Therapeutic intranasal delivery of NanoSTING provides broad protection against seasonal and highly pathogenic influenza strains

Introduction/Rationale: Seasonal and highly pathogenic influenza strains pose major public health challenges. Broad-spectrum therapies that protect vulnerable populations, accelerate recovery, and reduce mortality are a long-sought goal for influenza. We developed NanoSTING, a liposomal formulation of 2’3’-cGAMP, the endogenous STING-activator, to activate mucosal innate immunity as a host-directed therapy.

Methods: NanoSTING stability was assessed by DLS, zeta potential, and HPLC. Pharmacokinetics (PK), pharmacodynamics (PD), and safety were assessed in BALB/c mice after a single intranasal dose of NanoSTING. The nasal/lung tissues were analyzed by qPCR for IFN genes (Ifnb1 and Cxcl10) and by H&E for safety. To model vulnerable populations, we tested aged (18–20 mo), cyclophosphamide-lymphodepleted, and dexamethasone-treated (immune-suppressed) mice for NanoSTING-induced mucosal IFN responses, safety, and protection in viral challenge. Therapeutic efficacy was tested against influenza (A/H1N1pdm, B/Brisbane, and H5N1) challenge models.

Results: NanoSTING was stable for 12 months at 4ºC with no loss of encapsulated cGAMP. A single intranasal dose induced robust Ifnb1 and Cxcl10 in nasal and lung tissues without histologic injury. In influenza A/H1N1 and B challenge models, one dose of NanoSTING reduced weight loss, accelerated recovery, and outperformed ten doses of oseltamivir. In models with highly pathogenic avian influenza (HPAI, H5N1), NanoSTING reduced viral titers and disease severity even when administered 48–72 h post-infection. NanoSTING-induced nasal innate immunity was preserved in lymphodepleted, dexamethasone-treated, and aged mice, supporting its use in vulnerable hosts.

Conclusion: Single-dose intranasal NanoSTING activates protective type I IFN programs and delivers broad therapeutic benefit across influenza A/B, including H5N1, with an extended treatment window, refrigeration stability, and dose-sparing administration–highlighting a cellular, host-directed path to durable respiratory antiviral defense.