Lengths of telomeric sequences in neonatal granulocytes and CD4⁺ T cells. Granulocytes and CD4⁺ T cells were purified from fresh cord blood samples. DNA was isolated, and the lengths of telomeres were determined by hybridization with a telomere repeat-specific probe. Median TRF lengths from each cell population are shown in correlation to the gestational age of the neonate. TRF lengths in granulocytes (filled circles) were stable throughout the third trimester. Although granulocytes and T cells derive from the same hematopoietic precursor cells, telomeric ends in CD4⁺ T cells (open circles) were elongated by 1500 to 2000 bp.