More specifically, these human cell infection-tropic viruses include the cellular primary receptors CD4 (T-helper-cell marker antigen) utilized by HIV-1 (Withers-Ward et al., 1997; Yunis et al., 2007) and angiotensin-converting enzyme-2 (ACE2) utilized by SARS-CoV-2 (Gheblaw et al., 2020; Kotani et al., 2022). Here, CD4 is linked to infection.