Postentry restriction to human immunodeficiency virus-based vector transduction in human monocytes

Cells of the monocyte lineage can be infected with human immunodeficiency v irus type 1 (HIV-1) both during clinical infection and in vitro. The abilit y of HIV-l-based vectors to transduce human monocytes, monocyte-derived mac rophages, and dendritic cells (DCs) was therefore examined, in order to dev elop an efficient protocol for antigen gene delivery to human antigen-prese nting cells. Freshly isolated monocytes were refractory to HIV-1-based vect or transduction but became transducible after in vitro differentiation to m ature macrophages. This maturation-dependent transduction was independent o f the HIV-1 accessory proteins Vif, Vpr, Vpu, and Nef in the packaging cell s and of the central polypurine tract in the vector, and it was also observ ed with a vesicular stomatitis virus-pseudotyped HIV-1 provirus, defective only in envelope and Nef, The level and extent of reverse transcription of the HIV-1-based vector was similar after infection of immature monocytes an d of mature macrophages. However, 2LTR vector circles could not be detected in monocytes, suggesting a block to vector nuclear entry in these cells. T ransduction of freshly isolated monocytes exposed to HIV-1-based vector cou ld be rescued by subsequent differentiation into DCs, This rescue was induc ed by fetal calf serum in the DC culture medium, which promoted vector nucl ear entry.