Characterization of long-term endogenous cardiac repair in children after heart transplantation

Aims Circulating cells repopulate the heart at a very low rate in adult humans. The knowledge about time-dependent cardiac regeneration is very limited and the contribution of circulating cells to cardiomyocytes or vascular cells in children is unknown. This study investigates the endogenous repair capacity and the long-term incorporation of circulating cells in heart-transplanted children. Methods and results Cardiac and endothelial chimerism was detected in endomyocardial biopsies of nine children (age 1 months-14 years) with sex-mismatched heart transplantation by fluorescence in situ hybridization. Time from transplantation to biopsy ranged from 1 month up to 10 years. The extent of repopulating cardiomyocytes was 2.39 +/- 1.54% (range: 0-4.2%) and correlated significantly with the time from transplantation to biopsy sampling (r(2) = 0.69, P = 0.006; n = 9). The calculated contribution of male cardiomyocytes in the female heart per year was 0.36 +/- 0.09%. Consistent with the previous reports, the incorporation of vascular cells was higher compared with cardiomyocytes (14.4 +/- 4.17%), but did not correlate in a time-dependent manner. Conclusion Circulating cells contribute to cardiomyocytes and endothelial cells in children after heart transplantation. The incidence of repopulating cardiomyocytes continuously increases in a time-dependent manner (similar to 4% Y- chromosome(+) cardiomyocytes/10 years) and resembles the cardiac regeneration activity observed in adults.