1. 2019 adult patients with new-type coronavirus pneumonia diagnosed with 2019-nCoV infection by PCR according to the Pneumonitis Diagnosis and Treatment Protocol for New-type Coronavirus Infection (Trial Version 5) 2. The absolute value of lymphocytes <0.6x10^9/L, 3. Severe respiratory failure does not exceed 48 hours and requires ICU treatment. Among them, severe respiratory failure is defined as PaO2 / FiO2 <200 mmHg and requires positive pressure mechanical ventilation (including non-invasive and invasive mechanical ventilation, PEEP >=5 cmH2O), 4. Sign the informed consent.

1. 2019 adult patients with new-type coronavirus pneumonia diagnosed with 2019-nCoV infection by PCR according to the Pneumonitis Diagnosis and Treatment Protocol for New-type Coronavirus Infection (Trial Version 5) 2. The absolute value of lymphocytes <0.6x10^9/L, 3. Severe respiratory failure does not exceed 48 hours and requires ICU treatment. Among them, severe respiratory failure is defined as PaO2 / FiO2 <200 mmHg and requires positive pressure mechanical ventilation (including non-invasive and invasive mechanical ventilation, PEEP >=5 cmH2O), 4. Sign the informed consent.