Cardiomyocytes of Noncardiac Origin in Myocardial Biopsies of Human Transplanted Hearts

Background— Cell replacement therapy with stem cells able to differentiate into cardiomyocytes has been discussed as a method for remodeling damaged myocardium. A physiological or pathophysiological situation in which this phenomenon might be relevant is not known. We studied the origin of cardiomyocytes in myocardial biopsies of male patients that had undergone sex-mismatched cardiac transplantation to determine whether cells containing a Y chromosome (and therefore being of recipient origin) are able to differentiate into cardiomyocytes. Methods and Results— Myocardial biopsies (n=21) were obtained from the right ventricles of male patients (n=13) who had undergone sex-mismatched heart transplantation. Tissue from 1 nontransplanted male and myocardial biopsies from sex-matched heart–transplanted patients served as controls. Cells from donor and recipient origins were identified by fluorescence in situ hybridization with the use of specific probes for X and Y chromosomes on paraffin sections of the biops...