Background
Despite effective HIV suppression by ART, the virus persists in latent reservoirs. Our single-cell data from human and primate studies show that individuals with better HIV control and smaller reservoirs have higher interferon stimulated gene (ISG) expression in CD4+ T cells, linked to greater chromatin accessibility and transcriptional activation. ISG expression could be induced by Toll-like receptors (TLRs) and IL-15. Thus, we hypothesize that; the activation of intrinsic innate antiviral immunity (IIAVI) in memory CD4+ T cells upregulates IRFs, enhancing ISG transcription. This “trained immunity” state will confer a poised antiviral response and limit reactivation of latent HIV upon exposure.
Methods
We established two co-culture systems: one using negative selection with immune cell markers and the other labeling cells with Cell Trace Violet (CTV). We evaluated HIV infection in these systems with Poly I:C (TLR3 agonist), R848 (TLR7/8 agonist), and IL-15 stimulation. Mechanisms of PRR and IL-15-mediated HIV protection were explored using high-dimensional flow cytometry.
Results
Activation of TLR3, TLR7/8, and the IL-15 pathway in the presence of macrophages, dendritic cells, and NK cells (first co-culture system) efficiently triggered intrinsic pathways, leading to both autocrine and paracrine IFN responses, conferring protection against HIV infection in memory CD4+ T cells. In the second system, memory CD4+ T cells induced and transferred IFN-mediated protection to neighboring bystander CD4+ T cells. We investigated the mechanisms of TLR3, TLR7/8, and IL-15-induced refractoriness, focusing on effector molecules of innate antiviral immunity i.e. pIRF3, pIRF7, IFNα, IFNγ, pSTAT1, and ISGs (e.g., IFIT1, APOBEC3G) using an optimized kinetic timeline. Results show TLR3 and TLR7/8 activation stimulates IRF3 and IRF7, inducing IFNs and ISGs, including HIV restriction factors in memory CD4+ T cells (Fig. 1A), promoting a poised innate antiviral immunity state or “trained immunity,” that contributes to HIV refractoriness (Fig. 1B). Similarly, IL-15 activation leads to IFN production, ISG induction, and HIV restriction (Fig. 1).
Conclusions
Our study shows that TLRs and IL-15-induced IFN responses, along with ISG expression in memory CD4+ T cells, create an antiviral innate memory state that protects against HIV infection and persistence upon re-exposure.