Immune Tolerance Induction Following AIT Is Associated with Induction of Circulating CD4+CXCR5+PD-1+FoxP3+ T Follicular Regulatory Cells

Rationale:  Circulating T follicular regulatory cells (CD4⁺CXCR5⁺PD-1⁺FoxP3⁺ Tfr) are a newly identified subset of CD4⁺T cells with regulatory properties. We hypothesised that Tfr cells are dysregulated in patients with seasonal allergic rhinitis (SAR) compared to non-atopic controls (NA). Furthermore, grass pollen immunotherapy (AIT) is associated with the induction of Tfr cells which may play a role in tolerance induction during AIT.

Methods:  In a cross-sectional study of AIT, PBMCs were isolated from SAR (n=13), NA (n=13) and AIT (subcutaneous, SCIT (n=10) and sublingual, SLIT (n=8) immunotherapy)-treated group. Circulating CD4⁺CXCR5⁺PD-1⁺FoxP3⁺ Tfr, CD4⁺CXCR5⁺PD-1⁺FoxP3^-T follicular helper (Tfh) cells were enumerated by flow cytometry. Allergen-induced Tfr and Tfh cell proliferation were also assessed.

Results:  Symptom scores were lower in SCIT (p<0.0001) and SLIT groups (p<0.05) compared to SAR. The frequency of circulating CD4⁺CXCR5⁺PD-1⁺FoxP3⁺ Tfr cells were lower in SAR compared to NA (median (IQR):13.90(4.42-18.50);p<0.05) and were elevated in SCIT (24.15(13.10-34.24);p<0.05) and SLIT (26.00(20.70-36.49);p<0.05). Conventional FoxP3⁺ Tregs were elevated in SCIT (6.83(4.83-7.92);p<0.01) and SLIT (6.64(5.48-7.92); p<0.001) compared to SAR (4.06(2.50-4.60). We also confirmed that Tfh cells were higher in SAR (86.10(81.50-95.58) compared to SCIT (75.58(65.76-86.90);p<0.05), SLIT (74.00 (63.51-79.30);p<0.001) and NA (77.60(49.25-85.15); p<0.05) groups. In addition, Tfh but not Tfr cells showed increased proliferative capacity in response to in vitrograss pollen allergen stimulation.

Conclusions:  For the first time, we show that Tfr and Tfh cells are dysregulated in patients with seasonal allergic rhinitis. AIT induces circulating Tfr cells and these cells may potentially be associated with tolerance induction during AIT.