F1 Domain of the Leishmania (Leishmania) donovani Nucleoside Hydrolase Promotes a Th1 Response in Leishmania (Leishmania) infantum Cured Patients and in Asymptomatic Individuals Living in an Endemic Area of Leishmaniasis

CD4+ Th1 and Th17 responses and multifunctional CD8 T lymphocytes associated with cure or disease worsening in human visceral leishmaniasis

Introduction

In VL, a proinflammatory phenotype is typically associated with enhanced phagocytosis and a Th1 mediated immune response resulting in infection control. In contrast, an anti-inflammatory phenotype, associated with a predominant regulatory response, typically enables intracellular multiplication of Leishmania parasites and disease progression.

Methods

To investigate the impact of chemotherapy on Th2 and Th17 immune responses in patients with visceral leishmaniasis (VL), we assessed all combinations of intracellular expression of IFN-γ, IL-10, IL-4 and IL-17 in the CD4+ and CD8+ T cell populations of peripheral blood mononuclear cell (PBMC) samples from patients, after antigenic stimulation with Leishmania lysate, throughout treatment and follow-up. As increases in spleen and liver sizes and decreases in hematocrit, hemogloblin, erythrocytes, monocytes, leukocytes and platelets levels are strongly related to the disease, we studied the correlations between the frequencies of T cells producing the afore mentioned cytokines, individually and in combination, and these variables, as markers of disease or cure.

Results

We found that the frequency of IFN-γ-producingCD4+ T cells increased until the end of chemotherapy with Glucantime® or AmBisome ®, while IL-10, IL-4 and IL-17-producing CD4+ T cells peaked on day 7 following the start of treatment. Although the frequency of CD4+IL-17+ cells decreased during treatment an increase was observed after clinical cure. The frequency of CD4+ T cells producing only IFN-γ or IL-17 correlated with blood monocytes levels. Frequencies of double-producers of IFN-γ and IL-10 or IL-4 correlated positively with eosinophils and platelets levels. Together, this suggest that IFN-γ drives the immune response towards Th1 at cure. In contrast, and associated with disease or Th2 response, the frequency of CD4+ IL-10+ cells correlated positively with spleen sizes and negatively with circulating monocyte levels, while the frequency of CD4+ producing both IL-4 and IL-10 correlated negatively with platelets levels. The frequency of CD8+ single-producers of IFN-γ increased from day 21 to 90 while that of single-producers of IL-10 peaked on day 7, of IL-4 on day 30 and of IL-17, on day 180. IFN-γ expression in CD8+ single- and double-producers of cytokines was indicative of an immune response associated with cure. In contrast, frequencies of CD8+ double-producers of IL-4 and IL-10, IL-4 and IL-17 and IL-10 and IL-17 and producers of three and four cytokines, were associated with disease and were low after the cure. Frequencies of CD8+ T cells producing IFN-γ alone or with IL-17 were positively correlated with platelets levels. In contrast, as markers of disease: 1) frequencies of single producers of IL-10 correlated negatively with leukocytes levels, 2) frequencies of double producers of IL-4 and IL-10 correlated negatively with platelet, leukocyte, lymphocyte and circulating monocyte levels, 3) frequencies of triple-producers of IFN-γ, IL-4 and IL-10 correlated negatively with platelet, leukocyte and neutrophil levels and 4) frequencies of producers of IFN-γ, IL-4, IL-10 and IL-17 simultaneously correlated positively with spleen size, and negatively with leukocyte and neutrophil levels.

Discussion

Our results confirmed that the clinical improvement of VL patients correlates with the decrease of an IL-4 and IL-10 CD4+Th2 response, the recovery of CD4+ Th1 and Th17 responses and the frequency of CD8+ single-producers of IFN-γ and double producers of IFN-γ and IL-17.

