No age-related telomere length reduction was observed in HMEC strains. (A) A linear regression comparing Flow-FISH measured RTL values with mean TRF values in a well characterized pre-stasis strain and an immortal derivative with critically short telomeres, n = 6, r2 = 0.7612, P < 0.0001. (B) A linear regression of RTL measurements in 41 different passage 4 strains of normal pre-stasis HMEC as a function of age in years, r2 = 0.0005126, P = 0.8883. (C) A linear regression of RTL measurements in HMEC strains at passage 4 as a function total PD starting from passage 2, before the strains eventually entered stasis, n = 41, r2 = 0.08262, P = 0.1380. (D) Linear regressions comparing RTL measurements with proportions of (left) CD227+/CD10- LEP (n = 41, r2 = 0.0005, P = 0.8935), (middle) CD227-/CD10+ MEP (n = 41, r2 = 0.0623, P = 0.1307), and (right) CD117/cKit+ HMEC (n = 41, r2 = 0.0018, P = 0.7962).