Sirolimus therapy restores the PD-1+ICOS+Tfh:CD45RA-Foxp3 high activated Tfr cell balance in primary Sjögren's syndrome

Primary Sjögren's syndrome (pSS) is a common chronic autoimmune disease characterized by lymphocytic infiltration of salivary and lacrimal glands. The current study was performed to investigate the roles of follicular helper T (Tfh) and follicular regulatory T (Tfr) subsets in patients with pSS, and to evaluate the effects of sirolimus on these cells. Levels of circulating Tfh and Tfr subsets in 58 pSS patients and 26 healthy controls (HC) were determined by flow cytometry. These T cell subsets were also analyzed in 12 patients before and after treatment with sirolimus. Clinical features and correlations with follicular T cells were analyzed systematically. The discriminative ability of the cells and ratios was evaluated based on the area under the receiver operating characteristic curves. Patients with pSS had higher percentage and absolute number of PD-1+ICOS+Tfh cells, while lower percentage and absolute number of Tfr, activated regulatory T (aTreg) cells, and CD45RA-Foxp3 activated Tfr cells. Furthermore, increased number of PD-1+ICOS+Tfh cells was associated with B cells, while decreased numbers of Tfr and their subsets was strongly associated with aTreg cells in pSS patients. Also, the higher proportion of PD-1+ICOS+Tfh cells was positively correlated with higher level of autoantibodies, ESR, IgG, cytokines (IL-2, IL-4, IL-10, IL-17, IFN-γ, TNF-α, IL-21 and sIL-2αR), and disease activity. Unexpectedly, the elevated PD-1+ICOS+Tfh:CD45RA-Foxp3 activated Tfr ratio had the greatest ability to discriminate between pSS and HC, and sirolimus therapy restored the PD-1+ICOS+Tfh cells:CD45RA-Foxp3 activated Tfr ratio, and controlled disease activity. The novel ratio of PD-1+ICOS+Tfh to CD45RA-Foxp3 activated Tfr cells can effectively discriminate the pSS patients from controls, and Tfr cell subsets may resemble Treg cell lineages. Furthermore, the PD-1+ICOS+Tfh cells can be used as a biomarker of disease activity and to verify the therapeutic effects of sirolimus in pSS.