Donor macrophages may also infiltrate organs like the skin and lungs of a HSCT recipient through CSF-1 receptor signaling; and studies have shown that these donor CSF-1R-dependent macrophages may contribute to both sclerodermatous (Scl)-cGvHD and lung cGvHD, otherwise known as bronchiolitis obliterans syndrome (BOS), via the expression of Transforming Growth Factor beta (TGF-β) (8). The gene discussed is CSF1R; the disease is bronchiolitis obliterans syndrome.