Abstract
The use of whole cell killed (WCK) oral cholera vaccines is an important strategy for cholera prevention in endemic areas. To overcome current vaccine limitations, we engineered strains of V. cholerae to be non-toxigenic and to express the protective protein colonization factor, toxin-coregulated pilus (TCP), under scale-up conditions potentially amenable to vaccine production. Two V. cholerae clinical strains were selected and their cholera toxin genes deleted. The tcp operon was placed under control of a rhamnose-inducible promoter. Production and stability of TCP were assessed under various conditions. The strains lack detectable cholera toxin production. The addition of 0.1% rhamnose to the growth medium induced robust production of TCP and TcpA antigen. The strains produced intact TCP in larger growth volumes (1 L), and pili appeared stable during heat-killing or acid treatment of the bacterial cultures. To date, no WCK cholera vaccines have included TCP. We have constructed putative strains of V. cholerae for use in a vaccine that produce high levels of stable TCP antigen, which has not previously been achieved.
Highlights
Vibrio cholerae is a globally important pathogen, causing an estimated 2.8 million cases of cholera and approximately 91,000 deaths in endemic countries, with an additional 87,000 cases and 2,500 deaths in non-endemic countries [1]
The toxin-coregulated pilus (TCP) is a filamentous surface component of V. cholerae that is produced in significant quantities only under certain environmental conditions
While TCP can be produced under specific laboratory cell growth conditions [19, 26, 27], the way in which the V. cholerae strains contained in the oral, whole cell vaccine Shanchol are grown does not result in production of TCP, as evidenced by a lack of the TCP major pilin protein TcpA on a western immunoblot (Fig 1A, right side)
Summary
Vibrio cholerae is a globally important pathogen, causing an estimated 2.8 million cases of cholera and approximately 91,000 deaths in endemic countries, with an additional 87,000 cases and 2,500 deaths in non-endemic countries [1]. Effective control measures rely on prevention and preparedness. Vaccines are a necessary component in preventing cholera. Many cholera vaccine iterations have been explored throughout the last 125 years. In the 1960s, a parenteral cellular killed cholera vaccine proved to be effective against the disease in adults, but resulted in a short protection period and caused reactogenic effects including fever and swelling [2]. Another challenge posed by a parenteral vaccine is the requirement of trained staff to use injection devices for administration [3].
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