In HeLa-CD4/CCR5 cells stably expressing minimal concentrations of CCR5 on the cell surface R5 HIV-1 infection occurred more efficiently in concomitance of “high” levels of CD4 expression, suggesting that a minimal number of CCR5 molecules are required when cell surface levels of CD4 reach a sufficient density [22]. The gene discussed is CD4; the disease is HIV-1 infection.