Table_1_A rhesus macaque intragastric challenge model for evaluating the safety, immunogenicity, and efficacy of live-attenuated Shigella dysenteriae 1 vaccine candidates.pdf

Shigellosis remains a significant global health challenge, particularly in Asia and Africa, where it is a major cause of morbidity and mortality among children. Despite the urgent need, the development of a licensed Shigella vaccine has been hindered, partly due to the lack of suitable animal models for preclinical evaluation. In this study, we used an intragastric adult rhesus macaque challenge model to evaluate the safety, immunogenicity, and efficacy of five live-attenuated Shigella dysenteriae 1 vaccine candidates, all derived from the 1617 parent strain. The vaccine strains included WRSd1, a previously tested candidate with deletions in virG(icsA), stxAB, and fnr, and four other strains—WRSd2, WRSd3, WRSd4, and WRSd5—each containing deletions in virG and stxAB, but retaining fnr. Additionally, WRSd3 and WRSd5 had further deletions in the Shigella enterotoxin gene senA and its paralog senB, with WRSd5 having an extra deletion in msbB2. Rhesus monkeys were immunized three times at two-day intervals with a target dose of 2 × 1010 CFU of the vaccine strains. Thirty days after the final immunization, all monkeys were challenged with a target dose of 2 × 109 CFU of the S. dysenteriae 1 1617 wild-type strain. Safety, immunogenicity, and efficacy were assessed through physical monitoring and the evaluation of immunologic and inflammatory markers following immunization and challenge. Initial doses of WRSd1, WRSd3, and WRSd5 led to mild adverse effects, such as vomiting and loose stools, but all five vaccine strains were well tolerated in subsequent doses. All strains elicited significant IgA and IgG antibody responses, as well as the production of antibody-secreting cells. Notably, none of the vaccinated animals exhibited shigellosis symptoms such as vomiting or loose/watery stool post-challenge, in stark contrast to the control group, where 39% and 61% of monkeys exhibited these symptoms, respectively. The aggregate clinical score used to evaluate Shigella attack rates post-challenge revealed a 72% attack rate in control animals, compared to only 13% in vaccinated animals, indicating a relative risk reduction of 81%. This study highlights the potential of this NHP model in evaluating the safety, immunogenicity, and efficacy of live-attenuated Shigella vaccine candidates, offering a valuable tool for preclinical assessment before advancing to Phase 1 or more advanced clinical trials.

志贺菌病（Shigellosis）仍是一项严峻的全球公共卫生挑战，尤其在亚洲与非洲地区，是导致儿童发病与死亡的主要诱因之一。尽管需求迫切，但获批上市的志贺菌疫苗研发仍举步维艰，部分原因在于缺乏适用于临床前评价的合适动物模型。本研究采用胃内接种的成年恒河猴攻击感染模型，对5株源自1617亲本菌株的减毒痢疾志贺菌1型（Shigella dysenteriae 1）候选疫苗的安全性、免疫原性与保护效力进行评估。本次研究的疫苗菌株包括WRSd1——这是此前已验证的候选株，其virG(icsA)、stxAB与fnr基因均发生缺失；另外4株分别为WRSd2、WRSd3、WRSd4与WRSd5，均缺失virG与stxAB基因，但保留fnr基因。此外，WRSd3与WRSd5还额外缺失了志贺菌肠毒素基因senA及其同源基因senB，而WRSd5还多了一处msbB2基因的缺失。

实验中，恒河猴以2×10¹⁰菌落形成单位（Colony-Forming Units, CFU）的疫苗菌株为目标剂量，每隔2天免疫一次，共免疫3次。末次免疫后30天，对所有恒河猴以2×10⁹ CFU的痢疾志贺菌1型1617野生型菌株进行攻击感染。通过体格监测以及免疫与炎症标志物检测，分别在免疫阶段与攻击感染阶段评估疫苗的安全性、免疫原性与保护效力。

结果显示，WRSd1、WRSd3与WRSd5的初始免疫剂量引发了轻度不良反应，如呕吐与稀便，但后续剂量的5株疫苗菌株均具有良好的耐受性。所有菌株均能诱导显著的免疫球蛋白A（Immunoglobulin A, IgA）与免疫球蛋白G（Immunoglobulin G, IgG）抗体应答，以及抗体分泌细胞的产生。值得注意的是，所有免疫组动物在攻击感染后均未出现志贺菌病相关症状，如呕吐或稀便/水样便；而对照组中分别有39%与61%的恒河猴出现了上述症状。用于评估攻击感染后志贺菌发病情况的综合临床评分显示，对照组动物的发病率为72%，而免疫组仅为13%，相对风险降低了81%。

本研究证实了该非人灵长类（Non-Human Primate, NHP）模型在评估减毒活志贺菌候选疫苗安全性、免疫原性与保护效力方面的应用潜力，可为推进至I期或更高级别临床试验前的临床前评价提供宝贵工具。