Multivalent fusion protein vaccine for lymphatic filariasis

Dose-Dependent Prophylactic Efficacy of Filarial Antigens Glutathione-S-Transferase and Abundant Larval Transcript-2 against Brugia malayi Challenge in Mastomys

Objective

To identify the most effective dose of filarial rBmALT-2 and rWbGST alone or in combination against B. malayi infection in vitro and in vivo.

Methods

Mastomys (n = 5-7/group) received intramuscular (i.m.) injection with three different doses (25, 50, and 100 μg) of rBmALT-2 or rWbGST, either alone or in combination with alum as the adjuvant. Protective immunity was studied by in vivo and in vitro cytotoxicity assay. To evaluate the cellular immune response, splenocyte proliferation and cytokine profile were assessed.

Results

Serological results revealed a substantial (p < 0.005) induction of IgG1, IgG2a, and IgG3 responses in vaccinated Mastomys. Mastomys immunized with 50 μg rBmALT-2 + alum induced 79-81% killing against the L3 larvae challenge in vivo and in vitro ADCC assay (p < 0.005); whereas rWbGST + alum alone or in combination with rBmALT-2 + alum induced 63-68% killing (p < 0.005) in vivo and in vitro. Antigen-specific cytokine profiles of Mastomys vaccinated with either BmALT-2, WbGST or a combination showed elevated IL-10, IL-4, and IFN-γ levels, signifying both Th1 and Th2 immune response.

Conclusions

These findings suggest that immunization of Mastomys with a 50 μg/dose of rBmALT-2 + alum four times at a 4-week interval demonstrated considerable protection against B. malayi infection.

Molecular insights and antibody response to Dr20/22 in dogs naturally infected with Dirofilaria repens

Subcutaneous dirofilariasis, caused by the parasitic nematode Dirofilaria repens, is a growing concern in Europe, affecting both dogs and humans. This study focused on D. repens Dr20/22, a protein encoded by an alt (abundant larval transcript) gene family. While well-documented in L3 larvae of other filariae species, this gene family had not been explored in dirofilariasis. The research involved cloning Dr20/22 cDNA, molecular characterization, and evaluating its potential application in the diagnosis of dirofilariasis. Although Real-Time analysis revealed mRNA expression in both adult worms and microfilariae, the native protein remained undetected in lysates from both developmental stages. This suggests the protein's specificity for L3 larvae and may be related to a process called SLTS (spliced leader trans-splicing), contributing to stage-specific gene expression. The specificity of the antigen for invasive larvae positions it as a promising early marker for dirofilariasis. However, ELISA tests using sera from infected and uninfected dogs indicated limited diagnostic utility. While further research is required, our findings contribute to a deeper understanding of the molecular and immunological aspects of host-parasite interactions and could offer insights into the parasite's strategies for evading the immune system.

Identification and prioritisation of potential vaccine candidates using subtractive proteomics and designing of a multi-epitope vaccine against Wuchereria bancrofti

This study employed subtractive proteomics and immunoinformatics to analyze the Wuchereria bancrofti proteome and identify potential therapeutic targets, with a focus on designing a vaccine against the parasite species. A comprehensive bioinformatics analysis of the parasite's proteome identified 51 probable therapeutic targets, among which "Kunitz/bovine pancreatic trypsin inhibitor domain-containing protein" was identified as the most promising vaccine candidate. The candidate protein was used to design a multi-epitope vaccine, incorporating B-cell and T-cell epitopes identified through various tools. The vaccine construct underwent extensive analysis of its antigenic, physical, and chemical features, including the determination of secondary and tertiary structures. Docking and molecular dynamics simulations were performed with HLA alleles, Toll-like receptor 4 (TLR4), and TLR3 to assess its potential to elicit the human immune response. Immune simulation analysis confirmed the predicted vaccine's strong binding affinity with immunoglobulins, indicating its potential efficacy in generating an immune response. However, experimental validation and testing of this multi-epitope vaccine construct would be needed to assess its potential against W. bancrofti and even for a broader range of lymphatic filarial infections given the similarities between W. bancrofti and Brugia.

Enhanced protective immunity against Baylisascaris schroederi infection in mice through a multi-antigen cocktail vaccine approach

Baylisascaris schroederi is among the most severe intestinal nematodes affecting giant pandas. Developing effective and secure vaccines can be used as a novel strategy for controlling repeated roundworm infection and addressing drug resistance. In our previous study, three recombinant antigens (rBsHP2, rBsGAL, and rBsUP) exhibited promising effects against B. schroederi infection in the mice model. This study extends the findings by formulating four-form cocktail vaccines (GAL+UP, HP2+UP, GAL+HP2, and GAL+HP2+UP) using three B. schroederi recombinant antigens to improve protection in mice further. Additionally, the protective differences after immunizing mice with different doses of cocktail antigens (150 μg, 100 μg, and 50 μg) were analyzed. Administration of rBs(GAL+UP), rBs(HP2+UP), rBs(GAL+HP2), and rBs(GAL+HP2+UP) significantly reduced liver and lung lesions, along with a decrease in L3 larvae by 83.7%, 82.1%, 76.4%, and 75.1%, respectively. These vaccines induced a Th1/Th2 mixed immunity, evidenced by elevated serum antibody levels (IgG, IgG1, IgG2a, IgE, and IgA) and splenocyte cytokines [interferon gamma (IFN-γ), interleukin (IL)-5, and IL-10]. Furthermore, varying cocktail vaccine dosages did not significantly affect protection. The results confirm that a 50 μg rBs(GAL+UP) dosage holds promise as a better candidate vaccine combination against B. schroederi infection, providing a basis for developing the B. schroederi vaccine.

Adjuvanted Fusion Protein Vaccine Induces Durable Immunity to Onchocerca volvulus in Mice and Non-Human Primates

Onchocerciasis remains a debilitating neglected tropical disease. Due to the many challenges of current control methods, an effective vaccine against the causative agent Onchocerca volvulus is urgently needed. Mice and cynomolgus macaque non-human primates (NHPs) were immunized with a vaccine consisting of a fusion of two O. volvulus protein antigens, Ov-103 and Ov-RAL-2 (Ov-FUS-1), and three different adjuvants: Advax-CpG, alum, and AlT4. All vaccine formulations induced high antigen-specific IgG titers in both mice and NHPs. Challenging mice with O. volvulus L3 contained within subcutaneous diffusion chambers demonstrated that Ov-FUS-1/Advax-CpG-immunized animals developed protective immunity, durable for at least 11 weeks. Passive transfer of sera, collected at several time points, from both mice and NHPs immunized with Ov-FUS-1/Advax-CpG transferred protection to naïve mice. These results demonstrate that Ov-FUS-1 with the adjuvant Advax-CpG induces durable protective immunity against O. volvulus in mice and NHPs that is mediated by vaccine-induced humoral factors.

