MECHANISM OF ANTIBODY PROTECTION AGAINST C. NEOFORMANS

描述（由申请人提供）：在美国8%的艾滋病患者中，新型隐球菌引起致命的脑膜脑炎。目前的治疗是不够的，尽管积极的抗真菌治疗，仍有10- 20%的患者死于隐球菌脑膜炎，并且在初始治疗期后存活的个体必须坚持终身治疗以防止复发。由于这些治疗的局限性，抗体已被认为是预防和治疗C.新生形式感染。抗荚膜单克隆抗体可以延长感染致死小鼠的生命，提高体内抗真菌药物的有效性。先前的观察表明，由这些抗体的恒定区介导的功能在决定其保护潜力方面至关重要。与这一观点一致的是，我们在基因缺陷小鼠中进行的初步研究表明，抗体与某些Fc受体（FcR）的相互作用在介导保护中很重要，而补体的存在可能对抗体的功效有害，特别是在没有FcR结合的情况下。在过去的几年中，我们开发了一个具有各种不同功能特性的重组抗体的大型文库。现在，我们将把抗隐球菌可变区移植到这些抗体上，单独或联合检测FcR结合、补体激活、贪婪性和半衰期等特征对新生隐球菌感染动物模型疗效的贡献。我们将首先通过测试FcR结合、抗体依赖细胞介导的细胞毒性（ADCC）和补体激活来确认这些抗体在体外的功能特性，并确定它们在体内的药代动力学。然后，我们将测试体内抗新生梭状菌感染的功效。具体来说，我们将研究抗体的有效性是否取决于i)体内持久性，ii)激活补体的能力，iii) fcr的参与或iv)表面抗原的有效交联。本文提出的实验旨在探索具有不同功能特性的抗体具有不同程度功效的假设。小鼠感染新生隐球菌是一个特别相关的系统，因为一种小鼠单克隆抗体目前正在进行I期评估，用于治疗艾滋病患者的隐球菌脑膜炎。如果这项试验被证明是有希望的，所提出的实验将为选择最佳的治疗候选者进行进一步研究提供基础。明确定义哪些特性与功效相关，将使我们能够在设计治疗人类疾病的有效治疗性抗体方面取得进展。

DESCRIPTION (provided by applicant): Cryptococcus neoformans causes a lethal meningoencephalitis in 8 percent of AIDS patients in the US. Current treatment is inadequate as 10-20 percent of patients die from cryptococcal meningitis despite aggressive antifungal therapy, and individuals who survive beyond the initial treatment period must be maintained on life-long therapy to prevent relapse. Because of these therapeutic limitations, antibodies have been considered as prevention and treatment for C. neoformans infection. Anti-capsular monoclonal antibodies can prolong the life of lethally infected mice and increase the effectiveness of antifungal agents in vivo. Previous observations indicate that functions mediated by the constant regions of these antibodies are crucial in determining their protective potential. Consistent with this idea are preliminary studies we have done in genetically deficient mice showing that antibody interactions with certain Fc receptors (FcRs) are important in mediating protection, while the presence of complement may be detrimental to antibody efficacy, particularly in the absence of FcR binding. Over the past several years, we have developed a large library of recombinant antibodies with a variety of different functional properties. We will now graft anti-cryptococcal variable regions onto these antibodies to examine, both alone and in combination, the contribution of such characteristics as FcR binding, complement activation, avidity and half life to efficacy in an animal model of infection with C. neoformans. We will first confirm the functional properties of these antibodies in vitro by testing FcR binding, antibody-dependant cell mediated cytotoxicity (ADCC), and complement activation and determine their pharmacokinetics in vivo. We will then test in vivo efficacy against infection with C. neoformans. Specifically, we will investigate whether antibody efficacy depends on i) in vivo persistence, ii) ability to activate complement, iii) engagement of FcRs or iv) effective cross-linking of surface antigen. The experiments proposed here are designed to explore the hypothesis that antibodies with different constellations of functional properties will have differing degrees of efficacy. Murine infection with C. neoformans is a particularly relevant system because a murine monoclonal antibody is currently undergoing Phase I evaluation for the treatment of cryptococcal meningitis in AIDS patients. If this trial proves promising, the experiments proposed will provide the basis for selecting the best therapeutic candidates for further study. A clear definition of what properties correlate with efficacy should allow us to move forward in designing effective therapeutic antibodies for treatment of disease in humans.