The permissiveness of thymic stroma for NK development

F. Vaz, E. Srour, G. A-Porada, J. L. Ascensao

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We set u a system in vitro to analyze NK and T cell development from human bone marrow (BM) progenitors over thymic stromas. CD34+LU1- progenitors were plated onto irradiated thymic stromal layers from human (16-28 weeks) or sheep (54-72 days) fetal thymus. In parallel experiments progenitors were separated from stromas by a Transwell membrane. The culture media was supplemented with human AB serum with or without 1L2 (1,000 U/ml) and IL7 (1,000 U/ml). The cellular composition of thymic stromas as analyzed by immunochemistry was similar: 20% of cells were positive for cytokeratin and 80% oi cells reacted with vimentin, fibronectin, cc-smooth muscle and were negative tor factor VIII. By RT-PCR, no mRNA for y-INF,ILl, G-CSF.GMCSF.1L10 or 1L7 was detected. After three weeks of culture CD45/56, CD3.CD4 and CDS cells were detected by flow cytometry. The development of CD45/56 positive cells was observed in all assays. With allogeneic stromas NK growth was higher in Transwell cultures supplemented with II.2 : 43.1%±14.2% (sroma-contact) versus 51% (Transwell) from CD34+LU1- and 23.0%±21.4% (stroma-contact) versus 60.8%±12.5% (Transwell) from CD34+Lin-DR+ cells. Only IL2 grown cells were cytotoxic against K562 targets. In xenogeneic experiments NK growth was also higher in cultures supplemented with IL2 and this difference was significant for CD34+Linprogenitors when compared to control (69.0% ±6.9% versus 9.5%± 9.2%, p<0.05). T cell growth was negligible over sheep stromas. On human stromas T cells grew better from CD34+DR+ progenitors in IL7 (31.5%) and control cultures (15.9%). We conclude that human CD56 cells can be generated from BM progenitors cultured over allogeneic and xenogeneic fetal thymic stromas in vitro, independently of IL2. Lyrically active effectors are obtained only in the presence of this cytokine. In the allogeneic setting IL2 favors NK development in the absence of stromal contact which indicates a direct inhibitory effect of human thymic srroma on NK progenitors; this effect was not observed in the xenogeneic experiments. T cells grew in small numbers only over human stromas, whitout the need for cytokines. This may be due to Uie insufficient content in epithelial cells of both stromas which would explain the growth Hvjmfrftge of NK cells in this system.

Original languageEnglish (US)
Number of pages1
JournalExperimental Hematology
Issue number8
StatePublished - Dec 1 1997
Externally publishedYes

ASJC Scopus subject areas

  • Molecular Biology
  • Hematology
  • Genetics
  • Cell Biology
  • Cancer Research

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