Potential of Nucleic Acid Receptor Ligands to Improve Vaccination Efficacy against the Filarial Nematode Litomosoides sigmodontis

More than two-hundred-million people are infected with filariae worldwide. However, there is no vaccine available that confers long-lasting protection against filarial infections. Previous studies indicated that vaccination with irradiated infective L3 larvae reduces the worm load. This present study investigated whether the additional activation of cytosolic nucleic acid receptors as an adjuvant improves the efficacy of vaccination with irradiated L3 larvae of the rodent filaria Litomosoides sigmodontis with the aim of identifying novel vaccination strategies for filarial infections. Subcutaneous injection of irradiated L3 larvae in combination with poly(I:C) or 3pRNA resulted in neutrophil recruitment to the skin, accompanied by higher IP-10/CXCL10 and IFN-β RNA levels. To investigate the impact on parasite clearance, BALB/c mice received three subcutaneous injections in 2-week intervals with irradiated L3 larvae in combination with poly(I:C) or 3pRNA prior to the challenge infection. Vaccination with irradiated L3 larvae in combination with poly(I:C) or 3pRNA led to a markedly greater reduction in adult-worm counts by 73% and 57%, respectively, compared to the immunization with irradiated L3 larvae alone (45%). In conclusion, activation of nucleic acid-sensing immune receptors boosts the protective immune response against L. sigmodontis and nucleic acid-receptor agonists as vaccine adjuvants represent a promising novel strategy to improve the efficacy of vaccines against filariae and potentially other helminths.

Pre-clinical development of a vaccine for human lymphatic filariasis

This study was conducted to optimize a fusion protein vaccine for translational development as a vaccine against the human tropical parasitic infection, lymphatic filariasis (LF). The vaccine candidate, His-tagged rBmHAXT was developed previously in our laboratory and was tested in various animal models including mouse, gerbils and Rhesus macaque where it exhibited significant levels of vaccine-induced protection. However, for commercial manufacturing and for regulatory approval for human use, there was a need to modify the vaccine antigen and its production and analytical release methods. Therefore, the major focus of this study was to develop a process for manufacturing an affinity tag-free rBmHAXT and evaluate its immunogenicity, potency and protective efficacy in both inbred and outbred mouse models, as well as in outbred gerbil models. Our results demonstrate that the tag-free rBmHAXT vaccine produced with a process suitable for cGMP production had protective properties equivalent to the original His-tagged rBmHAXT.

Harnessing Immune Evasion Strategy of Lymphatic Filariae: A Therapeutic Approach against Inflammatory and Infective Pathology

Human lymphatic filariae have evolved numerous immune evasion strategies to secure their long-term survival in a host. These strategies include regulation of pattern recognition receptors, mimicry with host glycans and immune molecules, manipulation of innate and adaptive immune cells, induction of apoptosis in effector immune cells, and neutralization of free radicals. This creates an anti-inflammatory and immunoregulatory milieu in the host: a modified Th2 immune response. Therefore, targeting filarial immunomodulators and manipulating the filariae-driven immune system against the filariae can be a potential therapeutic and prophylactic strategy. Filariae-derived immunosuppression can also be exploited to treat other inflammatory diseases and immunopathologic states of parasitic diseases, such as cerebral malaria, and to prevent leishmaniasis. This paper reviews immunomodulatory mechanisms acquired by these filariae for their own survival and their potential application in the development of novel therapeutic approaches against parasitic and inflammatory diseases. Insight into the intricate network of host immune-parasite interactions would aid in the development of effective immune-therapeutic options for both infectious and immune-pathological diseases.

Lymphatic filariasis and visceral leishmaniasis coinfection: A review on their epidemiology, therapeutic, and immune responses

Coinfection is less commonly observed in individuals around the world, yet it is more common than the single infection. Around 800 million people worldwide are infected with helminths as a result of various diseases. Lymphatic filariasis (LF) and visceral leishmaniasis (VL) are chronic, deadly, crippling, and debilitating neglected tropical diseases (NTDs) that are endemic in tropical and subtropical regions of the world. Due to poor hygienic conditions, poverty, and genetic predisposition, those living in endemic areas are more likely to develop both leishmaniasis and filariasis. One of the key challenges in the management of LF/VL coinfection is the development of an effective therapeutic strategy that not only treats the first episode of VL but also prevents LF. However, there is a scarcity of knowledge and data on the relationship between LF and VL coinfection. While reviewing it was apparent that only a few studies relevant to LF/VL coinfections have been reported from southeastern Spain, Sudan, and the Indian subcontinents, highlighting the need for greater research in the most affected areas. We also looked at LF and VL as a single disease and also as a coinfection. Some features of the immune response evolved in mammalian hosts against LF and VL alone or against coinfection are also discussed, including epidemiology, therapeutic regimens, and vaccines. In addition to being potentially useful in clinical research, our findings imply the need for improved diagnostic methodology and therapeutics, which could accelerate the deployment of more specific and effective diagnosis for treatments to lessen the impact of VL/LF coinfections in the population.

Lymphatic filariasis vaccine development: neglected for how long?

INTRODUCTION

Lymphatic filariasis (LF), also known as elephantiasis, has been recognized by the world health organization and the centers for disease control and prevention as one of the neglected tropical diseases. The huge prevalence and risk of manifestation to date reflect the poor management of this disease. The disease poses vast public health and socio-economic burdens and generates a dire need for the development of a prophylactic solution for mass administration.

AREAS COVERED

Vaccination has been a sought-out strategy for dealing with ever-evolving infectious diseases and can be duly tuned to become a cost effective means of disease control and eventual eradication. In this review, we highlight the epidemiology of LF with the current diagnosis and treatment modules. The need for the development of a potential vaccine candidates, and challenges are discussed. The evidence presented in this review aims to enlighten the readers regarding the essential factors governing LF and its management using prophylactic measures.

EXPERT OPINION

The complex nature of filarial parasites is evident from the absence of a single vaccine for LF. The development and selection of an appropriate preclinical model and its translation into clinical practice is deemed to be a major task needing in-depth evaluation to formulate an effective vaccine. Explorations of the existing vaccine platforms would serve to be an apt strategy in this direction.

Highlighting the Relevance of CD8+ T Cells in Filarial Infections

The T cell immune responses in filarial infections are primarily mediated by CD4+ T cells and type 2-associated cytokines. Emerging evidence indicates that CD8+ T cell responses are important for anti-filarial immunity, however, could be suppressed in co-infections. This review summarizes what we know so far about the activities of CD8+ T cell responses in filarial infections, co-infections, and the associations with the development of filarial pathologies.

