Vaccination of mice with a combination of BCG and killed Leishmania promastigotes reduces acute Trypanosoma cruzi infection by promoting an IFN-gamma response

Mycobacterium bovis BCG as immunostimulating agent prevents the severe form of chronic experimental Chagas disease

Introduction

There is currently no vaccine against Chagas disease (ChD), and the medications available confer multiple side effects. Mycobacterium bovis Bacillus Calmette-Guérin (BCG) produces balanced Th1, Th2, and Th17 modulatory immune responses and has improved efficacy in controlling chronic infections through nonspecific immunity. We aimed to improve the response to infection by inducing a stronger immune response and greater protection against the parasite by trained immunity.

Methods

BALB/c mice were immunized with BCG subcutaneously, and 60 days later, they were infected with Trypanosoma cruzi intraperitoneally. An evaluation of the progression of the disease from the acute to the chronic stage, analyzing various aspects such as parasitemia, survival, clinical status, and humoral and cellular immune response, as well as the appearance of visceral megas and the histopathological description of target organs, was performed.

Results

Vaccination reduced parasitemia by 70%, and 100% survival was achieved in the acute stage; although the presentation of clinical signs was reduced, there was no increase in the antibody titer or in the differential production of the isotypes.

Conclusion

Serum cytokine production indicated a proinflammatory response in infected animals, while in those who received BCG, the response was balanced by inducing Th1/Th2-type cytokines, with a better prognosis of the disease in the chronic stage.

Immunization of Mice by BCG Formulated HCV Core Protein Elicited Higher Th1-Oriented Responses Compared to Pluronic-F127 Copolymer

BACKGROUND

A supreme vaccine for Hepatitis C virus (HCV) infection should elicit strong Th1-oriented cellular responses. In the absence of a Th1-specific adjuvant, immunizations by protein antigens generally induce Th2-type and weak cellular responses.

OBJECTIVES

To evaluate the adjuvant effect of BCG in comparison with nonionic copolymer-Pluronic F127 (F127) as a classic adjuvant in the formulation of HCV core protein (HCVcp) as a candidate vaccine for induction of Th1 immune responses.

MATERIALS AND METHODS

Expression of N-terminally His-Tagged HCVcp (1-122) by pIVEX2.4a-core vector harboring the corresponding gene under the control of arabinose-inducible (araBAD) promoter was achieved in BL21-AI strain of E.coli and purified through application of nitrilotriacetic acid (Ni-NTA) chromatography. Mice were immunized subcutaneously (s.c.) in base of the tail with 100 μl of immunogen (F127+HCVcp or BCG+HCVcp; 5 μgHCVcp/mouse/dose) or control formulations (PBS, BCG, F127) at weeks 0, 3, 6. Total and subtypes of IgG, as well as cellular immune responses (Proliferation, In vivo CTL and IFN-γ/IL-4 ELISpot assays against a strong and dominant H2-d restricted, CD8+-epitopic peptide, core 39-48; RRGPRLGVRA of HCVcp) were compared in each group of immunized animals.

RESULTS

Expression and purification of core protein around the expected size (21 kDa) was confirmed by Western blotting. The HCVcp + BCG vaccinated mice showed significantly higher lymphocyte proliferation and IFN-γ production but lower levels of cell lysis (45% versus 62% in CTL assay) than the HCVcp+F127 immunized animals. "Besides, total anti-core IgG and IgG1 levels were significantly higher in HCVcp + F127 immunized mice as compared to HCVcp + BCG vaccinated animals, indicating relatively higher efficacy of F127 for the stimulation of humoral and Th2-oriented immune responses".

CONCLUSIONS

Results showed that HCVcp + BCG induced a moderate CTL and mixed Th1/Th2 immune responses with higher levels of cell proliferation and IFN-γ secretion, indicating that BCG may have a better outcome when formulated in HCVcp-based subunit vaccines.

A review of adjuvants for Leishmania vaccine candidates

Over the last decade, there has been a flurry of research on adjuvants for vaccines, and several novel adjuvants are now licensed products or in late stage clinical development. The success of adjuvants in enhancing the immune response to antigens has led many researchers to re-focus their vaccine development programs. Although several vaccine candidates have been tested against leishmaniasis, there is yet no effective vaccine against this parasitic disease. Recent research has documented that efforts to develop effective Leishmania vaccine have been limited due to lack of an appropriate adjuvant. In view of this, this review paper outlines some of the adjuvants that have been used in Leishmania vaccine candidates and cites a few of the responses obtained from these studies. The aim of the present review is to consolidate these findings to facilitate the application of these adjuvants in general and experimental vaccinology.

