BackgroundInducible nitric oxide synthase (iNOS) and its product nitric oxide (NO) were historically linked to poor melanoma outcomes, yet recent evidence shows NO supports anti-tumor immunity. This study examines how iNOS shapes anti–PD-1 efficacy, particularly through interferon signaling.MethodsB16-D5 melanoma tumors were implanted in wild-type (WT) and iNOS knockout (KO) mice to compare tumor growth and response to anti–PD-1 therapy.
Flow cytometry, apoptosis assays, and RNA sequencing assessed NO production, PD-L1 expression, and interferon-related gene activation. In vitro, melanoma cells were treated with NO donors (DETA NONOate, SNAP) to assess proliferation and apoptosis.
Peripheral blood mononuclear cells from 27 melanoma patients receiving anti–PD-1 therapy were analyzed with multiparameter flow cytometry to correlate NO-associated immune subsets with progression-free survival (PFS).ResultsTumors grew significantly faster in iNOS KO mice, and anti–PD-1 therapy had no effect, demonstrating that iNOS-derived NO contributes to treatment efficacy. NO donors inhibited melanoma proliferation and induced apoptosis in vitro.
Transcriptomic analysis showed anti–PD-1 upregulated interferon pathway genes (STAT1, IRF1, IFNB1) in WT but not iNOS KO mice.
Frontiers in Immunology published a clinical update in Infectious Disease on 22 Jun 2026.
The item focuses on iNOS is a key mediator of anti-PD-1 melanoma therapy response.
Review the original article for the full source wording and details.