The invasiveness and virulence of Shigella spp. are largely due to the expression of plasmid-encoded virulence factors, among which are the invasion plasmid antigens (Ipa proteins). After infection, the host immune response is directed primarily against lipopolysaccharide (LPS) and the virulence proteins (IpaB, IpaC, and IpaD). Recent observations have indicated that the Ipa proteins (IpaB, IpaC, and possibly IpaD) form a multiprotein complex capable of inducing the phagocytic event which internalizes the bacterium. We have isolated a complex of invasins and LPS from water-extractable antigens of virulent shigellae by ion-exchange chromatography. Western blot analysis of the complex indicates that all of the major virulence antigens of Shigella, including IpaB, IpaC, and IpaD, and LPS are components of this macromolecular complex. Mice or guinea pigs immunized intranasally with purified invasin complex (invaplex), without any additional adjuvant, mounted a significant immunoglobulin G (IgG) and IgA antibody response against the Shigella virulence antigens and LPS. The virulence-specific response was very similar to that previously noted in primates infected with shigellae. Guinea pigs (keratoconjunctivitis model) or mice (lethal lung model) immunized intranasally on days 0, 14, and 28 and challenged 3 weeks later with virulent shigellae were protected from disease (P < 0.01 for both animal models).Shigellosis is a leading cause of human diarrheal disease. Each year millions of cases occur, particularly in developing countries, with over 1 million cases resulting in death (15). The constant emergence of antibiotic resistance in Shigella spp. (12), even to the newest antibiotics, underscores the need for an effective vaccine to help control Shigella disease. Vaccine strategies must consider the need for protection against four species of Shigella (S. flexneri, S. sonnei, S. dysenteriae, and S. boydii) with over 45 different serotypes, and also enteroinvasive Escherichia coli (EIEC), as cross-protection is not significant between the species. Historically, successful Shigella vaccines have emphasized presentation of lipopolysaccharide (LPS) in a manner that will elicit protection. Such vaccines include live attenuated vaccines (25, 32) and delivery of Shigella LPS or O polysaccharides with carriers such as proteosomes (28), tetanus toxoid (6), or ribosomes (16). Of these vaccine approaches, only the live attenuated vaccines utilize the native invasiveness of the shigellae to deliver the LPS and other antigens to the mucosal immune system, presumably via the follicle-associated epithelium (33). The residual pathogenicity of the attenuated vaccine strains may limit this approach unless further attenuation is achieved (7).The pathogenesis of Shigella is attributed to the organism's ability to invade, replicate intracellularly, and spread intercellularly within the colonic epithelium. The invasion of host cells by Shigella spp. is a complex multifactorial event in which many different bacterial proteins are involved. M...

The native Invaplex (Invaplex) vaccine and adjuvant is an ion exchange-purified product derived from the water extract of virulent species. The key component of Invaplex is a high-molecular-mass complex (HMMC) consisting of the lipopolysaccharide (LPS) and the invasin proteins IpaB and IpaC. To improve product purity and immunogenicity, artificial Invaplex (Invaplex) was developed using recombinant IpaB and IpaC proteins and purified LPS to assemble an HMMC consisting of all three components. Characterization of Invaplex by various methods demonstrated similar characteristics as the previously reported HMMC in Invaplex. The well-defined Invaplex vaccine consistently contained greater quantities of IpaB, IpaC, and LPS than Invaplex. Invaplex and Invaplex immunogenicities were compared in mouse and guinea pig dose escalation studies. In both models, immunization induced antibody responses specific for Invaplex and LPS while Invaplex 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 than Invaplex and mice receiving Invaplex lost significantly less weight than mice receiving the same amount of Invaplex. Moreover, mice immunized with Invaplex were protected from challenge with both homologous and heterologous serotypes. Guinea pigs receiving approximately 5-fold less Invaplex compared to cohorts immunized with Invaplex were protected from ocular challenge. Furthermore, adjuvanticity previously attributed to Invaplex was retained with Invaplex. The second-generation Invaplex vaccine, Invaplex, offers significant advantages over Invaplex in reproducibility, flexible yet defined composition, immunogenicity, and protective efficacy. 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 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 infection. The next step in the product's development will be to test the safety and immune response induced in humans immunized with Invaplex.

Results: There were no serious adverse events and the majority of adverse events (98%) were mild. Antibody secreting cells (ASC), plasma, and mucosal immune responses to Shigella antigens were detected at all three dose levels with the 690 g dose inducing the highest magnitude and frequency of responses. Vaccination with comparable doses of Invaplex 50 via the Dolphin TM resulted in higher plasma and ASC immune responses as compared to pipette delivery. Conclusion: In this trial the S. flexneri 2a Invaplex 50 vaccine was safe, well-tolerated and induced robust levels of antigen-specific intestinal IgA and ASC responses. The spray device performed well and offered an advantage over pipette intranasal delivery.Published by Elsevier Ltd.

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