Current status and future prospects for a vaccine against American trypanosomiasis

The clinically relevant pathognomonic consequences of human infection by Trypanosoma cruzi are dilation and hypertrophy of the left ventricle walls and thinning of the apex. The major complications and debilitating evolutionary outcomes of chronic infection include ventricular fibrillation, thromboembolism and congestive heart failure. American trypanosomiasis (Chagas disease) poses serious public healthcare and budgetary concerns. The currently available drugs, although effective against acute infection, are highly toxic and ineffective in arresting or attenuating clinical disease symptoms in chronic patients. The development of an efficacious prophylactic vaccine faces many challenges, and progress is slow, despite several years of effort. Studies in animal models and human patients have revealed the pathogenic mechanisms during disease progression, pathology of disease and features of protective immunity. Accordingly, several antigens, antigen-delivery vehicles and adjuvants have been tested in animal models, and some efforts have been successful in controlling infection and disease. This review will summarize the accumulated knowledge about the parasite and disease, as well as pathogenesis and protective immunity. The authors will discuss the efforts to date, and the challenges faced in achieving an efficient prophylactic vaccine against human American trypanosomiasis, and present the future perspectives.

Vaccination with Trypanosoma rangeli reduces the infectiousness of dogs experimentally infected with Trypanosoma cruzi

The goal of this work was to test the efficacy of the vaccination with Trypanosoma rangeli in dogs. Mongrel dogs received three subcutaneous injections of fixed T. rangeli epimastigotes at 6-week intervals. Such immunisation induced antibodies against Trypanosoma cruzi. While both control and immunised dogs developed detectable parasitemia, this was lower and shorter in vaccinated animals. Interestingly, feeding of Triatoma infestans nymphs on vaccinated and chronically infected dogs led to a sharp reduction in the rate of bug infection. These results suggest that it might be possible to reduce the vectorial parasitemia through vaccination of dogs. As dogs are known to play a major role in the domestic cycle of T. cruzi, this might represent a strategy to reduce parasite transmission to humans.

Acute Trypanosoma cruzi infection: IL-12, IL-18, TNF, sTNFR and NO in T. rangeli-vaccinated mice

We have developed an experimental model of vaccination against the infection with the protozoa Trypanosoma cruzi, the agent of Chagas disease in Latin America. Vaccination was performed with Trypanosoma rangeli, a non-pathogenic protozoa sharing many antigens with T. cruzi. It strongly protected BALB/c mice, sharply reducing parasitaemia and mortality rate of the acute T. cruzi infection. The aim of the present work was to complete our previous study on the production of IFN-gamma and IL-10 in this vaccination model by investigating the production of IL-12p35 and p40, IL-18, TNF, TNF soluble receptors (sTNFR), and nitric oxide (NO), factors known to play a key role in the outcome of T. cruzi infection. We show that the protection obtained against the acute T. cruzi infection was surprisingly associated with reduced circulating levels of IL-18 and NO, whereas the release of IL-12p40 was enhanced in comparison to non-vaccinated infected animals. IL-12p35 remained undetectable in infected animals, vaccinated or not. The balance between sTNFR and TNF suggested a decrease of TNF bioactivity in vaccinated mice. These results show that the protection induced by the vaccination with T. rangeli against a challenging infection with T. cruzi is not associated with the strong type 1 immune response usually involved in the control of intracellular pathogens, particularly questioning the protective role of NO during the acute phase of T. cruzi infection.

IFN-gamma, IL-4, IL-10 and IL-12 gene expression in BCG-Leishmania vaccination of Trypanosoma cruzi-infected mice

We have previously shown that vaccination of BALB/c mice with a combination of BCG plus killed Leishmania promastigotes, applied by the i.p. route 10 and 3 days before Trypanosoma cruzi inoculation, prolonged their survival and decreased their parasitaemia. In the present study we show that the BCG-Leishmania vaccine induced higher levels of circulating IFN-gamma in acute and chronic infection of mice [on day 25 and 40 post-infection (p.i.) respectively], in comparison to unvaccinated animals (PBS-treated). Though the IFN-gamma mRNA content of spleen cells of vaccinated and infected mice (on day 25 p.i.) was similar to that of unvaccinated animals, the BCG-Leishmania vaccine enhanced significantly the production of IFN-gamma by spleen cells stimulated with T. cruzi antigens. This effect was observed to a lower extent in BCG- and Leishmania-treated mice. The BCG-Leishmania vaccine reduced the expression of the IL-10 mRNA of splenocytes as soon as day 12 p.i., before the peak parasitaemia. Such this effect was not observed in BCG- or Leishmania-treated animals. On day 25 p.i., the BCG plus Leishmania- or BCG-treatment of mice abolished the capacity of spleen cells to produce IL-10 in response to T. cruzi antigens. The levels of mIL-4 RNA and protein production were not modified in any group of mice. T. cruzi infection in BCG-Leishmania-vaccined mice stimulated an early and high production of IL-12 transcripts in spleen cells during the acute phase of the infection, that was prolonged during the chronic phase of infection. This effect was weaker or absent in BCG- and Leishmania-treated animals, respectively. These results indicate that the BCG-Leishmania vaccine stimulates the production of IL-12 and IFN-gamma, but inhibits that of IL-10 and is without effect on IL-4 when mice are infected with T. cruzi. This highlights the key role of endogenously produced IFN-gamma, IL-10 and IL-12 in the control of T. cruzi acute and chronic infection in mice and the favorable modulation of their balance by a vaccination combining BCG and Leishmania.