Multifunctional, TNF-α and IFN-γ-Secreting CD4 and CD8 T Cells and CD8High T Cells Are Associated With the Cure of Human Visceral Leishmaniasis

Visceral leishmaniasis (VL) is a chronic and often fatal disease caused by protozoans of the genus Leishmania that affects millions of people worldwide. Patients with symptomatic VL have an impaired anti-Leishmania-specific CD4⁺ T-cell response, which is reversed after clinical cure. In contrast, the quality of the CD4⁺ and CD8⁺ T-cell responses involved in resistance and/or cure of VL relies on the capability of these cells to activate polyfunctional and memory responses, which are associated with the simultaneous production of three cytokines: IFN-γ, IL-2, and TNF-α. Models for the development of CD4 and CD8 T-cell quality in memory and protection to leishmaniasis have been described previously. We aimed to assess the functionality of the T cells involved in the recovery of the immune suppression throughout the VL treatment. Therefore, we cultured peripheral blood mononuclear cells (PBMCs) from VL patients and healthy controls in vitro with soluble Leishmania antigen (SLA). Cell surface markers and intracellular cytokine production were determined on days 7, 14, 21, 30, 60, 90, and 180 after the beginning of chemotherapy. We observed that the frequencies of CD4⁺TNF-α⁺IFN-γ⁺ and the multifunctional CD4⁺IL-2⁺TNF-α⁺IFN-γ⁺, together with CD4⁺TNF-α⁺ and CD4⁺IFN-γ⁺ T cells, increased throughout and at the end of the treatment, respectively. In addition, enhanced frequencies of CD8⁺IL-2⁺TNF-α⁺IFN-γ⁺ and CD8⁺TNF-α⁺IFN-γ T cells were also relevant in the healing process. Noteworthy, the frequencies of the CD4⁺ and CD8 central-memory T cells, which produce IL-2, TNF-α, and IFN-γ and ensure the memory response against parasite reinfection, are significantly enhanced in cured patients. In addition, the subset of the non-functional CD8^Low population is predominant in VL untreated patients and decreases along the chemotherapy treatment. In contrast, a CD8^High subset increased towards the cure. Furthermore, the cure due to treatment with meglumine antimoniate or with liposomal amphotericin B was associated with the recovery of the T-cell immune responses. We described the evolution and participation of functional T cells during the treatment of patients with VL. Our results disclosed that the clinical improvement of patients is significantly associated with the participation of the CD4⁺ and CD8⁺ cytokine-secreting T cells.

Protective Efficacy in a Hamster Model of a Multivalent Vaccine for Human Visceral Leishmaniasis (MuLeVaClin) Consisting of the KMP11, LEISH-F3+, and LJL143 Antigens in Virosomes, Plus GLA-SE Adjuvant

Visceral leishmaniasis (VL) is the most severe clinical form of leishmaniasis, fatal if untreated. Vaccination is the most cost-effective approach to disease control; however, to date, no vaccines against human VL have been made available. This work examines the efficacy of a novel vaccine consisting of the Leishmania membrane protein KMP11, LEISH-F3+ (a recombinant fusion protein, composed of epitopes of the parasite proteins nucleoside hydrolase, sterol-24-c-methyltransferase, and cysteine protease B), and the sand fly salivary protein LJL143, in two dose ratios. The inclusion of the TLR4 agonist GLA-SE as an adjuvant, and the use of virosomes (VS) as a delivery system, are also examined. In a hamster model of VL, the vaccine elicited antigen-specific immune responses prior to infection with Leishmania infantum. Of note, the responses were greater when higher doses of KMP11 and LEISH-F3+ proteins were administered along with the GLA-SE adjuvant and/or when delivered within VS. Remarkably, hamsters immunized with the complete combination (i.e., all antigens in VS + GLA-SE) showed significantly lower parasite burdens in the spleen compared to those in control animals. This protection was underpinned by a more intense, specific humoral response against the KMP11, LEISH-F3+, and LJL143 antigens in vaccinated animals, but a significantly less intense antibody response to the pool of soluble Leishmania antigens (SLA). Overall, these results indicate that this innovative vaccine formulation confers protection against L. infantum infection, supporting the advancement of the vaccine formulation into process development and manufacturing and the conduction of toxicity studies towards future phase I human clinical trials.

