Fig. 1

The timeline for virus inoculation and MSC administration in the mouse experiments. Seventy-six BALB/c mice were used in this study. The animals were divided into three groups; MSC-treated group (n = 30), mock-treated group (n = 30), and control group (n = 16). All mice except for the control group were intranasally inoculated with a dose of 500 MLD50 of a highly pathogenic avian influenza A/H5N1 virus on day 0. The MSC -treated group was further divided into 3 subgroups of D2, D2–4, and D2–4-6 (each group, n = 10); subgroup D2 received intravenously 100 μL phosphate buffered saline (PBS) containing 5.5 × 105 of MSCs on day 2, and six mice were terminated day 3 for sampling. Subgroup D2–4 received MSCs on days 2 and 4, and six mice were terminated on day 5. Subgroup D2–4-6 received MSCs on days 2, 4, and 6, and six mice were terminated on day 7. The mock-treated group was a therapy control group with virus infection that received 100 μL of PBS without MSCs. This group was also divided into 3 subgroups of D2, D2–4, and D2–4-6. With the same schedule as for the MSC-treated subgroups, they received PBS and were terminated. The control group was a virus-uninfected and MSC-untreated group. Mice in the control group were terminated on day 0 (n = 6) after being randomly selected. All mice were subjected to daily measurement of body weight and examination for survival until day 9. All surviving mice on day 9 were subjected to euthanasia using intraperitoneal injection of high dose ketamine and xylasin