CD4 and HIV infectious disease: Engaging PD-1 using PD-1 ligand-Fc (PDL-1-Fc) or inhibiting AEP using an inhibitor increased FOXP3 expression in HIV-infected CD4+ cells (Fig. 6C), suggesting that active PD-1 signaling in the context of IL-1β is involved in the stability of FOXP3 expression during HIV infection.