Conditionally controlled, attenuated hiv vaccine

Abstract

A live attenuated human immunodeficiency virus type 1 (HIV-1) whose replication is not constitutive but is instead conditionally regulated (such that rounds of reverse transcription with accompanying potential for error are strictly limited) might yield a paradigm that minimizes evolution to virulence and facilitate vaccine development. We have broached the concept of conditional control of HIV-1 through gain-of-function. Here, we describe the design of constitutively inactive HIV-1 genomes (HIV-DoxT and HIV-DoxSp) which can be conditionally resuscitated to an active state by tetracycline or related analogues. The HIV-DoxT construct comprises an inactivating mutation engineered into TAR, thereby rendering the virus non-responsive to Tat, a 302-bp DNA fragment (TetopT) which contains the tet-operator ligated into a position upstream of the HIV TATAA box, in both the 5′ and 3′ LTRs, and a reverse tetracycline-controlled activator (RTTA) coding sequence in place of the nef coding region. The HIV-DoxSp construct contains three additional Sp1 sites in the TetopT promoter upstream of the TATAA box thereby generating the promoter TetopSp. Genotypically, HIVDoxT is tat(+)tar(−)nef(−)Sp1(−) and HIVDoxSp is tat(+)tar(−)nef(−)Sp1(+). Since both genomes are genetically tar(−), they would ordinarily be expected to be wholly defective in producing viral proteins and/or particles. However, following transfection into an appropriate cell target, both proviruses, in a doxycycline-dependent fashion, capably released Gag and RT from cells. In the absence of doxycycline, no replication competent virus could be recovered. These findings suggest that the heterologous RTTA+Dox mechanism substituted effectively for Tat/TAR. These constructs should prove useful in the development of HIV-specific immunological and diagnostic reagents.