The present application relates to methods and compositions for the generation of therapeutic cells having reduced incidence of karyotypic abnormalities. In several embodiments cardiac stem cells are cultured in an antioxidant-supplemented media that reduces levels of reactive oxygen species, but does not down regulate DNA repair mechanisms. In several embodiments, physiological oxygen concentrations are used during culture in order to increase the proliferation of stem cells, decrease the senescence of the cells, decrease genomic instability, and/or augment the functionality of such cells for cellular therapies.