Clonal analysis of CD4 CD8‐ human thymocytes expressing a T cell receptor γ/δ chain. Direct evidence for the de novo expression of CD8 surface antigen and of cytolytic activity against tumor targets*

摘要

AbstractCD4−CD8−human thymocytes were obtained by treating total thymocyte suspensions with antiCD4 and anti‐CD8 monoclonal antibodies (mAb) and complement. The resulting cell populations contained virtually no CD4+, CD8+or WT31+cells and 17–65% CD3+cells. In addition, analysis of cell reactivity with delta‐TCS‐1 mAb (specific for the Cγ2‐encoded, nondisulfide‐linked form of TcR γ/δ), revealed the presence of a variable proportion of δ‐TCS‐1+cells (the % of δ‐TCS‐1+cells were lower than the percentage of CD3+cells). Upon culture in recombinant interleukin 2 (IL2, in the presence of irradiated mononuclear cells), CD4−CD8−thymocytes underwent extensive proliferation. In addition, a progressive increase of CD8+cells (but not of CD4+or WT31+cells) could be detected. Cells also progressively acquired cytolytic activity against K‐562 or fresh melanoma cells. Fresh CD4−CD8−thymocytes were cloned under limiting dilution conditions. The cloning efficiencies were relatively high (1/3 cells); in addition, virtually all the clonal progenies obtained displayed cytolytic activity and expressed the CD3+WT31−δ‐TCS‐1+surface phenotype. About half of the clones analyzed were CD8+, whereas none expressed CD4 antigens. We conclude that (a) only δ‐TCS‐l‐reactive, TcRγ/δ+cells can be isolated from CD4−CD8−thymocytes cultured in IL2, and (b) the expression of CD8 antigen and of cytolytic activity reflects a truein vitrophenotypic change of CDK, noncytolytic precursors (a