Blood exchange experiments in heterochronic parabionts or heterochronic plasma transfer have revealed that age‐associated changes in blood composition contribute to neurogenesis and cognitive impairment in the elderly.[14, 15, 32] Blood‐born pro‐aging factors, including β2‐microglobulin, transforming growth factor‐β1 (TGF‐β1), chemokine (C‐C motif) ligand 11 (CCL11), chemokine (C‐C motif) ligand 2 (CCL2), interlukin‐6 (IL‐6), and tumor necrosis factor‐α (TNF‐α),[32a,c–e] have been identified as causal factors to accelerate age‐dependent brain changes. The gene discussed is HLA-G; the disease is Cognitive impairment.