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Infection and Immunity, October 2008, p. 4422-4430, Vol. 76, No. 10
0019-9567/08/$08.00+0     doi:10.1128/IAI.00487-08
Copyright © 2008, American Society for Microbiology. All Rights Reserved.

Use of mchI Encoding Immunity to the Antimicrobial Peptide Microcin H47 as a Plasmid Selection Marker in Attenuated Bacterial Live Vectors

Chee-Mun Fang,^1,2* Jin Yuan Wang,^1,2 Magaly Chinchilla,^1,2 Myron M. Levine,^1,2,3 William C. Blackwelder,^1,2 and James E. Galen^1,2

Center for Vaccine Development,¹ Division of Geographic Medicine, Department of Medicine,² Division of Infectious Diseases and Tropical Pediatrics, Department of Pediatrics, University of Maryland School of Medicine, Baltimore, Maryland 21201³

Received 19 April 2008/ Returned for modification 22 May 2008/ Accepted 22 July 2008

Live attenuated bacterial strains expressing heterologous antigens represent an attractive vaccine development strategy. However, the use of drug resistance genes for the selection of expression plasmids introduced into live vectors poses theoretical health risks. Therefore, we developed a novel approach for plasmid selection based on immunity to the antimicrobial peptide microcin H47 (MccH47). Two expression plasmids encoding the reporter green fluorescent protein (GFPuv) were constructed; selection markers comprised either mchI, conferring immunity to MccH47 (pGEN222I), or bla (encoding β-lactamase), conferring conventional resistance to ampicillin (pGEN222). GFPuv-specific serum immunoglobulin G (IgG) antibody responses were analyzed in mice immunized intranasally either with Salmonella enterica serovar Typhi CVD 908-htrA or Shigella flexneri 2a CVD 1208S live vector and were boosted parenterally with purified GFPuv. Similar IgG antibody responses were observed for both pGEN222 and pGEN222I when either CVD 1208S or CVD 908-htrA(pGEN222I) was used as the carrier. Interestingly, CVD 908-htrA(pGEN222I) elicited a significantly higher IgG response than CVD 908-htrA(pGEN222). We also compared the priming potential of homologous priming either with CVD 908-htrA(pGEN222I) or CVD 1208S(pGEN222I) to heterologous priming first with CVD 908-htrA(pGEN222I) and then with CVD 1208S(pGEN222I) and vice versa. Immunization with two unrelated live vectors significantly enhanced the IgG responses compared to responses engendered by homologous CVD 908-htrA(pGEN222I) but not to those of CVD 1208S(pGEN222I). MccH47 offers an alternate system for plasmid selection in bacterial live vectors that greatly improves their clinical acceptability. Furthermore, the success of the heterologous priming strategy supports the feasibility of the future development of multivalent live vector-based immunization strategies against multiple human pathogens.

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* Corresponding author. Mailing address: Center for Vaccine Development, University of Maryland School of Medicine, 685 W. Baltimore St., HSF Bldg I, Rm 480, Baltimore, MD 21201. Phone: (410) 706-5328. Fax: (410) 706-6205. E-mail: cfang{at}medicine.umaryland.edu

Published ahead of print on 28 July 2008.

Editor: A. J. Bäumler

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Infection and Immunity, October 2008, p. 4422-4430, Vol. 76, No. 10
0019-9567/08/$08.00+0     doi:10.1128/IAI.00487-08
Copyright © 2008, American Society for Microbiology. All Rights Reserved.