Adaptive immunity against Leishmania nucleoside hydrolase maps its c-terminal domain as the target of the CD4+ T cell-driven protective response

Nucleoside hydrolases (NHs) show homology among parasite protozoa, fungi and bacteria. They are vital protagonists in the establishment of early infection and, therefore, are excellent candidates for the pathogen recognition by adaptive immune responses. Immune protection against NHs would prevent disease at the early infection of several pathogens. We have identified the domain of the NH of L. donovani (NH36) responsible for its immunogenicity and protective efficacy against murine visceral leishmaniasis (VL). Using recombinant generated peptides covering the whole NH36 sequence and saponin we demonstrate that protection against L. chagasi is related to its C-terminal domain (amino-acids 199-314) and is mediated mainly by a CD4+ T cell driven response with a lower contribution of CD8+ T cells. Immunization with this peptide exceeds in 36.73±12.33% the protective response induced by the cognate NH36 protein. Increases in IgM, IgG2a, IgG1 and IgG2b antibodies, CD4+ T cell proportions, IFN-γ secretion, ratios of IFN-γ/IL-10 producing CD4+ and CD8+ T cells and percents of antibody binding inhibition by synthetic predicted epitopes were detected in F3 vaccinated mice. The increases in DTH and in ratios of TNFα/IL-10 CD4+ producing cells were however the strong correlates of protection which was confirmed by in vivo depletion with monoclonal antibodies, algorithm predicted CD4 and CD8 epitopes and a pronounced decrease in parasite load (90.5-88.23%; p = 0.011) that was long-lasting. No decrease in parasite load was detected after vaccination with the N-domain of NH36, in spite of the induction of IFN-γ/IL-10 expression by CD4+ T cells after challenge. Both peptides reduced the size of footpad lesions, but only the C-domain reduced the parasite load of mice challenged with L. amazonensis. The identification of the target of the immune response to NH36 represents a basis for the rationale development of a bivalent vaccine against leishmaniasis and for multivalent vaccines against NHs-dependent pathogens.

Nucleoside hydrolase DNA vaccine against canine visceral leishmaniasis

The Nucleoside Hydrolase (NH36) is the main marker of the FML complex of Leishmania donovani, antigen of the licensed Leishmune® vaccine for prophylaxis of canine visceral leishmaniasis. As a DNA vaccine in mice, it induces a TH1 immune response. We vaccinated mongrel dogs with the VR1012NH36 vaccine for prophylaxis and immunotherapy against a high dose Leishmania chagasi infection (7 x 108 infective amastigotes). The untreated controls developed more symptoms, higher parasite/lymphocyte ratio, smaller DTH reactions, lower proportions of NH36-specific CD4+ cells and sustained NH36-specific CD8+ cell counts than dogs of the prophylaxis group. In the immunotherapy treated group, enlarged DTH reactions, enhanced CD4+ and sustained CD8+ lymphocyte proportions were also detected, however, without reduction of symptoms or parasite/lymphocyte ratio, indicating that the vaccine was sufficiently potent to prevent but not to control the disease. Both treatments determined higher survival rates. Anti-FML antibodies increased in vaccinated and control dogs while anti-NH36 antibodies were only increased in vaccinees (p= 0.000). The parasite load of an untreated survivor control dog (638.05 parasites) felt outside the IC95% of that of vaccinated dogs (32.02, IC95% 9.45-64.59) suggesting that both vaccination treatments succeeded in reducing the Leishmania infective burden. Accordingly, an untreated control dog showed lower levels of IFN γ-β, IL-2, IL4 but not IL-10 β actin-relative quantification. We conclude that the VR1012-NH36 vaccine induces strong prophylactic protection and a milder immunotherapeutic effect against a high dose canine experimental infection with Leishmania chagasi.

Immunogenicity assay of the Leishmune vaccine against canine visceral leishmaniasis in Brazil

