We characterized the ex vivo ability of different leukocyte subsets of patients admitted to the hospital with COVID-19 to produce GrB, perforin, tumor necrosis factor (TNF-α) and interferon-gamma (IFN-γ) after short-term ex vivo stimulation with phorbol myristate acetate (PMA)/ionomycin. The gene discussed is GZMB; the disease is COVID-19.