Retroviral Immunotoxins for Leukemia

说明(申请人提供)：免疫毒素(IT)是一种实验性的药理制剂，它是通过将与癌细胞特异结合的抗体或细胞因子与有效的催化毒素联系起来制成的，其中单个分子可以杀死一个细胞。它们的主要目的是有选择地向癌细胞提供治疗，而不是像传统化疗那样对非靶器官进行治疗。虽然这些药物选择性地结合和杀死癌细胞，但在临床上，它们受到以下限制：1)它们不能穿透并以足够的浓度定位于癌症靶组织；2)定位于非靶器官，限制了耐受剂量，并使治疗窗口坍塌。在这份提案中，我们将探索解决这一问题的办法。免疫系统的细胞，如T细胞，是穿透、攻击和摧毁癌细胞的最主要的细胞类型，天然地适合于表达和产生细胞因子以响应抗原的挑战。因此，在第一轮资助中，我们利用了T细胞的一个众所周知的属性，即它们向肿瘤迁移的能力，并提供了证据，证明它们可以通过基因治疗在体内将免疫毒素传递给白血病。我们发现，T细胞可以在白血病部位局部传递由IL-3拼接到转基因毒素上的逆转录病毒IT(RetlT)，并产生显著的抗白血病作用。我们的研究现在已经产生了关于这一新类别的代理人的几个重要问题，在这个提案中，我们将试图确定它们是如何工作的。我们已经建立了一种新的RetlT治疗模式，我们将使用该模式作为未来尝试修改和改进retlT的基础。该模型利用了抗原特异性T细胞克隆的优势。我们将利用这一点来测试retlT白血病治疗的有效性。以往的研究主要集中在单个配体(IL-3)上。现在，在目标1中，我们将描述T细胞在这个已建立的模型中的作用，确定使用CD4或CD8 T细胞克隆进行分娩是更好的选择。然后，在目标2、3和4中，我们将确定我们的方法如何以及为什么有效。目标2将重点放在模型的T细胞成分上，我们将询问与其他肿瘤外部位相比，体内有多少T细胞定位于肿瘤。这些分泌retlT的T细胞的本地化会导致毒性吗？目标3侧重于IT部分，我们将确定秘密IT的角色以及需要多少。最后，在目标4中，我们将确定与传统IT相比，retlT是否可以降低毒性，以及它们是否对宿主免疫系统的组成部分有影响。

DESCRIPTION (provided by applicant): Immunotoxins (IT) are experimental pharmacologic agents that are made by linking antibodies or cytokines that specifically bind to cancer cells to potent catalytic toxins of which a single molecule can kill a cell. Their major purpose is to deliver therapy selectively to cancer cells instead of non-target organs, as does conventional chemotherapy. Although these agents selectively bind and kill cancer cells, clinically they have been limited by their 1) failure to penetrate and localize in adequate concentrations in cancer target tissue 2) localization in nontarget organs limiting the tolerated dose and collapsing the therapeutic window. In this proposal, we will explore a solution to this problem. Cells of the immune system such as T cells are the most prominent cell types which penetrate, attack, and destroy cancer cells and are naturally suited for the expression and production of cytokines in response to antigenic challenge. Therefore, in the first cycle of funding we took advantage of the a well-known property of T cells which is their ability to migrate to tumors and provided proof that they could be used to deliver immunotoxin to leukemia in vivo using gene therapy. We showed that T cells could deliver retroviral IT (retlT) consisting of IL-3 spliced to genetically modified toxin locally at the site of the leukemia and produce a significant anti-leukemia effect. Our studies have now generated several important questions concerning this new class of agent, and in this proposal, we will attempt to determine how they work. We have established a new model of retlT therapy which we will use as a foundation for future attempts to modify and improve retlT. The model takes advantage of the use of antigen specific T cell clones. We will use this to test the usefulness of retlT leukemia therapy. Previous studies focused us on a single ligand (IL-3). Now, in aim 1 we will characterize the role of T cells in this established model, determining whether it is better to use CD4+ or CD8+ T cell clones for delivery. Then in aims 2, 3, and 4 we will determine just how and why our approach works. Aim 2 will focus on the T cell component of the model and we will ask how many T cells localize to the tumor in vivo as compared to other extratumoral sites. Will the localization of T these retlT secreting T cells cause toxicity? Aim 3 focuses on the IT moiety and we will determine the role of secreted IT and how much is necessary. Finally in aim 4, we will determine if retlT can reduce toxicity compared to conventional IT and whether they have effects on components of the host immune system.