Evidence that SAMHD1 does not contribute to the early IFN-α block to HIV-1 transduction. (A) IFN-α inhibits Vpx helper effect toward HIV-1. MDMs were treated with increasing doses of IFN-α for 24 hours, incubated with empty or Vpx-containing VLP (X- or X+, respectively) for 2 h, then transduced with a VSV-G pseudotyped luciferase-encoding HIV-1 virus (HIV-1-Luc) normalized for infectivity, for 2 h. The transduction rate (Luc activity) was measured 2 days post-transduction (left panel). Vpx helper effect corresponds to the fold increase of luciferase activity between cells transduced with Vpx versus cells transduced without Vpx (right). The results shown are representative of three independent experiments. (B) Analysis of SAMHD1, APOBEC3A and ISG15 expression in MDMs treated as in (A). (C) Vpx is unable to rescue SIVmac from the IFN-α block. MDMs were treated with the indicated doses of IFN-α, incubated with empty or Vpx containing VLP (X- or X+, respectively) to trigger SAMHD1 degradation, before being transduced with a Vpx-deleted SIVmac-GFP reporter virus (MOI 1). The percentage of transduction (% GFP + cells) was measured by flow cytometry 3 days post-transduction. The bar graph is representative of the results obtained in two independent experiments with different MDMs donors.