Characterization of ‘adult‐type’ mast cells derived from human bone marrow CD34+ cells cultured in the presence of stem cell factor and interleukin‐6. Interleukin‐4 is not required for constitutive expression of CD54, FcεRIα and chymase, and CD13 expression is reduced during differentiation

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Abstract
Background In vitro‐derived human mast cells exhibit different properties, depending in part on the source of progenitor cells. Most investigations have used fetal liver, cord blood or peripheral blood. Few have used adult bone marrow. Objective Human mast cells derived in vitro from the CD34+ progenitors in bone marrow and cord blood that had been cultured with recombinant human stem cell factor (rhSCF) and recombinant human interleukin‐6 (rhIL‐6) were compared. Methods and results After 12 weeks of culture, nearly all of the cells were mast cells, and nearly all of these had cytoplasmic granules containing both tryptase and chymase (MCTC type), stained metachromatically with acidic toluidine blue, and expressed CD117 on the cell surface. Both tryptase protein and mRNA were detected by two weeks of culture. Chymase mRNA and protein were detected at 4 weeks but not at 2 weeks of culture. By 12 weeks, chymase content per cell, measured by ELISA, was significantly higher (P < 0.05) in human bone marrow‐derived mast cells (HBMMC) (5.6 ± 0.9 pg) than in cord blood‐derived mast cells (CBMC) (2.4 ± 0.9 pg), whereas histamine and tryptase levels were not significantly different. Of the cluster designations tested, CD29, CD49d, CD51 and CD61 were strongly expressed on HBMMC. CD54 and FcεRIα also were expressed constitutively. Approximately half of CD34‐sorted cells at day 0 were CD13+ and this diminished as mast cell maturation occurred. Electron microscopy revealed that 12‐week‐old HBMMC had many secretory granules that contained spherical electron dense cores surrounded by electron lucent space, consistent with previous reports of immature MCTC cells developing in vivo. Conclusions CD34+ progenitors of human bone marrow are a rich source of mast cell progenitors capable of expressing granule and surface markers of mature mast cells in the presence of rhSCF and rhIL‐6.