inclusion criteria: 1.laboratory diagnosis: adult sari patients with 2019-ncov infection confirmed by pcr; absolute value of lymphocytes \< 0. 6x 109/l; severe respiratory failure within 48 hours and requires admission to icu. (severe respiratory failure was defined as pao2/fio2 \< 200 mmhg and was supported by positive pressure mechanical ventilation (including non-invasive and invasive mechanical ventilation, peep\>=5cmh2o))

inclusion criteria: 1.laboratory diagnosis: adult sari patients with 2019-ncov infection confirmed by pcr; absolute value of lymphocytes \< 0. 6x 109/l; severe respiratory failure within 48 hours and requires admission to icu. (severe respiratory failure was defined as pao2/fio2 \< 200 mmhg and was supported by positive pressure mechanical ventilation (including non-invasive and invasive mechanical ventilation, peep\>=5cmh2o))

inclusion criteria: 1.laboratory diagnosis: adult sari patients with 2019-ncov infection confirmed by pcr; absolute value of lymphocytes < 0. 6x 109/l; severe respiratory failure within 48 hours and requires admission to icu. (severe respiratory failure was defined as pao2/fio2 < 200 mmhg and was supported by positive pressure mechanical ventilation (including non-invasive and invasive mechanical ventilation, peep>=5cmh2o))

inclusion criteria: 1.laboratory diagnosis: adult sari patients with 2019-ncov infection confirmed by pcr; absolute value of lymphocytes < 0. 6x 109/l; severe respiratory failure within 48 hours and requires admission to icu. (severe respiratory failure was defined as pao2/fio2 < 200 mmhg and was supported by positive pressure mechanical ventilation (including non-invasive and invasive mechanical ventilation, peep>=5cmh2o))