Transcriptional responses to oral live attenuated typhoid vaccines

Enteric fever is a major public health problem and causes numerous deaths annually. Ty21a is the only efficacious oral, live attenuated typhoid vaccine currently licensed for use, however, its mechanism of protection is poorly understood. To address this knowledge gap, we interrogated transcriptional profiles following vaccination with Ty21a and an immunogenic experimental oral live attenuated vaccine, M01ZH09, and related these findings to immunogenicity, and incubation period and disease severity following challenge with Salmonella Typhi four weeks after vaccination. Despite originating from the same parent strain (Ty2), we detected marked differences in the gene expression between both vaccines. Analysis of the transcriptome 7 days after M01ZH09 vaccination implicated transcriptional patterns associated with the cell cycle correlated significantly with humoral immunogenicity 28 days after vaccination. In contrast, significantly induced T and NK cell responses were associated with Ty21a vaccination, and integrative analysis indicated signatures reflecting amino acid metabolism with delayed onset of disease. Stimulation of PBMCs collected from participants prior to and following vaccination with the two vaccine strains in vitro confirmed the superior capacity of Ty21a to induce NK cells, validating gene expression results. These data provide insight into the effects of oral live attenuated typhoid vaccines on the human molecular immune response and underline the involvement of T cell response signatures with protection following challenge. A Single Centre, Randomised, Doubleblind, Placebo Controlled Study to Evaluate M01ZH09 in a Healthy Adult Challenge Model, Using Ty21a Vaccine as a Positive Control. In total, 161 samples were analysed, including paired pre-vaccination control samples. Several post-vaccination time points were included, for details please refer to Figure 1A&B, Supplementary Figure 1A in the manuscript Differential induction of cell cycle and NK cell responses by two live-attenuated oral vaccines against typhoid fever.