Leishmune is the industrialized version of the FML-saponin vaccine which has been shown to develop 92-95% protection in vaccinated dogs and 76-80% vaccine efficacy against field canine visceral leishmaniasis (CVL) in Brazil. Leishmune has been proven to be safe and tolerable and a transmission-blocking vaccine which renders vaccinated dogs non-infectious to sand fly vectors. In the present investigation, 550 healthy seronegative dogs of endemic and epidemic areas of Brazil were monitored for Leishmune-induced immunogenicity during a 2-year trial. Another group of 588 untreated exposed dogs was also studied in parallel. Both groups were seronegative on day 0. The strong immunogenicity induced by Leishmune vaccine was demonstrated by the 98% of FML-seroconversion, increase in absorbencies, the 82.7% DTH positive reactions and increase in skin test size diameters, the average increase in CD8+ total lymphocytes population in blood (27.1%), expected for QS21 saponin-containing vaccine, the sustained proportions of CD4+ T cells, and the average increased proportions of CD21+ B lymphocytes (42.3%). The Leishmune-induced protection against CVL is demonstrated by the results: 98.8% asymptomatic dogs (at the end of first year) and 99% healthy survivors (at the end of the second year) among vaccinated dogs, compared to the 79.4% asymptomatic and 61% survivor dogs (p<0.001) monitored in the untreated exposed cohort. In spite of the low vaccine coverage, it was possible to detect a 66.1% (p<0.005) reduction in Belo Horizonte and an 80.2% (p<0.005) reduction in Araçatuba of the incidence of CVL among vaccinated dogs, when compared to the global incidence of CVL of each town, respectively. Our preliminary results support the potential use of Leishmune to prevent CVL epidemics.

FML vaccine against canine visceral leishmaniasis: from second-generation to synthetic vaccine

The Leishmania donovani glycoprotein fraction, known as FML, successfully underwent preclinical and clinical (Phase I-III) vaccine trials against canine visceral leishmaniasis (92-95% of protection and 76-80% of vaccine efficacy) when formulated with a QS21 saponin-containing adjuvant. It became the licensed Leishmune vaccine for canine prophylaxis in Brazil. The immune response raised by the vaccine is long lasting, immunotherapeutic and reduces dog infectivity blocking the transmission of the disease, as revealed by an in vivo assay. The preliminary epidemiological control data of vaccinated areas in Brazil indicate that, in spite of the still low vaccine coverage, there was a significant decrease in the incidence of the human and canine disease. A 36-kDa glycoprotein, in the FML complex, is the human marker of the disease, which was protective in mice as native recombinant protein or DNA vaccine. The DNA vaccine is now being tested against the canine disease. This review resumes the development of the second-generation FML-saponin-Leishmune vaccine, its adjuvant and of the NH36 DNA vaccine, toward the identification of its major epitopes that might be included in a possible future synthetic vaccine.

Assessment of the monoterpene, glycidic and triterpene-moieties’ contributions to the adjuvant function of the CP05 saponin of Calliandra pulcherrima Benth during vaccination against experimental visceral leishmaniasis

The CP05 saponin from Calliandra pulcherrima Benth, shows remarkable similarities to the QS21 saponin of Quillaja saponaria Molina. Both shared a monoterpene hydrophobic moiety, a glycidic chain attached to the triterpene C28, and three sugars attached to C3. Different from QS21, the CP05 does not show the aldehyde group in triterpene C4 involved in TH1 response. Balb/c mice were immunized either intact saponin (CP05), the monoterpene-deprived (BS), the C28 carbohydrate-deprived (HS) or the sapogenin fraction, in formulation with the FML antigen of Leishmania donovani and challenged with 2 x 10(8) amastigotes of L. chagasi. While the CP05 induced 90% survival and 92.1% parasite reduction, a 100% survival and 94.1% protection were detected after the BS-vaccine treatment, indicating that the monoterpene acylated moiety, absent in the BS vaccine, is not necessary for the induction of a protective global TH1 response. Only the DTH response of BS vaccines was mildly lower than that of CP05 vaccinees. Maximal anti-FML antibody, CD4(+) and CD8(+) Leishmania specific lymphocytes, IFN-gamma splenocyte secretion, reduction in parasite load and survival was also detected for the BS vaccine. The HSFML vaccine showed diminished responses in all tested variables, except for IFN-gamma secretion, indicating that the integrity of the carbohydrate moiety attached to C28 is mandatory for the these functions. No protection was induced by the sapogenin-FML indicating that the CP05 triterpene which lacks the C4 aldehyde group, is not a immunostimulating compound. No contribution to protection was detected in the CP05 saponin treated control group supporting the specificity of the FML antigenic preparation.

