Allergen-specific immunotherapy enhances CD8⁺ CD25⁺ CD137⁺ regulatory T cells and decreases nasal nitric oxide

Background: 4-1BB (CD137), a member of the inducible tumor necrosis factor receptor (TNFR) family, is expressed on regulatory T (Treg) cells and regulates Treg cells to control allergic inflammation. Pam3CSK4, a synthetic TLR2 ligand that can expand CD8⁺ Treg function, is a promising adjuvant for allergen immunotherapy (IT). We examined whether Dermatophagoides pteronyssinus (Der p) IT and Pam3CSK4 could enhance CD8⁺ CD25⁺ CD137⁺ Treg suppressive function to decrease nasal nitric oxide (nNO) levels. Methods: Nasal symptom scores, nNO levels, PBMCs, and inferior turbinate biopsies were obtained from 40 mite-sensitive perennial allergic rhinitis (PAR) patients before and after one year of Der p IT and 30 non-allergic control subjects. CD137 expression on CD8⁺ CD25⁺ T cells and suppressive function of CD8⁺ CD25⁺ CD137⁺ Tregs was measured using flow cytometry. Cytokine levels were analyzed by ELISA. Inducible nitric oxide synthase production by nasal epithelial cells after co-culturing with CD8⁺ CD25⁺ CD137⁺ T cells was analyzed by Western blotting. Results: Der p IT improved nasal symptom scores, decreased nNO levels, and increased CD137 expression on CD8⁺ T cells in PBMCs and nasal mucosa. Pam3CSK4 expanded the CD8⁺ CD25⁺ CD137⁺ population in PBMCs. Pam3CSK4-stimulated CD8⁺CD25⁺CD137⁺ Tregs induced IL-10 and TGF-β and suppressed CD4⁺CD25- T-cell proliferation mainly by cell contact inhibition. CD8⁺CD25⁺CD137⁺ Tregs cultured with nasal epithelial cells suppressed Der p 2–induced iNOS production. Silencing CD137 in sorted CD8⁺CD25⁺ T cells decreased Pam3CSK4-activated Foxp3 expression. Conclusion: Der p IT expanded CD8⁺CD25⁺CD137⁺ Tregs and decreased nNO levels. Induced CD137 expression on CD8⁺CD25⁺ Tregs by Pam3CSK4 stimulation may help suppress allergic inflammation during IT.