S100B and infection: Seven days later, we infected these cells with IN− NL-GFPΔEnv10, an HIV-1 derivative harbouring a deletion in env, the inactivating D64V mutation16 in IN, and the green fluorescent protein (GFP) open reading frame in place of nef. This virus retains intact copies of the other six HIV-1 genes, including vpr. At 48 h post infection (hpi), GFP+ cells were collected by fluorescence activated cell sorting (FACS), the sgRNAs recovered by (polymerase chain reaction) PCR then cloned into the same lentiviral vector.