Parenteral Adjuvant Effects of an Enterotoxigenic Escherichia coli Natural Heat-Labile Toxin Variant

Abstract

Native type I heat-labile toxins (LTs) produced by enterotoxigenic Escherichia coli (ETEC) strains exert strong adjuvant effects on both antibody and T cell responses to soluble and particulate antigens following co-administration via mucosal routes. However, inherent enterotoxicity and neurotoxicity (following intra-nasal delivery) had reduced the interest in the use of these toxins as mucosal adjuvants. LTs can also behave as powerful and safe adjuvants following delivery via parenteral routes, particularly for activation of cytotoxic lymphocytes. In the present study, we evaluated the adjuvant effects of a new natural LT polymorphic form (LT2), after delivery via intradermal (i.d.) and subcutaneous (s.c.) routes, with regard to both antibody and T cell responses. A recombinant HIV-1 p24 protein was employed as a model antigen for determination of antigen-specific immune responses while the reference LT (LT1), produced by the ETEC H10407 strain, and a non-toxigenic LT form (LTK63) were employed as previously characterized LT types. LT-treated mice submitted to a four dose-base immunization regimen elicited similar p24-specific serum IgG responses and CD4+ T cell activation. Nonetheless, mice immunized with LT1 or LT2 induced higher numbers of antigen-specific CD8+ T cells and in vivo cytotoxic responses compared to mice immunized with the non-toxic LT derivative. These effects were correlated with stronger activation of local dendritic cell populations. In addition, mice immunized with LT1 and LT2, but not with LTK63, via s.c. or i.d. routes developed local inflammatory reactions. Altogether, the present results confirmed that the two most prevalent natural polymorphic LT variants (LT1 or LT2) display similar and strong adjuvant effects for subunit vaccines administered via i.d. or s.c. routes.

Impact of Toxin-Specific Antibodies on the Adjuvanticity and Inflammatory Effects Induced by Parenterally Administered Escherichia coli heat-Labile Toxin

“…delivered LT administration, including non-toxic derivatives, has raised safety issues for humans [3,30,31], while similar concerns have not been observed following non-toxic LT administration by parenteral routes. Preclinical studies based on LT derivatives delivered via parenteral routes have demonstrated that these molecules are safe and robust inducers of humoral and cellular immune responses [8][9][10][11]. In this context the present study is the first to demonstrate that preexisting immunity to LT did not affect immunogenicity and humoral adjuvant effects of LT, thus adding another supporting evidence for the potential usefulness of LT as parenteral delivered adjuvants.…”

“…However, the inherent toxicity of LT, even after inoculation of low amounts, has precluded its use as a vaccine adjuvant for humans, particularly under mucosal route [3,4,7,8]. On the other hand, detoxified LT mutants and natural variants have demonstrated safety features after parenteral inoculation [8][9][10][11].Thus, parenteral administration of LT-derivatives represents a new and promising alternative for clinical use of this class of vaccine adjuvant.…”

Toxinas termo-lábeis (LTs) do tipo II de Escherichia coli enterotoxigênica (ETEC): efeito adjuvante e atividade inflamatória.

“…Além de importantes fatores de virulência, as LTs são empregadas como adjuvantes vacinais, com alguns derivados de LT-I (recombinantes, mutantes ou não) sendo testados como antígeno/adjuvante vacinal em estudos clínicos (BEHRENS et al, 2014;GÜEREÑA-BURGUEÑO et al, 2002;MCKENZIE et al, 2007;STEPHENSON et al, 2006 (BARRETTE et al, 2011;BELYAKOV et al, 2001;BRAGA et al, 2014;GREENE et al, 2013;LOSONSKY;KOTLOFF;WALKER, 2003;NEGRI et al, 2010;TIERNEY et al, 2003). A grande maioria dos estudos avalia o potencial de aplicação de LT-I como adjuvante, fato que pode ser atribuído à maior facilidade de obtenção da toxina, que já foi inclusive comercializada por grandes empresas como a Sigma-Aldrich.…”

“…ii) aumento da expressão de moléculas co-estimulatórias na superfície de células apresentadoras de antígenos(BRAGA et al, 2014); iii) ativação do inflamassoma Nalp3(LI et al, 2014); iv) produção da citocina IL-17 por células monocíticas de sangue periférico mediada…”

Identificação de epítopos presentes na proteína e do vírus dengue tipo 2 (DENV2) capazes de gerar anticorpos neutralizantes sem a promoção da exacerbação da replicação viral.

“…BRERETON et al, 2011;BRAGA et al, 2014;BATISTA et al, 2017). Em estudos relacionados à resposta imunológica humoral induzida pela administração de LT e seus mutantes ou derivados atóxicos, a investigação da potência e modulação de resposta é limitada a determinação dos títulos e subclasses de anticorpos antígeno-específicos(HAAN et al, 1999; FRASER et al, 2003).…”