CD3 delta and epsilon gene expression in CD3-CD16+ natural killer cell clones derived from thymic precursors

To better understand the maturational stages during T-cell development, we studied the expression of CD3 delta and CD3 epsilon genes, as well as the presence of TCR gene rearrangements, within CD3-CD16+ NK clones derived from thymic precursors in vitro. Northern blot analysis revealed that CD3-CD16+ clones derived from CD7+CD3-CD4-CD8- (TN) thymocytes expressed transcripts for the CD3 epsilon gene; however, no transcripts for the CD3 delta gene were detected. Importantly, both the CD3 epsilon and CD3 delta genes were expressed in TN thymocytes examined prior to cloning. A CD7+CD8+CD3-CD4- thymocyte population that makes up only 0.4% of the total thymocyte pool was also isolated from human thymus. We determined the maturation potential of this CD7+CD8+CD3-CD4- population by limiting dilution cloning and found that 67% of the clones generated in vitro had a CD3-CD16+CD8+ phenotype. In contrast to the NK clones derived from TN precursors, most CD3-CD16+ clones derived from CD7+CD8+CD3-CD4- thymocytes expressed transcripts for both CD3 epsilon and CD3 delta genes. Southern blot analysis of the NK clones derived from either thymic precursor population revealed no rearrangement of the TCR beta or gamma genes. These results demonstrate that the TN progenitor population and their CD3-CD16+ progeny differ in their expression of the CD3 delta transcript and during in vitro culture there is loss of CD3 delta expression and acquisition of surface CD16 within these NK clones. Furthermore, the CD3-CD16+ clones derived from TN versus CD7+CD8+CD3-CD4- thymocytes differed in their expression of the CD3 delta gene. The signaling events regulating the expression of the CD3 invariant chain genes within immature lymphoid progenitor cells may be important in determining their eventual maturation into T-cell and NK-cell lineages in vivo.