A key finding of this study is that the HIV-1 infection of macrophages is inhibited by the cellular protein SAMHD1, which restricts viral cDNA synthesis. The Vpx protein of HIV-2 and related simian immunodeficiency viruses (SIVsm/mac) counteracts this inhibition by targeting SAMHD1 for proteasome-dependent degradation via the CRL4DCAF1 E3 ubiquitin ligase. This mechanism allows these viruses to efficiently infect macrophages, unlike HIV-1. SAMHD1 mutations are associated with Aicardi-Goutieres syndrome (AGS), a disease that mimics congenital viral infection due to inappropriate innate immune responses. The study shows that SAMHD1 inhibits HIV-1 infection by preventing an unwanted interferon response triggered by self nucleic acids. Vpx binds to the DCAF1/VprBP substrate receptor subunit of the CRL4DCAF1 E3 ubiquitin ligase, leading to efficient degradation of SAMHD1. This process is confirmed through experiments showing that wild-type Vpx significantly enhances macrophage transduction by HIV-1–GFP, while a Vpx variant (VpxQ76A) that does not bind DCAF1 does not. The study also demonstrates that SAMHD1 is targeted for degradation in macrophages by Vpx, and that depletion of SAMHD1 by RNAi enhances HIV-1 infection. These findings reveal an intricate relationship between innate immune mechanisms that control responses to self and retroviral pathogens. The study also shows that SAMHD1 is essential for the restriction of lentivirus infection in macrophages, and that its depletion by Vpx allows efficient viral replication. The results highlight the role of SAMHD1 in the innate immune response to HIV-1 and suggest that targeting SAMHD1 could be a potential therapeutic strategy for HIV-1 infection.A key finding of this study is that the HIV-1 infection of macrophages is inhibited by the cellular protein SAMHD1, which restricts viral cDNA synthesis. The Vpx protein of HIV-2 and related simian immunodeficiency viruses (SIVsm/mac) counteracts this inhibition by targeting SAMHD1 for proteasome-dependent degradation via the CRL4DCAF1 E3 ubiquitin ligase. This mechanism allows these viruses to efficiently infect macrophages, unlike HIV-1. SAMHD1 mutations are associated with Aicardi-Goutieres syndrome (AGS), a disease that mimics congenital viral infection due to inappropriate innate immune responses. The study shows that SAMHD1 inhibits HIV-1 infection by preventing an unwanted interferon response triggered by self nucleic acids. Vpx binds to the DCAF1/VprBP substrate receptor subunit of the CRL4DCAF1 E3 ubiquitin ligase, leading to efficient degradation of SAMHD1. This process is confirmed through experiments showing that wild-type Vpx significantly enhances macrophage transduction by HIV-1–GFP, while a Vpx variant (VpxQ76A) that does not bind DCAF1 does not. The study also demonstrates that SAMHD1 is targeted for degradation in macrophages by Vpx, and that depletion of SAMHD1 by RNAi enhances HIV-1 infection. These findings reveal an intricate relationship between innate immune mechanisms that control responses to self and retroviral pathogens. The study also shows that SAMHD1 is essential for the restriction of lentivirus infection in macrophages, and that its depletion by Vpx allows efficient viral replication. The results highlight the role of SAMHD1 in the innate immune response to HIV-1 and suggest that targeting SAMHD1 could be a potential therapeutic strategy for HIV-1 infection.