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ObjectiveWe sought to define the intrinsic stem cell capacity in pediatric heart lesions, and the effects of diagnosis and of age, in order to inform evidence-based use of potential autologous stem cell sources for regenerative medicine therapy.MethodsVentricular explants derived from patients with hypoplastic left heart syndrome (HLHS), tetralogy of Fallot (TF), dilated cardiomyopathy (DCM) and ventricular septal defect (VSD) were analyzed following standard in vitro culture conditions, which yielded cardiospheres (C-spheres), indicative of endogenous stem cell capacity. C-sphere counts generated per 5 mm3 tissue explant and the presence of cardiac progenitor cells were correlated to patient age, diagnosis and echocardiographic function.ResultsCardiac explants from patients less than one year of age with TF and DCM robustly generated c-kit- and/or vimentin-positive cardiac mesenchymal cells (CMCs), populating spontaneously forming C-spheres. Beyond one year of age, there was a marked reduction or absence of cardiac explant-derivable cardiac stem cell content in patients with TF, VSD and DCM. Stem cell content in HLHS and DCM strongly correlated to the echocardiographic function in the corresponding ventricular chamber, with better echocardiographic function correlating to a more robust regenerative cellular content.ConclusionsWe conclude that autologous cardiomyogenic potential in pediatric heart lesions is robust during the first year of life and uniformly declines thereafter. Depletion of stem cell content occurs at an earlier age in HLHS with the onset of ventricular failure in a chamber-specific pattern that correlates directly to ventricular dysfunction. These data suggest that regenerative therapies using autologous cellular sources should be implemented in the neonatal period before the potentially rapid onset of single ventricle failure in HLHS or the evolution of biventricular failure in DCM.

BACKGROUND Patients with blood, immune, or metabolic diseases may require a stem cell transplant as part of their treatment. However, 70% of patients do not have a suitable human leukocyte antigen match in their family, and need an unrelated donor. Individuals can register as potential donors at stem cell drives, where they provide consent and a tissue sample for human leukocyte antigen typing. The ideal donors are young, male, and from a diversity of ethnic backgrounds. However, in Canada, non‐Caucasian males ages 17 to 35 years represent only 8.8% of listed donors. STUDY DESIGN AND METHODS The Stem Cell Club is a non‐profit organization founded in 2011 in Canada that aims to augment recruitment of the most needed donors. The initiative published a recruitment toolkit online (http://www.stemcellclub.ca). Currently, there are 12 chapters at universities across Canada. RESULTS To date, the Stem Cell Club has recruited 6585 potential registrants, representing 1.63% of donors on Canada's donor‐database. Of the recruited registrants, 58.3% were male; 60.3% of males self‐reported as non‐Caucasian, and 78.5% were ages 17 to 25 years. From 2015 to 2016, the initiative recruited 13.7% of all ethnically diverse males ages 17 to 35 years listed in Canada's donor database. Data from this initiative demonstrate sustainability and performance on key indicators of stem cell drive quality. CONCLUSION The Stem Cell Club has developed a capacity to recruit 2600 donors annually, with the majority being males with a high degree of ethnic diversity. The initiative enhances the quality of Canada's unrelated donor‐database, improving the chances that patients in need of an unrelated donor will find a match for transplant. The Stem Cell Club is a model relevant to recruitment organizations around the world.