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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 (T) cells provide immediate adaptive effector immune responsiveness at the infection site. However, the mechanism(s) by which S. Typhi induces T in the intestinal mucosa are unknown. Here, we focus on the induction of S. Typhi-specific CD4+T 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+T 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+T were significant decreased, both CD103+ and CD103- CD4+T 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+T (IFNγ and IL-17A) and CD103- CD4+T (IL-2 and IL-17A) responses following Ty21a-immunization. Further, differences in S. Typhi-specific responses between these two CD4+T 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+T (increase) following immunization. Finally, we observed that IEL CD103- CD4+T, but not CD103+ CD4+T, 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+T (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).

BACKGROUND

METHODS

RESULTS

CONCLUSIONS

背景

伤寒沙门氏菌血清型 Typhi（S. Typhi）是一种高度侵袭性细菌，感染人类肠道黏膜，导致全球每年约有 1190 万至 223 万例感染和 13 万至 22.3 万人死亡。口服伤寒疫苗 Ty21a 在野外提供适度的长期保护（5-7 年）。需要针对肠道病原体的新的和改进的疫苗，但由于缺乏保护的免疫相关性，特别是在感染部位，其发展受到阻碍。组织驻留记忆 T（T）细胞在感染部位提供即时的适应性效应免疫反应。然而，伤寒沙门氏菌诱导肠道黏膜中 T 的机制尚不清楚。在这里，我们专注于 Ty21a 在人类末端回肠固有层和上皮细胞中诱导 S. Typhi 特异性 CD4+T 亚群。

方法

从同意接受常规结肠镜检查的志愿者中获得末端回肠活检，这些志愿者要么口服接受 4 剂 Ty21a 免疫，要么不接受免疫。使用 S. Typhi 感染或未感染的自体 EBV-B 细胞系作为刺激细胞，确定分离的固有层单核细胞（LPMC）和上皮内淋巴细胞（IEL）CD4+T 免疫反应。通过 36 名志愿者（18 名疫苗接种者和 18 名对照志愿者）产生 4 种细胞因子[干扰素（IFN）γ、白细胞介素（IL）-2、IL-17A 和肿瘤坏死因子（TNF）α]来评估 T-CMI。

结果

尽管 LPMC CD103+ CD4+T 的频率显著降低，但 Ty21a 免疫后，CD103+和 CD103- CD4+T 亚群自发产生更高水平的细胞因子（IFNγ和 IL-17A）。重要的是，我们观察到 Ty21a 免疫后 S. Typhi 特异性 LPMC CD103+ CD4+T（IFNγ和 IL-17A）和 CD103- CD4+T（IL-2 和 IL-17A）反应显著增加。此外，在多功能分析中观察到这两个 CD4+T 亚群之间 S. Typhi 特异性反应的差异。此外，我们还测定了 Ty21a 免疫对 IEL 的影响，并观察到免疫后 IEL CD103+（减少）和 CD103- CD4+T（增加）的频率发生变化。最后，我们观察到 IEL CD103- CD4+T，但不是 CD103+ CD4+T，在 Ty21a 免疫后对 S. Typhi 特异性刺激产生增加的细胞因子（IFNγ、TNFα 和 IL-17A）。