Inducible Gene Expression of the Human Immunodeficiency Virus LTR in a Replication-Incompetent Herpes Simplex Virus Vector

Abstract

Although replication-incompetent herpes simplex virus (HSV) vectors have the capability to express foreign genes, successful development of these vectors for gene delivery would require that expression of the foreign gene be regulated. To investigate the feasibility of obtaining inducible expression of a foreign gene in such a vector, a replication-incompetent HSV vector, vd120/LTRβ, was developed that used the human immunodeficiency virus type 1 (HIV-1) long terminal repeat (LTR) to express theEscherichia coli lacZgene. Examination oflacZexpression from the HIV-1 LTR in vd120/LTRβ-infected cells indicated that the LTR was active as a promoter under both replicating and nonreplicating conditions, although expression oflacZunder nonreplicating conditions was approximately 4-fold lower. In addition, the LTR expressedlacZin a manner distinct from that of well-characterized HSV-1 promoters of each temporal class. The effect of the HIV-1 regulatory protein Tat on expression from the LTR in vd120/LTRβ was examined by infection of two different HeLa-derived cell lines that constitutively expressed Tat, HL2/3, and HLtat. Compared to infection of HeLa cells,lacZexpression from vd120/LTRβ-infected HL2/3 and HLtat cells increased from 4- to 24-fold, depending on the multiplicity of vector infection. Sustained expression oflacZfrom the LTR in vd120/LTRβ-infected cells was not observed even in the continuous presence of Tat, although vector could be recovered for up to 5 days after infection. However, the amount of recoverable vector decreased during this time, suggesting that cellular cytotoxicity may account for some of the decrease in Tat-mediated expression from the LTR.