CD4 and HIV-1 infection: Inhibitors of HIV-1 infection targeting the crucial step of viral entry can be divided into three groups: (i) inhibitors of the interaction between HIV-1 glycoprotein and its receptors CD4 and its co-receptors CCR5/CXCR4, (ii) inhibitors of the maturation of HIV-1 envelope glycoprotein gp160 precursor and (iii) fusion inhibitors.