Variations in the Abortive HIV-1 RNA Hairpin Do Not Impede Viral Sensing and Innate Immune Responses.

The highly conserved trans-acting response element (TAR) present in the RNA genome of human immunodeficiency virus 1 (HIV-1) is a stably folded hairpin structure involved in viral replication. However, TAR is also sensed by viral sensors, leading to antiviral immunity. While high variation in the TAR RNA structure renders the virus replication-incompetent, effects on viral sensing remain unclear. Here, we investigated the role of TAR RNA structure and stability on viral sensing. TAR mutants with deletions in the TAR hairpin that enhanced thermodynamic stability increased antiviral responses. Strikingly, TAR mutants with lower stability due to destabilization of the TAR hairpin also increased antiviral responses without affecting pro-inflammatory responses. Moreover, mutations that affected the TAR RNA sequence also enhanced specific antiviral responses. Our data suggest that mutations in TAR of replication-incompetent viruses can still induce immune responses via viral sensors, hereby underscoring the robustness of HIV-1 RNA sensing mechanisms.