Development of A Synthetic Typhoid Fever Vaccine as A Substitution of Vi Vaccine

描述（由申请人提供）伤寒是全球发病的主要原因，估计每年有1600万至3300万例感染和50万至60万例死亡。它是由伤寒沙门氏菌（S. typhi）引起的。伤寒沙门氏菌的Vi荚膜多糖是保护性抗原，目前已获批用于2岁人群伤寒预防免疫的Vi疫苗中。目前获得许可的流感疫苗是通过昂贵和危险的伤寒葡萄球菌野生型细菌发酵和复杂的纯化过程生产的。目前正在开发基于Vi多糖-蛋白偶联物的第二代伤寒疫苗，这种疫苗可能对2岁以下儿童具有更强的免疫原性和有效性。一种来自植物的高分子量PGA （HPGA）已经被开发出来，并在cGMP的纳米疗法下以公斤（kg）的规模生产。最终产物也具有与天然Vi多糖相似的高分子量（bbb2 x 106 Da）。o -乙酰化HPGA （OAcHPGA）不仅与多糖具有相同的抗原性，而且在实验动物中具有免疫原性。OAcHPGA诱导的抗体反应水平与市场上销售的Vi疫苗相当。这些研究表明，这种OAcHPGA可能被用于制造一种合成伤寒疫苗，这种疫苗可以从植物性起始材料（HPGA）大量生产。与现有的Vi多糖疫苗相比，OAcHPGA可能是一种更安全、更便宜的疫苗。经济优势使得在世界范围内，特别是在发展中国家的流行地区扩大伤寒疫苗的生产和使用更加容易和负担得起。因此，我们建议继续开发基于OAcHPGA的合成伤寒疫苗，其具体目标有以下两个：（具体目标1 -免疫原性和保护研究）基于效价指标（DOAc和分子量）评估OAcHPGA的免疫原性，并在动物模型上证明OAcHPGA对伤寒沙门氏菌的保护作用。这将确定OAcHPGA具有免疫原性和对伤寒沙门氏菌的保护作用，并有助于在未来建立产品规范。（具体目标2 -工艺开发）完善和建立o -乙酰化工艺，以生产具有所需DOAc，分子量和其他性能的OAcHPGA。这将与相关的检测开发以及Specific Aim 1一起进行。此外，将制备并评价oachpga蛋白偶联物。这两个特定目标的实现将为下一阶段的开发奠定基础，即cGMP试点生产、动物毒理学研究和OAcHPGA疫苗的临床研究，以及更重要的是，开发可能更具免疫原性且适合2岁以下儿童的OAcHPGA蛋白结合疫苗。

DESCRIPTION (provided by applicant) Typhoid fever is a major cause of morbidity worldwide with an estimated incidence of 16 to 33 million infections and 500,000 to 600,000 deaths annually. It is caused by Salmonella typhi (S. typhi). The Vi capsular polysaccharide of S. typhi is the protective antigen and is used in current licensed Vi vaccines for prophylactic immunization against typhoid fever for people of e 2 years. The current licensed Vi vaccines are produced by costly and hazardous fermentation of S. typhi wild type bacteria and elaborate purification processes. A second generation of typhoid vaccines based on Vi polysaccharide-protein conjugate is being developed that may potentially be more immunogenic and effective in children under 2 years. A high-molecular-weight PGA (HPGA) from a plant source has been developed and is manufactured by Nanotherapeutics under cGMP at a kilogram (kg) scale. The end product also had a high molecular weight (>2 x 106 Da) similar to that of the native Vi polysaccharide. The O-acetylated HPGA (OAcHPGA) not only shared the same antigenicity with the Vi polysaccharide, but was also immunogenic in laboratory animals. The antibody response level induced by OAcHPGA was comparable to that of a marketed Vi vaccine. These studies indicate that this OAcHPGA could potentially be used to make a synthetic typhoid vaccine that can be produced in large quantities from a plant-based starting material (HPGA). Compared to the existing Vi polysaccharide vaccine, OAcHPGA could be a much safer and less expensive vaccine. The economic advantage makes it easier and more affordable to expand production and use of the typhoid vaccine worldwide, especially in endemic areas of developing countries. Thus, we propose to continue developing a synthetic typhoid vaccine based on OAcHPGA with the following two specific aims: (Specific Aim 1 - Immunogenicity and protection studies) To evaluate the immunogenicity of OAcHPGA based on the potency indicators (DOAc and molecular weight) and to demonstrate the protective effect of the OAcHPGA against the S. typhi challenge in animal models. This will establish that the OAcHPGA is immunogenic and protective against the S. typhi, and help establish product specifications in the future. (Specific Aim 2 - Process development) To refine and establish the O-acetylation process for producing OAcHPGA with desired DOAc, molecular weight, and other properties. This will be conducted together with related assay development and in conjunction with Specific Aim 1. In addition, the OAcHPGA-protein conjugate will be prepared and evaluated. Accomplishment of these two specific aims will form the base for next development phases toward pilot cGMP manufacturing, animal toxicology studies, and clinical studies of the OAcHPGA vaccine and, also importantly, the development of an OAcHPGA-protein conjugate vaccine that may potentially be more immunogenic and suitable for children under the age of 2. PUBLIC HEALTH RELEVANCE: Typhoid fever is a major cause of morbidity worldwide with an estimated incidence of 16 to 33 million infections and 500,000 to 600,000 deaths annually. The current licensed Vi vaccines are produced by costly and hazardous fermentation of S. typhi wild type bacteria and elaborate purification processes. A second generation of typhoid vaccines based on Vi polysaccharide-protein conjugate is being developed that may potentially be more immunogenic and effective in children under 2 years.