Establishment of a reverse genetics system for studying human immune functions in mice.

Reverse genetics approaches in mice are widely used to understand gene functions and their aberrations in diseases. However, limitations exist in translating findings from animal models to human physiology. Humanized mice provide a powerful bridge to understanding human physiology and mechanisms of disease pathogenesis while maintaining the feasibility of working with small animals. Methods for generating humanized mouse models that allow scientists to probe contributions of particular genes have been rudimentary. Here, we established an efficient method for generating genetically modified human cord blood-derived CD34(+) cells for transplantation, resulting in humanized mice with near-complete loss of specific gene expression by the human immune system. Mice transplanted with Cas9-edited human CD34(+) cells recapitulate functional consequences of specific gene losses in the human immune system. Our approach enables targeted gene knockouts in humanized mice, offering a valuable tool for human gene function studies in vivo.