Genome editing as control tool for filarial infections

Human filarial infections are vector-borne nematode infections, which include lymphatic filariasis, onchocerciasis, loiasis, and mansonella filariasis. With a high prevalence in developing countries, filarial infections are responsible for some of the most debilitating morbidities and a vicious cycle of poverty and disease. Global initiatives set to eradicate these infections include community mass treatments, vector control, provision of care for morbidity, and search for vaccines. However, there are growing challenges associated with mass treatments, vector control, and antifilarial vaccine development. With the emergence of genome editing tools and successful applications in other infectious diseases, the integration of genetic editing techniques in future control strategies for filarial infections would offer the best option for eliminating filarial infections. In this review, we briefly discuss the mechanisms of the three main genetic editing techniques and explore the potential applications of these powerful tools to control filarial infections.

Advances in Vaccine Development for Human Lymphatic Filariasis

According to the World Health Organization, over 880 million people are currently at risk of acquiring lymphatic filariasis (LF) in over 52 countries worldwide. Current approaches to control LF by 2020 are short of the anticipated goal. Several studies suggest the existence of protective immunity against LF in humans. Thus, it is possible to develop a prophylactic vaccine against LF in humans. Several potential vaccine candidates were identified and tested for their potential against LF. To date, preclinical studies suggest that it is possible to develop a prophylactic vaccine against LF. Much work needs to be done, but it is clear that a prophylactic vaccine, combined with targeted chemotherapy, is critically required for eliminating LF worldwide.

CpG enhances the immunogenicity of heterologous DNA-prime/protein-boost vaccination with the heavy chain myosin of Brugia malayi in BALB/c mice

The recombinant heavy chain myosin of Brugia malayi (Bm-Myo) has earlier been reported as a potent vaccine candidate in our lab. Subsequently, we further enhanced its efficacy employing heterologous DNA prime/protein boost (Myo-pcD+Bm-Myo) immunization approach that produced superior immune-protection than protein or DNA vaccination. In the present study, we evaluated the efficacy of heterologous prime boost vaccination in combination with CpG, synthetic oligodeoxynucleotides (ODN) adjuvant in BALB/c mice. The results showed that CpG/Myo-pcD+Bm-Myo conferred 84.5 ± 0.62% protection against B. malayi infective larval challenge which was considerably higher than Myo-pcD+Bm-Myo (75.6 ± 1.10%) following immunization. Although, both the formulations of immunization elicited robust production of specific IgG antibody and their isotypes (IgG1, IgG2a, IgG2b, and IgG3); however, CpG/Myo-pcD+Bm-Myo predominantly enhanced the level of IgG2a suggesting Th1 biased immune response in presence of CpG. Furthermore, spleen isolated from mice that immunized with CpG/Myo-pcD+Bm-Myo had greater accumulation of CD4+, CD8+, and CD19+ B cells and there was an augmented expression of co-stimulatory molecules CD40, CD86 on host dendritic cells (DCs). In contrast to Myo-pcD+Bm-Myo group, the splenocytes of CpG/Myo-pcD+Bm-Myo immunized mice developed comparatively higher pro-inflammatory cytokines IL-2 and IFN-γ leaving anti-inflammatory cytokine levels unchanged. Moreover, CpG formulation also upregulated the RNA expression of IL-12 and TNF-α in spleenocytes. The current findings suggest that the use of CpG would be more advantageous as an adjuvant predominantly in DNA/protein prime boost vaccine against Bm-Myo and presumably also for filarial infection.

Troponin 1 of human filarial parasite Brugia malayi: cDNA cloning, expression, purification, and its immunoprophylactic potential

In the search for immunoprophylactics for the control of human lymphatic filariasis, we recently identified troponin 1 (Tn1) in Brugia malayi adult worms. The present study reports the cloning and expression of the B. malayi Tn1 (Tn1bm), its immunoprophylactic efficacy against B. malayi infection, and the immunological responses of the host. The Tn1bm gene was cloned (Acc no. JF912447) and expressed, and the purified recombinant Tn1bm (rTn1bm) presented a single ~ 27 kDa band. Parasite load in rTn1bm-immunized BALB/c mice challenged with B. malayi infective larvae (L₃) was assessed. In rTn1bm-immunized animals, IgE, IgG, and IgG subclasses in the serum, cell proliferative response, Th1 and Th2 cytokine secretion (from splenocytes), and NO release (from peritoneal macrophages) were determined. Antibody-dependent cell-mediated cytotoxicity (ADCC) to L₃ was assayed using rTn1bm-immune serum. The innate immune response markers MHC class-I, MHC class-II, TLR2, TLR4, and TLR6 expression in peritoneal macrophages and CD3+, CD4+, CD8+, and CD19+ in the splenocyte population were determined in Tn1bm-exposed cells from naïve mice. rTn1bm-immunized L₃-challenged animals showed a 60% reduction in parasite burden. Immunization upregulated cellular proliferation, cytokine (IFN-γ, TNF-α, IL-1β, IL-4, IL-6, and IL-10) secretion, NO release, and antigen-specific IgG, IgG1, and IgG2b antibody levels. rTn1bm-immune serum killed > 65% of L₃ in the ADCC assay. Increased MHC class-II, TLR2, and TLR6 expression and the relative CD4+ and CD19+ cell populations of naïve animal cells indicated the ability of rTn1bm to mobilize innate immune responses. This is the first report of the immunoprophylactic potential of rTn1bm against B. malayi.

A 21.6 kDa tegumental protein of Clonorchis sinensis induces a Th1/Th2 mixed immune response in mice

Introduction

Clonorchis sinensis is a major parasite affecting the Korea population. Despite the high infection rate and pathogenicity, very few studies have been conducted to investigate the immune responses against the proteins of C. sinensis.

Methods

In this study, in vitro immune response induced by a recombinant 21.6 kDa tegumental protein derived from C. sinensis (rCsTegu21.6) was confirmed in murine dendritic cells and T cells. For the in vivo analysis, each mouse was immunized three times. Total serum IgG and T cell cytokine production were determined by ELISA, while T cell proliferation was detected by a WST (Water‐Soluble Tetrazolium salt)‐1 assay.

