《自然—免疫学》上的一篇报告介绍了在人体骨髓中发现的一类独特细胞群。该细胞群可以表达L-选择素，该表达过程是已知的特定种类白细胞产生的最早阶段。该细胞群的发现将有助我们了解正常血细胞的发育并可能找到在引起各类白血病的细胞不稳定发育中的重要线索。
Gay Crooks等人通过人体干细胞/祖细胞移植手段让免疫缺陷小鼠发育出血细胞，然后对比观察人体骨髓细胞在该小鼠体内和培养皿中的发育情况。他们发现骨髓细胞中产生了一种L-选择素阳性细胞群，该细胞群属于一种发育中间物，介于静止造血干细胞和一种之前发现的可促使产生抗体B细胞形成的细胞群之间。虽然该选择素细胞群缺少制造血红细胞和血小板的功能，但其可以产生各种白细胞，包括T细胞和自然杀伤细胞。
重要的是，骨髓中这种新发现的细胞群与在新生儿脐带血中发现的始祖细胞是不同的。虽然脐带血细胞更容易获取并具有高度增殖特性，但其在发育能力方面有更多限制，而新发现的骨髓细胞则更具有普适性。（生物谷Bioon.com）
doi:10.1038/ni.2405
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Lymphoid priming in human bone marrow begins before expression of CD10 with upregulation of L-selectin
Kohn LA, Hao QL, Sasidharan R, Parekh C, Ge S, Zhu Y, Mikkola HK, Crooks GM.
Expression of the cell-surface antigen CD10 has long been used to define the lymphoid commitment of human cells. Here we report a unique lymphoid-primed population in human bone marrow that was generated from hematopoietic stem cells (HSCs) before onset of the expression of CD10 and commitment to the B cell lineage. We identified this subset by high expression of the homing molecule L-selectin (CD62L). CD10(-)CD62L(hi) progenitors had full lymphoid and monocytic potential but lacked erythroid potential. Gene-expression profiling placed the CD10(-)CD62L(hi) population at an intermediate stage of differentiation between HSCs and lineage-negative (Lin(-)) CD34(+)CD10(+) progenitors. CD62L was expressed on immature thymocytes, and its ligands were expressed at the cortico-medullary junction of the thymus, which suggested a possible role for this molecule in homing to the thymus. Our studies identify the earliest stage of lymphoid priming in human bone marrow
