* onset of covid-19 symptoms \> 14 days prior to randomization * hospitalized \> 7 days prior to randomization * need for invasive mechanical ventilation (only for cohort 1) * need for ecmo * serious prior or concomitant illness that in the opinion of the investigator precludes the subject from enrolling in the trial * recent treatment with cell-depleting biological therapies (eg, anti-cd20) within 12 months, non-cell-depleting biological therapies (such as anti-tumor necrosis factor \[tnf\], anakinra, anti-il-6 receptor \[eg, tocilizumab\], or abatacept) within 8 weeks (or 5 half-lives, whichever is longer), treatment with alkylating agents within 12 weeks, treatment with cyclosporine a, azathioprine, cyclophosphamide, mycophenolate mofetil (mmf), or other immunosuppressant (except for corticosteroids) within 4 weeks prior to randomization. medications that become standard of care for covid-19 and/or receive emergency use authorization may be allowed after discussion with the medical monitor. * if subject is receiving or has received hydroxychloroquine within 3 months prior to screening visit, a corrected qt interval by federicia method (qtcf) on screening electrocardiogram (ecg) ≥500ms is exclusionary. if subject has a pacemaker, this criterion does not apply. * enrolled in another investigational study of a medical intervention within 30 days prior to randomization. participation in open label trials involving investigational treatments for covid-19 may be allowed upon approval by the sponsor. * life expectancy less than 48 hours, in the opinion of the investigator * known human immunodeficiency virus infection (regardless of immunological status), known hepatitis b virus surface antigen positivity and/or anti-hepatitis c virus positivity

* onset of covid-19 symptoms \> 14 days prior to randomization * hospitalized \> 7 days prior to randomization * need for invasive mechanical ventilation (only for cohort 1) * need for ecmo * serious prior or concomitant illness that in the opinion of the investigator precludes the subject from enrolling in the trial * recent treatment with cell-depleting biological therapies (eg, anti-cd20) within 12 months, non-cell-depleting biological therapies (such as anti-tumor necrosis factor \[tnf\], anakinra, anti-il-6 receptor \[eg, tocilizumab\], or abatacept) within 8 weeks (or 5 half-lives, whichever is longer), treatment with alkylating agents within 12 weeks, treatment with cyclosporine a, azathioprine, cyclophosphamide, mycophenolate mofetil (mmf), or other immunosuppressant (except for corticosteroids) within 4 weeks prior to randomization. medications that become standard of care for covid-19 and/or receive emergency use authorization may be allowed after discussion with the medical monitor. * if subject is receiving or has received hydroxychloroquine within 3 months prior to screening visit, a corrected qt interval by federicia method (qtcf) on screening electrocardiogram (ecg) ≥500ms is exclusionary. if subject has a pacemaker, this criterion does not apply. * enrolled in another investigational study of a medical intervention within 30 days prior to randomization. participation in open label trials involving investigational treatments for covid-19 may be allowed upon approval by the sponsor. * life expectancy less than 48 hours, in the opinion of the investigator * known human immunodeficiency virus infection (regardless of immunological status), known hepatitis b virus surface antigen positivity and/or anti-hepatitis c virus positivity

onset of covid-19 symptoms > 14 days prior to randomization hospitalized > 7 days prior to randomization need for invasive mechanical ventilation (only for cohort 1) need for ecmo serious prior or concomitant illness that in the opinion of the investigator precludes the subject from enrolling in the trial recent treatment with cell-depleting biological therapies (eg, anti-cd20) within 12 months, non-cell-depleting biological therapies (such as anti-tumor necrosis factor [tnf], anakinra, anti-il-6 receptor [eg, tocilizumab], or abatacept) within 8 weeks (or 5 half-lives, whichever is longer), treatment with alkylating agents within 12 weeks, treatment with cyclosporine a, azathioprine, cyclophosphamide, mycophenolate mofetil (mmf), or other immunosuppressant (except for corticosteroids) within 4 weeks prior to randomization. medications that become standard of care for covid-19 and/or receive emergency use authorization may be allowed after discussion with the medical monitor. if subject is receiving or has received hydroxychloroquine within 3 months prior to screening visit, a corrected qt interval by federicia method (qtcf) on screening electrocardiogram (ecg) ≥500ms is exclusionary. if subject has a pacemaker, this criterion does not apply. enrolled in another investigational study of a medical intervention within 30 days prior to randomization. participation in open label trials involving investigational treatments for covid-19 may be allowed upon approval by the sponsor. life expectancy less than 48 hours, in the opinion of the investigator known human immunodeficiency virus infection (regardless of immunological status), known hepatitis b virus surface antigen positivity and/or anti-hepatitis c virus positivity

