144 The Cytosolic Exonuclease TREX1 Digests HIV Reverse Transcripts to Avoid Triggering an Antiviral Interferon Response in T Cells and Macrophages

Abstract

Viral infection triggers cytoplasmic innate nucleic acid immune sensors to produce type I interferons (IFN). However, although HIV introduces its genomic RNA into the cytosol of infected T cells and macrophages and reverse transcribes it to DNA, HIV infection of its main target cells does not trip these alarms. We found that HIV reverse transcripts trigger type I IFNs when the cytosolic exonuclease Trex1 is deficient. In Trex1-/- mouse cells and human CD4+ T cells and macrophages in which TREX1 was inhibited by RNA interference, cytosolic HIV DNA accumulated, and HIV infection induced type I IFN that inhibited HIV replication and spreading. Trex1 bound to cytosolic HIV DNA and digested excess HIV DNA that would otherwise activate IFN expression via a TBK1, STING and IRF3 dependent pathway. The nucleic acid sensor that recognizes HIV reverse transcripts is still unknown. The lack of an innate antiviral immune response in the first cells infected by HIV during sexual transmission may enable HIV to establish a foothold in the host genital tract. We recently developed a way to induce gene silencing in all CD4+ cells in vivo with a chimeric RNA composed of a CD4 aptamer (for specific uptake into HIV-susceptible cells) linked to an siRNA. CD4 aptamer-siRNA chimeras designed to target CCR5 and conserved HIV sequences inhibit HIV transmission in humanized mice. Protection from HIV challenge lasted for about a week. We next investigated whether TREX1 knockdown would induce an immediate local IFN response at the site of transmission to inhibit transmission. In polarized human ectocervical explants, knocking down TREX1 interfered with transmission of HIV. Experiments to test this strategy in humanized mice are planned.