Abstract：
Clostridioides difficile infection (CDI) is a serious healthcare-associated disease, causing symptoms such as diarrhea and pseudomembranous colitis. The major virulence factors responsible for the disease symptoms are two secreted cytotoxic proteins, TcdA and TcdB. A parenteral vaccine based on formaldehyde-inactivated TcdA and TcdB supplemented with alum adjuvant, has previously been investigated in humans but resulted in an insufficient immune response. In search for an improved response, we investigated a novel toxin inactivation method and a novel, potent adjuvant. Inactivation of toxins by metal-catalyzed oxidation (MCO) was previously shown to preserve neutralizing epitopes and to annihilate reversion to toxicity. The immunogenicity and safety of TcdA and TcdB inactivated by MCO and combined with a novel carbohydrate fatty acid monosulphate ester-based (CMS) adjuvant were investigated in rabbits. Two or three intramuscular immunizations generated high serum IgG and neutralizing antibody titers against both toxins. The CMS adjuvant increased antibody responses to both toxins while an alum adjuvant control was effective only against TcdA. Systemic safety was evaluated by monitoring body weight, body temperature, and analysis of red and white blood cell counts shortly after immunization. Local safety was assessed by histopathologic examination of the injection site at the end of the study. Body weight gain was constant in all groups. Body temperature increased up to 1 ˚C one day after the first immunization but less after the second or third immunization. White blood cell counts, and percentage of neutrophils increased one day after immunization with CMS-adjuvanted vaccines, but not with alum. Histopathology of the injection sites 42 days after the last injection did not reveal any abnormal tissue reactions. From this study, we conclude that TcdA and TcdB inactivated by MCO and combined with CMS adjuvant demonstrated promising immunogenicity and safety in rabbits and could be a candidate for a vaccine against CDI.
摘要：
艰难梭菌感染（CDI）是一种严重的医疗保健相关疾病，引起腹泻和伪膜性结肠炎等症状。导致疾病症状的主要毒力因子是两种分泌的细胞毒性蛋白，TcdA和TcdB。一种基于甲醛灭活的TcdA和TcdB补充明矾佐剂的肠胃外疫苗，以前曾在人类中进行过研究，但导致免疫反应不足。为了寻找改进的响应，我们研究了一种新的毒素灭活方法和一种新的,强效佐剂。先前已证明通过金属催化的氧化（MCO）使毒素失活可保留中和表位并消除毒性的逆转。在兔中研究了MCO灭活的TcdA和TcdB与新型碳水化合物脂肪酸单硫酸酯（CMS）佐剂的免疫原性和安全性。两次或三次肌内免疫产生高血清IgG和针对两种毒素的中和抗体滴度。CMS佐剂增加了对两种毒素的抗体应答,而明矾佐剂对照仅对TcdA有效。通过监测体重评估系统安全性，体温,免疫后不久的红细胞和白细胞计数分析。在研究结束时通过注射部位的组织病理学检查评估局部安全性。在所有组中体重增加是恒定的。第一次免疫后一天，体温升高至1℃，但第二次或第三次免疫后体温升高较少。白细胞计数,用CMS佐剂疫苗免疫后一天，中性粒细胞的百分比增加，但不是明矾。最后一次注射后42天注射部位的组织病理学没有发现任何异常组织反应。从这项研究中,我们得出的结论是，MCO灭活的TcdA和TcdB与CMS佐剂联合在兔体内表现出很有希望的免疫原性和安全性，可能是抗CDI疫苗的候选物。
