In conclusion, due to its low diarrhoea attack risk, TW11681 is probably not suitable for testing the efficacy of new vaccines in human challenge studies at doses 1 106 to 1 1 108

In conclusion, due to its low diarrhoea attack risk, TW11681 is probably not suitable for testing the efficacy of new vaccines in human challenge studies at doses 1 106 to 1 1 108. = 0.016)), while the CD4+ T cell responses specific for Colonization Factor Antigen I (CFA/I) major fimbrial subunit (CfaB) peaked after 28 days (3.6-fold (p = 0.063)). The serum CfaB-specific anti-IgA and anti-IgG/IgM levels were significantly increased and peaked 3 months after infection. Both remained elevated for the duration of the 12-month follow-up. The corresponding anti-YghJ serological response was strongest after 10 days, although a significant increase was seen only for IgA levels (3.2-fold (p = 0.008)). In conclusion, due to its low diarrhoea attack risk, TW11681 is probably not suitable for testing the efficacy of new vaccines in Zofenopril calcium human challenge studies at doses 1 106 to 1 1 108. However, the strain may still CDC2 be useful in CHIMs for studying ETEC host-pathogen interactions. (ETEC) is a major cause of diarrhoeal disease in low- and middle-income countries (LMICs) [1]. Developing an effective vaccine against ETEC has been Zofenopril calcium a long-standing goal, and several candidates are in the development pipeline [1]. ETEC are defined as that produce one or both of the two protein enterotoxins called heat-stable toxin (ST), which is small and non-immunogenic, and heat-labile toxin (LT), which is large and immunogenic. Infections with ST-producing ETEC strains (with or without LT) are among Zofenopril calcium the most important bacterial causes of moderate-to-severe diarrhoea in children under 5 years of age in LMICs. ST-ETEC is also associated with an increased risk of death [2]. Developing an effective ST-based vaccine, therefore, represents a promising strategy to confer broad protection against ETEC-induced diarrhoea. Two variants of ST exist, called porcine ST (STp) and human ST (STh). STh-producing ETEC are more pathogenic for young children in LMICs than STp-producing ETEC [3,4]. To estimate the efficacy of ST-based ETEC vaccine candidates in a controlled human infection model (CHIM) it is important that the challenge strain produces ST, but not LT, since the secretion of LT could mask an otherwise protective Zofenopril calcium immune response to ST. It is also important that the strain reliably induces diarrhoea in most of the challenged individuals in order to minimise the number of volunteers needed to test the vaccines. In the close to five decades that have passed since the development of the first CHIM for ETEC, only one ST-only ETEC strain has been tested [5,6,7]. These trials were based on ETEC strain 214-4, which was isolated in Zofenopril calcium 1975 from a 29 year-old traveller in Mexico who developed watery diarrhoea [8]. The strain induced diarrhoea in adult volunteers with attack risks of 60C80% when inoculum doses of 1 1 108 and 1 1010 colony-forming units (CFU) were used [5,6]. It could, therefore, be suitable for use in a vaccine challenge model to test ST-based vaccines. However, since 214-4 has not been well characterized, and also is an STp-producer (Myron M. Levine, personal communication), it may not be as relevant for testing ST-based vaccines that target young children in LMICs, in whom STh-producing ETEC are epidemiologically much more important [3,4,9]. Here, we evaluate whether TW11681, which produces STh and represents an ETEC lineage commonly found associated with childhood diarrhoea, would be suitable for use in a vaccine challenge model. We experimentally infected 9 volunteers with TW11681 and followed them with daily clinical assessments as well as regular serum sample collection to evaluate their serum antibody responses to the ETEC Colonization Factor Antigen I (CFA/I) and to YghJ. YghJ is an mucinase and has in recent years been described as an important contributor to ETEC pathogenesis due to its ability to degrade the protective mucin layer covering the intestinal wall, allowing bacteria to access.