onset of covid-19 symptoms > 14 days prior to randomization hospitalized > 7 days prior to randomization need for invasive mechanical ventilation (only for cohort 1) need for ecmo serious prior or concomitant illness that in the opinion of the investigator precludes the subject from enrolling in the trial recent treatment with cell-depleting biological therapies (eg, anti-cd20) within 12 months, non-cell-depleting biological therapies (such as anti-tumor necrosis factor [tnf], anakinra, anti-il-6 receptor [eg, tocilizumab], or abatacept) within 8 weeks (or 5 half-lives, whichever is longer), treatment with alkylating agents within 12 weeks, treatment with cyclosporine a, azathioprine, cyclophosphamide, mycophenolate mofetil (mmf), or other immunosuppressant (except for corticosteroids) within 4 weeks prior to randomization. medications that become standard of care for covid-19 and/or receive emergency use authorization may be allowed after discussion with the medical monitor. if subject is receiving or has received hydroxychloroquine within 3 months prior to screening visit, a corrected qt interval by federicia method (qtcf) on screening electrocardiogram (ecg) ≥500ms is exclusionary. if subject has a pacemaker, this criterion does not apply. enrolled in another investigational study of a medical intervention within 30 days prior to randomization. participation in open label trials involving investigational treatments for covid-19 may be allowed upon approval by the sponsor. life expectancy less than 48 hours, in the opinion of the investigator known human immunodeficiency virus infection (regardless of immunological status), known hepatitis b virus surface antigen positivity and/or anti-hepatitis c virus positivity

- onset of covid-19 symptoms or positive covid-19 test result > 14 days prior to randomization - hospitalized > 7 days prior to randomization - need for invasive mechanical ventilation (only for cohort 1) - need for ecmo - serious prior or concomitant illness that in the opinion of the investigator precludes the subject from enrolling in the trial - recent treatment with cell-depleting biological therapies (eg, anti-cd20) within 12 months, non-cell-depleting biological therapies (such as anti-tumor necrosis factor [tnf], anakinra, anti-il-6 receptor [eg, tocilizumab], or abatacept) within 8 weeks (or 5 half-lives, whichever is longer), treatment with alkylating agents within 12 weeks, treatment with cyclosporine a, azathioprine, cyclophosphamide, mycophenolate mofetil (mmf), or other immunosuppressant (except for corticosteroids) within 4 weeks prior to randomization - corrected qt interval fridericia's formula (qtcf) on screening electrocardiogram (ecg) ≥500 ms - enrolled in another investigational study of a medical intervention - life expectancy less than 48 hours - known human immunodeficiency virus infection (regardless of immunological status), known hepatitis b virus surface antigen positivity and/or anti-hepatitis c virus positivity

- onset of covid-19 symptoms or positive covid-19 test result > 14 days prior to randomization - hospitalized > 7 days prior to randomization - need for invasive mechanical ventilation (only for cohort 1) - need for ecmo - serious prior or concomitant illness that in the opinion of the investigator precludes the subject from enrolling in the trial - recent treatment with cell-depleting biological therapies (eg, anti-cd20) within 12 months, non-cell-depleting biological therapies (such as anti-tumor necrosis factor [tnf], anakinra, anti-il-6 receptor [eg, tocilizumab], or abatacept) within 8 weeks (or 5 half-lives, whichever is longer), treatment with alkylating agents within 12 weeks, treatment with cyclosporine a, azathioprine, cyclophosphamide, mycophenolate mofetil (mmf), or other immunosuppressant (except for corticosteroids) within 4 weeks prior to randomization - corrected qt interval fridericia's formula (qtcf) on screening electrocardiogram (ecg) ≥500 ms - enrolled in another investigational study of a medical intervention - life expectancy less than 48 hours - known human immunodeficiency virus infection (regardless of immunological status), known hepatitis b virus surface antigen positivity and/or anti-hepatitis c virus positivity

- onset of covid-19 symptoms or positive covid-19 test result > 14 days prior to randomization - hospitalized > 7 days prior to randomization - need for invasive mechanical ventilation (only for cohort 1) - need for ecmo - serious prior or concomitant illness that in the opinion of the investigator precludes the subject from enrolling in the trial - recent treatment with cell-depleting biological therapies (eg, anti-cd20) within 12 months, cell-depleting biological therapies (such as anti-tumor necrosis factor [tnf], anakinra, anti-il-6 receptor [eg, tocilizumab], or abatacept) within 8 weeks (or 5 half-lives, whichever is longer), treatment with alkylating agents within 12 weeks, treatment with cyclosporine a, azathioprine, cyclophosphamide, mycophenolate mofetil (mmf), covid-19-immune plasma, or other immunosuppressant within 4 weeks prior to randomization - corrected qt interval fridericia's formula (qtcf) on screening electrocardiogram (ecg) ≥450 ms - chronic or recent (within 7 days prior to randomization) corticosteroid use >10 mg/day

- onset of covid-19 symptoms or positive covid-19 test result > 14 days prior to randomization - hospitalized > 7 days prior to randomization - need for invasive mechanical ventilation (only for cohort 1) - need for ecmo - serious prior or concomitant illness that in the opinion of the investigator precludes the subject from enrolling in the trial - recent treatment with cell-depleting biological therapies (eg, anti-cd20) within 12 months, cell-depleting biological therapies (such as anti-tumor necrosis factor [tnf], anakinra, anti-il-6 receptor [eg, tocilizumab], or abatacept) within 8 weeks (or 5 half-lives, whichever is longer), treatment with alkylating agents within 12 weeks, treatment with cyclosporine a, azathioprine, cyclophosphamide, mycophenolate mofetil (mmf), covid-19-immune plasma, or other immunosuppressant within 4 weeks prior to randomization - corrected qt interval fridericia's formula (qtcf) on screening electrocardiogram (ecg) ≥450 ms - chronic or recent (within 7 days prior to randomization) corticosteroid use >10 mg/day