Biologicals targeting the Th2-eosinophil nexus such as anti–interleukin (IL)-4, anti–IL-5, and anti–IL-13 are ineffective in asthma as a whole but are more effective if patients are selected using cellular (eg, eosinophils) or molecular (eg, periostin) biomarkers. The gene discussed is POSTN; the disease is asthma.