Telomerase gene therapy leads to telomere elongation in peripheral blood and bone marrow cells from mice with specific deletion of Tert in the bone marrow. (A) Longitudinal HT-Q-FISH analysis of telomere length in PBMCs of irradiated wild-type mice transplanted with bone marrow from G3 Tert^−/− mice (see also Figure 4A). Blood was extracted at 3 different time points (time point 1, after G3 Tert^−/− bone marrow engraftment and before AAV9 injection; time point 2, 3 months after AAV9 injection; and time point 3, 5 months after AAV9 injection). (B) Relative variation (Δ) of telomere length in AAV9-Tert-treated and AAV9-empty-treated animals between time points 1 and 3. (C) Telomere Q-FISH analysis on bone marrow sections from animals transplanted with G3 Tert^−/− bone marrow and treated with AAV9-empty or AAV9-Tert for 5 months before euthanasia. Each square or triangle represents the mean telomere length per nucleus (expressed as arbitrary units of fluorescence) of an individual mouse. (D) Representative images of bone marrow sections from AAV9-Tert-treated and AAV9-empty-treated mice used for Q-FISH analysis. Cell nuclei are stained blue (DAPI) and telomeres are stained red (Cy3). White arrowheads indicate nonspecific extranuclear signals and yellow arrowheads indicate specific telomere signals within DAPI-stained nuclei. Bars represent 10 μm. For all experiments, n indicates number of mice. Data are mean ± SEM. Statistical analysis: 2-way analysis of variance in panel A; 2-sided Student t test in panels B and C; P values are shown.