Coronavirus Disease 2019 (COVID-19) is spreading worldwide and has become a public health emergency of major international concern. Currently, no specific drugs or vaccines are available.

This study aims to investigate the safety and efficacy of intravenous infusion of natural killer cells patients with COVID-19.

In March 2020, the World Health Organization secreted COVID-19 as a pandemic. Although most infected individuals can develop effective immunity, the population at risk (elderly, obese and individual with comorbidities) develop a rapid and frequently fatal disease, with severe acute respiratory syndrome, cytokine storm and coagulopathies; for those who recover, severe pulmonary sequels are frequently observed. We propose a phase I clinical trial to test safety and feasibility of NK cells adoptive immunotherapy for COVID-19. Natural Killer cells are innate granular lymphocytes able to rapidly recognize and kill, without previous exposition, altered cells; it is widely recognized as immune effectors specialized in lysing virus infected cells releasing antigens and activating cytokines to antigen presenting cells and, by doing so, stimulating effective adaptive immunity. We hypothesize that the early infusion of highly activated NK cells will activate adaptive immune effectors preventing the severe clinical evolution of COVID-19 infection. Adoptive NK cell immunotherapy for severe virus infections is innovative. Our proposition is in line with the Brazilian Public Health system purposes, which is to offer secure and effective therapies for all COVID-19 infected individuals. Upon proving NK cell immunotherapy effectiveness for serious virus infections, we can evolve to test this strategy for common viruses that cause epidemics and endemics such as the ones caused by Dengue, Zika, Chikungunya, C and B hepatitis and HIV.

Inclusion Criteria:

• Laboratory confirmation of COVID19 infection by reverse-transcription polymerase chain reaction (RT-PCR);
• The patient or legal donor agrees to participate in the study and signs the informed consent;
• Patients with white or yellow criteria according to the score proposed by Liao et al (2020).

Exclusion Criteria:

• Patient with pregnancy, are planning to become pregnant or breastfeeding;
• Patients with malignant blood-borne diseases such as HIV or syphilis;
• Not consenting for clinical trial;
• Patients with other than white or yellow criteria according to the score proposed by Liao et al (2020).