The Delay in the Licensing of Protozoal Vaccines: A Comparative History

Although viruses and bacteria have been known as agents of diseases since 1546, 250 years went by until the first vaccines against these pathogens were developed (1796 and 1800s). In contrast, Malaria, which is a protozoan-neglected disease, has been known since the 5th century BCE and, despite 2,500 years having passed since then, no human vaccine has yet been licensed for Malaria. Additionally, no modern human vaccine is currently licensed against Visceral or Cutaneous leishmaniasis. Vaccination against Malaria evolved from the inoculation of irradiated sporozoites through the bite of Anopheles mosquitoes in 1930's, which failed to give protection, to the use of controlled human Malaria infection (CHMI) provoked by live sporozoites of Plasmodium falciparum and curtailed with specific chemotherapy since 1940's. Although the use of CHMI for vaccination was relatively efficacious, it has some ethical limitations and was substituted by the use of injected recombinant vaccines expressing the main antigens of the parasite cycle, starting in 1980. Pre-erythrocytic (PEV), Blood stage (BSV), transmission-blocking (TBV), antitoxic (AT), and pregnancy-associated Malaria vaccines are under development. Currently, the RTS,S-PEV vaccine, based on the circumsporozoite protein, is the only one that has arrived at the Phase III trial stage. The “R” stands for the central repeat region of Plasmodium (P.) falciparum circumsporozoite protein (CSP); the “T” for the T-cell epitopes of the CSP; and the “S” for hepatitis B surface antigen (HBsAg). In Africa, this latter vaccine achieved only 36.7% vaccine efficacy (VE) in 5–7 years old children and was associated with an increase in clinical cases in one assay. Therefore, in spite of 35 years of research, there is no currently licensed vaccine against Malaria. In contrast, more progress has been achieved regarding prevention of leishmaniasis by vaccine, which also started with the use of live vaccines. For ethical reasons, these were substituted by second-generation subunit or recombinant DNA and protein vaccines. Currently, there is one live vaccine for humans licensed in Uzbekistan, and four licensed veterinary vaccines against visceral leishmaniasis: Leishmune® (76–80% VE) and CaniLeish® (68.4% VE), which give protection against strong endpoints (severe disease and deaths under natural conditions), and, under less severe endpoints (parasitologically and PCR-positive cases), Leishtec® developed 71.4% VE in a low infective pressure area but only 35.7% VE and transient protection in a high infective pressure area, while Letifend® promoted 72% VE. A human recombinant vaccine based on the Nucleoside hydrolase NH36 of Leishmania (L.) donovani, the main antigen of the Leishmune® vaccine, and the sterol 24-c-methyltransferase (SMT) from L. (L.) infantum has reached the Phase I clinical trial phase but has not yet been licensed against the disease. This review describes the history of vaccine development and is focused on licensed formulations that have been used in preventive medicine. Special attention has been given to the delay in the development and licensing of human vaccines against Protozoan infections, which show high incidence worldwide and still remain severe threats to Public Health.

Expression, purification and spectrophotometric analysis of nucleoside hydrolase from Leishmania chagasi (LcNH)

Leishmaniasis represents an important public health problem in several countries. The main target in this study is the nucleoside hydrolase Leishmania chagasi (LcNH) that is responsible for causing visceral leishmaniasis, principally in Brazil. Nucleoside hydrolase enzymes are members of this pathway, hydrolyzing the N-glycosidic bond of ribonucleosides for the synthesis of nucleic acids. We present here for the first time, the expression and purification protocols to obtain the enzymes LcNH1 and LcNH2 that can be employed to explore novel strategies to produce nucleoside hydrolase inhibitors for use in chemotherapy. Protein integrity was also confirmed by SDS-PAGE gel, mass spectrometry and enzymatic activity.

Nucleoside Hydrolase NH 36: A Vital Enzyme for the Leishmania Genus in the Development of T-Cell Epitope Cross-Protective Vaccines

NH36 is a vital enzyme of the DNA metabolism and a specific target for anti-Leishmania chemotherapy. We developed second-generation vaccines composed of the FML complex or its main native antigen, the NH36 nucleoside hydrolase of Leishmania (L.) donovani and saponin, and a DNA vaccine containing the NH36 gene. All these vaccines were effective in prophylaxis and treatment of mice and dog visceral leishmaniasis (VL). The FML-saponin vaccine became the first licensed veterinary vaccine against leishmaniasis (Leishmune®) which reduced the incidence of human and canine VL in endemic areas. The NH36, DNA or recombinant protein vaccines induced a Th1 CD4+IFN-γ+ mediated protection in mice. Efficacy against VL was mediated by a CD4+TNF-α T lymphocyte response against the NH36-F3 domain, while against tegumentary leishmaniasis (TL) a CD8+ T lymphocyte response to F1 was also required. These domains were 36-41 % more protective than NH36, and a recombinant F1F3 chimera was 21% stronger than the domains, promoting a 99.8% reduction of the parasite load. We also identified the most immunogenic NH36 domains and epitopes for PBMC of active human VL, cured or asymptomatic and DTH+ patients. Currently, the NH36 subunit recombinant vaccine is turning into a multi-epitope T cell synthetic vaccine against VL and TL.

