实验表明：T细胞发育过程比想象得要“灵活”

T细胞和其它所有类型的血细胞均来源于骨髓中的造血干细胞（HSCs）。造血干细胞具有分化成血液中各种各样细胞的能力，分化的*步则是转变成多能祖细胞（MPPs）。
关于接下来的分化过程，广为接受的理论是存在两条分化路径。一条称为骨髓路径，即MPPs转变成红细胞和非淋巴白细胞的“”；另一条称为淋巴路径，即MPPs转变成T细胞和B细胞的“”。而T细胞的接着会进入胸腺，在这里它们被称作早胸腺祖细胞（ETPs）。
论文作者、宾夕法尼亚大学病理学教授Avinash Bhandoola表示：“如果目前关于T细胞发育的模型是正确的，那么ETPs就应该只能产生T细胞，而不能产生骨髓细胞（myeloid cells）。”
研究人员对此进行了验证。他们首先应用表面标签将小鼠胸腺里的ETPs与其它细胞分开，然后将每个ETP细胞进行单独培养，以观察它们的分化情况。
结果令人吃惊。大多数盛有单个ETP细胞的培养皿都充满了T细胞和骨髓细胞。这意味着大部分ETPs在进入胸腺后并不于转变成T细胞，它们仍然保留着在T细胞和骨髓细胞间二选一的能力。接下来研究人员证实了，在正常的胸腺中，ETPs确实会产生骨髓细胞。Bhandoola说：“很难将观测结果与过去我们对T细胞发育的看法协调起来。”
论文*作者、宾夕法尼亚大学博士后Jeremiah Bell说：“弄清T细胞的生活史及确定MPPs转变成T细胞的步骤极为重要。现在我们想要弄清的是，ETPs怎样作出决定，以转变成骨髓细胞或T细胞。虽然我们的研究着重于基本科学，但它有助于弄清早期祖细胞怎样导致T细胞性白血病。另外，胸腺中由ETPs产生的骨髓细胞也将引起我们的进一步关注。”（科学网 梅进/编译）
（Nature），452, 764-767，J. Jeremiah Bell，Avinash Bhandoola
The earliest thymic progenitors for T cells possess myeloid lineage potential
J. Jeremiah Bell1 & Avinash Bhandoola1
Department of Pathology and Laboratory Medicine, University of Pennsylvania School of Medicine, Philadelphia, Pennsylvania 19104, USA
Correspondence to: Avinash Bhandoola1 Correspondence and requests for materials should be addressed to A.B. (: bhandooa@mail.med.upenn.edu).
There exists controversy over the nature of haematopoietic progenitors of T cells. Most T cells develop in the thymus, but the lineage potential of thymus-colonizing progenitors is unknown. One approach to resolving this question is to determine the lineage potentials of the earliest thymic progenitors (ETPs). Previous work has shown that ETPs possess T and natural killer lymphoid potentials, and rare subsets of ETPs also possess B lymphoid potential1, suggesting an origin from lymphoid-restricted progenitor cells. However, whether ETPs also possess myeloid potential is unknown. Here we show that nearly all ETPs in adult mice possess both T and myeloid potential in clonal assays. The existence of progenitors possessing T and myeloid potential within the thymus is incompatible with the current dominant model of haematopoiesis, in which T cells are proposed to arise from lymphoid-2. Our results indicate that alternative models for lineage commitment during haematopoiesis must be considered.