SAMHD1 regulation, dNTP metabolism, and lentiviral transduction in human primary alveolar macrophages

Host dNTPase SAMHD1 kinetically restricts HIV-1 replication in nondividing cells, including myeloid cells and resting CD4⁺ T cells, by depleting cellular dNTP pools required for viral reverse transcription. In contrast, some SIVs and HIV-2 encode a viral accessory protein, Vpx, which promotes SAMHD1 protein degradation, thereby elevating cellular dNTP pools and enhancing viral replication kinetics in nondividing target cells. Here, we investigated the regulation dynamics of SAMHD1 and dNTP pools in human primary alveolar macrophages (AMs). We found that SAMHD1 in AMs was predominantly unphosphorylated and that CDK1 expression was limited, whereas early differentiated MDMs expressed CDK1 and phosphorylated SAMHD1. In contrast, human primary monocyte-derived macrophages (MDMs) transiently expressed CDK1 and phosphorylated SAMHD1 during early differentiation. Additionally, AMs displayed a distinct nucleotide-metabolism enzyme profile, with undetectable RRM2 and minimal TK1 expression but detectable RRM1, RRM2B/p53R2, DCK, and NDPK. Indeed, quantification of cellular dNTPs revealed substantially lower basal dNTP levels in AMs than in MDMs. Although Vpx treatment increased dNTP levels in AMs, the nucleotide pools were lower than those in MDMs treated with Vpx. In AMs, HIV-1 vector transduction kinetics is delayed; however, Vpx treatment accelerates the vector transduction. Furthermore, Vpx-deficient SIV vector exhibited minimal transduction in AMs, highlighting the critical role of Vpx in overcoming SIV restriction by SAMHD1 in AMs. Collectively, these findings identify a SAMHD1-mediated dNTP metabolic barrier that limits lentiviral transduction in tissue-resident macrophages such as AMs.