Interleukin-12 and protective immunity to schistosomes

Preventive CTLA-4-Ig Treatment Reduces Hepatic Egg Load and Hepatic Fibrosis in Schistosoma mansoni-Infected Mice

Background

Hepatic fibrosis and granuloma formation as a consequence of tissue entrapped eggs produced by female schistosomes characterize the pathology of Schistosoma mansoni infection. We have previously shown that single-sex infection with female schistosomes mitigates hepatic fibrosis after secondary infection. This was associated with an increased expression of cytotoxic T-lymphocyte-associated protein-4 (CTLA-4), known as a negative regulator of T cell activation. Based on these findings, we hypothesized that administration of agonistic CTLA-4-Ig (Belatacept) is capable to prevent and/or treat hepatic fibrosis during schistosomiasis.

Methods

Mice were infected with 50 S. mansoni cercariae and CTLA-4-Ig, or appropriated control-Ig was administered for 4 weeks. Preventive treatment started 4 weeks after infection, before onset of egg production, and therapeutic treatment started 8 weeks after infection when hepatic fibrosis was already established.

Results

When given early after infection, livers of CTLA-4-Ig-treated mice showed significantly reduced collagen deposition and decreased expression of profibrotic genes in comparison to controls. In addition, administration of CTLA-4-Ig suppressed the inflammatory T cell response in infected mice. If therapy was started at a later time point when fibrogenesis was initiated, CTLA-4-Ig had no impact on hepatic fibrosis.

Conclusion

We could demonstrate that an early preventive administration of CTLA-4-Ig suppresses effector T cell function and therefore ameliorates liver fibrosis. CTLA-4-Ig administration after onset of egg production fails to treat hepatic fibrosis.

Immunogenicity and anti-fecundity effect of nanoparticle coated glutathione S-transferase (SjGST) DNA vaccine against murine Schistosoma japonicum infection

There is still urgent need for a vaccine against schistosomiasis, especially in Schistosoma japonicum endemic areas where even a vaccine that will interrupt zoonotic transmission will be potentially effective as an intervention tool. We had developed a novel nanoparticle gene delivery system, which has proven efficacious in gene transfection to target immune cells with complementary adjuvant effect and high protective efficacy in several diseases. Here, we applied this nanoparticle system in combination with S. japonicum glutathione S-transferase (SjGST) DNA vaccine to show the immunogenicity and anti-fecundity effect of the nanoparticle coated vaccine formulation against murine schistosomiasis. The nanoparticle-coated DNA vaccine formulation induced desired immune responses. In comparison with the nanoparticle coated empty vector, it produced significantly increased antigen-specific humoral response, T-helper 1 polarized cytokine environment, higher proportion of IFN-γ producing CD4(+) T-cells and the concomitant decrease in IL-4 producing CD4(+) T-cells. Although there was no effect on worm burden, we recorded a marked reduction in tissue egg burden. There was up to 71.3% decrease in tissue egg burden and 55% reduction in the fecundity of female adult worms. Our data showed that SjGST DNA vaccine, delivered using the nanoparticle gene delivery system, produced anti-fecundity effect on female adult schistosomes as previously described by using conventional subunit vaccine with adjuvant, proving this DNA vaccine formulation as a promising candidate for anti-pathology and transmission blocking application.

Review: novel nonviral delivery approaches for interleukin-12 protein and gene systems: curbing toxicity and enhancing adjuvant activity