Mycobacterium leprae Recombinant Antigen Induces High Expression of Multifunction T Lymphocytes and Is Promising as a Specific Vaccine for Leprosy

Leprosy is a chronic disease caused by M. leprae infection that can cause severe neurological complications and physical disabilities. A leprosy-specific vaccine would be an important component within control programs but is still lacking. Given that multifunctional CD4 T cells [i.e., those capable of simultaneously secreting combinations of interferon (IFN)-γ, interleukin (IL)-2, and tumor necrosis factor (TNF)] have now been implicated in the protective response to several infections, we tested the hypothesis if a recombinant M. leprae antigen-specific multifunctional T cells differed between leprosy patients and their healthy contacts. We used whole blood assays and peripheral blood mononuclear cells to characterize the antigen-specific T cell responses of 39 paucibacillary (PB) and 17 multibacillary (MB) leprosy patients and 31 healthy household contacts (HHC). Cells were incubated with either crude mycobacterial extracts (M. leprae cell sonicate–MLCS) and purified protein derivative (PPD) or recombinant ML2028 protein, the homolog of M. tuberculosis Ag85B. Multiplex assay revealed antigen-specific production of IFN-γ and IL-2 from cells of HHC and PB, confirming a Th1 bias within these individuals. Multiparameter flow cytometry then revealed that the population of multifunctional ML2028-specific T cells observed in HHC was larger than that observed in PB patients. Taken together, our data suggest that these multifunctional antigen-specific T cells provide a more effective response against M. leprae infection that prevents the development of leprosy. These data further our understanding of M. leprae infection/leprosy and are instructive for vaccine development.

Enzymatic Transition States and Drug Design

Transition state theory teaches that chemically stable mimics of enzymatic transition states will bind tightly to their cognate enzymes. Kinetic isotope effects combined with computational quantum chemistry provides enzymatic transition state information with sufficient fidelity to design transition state analogues. Examples are selected from various stages of drug development to demonstrate the application of transition state theory, inhibitor design, physicochemical characterization of transition state analogues, and their progress in drug development.

NH36 and F3 Antigen-Primed Dendritic Cells Show Preserved Migrating Capabilities and CCR7 Expression and F3 Is Effective in Immunotherapy of Visceral Leishmaniasis

Physical contact between dendritic cells (DCs) and T cell lymphocytes is necessary to trigger the immune cell response. CCL19 and CCL21 chemokines bind to the CCR7 receptor of mature DCs, and of T cells and regulate DCs migration to the white pulp (wp) of the spleen, where they encounter lymphocytes. In visceral leishmaniasis (VL), cellular immunosuppression is mediated by impaired DC migration due to the decreased chemokine secretion by endothelium and to the reduced DCs CCR7 expression. The Leishmania (L.) donovani nucleoside hydrolase NH36 and its C-terminal domain, the F3 peptide are prominent antigens in the generation of preventive immunity to VL. We assessed whether these vaccines could prevent the migrating defect of DCs by restoring the expression of CCR7 receptors. C57Bl6 mice were vaccinated with NH36 and F3 and challenged with L. (L.) infantum chagasi. The F3 vaccine induced a 100% of survival and a long-lasting immune protection with an earlier CD4+Th1 response, with secretion of higher IFN-γ and TNF-α/IL-10 ratios, and higher frequencies of CD4+ T cells secreting IL-2+, TNF-α+, or IFN-γ+, or a combination of two or the three cytokines (IL-2+TNF-α+IFN-γ+). The CD8+ T cell response was promoted earlier by the NH36-vaccine, and later by the F3-vaccine. Maximal number of F3-primed DCs migrated in vitro in response to CCL19 and showed a high expression of CCR7 receptors (26.06%). Anti-CCR7 antibody treatment inhibited DCs migration in vitro (90%) and increased parasite load in vivo. When transferred into 28-day-infected mice, only 8% of DCs from infected, 59% of DCs from NH36-vaccinated, and 84% of DCs from F3-vaccinated mice migrated to the wp. Consequently, immunotherapy of infected mice with F3-primed DCs only, promoted increases in corporal weight and reductions of spleen and liver parasite loads and relative weights. Our findings indicate that vaccination with F3-vaccine preserves the maturation, migration properties and CCR7 expression of DCs, which are essential processes for the generation of cell-mediated immunity. The F3 vaccine is more potent in reversing the migration defect that occurs in VL and, therefore, more efficient in immunotherapy of VL.

