Single-cell RNA sequencing in lungs from the Hhip-haploinsufficient mouse model, which exhibits a similar inflammatory phenotype as seen in patients with COPD even in the absence of smoke exposure, revealed progressive activation of CD8+ T cells with age and increased expression of IFN-γ preceding emphysematous changes in Hhip+/– lungs. The gene discussed is CD8A; the disease is chronic obstructive pulmonary disease.