TREC copy number and telomere length in different T-cell subsets. (A) Purity of purified CD4⁺ cells, CD8⁺ cells, and CD4⁺CD8⁺ cells after magnetic bead separation. (B) TREC copy number was determined by real-time PCR in each subpopulation and found to be lower in CD4⁺CD8⁺ (DP) than in CD4⁺ and CD8⁺ cell populations. (C) Telomere length was determined by Southern blot in each subpopulation. Arrows indicate long telomeres for CD4⁺ and CD8⁺ cells and short telomeres for the CD4⁺CD8⁺ population.