Background:
When antiretroviral therapy (ART) is interrupted, most people living with HIV (PLWH) experience rapid viral rebound within a few weeks. We currently have no reliable non-viral biomarkers of imminent viral rebound. Rebound viremia is defined by circulating HIV RNA, but we hypothesize that low levels of virus replicating in tissues may create measurable biological changes in the immune landscape prior to detectable viremia. These changes may be most detectable directly preceding rebound viremia, when the viral load has not reached the limit of detection and is still under tentative immune control.
Methods:
To investigate changes in the immune system indicative of the first signs of viral rebound, we performed two separate analyses on a cohort of donors with HIV-1 who participated in an observational analytical treatment interruption (ATI). We performed single cell RNAseq on peripheral blood mononuclear cells (PBMCs) from a subset of 10 donors and analyzed soluble protein levels in plasma using three Olink 92-plex panels on 19 donors. For the purposes of analysis, we compared three distinct timepoints: on-ART (before ATI), pre-rebound (during ATI, before detectable viremia), and post-rebound (detectable viremia). scRNAseq data was analyzed using the Seurat integration workflow. Pathway analysis using MSigDB hallmark gene sets collection was performed on scRNAseq data. Olink protein levels were log-normalized and assessed with a paired Wilcox test.
Results:
In these PLWH, we found a significant increase in monocyte subsets prior to detectable viral rebound. Non-classical inflammatory CD14-CD16++ monocytes increased in proportion by 1.9% (p=0.008) while classical CD14++CD16- monocytes increased in proportion by 3.6% (p=0.054) (Fig. 1). Pathway analysis indicated enrichment for IFNγ, IFNα, and inflammatory response pathways within monocyte subsets. Olink analysis indicated an increase in soluble inflammatory plasma proteins post-rebound related to immune activation (PD-L2, TRAIL), cytokine signaling (TNF, LAG3, GZMB), and NFkB signaling (CXCL9, CXCL10, IL12).
Conclusions:
Our data suggest that prior to detectable viremia, a subset of circulating monocytes activate and expand in response to low level viral replication. These cells shift to a more inflammatory phenotype, indicating innate immune sensing of early viral rebound activity. This has the potential to be a non-viral biomarker of imminent viral rebound.
