Assembly, Biochemical Characterization, Immunogenicity, Adjuvanticity, and Efficacy of Artificial Invaplex.

The native Invaplex (Invaplex(NAT)) vaccine and adjuvant is an ion exchange-purified product derived from the water extract of virulent Shigella species. The key component of Invaplex(NAT) is a high-molecular-mass complex (HMMC) consisting of the Shigella lipopolysaccharide (LPS) and the invasin proteins IpaB and IpaC. To improve product purity and immunogenicity, artificial Invaplex (Invaplex(AR)) was developed using recombinant IpaB and IpaC proteins and purified Shigella LPS to assemble an HMMC consisting of all three components. Characterization of Invaplex(AR) by various methods demonstrated similar characteristics as the previously reported HMMC in Invaplex(NAT). The well-defined Invaplex(AR) vaccine consistently contained greater quantities of IpaB, IpaC, and LPS than Invaplex(NAT). Invaplex(AR) and Invaplex(NAT) immunogenicities were compared in mouse and guinea pig dose escalation studies. In both models, immunization induced antibody responses specific for Invaplex(NAT) and LPS while Invaplex(AR) induced markedly higher anti-IpaB and -IpaC serum IgG and IgA endpoint titers. In the murine model, homologous protection was achieved with 10-fold less Invaplex(AR) than Invaplex(NAT) and mice receiving Invaplex(AR) lost significantly less weight than mice receiving the same amount of Invaplex(NAT). Moreover, mice immunized with Invaplex(AR) were protected from challenge with both homologous and heterologous Shigella serotypes. Guinea pigs receiving approximately 5-fold less Invaplex(AR) compared to cohorts immunized with Invaplex(NAT) were protected from ocular challenge. Furthermore, adjuvanticity previously attributed to Invaplex(NAT) was retained with Invaplex(AR). The second-generation Shigella Invaplex vaccine, Invaplex(AR), offers significant advantages over Invaplex(NAT) in reproducibility, flexible yet defined composition, immunogenicity, and protective efficacy. IMPORTANCE Shigella species are bacteria that cause severe diarrheal disease worldwide, primarily in young children. Treatment of shigellosis includes oral fluids and antibiotics, but the high burden of disease, increasing prevalence of antibiotic resistance, and long-term health consequences clearly warrant the development of an effective vaccine. One Shigella vaccine under development is termed the invasin complex or Invaplex and is designed to drive an immune response to specific antigens of the bacteria in an effort to protect an individual from infection. The work presented here describes the production and evaluation of a new generation of Invaplex. The improved vaccine stimulates the production of antibodies in immunized mice and guinea pigs and protects these animals from Shigella infection. The next step in the product's development will be to test the safety and immune response induced in humans immunized with Invaplex.