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

现代非侵入性成像是推进我们对生物过程和疾病评估的知识不可或缺的。分子成像通过量化特定目标标记物的量和/或功能进一步采用成像的概念。由于其对同源抗原的高亲和力，抗体（Ab）是用于分子成像和治疗的有用试剂。肿瘤学领域已经受益于基于Ab的免疫疗法，因为已经鉴定出与正常组织相比在某些类型的癌细胞上过表达的许多抗原。用放射性同位素标记抗体可以通过非侵入性地识别适当的靶标来为该领域提供重要的发展。实施分子Ab成像的主要挑战是实现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，生物系统将始终具有固有的非特异性Ab摄取水平，其可归因于血管渗透性，并且其可作为时间和治疗的函数而变化。我们的研究目的是开发适当的方法，在体内精确定量的抗体。我们将用89 Zr（一种长寿命PET放射性同位素）标记抗程序性死亡配体-1（PDL 1）的抗体。我们的化合物的独创性是螯合剂4 HMSA，与用于Ab标记的标准螯合剂相比，其更稳定地螯合89 Zr。我们将探索药代动力学方法，以校正（按受试者）PDL 1示踪剂的非特异性摄取。我们还将通过动态对比增强磁共振成像（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。我们的研究将测试PET/DCE-MRI在小鼠癌症模型中体内成像PDL 1的联合应用。该计划的长期目标是：开发定量工具和方法，以测量免疫相关的细胞表面标志物表达，组织的免疫细胞组成和癌症模型系统中的整体免疫反应。这些成像工具是缺乏的，并且将通过实现对各种癌症中的局部免疫应答的纵向监测而极大地有益于肿瘤学领域。我们的计划将为新的放射性标记抗体的设计和分析提供基础，这将扩大可以从诊断PET和MR成像中受益的医疗条件的数量。我们的计划旨在使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学员能够获得免疫学，放射化学，放射生物学和生物医学成像技能的独特组合。我们将开发的方法适用于其他抗体的成像，因此可以在科学和医学上有广泛的应用。

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.