CD34‐positive early human thymocytes: T cell receptor and cytokine receptor gene expression

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Abstract
CD34, a stem cell marker, has been shown to be expressed on human CD3−CD4−CD8− (triple‐negative; TN) thymocytes. Phenotypic and functional analyses suggest the following differentiation sequence: CD34+ 1−3−4−8− → CD34+ 1+3−4→8− → CD34−1++3−4+8 → CD34−1++3−4+8+. In this report, we examined cytokine receptor gene expression on these subsets by reverse transcription‐polymerase chain reaction analysis (RT‐PCR). We were able to detect interleukin‐7 receptor (IL‐7R), c‐kit and IL‐2Rγ in all CD34+ thymocyte subsets, consistent with previous functional studies. We found IL‐1R, granulocyte/macrophage colony‐stimulating factor receptor‐α and IL‐4R transcripts in CD3− and CD34+ subsets. Secondly, we investigated T cell receptor (TCR)‐δ and ‐β gene rearrangement and transcription in CD34+ thymocytes. Our results show that a full‐length TCR‐δ transcript and the recombination activating genes RAG‐1 and RAG‐2 mRNA were already expressed in the CD34+1− subset. Mature Vβ‐containing TCR transcripts were also detected in the CD34+ 1+ subset, but not in the CD1− fraction. Furthermore, PCR analysis of D‐Jβ gene rearrangements showed that ≥ 70% of CD34+ 1− cells are in a TCRβ germ‐line configuration, although D‐Jβ recombination had already started in this population.