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Background: Salmonella enterica serovar Typhi (S. Typhi) is a highly invasive bacterium that infects the human intestinal mucosa and causes ~ 11.9-20.6 million infections and ~ 130,000-223,000 deaths annually worldwide. Oral typhoid vaccine Ty21a confers a moderate level of long-lived protection (5-7 years) in the field. New and improved vaccines against enteric pathogens are needed but their development is hindered by a lack of the immunological correlates of protection especially at the site of infection. Tissue resident memory T (TRM) cells provide immediate adaptive effector immune responsiveness at the infection site. However, the mechanism(s) by which S. Typhi induces TRM in the intestinal mucosa are unknown. Here, we focus on the induction of S. Typhi-specific CD4+TRM subsets by Ty21a in the human terminal ileum lamina propria and epithelial compartments.Methods: Terminal ileum biopsies were obtained from consenting volunteers undergoing routine colonoscopy who were either immunized orally with 4 doses of Ty21a or not. Isolated lamina propria mononuclear cells (LPMC) and intraepithelial lymphocytes (IEL) CD4+TRM immune responses were determined using either S. Typhi-infected or non-infected autologous EBV-B cell lines as stimulator cells. T-CMI was assessed by the production of 4 cytokines [interferon (IFN)γ, interleukin (IL)-2, IL-17A and tumor necrosis factor (TNF)α] in 36 volunteers (18 vaccinees and 18 controls volunteers).Results: Although the frequencies of LPMC CD103+ CD4+TRM were significant decreased, both CD103+ and CD103- CD4+TRM subsets spontaneously produced significantly higher levels of cytokines (IFNγ and IL-17A) following Ty21a-immunization. Importantly, we observed significant increases in S. Typhi-specific LPMC CD103+ CD4+TRM (IFNγ and IL-17A) and CD103- CD4+TRM (IL-2 and IL-17A) responses following Ty21a-immunization. Further, differences in S. Typhi-specific responses between these two CD4+TRM subsets were observed following multifunctional analysis. In addition, we determined the effect of Ty21a-immunization on IEL and observed significant changes in the frequencies of IEL CD103+ (decrease) and CD103- CD4+TRM (increase) following immunization. Finally, we observed that IEL CD103- CD4+TRM, but not CD103+ CD4+TRM, produced increased cytokines (IFNγ, TNFα and IL-17A) to S. Typhi-specific stimulation following Ty21a-immunization.Conclusions: Oral Ty21a-immunization elicits distinct compartment specific immune responses in CD4+TRM (CD103+ and CD103-) subsets. This study provides novel insights in the generation of local vaccine-specific responses. Trial registration This study was approved by the Institutional Review Board and registered on ClinicalTrials.gov (identifier NCT03970304, Registered 29 May 2019-Retrospectively registered, http://www.ClinicalTrials.gov/NCT03970304). [ABSTRACT FROM AUTHOR]

Our current understanding of CD4+ T-cell-mediated immunity (CMI) elicited by the oral live attenuated typhoid vaccine Ty21a is primarily derived from studies using peripheral blood. Very limited data are available in humans regarding mucosal immunity (especially CD4+ T) at the site of infection (e.g. terminal ileum; TI). Here using multiparametric flow cytometry, we examined the effect of Ty21a immunization on TI-lamina propria mononuclear cells (LPMC) and peripheral blood CD4+ T memory (TM) subsets in volunteers undergoing routine colonoscopy. Interestingly, we observed significant increases in the frequencies of LPMC CD4+ T cells following Ty21a immunization, restricted to the T effector/memory (TEM)-CD45RA+ (TEMRA) subset. Importantly, Ty21a immunization elicited Salmonella Typhi-responsive LPMC CD4+ T cells in all major TM subsets [interferon (IFN)γ and interleukin (IL)-17A in TEM; IFNγ and macrophage inflammatory protein (MIP)1β in T central/memory (TCM); and IL-2 in TEMRA]. Subsequently, we analyzed LPMC S. Typhi-responsive CD4+ T cells in depth for multifunctional (MF) effectors. We found that LPMC CD4+ TEM responses were mostly MF, except for those cells exhibiting the characteristics associated with IL-17A responses. Finally, we compared mucosal to systemic responses and observed that LPMC CD4+ S. Typhi-specific responses were unique and distinct from their systemic counterparts. This study provides the first demonstration of S. Typhi-specific CD4+ TM responses in the human TI mucosa and provides valuable information about the generation of mucosal immune responses following oral Ty21a immunization. [ABSTRACT FROM AUTHOR]

Our current understanding of CD4+ T-cell-mediated immunity (CMI) elicited by the oral live attenuated typhoid vaccine Ty21a is primarily derived from studies using peripheral blood. Very limited data are available in humans regarding mucosal immunity (especially CD4+ T) at the site of infection (e.g. terminal ileum; TI). Here using multiparametric flow cytometry, we examined the effect of Ty21a immunization on TI-lamina propria mononuclear cells (LPMC) and peripheral blood CD4+ T memory (TM) subsets in volunteers undergoing routine colonoscopy. Interestingly, we observed significant increases in the frequencies of LPMC CD4+ T cells following Ty21a immunization, restricted to the T effector/memory (TEM)-CD45RA+ (TEMRA) subset. Importantly, Ty21a immunization elicited Salmonella Typhi-responsive LPMC CD4+ T cells in all major TM subsets [interferon (IFN)γ and interleukin (IL)-17A in TEM; IFNγ and macrophage inflammatory protein (MIP)1β in T central/memory (TCM); and IL-2 in TEMRA]. Subsequently, we analyzed LPMC S. Typhi-responsive CD4+ T cells in depth for multifunctional (MF) effectors. We found that LPMC CD4+ TEM responses were mostly MF, except for those cells exhibiting the characteristics associated with IL-17A responses. Finally, we compared mucosal to systemic responses and observed that LPMC CD4+S. Typhi-specific responses were unique and distinct from their systemic counterparts. This study provides the first demonstration of S. Typhi-specific CD4+ TM responses in the human TI mucosa and provides valuable information about the generation of mucosal immune responses following oral Ty21a immunization., (© The Author(s) 2018. Published by Oxford University Press on behalf of The Japanese Society for Immunology.)