Gut Adhesive Bacillus subtilis Spores as a Platform for Mucosal Delivery of Antigens

Abstract

Bacterial carriers for the mucosal delivery of antigens, particularly those capable of colonizing or invading through the mucosal epithelia, have been intensively investigated (1). Live bacterial vectors can be generated with attenuated pathogens, such as Salmonella and Listeria, or nonpathogenic commensal species, such as Lactococcus and Lactobacillus. Bacteria in the former group of are capable of inducing strong and long-lasting immune responses to passenger antigens but present serious safety concerns, whereas bacteria in the latter group are safer but typically induce much lower immune responses to the passenger antigens (1-3). As a safe nonpathogenic live bacterial vector, Bacillus subtilis, a spore-forming soil Gram-positive bacterial species, has been engineered to express antigens as either vegetative cells or spores (4, 5). As antigen carriers, B. subtilis spores have several attractive features, including a safe record of human and animal use as both probiotic and food additives, remarkable heat resistance, and rather easy genetic and bacteriological manipulation.Currently, two major genetic approaches have been proposed to generate recombinant B. subtilis spores as vaccine delivery vectors. The first approach relies on the expression of a heterologous protein genetically fused to surface-exposed spore coat proteins, such as CotB, CotC, or CotG (6, 7). Such a strategy would allow a better presentation of the passenger antigen to the mucosa-associated lymphoid tissue (MALT) afferent sites, leading to the induction of adaptive immune responses, such as mucosal secretory (IgA) or systemic (IgG) antigen-specific antibody responses (6-8). The second approach is based on a distinct rationale and has employed episomal vectors in which the target antigen is expressed under the control of a promoter (PgsiB) active only at the vegetative cell stage, which means immediately after spore germination (9-11). This antigen delivery approach relies on the fact that B. subtilis spores germinate during transit through the gastrointestinal tract and produce the target antigen at the intestinal lumen or inside the phagocytes of antigen-presenting cells (APCs), leading to the induction of antibody responses in the serum (IgG) and mucosa (fecal IgA) (9-11).However, in both cases, the administration of recombinant spores via mucosal routes typically confers immune responses to the passenger antigen lower than those achieved with delivery systems based on attenuated bacterial strains capable of colonizing the mammalian gastrointestinal tract. The reduced mucosal adjuvant effects of B. subtilis spores have been attributed to several factors, such as a previously established immunity generated by the frequent ingestion of spores, the reduced amount of expressed antigens, and the rapid transit through the gastrointestinal tract, which reduces the chances of a productive interaction with the gut-associated lymphoid tissue (GALT), such as M cells and APCs at Peyer's patches (PPs) (12, 13).In an attempt to improve the performance o...

Effect of oral administration of Bacillus coagulans B37 and Bacillus pumilus B9 strains on fecal coliforms, Lactobacillus and Bacillus spp. in rat animal model

“…The Bacillus counts in feces of the control rats as well as the rats fed only skim milk (T1) were found to be very low or sometimes non-detectable. The significant increment of the Bacillus counts after feeding of B. coagulans B37 and B. pumilus B9 in rats strongly supports the previous reports on use of gut-colonizing B. subtilis spores as a new platform for the mucosal delivery of vaccine antigens [ 32 ] as well as survivability of Bacillus clausii spores in the human gastrointestinal (GI) tract, and thereafter germination, outgrowth, and multiplication as vegetative forms following oral administration as spore-based probiotic formulation [ 33 ]. In the present study, the feeding of B. coagulans B37 revealed that the fecal Bacillus count remained stable for 10 days after withdrawal of feeding of B. coagulans B37.…”

The immunological characteristics and probiotic function of recombinant Bacillus subtilis spore expressing Clonorchis sinensis cysteine protease

“…They have previously served as effective adjuvants as well [15, 16, 34]. Bacillus subtilis spores (approximately 1.2 μm in length) are well uptaken by M cells, transported into Peyer’s patches, processed by antigen-presenting cells, presented to B cells or T cells, and are transported to other gut-associated lymphoid tissues (GALTs) and systemic lymphoid tissues [14, 35]. During this process, a series of antigen-specific immune responses are induced and abundant immune globulins are secreted by plasma cells [36].…”

Immunogenicity and In Vitro and In Vivo Protective Effects of Antibodies Targeting a Recombinant Form of the Streptococcus mutans P1 Surface Protein

“…Recently, we have shown that another P1-derived fragment generated in Bacillus subtilis, encompassing amino acids 39 to 512 and named P1 , is immunogenic in mice and induces antibodies that interfere with S. mutans adhesive properties in vitro (25). We furthermore demonstrated that a mucosal delivery system based on genetically modified B. subtilis spores that express P1 39 -512 in vivo induced specific antibodies in serum and saliva that interfered with S. mutans adhesion to abiotic surfaces without preventing bacterial aggregation (26). These findings highlight the need for an understanding of the immunological, structural, and functional characteristics of P1 39 -512 as an alternative to the full-length protein as a target antigen to generate protective immunity against dental caries.…”