DN-hTERT–transduced cells show chromosomal abnormalities. Q-FISH analysis of metaphase chromosomes isolated from human CD4⁺ T cells that have undergone approximately 45 PD and were transduced with DN-hTERT (Asp868Ala, Asp869Ala)–GFP or hTERT-GFP at approximately 24 PD. Telomeres are visualized in yellow by hybridization with the Cy-3–labeled (CCCTAA)₃ PNA probe. The arrow indicates a dicentric chromosome found in DN-hTERT (Asp868Ala, Asp869Ala)–GFP–transduced cells. Results are representative of 16 metaphases of DN-hTERT–transduced cells and 20 metaphases of hTERT-transduced cells analyzed.