Results

In vitro tests indicated that rCsTegu21.6 treatment increased the expression of surface molecules, such as CD40 (77%), CD80 (52%) and CD86 (46%), on murine dendritic cells and the secretion of cytokines (TNF‐α, IL‐6, IL‐1β, IL‐10, and IL‐12p70). Moreover, co‐culturing dendritic cells activated by rCsTegu21.6 with allogenic T cells induced T cell proliferation over time. rCsTegu21.6 also stimulated specific antibody production and cytokine secretion [IL‐2, IL‐4, and interferon (IFN)‐γ)] from T cells following immunization in vivo. Notably, rCsTegu21.6 predominantly induced IgG1 production and secretion of the Th2 cytokine IL‐4, regardless of the type of adjuvant used.

Conclusion

These results serve as a foundation for the development of tegumental protein‐based vaccines against C. sinensis.

Evaluating the Vaccine Potential of a Tetravalent Fusion Protein (rBmHAXT) Vaccine Antigen Against Lymphatic Filariasis in a Mouse Model

Lymphatic filariasis (LF) is a tropical parasitic infection of human transmitted by mosquitoes. Chronic infection results in severe physical disability in the infected patients. Although several potential vaccine antigens were identified by several groups, there are no licensed prophylactic vaccine to date against this infection in the human. Previous attempts from our laboratory to develop a trivalent prophylactic vaccine against LF showed that >90% protection could be achieved in rodent models. However, this trivalent vaccine gave only 35% protection in non-human primates. The major focus of this study was to develop a tetravalent prophylactic vaccine (rBmHAXT) and test the vaccine potential in a mouse model. We evaluated three different adjuvant formulations; alum, glucopyranosyl lipid adjuvant in stable emulsion (GLA/SE) alum (AL019), and mannosylated chitosan (MCA) to determine the optimum adjuvant formulation for rBmHAXT. Results presented in this study show that rBmHAXT + AL019 gave the highest rate of protection (>88%) against challenge infection, compared to rBmHAXT + AL007 (79%), rBmHAXT + MCA (79%) and controls. Analysis of the immune correlates of protection showed that all three adjuvants elicited high titer of antigen-specific IgG1, IgG2a, and IgG2b antibodies. High number of IFN-γ-producing antigen-specific memory cells were generated in the vaccinated animals irrespective of the adjuvants used. Similarly, spleen cells from rBmHAXT-vaccinated animals secreted IL-4, IL-10, and IFN-γ in response to rBmHAXT suggesting the generation of a balanced Th1/Th2 response. There was also an increase in IL-17-secreting cells in rBmHAXT-vaccinated animals. These findings thus suggest that rBmHAXT + AL019 is a better prophylactic formulation for LF.

Prospects of developing a prophylactic vaccine against human lymphatic filariasis - evaluation of protection in non-human primates

Lymphatic filariasis (LF) affects 120 million people around the world and another 856 million people are at risk of acquiring the infection. Mass Drug Administration (MDA) spearheaded by the World Health Organization is the only current strategy to control this infection. Recent reports suggest that despite several rounds of MDA, elimination has not been achieved and there is a need for more stringent control strategies for control of LF. An effective prophylactic vaccine combined with MDA has significant potential. Initial trials using a prophylactic trivalent recombinant Brugia malayi heat shock protein 12.6, abundant larval transcript -2 and tetraspanin large extra-cellular loop (rBmHAT) vaccine developed in our laboratory conferred only 35% protection in macaques. Therefore, the focus of the present study was to improve the current vaccine formulation to obtain better protection in non-human primates. We made two modifications to the current formulation: (i) the addition of another antigen, thioredoxin peroxidase-2 (TPX-2) to make it a tetravalent vaccine (rBmHAXT) and (ii) the inclusion of an adjuvant; AL019 (alum plus glucopyranosyl lipid adjuvant-stable emulsion) that is known to promote a balanced Th1/Th2 response. A double-blinded vaccination trial was performed with 40 macaques that were divided into three treatment groups and one control group (n = 10/group). Vaccinated animals received 4 immunisations at 1 month intervals with 150 µg/ml of rBmHAT plus alum, rBmHAT plus AL019 or rBmHAXT plus AL019. Control animals received AL019 only. All vaccinated macaques developed significant (P ≤ 0.003) titers of antigen-specific IgG antibodies (1:20,000) compared with the controls. One month after the last dose, all macaques were challenged s.c. with 130-180 B. malayi L3s. Our results showed that seven out of 10 (70%) of macaques given the improved rBmHAXT vaccine did not develop the infection compared with AL019 controls, of which seven out of 10 macaques developed the infection. Titers of antigen-specific IgG1 and IgG2 antibodies were significantly (P ≤ 0.01) higher in vaccinated animals and there was an increase in the percentage of IL-4 and IFN-γ secreting antigen-responding memory T cells. These studies demonstrated that the improved formulation (rBmHAXT plus AL019) is a promising vaccine candidate against human lymphatic filariasis.

Metazoan Parasite Vaccines: Present Status and Future Prospects

Eukaryotic parasites and pathogens continue to cause some of the most detrimental and difficult to treat diseases (or disease states) in both humans and animals, while also continuously expanding into non-endemic countries. Combined with the ever growing number of reports on drug-resistance and the lack of effective treatment programs for many metazoan diseases, the impact that these organisms will have on quality of life remain a global challenge. Vaccination as an effective prophylactic treatment has been demonstrated for well over 200 years for bacterial and viral diseases. From the earliest variolation procedures to the cutting edge technologies employed today, many protective preparations have been successfully developed for use in both medical and veterinary applications. In spite of the successes of these applications in the discovery of subunit vaccines against prokaryotic pathogens, not many targets have been successfully developed into vaccines directed against metazoan parasites. With the current increase in -omics technologies and metadata for eukaryotic parasites, target discovery for vaccine development can be expedited. However, a good understanding of the host/vector/pathogen interface is needed to understand the underlying biological, biochemical and immunological components that will confer a protective response in the host animal. Therefore, systems biology is rapidly coming of age in the pursuit of effective parasite vaccines. Despite the difficulties, a number of approaches have been developed and applied to parasitic helminths and arthropods. This review will focus on key aspects of vaccine development that require attention in the battle against these metazoan parasites, as well as successes in the field of vaccine development for helminthiases and ectoparasites. Lastly, we propose future direction of applying successes in pursuit of next generation vaccines.

