In addition, blood tests with lymphocytopenia, BALF with decreased CD4/CD8 ratio, and increased neutralizing antibody titer suggested that not only low humoral immune responses but also CD4 T-cell depletion by bendamustine were associated with virus clearance. Even if neutralizing antibodies are adequate, we must be careful of prolonged COVID-19 due to CD4 T-cell depletion and low humoral immune responses. Here, CD4 is linked to COVID-19.