Work from this group identified a transcriptionally active element within the HIV-1 env coding region that functions as an intragenic promoter. This element mediates the expression of truncated or aberrant HIV-1 RNAs from proviral genomes that are defective for production of infectious virions. These intragenic transcripts are distinct from canonical LTR-driven full-length viral RNAs.
In clinical samples from people with HIV (PWH) who have suppressed plasma viremia on antiretroviral therapy (ART), the investigators observed correlations between serum levels of inflammatory cytokines and levels of HIV-1 transcripts that originate from the intragenic env promoter. These observations motivated experiments to test whether transcription from defective proviruses can directly induce inflammatory responses in myeloid cells.
To isolate the impact of defective proviral expression independent of canonical LTR-driven transcription, the authors used CRISPR-Cas9 to disrupt the 5' long terminal repeat (LTR), which normally functions as the proviral enhancer and promoter. This genetic manipulation rendered the LTR nonfunctional, modeling proviral genomes that cannot initiate transcription from the conventional promoter yet can still produce intragenic transcripts from internal elements.
Cells infected with HIV-1 genomes carrying the 5' LTR deletion produced significantly higher amounts of the chemokines IP-10 (CXCL10) and IL-8 in vitro. This effect was observed both in monocytic cell lines and in primary monocyte-derived macrophages. The increased production of these inflammatory mediators indicates that expression from defective proviral templates can activate myeloid inflammatory pathways even when canonical LTR activity is absent.
Transcripts initiated at the intragenic env promoter were found to bear a 5' cap and a polyadenylated tail, consistent with processing by host RNA maturation pathways. The presence of these features indicates that intragenic transcription yields RNAs that resemble cellular mRNAs and therefore have the potential to be recognized by cytosolic RNA sensors.
Mechanistic experiments identified the cytosolic innate immune sensing axis required for chemokine induction. The induction of IP-10 in response to intragenic transcripts was dependent on the cytosolic RNA-sensing proteins MDA5 and its adaptor MAVS. In contrast, the DNA sensor cGAS and the RNA sensor RIG-I were not required for this response. These results implicate an MDA5–MAVS–type I interferon signaling pathway in the myeloid cell recognition of RNAs derived from defective proviruses.
Based on their data, the authors propose that spurious expression from the large pool of defective HIV-1 proviruses persisting in PWH contributes to chronic inflammation by generating RNA species that engage MDA5 and MAVS, leading to activation of type I interferon pathways and downstream chemokine production. This mechanism could help explain persistent immune activation and comorbidities affecting the central nervous system, cardiovascular system, gut, and features of accelerated or age-associated inflammation in treated PWH.
The findings emphasize that defective proviruses—historically considered biologically inert with respect to virion production—can nonetheless be transcriptionally active and immunostimulatory. By linking defective proviral transcription to MDA5-dependent interferon pathway activation and to increased production of IP-10 and IL-8 in myeloid cells, the study highlights a potential contributor to systemic inflammation observed in PWH despite ART suppression of viremia.
These results underscore the importance of further characterizing the transcriptional activity of the defective proviral reservoir and its contributions to immune activation. Understanding these processes could inform strategies aimed at reducing chronic inflammation and improving long-term health and aging outcomes for people living with HIV-1.
All statements in this summary derive from the published abstract and accompanying metadata. Specific experimental parameters, sample sizes, quantitative results, temporal dynamics, and additional methodological details were not reported in the provided source text and therefore are not described here.