Combined effects of restriction factors and transduction adjuvants on lentiviral vector gene transfer efficacy

Restriction factors include various cellular proteins that detect and impede viral infections. Among them, interferon-induced transmembrane (IFITM) and serine incorporator (SERINC) proteins interfere with the infectious cycle of HIV-1. Consequently, such restriction factors can also interfere with gene transfer efficacy when using recombinant lentiviral vectors derived from HIV-1, but these parameters remain incompletely understood. Here, using overexpressing human cell lines, we investigated the effects of IFITM and SERINC proteins on key parameters in the infectivity of lentiviral vectors, e.g. the nature of the vector envelope glycoprotein pseudotype and the use of transduction adjuvants. Vectors pseudotyped with glycoproteins from vesiculoviruses were mostly insensitive to the effects of restriction factors whereas those pseudotyped with glycoproteins of retroviral origin displayed contrasted responses. IFITM2 and IFITM3 very effectively restricted Syncytin1-pseudotyped vectors. Two transduction adjuvants, Vectofusin and cyclosporin H, counteracted these effects. Addition of either of these compounds led to reduced IFITM2 and IFITM3 protein levels. These results may rationalize the choice of pseudotypes as well as transduction conditions to use for gene transfer. Together, these parameters can strongly enhance the transduction efficacy, especially in target cells that naturally express IFITM proteins, including human hematopoietic cells that are of particular clinical interest.