How might the variant alter drug response?

• The SERPINE1 variant appears in roughly 60% of the population.
• During viral infection, it drives extra PAI1 production.
• Excess PAI1 leads to airway scarring and a weaker antiviral response.
• Mepolizumab triggers additional inflammatory pathways in carriers — but not in non-carriers.
• Non-carriers do not show these extra damaging pathways.

Why could this matter for treatment?

Kumar said the finding could help doctors identify children who would not benefit from mepolizumab — or who might even face worsened inflammation the drug cannot target.

"We know from previous studies that children with this genetic variant are more likely to have asthma exacerbations during a viral illness, and now we have a greater understanding of how that happens," Kumar said.

He added that flagging these patients early could redirect them to better options sooner. "This is important to know in advance so the best therapeutic options could be considered earlier for these children. We are paving the way for precision medicine in pediatric asthma."

How strong is the evidence?

Kumar stressed clear limits. The study describes what happens inside the airways of children with the variant during a viral illness and after mepolizumab — not what would show up in routine clinical care.

The cohort was too small for a clinical conclusion, he said. The number of participants analyzed was not large enough to draw direct treatment recommendations. Still, based on how the inflammatory pathways behave, he expects children carrying the variant could have worse asthma outcomes on mepolizumab. A larger clinical trial would be needed to confirm that.

"Our findings also may lead to future studies to help identify patients for whom treatment with mepolizumab may not be as effective and who may even have more inflammation of types that the drug does not block," Kumar said.

"Our study implies that during a viral illness, children with asthma who have the genetic variant may have more inflammation in the airway lining than children without the variant, and this genetic difference creates distinct responses to mepolizumab," he added.

What comes next?

The journal lists the work in its 2026 volume. The team frames the finding as a building block for precision medicine — treatments selected by a patient's genetic profile rather than population-wide averages.

Future studies, Kumar said, will need to translate these airway-level findings into clinical guidance and test whether genetic screening before prescribing mepolizumab can prevent harm and improve outcomes for children with asthma.