dominated by antibodies of the IgG2a isotype. Both CD4⁺ and CD8⁺ T cells contributed to the IFN-γ production, showing that both T cell subtypes contribute to the resistance against infection. Regarding its value as a diagnostic marker, rSGT showed maximum sensitivity and specificity to serologically identify L. infantum-infected dog and human sera. No cross-reactivity with sera from humans or dogs that had other diseases was found. Although further studies are necessary to validate these findings, data showed here suggest immunogenicity of rSGT and its protective effect against murine VL, as well as its potential for the serodiagnosis of human and canine VL.

Diagnostic Challenges in the Era of Canine Leishmania infantum Vaccines

The diagnosis of canine leishmaniosis (CanL) is complex due to its variable clinical manifestations and laboratory findings. The availability of vaccines to prevent CanL has increased the complexity of diagnosis, as serological tests may not distinguish between naturally infected and vaccinated dogs. Current practices of prevaccination screening are not sufficiently sensitive to detect subclinically infected dogs, resulting in the vaccination of infected animals, which may lead to disease in vaccinated dogs that are also infectious to sand flies. This review evaluates the current techniques for diagnosing CanL, and focuses on new challenges raised by the increasing use of vaccines against this disease. Important gaps in knowledge regarding the diagnosis of CanL are underscored to highlight the need for novel diagnostic test development.

Novel Areas for Prevention and Control of Canine Leishmaniosis

There have been multiple recent advances regarding tools for the control and prevention of canine leishmaniosis (CanL), including new preventative vaccines. In this review, these advances are evaluated based on control targets, including vector and parasite. Leishvet recommendations are provided for control practices based on the dog's risk of infection. New topical insecticide formulations have proven to be effective in preventing sand fly bites, and subsequently infection. Parasite control occurs through chemotherapeutic or immunologic means, which decrease or prevent transmission to other animals, including humans. Leishmaniosis control programs that include a combination of coordinated measures, either in individuals or for prevention across reservoir populations, are required.

The inflammatory cytokine effect of Pam3CSK4 TLR2 agonist alone or in combination with Leishmania infantum antigen on ex-vivo whole blood from sick and resistant dogs

BACKGROUND

A wide spectrum of clinical manifestations and immune responses exist in canine L. infantum infection. Ibizan hounds are more "resistant" to disease than other dog breeds. Recognition of pathogen-associated molecule patterns by toll like receptors (TLRs) rapidly triggers a variety of anti-microbial immune responses through the induction of pro-inflammatory cytokines such as TNF-α and IL-6 which may play an important role in controlling Leishmania infection. The main objective of this study was to investigate and compare the effect of a TLR2 agonist (TLR2a) alone or in combination with L. infantum antigen (LSA) on ex vivo whole blood cytokine production from healthy seronegative IFN-γ non-producer dogs from an area of low in canine leishmaniosis endemicity (n = 11); sick seropositive dogs with low production of IFN-γ (n = 17) and healthy seronegative or low positive Ibizan hounds with a predominant IFN-γ production (n = 21) from a highly endemic area. Whole blood was stimulated with medium alone (Ø), LSA, concanavalin A, TLR2 (Pam3CSK4) receptor agonist (Ø + TLR2a) and TLR2a and LSA (LSA + TLR2a) for 48 h. Supernatants were harvested for measurement of canine TNF-α and IL-6 cytokines by ELISA.

RESULTS

A significant increase of TNF-α was found in the supernatants of stimulated blood from all groups (Ø + TLR2a and LSA + TLR2a) when compared with medium alone. A similar pattern was observed for IL-6. Interestingly, a significant increase of TNF-α production was only observed when stimulation with LSA + TLR2a was compared with TLR2a alone in Ibizan hounds. A significant increase of TNF-α production was observed with stimulation of LSA + TLR2a when compared with LSA in all groups. Significantly higher concentrations of TNF-α and IL-6 were detected in Ibizan hounds, especially for the Ø + TLR2a and LSA + TLR2a treatments compared with other groups.

CONCLUSIONS

This study demonstrated that TLR2a alone enhances the production of the inflammatory cytokines TNF-α and IL-6 in sick, "resistant" and healthy non-infected dogs. In addition, a combination of LSA+TLR2a promoted a synergistic pro-inflammatory effect with TNF-α in Ibizan hounds but not in seropositive sick dogs and seronegative healthy dogs. These findings might suggest the importance of Pam3CSK4 as a possible immunomodulator for CanL.