Safety trial using the Leishmune vaccine against canine visceral leishmaniasis in Brazil

A group of 600 healthy and asymptomatic dogs from Brazilian canine visceral leishmaniasis endemic areas was vaccinated with three sc doses of Leishmune which is the industrialized formulation of the FML-saponin, recently licensed for commercialization in Brazil, which previously showed 76-80% vaccine efficacy against canine visceral leishmaniasis. Safety evaluation was performed for 14 days after each vaccine injection and disclosed transient reactions of local pain (40.87%), anorexia (20.48%), apathy (24.17%), local swelling reactions (15.90%), vomit (2.4%) and diarrhoea (1.5%). All effects showed significantly correlating declines, from the first to the third dose (p<0.0001). Most of the noticed reactions of pain (73%), anorexia (79%) and local swelling (84.7%) were mild. No significant differences between puppies and adults dogs were found in the number of adverse reactions. Adult dogs developed however, 94.5% of the small swelling reactions (<3 cm), and indicating that they are more resistant to the inflammatory response promoted by the saponins. No dead by anaphylaxis occurred, and only two dogs (0.1%) showed allergic reactions (facial oedema and itching) after the third dose. Transient alopecia on injection site occurred in only five poodles (0.28%) with total recovery and no need of treatment. All the mild adverse events in response to Leishmune injection were transient and disappeared before the injection of the following vaccine dose, confirming the tolerability of the vaccine. The Leishmune preparation was less haemolytic (HD(50)=180 microg/ml) than expected for a QS21 saponin-containing vaccine, indicating that its formulation with the FML antigen diminished the potential in vitro toxicity.

Immunotherapy against visceral leishmaniasis with the nucleoside hydrolase-DNA vaccine of Leishmania donovani

The nucleoside hydrolase (NH36) of Leishmania (L.) donovani is a vital enzyme which releases purines or pyrimidines of foreign DNA to be used in the synthesis of parasite DNA. As a bivalent DNA vaccine, the VR1012-NH36 was immunoprotective against visceral and cutaneous murine leishmaniasis. In this work we tested the immunotherapy against Leishmania (L.) chagasi infection, using two doses of 100 or 20 microg VR1012-NH36 vaccine (i.m. route), and, as a possible immunomodulator, aqueous garlic extract (8 mg/kg/day by the i.p. route), which was effective in immunotherapy of cutaneous murine leishmaniasis. Liver parasitic load was significantly reduced following treatment with 100 microg (91%) and 20 microg (77%) of the DNA vaccine, and by 20 microg DNA vaccine and garlic extract (76%) (p=0.023). Survival was 33% for saline controls, 100% for the 100 microg vaccine, and 83 and 67% for the 20 microg vaccine with and without garlic extract addition, respectively. Garlic treatment alone did not reduce parasite load (p>0.05), but increased survival (100%). The NH36-DNA vaccine was highly effective as a new tool for the therapy and control of visceral leishmaniasis, while the mild protective effect of garlic might be related to an unspecific enhancement of IFN-gamma secretion.

Acylated and deacylated saponins of Quillaja saponaria mixture as adjuvants for the FML-vaccine against visceral leishmaniasis

The adjuvant of the FML-vaccine against murine and canine visceral leishmaniasis, the Riedel de Haen saponin mixture, was fractionated by ion exchange chromatography on DEAE-cellulose to afford one TLC homogeneous Quillaja saponaria Molina QS21 saponin fraction (18.0%), a mixture of two deacylsaponins (19.4%), sucrose (39.9%), sucrose and glucose (19.7%), rutin (0.8%) and quercetin (2.2%), that were identified by comparison of 1H and 13C NMR spectroscopy. The QS21 shows the typical aldehyde group in C-23 (65% equatorial) and a normonoterpene moiety acylated in C-28. The deacylsaponins show the aldehyde group but do not have the normonoterpene moiety. Balb/c mice were vaccinated with 150 microg of FML antigen of Leishmania donovani and 100 microg of each obtained fraction and further challenged by infection with 10(8) amastigotes of Leishmania chagasi. The safety analysis and the effect on humoral and cellular immune responses and in clinical signs showed that the QS21 saponin and the deacylsaponins are the most active adjuvant compounds of the Riedel the Haen saponin mixture. Both induced the highest and non-significantly different increases in DTH, CD4+ T lymphocytes in spleen, IFN-gamma in vitro, body weight gain and the most pronounced reduction of parasite burden in liver (95% for QS21 and 86% for deacylsaponins; p>0.05). While the QS21 showed mild toxicity, significant adjuvant effect on the anti-FML humoral response before and after infection, and decrease in liver relative weight, the deacylsaponins showed no toxicity, less haemolysis and antibody and DTH responses increased mainly after infection, still inducing a stronger Leishmania-specific in vitro splenocyte proliferation. Our results confirm in the Riedel de Haen saponin extract the presence of deacylsaponins normonoterpene-deprivated which are non-toxic and capable of inducing a specific and strong immunoprotective response in vaccination against murine visceral leishmaniasis.

