Lebanese American University 1 article published in JoVE Developmental Biology Genetic Engineering of Primary Mouse Intestinal Organoids Using Magnetic Nanoparticle Transduction Viral Vectors for Frozen Sectioning Lingling Xian1, Lionel Chia1,5, Dan Georgess2, Li Luo1, Shuai Shuai1, Andrew J. Ewald3,4, Linda M.S. Resar1,4,5,6 1Department of Medicine, Division of Hematology, Johns Hopkins University School of Medicine, 2Department of Natural Sciences, School of Arts & Sciences, Lebanese American University, 3Department of Cell Biology, Johns Hopkins University School of Medicine, 4Department of Oncology, Johns Hopkins University School of Medicine, 5Department of Pathology, Johns Hopkins University School of Medicine, 6Institute for Cell Engineering, Johns Hopkins University School of Medicine We describe step-by-step instructions to: 1) efficiently engineer intestinal organoids using magnetic nanoparticles for lenti- or retroviral transduction, and, 2) generate frozen sections from engineered organoids. This approach provides a powerful tool to efficiently alter gene expression in organoids for investigation of downstream effects.