CD4 and HIV-1 infection: These included: the observed decline in peripheral CD4+ T cells in homosexual patients presenting a “newly acquired cellular immunodeficiency syndrome” (AIDS) [9], the ability of HIV-1 isolated from these patients to infect CD4 T cells [10,11], the blockade of HIV-1 infection in vitro by anti-CD4 antibodies [12], and infection of virus-resistant human cells following transfection with the human CD4 gene (hCD4) [13].