CD4 and HIV-1 infection: We first constructed a CD4-PE40-like recombinant protein by using mD1.22 to replace CD4 and DM1 to substitute for PE40 because 1) mD1.22 has more potent anti-HIV-1 activity (20) and is safer than sCD4, which could enhance HIV-1 infection in CD4-CCR5+ cells (13, 18), and 2) a recombinant protein with PE40 (MW: 66 kDa) may have less accessibility to the limited space of HIV latent reservoir than that containing the small-molecule toxin DM1.