Transgene integration in mammalian cells: The tools, the challenges, and the future

Robust and stable expression of genes of interest is crucial for studying and engineering biology. While expressing desired gene products in some microorganisms is well established, achieving stable expression in mammalian systems is still a complex task. Over the years, various methods have been developed to integrate transgenes into mammalian cells, including the use of viral vectors, transposases, nucleases, and recombinases. This review aims to provide an overview of some of the commonly used integration strategies in mammalian cells, with a particular focus on methods toward site-specific integration, highlighting respective advantages and limitations and providing a summary of recent advances. Additionally, it also explores some of the challenges in the field, offering insights into potential directions for future development.