Ex vivo and in vivo methods of expanding a population of stem and/or progenitor cells, while at the same time reversibly inhibiting differentiation of the stem and/or progenitor cells by providing the stem and/or progenitor cells with an effective amount of at least one copper chelate, so as to maintain a free copper concentration available to said cells substantially unchanged, to thereby expand the population of said stem and/or progenitor cells, while at the same time reversibly inhibit differentiation of said stem and/or progenitor cells.