Askenasy Nadir, Zorina Tatiana, Farkas Daniel L, Shalit Itamar
Center for Light Microscope Imaging and Biotechnology, Carnegie Mellon University, Pittsburgh, Pennsylvania, USA.
Stem Cells. 2002;20(4):301-10. doi: 10.1634/stemcells.20-4-301.
The process of hematopoietic stem and progenitor cell (HSPC) seeding in recipient bone marrow (BM) early after transplantation is not fully characterized. In vivo tracking of HSPCs, labeled with PKH dyes, through an optical window surgically implanted on the mouse femur revealed that transplanted cells cluster in the recipient BM. Within the first day after intravenous injection, 86 +/- 6% of the cells seeded in clusters (p < 0.001 versus scattered cells) in the endosteal surfaces of the epiphyses. The primary clusters were formed by concomitant seeding of 6-10 cells over an area of approximately 70 microm, and secondarily injected cells did not join the already existing clusters but formed new clusters. Major antigen-disparate HSPCs participated in formation of the primary clusters, and T lymphocytes were also incorporated. After 4 to 5 days, some cellular clusters were observed in the more central regions of the BM, where the brightness of PKH fluorescence decreased, indicating cellular division. These later clusters were classified as secondary, assuming that the mechanisms of migration in the BM might be different from those of primary seeding. Some clusters remained in the periphery of the BM and retained bright fluorescence, indicating cellular quiescence. The number of brightly fluorescent cells in the clusters decreased exponentially to two to three cells after 24 days (p < 0.001). The data suggest that the hematopoietic niche is a functional unit of the BM stromal microenvironment that hosts seeding of a number of transplanted cells, which form a cluster. This may be the site where auxiliary non-HSPC cells, such as T lymphocytes, act in support of HSPC engraftment.
造血干细胞和祖细胞（HSPC）在移植后早期植入受体骨髓（BM）的过程尚未完全明确。通过手术植入小鼠股骨上的光学窗口，对用PKH染料标记的HSPC进行体内追踪，发现移植细胞在受体BM中聚集。静脉注射后的第一天内，86±6%的细胞在骨骺骨内膜表面呈簇状植入（与散在细胞相比，p<0.001）。初级簇是由6-10个细胞在约70微米的区域内同时植入形成的，二次注射的细胞不加入已有的簇，而是形成新的簇。主要抗原不相合的HSPC参与了初级簇的形成，T淋巴细胞也被纳入其中。4至5天后，在BM的更中心区域观察到一些细胞簇，其中PKH荧光亮度降低，表明细胞分裂。假设BM中的迁移机制可能与初级植入不同，这些后来的簇被归类为次级簇。一些簇留在BM的外围并保留明亮的荧光，表明细胞静止。24天后，簇中明亮荧光细胞的数量呈指数下降至2至3个细胞（p<0.001）。数据表明，造血龛是BM基质微环境的一个功能单位，容纳许多移植细胞的植入，这些细胞形成一个簇。这可能是辅助性非HSPC细胞（如T淋巴细胞）支持HSPC植入的部位。
