Development of a conjugate vaccine for the prevention of tularemia

图拉氏方济氏菌是一种多形性、革兰氏阴性、兼性胞内细菌病原菌，是 图拉热症的病原体，一种潜在的致命人类疾病。图拉氏针叶蝉可以很容易地 雾化和吸入时的高度传染性引起了人们对其在 生物恐怖主义。一种经验性衍生的、仍未获得许可的图拉氏F菌疫苗株，即LVS，因 几个问题：(I)在某些动物感染模型中，LVS仍然具有很高的毒力，(Ii)LVS疫苗已被 与严重的不良副作用有关：(3)LVS疫苗的接受者出现不完全 免疫，(Iv)Ft.LVS减弱的分子基础尚不清楚。免疫机制研究进展 对图拉氏丝虫，特别是高毒力的A型菌株的保护作用尚不明确。我们的工作， 与其他研究人员的研究表明，体液免疫(针对O侧的抗体 (脂多糖链)和细胞免疫对于抵御这种生物是至关重要的。 由于对图拉氏丝虫免疫的不完全了解，我们使用了三种方法来 疫苗开发：(1)筛选图拉氏丝孢子虫蛋白质组中的绝大多数蛋白质 潜在的保护性抗原；(2)活疫苗株(Ft.LVS)通过 O-多糖(OPS)生物合成位点两个必需基因的突变；(3) 由连接到载体蛋白的全长OPS组成的糖结合疫苗。我们已经获得了 关于保护性免疫性质的关键信息，并利用这些信息来完善我们的 实验策略。我们目前的数据表明，最有效的方法可能是 我们的原型疫苗的组合。通过将糖结合疫苗与减毒突变株相结合 我们已经用野生型A型菌株Schu S4诱导了对呼吸攻击的保护。至 据我们所知，这种保护以前只在Ft.LVS免疫中报道过。组合在一起 我们开发的疫苗在动物模型中的毒力比Ft.LVS低7个对数；因此，我们预计 这样会安全得多。

Francisella tularensis, a pleomorphic, gram-negative, facultative intracellular bacterial pathogen, is the etiologic agent of tularemia, a potentially fatal human disease. The ease with which F. tularensis can be aerosolized and its high degree of infectivity when inhaled have raised concerns about its potential for use in bioterrorism. An empirically derived, still-unlicensed vaccine strain of F. tularensis, LVS, is complicated by several issues: (i) Ft.LVS is still highly virulent in some animal models of infection, (ii) LVS vaccine has.been associated with significant undesirable side effects, (iii) Recipients of LVS vaccine develop incomplete immunity, (iv) The molecular basis for the attenuation of Ft.LVS is unknown. The mechanisms of immune protection against F. tularensis, particularly the highly virulent type A strains, are poorly defined. Our work, along with that of other investigators, has suggested that both humoral immunity (antibody to the O side chain of the lipopolysaccharide) and cellular immunity are critical for protection against this organism. Because of the incomplete understanding of immunity to F. tularensis, we have used three approaches to vaccine development: (1) screening of the vast majority of proteins in the F. tularensis proteome for potentially protective antigens; (2) marked attenuation of the live vaccine strain (Ft.LVS) through the mutation of two essential genes in the O polysaccharide (OPS) biosythesis locus, and (3) construction of a glycoconjugate vaccine composed of the full-length OPS conjugated to a carrier protein. We have obtained critical information on the nature of protective immunity and have used this information to refine our experimental strategy. Our data at this point indicate that the most effective approach will likely be some combination of our prototype vaccines. By combining the glycoconjugate vaccine with an attenuated mutant strain we have elicited protection against respiratory challenge with the wild-type type A strain Schu S4. To our knowledge, such protection has previously been reported only for Ft.LVS immunization. The combination vaccine we have developed is 7 logs less virulent in animal models than Ft.LVS; therefore, we anticipate that it will be considerably safer.