HHLA2 and chronic obstructive pulmonary disease: NSCLC with COPD showed a down-regulation of HERV–H LTR-associating protein 2 (HHLA2), which was an immune checkpoint molecule, and the HHLA2low group demonstrated the enrichment of CD8+CD103+ tissue-resident memory T cells (TRM) compared to the HHLA2high group (11.9% vs. 4.2%, P = 0.013).