Presence of CD8α‐CD8β‐positive TcR γ/δ thymocytes in the fetal murine thymus and their in vitro expansion with interleukin‐7

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Abstract
Several groups have described that a low percentage of in vitro cultured T cell receptor (TcR) γ/δ cells express CD8. Contrary to TcR α/β cells, however, CD8 on these TcR γ/δ cells was shown to be a CD8α homodimer. We describe here that addition of interleukin-7 (IL-7) to a short-term in vitro culture of fetal day 14 thymic lobes in an organ culture system or of fetal day 18 fetal thymocytes in cell suspension yields CD8β-positive TcR γ/δ cells. This is not the result of IL-7-induced expression of CD8β on previously CD8β-negative cells. It is due to IL-7-induced expansion of CD8α-CD8β-positive TcR γ/δ cells which are shown to be present in the starting fetal thymocyte cell population.