Vaccination with leishmania hemoglobin receptor-encoding DNA protects against visceral leishmaniasis

Visceral Leishmaniasis: Advancements in Vaccine Development via Classical and Molecular Approaches

Visceral leishmaniasis (VL) or kala-azar, a vector-borne protozoan disease, shows endemicity in larger areas of the tropical, subtropical and the Mediterranean countries. WHO report suggested that an annual incidence of VL is nearly 200,000 to 400,000 cases, resulting in 20,000 to 30,000 deaths per year. Treatment with available anti-leishmanial drugs are not cost effective, with varied efficacies and higher relapse rate, which poses a major challenge to current kala-azar control program in Indian subcontinent. Therefore, a vaccine against VL is imperative and knowing the fact that recovered individuals developed lifelong immunity against re-infection, it is feasible. Vaccine development program, though time taking, has recently gained momentum with the emergence of omic era, i.e., from genomics to immunomics. Classical as well as molecular methodologies have been overtaken with alternative strategies wherein proteomics based knowledge combined with computational techniques (immunoinformatics) speed up the identification and detailed characterization of new antigens for potential vaccine candidates. This may eventually help in the designing of polyvalent synthetic and recombinant chimeric vaccines as an effective intervention measures to control the disease in endemic areas. This review focuses on such newer approaches being utilized for vaccine development against VL.

Antimony resistant Leishmania donovani but not sensitive ones drives greater frequency of potent T-regulatory cells upon interaction with human PBMCs: role of IL-10 and TGF-β in early immune response

In India the sand fly, Phlebotomus argentipes, transmitted parasitic disease termed kala-azar is caused by Leishmania donovani (LD) in humans. These immune-evading parasites have increasingly developed resistance to the drug sodium antimony gluconate in endemic regions.

Lack of early diagnosis methods for the disease limits the information available regarding the early interactions of this parasite with either human tissues or cell lineages. We reasoned that peripheral blood mononuclear cells (PBMCs) from healthy human beings could help compare some of their immune signatures once they were exposed for up to 8 days, to either pentavalent antimony sensitive (Sb^S-LD) or resistant (Sb^R-LD) Leishmania donovani isolates.

At day 2, PBMC cultures exposed to Sb^S-LD and Sb^R-LD stationary phase promastigotes had four and seven fold higher frequency of IL-10 secreting monocyte-macrophage respectively, compared to cultures unexposed to parasites. Contrasting with the CD4⁺CD25⁻CD127⁻ type-1 T-regulatory (Tr1) cell population that displayed similar features whatever the culture conditions, there was a pronounced increase in the IL-10 producing CD4⁺CD25⁺CD127^low/− inducible T-regulatory cells (iTregs) in the PBMC cultures sampled at day 8 post addition of Sb^R-LD.

Sorted iTregs from different cultures on day 8 were added to anti-CD3/CD28 induced naïve PBMCs to assess their suppressive ability. We observed that iTregs from Sb^R-LD exposed PBMCs had more pronounced suppressive ability compared to Sb^S-LD counterpart on a per cell basis and is dependent on both IL-10 and TGF-β, whereas IL-10 being the major factor contributing to the suppressive ability of iTregs sorted from PBMC cultures exposed to Sb^S–LD. Of note, iTreg population frequency value remained at the basal level after addition of genetically modified Sb^R-LD lacking unique terminal sugar in surface glycan.

Even with limitations of this artificial in vitro model of L. donovani-human PBMC interactions, the present findings suggest that Sb^R-LD have higher immunomodulatory capacity which may favour aggressive pathology.

The disease Kala-azar is caused by Leishmania donovani (LD). The disease is characterized by the depression of cellular immune response. In the Indian subcontinent LD parasites are mostly resistant to commonly used antileishmanial drug, like sodium antimony gluconate (SAG). It is known that infection with pentavalent antimony (Sb)-resistant parasites induces aggressive pathology- the cause is still not known. Sb-resistant parasites endowed with unique glycan which may also play an important role in the pathogenesis as following removal of terminal sugar of glycan these parasites behave like sensitive parasites. The diagnosis of the disease is possible after the disease sets in and therefore limited information is available on the host-parasite interaction at the onset of disease. As a surrogate of in vivo scenario we studied the interaction between normal human PBMC with Sb-sensitive and Sb-resistant parasites. The Sb-resistant parasites upon interaction with human peripheral blood mononuclear cells (PBMC) in vitro produced two distinct inhibitory cytokines, IL-10 and TGF-β. Similar experiment with Sb-sensitive LD induced much less amount of above cytokines. Thus aggressive pathology induced by Sb-resistant LD, may be, in part attributed to production of dual inhibitory cytokines where surface glycan of the parasite may play a decisive role.

Vaccines to prevent leishmaniasis

Leishmaniasis is a parasitic disease that encompasses a range of clinical manifestations affecting people in tropical and subtropical regions of the world. Epidemiological and experimental data indicate that protection from disease can be achieved in most people. In addition, we know how the host immune system must respond to infection in order to control parasite growth. However, there is still no vaccine for use in humans. Here, we review our understanding of host immunity following Leishmania infection and also discuss recent advances in the development of vaccines to prevent leishmaniasis, highlighting a new promising approach that targets the parasite hemoglobin receptor.

Extracellular functions of glycolytic enzymes of parasites: unpredicted use of ancient proteins

In addition of their usual intracellular localization where they are involved in catalyzing reactions of carbohydrate and energy metabolism by glycolysis, multiple studies have shown that glycolytic enzymes of many organisms, but notably pathogens, can also be present extracellularly. In the case of parasitic protists and helminths, they can be found either secreted or attached to the surface of the parasites. At these extracellular localizations, these enzymes have been shown to perform additional, very different so-called "moonlighting" functions, such as acting as ligands for a variety of components of the host. Due to this recognition, different extracellular glycolytic enzymes participate in various important parasite-host interactions such as adherence and invasion of parasites, modulation of the host's immune and haemostatic systems, promotion of angiogenesis, and acquisition of specific nutrients by the parasites. Accordingly, extracellular glycolytic enzymes are important for the invasion of the parasites and their establishment in the host, and in determining their virulence.