Extended Data Fig. 2: Lung histopathology.
Representative histopathology of haematoxylin and eosin-stained lung sections from prime-only and prime-boost vaccination experiments at 5 dpc. Images are representative of n = 5 hamsters per indicated group. Prime and prime-boost experiments were performed independently. For both experiments, columns show, from left to right, bronchitis, pneumonia affecting the respiratory alveoli and blood vessels with endothelialitis. In the prime-only approach, and in contrast to all other groups that developed necrosupperative and hyperplastic bronchitis, only sCPD9 vaccinated hamsters had negligible bronchitis in the presence of BALT-like subepithelial infiltration with lymphocytes and plasma cells. In the lungs, alveoli of sCPD9 vaccinated animals presented with much less consolidated respiratory parenchyma, with less infiltrating macrophages and neutrophils. Only Ad2 and mock- vaccinated animals developed marked alveolar metaplastic remodeling, indicating regeneration after necrosis of alveolar epithelia. Endothelialitis was milder in all vaccinated groups compared to mock-vaccinated animals. In the prime-boost experiments, hyperplastic bronchitis was mildest in sCPD9+sCPD9 and mRNA+sCPD9 vaccinated hamsters. Consolidation of respiratory parenchyma and alveolitis were least severe in both sCPD9 boostered groups. Metaplastic epithelial remodeling was particularly pronounced in Ad2-Ad2 vaccinated animals. Endothelialitis was strongly reduced to similar degrees in all boostered groups. Scale bars = 20 μm for each column.
