Department of Medical Biophysics, University of Western Ontario, London, ON, Canada.
Cellular and Molecular Imaging Group, Robarts Research Institute, London, ON, Canada.
Mol Imaging Biol. 2022 Dec;24(6):886-897. doi: 10.1007/s11307-022-01738-w. Epub 2022 Jun 1.
The purpose of this study was to evaluate magnetic particle imaging (MPI) as a method for the in vivo tracking of dendritic cells (DC). DC are used in cancer immunotherapy and must migrate from the site of implantation to lymph nodes to be effective. The magnitude of the ensuing T cell response is proportional to the number of lymph node-migrated DC. With current protocols, less than 10% of DC are expected to reach target nodes. Therefore, imaging techniques for studying DC migration must be sensitive and quantitative. Here, we describe the first study using MPI to detect and track DC injected into the footpads of C57BL/6 mice migrating to the popliteal lymph nodes (pLNs).
DC were labelled with Synomag-D™ and injected into each hind footpad of C57BL/6 mice (n = 6). In vivo MPI was conducted immediately and repeated 48 h later. The MPI signal was measured from images and related to the signal from a known number of cells to calculate iron content. DC numbers were estimated by dividing iron content in the image by the iron per cell measured from a separate cell sample. The presence of SPIO-labeled DC in nodes was validated by ex vivo MPI, histology, and fluorescence microscopy.
Day 2 imaging showed a decrease in MPI signal in the footpads and an increase in signal at the pLNs, indicating DC migration. MPI signal was detected in the left pLN in four of the six mice and two of the six mice showed MPI signal in the right pLN. Ex vivo imaging detected signal in 11/12 nodes. We report a sensitivity of approximately 4000 cells (0.015 µg Fe) in vivo and 2000 cells (0.007 µg Fe) ex vivo.
Here, we describe the first study to use MPI to detect and track DC in a migration model with immunotherapeutic applications. We also bring attention to the issue of resolving unequal signals within close proximity, a challenge for any pre-clinical study using a highly concentrated tracer bolus that shadows nearby lower signals.
本研究旨在评估磁粒子成像（MPI）作为一种体内跟踪树突状细胞（DC）的方法。DC 用于癌症免疫治疗，必须从植入部位迁移到淋巴结才能发挥作用。随之而来的 T 细胞反应的程度与迁移到淋巴结的 DC 数量成正比。根据目前的方案，预计只有不到 10%的 DC 能够到达靶节点。因此，用于研究 DC 迁移的成像技术必须具有敏感性和定量性。在这里，我们描述了第一项使用 MPI 检测和跟踪注入 C57BL/6 小鼠后脚掌并迁移到腘淋巴结（pLN）的 DC 的研究。
将 DC 用 Synomag-DTM 标记，然后注入每组 C57BL/6 小鼠的后脚掌（n=6）。立即进行体内 MPI 检测，并在 48 小时后重复进行。从图像中测量 MPI 信号，并将其与已知数量的细胞的信号相关联，以计算铁含量。通过将图像中的铁含量除以从单独的细胞样本中测量的每个细胞的铁含量来估计 DC 数量。通过离体 MPI、组织学和荧光显微镜验证节点中存在 SPIO 标记的 DC。
第 2 天的成像显示，后脚掌的 MPI 信号降低，pLN 的信号增加，表明 DC 迁移。在 6 只小鼠中的 4 只和 6 只小鼠中的 2 只的左 pLN 中检测到 MPI 信号。离体成像检测到 12 个节点中的 11 个有信号。我们报告了体内约 4000 个细胞（0.015μg Fe）和离体 2000 个细胞（0.007μg Fe）的灵敏度。
在这里，我们描述了第一项使用 MPI 检测和跟踪具有免疫治疗应用的迁移模型中的 DC 的研究。我们还提请注意解决近距离内不均匀信号的问题，这是任何使用高浓度示踪剂团块进行的临床前研究都面临的挑战，该示踪剂团块会遮挡附近的低信号。
