RAB11FIP5 (RAB11 family interacting protein 5) is a RAB11 effector protein that regulates endosomal trafficking and recycling pathways. The protein functions as a component of the FERARI tethering platform, coordinating membrane fusion and fission activities at sorting endosomes to facilitate cargo recycling to the plasma membrane 1. RAB11FIP5 plays critical roles in cellular transport processes, including regulation of extracellular vesicle transcytosis across the blood-brain barrier, where its upregulation facilitates vesicle recycling and promotes breast cancer brain metastasis 2. In primary cilia, RAB11FIP5 regulates axonemal glutamylation and ciliary trafficking, with dysregulation contributing to cyst progression in polycystic kidney disease 3. The protein is essential for proper telencephalon development through regulation of ephrinB1 recycling, affecting cell proliferation and brain development 4. RAB11FIP5 also modulates immune responses by regulating cytokine production in T cells and NK cell function, with altered expression associated with HIV broadly neutralizing antibody responses 56. Additionally, RAB11FIP5 exhibits antiviral properties by promoting lysosomal degradation of viral proteins, thereby inhibiting KSHV particle release 7. Clinically, RAB11FIP5 high expression serves as a poor prognostic biomarker in ovarian serous carcinomas 8.