Paracoccidioides brasiliensis Vaccine Formulations Based on the gp43-Derived P10 Sequence and the Salmonella enterica FliC Flagellin

Abstract

Paracoccidioidomycosis (PCM) is a systemic granulomatous disease caused by the dimorphic fungusParacoccidioidomycosis (PCM) is a granulomatous disease caused by the thermodimorphic fungus Paracoccidioides brasiliensis, which is prevalent in Brazil and other Latin American countries (5, 6, 33). Some individuals develop one of the two main clinical forms of PCM. The acute form is characterized by impaired cellular immunity, negative delayed-type hypersensitivity reactions, increased systemic proliferation of the fungus, and high mortality rate. The chronic form, ranging from mild to severe chronic disease, shows exacerbated host cellular immune responses and formation of granulomas containing fungal cells and may evolve to develop extensive sequelae, including fibrotic lesions and impairment of lung function (33, 39).Vaccines against PCM are still not available for human use, but promising formulations have been experimentally tested during the last few years. Irradiated P. brasiliensis or cellular antigens fractionated by anion-exchange chromatography conferred partial protection against fungal proliferation in the murine model (11). The extracellular gp43 glycoprotein, the major diagnostic antigen of P. brasiliensis, is the most intensively studied component aimed at a vaccine for PCM control. Previous reports have shown that mice immunized with the purified protein, DNA, or anti-idiotypic monoclonal antibody were partially protected against challenges by P. brasiliensis (28,36,37,40). A 15-amino-acid peptide (QTLIAIHTLAIRY AN), designated P10, contains the gp43 immunodominant CD4 ϩ T-cell-specific epitope presented by major histocompatibility complex class II molecules from three different mouse haplotypes (37) and most human HLA-DR alleles (17, 18). Indeed, parenteral immunization with P10 in complete Freund adjuvant (CFA), or in the form of a truncated multiple-antigen peptide (MAP) complex, induced protective Th1 cellular immune responses in mice against intratracheal (i.t.) challenge with a virulent P. brasiliensis isolate (37,38,41).The rational use of vaccines has been significantly improved after elucidation of innate immune mechanisms in mammalian cells. The recognition of distinct pathogen-associated molecular patterns by members of the Toll-like receptor (TLR) family initiates a signaling cascade mediated by adaptor proteins, including MyD88 and interleukin-1 (IL-1) receptor-associated kinase, that culminates in the production of proinflammatory cytokines, such as tumor necrosis factor alpha and IL-12, and increased expression of cell surface molecules involved in epitope presentation by antigen-presenting cells (APC) (1,19). Proper APC activation by TLR agonists represents a key step for an effective adaptive immune response induced by pathogens or vaccines and explains, at least in part, the marked adjuvant effects of several bacterial molecules, including lipopolysaccharides, lipoproteins, peptidoglycan fragments, and flagellins (2).Flagellin, the structural subunit of bacterial flagellum, is a

Salmonella enterica Serovar Typhimurium Vaccine Strains Expressing a Nontoxic Shiga-Like Toxin 2 Derivative Induce Partial Protective Immunity to the Toxin Expressed by Enterohemorrhagic Escherichia coli

“…Bacterial flagellins show strong adjuvant effects when delivered to mammalian hosts, via mucosal or parenteral routes, either in the form of purified protein admixed with target antigens or as hybrid proteins genetically fused to the antigen (4,8,22,23,36). Our results demonstrate that derivatives of S. Typhimurium strain SL3261, proficient in the expression of both FliCI and FljB, and strain LDV321, in which the expression of both flagellar phases is specifically blocked (31), did not differ significantly in their immunogenicity as vaccine vectors for passenger antigens regarding activation of either Stx2-specific systemic or mucosal antibody responses in orally vaccinated mice.…”

“…Bacterial flagellins have been shown to bind both extracellular and intracellular receptors of antigen-presenting cells, leading to inflammation and increased adaptive immune responses, including the generation of antigen-specific antibodies and T cells (2,26). The strong adjuvant effects of Salmonella flagellins, either when admixed with purified antigens or when used as hybrid proteins genetically fused to the target antigens, have been demonstrated recently (4,8,22,23,36). However, there is no clear evidence that the expression of flagellin affects the immunogenicity of heterologous antigens expressed by attenuated Salmonella vaccine strains.…”

Mucosal vaccines

“…116 The TLR5 ligand, flagellin, combined with various antigens has been shown to enhance IgA response after i.n administration and protect against various toxins and pathogens challenge in preclinical models. [117][118][119] Indeed, Salmonella flagellins has been shown to be flexible adjuvants leading to activation of antibody and T cell responses based on the administration via mucosal and parenteral routes either as recombinant protein genetically fused with the target antigen or admixed with the soluble or particulate antigens. 120 Recently, it has been shown that the i.n delivery of virus like particles (VLPs) in combination with TLR7 or TLR9 agonists led to a significantly better dose-sparing effects than TLR3, TLR5 or TLR8 agonists for the induction of specific and functional antibody responses in the respiratory, gastrointestinal, and reproductive tracts.…”

Universal fungal vaccines

“…48 Immunization of Balb/c mice with P. brasiliensis-derived P10 peptide fused to Salmonella entericaderived FliC flagellin, a TLR-5 binding protein, was reported to induce Th1-dependent protection against P. brasiliensis infection. 49 Administration of conjugates consisting of the B. anthracis-derived PA antigen and the C. neoformans-derived GalXM protein can induce robust and sustained T cell-dependent protective Ab responses against cryptococcosis in mice. 50 Additionally, several putative MHC II-binding proteins deduced from E. coli were reported to protect against C. posadasii infections in mice.…”