Identification of a novel population of human cord blood cells with hematopoietic and chondrocytic potential
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With the exception of mature erythrocytes, cells within the human hematopoietic system are characterized by the cell surface expression of the pan-leukocyte receptor CD45. Here, we identify a novel subset among mononuclear cord blood cells depleted of lineage commitment markers (Lin-) that are devoid of CD45 expression. Surprisingly, functional examination of Lin-CD45- cells also lacking cell surface CD34 revealed they were capable of multipotential hematopoietic progenitor capacity. Co-culture with mouse embryonic limb bud cells demonstrated that Lin-CD45-CD34- cells were capable of contributing to cartilage nodules and differentiating into human chondrocytes. BMP-4, a mesodermal factor known to promote chondrogenesis, significantly augmented Lin-CD45-CD34- differentiation into chondrocytes. Moreover, unlike CD34+ human hematopoietic stem cells, Lin-CD45-CD34- cells were unable to proliferate or survive in liquid cultures, whereas single Lin-CD45-CD34- cells were able to chimerize the inner cell mass (ICM) of murine blastocysts and proliferate in this embryonic environment. Our study identifies a novel population of Lin-CD45-CD34- cells capable of commitment into both hematopoietic and chondrocytic lineages, suggesting that human cord blood may provide a more ubiquitous source of tissue with broader developmental potential than previously appreciated.