A method of delivering a gene product to a recipient, the method comprises (a) providing a micro-organ explant expressing at least one recombinant gene product, the micro-organ explant comprising a population of cells, the micro-organ explant maintaining a microarchitecture and a three dimensional structure of an organ from which it is obtained and at the same time having dimensions selected so as to allow diffusion of adequate nutrients and gases to cells in the micro-organ explant and diffusion of cellular waste out of the micro-organ explant so as to minimize cellular toxicity and concomitant death due to insufficient nutrition and accumulation of the waste in the micro-organ explant, at least some of the cells of the population of cells of the micro-organ explant expressing at least one recombinant gene product; and (b) implanting the micro-organ explant in the recipient.