Fig. 2: Forced in vivo passaging confirms robust attenuation of OTS-228.
a Experimental setup: Intranasal inoculation of six index hamsters with OTS-228 (103.8 TCID50/animal), followed by three consecutive passages using either nasal wash samples (“washing group”) or conchae samples (“tissue group”) as inoculum. b Body weight: None of the hamsters in the washing group or (c) tissue group experienced body weight loss, regardless of passage number. d Viral genome detection: Virus genome was found only in the nasal washing samples of the tissue group and in the (e) tissue samples, while the washing group remained negative throughout all passages. f, g Transmission: Direct contact animals did not become infected when co-housed with inoculated animals during passage 1. h Viral load: The viral quantity in the inoculum was determined by titration and RT-qPCR. i Histopathology: Examination of animals from passage 1 and passage 4 revealed no pneumonia-related atelectasis, shown as a percentage of the affected area. Representative hematoxylin-eosin stained sections showed no atelectasis (whole slide image, bar = 2.5 mm), no alveolar immune cell infiltration (green asterisk), but the presence of perivascular (green arrowhead) and peribronchial inflammatory infiltrates (green arrow), detailed images, bar = 100 µm. j Antigen detection: The same samples were screened for SARS-CoV N-protein antigen. The antigen score and representative immunohistochemistry lung sections illustrate multifocal viral antigen presence in type-I pneumocytes (green arrowhead) and bronchial epithelial cells (green arrow), bar = 100 µm.
