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.