Abstract: Embodiments of the disclosure encompass systems, methods, and compositions related to selective advantages to somatic cells that harbor one or more particular genetic modifications. In particular embodiments, there is selective expansion of gene-targeted cells wherein the strategy involves deletion of an essential gene product that is replaced with targeted integration that also includes integration of a therapeutic transgene. The cells that harbor the replaced essential gene product, and thereby the therapeutic transgene, are selected for using pharmaceutical or nutritional agents that are linked to the function of the essential gene product.