It has become increasingly apparent that the ability to generate an optimal host immune response requires effective cross talk between the innate and adaptive components of the immune system. Pro-inflammatory cytokines, in particular those that can induce a danger signal, often called signal 3, are crucial in this role of initiating and augmenting the presentation of exogenous antigen to T cells by dendritic cells. Interleukin-12 (IL-12) in particular has been defined as a "signal 3" cytokine required for the antigen cross priming. Given this unique interactive function, a significant amount of work has been performed to define possible therapeutic applications for IL-12. Systemic IL-12 administration can clearly act as a potent adjuvant for postvaccination T cell responses in a variety of diseases. As an example, in the cancer setting, systemic IL-12 is capable of suppressing tumor growth, metastasis, and angiogenesis in vivo. IL-12, however, has been associated with significant dose- and schedule-dependent toxicity in early clinical trials, results that have proven to be a major obstacle to its clinical application. Recent research has focused on decreasing the toxicity of IL-12 using different delivery approaches, including virus-based and gene-modified cell-based delivery. Although effective, these approaches also have limitations, including the generation of neutralizing antibodies, in addition to lacking the simplicity and versatility required for universal clinical application. Thus, there is a significant interest in the development of alternative delivery approaches for IL-12 administration that can overcome these issues. Several nonviral delivery approaches for IL-12 protein or gene expression vectors are being defined, including alum, liposomes, and polymer-based delivery. These developing approaches have shown promising adjuvant effects with significantly lessened systemic toxicity. This article discusses the potential capabilities of these nonvirus-based IL-12 delivery systems in different disease settings, including allergy, infection, and cancer.

T-helper-2 cytokine responses to Sj97 predict resistance to reinfection with Schistosoma japonicum

Although schistosomiasis is effectively treated with Praziquantel, rapid reinfection with rebound morbidity precludes effective control based on chemotherapy alone and justifies current efforts to develop vaccines for these parasites. Using a longitudinal treatment-reinfection study design with 616 participants 7 to 30 years of age, we evaluated the relationship between cytokine responses to Schistosoma japonicum soluble adult worm extract (SWAP), Sj97, Sj22.6, and Sj67, measured 4 weeks after treatment with Praziquantel, and resistance to reinfection in a population from Leyte, The Philippines, where S. japonicum is endemic. S. japonicum transmission was high: 54.8% and 91.1% were reinfected within 6 and 18 months, respectively. A Th2 bias in the following cytokine ratios, interleukin-4 (IL-4)/IL-12, IL-5/IL-12, IL-13/IL-12, IL-4/gamma-IFN (IFN-gamma), IL-5/IFN-gamma, and IL-13/IFN-gamma, in response to SWAP predicted a 1.4- to 2.9-month longer time to reinfection (P < 0.05) and a 27 to 55% lower intensity of reinfection (P < 0.05). Similarly, a Th2 bias in response to Sj97 predicted a 1.6- to 2.2-month longer time to reinfection (P < 0.05) and a 30 to 41% lower intensity of reinfection (P < 0.05). Only a high IL-5/IL-10 ratio in response to Sj22.6 predicted a 3.0-month-longer time to reinfection (P = 0.03). Cytokine responses to Sj67 were not associated with protection. In a large population-based treatment-reinfection study we found that Th2 responses to SWAP and Sj97 consistently predicted resistance to reinfection. These findings underscore Th2-type immune responses as central in human resistance to S. japonicum and support Sj97 as a leading vaccine candidate for this parasite.

Recent Advances in Schistosomiasis

Schistosomiasis is a major parasitic disease, affecting nearly 200 million persons, worldwide. Major advances in our knowledge-in terms of pathogenesis, improved diagnosis, therapeutics (both drugs and strategies), and morbidity assessment-now make schistosomiasis a curable, often preventable disease. In contrast to most other illnesses, most schistosomiasis pathology appears to be reversible over time. For the future, several promising vaccine candidates are already in phase-I or phase-II testing. On the other hand, the range of this disease has been increasing, as water resources are developed in several newly industrialized countries and much of schistosomiasis in sub-Saharan Africa remains largely untreated.

Interleukin-12 and the host response to parasitic helminths; the paradoxical effect on protective immunity and immunopathology

In general, helminth infections are associated with the development of dominant Th2-mediated immune responses which may be host protective but can also be the cause of immunopathology. Interleukin 12 (IL-12) is known to be a potent inhibitor of Th2 immune responses and as such it might be expected to have an important modulatory role in helminth-induced immune responses. In this review, we discuss the effect of IL-12 on susceptibility to infection, protective immunity and immunopathology, in the context of exposure to a range of helminths including intestinal nematodes, filariae and schistosomes. It is apparent that the effects of IL-12 are complex and can be beneficial as well as detrimental for the host. The precise role of IL-12 depends upon a number of factors including the type of helminth and the specific tissue involved in the inflammatory response.