title: Delivery of heterologous protein antigens via hemolysin or autotransporter systems by an attenuated ler mutant of rabbit enteropathogenic Escherichia coli.
abstract: In this report, we describe the use of an attenuated regulatory mutant of a rabbit enteropathogenic Escherichia coli (rEPEC) as a live vaccine vector to deliver heterologous protein antigens using two dedicated transport systems, a Salmonella autotransporter and the E. coli hemolysin apparatus. We previously reported that an isogeneic ler (LEE encoded regulator) mutant of rEPEC O103:H2 is attenuated and immunogenic in rabbits. We first evaluated the Salmonella autotransporter MisL containing the immunodominant B-cell epitope of the circumsporozoite protein from Plasmodium falciparum, (NANP)8, fused to the C-terminal translocator domain under the control of the constitutive Tac17 promoter. The rEPEC ler mutant was able to express and to translocate the (NANP)8 passenger peptide to the bacterial surface. We next investigated the delivery of Shiga toxin B subunit (Stx1B) from human enterohemorrhagic E. coli by the rEPEC ler mutant via the MisL autotransporter or the E. coli hemolysin secretion apparatus. The autotransporter and hemolysin plasmids expressed similar levels of Stx1B (30-40 ng/ml/OD600). Only 6% of Stx1B was found in the autotransporter supernatants; the rest was cell-associated, with a small fraction of the Stx1B surface-exposed as determined by immunofluorescence. In contrast, 88% of Stx1B was secreted into culture supernatants by the hemolysin secretion system. In an in vivo study, no significant protection was observed in rabbits inoculated with the ler mutant harboring the Stx1B-autotransporter plasmid following experimental challenge with RDEC-H19A, the prototype rEPEC containing an Stx-converting phage. In contrast, rabbits inoculated with the rEPEC ler mutant containing the Stx1B-hemolysin fusion were partially protected from RDEC-H19A infection as demonstrated by decreased weight loss (p<0.008) when compared to rabbits inoculated with the parent ler mutant. Our results suggest that attenuated rEPEC are capable of serving as vaccine vectors to express heterologous protein antigens from different cellular locations and deliver these antigens to the intestinal mucosa. With this system, secreted proteins may be more effective than cell-associated antigens in generating protection.
authors.affiliation: Center for Vaccine Development, University of Maryland School of Medicine, 685 West Baltimore Street, Baltimore, MD 21201, USA.
authors.forename: Chengru
authors.initials: C
authors.lastname: Zhu
authors.forename: Fernando
authors.initials: F
authors.lastname: Ruiz-Perez
authors.forename: Zhuolu
authors.initials: Z
authors.lastname: Yang
authors.forename: Ying
authors.initials: Y
authors.lastname: Mao
authors.forename: Veronica L
authors.initials: VL
authors.lastname: Hackethal
authors.forename: Karla M
authors.initials: KM
authors.lastname: Greco
authors.forename: Wendy
authors.initials: W
authors.lastname: Choy
authors.forename: Katherine
authors.initials: K
authors.lastname: Davis
authors.forename: Joan R
authors.initials: JR
authors.lastname: Butterton
authors.forename: Edgar C
authors.initials: EC
authors.lastname: Boedeker
mesh_terms: D000818:Animals; D001426:Bacterial Proteins / Q000235:genetics / Q000276:immunology*; D001428:Bacterial Vaccines / Q000008:administration & dosage / Q000235:genetics / Q000276:immunology*; D002462:Cell Membrane / Q000737:chemistry; D004591:Electrophoresis, Polyacrylamide Gel; D018985:Epitopes, B-Lymphocyte / Q000235:genetics / Q000276:immunology / Q000378:metabolism; D004926:Escherichia coli / Q000737:chemistry / Q000235:genetics / Q000276:immunology; D004927:Escherichia coli Infections / Q000473:pathology / Q000517:prevention & control; D029968:Escherichia coli Proteins / Q000235:genetics* / Q000276:immunology / Q000378:metabolism; D022361:Escherichia coli Vaccines / Q000008:administration & dosage / Q000235:genetics / Q000276:immunology*; D005243:Feces / Q000382:microbiology; D005822:Genetic Vectors; D006460:Hemolysin Proteins; D018928:Immunity, Mucosal; D026901:Membrane Transport Proteins / Q000235:genetics / Q000276:immunology*; D010957:Plasmids; D010963:Plasmodium falciparum / Q000276:immunology; D021381:Protein Transport; D015800:Protozoan Proteins / Q000235:genetics / Q000276:immunology*; D011817:Rabbits; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000276:immunology / Q000378:metabolism; D022622:Shiga Toxin 1 / Q000235:genetics / Q000276:immunology* / Q000378:metabolism; D015534:Trans-Activators / Q000235:genetics*; D014613:Vaccines, Attenuated / Q000008:administration & dosage / Q000235:genetics / Q000276:immunology; D014614:Vaccines, Synthetic / Q000008:administration & dosage / Q000276:immunology
chemical_list: D001426:Bacterial Proteins; D001428:Bacterial Vaccines; D018985:Epitopes, B-Lymphocyte; D029968:Escherichia coli Proteins; D022361:Escherichia coli Vaccines; D006460:Hemolysin Proteins; C036507:Hlya protein, E coli; C465556:Ler protein, E coli; D026901:Membrane Transport Proteins; C460865:MisL protein, Salmonella enterica; D015800:Protozoan Proteins; D011993:Recombinant Fusion Proteins; D022622:Shiga Toxin 1; D015534:Trans-Activators; D014613:Vaccines, Attenuated; D014614:Vaccines, Synthetic; C041595:circumsporozoite protein, Protozoan