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Infection and Immunity, April 2002, p. 1739-1749, Vol. 70, No. 4
0019-9567/02/$04.00+0     DOI: 10.1128/IAI.70.4.1739-1749.2002
Copyright © 2002, American Society for Microbiology. All Rights Reserved.

Immune Responses to Recombinant Pneumococcal PspA Antigen Delivered by Live Attenuated Salmonella enterica Serovar Typhimurium Vaccine

Ho Young Kang,,{dagger} Jay Srinivasan, and Roy Curtiss, III*

Department of Biology, Washington University, St. Louis, Missouri 63130

Received 10 October 2001/ Returned for modification 26 November 2001/ Accepted 28 December 2001

Attenuated Salmonella enterica serovar Typhimurium expressing recombinant antigens from other pathogens elicits primarily a Th1-type dominant immune response to both recombinant and Salmonella antigens. The immunogenicity and appropriate subcellular location of the recombinant antigen in the Salmonella vaccine strain may contribute to augmenting immune responses by facilitating adequate exposure of recombinant antigen to antigen-presenting cells for processing. To allow for secretion from gram-negative bacteria and overexpression of antigen, a DNA fragment encoding a highly antigenic {alpha}-helical region of PspA (pneumococcal surface protein A) was subcloned downstream from the ß-lactamase signal sequence in the multicopy Asd+ pYA3493 vector to create pYA3494. pYA3493 was derived from a class of Asd+ vectors with reduced expression of Asd to minimize selective disadvantage and enhance immunization of expressed recombinant antigens. The S. enterica serovar Typhimurium vaccine strain was constructed by the introduction of deletion mutations {Delta}crp-28 and {Delta}asdA16. Approximately 50% of the recombinant PspA (rPspA) expressed in a Salmonella strain harboring pYA3494 was detected in the combined supernatant and periplasmic fractions of broth-grown recombinant Salmonella. After a single oral immunization in BALB/c mice with 109 CFU of the recombinant Salmonella vaccine strain carrying pYA3494, immunoglobulin G (IgG) antibody responses were stimulated to both the heterologous antigen rPspA and Salmonella lipopolysaccharide (LPS) and outer membrane proteins (OMPs). About half, and even more at later times after immunization, of the antibodies induced to rPspA were IgG1 (indicating a Th2-type response), whereas 60 to 70% of the antibodies to LPS and 80 to 90% of those to OMPs were IgG2a (indicating a Th1-type response). A sublethal infection with Streptococcus pneumoniae WU2 boosted PspA antibody levels and maintained IgG2a/IgG1 ratios similar to those seen before the challenge. Oral immunization with Salmonella-PspA vaccine protected 60% of immunized mice from death after intraperitoneal challenge with 50 times the 50% lethal dose of virulent S. pneumoniae WU2.


* Corresponding author. Mailing address: Department of Biology, Washington University, Campus Box 1137, One Brookings Dr., St. Louis, MO 63130-4899. Phone: (314) 935-6819. Fax: (314) 935-7246. E-mail: rcurtiss{at}biology.wustl.edu.

Editor: E. I. Tuomanen

{dagger} Present address: Department of Microbiology, College of Natural Sciences, Pusan National University, Pusan 609-735, Korea.


Infection and Immunity, April 2002, p. 1739-1749, Vol. 70, No. 4
0019-9567/02/$04.00+0     DOI: 10.1128/IAI.70.4.1739-1749.2002
Copyright © 2002, American Society for Microbiology. All Rights Reserved.




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Copyright © 2002 by the American Society for Microbiology. All rights reserved.