Morel F, Szilvassy S J, Travis M, Chen B, Galy A
SyStemix Inc, Palo Alto, CA 94304, USA.
Blood. 1996 Nov 15;88(10):3774-84.
The CD34 antigen is expressed on most, if not all, human hematopoietic stem cells (HSCs) and hematopoietic progenitor cells, and its use for the enrichment of HSCs with repopulating potential is well established. However, despite homology between human and murine CD34, its expression on subsets of primitive murine hematopoietic cells has not been examined in full detail. To address this issue, we used a novel monoclonal antibody against murine CD34 (RAM34) to fractionate bone marrow (BM) cells that were then assayed in vitro and in vivo with respect to differing functional properties. A total of 4% to 17% of murine BM cells expressed CD34 at intermediate to high levels, representing a marked improvement over the resolution obtained with previously described polyclonal anti-CD34 antibodies. Sixty percent of CD34+ BM cells lacked lineage (Lin) markers expressed on mature lymphoid or myeloid cells. Eighty-five percent of Sca-1+Thy-1(10)Lin-/10 cells that are highly enriched in HSCs expressed intermediate, but not high, levels of CD34 antigen. The remainder of these phenotypically defined stem cells were CD34-. In vitro colony-forming cells, day-8 and -12 spleen colony-forming units (CFU-S), primitive progenitors able to differentiate into B lymphocytes in vitro or into T lymphocytes in SCID mice, and stem cells with radioprotective and competitive long-term repopulating activity were all markedly enriched in the CD34+ fraction after single-parameter cell sorting. In contrast, CD34-BM cells were depleted of such activities at the cell doses tested and were capable of only short-term B-cell production in vitro. The results indicate that a significant proportion of murine HSCs and multilineage progenitor cells express detectable levels of CD34, and that the RAM34 monoclonal antibody is a useful tool to subset primitive murine hematopoietic cells. These findings should facilitate more direct comparisons of the biology of CD34+ murine and human stem and progenitor cells.
CD34抗原在大多数（即便不是全部）人类造血干细胞（HSC）和造血祖细胞上表达，并且其用于富集具有重建造血潜力的HSC已得到充分证实。然而，尽管人类和小鼠的CD34存在同源性，但尚未对其在原始小鼠造血细胞亚群上的表达进行全面详细的研究。为了解决这个问题，我们使用了一种针对小鼠CD34的新型单克隆抗体（RAM34）对骨髓（BM）细胞进行分馏，然后针对不同的功能特性在体外和体内进行检测。总共4%至17%的小鼠BM细胞以中等至高表达水平表达CD34，相较于先前描述的多克隆抗CD34抗体所获得的分辨率有显著提高。60%的CD34⁺ BM细胞缺乏在成熟淋巴细胞或髓细胞上表达的谱系（Lin）标志物。在高度富集HSC的Sca-1⁺Thy-1(10)Lin⁻/10细胞中，85%表达中等水平而非高水平的CD34抗原。这些表型定义的干细胞的其余部分为CD34⁻。在单参数细胞分选后，体外集落形成细胞、第8天和第12天的脾集落形成单位（CFU-S）、能够在体外分化为B淋巴细胞或在SCID小鼠中分化为T淋巴细胞的原始祖细胞以及具有辐射防护和竞争性长期重建造血活性的干细胞在CD34⁺组分中均显著富集。相比之下，在测试的细胞剂量下，CD34⁻ BM细胞缺乏这些活性，并且仅能在体外进行短期B细胞生成。结果表明，相当一部分小鼠HSC和多谱系祖细胞表达可检测水平的CD34，并且RAM34单克隆抗体是对原始小鼠造血细胞进行亚群分析的有用工具。这些发现应有助于更直接地比较CD34⁺小鼠和人类干细胞及祖细胞的生物学特性。
