Viral supernatant titres were determined using the Lentivector Rapid Titer Kit from System Biosciences, according to the manufacturer's instructions. The number of infectious units per ml of supernatant (IFU ml−1) was calculated as follows: Multiplicity of infection (MOI) of the sample × the number of cells in the well upon infection × 1,000 / μl of viral supernatant used.