Antigenicity of Leishmania-Activated C-Kinase Antigen (LACK) in Human Peripheral Blood Mononuclear Cells, and Protective Effect of Prime-Boost Vaccination With pCI-neo-LACK Plus Attenuated LACK-Expressing Vaccinia Viruses in Hamsters

Leishmania-activated C-kinase antigen (LACK) is a highly conserved protein among Leishmania species and is considered a viable vaccine candidate for human leishmaniasis. In animal models, prime-boost vaccination with LACK-expressing plasmids plus attenuated vaccinia viruses (modified vaccinia Ankara [MVA] and mutant M65) expressing LACK, has been shown to protect against cutaneous leishmaniasis (CL). Further, LACK demonstrated to induce the production of protective cytokines in patients with active CL or cured visceral leishmaniasis, as well as in asymptomatic individuals from endemic areas. However, whether LACK is capable to trigger cytokine release by peripheral blood mononuclear cells from patients cured of CL due to Leishmania infantum (L. infantum) or induce protection in L. infantum-infected hamsters [visceral leishmaniasis (VL) model], has not yet been analyzed. The present work examines the ex vivo immunogenicity of LACK in cured VL and CL patients, and asymptomatic subjects from an L. infantum area. It also evaluates the vaccine potential of LACK against L. infantum infection in hamsters, in a protocol of priming with plasmid pCI-neo-LACK (DNA-LACK) followed by a booster with the poxvirus vectors MVA-LACK or M65-LACK. LACK-stimulated PBMC from both asymptomatic and cured subjects responded by producing IFN-γ, TNF-α, and granzyme B (Th1-type response). Further, 78% of PBMC samples that responded to soluble Leishmania antigen showed IFN-γ secretion following stimulation with LACK. In hamsters, the protocol of DNA-LACK prime/MVA-LACK or M65-LACK virus boost vaccination significantly reduced the amount of Leishmania DNA in the liver and bone marrow, with no differences recorded between the use of MVA or M65 virus vector options. In summary, the Th1-type and cytotoxic responses elicited by LACK in PBMC from human subjects infected with L. infantum, and the parasite protective effect of prime/boost vaccination in hamsters with DNA-LACK/MVA-LACK and DNA-LACK/M65-LACK, revealed the significance of LACK in activating human and hamster immune responses and support LACK to be a valuable candidate for inclusion in a vaccine against human VL.

Liposomal Elongation Factor-1α Triggers Effector CD4 and CD8 T Cells for Induction of Long-Lasting Protective Immunity against Visceral Leishmaniasis

Despite advances, identification and formulation of safe and effective vaccine for long-lasting protection against leishmaniasis is still inadequate. In this study, we have identified a novel antigen, leishmanial elongation factor-1α (EF1-α), as an immunodominant component of solubilized leishmanial membrane antigens that reacts with visceral leishmaniasis (VL) sera and induces cellular proliferative and cytokine response in PBMCs of cured VL subjects. Leishmanial EF1-α is a 50 kDa antigen that plays a crucial role in pathogen survival by regulating oxidative burst in the host phagocytes. Previously, immunodominant truncated forms of EF1-α from different species of Leishmania have been reported. Formulation of the L. donovani 36 kDa truncated as well as the cloned recombinant EF1-α in cationic liposomes induce strong resistance to parasitic burden in liver and spleen of BALB/c mice through induction of DTH and a IL-10 and TGF-β suppressed mixed Th1/Th2 cytokine responses. Multiparametric analysis of splenocytes for generation of antigen-specific IFN-γ, IL2, and TNF-α producing lymphocytes indicate that cationic liposome facilitates expansion of both CD4⁺ as well as CD8⁺ memory and effector T cells. Liposomal EF1-α is a novel and potent vaccine formulation against VL that imparts long-term protective responses. Moreover, the flexibility of this formulation opens up the scope to combine additional adjuvants and epitope selected antigens for use in other disease forms also.