Immunosuppression Has Long-Lasting Effects on Circulating Follicular Regulatory T Cells in Kidney Transplant Recipients

Abstract

Background: FoxP3 + follicular regulatory T cells (Tfr) have been identified as the cell population controlling T follicular helper (Tfh) cells and B cells which, are both involved in effector immune responses against transplanted tissue. Methods: To understand the biology of Tfr cells in kidney transplant patients treated with tacrolimus and mycophenolate mofetil (MMF) combination immunosuppression, we measured circulating (c)Tfh and cTfr cells in peripheral blood by flow cytometry in n = 211 kidney transplant recipients. At the time of measurement patients were 5–7 years after transplantation. Of this cohort of patients, 23.2% (49/211) had been previously treated for rejection. Median time after anti-rejection therapy was 4.9 years (range 0.4–7 years). Age and gender matched healthy individuals served as controls. Results: While the absolute numbers of cTfh cells were comparable between kidney transplant recipients and healthy controls, the numbers of cTfr cells were 46% lower in immunosuppressed recipients ( p < 0.001). More importantly, in transplanted patients, the ratio of cTfr to cTfh was decreased (median; 0.10 vs. 0.06), indicating a disruption of the balance between cTfr and cTfh cells. This shifted balance was observed for both non-rejectors and rejectors. Previous pulse methylprednisolone or combined pulse methylprednisolone + intravenous immunoglobulin anti-rejection therapy led to a non-significant 30.6% (median) and 51.2% (median) drop in cTfr cells, respectively when compared to cTfr cell numbers in transplant patients who did not receive anti-rejection therapy. A history of alemtuzumab therapy did lead to a significant decrease in cTfr cells of 85.8% (median) compared with patients not treated with anti-rejection therapy ( p < 0.0001). No association with tacrolimus or MMF pre-dose concentrations was found. Conclusion: This cross-sectional study reveals that anti-rejection therapy with alemtuzumab significantly lowers the number of cTfr cells in kidney transplant recipients. The observed profound effects by these agents might dysregulate cTfr functions.

Potential Application of T-Follicular Regulatory Cell Therapy in Transplantation

“…There has also been a trend in some studies (100) of a positive Tfr : Tfh associating with less DSA formation. However, Niu et al (61), found patients with anti-HLA antibodies or DSA at 5-7 years post-transplant or any form of rejection had similar bTfr and bTfh cell numbers as those without antibodies or rejection. This is in opposition to Macedo et al (104), who demonstrated lower Tfh.…”

“…However, Niu et al. ( 61 ), found patients with anti-HLA antibodies or DSA at 5–7 years post-transplant or any form of rejection had similar bTfr and bTfh cell numbers as those without antibodies or rejection. This is in opposition to Macedo et al.…”

“…It is at this stage that they lose the CD25 expression and upregulate Bcl-6, ICOS and PD-1 ( 60 ). In human, these cells are able, not only to inhibit Tfh activation (therefore decreasing their production of IL-4, IL-21) and suppress Tfh cell-GC B cell interactions leading to antibody production ( 61 ) but also decrease the activation of B cells through PD-1/PD-L1 interactions and the inhibitory function of CTLA4 molecules. Moreover, it has been demonstrated that they inhibit the capacity of class switching from IgM to IgG in mouse ( 23 ) and decrease IgA production by B cells in human ( 62 ), therefore inhibiting the selection of non-antigen-specific B cells (including those with self-reacting BCR) and limiting the number of B cells (indirect regulation).…”

“…Niu et al. ( 61 ), evaluated Tfr in the clinical context of long term multiple agent immunosuppression in 211 patients with a functioning renal transplant over 5 years post transplantation. They found absolute numbers of Tfr (total CD3 + CD4 + CXCR5 + FOXP3 − ) including subsets that were PD1+ and Helios+, were lower in transplant recipients compared to healthy controls.…”

Single-Cell Profiling of Kidney Transplant Recipients With Immunosuppressive Treatment Reveals the Dynamic Immune Characteristics

“…Other studies in renal transplant recipients have demonstrated increased Tfh cell numbers before the development of donor-specific antibodies (DSA), in association with antibody-mediated rejection (ABMR) or with the development of anti-HLA antibodies (36)(37)(38). Furthermore, anti-rejection therapy with alemtuzumab significantly lowers the number of Tfh cells in kidney transplant recipients and contributes to the stable status of the kidney transplant (39). A study compared the proportion and function of follicular helper T cells in the blood between patients with operative tolerance and patients with stable graft function.…”