AP3D1 encodes the delta subunit of the AP-3 adaptor complex, a non-clathrin-associated protein complex that mediates vesicle budding from the Golgi and trafficking to lysosomes and lysosome-related organelles 1. AP3D1 functions in sorting cargo proteins destined for secretory lysosomes and is essential for both ubiquitous and neuron-specific forms of the AP-3 complex 2. The protein plays critical roles in CD8+ T-cell and NK cell degranulation and synaptic vesicle transport 2. Mechanistically, AP3D1 sorts palmitoylated interferon gamma receptor 1 (IFNGR1) to lysosomes for degradation, a process regulated by optineurin; loss of this regulatory interaction drives immune evasion in colorectal cancer 3. Biallelic AP3D1 mutations cause Hermansky-Pudlak syndrome type 10 (HPS10), characterized by oculocutaneous albinism, immunodeficiency, neutropenia, seizures, neurodevelopmental delay, and platelet dysfunction 24. AP3D1 mutations represent a primary immune regulatory disorder affecting immune cell function and secretory organelle biogenesis 5. Additionally, serum anti-AP3D1 antibodies serve as atherosclerosis biomarkers associated with acute ischemic stroke risk 6. Dysregulation of AP3D1 expression has been implicated in inflammatory conditions including acute gouty arthritis and systemic autoimmune diseases 78.