Vaccination against Fasciola hepatica using cathepsin L3 and B3 proteases delivered alone or in combination

No licensed vaccine is currently available for prevention of Fasciola hepatica infections. However, considering the alarming increase in drug resistance, there is an urgent need for a safe and fully effective vaccine against fasciolosis. Here, we tested if cathepsins L (FhCL3-1, FhCL3-2) and B (FhCB3) secreted by juvenile liver flukes are viable vaccine targets when delivered alone or in combination in a rat model. Since control over the early immune response is crucial for parasite's establishment in its host, it was hypothesised that targeting fluke juvenile stages may prove beneficial. Moreover, it was assumed that selected antigens will act in a cumulative manner to interfere with liver fluke migration and thereby will reduce F. hepatica infection. Recombinant FhCL3-1 and FhCL3-2 delivered alone reduced liver fluke burdens by 47 % and 63 %, respectively. A trivalent vaccine containing rFhCL3-1/CL3-2/CB3 did not increase the protective vaccine efficacy compared to the rFhCL3-2 vaccinated group (53 %), although, reductions in liver fluke wet weight (statistically significant) and liver damage score were most pronounced. Further, the highest IgG1 and IgG2a levels were seen in rFhCL3-2 vaccinated rats, the group for which the highest reduction in worm burden was demonstrated. Moreover, IgG1 and IgG2a levels in vaccinated rats were significantly elevated compared to those reported for control groups up to 4 week post-infection. While the mechanism of protection remains unknown, it appears that it depends on vaccine-induced antibodies directed against cathepsins. The obtained results imply that F. hepatica juvenile-specific cathepsins are promising vaccine candidates that induce responses that successfully target early migratory liver fluke stages. Now, the challenge is to evaluate these juvenile-specific cathepsins for use in livestock.

Improving the efficacy of a prophylactic vaccine formulation against lymphatic filariasis

Mass drug administration (MDA) is the current strategy for interrupting the transmission of lymphatic filariasis (LF) infection and control of the disease in endemic areas. However, subject non-compliance has resulted in the presence of several "transmission hotspots" in the endemic regions threatening the reemergence of LF. This situation is further complicated by the fact that the drugs used in MDA are not effective against adult LF worms, a major concern for the control strategy. Thus, there is clearly a need for an effective and sustainable approach to control LF. Prophylactic vaccine combined with targeted treatment of infected patients and vector control is suggested as a more sustainable strategy to eliminate LF infection from endemic regions. A multivalent vaccine (rBmHAT) developed in our laboratory conferred about 90% protection in rodents. However, when we tested the rBmHAT vaccine along with alum in rhesus macaques, only about 40% protection was achieved and the immune response obtained was Th2 biased. In an attempt to improve the vaccine, in this study, we tested two vaccine antigens (rBmHAT and rBmHAX) along with two adjuvant formulations [alum + GLA (AL019) and mannosylated chitosan (MCA)] in a mouse model. Our results show that rBmHAT is a better vaccine antigen than rBmHAX. Combination of rBmHAT with AL019 or MCA adjuvants gave 94 and 88% protection, respectively, against challenge infections. Immunized animals developed antigen-specific memory T cells that secreted significant levels of IL-4, IFN-γ, and IL-17 suggesting the generation of a balanced Th1/Th2 responses following immunization. A major advantage of MCA adjuvant is that the vaccine booster doses can be administered orally. These studies thus showed that rBmHAT is a better vaccine antigen and can be given in combination with AL019 or MCA adjuvant to obtain excellent results.

Heat shock proteins 70 and 90 from Clonorchis sinensis induce Th1 response and stimulate antibody production

Background

Heat shock proteins (HSPs) are found in all prokaryotes and most compartments of eukaryotic cells. Members of the HSP family mediate immune responses to tissue damage or cellular stress. However, little is known about the immune response induced by the oriental liver fluke, Clonorchis sinensis, even though this organism is carcinogenic to humans. We address this issue in the present study in mouse bone marrow dendritic cells (mBMDCs), using recombinant HSP70 and 90 from C. sinensis (rCsHSP70 and rCsHSP90).

Methods

rCsHSP70 and rCsHSP90 were produced in an E. coli system. Purified recombinant proteins were treated in BMDCs isolated from C57BL/6 mice. T cells were isolated from Balb/c mice and co-cultured with activated mBMDCs. Expression of surface molecules was measured by flow cytometry and cytokine secretion was quantified using ELISA. C57BL/6 mice were divided into four groups, including peptide alone, peptide/Freund’s adjuvant, peptide/CsHSP70, peptide/CsHSP90, and were immunized intraperitoneally three times. Two weeks after final immunization, antibodies against peptide were measured using ELISA.

Results

Both proteins induced a dose-dependent upregulation in major histocompatibility complex and co-stimulatory molecule expression and increased secretion of pro-inflammatory cytokines including interleukin (IL)-1β, -6, and -12p70 and tumor necrosis factor-α in mBMDCs. Furthermore, when allogenic T cells were incubated with mBMDCs activated by rCsHSP70 and rCsHSP90, the helper T cell (Th)1 cytokine interferon-γ was up-regulated whereas the level of the Th2 cytokine IL-4 was unchanged. These results indicate that rCsHSPs predominantly induce a Th1 response. Over and above these results, we also demonstrated that the production of peptide-specific antibodies can be activated after immunization via in vitro peptide binding with rCsHSP70 or rCsHSP90.

Conclusion

This study showed for the first time that the HSP or HSP/peptide complexes of C. sinensis could be considered as a more effective vaccine against C. sinensis infection as results of the activator of host immune response as well as the adjuvant for antigenic peptide conjugate to induce peptide-specific antibody response in mice.

Killing filarial nematode parasites: role of treatment options and host immune response

Background

There is compelling evidence that not only do anti-filarials significantly reduce larval forms, but that host immune responses also contribute to the clearance of filarial parasites; however, the underlying mechanisms have not been fully elucidated.

Main text

Filarial infections caused by Wuchereria bancrofti and Brugia species (lymphatic filariasis) and Onchocerca volvulus (onchocerciasis) affect almost 200 million individuals worldwide and pose major public health challenges in endemic regions. Indeed, the collective disability-adjusted life years for both infections is 3.3 million. Infections with these thread-like nematodes are chronic and, although most individuals develop a regulated state, a portion develop severe forms of pathology. Mass drug administration (MDA) programmes on endemic populations focus on reducing prevalence of people with microfilariae, the worm's offspring in the blood, to less than 1 %. Although this has been successful in some areas, studies show that MDA will be required for longer than initially conceived.

Conclusion

This paper highlights the mode of action of the various antifilarial treatment strategies and role of host immune response.

Electronic supplementary material

The online version of this article (doi:10.1186/s40249-016-0183-0) contains supplementary material, which is available to authorized users.

