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Vaccine. 2019 Mar 22;37(13):1807-1818. doi: 10.1016/j.vaccine.2019.02.022. Epub 2019 Feb 20.

Non-pathogenic Borrelia burgdorferi expressing Treponema pallidum TprK and Tp0435 antigens as a novel approach to evaluate syphilis vaccine candidates.

Author information

1
Department of Microbiology, Biochemistry and Molecular Genetics, Rutgers-New Jersey Medical School, Newark, NJ 07103, United States.
2
Department of Medicine, Division of Allergy and Infectious Diseases, University of Washington, Harborview Medical Center, Seattle, WA 98104, United States.
3
Department of Medicine, Division of Allergy and Infectious Diseases, University of Washington, Harborview Medical Center, Seattle, WA 98104, United States; Department of Dermatology, Affiliated Wuxi No.2 People's Hospital of Nanjing Medical University, 214002 Wuxi, China.
4
School of Public Health, Universidad Peruana Cayetano Heredia, Lima 30, Peru.
5
Department of Medicine, Division of Allergy and Infectious Diseases, University of Washington, Harborview Medical Center, Seattle, WA 98104, United States; Department of Global Health, University of Washington, Seattle, WA 98104, United States. Electronic address: giacal@u.washington.edu.

Abstract

BACKGROUND:

Syphilis is resurgent in many developed countries and still prevalent in developing nations. Current and future control campaigns would benefit from the development of a vaccine, but although promising vaccine candidates were identified among the putative surface-exposed integral outer membrane proteins of the syphilis spirochete, immunization experiments in the rabbit model using recombinant antigens have failed to fully protect animals upon infectious challenge. We speculated that such recombinant immunogens, purified under denaturing conditions from Escherichia coli prior to immunization might not necessarily harbor their original structure, and hypothesized that enhanced protection would result from performing similar immunization/challenge experiments with native antigens.

METHODS:

To test our hypothesis, we engineered non-infectious Borrelia burgdorferi strains to express the tp0897 (tprK) and tp0435 genes of Treponema pallidum subsp. pallidum and immunized two groups of rabbits by injecting recombinant strains intramuscularly with no adjuvant. TprK is a putative integral outer membrane protein of the syphilis agent, while tp0435 encodes the highly immunogenic T. pallidum 17-kDa lipoprotein, a periplasmic antigen that was also shown on the pathogen surface. Following development of a specific host immune response to these antigens as the result of immunization, animals were challenged by intradermal inoculation of T. pallidum. Cutaneous lesion development was monitored and treponemal burden within lesions were assessed by dark-field microscopy and RT-qPCR, in comparison to control rabbits.

RESULTS:

Partial protection was observed in rabbits immunized with B. burgdorferi expressing TprK while immunity to Tp0435 was not protective. Analysis of the humoral response to TprK antigen suggested reactivity to conformational epitopes.

CONCLUSIONS:

Immunization with native antigens might not be sufficient to obtain complete protection to infection. Nonetheless we showed that non-infectious B. burgdorferi can be an effective carrier to deliver and elicit a specific host response to T. pallidum antigens to assess the efficacy of syphilis vaccine candidates.

KEYWORDS:

Borrelia burgdorferi; Syphilis; Tp0435; TprK; Treponema pallidum

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