Imaging reveals flu transcription bottleneck, host-targeted antivirals offer broad-spectrum hope

For the first time, scientists have tracked the influenza virus throughout its entire life cycle inside human airway cells and discovered that most infections fail because of errors in reading the viral genetic material, or transcription, according to a study published in Cell Systems. The findings spotlight a vulnerable step in the viral replication process, while separate research explores a host-targeted strategy to create broad-spectrum antivirals that could overcome the rapid drug resistance seen with conventional treatments.

Researchers from the Hubrecht Institute developed a technique called VISUN, which attaches a fluorescent flag to individual viral RNA molecules so they can be observed under a microscope as bright spots moving through the cell. Collaborating with the Clevers group, they studied influenza A virus (IAV) infection in human airway organoids—miniature airway tissue grown in a lab dish. The team observed that only a small minority of viral particles successfully complete all the steps needed to produce new virus. Many infections stalled, with the largest bottleneck occurring at viral transcription. “If this goes wrong in the early stages of the infection, the chance of a successful infection decreases greatly,” the researchers noted.

This newly visible weak point could aid the development of new antiviral drugs and improve existing ones. Currently, over 200 viruses are known to cause disease in humans, but only about 10 viral infections can be treated by approved antiviral drugs. Traditional direct-acting antivirals target viral proteins, but viruses can evolve resistance quickly because of their high mutation rates and rapid replication. Developing a new drug typically takes 8 to 12 years and costs more than $2 billion, with no guarantee it will remain effective.

An alternative approach, pursued by researchers at Stanford, is to target host cell machinery that viruses hijack to replicate. Because viruses are obligate parasites that rely on cellular enzymes, disrupting these host factors could stop infection without directly attacking the virus itself, making it harder for the virus to develop resistance. This host-directed strategy could potentially yield a single broad-spectrum drug effective against multiple viral families, addressing a critical gap for future pandemics.

The Hubrecht team also validated VISUN with a wide range of influenza variants, including viruses isolated from animals, in collaboration with the group of Ron Fouchier at Erasmus MC. The platform can be used to assess whether an animal virus has the potential to infect humans, contributing to predictions of future threats. Together, these advances underscore the importance of understanding viral life cycle bottlenecks and host-virus interactions to design more robust antiviral therapies.