Leishmune vaccine blocks the transmission of canine visceral leishmaniasis: absence of Leishmania parasites in blood, skin and lymph nodes of vaccinated exposed dogs

Leishmune vaccine is the first licensed vaccine against canine visceral leishmaniasis. It contains the Fucose-Mannose-ligand (FML) antigen of Leishmania donovani. The potential Leishmune vaccine effect on the interruption of the transmission of the disease, was assayed by monitoring, in untreated (n=40) and vaccinated dogs (n=32) of a Brazilian epidemic area: the kala-azar clinical signs, the FML-seropositivity and the Leishmania parasite evidence by immunohistochemistry of skin and PCR for Leishmanial DNA of lymph node and blood samples. On month 11 after vaccination, untreated controls showed: 25% of symptomatic cases, 50% of FML-seropositivity, 56.7% of lymph node PCR, 15.7% of blood PCR and 25% of immunohistochemical positive reactions. The Leishmune-vaccinated dogs showed 100% of seropositivity to FML and a complete absence of clinical signs and of parasites (0%) in skin, lymph node and blood PCR samples (p<0.01). The positivity in FML-ELISA in untreated dogs significantly correlates with the PCR in lymph node samples (p<0.001) and with the increase in number of symptoms (p=0.006) being strong markers of infectiousness. The absence of symptoms and of evidence of Leishmania DNA and parasites in Leishmune-vaccinated animals indicates the non-infectious condition of the Leishmune-vaccinated dogs.

Improving methods for epidemiological control of canine visceral leishmaniasis based on a mathematical model. Impact on the incidence of the canine and human disease

The mathematical model described by Dye (1996) condemned the epidemiological canine visceral leishma-niasis control campaign, considering it non-efficient. Using this model, we mathematically demonstrate that the control is not efficient, only at low values (rate at which latent and infectious dogs are lost by the destruction program) which match the canine seropositivity observed in the field by the immunofluorescency (IF) blood eluates analysis. With higher k values, corresponding to IF (k = 0.07) or ELISA ( k = 0.25) results in sera samples, the number of infectious dogs declines to a Ro =1 or Ro =0, respectively, interrupting the transmission and the advancement of epidemics. We also experimentally demonstrate that the dog removal, following the results of IF of sera, instead of eluates lead to a 57% (p < 0.005) decrease in canine cases and 87.5% (p < 0.005) in human cases. Our mathematical and experimental results indicate that the control campaign become more efficient by enhancing the sensitivity of the diagnostic assay.

Long lasting protection against canine kala-azar using the FML-QuilA saponin vaccine in an endemic area of Brazil (São Gonçalo do Amarante, RN)

Naturally exposed dogs of an endemic area were vaccinated with the fucose mannose ligand (FML) antigen of Leishmania donovani in formulation with QuilA saponin. The 100% of vaccinees were seropositive to FML and showed intradermal reaction to L. donovani lysate, 2 months after vaccination. The absorbency values and size of intradermal reaction were both significantly higher in vaccinees than in controls along a 3.5 years period (ANOVA, P<0.0001). The 25% of the control animals (two dogs on the first year and six dogs on the fourth year, respectively) and 5% of the vaccinees (one dog during the fourth year) developed clinical and fatal disease until the end of experiment. This difference was significant (chi(2)=3.93, P<0.05). This means that 95% protection against kala-azar was achieved in vaccinees, after FML-QuilA vaccination (80% of vaccine efficacy (VE)). Leishmania infection was also confirmed, 3.5 years after vaccination, in saline controls that showed positive polymerase chain reaction (PCR) for Leishmania DNA and FML-serology with no intradermal reaction. Higher seropositivities and intradermal reactions with no Leishmanial DNA were detected in vaccinees. The FML-QuilA vaccine induced a significant, long lasting and strong protective effect against canine kala-azar in the field.

A phase III trial of efficacy of the FML-vaccine against canine kala-azar in an endemic area of Brazil (São Gonçalo do Amaranto, RN)

Protection against canine kala-azar was investigated in naturally exposed dogs of an endemic area, vaccinated with the fucose mannose ligand (FML)-vaccine of Leishmania donovani. A total of 97% of vaccinees were seropositive to FML and 100% showed intradermal reaction to L. donovani lysate, 7 months after vaccination. The absorbency values and size of intradermal reaction were both significantly higher in vaccinees than in controls (ANOVA, P<0.0001). After 2 years, 92% (chi(2)=6.996; P<0.0025) protection was achieved: only 8% of vaccinees showed mild signs of kala-azar with no deaths while 33% of controls developed clinical or fatal disease. The FML-vaccine induced a significant, long-lasting and strong protective effect against canine kala-azar in the field.