Comparative immunogenicity and protective efficacy of BECC438 and BECC470 adjuvants in a vaccine formulation against Pseudomonas aeruginosa.

The development of effective vaccines against the opportunistic pathogen Pseudomonas aeruginosa (Pa) remains a critical public health priority for susceptible individuals due, in part, to the pathogen's intrinsic resistance mechanisms. This study evaluates the comparative immunogenicity and protective efficacy of two novel lipid A mimetic adjuvants, BECC438 (BECC438s or BECC438b) and BECC470 (BECC470s or BECC470b), in a subunit vaccine (L-PaF - a genetic fusion of Pa type III secretion system proteins PcrV and PopB with LTA1, the active moiety of heat-labile enterotoxin from enterotoxigenic E. coli) formulated into an oil-in-water (o/w) emulsion to target Pa. BECC438b and BECC470b are biologically derived lipid A analogues produced using a Bacterial Enzymatic Combinatorial Chemistry (BECC) platform. In contrast, BECC438s and BECC470s are chemically synthesized counterparts designed to achieve high purity, eliminating congener species that could interfere with selective Toll-like receptor 4 (TLR4) activation while minimizing potential reactogenicity. Vaccine formulations incorporating BECC438 or BECC470 with Pa antigens were administered to mice via intranasal (IN) or intramuscular (IM) routes, followed by assessment of immune responses and lung burden post-challenge with Pa. IN immunization with BECC438s or BECC438b induced robust antigen-specific IgG and IgA responses, with a balanced IgG1/IgG3 profile that is indicative of mixed Th1/Th2 polarization, however, IgG1 remained the predominant antibody subclass. BECC438s conferred the highest protection against Pa challenge by reducing bacterial burden and improving immune responses following IN immunization. Moreover, L-PaF/ME/BECC438s delivered IN provided superior protection when compared to IM immunization. Serum antibody titers and pre-challenged or post-challenged cytokine responses were directly correlated with bacterial clearance upon Pa pulmonary challenge. These findings suggest that BECC438 offers enhanced mucosal and systemic immunity over BECC470 in this infection model, making it a promising candidate for inclusion in mucosal next-generation Pa vaccines. Overall, this comparative analysis highlights the potential of BECC derived adjuvants to improve vaccine performance against multidrug-resistant pathogens like Pa following IN immunization. Further studies are warranted to evaluate their translational potential in human populations.