Although a previous study has shown increased concentration of the cytotoxic effector molecules GZMB and perforin in airway supernatant of patients with COVID-19 (22), we believe our study is the first to demonstrate the marked induction of GZMB in situ within the CD8+ T cell compartment in early COVID-19 (Figure 5) and the correlation of lymphocyte cytotoxicity with alveolar epithelial cell loss (Figure 6B and Supplemental Table 4). This evidence concerns the gene PRF1 and COVID-19.