Effect of muramyl dipeptide and alum adjuvants on immunization with Filarial multi antigen peptide vaccine in mice model

Filarial thioredoxin and transglutaminase are enzymes that are secreted throughout the lifecycle of the parasites which are mandatory for the survival of the parasite. They are reported to be promising vaccine candidates, yet the limitation factors of these proteins to be developed as vaccines is their homology they share with the host proteins. Hence immunodominant epitopes from these proteins were constructed as peptides and immunised in mice model with Muramyl dipeptide (MDP) as adjuvant. Immunodominant epitopic portions from Filarial thioredoxin and transglutaminase which are non-homologous with host proteins were constructed as Multi Antigen Peptide (MAP) and assembled in an inert lysine core. The synthesised MAP was immunised with MDP as adjuvant in Balb/c mice model, humoral and cellular immune response were studied. Antibody titre levels for TT MAP with MDP was in par with alum as adjuvant in mice models. T cell responses of TT MAP with MDP showed a balanced TH1/TH2 response. The TH1 cytokines namely IL-2 and IFN-ɤ were also higher in TT MAP immunised groups with MDP as adjuvant whereas alum immunised groups was TH2 biased. TT MAP admixed with MDP as adjuvant proves to be safe in mice model. Further vaccination studies are underway in permissive animal models to determine the role of TT MAP with MDP as adjuvant in protective immunity against W. bancrofti and B. malayi infections.

Vaccination of Gerbils with Bm-103 and Bm-RAL-2 Concurrently or as a Fusion Protein Confers Consistent and Improved Protection against Brugia malayi Infection

Background

The Brugia malayi Bm-103 and Bm-RAL-2 proteins are orthologous to Onchocerca volvulus Ov-103 and Ov-RAL-2, and which were selected as the best candidates for the development of an O. volvulus vaccine. The B. malayi gerbil model was used to confirm the efficacy of these Ov vaccine candidates on adult worms and to determine whether their combination is more efficacious.

Methodology and Principle Findings

Vaccine efficacy of recombinant Bm-103 and Bm-RAL-2 administered individually, concurrently or as a fusion protein were tested in gerbils using alum as adjuvant. Vaccination with Bm-103 resulted in worm reductions of 39%, 34% and 22% on 42, 120 and 150 days post infection (dpi), respectively, and vaccination with Bm-RAL-2 resulted in worm reductions of 42%, 22% and 46% on 42, 120 and 150 dpi, respectively. Vaccination with a fusion protein comprised of Bm-103 and Bm-RAL-2 resulted in improved efficacy with significant reduction of worm burden of 51% and 49% at 90 dpi, as did the concurrent vaccination with Bm-103 and Bm-RAL-2, with worm reduction of 61% and 56% at 90 dpi. Vaccination with Bm-103 and Bm-RAL-2 as a fusion protein or concurrently not only induced a significant worm reduction of 61% and 42%, respectively, at 150 dpi, but also significantly reduced the fecundity of female worms as determined by embryograms. Elevated levels of antigen-specific IgG were observed in all vaccinated gerbils. Serum from gerbils vaccinated with Bm-103 and Bm-RAL-2 individually, concurrently or as a fusion protein killed third stage larvae in vitro when combined with peritoneal exudate cells.

Conclusion

Although vaccination with Bm-103 and Bm-RAL-2 individually conferred protection against B. malayi infection in gerbils, a more consistent and enhanced protection was induced by vaccination with Bm-103 and Bm-RAL-2 fusion protein and when they were used concurrently. Further characterization and optimization of these filarial vaccines are warranted.

Onchocerciasis and Lymphatic filariasis (LF) are debilitating neglected tropical diseases (NTDs). Practical challenges in implementation of mass drug administration (MDA) such as prolonged treatment regime requirements and the possible emergence of drug resistance will likely impede the elimination of these NTDs. Hence, the availability of an efficacious prophylactic vaccine would be an invaluable tool. The objective of the present studies was to use the B. malayi-gerbil model of filariasis as a surrogate system to test the efficacy of filarial molecules as vaccine targets for an onchocerciasis vaccine. The vaccine efficacy of Onchocerca volvulus recombinant proteins Ov-RAL-2 and Ov-103 was recently demonstrated using a mouse diffusion chamber model. In this communication, we provide encouraging results on the vaccine efficacy of Bm-RAL-2 and Bm-103, individually or in combination. Our data demonstrate that vaccination with Bm-RAL-2 and Bm-103 concurrently and as a fusion protein confers not only a consistent and significant protection against B. malayi infection in gerbils, but also reduces the fecundity of female worms as demonstrated in embryogram analyses. Our results support the contention that Ov-RAL-2 and Ov-103 are excellent onchocerciasis vaccine candidates and that further investigations leading to their development as a vaccine are warranted.

Immunization with Wuchereria bancrofti Glutathione-S-transferase Elicits a Mixed Th1/Th2 Type of Protective Immune Response Against Filarial Infection in Mastomys

Lymphatic filariasis is a mosquito borne parasitic infection and can severely affect the normal working ability of an individual. Currently there is no vaccine available to prevent this infection and the development of a potential vaccine could effectively support the on-going mass drug administration program by World Health Organization (WHO). Filarial parasites have complex mechanisms to modulate the host immune responses against them. The glutathione-S-transferases (GST) are the important enzymes effectively involved to counteract the oxidative free radicals produced by the host. In the present study, we have shown that the mastomys which are fully permissible rodents for Brugia malayi when immunized with Wuchereria bancrofti recombinant GST (rWbGST) could induce 65.5 % in situ cytotoxicity against B. malayi infective (L3) larvae. There was a balanced Th1/Th2 immune response in the vaccinated animals, characterized by higher levels of WbGST-specific IgG1 and IgG2a antibodies and pronounced IFN-γ, IL-10 and IL-4 cytokines production by the spleen cells.

Chimeric Epitope Vaccine from Multistage Antigens for Lymphatic Filariasis

Lymphatic filariasis, a mosquito-borne parasitic disease, affects more than 120 million people worldwide. Vaccination for filariasis by targeting different stages of the parasite will be a boon to the existing MDA efforts of WHO which required repeated administration of the drug to reduce the infection level and sustained transmission. Onset of a filaria-specific immune response achieved through antigen vaccines can act synergistically with these drugs to enhance the parasite killing. Multi-epitope vaccine approach has been proved to be successful against several parasitic diseases as it overcomes the limitations associated with the whole antigen vaccines. Earlier results from our group suggested the protective efficacy of multi-epitope vaccine comprising two immunodominant epitopes from Brugia malayi antioxidant thioredoxin (TRX), several epitopes from transglutaminase (TGA) and abundant larval transcript-2 (ALT-2). In this study, the prophylactic efficacy of the filarial epitope protein (FEP), a chimera of selective epitopes identified from our earlier study, was tested in a murine model (jird) of filariasis with L3 larvae. FEP conferred a significantly (P < 0.0001) high protection (69.5%) over the control in jirds. We also observed that the multi-epitope recombinant construct (FEP) induces multiple types of protective immune responses, thus ensuring the successful elimination of the parasite; this poses FEP as a potential vaccine candidate.

