Development of an immune imaging method to accurately determine the immune status of tumors

现代非侵入性成像对于提高我们对生物过程和疾病评估的知识是不可或缺的。分子成像通过量化特定的感兴趣标记物的数量和/或功能，使成像的概念更进一步。由于对同源抗原的高度亲和力，抗体在分子成像和治疗中都是有用的试剂。肿瘤学领域受益于基于抗体的免疫疗法，因为与正常组织相比，许多抗原在某些类型的癌细胞上过度表达。用放射性同位素标记抗体可以非侵入性地识别合适的靶点，从而为该领域提供重要的发展。实现分子抗体成像的一个主要挑战是获得高对比度的信号与背景比。这将取决于许多变量，包括抗体的形式(可变片段、单链可变片段)、抗体克隆、放射性同位素、螯合剂和成像能力。此外，生物系统总是会有一个固有的非特异性抗体摄取水平，这可以归因于血管通透性，并可以随着时间和治疗的变化而变化。我们研究的目的是开发足够的方法来精确地在体内定量抗体。我们将用一种长寿的PET放射性同位素89Zr标记抗程序性死亡配体-1(PDL1)的抗体。我们化合物的一个独创性是螯合剂4HMSA，与用于抗体标记的标准螯合剂相比，它对89Zr的螯合更稳定。我们将探索药代动力学方法，以纠正受试者对PDL1示踪剂的非特异性摄取。我们还将通过动态增强磁共振成像(DCE-MRI)评估血管通透性，以确定非特异性示踪剂摄取的校正因子。我们的研究将在小鼠癌症模型中测试PET/DCE-MRI在体内成像PDL1的联合应用。该计划的长期目标是：开发定量工具和方法，在癌症模型系统中测量免疫相关细胞表面标志物的表达、组织的免疫细胞组成和整体免疫反应。这些成像工具是缺乏的，通过能够对各种癌症的局部免疫反应进行纵向监测，将极大地有利于肿瘤学领域。我们的计划将为设计和分析新的放射性标记抗体提供基础，这将扩大可以受益于诊断PET和MR成像的医疗条件的数量。我们的计划是这样设计的，HQP的培训是推进我们研究的基石。我们研究的跨学科性质将使受训者获得免疫学、放射化学、放射生物学和生物医学成像的独特技能组合。我们将开发的方法适用于其他抗体的成像，因此在科学和医学上具有广泛的应用前景。

Modern non-invasive imaging is integral to advancing our knowledge of biological processes and disease assessment. Molecular imaging takes the concept of imaging a step further by quantifying the amount and/or function of a specific marker of interest. Because of their high affinity toward cognate antigens, antibodies (Abs) are useful agents for both molecular imaging and therapy. The field of oncology has benefited from Ab-based immunotherapies because numerous antigens have been identified that are overexpressed on certain types of cancer cells compared to normal tissues. Labeling of Abs with radioisotopes can provide an important development for the field by identifying the appropriate target non-invasively. A major challenge with implementation of molecular Ab imaging is to achieve a high contrast signal to background ratio. This will depend on a number of variables including the form of the antibody (variable fragments, single chain variable fragments), the antibody clone, the radioisotope, the chelator and the imaging capabilities. In addition, biological systems will always have an inherent level of unspecific Ab uptake that can be attributed to vascular permeability and which can vary as a function of time and treatment. The objective of our research is to develop adequate methods for precise quantification of Abs in vivo. We will label antibodies against programmed-death ligand-1 (PDL1) with 89Zr, a long-lived PET radioisotope. An originality of our compound is the chelator 4HMSA, which chelates 89Zr more stably compared to standard chelators used for Ab labelling. We will explore pharmacokinetic methods to correct subject-wise for the unspecific uptake of the PDL1 tracer. We will also assess vascular permeability by dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI) to determine a correction factor for non-specific tracer uptake. Our research will test the combined application of PET/DCE-MRI for imaging PDL1 in vivo in mouse models of cancer. The long term objective of this program is to: develop quantitative tools and methods to measure immune-related cell surface marker expression, immune cell composition of tissues and the immune response as a whole in cancer model systems. These imaging tools are lacking and would greatly benefit the field of oncology by enabling longitudinal monitoring of the local immune response in various cancers. Our program will provide a base for the design and analysis of new radiolabeled Abs which will expand the number of medical conditions that can benefit from diagnostic PET and MR imaging. Our program is designed such that training of HQP is a cornerstone of advancing our research. The interdisciplinary nature of our research will allow trainees to acquire a unique combination of skills from immunology, radiochemistry, radiobiology and biomedical imaging. The methods we will develop are adaptable to imaging other Abs and therefore can have wide applications in science and medicine.