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Infection and Immunity, December 2009, p. 5509-5518, Vol. 77, No. 12
0019-9567/09/$08.00+0     doi:10.1128/IAI.00899-09
Copyright © 2009, American Society for Microbiology. All Rights Reserved.

A Heterologous Helper T-Cell Epitope Enhances the Immunogenicity of a Multiple-Antigenic-Peptide Vaccine Targeting the Cryptic Loop-Neutralizing Determinant of Bacillus anthracis Protective Antigen{triangledown}

Jon Oscherwitz,1,2* Fen Yu,1 and Kemp B. Cease1,2

Division of Hematology-Oncology, Department of Internal Medicine, University of Michigan Medical School, Ann Arbor, Michigan 48105,1 Veterans Affairs Medical Center, 2215 Fuller Road, Ann Arbor, Michigan 481052

Received 7 August 2009/ Returned for modification 8 September 2009/ Accepted 28 September 2009

We previously showed that a multiple antigenic peptide (MAP) displaying amino acids (aa) 305 to 319 from the 2β2-2β3 loop of protective antigen (PA) can elicit high-titered antibody that neutralizes lethal toxin (LeTx) in vitro and that this loop-neutralizing determinant (LND) specificity is absent in PA-immune rabbits. Some immune rabbits were, however, nonresponders to the MAP. We hypothesized that the immunogen elicited suboptimal major histocompatibility complex (MHC) class II-restricted T-cell help and that introduction of a functional helper T-cell epitope would increase MHC-restricted responsiveness and the magnitude and affinity of the antibody responses. In the current study, we characterized the T- and B-cell responses to LND peptides in mice, then designed second-generation MAP immunogens for eliciting LND-specific immunity, and tested them in rabbits. The 305-319 sequence was devoid of helper T-cell epitopes in three strains of mice; however, a T-B peptide comprising aa 305 to 319, colinearly synthesized with the P30 helper epitope of tetanus toxin, elicited robust LeTx-neutralizing immunity in mice. T-B MAPs displaying B-cell epitopes 304 to 319 (MAP304) or 305 to 319 (MAP305) elicited high-titer, durable antibody responses in rabbits which exhibited potent neutralization of LeTx in vitro. All MAP304-immune rabbits demonstrated neutralization titers exceeding that of hyperimmune sera of rabbits immunized with PA in Freund's adjuvant, with peak neutralization titers 23-, 6-, and 3-fold higher than that of the PA antiserum. Overall, immunization with MAPs containing the P30 epitope elicited higher antibody and toxin neutralization titers and peptide-specific affinity than immunization with an LND MAP lacking a helper epitope. P30-containing MAP304 represents a promising LND-specific vaccine for anthrax.

* Corresponding author. Mailing address: Ann Arbor Veterans Affairs Medical Center, Research Service 11R, 2215 Fuller Rd., Ann Arbor, MI 48105. Phone: (734) 845-5195. Fax: (734) 845-3246. E-mail: joscher{at}umich.edu

{triangledown} Published ahead of print on 5 October 2009.

Editor: R. P. Morrison

Infection and Immunity, December 2009, p. 5509-5518, Vol. 77, No. 12
0019-9567/09/$08.00+0     doi:10.1128/IAI.00899-09
Copyright © 2009, American Society for Microbiology. All Rights Reserved.





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