Co-delivery of Vi polysaccharide in enhancing stability and immunity of LcrV protein—a potential vaccine candidate of Yersinia pestis against plague

Transmittable diseases are considered a serious threat to human health as they are spread due to environmental, socioeconomic, and behavioral factors in humans. Plague, a zoonotic disease caused by the etiological pathogen Yersinia pestis, is deadly and is considered a biological warfare agent. The type-III secretion protein of Y. pestis called the LcrV (low calcium response V) antigen is one of the biomarkers for plague, but suffers from thermal instability and is also poorly immunogenic. The present study evaluates the efficiency of the capsular polysaccharide antigen of Salmonella Typhi , Vi Polysaccharide, in stabilizing the plague vaccine antigen, thereby facilitating an improved humoral immune response without an adjuvant. Osmolyte taurine was used as a co-excipient and as a natural linker to provide dynamic covalent bonding between the excipients. The structural stability was characterized by various analytical techniques including protein thermodynamic studies using high-throughput differential scanning calorimetry (DSC) and circular dichroism (CD) in different time intervals. A reliable formulation has augmented efficient structural stability for 4 weeks at room temperature (30 ± 2 °C) with Vi polysaccharide as a major excipient. An increase in the thermal transition midpoint (Tm) from 61.30 to 86.04 °C in DSC and retainment of α-helix content (51%) in CD spectroscopy expresses the structural compactness of LcrV in the formulation. The biological activity of the formulated antigen was also maintained for up to 4 weeks, characterized by in vivo antibody response studies (IgG) showing a significant difference (p-value = 0.009) compared to the adjuvanted pure antigen stored at optimal temperature (4–8 °C), after two boosters. Graphical Abstract