体内免疫细胞追踪技术利用磁共振成像（MRI）是研究癌症治疗成功机制的有价值工具。目前使用超顺磁铁氧化物（SPIO）标记细胞的方法缺乏持久性，无法长期追踪移植细胞的命运和位置。Magnetospirillum magneticum 是一种商业可用、产生铁的细菌，可以被哺乳动物细胞作为磁共生体（MEs）摄取并和谐共存。MEs在体内干细胞和癌细胞追踪方面表现出潜力，但在免疫细胞方面尚未得到评估。该初步研究探讨了将MEs标记应用于髓源性抑制细胞（MDSCs）、细胞毒性T淋巴细胞（CTLs）和树突状细胞（DCs）的效果，并对细胞纯度、功能和MRI对比度进行了评估。MDSCs、CTLs和DCs与MEs在不同的ME标记比例（MLR）下共培养，评估了各种生物学指标和铁摄取。MDSCs在体内成像时，采用MEs或SPIO（Molday ION Rhodamine B）进行了标记，然后通过尾静脉注射到C3肿瘤携带的小鼠体内，并在植入后的第24天开始每天使用MRI进行扫描，以评估细胞定量。培养后，MDSCs的铁含量超过0.6 pg Fe/细胞。CTLs的铁载荷小于0.5 pg/细胞，而DCs的铁载荷约为1.4 pg/细胞。MDSCs在1000 MLR下的抑制功能受ME标记的影响不大，但在2000 MLR下受到影响。CTL功能异常标记物受ME标记的影响不大，DC标记物也没有明显受到影响。体内数据显示，用MEs标记的MDSCs在TurboSPI中生成足够的对比度，与SPIO标记的细胞类似。细胞可以标记足够数量的MEs以在MRI中可检测，同时不影响细胞存活。需注意在较高浓度的MEs下，可能会影响某些细胞类型的功能活性和/或形态。对于具有最小吞噬行为的免疫细胞，在与MEs共培养后，每个细胞的铁含量较低，相比于SPIO。然而，MEs可以成功用作吞噬性免疫细胞的对比剂。©2023. 作者，独家授权给World Molecular Imaging Society.

In vivo immune cell tracking using MRI can be a valuable tool for studying the mechanisms underlying successful cancer therapies. Current cell labeling methods using superparamagnetic iron oxide (SPIO) lack the persistence to track the fate and location of transplanted cells long-term. Magnetospirillum magneticum is a commercially available, iron-producing bacterium that can be taken up by and live harmoniously within mammalian cells as magneto-endosymbionts (MEs). MEs have shown promise as labeling agents for in vivo stem and cancer cell tracking but have yet to be evaluated in immune cells. This pilot study examined ME labeling in myeloid-derived suppressor cells (MDSCs), cytotoxic T lymphocytes (CTLs), and dendritic cells (DCs) and its effects on cell purity, function, and MRI contrast.MDSCs, CTLs, and DCs were incubated with MEs at various ME labeling ratios (MLR), and various biological metrics and iron uptake were assessed. For in vivo imaging, MDSCs were labeled overnight with either MEs or SPIO (Molday ION Rhodamine B) and injected into C3 tumor-bearing mice via tail vein injection 24 days post-implant and scanned daily with MRI for 1 week to assess cellular quantification.Following incubations, MDSCs contained > 0.6 pg Fe/cell. CTLs achieved Fe loading of < 0.5 pg/cell, and DCs achieved Fe loading of ~ 1.4 pg/cell. The suppressive functionality of MDSCs at 1000 MLR was not affected by ME labeling but was affected at 2000 MLR. Markers of CTL dysfunction were not markedly affected by ME labeling nor were DC markers. In vivo data demonstrated that the MDSCs labeled with MEs generated sufficient contrast to be detectable using TurboSPI, similar to SPIO-labeled cells.Cells can be labeled with sufficient numbers of MEs to be detectable with MRI without compromising cell viability. Care must be taken at higher concentrations of MEs, which may affect some cell types' functional activity and/or morphology. Immune cells with minimal phagocytic behavior have much lower iron content per cell after incubation with MEs vs SPIO; however, MEs can successfully be used as a contrast agent for phagocytic immune cells.© 2023. The Author(s), under exclusive licence to World Molecular Imaging Society.