Real-time tracking of single cells in live animals

 描述：基于干细胞移植的再生疗法有着巨大的临床前景，特别是对于心脏受损和终末期心力衰竭的患者。通过跟踪移植细胞的命运，成像在这些治疗中扮演着重要的角色。然而，现有的成像方法只能直观地显示大量移植细胞在哪里积累，而不是单个细胞如何到达那里。这些成像工具的有限能力阻碍了我们充分了解单个移植细胞的命运和动态行为。提高基于细胞的治疗的效率和功能结果是心血管研究的长期目标。我们在这项建议中的目标是开发一种新的成像方法，当单个移植细胞回到心脏损伤部位时，可以实时跟踪它们。我们的 假设在一定条件下，微正电子发射断层扫描(MicroPET)可以跟踪单个移植细胞在活体小鼠体内，具有亚毫米级的空间分辨率和亚秒级的时间分辨率。由于之前的研究完全依赖于传统的重建算法来跟踪标记的细胞，所以microPET的这些能力还没有被探索过。通过利用只有稀疏的细胞集包含放射性的知识，可以制定用于重建单细胞轨迹的算法 来自具有更高灵敏度和空间分辨率的microPET测量。这项拟议研究的基本原理是，与传统的整体组织技术相比，在全身水平上跟踪体内单个细胞将允许更详细地了解移植细胞的动态行为和命运，以及它们与受伤心脏组织的相互作用。我们的初步模拟表明，在活体内，可以用microPET跟踪标记1-10Bq的单个细胞。我们将通过以下两个目标来验证我们的假设：(1)扩展轨迹重建以并行跟踪多个单个细胞；(2)优化细胞标记和跟踪 体内的单个细胞。在第一个目标中，我们将实现一个新的重建算法，该算法采用 来自小动物PET扫描仪的原始列表模式数据，并并行重建多个单细胞的时空轨迹。在第二个目标中，我们将优化骨髓单个核细胞的放射性标记，使其达到10Bq/cell。然后，我们将追踪这些单个细胞在心肌梗死小鼠模型中心脏损伤部位的归巢情况。我们计划开发的重建算法是创新的，因为与以前的算法不同，它考虑了放射性只包含在移植细胞内的事实；因此，它以最佳方式使用所有可用的测量。这项研究具有重要意义，因为在全身水平上重建移植细胞的时空轨迹将提供关于活生物中细胞运输动力学的前所未有的信息，并可用于改进细胞移植方案，以实现更有效的细胞植入。

 DESCRIPTION: Regenerative therapies based on stem cell transplantation hold great clinical promise, particularly for patients with damaged hearts and end-stage heart failure. Imaging plays an important role in these therapies by tracking the fate of the transplanted cells. However, existing imaging methods can only visualize where large groups of transplanted cells accumulate and not how single cells arrive there. The limited capabilities of these imaging tools prevent us from fully understanding the fate and dynamic behavior of single transplanted cells. Improving the efficiency and functional outcomes of cell-based therapies is a long-term goal of cardiovascular research. Our objective in this proposal is to develop a new imaging approach that can follow single transplanted cells in real time as they home to sites of cardiac injury. Our hypothesis is that, under certain conditions, micro positron emission tomography (microPET) can track single transplanted cells in live mice, with sub-millimeter spatial resolution and sub-second time resolution. These capabilities of microPET have not been explored yet because previous studies have exclusively relied on conventional reconstruction algorithms to track radiolabelled cells. By leveraging the knowledge that only a sparse set of cells contain radioactivity, it is possible to formulate an algorithm for reconstruction single cell trajectories from microPET measurements with much higher sensitivity and spatial resolution. The rationale for the proposed research is that tracking single cells in vivo at the whole-body level will allow for far more detailed insight into the dynamic behavior and fate of transplanted cells and their interaction with injured heart tissue than conventional bulk-tissue techniques. Our preliminary simulations indicate that a single cell labeled with 1-10 Bq can be tracked with microPET in vivo. We will test our hypothesis by pursuing the following two aims: (1) Expand trajectory reconstruction to track multiple single cells in parallel; and (2) Optimize cell labeling and track single cells in vivo. In the first aim, we will implement a new reconstruction algorithm that takes raw list-mode data from a small-animal PET scanner and reconstructs spatiotemporal trajectories for multiple single cells, in parallel. In the second aim, we will optimize radionuclie labeling of bone-marrow mononuclear cells to achieve 10 Bq/cell. We will then track the homing of these single cells to sites of cardiac injury in a mouse model of myocardial infarction. The reconstruction algorithm we plan to develop is innovative because, unlike previous algorithms, it accounts for the fact that radioactivity is only contained within the transplanted cells; thus it ues all available measurements in an optimal way. The proposed research project is significant because reconstructing the spatiotemporal trajectory of transplanted cells at the whole-body level would provide unprecedented information on the dynamics of cell trafficking in living organisms and could be applied to improve cell transplantation protocols for more efficient cell engraftment.