A Small Peptide Fragment of Growth Hormone Protects Mice from Deadly Influenza

Intranasal LAT9997 (6-amino acid growth hormone fragment) significantly improved survival in severe murine influenza by reducing viral burden, cytokine storm, neutrophil infiltration, vascular leak, and epithelial cell death while preserving protective alveolar macrophages, even when initiated after symptom onset.

Mice were infected with influenza virus to model severe disease. LAT8881 (16 aa cyclic) and LAT9997 (6 aa linear fragment) were administered intranasally from day 1 post-infection or after symptom onset. Outcomes: survival, lung pathology, damage markers, vascular leak, epithelial death, viral load, cytokines, immune cell infiltration. Structure-activity relationship studied by sequential amino acid trimming.

Current flu treatments (like Tamiflu) only work if given very early. A treatment that works after severe disease develops — by calming the immune overreaction rather than just fighting the virus — could save lives during flu pandemics and severe seasonal outbreaks. Using a natural human peptide fragment reduces the risk of off-target effects.

The biggest killer in severe flu isn't the virus itself — it's the body's own immune overreaction (cytokine storm). Most antiviral drugs target the virus but do nothing about the inflammatory damage. This peptide takes the opposite approach: it calms the immune overreaction while also reducing viral load, hitting severe influenza from both angles. If it works in humans, it could fill the critical gap in treatment options for patients already severely ill with influenza.

Preclinical mouse model only — mouse and human immune responses to influenza differ significantly. Intranasal delivery may be challenging in severely ill patients who are intubated. The relationship between this growth hormone fragment and growth hormone receptor signaling needs clarification. Manufacturing and stability of the peptide for clinical use not addressed.