CD4 and coinfection: Thus, to determine whether Vpr in combination with HDACi enhances HIV expression when Vpr expression is LTR-independent, we used a co-infection model: Primary CD4+ T cells were co-infected with HIV-GFP and an EF1α-driven lentiviral vector expressing either mCherry alone or co-expressing Vpr and mCherry (mCherry and Vpr-mCherry, respectively) followed by vorinostat treatment beginning at 2–3dpi and monitored by flow cytometry for 21 days (Fig 2A, 2B).