Immunohistochemical characterization of hBVOs throughout differentiation. PDGFR-β (yellow) marks mural cells, and CD31 (magenta) marks ECs. Scale bar: 50 μm (days 3–5), 100 μm (days 6 and 14), 150 μm (day 7), 200 μm (day 21). MIP, maximum intensity projection.