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cGAS inhibitor IMSB301 modifies interferon signalling in peripheral mononuclear cells of SAMHD1 genetic interferonopathy in vitro

The finding

Using single-cell RNA sequencing, the authors profiled PBMCs from a single patient with biallelic (fully loss-of-function) SAMHD1-related Aicardi-Goutières syndrome and an age/sex-matched control. At baseline, the patient's cells showed strong upregulation of antiviral and type I interferon response pathways, led by classic ISGs (IFIT1, IFIT3, IFI44L, ISG15, OAS1). Treating patient PBMCs in vitro for 24 hours with IMSB301, a clinical-stage cGAS inhibitor, brought expression of these same top ISGs — and the enriched pathways they define — back down toward control levels.

Where it fits

This is squarely ARM 1 (interferon/JAK-STAT) evidence: it targets cGAS, the upstream DNA-sensing node that feeds STING → IRF3/7 → tonic type I IFN. For the SAMHD1 A565T model, it supports the idea that cGAS-STING sensing is a druggable point of entry upstream of the ANKIB1 gain-control node, and it's a proof-of-concept that pharmacologically dialing back cGAS activity can normalize an ISG signature driven by SAMHD1 dysfunction. Because ARM 1 is described as JAK-inhibitor-responsive, this cGAS-targeted approach offers a complementary, potentially more upstream lever on the same arm — relevant to thinking about combination or alternative strategies if JAK inhibition alone is insufficient or if ARM 2/3 activity persists.

Caveats

  • This is biallelic, fully loss-of-function SAMHD1 (classic AGS), not the heterozygous, partial loss-of-function A565T variant central to this project — the degree of cGAS/STING pathway engagement may differ substantially.
  • N = 1 patient, PBMCs only, in vitro drug exposure — no data on primary cell types most relevant to A565T biology (e.g., monocytes/macrophages, endothelium) and no in vivo or clinical outcome data.
  • The study shows transcriptional correlation (ISG downregulation) with cGAS inhibition, not direct mechanistic proof that cGAS-STING signaling is the dominant driver of baseline ISG elevation versus other sensors (e.g., MDA5) or arms (mitochondrial, NLRP3).

What to watch

The key open question is whether IMSB301 or similar cGAS inhibitors produce comparable ISG suppression in heterozygous, partial-function SAMHD1 A565T cells, and whether such suppression extends to ARM 2/3 readouts (mtDNA release, NLRP3 activation) or remains confined to ARM 1.

Source: cGAS inhibitor IMSB301 modifies interferon signalling in peripheral mononuclear cells of <i>SAMHD1</i> genetic interferonopathy <i>in vitro</i> — 2026.