The way forward for ETEC controlled human infection models (CHIMs).

In the absence of good animal models, Controlled Human Infection Models (CHIMs) are useful to assess efficacy of new vaccine candidates against Enterotoxic Escherichia coli (ETEC), as well as other preventive or therapeutic interventions. At the 2018 Vaccines Against Shigella and ETEC (VASE) conference, a workshop was held to further review and discuss new challenge model developments and key issues related to further model standardization. During the workshop, invited speakers briefly summarized for attendees recent developments and main agenda issues before workshop participants were divided into four groups for more focused discussions. The main issues discussed were: (1) whether there is a need for more ETEC strains to test a diversity of vaccine candidates, and if so, what criteria/qualities are desirable in strain selection; (2) how ETEC CHIMs could be more standardized to better support ETEC vaccine development; (3) how volunteer selection criteria and screening should be performed, and; (4) how an expanded sample collection schema and collaborative analysis plan may facilitate a more in-depth assessment of the role of antigen-specific humoral and cellular immune responses in ETEC infection, and provide better insights into ETEC pathogenesis and correlates of protection. The workshop concluded that additional challenge strains may need to be developed to better support new vaccines and therapeutics that are advancing in the development pipeline. In this regard, the need for a well characterized ST-only expressing ETEC strain was highlighted as a priority given that promising new heat stable toxoid based vaccine candidates are on the horizon. In addition, further standardization of the ETEC CHIMs was strongly encouraged, noting that it may not be realistic to standardize across all strains. Also, intensified volunteer screening may result in higher attack rates, although more stringent eligibility criteria may contribute to a more limited application of the model and diminish its representativeness. Finally, a sampling schedule and priority list for minimum set of samples was also proposed. Future workshops could be held to further refine standards for ETEC CHIMS and to facilitate more collaborative work on stored sample sets from previous and future ETEC CHIMs to maximize the contribution of these trials to our understanding of ETEC pathogenesis and our development of better prevention and control measures for this important pathogen.

Development of a fast-dissolving tablet formulation of a live attenuated enterotoxigenic E. coli vaccine candidate.

Vaccination is considered the most cost-effective approach to preventing infectious diseases, yet better formulations and delivery methods for efficient distribution and administration of vaccines are needed, especially for low-resource settings. A fast-dissolving tablet (FDT) that could be packaged in a compact stackable blister sheet is a potentially attractive option for formulating oral vaccines, since it would minimally impact the cold chain and could potentially be administered directly to patients without reconstitution. This study focused on using one component of a live attenuated trivalent vaccine under development to produce a FDT for the prevention of diarrhea induced by enterotoxigenic Escherichia coli (ETEC). Ten formulations were prepared and freeze dried to produce FDTs. Three freezing conditions were explored, along with different drying and package sealing methods. Physical properties examined included structural integrity, dissolution time, moisture content, and glass transition temperature. Bacterial viability was tested by assaying for colony-forming units. The formulation compositions and freeze-drying parameters were adjusted in an iterative process to arrive at a promising formulation for the ETEC vaccine tablet. This formulation included sucrose and trehalose as cryoprotectants; phosphate and glutamate salts as buffers and stabilizers; and Natrosol(®), polyvinylpyrrolidone, and mannitol as binders. The process loss in viability during freeze drying was less than 0.3 log 10 (50% recovery) for the optimized vaccine tablet formulation. The final tablets were robust, disintegrated in less than 10s, and preserved the bacteria at 2-8°C for at least 12 months with less than 0.4 log 10 loss (40% recovery) in viability during storage. This study indicates that the FDT produced by freeze drying directly in a blister sheet could be a practical option for formulating ETEC vaccines for oral immunization and help to facilitate delivery of lifesaving vaccines, particularly in low-resource settings.

Comparison of the antibodies in lymphocyte supernatant and antibody-secreting cell assays for measuring intestinal mucosal immune response to a novel oral typhoid vaccine (M01ZH09).

Antibody-secreting cell (ASC) and antibodies in lymphocyte supernatant (ALS) assays are used to assess intestinal mucosal responses to enteric infections and vaccines. The ALS assay, performed on cell supernatants, may represent a convenient alternative to the more established ASC assay. The two methods, measuring immunoglobulin A to Salmonella enterica serovar Typhi lipopolysaccharide, were compared in volunteers vaccinated with a live-attenuated typhoid vaccine M01ZH09. The specificity of the ALS assay compared to the ASC assay was excellent (100%), as was sensitivity (82%). The ALS assay was less sensitive than the ASC assay at