# Investigating Syphilis Pathogenesis Through Genetic Engineering of Treponema pallidum

> **NIH NIH R56** · UNIVERSITY OF WASHINGTON · 2024 · $771,690

## Abstract

ABSTRACT
 In several high-income nations, including the United States, infectious syphilis has been resurgent
for over two decades now, while syphilis is still endemic in low- and middle-income countries. Syphilis is
therefore still a public global health concern, particularly in consideration that it can lead to neurological
sequelae such as dementia and stroke-like syndrome, as well as cardiovascular manifestations potentially
leading to death. Furthermore, every year, about half a million pregnancies are adversely affected by
congenital transmission of the pathogen. The partial success of recent syphilis control campaigns promoted
by the CDC and WHO clearly highlights the necessity of devising novel ways to control this serious infection.
Improving our understanding of syphilis pathogenesis and the virulence factors that allow the syphilis agent,
Treponema pallidum subsp. pallidum (T. pallidum) to establish infection and persist in the host despite a
robust immune response might be the key to new control strategies.
 However, two significant obstacles have hindered our ability to unravel the complexities of syphilis
pathogenesis since the first T. pallidum strain was isolated in 1912. These barriers were the inability to
propagate T. pallidum in vitro and, consequently, to genetically manipulate this difficult pathogen. In 2018,
the “in vitro propagation” barrier was overcome by the discovery that T. pallidum could be propagated in a
cell culture-based system. In 2021, for the first time, we overcame the “genetic manipulation” barrier and
derived a T. pallidum knock-out (KO) isolate, in which a functional kanamycin resistance (kanR) cassette
was used to successfully replace the non-essential T. pallidum tprA (tp0009) locus through homologous
recombination after transforming the syphilis agent with a suicide vector.
 This newly found ability to genetically alter T. pallidum will allow us to pinpoint more clearly the role
of putative virulence factors of this pathogen during infection. Here, by using an array of newly generated T.
pallidum KO strains lacking critical components of the pathogen`s antigenic variation system, we propose to
study the contribution of antigenic variation to T. pallidum ability for immune evasion and persistence during
infection.
 If successful, these studies will provide our research community with an array of T. pallidum mutants
to be used in comparative studies. Furthermore, our results will help settle ongoing controversies
surrounding the function of the T. pallidum TprK virulence factors that originated over the last two decades
due to working with a difficult pathogen that, until now, could not be genetically engineered.

## Key facts

- **NIH application ID:** 11131626
- **Project number:** 1R56AI175016-01A1
- **Recipient organization:** UNIVERSITY OF WASHINGTON
- **Principal Investigator:** Lorenzo Giacani
- **Activity code:** R56 (R01, R21, SBIR, etc.)
- **Funding institute:** NIH
- **Fiscal year:** 2024
- **Award amount:** $771,690
- **Award type:** 1
- **Project period:** 2024-08-05 → 2026-07-31

## Primary source

NIH RePORTER: https://reporter.nih.gov/project-details/11131626

## Citation

> US National Institutes of Health, RePORTER application 11131626, Investigating Syphilis Pathogenesis Through Genetic Engineering of Treponema pallidum (1R56AI175016-01A1). Retrieved via AI Analytics 2026-06-12 from https://api.ai-analytics.org/grant/nih/11131626. Licensed CC0.

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