dmLT Adjuvant Enhances Cytokine Responses to T Cell Stimuli, Whole Cell Vaccine Antigens and Lipopolysaccharide in Both Adults and Infants

Abstract

Enhancement of mucosal immune responses in children and infants using novel adjuvants such as double mutant heat labile toxin (dmLT) is an important goal in the enteric vaccine field. dmLT has been shown to enhance mucosal IgA responses to the oral inactivated enterotoxigenic Escherichia coli (ETEC) vaccine ETVAX. dmLT can enhance IL-17A production from adult T cells, which may increase the production and secretion of mucosal IgA antibodies. However, the adjuvant mechanism remains to be fully elucidated and might differ between infants and adults due to age-related differences in the development of the immune system. The main objective of this study was to determine how dmLT influences antigen presenting cells and T cells from infants compared to adults, and the role of IL-1β for mediating the adjuvant activity. Peripheral blood mononuclear cells (PBMCs) from Bangladeshi infants (6-11 months) and adults (18-40 years) were stimulated with the mitogen phytohaemagglutinin (PHA), the superantigen Staphylococcal enterotoxin B (SEB), ETVAX whole cell component (WCC) or E. coli lipopolysaccharide (LPS) ± dmLT, and cytokine production was measured using ELISA and electrochemiluminescence assays. The adjuvant dmLT significantly enhanced SEB- and PHA-induced IL-17A, but not IFN-γ responses, in PBMCs from both infants and adults. Blocking experiments using an IL-1 receptor antagonist demonstrated the importance of IL-1 signaling for the adjuvant effect. dmLT, ETVAX WCC and LPS induced dose-dependent IL-1β responses of comparable magnitudes in infant and adult cells. Depletion experiments suggested that IL-1β was mainly produced by monocytes. dmLT enhanced IL-1β responses to low doses of WCC and LPS, and the adjuvant effect appeared over a wider dose-range of WCC in infants. dmLT and WCC also induced IL-6, IL-23 and IL-12p70 production in both age groups and dmLT tended to particularly enhance IL-23 responses to WCC. Our results show that dmLT can induce IL-1β as well as other cytokines, which in turn may enhance IL-17A and potentially modulate other immunological responses in both infants and adults. Thus, dmLT may have an important function in promoting immune responses to the ETVAX vaccine, as well as other whole cell- or LPS-based vaccines in infants in low- and middle-income countries.

Oral inactivated whole cell vaccine for mucosal immunization: ETVAX case study

“…Seventy-eight (56%) of 139 infants aged 6-11 months who were vaccinated developed mucosal responses against at least three of the vaccine antigens versus 14 (29%) of 49 of the infants given placebo. Addition of the adjuvant dmLT enhanced the magnitude, breadth, and kinetics (based on number of responders after the first dose of vaccine) of immune responses in infants (19). A similar positive dmLT effect was observed on the mucosal antibody response in the 12-23 month age group in this study when the antigenic breath of the responses was considered.…”

New-age vaccine adjuvants, their development, and future perspective

“…Vaccine preparation with dmLT has been found to be effective against mucosal infections. It has been concluded that dmLT will be useful to overcome hypo-responsiveness to other whole cell-or LPSbased vaccines such as cholera, Salmonella typhi, and Shigella vaccines in infants in economically less developed countries (215). We predict that the use of dmLT in vaccine preparations for infants will be highly effective in the future.…”

GM‐CSF is key in the efficacy of vaccine‐induced reduction of Helicobacter pylori infection

“…CTB (e.g., Dukoral ® vaccine), the Escherichia coli LT subunit B (LTB), or double mutant LT (dmLT) are also promising mucosal adjuvants to trigger specific Th17 immune responses. CTB as adjuvant has been almost evaluated fused to the vaccine antigen 72–75 . In addition to CTB, LTB and dmLT, recent adjuvant alternatives have been also evaluated such as mucosal administration of cyclic dinucleotides, 75 suggesting that the stimulation of mucosal H. pylori ‐specific Th17 responses could be envisioned in the future clinical trials.…”

“…CTB as adjuvant has been almost evaluated fused to the vaccine antigen. 72 , 73 , 74 , 75 In addition to CTB, LTB and dmLT, recent adjuvant alternatives have been also evaluated such as mucosal administration of cyclic dinucleotides, 75 suggesting that the stimulation of mucosal H. pylori ‐specific Th17 responses could be envisioned in the future clinical trials.…”