Mucosal Adjuvanticity of a Shigella Invasin Complex with DNA-Based Vaccines

Abstract

Protection against many infectious diseases may require the induction of cell-mediated and mucosal immunity. Immunization with plasmid DNA-based vaccines has successfully induced cell-mediated immune responses in small animals but is less potent in humans. Therefore, several methods are under investigation to augment DNA vaccine immunogenicity. In the current study, a mucosal adjuvant consisting of an invasin protein-lipopolysaccharide complex (Invaplex) isolated from Shigella spp. was evaluated as an adjuvant for DNA-based vaccines. Coadministration of plasmid DNA encoding the Orientia tsutsugamushi r56Karp protein with Invaplex resulted in enhanced cellular and humoral responses in intranasally immunized mice compared to immunization with DNA without adjuvant. Mucosal immunoglobulin A, directed to plasmid-encoded antigen, was detected in lung and intestinal compartments after Invaplex-DNA immunization followed by a protein booster. Moreover, immunization with Invaplex elicited Shigella-specific immune responses, highlighting its potential use in a combination vaccine strategy. The capacity of Invaplex to enhance the immunogenicity of plasmid-encoded genes suggested that Invaplex promoted the uptake and expression of the delivered genes. To better understand the native biological activities of Invaplex related to its adjuvanticity, interactions between Invaplex and mammalian cells were characterized. Invaplex rapidly bound to and was internalized by nonphagocytic, eukaryotic cells in an endocytic process dependent on actin polymerization and independent of microtubule formation. Invaplex also mediated transfection with several plasmid DNA constructs, which could be inhibited with monoclonal antibodies specific for IpaB and IpaC or Invaplex-specific polyclonal sera. The cellular binding and transport capabilities of Invaplex likely contribute to the adjuvanticity and immunogenicity of Invaplex.Immunization with plasmid DNA encoding vaccine antigens holds the promise of inducing cell-mediated and humoral immunity while offering several advantages over traditional immunization technologies, including ease of production, low cost, and the ability to engineer a highly defined product (10). However, several obstacles must be overcome prior to the widespread use of DNA vaccines. For example, although potent cell-mediated and humoral responses have been induced in small animal models, the success of DNA-based vaccines in humans is limited (22). The modest immune responses elicited in humans have highlighted the need for methods to enhance the immunogenicity of DNA-based vaccines. Inducing antigenspecific immune responses after plasmid DNA immunization is dependent on either in vivo transfection of antigen-presenting cells (APCs), expression of intracellular peptide and presentation in major histocompatibility complex (MHC) class I by transfected nonprofessional APCs, or presentation of phagocytosed antigen, exported from transfected cells, in MHC class I or class II by APCs (6). Thus, several approaches have been used ...

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

“…Adjuvanticity of S. flexneri 2a Invaplex AR . In addition to inducing Shigella-specific immune responses, Invaplex NAT also functions as an adjuvant, capable of enhancing the magnitude of the immune response directed to coadministered protein antigens (26) or antigens encoded on plasmid DNA (27). To determine if adjuvanticity was retained with Invaplex AR , groups of mice were intranasally immunized with either ovalbumin (OVA) alone or in combination with S. flexneri 2a Invaplex NAT , Invaplex AR , or cholera toxin (CT), a known mucosal adjuvant.…”

“…Studies conducted with protein antigens (ovalbumin, protective antigen from Bacillus anthracis, CFA/I antigen from enterotoxigenic E. coli, and FlaA from Campylobacter jejuni) have demonstrated that Invaplex NAT increases the magnitude of the humoral and cellular immune response directed to the coadministered antigen (26). Furthermore, Invaplex NAT also enhanced the immune response directed to vaccine antigens encoded on DNA plasmids (27). The adjuvanticity of Invaplex has been partially attributed to its inherent ability to induce cellular uptake of coadministered antigens as well as providing the necessary Toll-like receptor 4 (TLR-4) agonist that stimulates robust immune responses.…”

“…The slightly larger size of Invaplex AR than Invaplex NAT may improve its interactions with antigen-presenting cells (APCs) and enhance its immunogenicity and adjuvanticity. The retention of the biological activity combined with inclusion of LPS allows Invaplex AR to also function as a mucosal adjuvant when codelivered with heterologous antigens such as ovalbumin (27). The adjuvanticity of Invaplex AR is very appealing when considering the development of a combination vaccine, such as an antidiarrheal vaccine to protect against enterotoxigenic Escherichia coli (ETEC) and Shigella infection.…”

DNA vaccines for targeting bacterial infections

“…Furthermore, intracellular bacteria can be a costeffective delivery method; these live-attenuated bacterial delivery vaccines have proven efficacious against infectious diseases and cancer. Some examples include: Salmonella typhi [82], Listeria monocytogenes [83,84], Shigella flexneri [85], Yersinia enterocolitica [86] and invasive E. coli [87]. Finally, nanotechnology that is complexed with DNA is currently being explored for the facilitation of receptor-mediated vaccine internalization.…”

Mucosal immunization: A realistic alternative

“…Cited results indicate that this complex was safe and immunogenic in humans. 259 What is of wider interest is that Invaplex has been demonstrated to be an effective mucosal adjuvant when co-administered intranasally with DNA-encoded antigens. 259 Further studies are clearly needed to assess the potential of the complex as an effective, non-toxic mucosal adjuvant.…”