PROJECT SUMMARY (APOE U19 Core E: Human iPSC Models Core) Human somatic and stem cell models have emerged as a powerful system for modeling the complexities of pathological gene expression, particularly in the early phase of disease. Further, human stem cells can be differentiated into cell-types that secrete apoE and that are affected in disease, such as neurons, astrocytes, microglia, and vascular mural cells (VMCs), as well as 3D “mini-brain” cerebral organoids. The Core E will build upon the existing resources and technology from three institutions at the forefront of stem cell modeling of apoE-related biology and pathobiology in AD: MCJ (Guojun Bu), WUSTL (Celeste Karch), and ISMMS (Julia TCW) to generate a comprehensive collection of well-characterized human iPSC lines with different APOE genotypes from deeply phenotyped patients and through isogenic conversions. The established iPSC lines with different APOE genotypes, sex, ethnicity, and disease status will serve both this U19 and the broader scientific community to address critical gaps in our knowledge of the effects of apoE isoforms in different human brain cell types. In so doing, Core E will support U19 Projects and the broader scientific community by testing a critical component of the ApoE Cascade Hypothesis (ACH): to understand the effects of apoE isoforms on biochemical and cellular events leading to eventual phenotypic outcomes. Thus, Core E will work synergistically with Core A, B, F, G and Projects 1-5 to address the ACH hypothesis and to become an invaluable resource for the broader scientific community.