This document summarizes research on the protein SAMHD1 and its role in restricting HIV-1 infection. It finds that SAMHD1 is an interferon-induced factor in macrophages and dendritic cells that is degraded by the HIV-2 protein Vpx, allowing infection. Silencing SAMHD1 in dendritic cells through RNA interference increased their susceptibility to HIV-1 infection. Therefore, SAMHD1 acts as an innate immune restriction factor that HIV-1 has not yet evolved to counteract, limiting its ability to productively infect dendritic cells.