Effect of 5 % lactose and 0.1 % polysorbate 80 buffer on protein-based multivalent ETEC vaccine candidate MecVax stabilization and immunogenicity.

MecVax is a protein-based vaccine candidate targeting the seven most important adhesins and the two toxins of enterotoxigenic Escherichia coli (ETEC), the top cause of children's diarrhea and travelers' diarrhea. In this study, we formulated MecVax protein antigens, toxoid fusion 3xSTa-mnLT and CFA/I/II/IV MEFA, with 5 % lactose and/or 0.1 % polysorbate 80 (Tween-80) or phosphate-buffered saline (PBS), and explored buffer formulations for this ETEC vaccine candidate. Data showed that CFA/I/II/IV MEFA protein remained stable at 37 °C for eight weeks in 0.1 % Tween-80 buffer or PBS, whereas toxoid fusion protein showed apparent physical degradation after three weeks, particularly buffered with 5 % lactose, based on visual examination with SDS-PAGE Coomassie blue staining. Mice intramuscularly immunized with MecVax, composed of the toxoid fusion protein and CFA/I/II/IV MEFA that were shelved at 37 °C for three and six weeks, respectively, developed robust antibody responses to ETEC heat-stable toxin (STa) and heat-labile toxin (LT) and seven ETEC adhesins (CFA/I, CS1-CS6). MecVax in 0.1 % Tween-80 buffer, with or without 5 % lactose, or in PBS induced significantly better anti-adhesin and antitoxin IgG responses, and the derived mouse serum antibodies had significantly better activities against adherence of the seven ETEC adhesins and STa and LT enterotoxicity in vitro. These results indicated that a 0.1 % Tween-80 buffer and PBS significantly improved MecVax's thermal stabilization and immunogenicity, providing instructive information for future buffer formulation and the development of this multivalent vaccine candidate against ETEC diarrhea.