To select mutants with a generally enhanced neutralization sensitivity, JR-CSF mutant pseudoviruses were screened against plasma from people with chronic, untreated HIV-1 infection (N = 18; S2 Table), the CD4 receptor analogue CD4-IgG2 and a range of weak-nAbs (CD4bs: b6 and b12, V3-crown: 1–79, 447-52D). The gene discussed is CD4; the disease is HIV-1 infection.