Immunogenicity and Protective Efficacy of Brugia malayi Heavy Chain Myosin as Homologous DNA, Protein and Heterologous DNA/Protein Prime Boost Vaccine in Rodent Model

We earlier demonstrated the immunoprophylactic efficacy of recombinant heavy chain myosin (Bm-Myo) of Brugia malayi (B. malayi) in rodent models. In the current study, further attempts have been made to improve this efficacy by employing alternate approaches such as homologous DNA (pcD-Myo) and heterologous DNA/protein prime boost (pcD-Myo+Bm-Myo) in BALB/c mouse model. The gene bm-myo was cloned in a mammalian expression vector pcDNA 3.1(+) and protein expression was confirmed in mammalian Vero cell line. A significant degree of protection (79.2%±2.32) against L3 challenge in pcD-Myo+Bm-Myo immunized group was observed which was much higher than that exerted by Bm-Myo (66.6%±2.23) and pcD-Myo (41.6%±2.45). In the heterologous immunized group, the percentage of peritoneal leukocytes such as macrophages, neutrophils, B cells and T cells marginally increased and their population augmented further significantly following L3 challenge. pcD-Myo+Bm-Myo immunization elicited robust cellular and humoral immune responses as compared to pcD-Myo and Bm-Myo groups as evidenced by an increased accumulation of CD4+, CD8+ T cells and CD19+ B cells in the mouse spleen and activation of peritoneal macrophages. Though immunized animals produced antigen-specific IgG antibodies and isotypes, sera of mice receiving pcD-Myo+Bm-Myo or Bm-Myo developed much higher antibody levels than other groups and there was profound antibody-dependent cellular adhesion and cytotoxicity (ADCC) to B. malayi infective larvae (L3). pcD-Myo+Bm-Myo as well as Bm-Myo mice generated a mixed T helper cell phenotype as evidenced by the production of both pro-inflammatory (IL-2, IFN-γ) and anti-inflammatory (IL-4, IL-10) cytokines. Mice receiving pcD-Myo on contrary displayed a polarized pro-inflammatory immune response. The findings suggest that the priming of animals with DNA followed by protein booster generates heightened and mixed pro- and anti-inflammatory immune responses that are capable of providing high degree of protection against filarial larval invasion.

Evaluation of a multivalent vaccine against lymphatic filariasis in rhesus macaque model

Lymphatic filariasis affects 120 million people worldwide and another 1.2 billion people are at risk of acquiring the infection. Chemotherapy with mass drug administration is substantially reducing the incidence of the infection. Nevertheless, an effective vaccine is needed to prevent the infection and eradicate the disease. Previously we reported that a multivalent fusion protein vaccine (rBmHAT) composed of small heat shock proteins 12.6 (HSP12.6), abundant larval transcript-2 (ALT-2) and large extracellular domain of tetraspanin (TSP LEL) could confer >95% protection against the challenge infection with Brugia malayi infective larvae (L3) in mouse and gerbil models. In this study we evaluated the immunogenicity and efficacy of rBmHAT fusion protein vaccine in a rhesus macaque model. Our results show that rBmHAT is highly immunogenic in rhesus macaques. All the vaccinated monkeys developed significant titers of antigen-specific IgG antibodies against each of the component antigens (16,000 for rBmHSP12.6), (24,000 for rBmALT-2) and (16,000 for rBmTSP-LEL). An in vitro antibody dependent cellular cytotoxicity (ADCC) assay performed using the sera samples from vaccinated monkeys showed that the anti-rBmHAT antibodies are functional with 35% killing of B. malayi L3s. Vaccinated monkeys also had antigen responding cells in the peripheral blood. Vaccine-induced protection was determined after challenging the monkeys with 500 B. malayi L3. Following challenge infection, 3 out of 5 vaccinated macaques failed to develop the infection. These three protected macaques had high titers of IgG1 antibodies and their PBMC secreted significantly high levels of IFN-γ in response to the vaccine antigens. The two vaccinated macaques that picked the infection had slightly low titers of antibodies and their PBMC secreted high levels of IL-10. Based on these findings we conclude that the rBmHAT vaccine is highly immunogenic and safe and can confer significant protection against challenge infections in rhesus macaques.

Emerging and reemerging neglected tropical diseases: a review of key characteristics, risk factors, and the policy and innovation environment

In global health, critical challenges have arisen from infectious diseases, including the emergence and reemergence of old and new infectious diseases. Emergence and reemergence are accelerated by rapid human development, including numerous changes in demographics, populations, and the environment. This has also led to zoonoses in the changing human-animal ecosystem, which are impacted by a growing globalized society where pathogens do not recognize geopolitical borders. Within this context, neglected tropical infectious diseases have historically lacked adequate attention in international public health efforts, leading to insufficient prevention and treatment options. This subset of 17 infectious tropical diseases disproportionately impacts the world's poorest, represents a significant and underappreciated global disease burden, and is a major barrier to development efforts to alleviate poverty and improve human health. Neglected tropical diseases that are also categorized as emerging or reemerging infectious diseases are an even more serious threat and have not been adequately examined or discussed in terms of their unique risk characteristics. This review sets out to identify emerging and reemerging neglected tropical diseases and explore the policy and innovation environment that could hamper or enable control efforts. Through this examination, we hope to raise awareness and guide potential approaches to addressing this global health concern.

Vaccines to combat river blindness: expression, selection and formulation of vaccines against infection with Onchocerca volvulus in a mouse model

Human onchocerciasis is a neglected tropical disease caused by Onchocerca volvulus and an important cause of blindness and chronic disability in the developing world. Although mass drug administration of ivermectin has had a profound effect on control of the disease, additional tools are critically needed including the need for a vaccine against onchocerciasis. The objectives of the present study were to: (i) select antigens with known vaccine pedigrees as components of a vaccine; (ii) produce the selected vaccine antigens under controlled conditions, using two expression systems and in one laboratory and (iii) evaluate their vaccine efficacy using a single immunisation protocol in mice. In addition, we tested the hypothesis that joining protective antigens as a fusion protein or in combination, into a multivalent vaccine, would improve the ability of the vaccine to induce protective immunity. Out of eight vaccine candidates tested in this study, Ov-103, Ov-RAL-2 and Ov-CPI-2M were shown to reproducibly induce protective immunity when administered individually, as fusion proteins or in combination. Although there was no increase in the level of protective immunity induced by combining the antigens into one vaccine, these antigens remain strong candidates for inclusion in a vaccine to control onchocerciasis in humans.

