Evaluation of Lsa46 and Lsa77 Leptospiral Proteins for Their Immunoprotective Activities in Hamster Model of Leptospirosis

Human leptospirosis: In search for a better vaccine

Leptospirosis is a neglected disease caused by bacteria of the genus Leptospira and is more prevalent in tropical and subtropical countries. This pathogen infects humans and other animals, responsible for the most widespread zoonosis in the world, estimated to be responsible for 60 000 deaths and 1 million cases per year. To date, commercial vaccines against human leptospirosis are available only in some countries such as Japan, China, Cuba and France. These vaccines prepared with inactivated Leptospira (bacterins) induce a short-term and serovar-specific immune response, with strong adverse side effects. To circumvent these limitations, several research groups are investigating new experimental vaccines in order to ensure that they are safe, efficient, and protect against several pathogenic Leptospira serovars, inducing sterilizing immunity. Most of these protocols use attenuated cultures, preparations after LPS removal, recombinant proteins or DNA from pathogenic Leptospira spp. The aim of this review was to highlight several promising vaccine candidates, considering their immunogenicity, presence in different pathogenic Leptospira serovars, their role in virulence or immune evasion and other factors.

In silico screening and epitope mapping of leptospiral outer membrane protein-Lsa46

Leptospirosis is one of the neglected diseases caused by the spirochete, Leptospira interrogans. Leptospiral surface adhesion (Lsa) proteins are surface exposed outer membrane proteins present in the pathogen. It acts as laminin and plasminogen binding proteins which enable them to infect host cells. The major target for the development of vaccine in the current era focuses on surface exposed outer membrane proteins, as they can induce strong and fast immune response in hosts. Therefore, the present study mapped the potential epitopes of the Leptospiral outer membrane proteins, mainly the surface adhesion proteins. Protein sequence analysis of Lsa proteins was done by in silico methods. The primary protein sequence analysis revealed Lsa46 as a suitable target which can be a potent Leptospiral vaccine candidate. Its structure was modelled by threading based method in I-TASSER server and validated by Ramachandran plot. The predicted epitope's interactions with human IgG, IgM(Fab) and T-cell receptor TCR(αβ) were performed by molecular docking studies using Biovia Discovery studio 2018. One of the predicted B-cell epitopes and the IgG showed desirable binding interactions, while four of the predicted B-cell epitopes and T-cell epitopes showed desirable binding interactions with IgM and TCR respectively. The molecular dynamic simulation studies carried out with the molecular docked complexes gave minimized energies indicating stable interactions. The structural analysis of the entire simulated complex showed a stable nature except for one of the Epitope-IgM complex. Further the binding free energy calculation of eight receptor-ligand complex predicted them energetically stable. The results of the study help in elucidating the structural and functional characterization of Lsa46 for epitope-based vaccine design.Communicated by Ramaswamy H. Sarma.

LigA formulated in AS04 or Montanide ISA720VG induced superior immune response compared to alum, which correlated to protective efficacy in a hamster model of leptospirosis

Leptospirosis is a zoonotic disease of global importance. The current vaccine provides serovar-specific and short-term immunity and does not prevent bacterial shedding in infected animals. Subunit vaccines based on surface proteins have shown to induce protection in an animal model. However, these proteins were tested with non-clinical adjuvants and induced low to moderate protective efficacy. We formulated a variable region of Leptospira immunoglobulin-like protein A (LAV) in clinical adjuvants, AS04 and Montanide ISA720VG, and then evaluated the immune response in mice and protective efficacy in a hamster model. Our results show that animals immunized with LAV-AS04 and LAV-Montanide ISA720VG (LAV-M) induced significantly higher levels of LAV-specific antibodies than LAV-Alum. While LAV-Alum induced Th2 response with the induction of IgG1 and IL-4, AS04 and LAV-M induced a mixed Th1/Th2 response with significant levels of both IgG1/IL-4 and IgG2c/IFN-γ. Both LAV-AS04 and LAV-M induced the generation of a significantly higher number of cytotoxic T cells (CTLs). The immune response in LAV-AS04- and LAV-M-immunized animals was maintained for a long period (>180 days) with the generation of a significant level of B- and T-cell memory. The strong immune response by both vaccines correlated to enhanced recruitment and activation of innate immune cells particularly DCs at draining lymph nodes and the formation of germinal centers (GCs). Furthermore, the immune response generated in mice correlated to protective efficacy in the hamster model of leptospirosis. These results indicate that LAV-AS04 and LAV-M are promising vaccines and can be further evaluated in clinical trials.

Revisiting the Development of Vaccines Against Pathogenic Leptospira: Innovative Approaches, Present Challenges, and Future Perspectives

Human vaccination against leptospirosis has been relatively unsuccessful in clinical applications despite an expressive amount of vaccine candidates has been tested over years of research. Pathogenic Leptospira encompass a great number of serovars, most of which do not cross-react, and there has been a lack of genetic tools for many years. These obstacles have hampered the understanding of the bacteria's biology and, consequently, the identification of an effective antigen. Thus far, many approaches have been used in an attempt to find a cost-effective and broad-spectrum protective antigen(s) against the disease. In this extensive review, we discuss several strategies that have been used to develop an effective vaccine against leptospirosis, starting with Leptospira-inactivated bacterin, proteins identified in the genome sequences of pathogenic Leptospira, including reverse vaccinology, plasmid DNA, live vaccines, chimeric multi-epitope, and toll- and nod-like receptors agonists. This overview should be able to guide scientists working in the field to select potential antigens and to choose the appropriate formulation to administer the candidates.

Vaccine potential of LenA and LcpA proteins of Leptospira interrogans in combination with Escherichia coli heat-labile enterotoxin, B subunit (LTB)

BACKGROUND AND OBJECTIVES

Leptospirosis is a zooanthroponosis caused by the genus of Leptospira. It is an emerging public health problem due to its increasing incidence. The achievement to a vaccine that prevent from entrance of Leptospira interrogans to the deeper tissues of the host is needed. This study aimed to investigate the immunogenicity of LcpA (rLcpA) and LenA (rLenA) recombinant proteins in combination with LTB (rLTB) recombinant protein as an adjuvant against leptospiral infection in hamsters.

MATERIALS AND METHODS

The genes encoding these proteins were cloned into pGH cloning vector and then lenA, lcpA and ltb genes subcloned into pET-15b and pET-28a expression vectors, respectively. The hamsters were immunized with the purified recombinant proteins and challenged with Leptospira interrogans for evaluation of their survival. The antibody responses to the recombinant proteins were determined by ELISA. Then, data entered into SPSS software. Statistical Kruskal-Wallis test was used to compare the significant differences among different groups. The groups with significant differences were further analyzed by post hoc tests. The p value < 0.05 statistically was considered significant.

RESULTS

Immunized hamsters with rLenA-plus-rLTB, rLcpA-plus-rLTB and rLenA-plus-rLcpA-plus-rLTB proteins showed 60%, 74%, and 80% survival rates, respectively. A significant amount of interleukin-17 (IL-17), interleukin-4 (IL-4) and gamma interferon (IFNγ) cytokines were produced in immunized hamsters.

CONCLUSION

Based on our findings, rLcpA and rLenA proteins in combination with rLTB can protect the hamsters against L. interrogans and effectively induce a protective antibody response. Thus, these proteins can be used as an additional prophylactic tool against leptospira.