Abstract
Deficiency in memory formation and increased immunosenescence are pivotal features of Trypanosoma cruzi infection proposed to play a role in parasite persistence and disease development. The vaccination protocol that consists in a prime with plasmid DNA followed by the boost with a deficient recombinant human adenovirus type 5, both carrying the ASP2 gene of T. cruzi, is a powerful strategy to elicit effector memory CD8+ T-cells against this parasite. In virus infections, the inhibition of mTOR, a kinase involved in several biological processes, improves the response of memory CD8+ T-cells. Therefore, our aim was to assess the role of rapamycin, the pharmacological inhibitor of mTOR, in CD8+ T response against T. cruzi induced by heterologous prime-boost vaccine. For this purpose, C57BL/6 or A/Sn mice were immunized and daily treated with rapamycin for 34 days. CD8+ T-cells response was evaluated by immunophenotyping, intracellular staining, ELISpot assay and in vivo cytotoxicity. In comparison with vehicle-injection, rapamycin administration during immunization enhanced the frequency of ASP2-specific CD8+ T-cells and the percentage of the polyfunctional population, which degranulated (CD107a+) and secreted both interferon gamma (IFNγ) and tumor necrosis factor (TNF). The beneficial effects were long-lasting and could be detected 95 days after priming. Moreover, the effects were detected in mice immunized with ten-fold lower doses of plasmid/adenovirus. Additionally, the highly susceptible to T. cruzi infection A/Sn mice, when immunized with low vaccine doses, treated with rapamycin, and challenged with trypomastigote forms of the Y strain showed a survival rate of 100%, compared with 42% in vehicle-injected group. Trying to shed light on the biological mechanisms involved in these beneficial effects on CD8+ T-cells by mTOR inhibition after immunization, we showed that in vivo proliferation was higher after rapamycin treatment compared with vehicle-injected group. Taken together, our data provide a new approach to vaccine development against intracellular parasites, placing the mTOR inhibitor rapamycin as an adjuvant to improve effective CD8+ T-cell response.
Highlights
The immunization regimen known as heterologous prime-boost vaccination uses two distinct vectors for priming and boosting, both carrying the target antigen
The blockade of mTOR by rapamycin was confirmed by ribosomal protein S6 staining, which is a target of mTOR kinase
We evaluated the production of cytokines IFNg and TNF, as well as the degranulation by the expression of the CD107a molecule (LAMP-1) in VNHRFTLV peptide-specific CD8+ T-cells obtained from splenocytes of immunized mice
Summary
The immunization regimen known as heterologous prime-boost vaccination uses two distinct vectors for priming and boosting, both carrying the target antigen. Different combinations of vectors have been tested and the application of this strategy has promoted an immune response against several experimental infections, such as simian immunodeficiency virus (SIV), malaria, Ebola, tuberculosis, Chagas disease, toxoplasmosis and COVID-19 (Li et al, 1993; McConkey et al, 2003; Wilson et al, 2006; Zhang et al, 2007; De Alencar et al, 2009; Elvang et al, 2009; Hensley et al, 2010; Hill et al, 2010; Martins et al, 2010; Chuang et al, 2013; Graham et al, 2020) This regimen began to be studied more than 20 years ago and has shown excellent protective responses both to intracellular pathogens and neoplastic cells due to the induction of cytotoxic CD8+ T-cells (Zavala et al, 2001; Gilbert et al, 2002; Ranasinghe and Ramshaw, 2009). The treatment consists of administering the chemotherapeutic benznidazole or nifurtimox, but these drugs have limited efficacy when started late, and there are still no vaccines for the disease (Pérez-Molina and Molina, 2017)
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