Isogenic Cell Lines (in the context of the Hansen et al. paper)

**What it means:** Creating isogenic cell lines means taking one starting cell line and editing it so that one version has the mutation (MEF2C knockout) and the other doesn't (wild-type control). They're "identical twins" except for that one gene difference. **Why this is the gold standard:** In normal research, you'd compare MEF2C-deficient microglia from one person against healthy microglia from another person. But those people have thousands of genetic differences — you can't tell which differences cause the inflammation. With isogenic lines, the ONLY difference is MEF2C, so any differences you observe are definitely caused by MEF2C loss. This is why the Cell Immunity paper is considered so definitive.