Abstract
S-layers are bacterial structures present on the surface of several Gram-positive and Gram-negative bacteria that play a role in bacterial protection. In Lactobacillus acidophilus (L. acidophilus ATCC 4356), the S-layer is mainly composed of the protein SlpA. A tandem of two copies of the protein domain SLP-A (pfam: 03217) was identified at the C-terminal of SlpA, being this double SLP-A protein domain (in short dSLP-A) necessary and sufficient for the association of the protein to the L. acidophilus cell wall. A variety of proteins fused to the dSLP-A domain were able to spontaneously associate with high affinity to the cell wall of L. acidophilus and Bacillus subtilis var. natto, in a process that we termed decoration. Binding of dSLP-A-containing-proteins to L. acidophilus was stable at conditions that mimic the gastrointestinal transit in terms of pH, proteases, and bile salts. To evaluate if protein decoration of L. acidophilus can be adapted to generate an oral vaccine platform, a chimeric antigen derived from the bacterial pathogen Shiga-toxin-producing Escherichia coli (STEC) was constructed by fusing the sequences encoding the polypeptides EspA36–192, Intimin653–953, Tir240–378, and H7 flagellin352–374 (EITH7) to the dSLP-A domain (EITH7-dSLP-A). Recombinantly expressed EITH7-dSLP-A protein was affinity purified and combined with L. acidophilus cultures to allow the association of the chimeric antigen to the bacterial surface. EITH7-decorated L. acidophilus was orally administered to BALB/c mice and the induction of anti-EITH7 specific antibodies in sera and feces determined by ELISA. Mice presenting significantly higher anti-EITH7 antibodies titers were able to control more efficiently an experimental STEC infection than mice that received the non-decorated L. acidophilus carrier, indicating that antigen-decorated L. acidophilus can be adapted as a mucosal immunization delivery platform to elicit a protective immune response for vaccine purposes.
Highlights
Vaccines have been the most successful medical therapy in Public Health preventing mortality and morbidity caused by several infectious diseases and saving millions of lives worldwide (Orenstein and Ahmed, 2017)
Proteins Fused in Frame With the denominated SLP-A (dSLP-A) Protein Domain Can Associate With the Surface of L. acidophilus
The sequence of the FLAG epitope was inserted between the heterologous protein of interest and the dSLP-A domain as a reporter tag
Summary
Vaccines have been the most successful medical therapy in Public Health preventing mortality and morbidity caused by several infectious diseases and saving millions of lives worldwide (Orenstein and Ahmed, 2017). It has been described that some oral vaccines performed poorly in developing countries compared with industrialized ones and this has been attributed to a syndrome named chronic environmental enteropathy (or tropical enteropathy) This syndrome is characterized by impairment in intestinal absorption that might lead to a reduction of bioavailability of zinc or vitamin A affecting the efficiency of adjuvant function and, impairing the induction of an effective immune response (Lycke, 2012). The selection of attenuated microorganisms has been historically a serendipitous process based on the sequential replication of a pathogen either in laboratory in vitro conditions or within a non-natural host in order to isolate non-virulent strains (Plotkin, 2014; Minor, 2015) By this method, a few protective vaccines have been developed that have been widely used such as Oral Polio Virus (Sabin), BCG for tuberculosis, and the Yellow Fever vaccine YF17D (Galler et al, 1997; Plotkin, 2014). In the case of vaccines based on genetically modified organisms (GMOs), they are subjected to strict regulations to allow its administration to animals or humans increasing production costs considerably (Seib et al, 2017)
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