Immune responses of B. malayi thioredoxin (TRX) and venom allergen homologue (VAH) chimeric multiple antigen for lymphatic filariasis

Although multiple vaccine strategy for lymphatic filariasis has provided tremendous hope, the choice of antigens used in combination has determined its success in the previous studies. Multiple antigens comprising key vaccine candidates from different life cycle stages would provide a promising strategy if the antigenic combination is chosen by careful screening. In order to analyze one such combination, we have used a chimeric construct carrying the well studied B. malayi antigens thioredoxin (BmTRX) and venom allergen homologue (BmVAH) as a fusion protein (TV) and evaluated its immune responses in mice model. The efficacy of fusion protein vaccine was explored in comparison with the single antigen vaccines and their cocktail. In mice, TV induced significantly high antibody titer of 1,28,000 compared to cocktail vaccine TRX+VAH (50,000) and single antigen vaccine TRX (16,000) or VAH (50,000). Furthermore, TV elicited higher level of cellular proliferative response together with elevated levels of IFN-γ, IL-4 and IL-5 indicating a Th1/Th2 balanced response. The isotype antibody profile showed significantly high level of IgG1 and IgG2b confirming the balanced response elicited by TV. Immunization with TV antigen induced high levels of both humoral and cellular immune responses compared to either cocktail or antigen given alone. The result suggests that TV is highly immunogenic in mice and hence the combination needs to be evaluated for its prophylactic potential.

Evaluating the efficacy of rBmHATαc as a multivalent vaccine against lymphatic filariasis in experimental animals and optimizing the adjuvant formulation

Developing an effective vaccine against lymphatic filariasis will complement the WHO's effort to eradicate the infection from endemic areas. Currently 83 different countries are endemic for this infection and over 1 billion people are at risk. An effective vaccine coupled with mass drug administration will reduce the morbidity and social stigma associated with this gruesome disease. Several potential vaccine candidates that can confer partial protection in experimental animals have been reported from different laboratories. However, no licensed vaccines are currently available for this disease. Among the several vaccine antigens identified from our laboratory, three most promising antigens; rBmHSPαc (α crystalline domain and c-terminal extension of Heat Shock Protein 12.6), rBmALT-2 (Abundant larval transcript) and rBmTSP LEL (Tetraspanin large extracellular loop) was further developed as a recombinant fusion protein vaccine (rBmHATαc). In a mouse model this fusion protein vaccine gave close to 68% protection following a challenge infection. To improve the vaccine efficiency of rBmHATαc, in this study we evaluated various preparations of alum (AL007, AL019, Alhydrogel and Imject® Alum) as adjuvants. Our results show that mice immunized with rBmHATαc formulated in AL007 (alum from IDRI) and/or AL019 (alum plus TLR-4 agonist from IDRI) gave the highest IgG antibody titer compared to other groups. Subsequent in vivo challenge experiments confirmed that >95% protection can be achieved when AL007 or AL019 was used as the adjuvant. However, when Imject® Alum or alhydrogel was used as the adjuvant only 76% and 72% protection respectively could be achieved. These results show that AL007 or AL019 (IDRI) is an excellent choice of adjuvant for the rBmHATαc vaccine against B. malayi L3 in mice.

Large extracellular loop of tetraspanin as a potential vaccine candidate for filariasis

Lymphatic filariasis affects nearly 120 million people worldwide and mass preventive chemotherapy is currently used as a strategy to control this infection. This has substantially reduced the incidence of the infection in several parts of the world. However, a prophylactic vaccine would be more effective in preventing future infections and will supplement the mass chemotherapy efforts. Unfortunately, there is no licensed vaccine available currently to prevent this infection. Molecules expressed on the surface of the parasite are potential candidates for vaccine development as they are exposed to the host immune system. In this study we show that the large extracellular loop of tetraspanin (TSP LEL), a protein expressed on the cuticle of Brugia malayi and Wuchereria bancrofti is a potential vaccine candidate. Our results showed that BmTSP LEL is expressed on the surface of B. malayi infective third stage larvae (L3) and sera from human subjects who are putatively immune to lymphatic filariasis carry high titer of IgG1 and IgG3 antibodies against BmTSP LEL and WbTSP LEL. We also showed that these antibodies in the sera of human subjects can participate in the killing of B. malayi L3 in an antibody dependent cell-mediated cytotoxicity mechanism. Vaccination trials in mice showed that close to 64% protection were achieved against challenge infections with B. malayi L3. Immunized animals showed high titer of anti-WbTSP LEL IgG1, IgG2a and IgG2b antibodies in the sera and IFN-γ secreting cells in the spleen. Onchocerca volvulus another filarial parasite also expresses TSP LEL. Cross-reactivity studies showed that IgG1 antibody in the sera of endemic normal subjects, recognize OvTSP LEL. Similarly, anti-OvTSP LEL antibodies in the sera of subjects who are immune to O. volvulus were also shown to cross-react with rWbTSP LEL and rBmTSP LEL. These findings thus suggested that rTSP LEL can be developed as a potential vaccine candidate against multiple filarial infections.

Single multivalent vaccination boosted by trickle larval infection confers protection against experimental lymphatic filariasis

The multivalent vaccine BmHAT, consisting of the Brugia malayi infective larval (L3) antigens heat shock protein12.6 (HSP12.6), abundant larval transcript-2 (ALT-2) and tetraspanin large extra cellular loop (TSP-LEL), was shown to be protective in rodent models from our laboratory. We hypothesize that since these antigens were identified using protective antibodies from immune endemic normal individuals, the multivalent vaccine can be augmented by natural L3 infections providing protection to the vaccinated host. This hypothesis was tested using single dose of DNA and protein or protein alone of the BmHAT vaccination in gerbils followed by live trickle L3 infection as booster dose. Vaccine-induced protection in gerbils was determined by worm establishment, micropore chamber assay and by antibody dependant cell cytotoxicity (ADCC) assay. Results were compared with the traditional prime-boost vaccination regimen. Gerbils vaccinated with BmHAT and boosted with L3 trickle infection were protected 51% (BmHAT DNA-protein) and 48% (BmHAT protein) respectively. BmHAT vaccination plus L3 trickle booster generated significant titer of antigen-specific IgG antibodies comparable to the traditional prime boost vaccination approach. BmHAT vaccination plus L3 trickle booster also generated antigen-specific cells in the spleen of vaccinated animals and these cells secreted predominantly IFN-γ and IL-4 in response to the vaccine antigens. These studies thus show that single dose of BmHAT multivalent vaccination followed by L3 trickle booster infection can confer significant protection against lymphatic filariasis.