Spontaneous expression of telomerase activity in neonatal T cells. Lymphocytes from adult blood and cord blood were assayed for telomerase activity. Representative results from 3 adults and one cord blood sample are shown (A). CD4⁺ and CD8⁺ T cells obtained from cord blood were purified and tested for telomerase activity (B). Telomerase activity was assayed with (+) and without (–) heat inactivation. Results are representative of 8 experiments. A positive (HeLa cells, Pos) and a negative (N) control and an assay control (C) were included in all assays.