KDR and diabetic retinopathy: Vascular endothelial growth factors (VEGF) and their broadly expressed cognate receptors (VEGFR) play an important role in angiogenesis and their expression is upregulated in highly angiogenic sites, such as the tumor microenvironment or in the retina in the event of age-related macular degeneration (AMD), diabetic retinopathy and retinal vein occlusions [250].Various groups generated nanobodies against vascular endothelial growth factor receptor-2 (VEGFR-2), which might serve as anti-angiogenic agents [251,252].