Circulating T follicular helper cells are a biomarker of humoral alloreactivity and predict donor-specific antibody formation after transplantation

Abstract

Donor-specific antibodies (DSA) contribute to renal allograft loss. However, biomarkers to guide clinical management of DSA post-transplant or detect humoral alloimmune responses before alloantibodies develop are not available. Circulating T follicular helper (Tfh) cells are CD4 + CXCR5 + Tfh-like cells in the blood that have been associated with alloantibodies in transplant recipients, but whether they precede antibody formation for their evaluation as a predictive biomarker in transplantation is unknown. To evaluate the ability of circulating Tfh (cTfh) cells to predict DSA, we utilized murine transplant models to determine the temporal relationship between cTfh cells, germinal center (GC) formation, and DSA development. We observed that donor-reactive CD4 + CXCR5 + cTfh cells expand following allotransplantation. These cTfh cells were equivalent to graft-draining lymph node-derived Tfh cells in their ability to provide B cell help for antibody production. Circulating Tfh cell expansion and differentiation into ICOS + PD-1 + cells temporally correlated with GC alloreactivity and preceded the generation of DSA in instances of modified and unmodified alloantibody formation. Importantly, delayed costimulation blockade initiated after the detection of ICOS + PD-1 + cTfh cells prevented DSA. These findings suggest that cTfh cells could serve as a biomarker for humoral alloreactivity prior to the detection of alloantibodies and inform therapeutic approaches to prevent DSA.

CXCR5+PD1+ICOS+ Circulating T Follicular Helpers Are Associated With de novo Donor-Specific Antibodies After Renal Transplantation

“…The frequency of activated cTfh subsets is also increased by immunizing events, including previous blood transfusions and/or pregnancies, and the presence of class II non-DSA anti-HLA antibodies. These data, in accordance with previous reports, suggest that pre-sensibilization increases the pool of activated cTfhs (10, 27, 40) and is consistent with the lack of effect of standard immunosuppression on activated Tfhs (23, 28). These results are also in line with reports exhibiting that T cells were unequally targeted by immunosuppressive treatments, memory T cells exhibiting a relative increase frequency after ATG depletion (41).…”

“…The authors analyzed de novo anti-HLA antibody appearance during the first year post-transplantation, whereas we focused on dn DSA occurrence after the first year of transplantation in patients who were DSA-free in this first year. In a murine model of skin transplantation, a rapid increase of donor-specific CXCR5 + PD1 + ICOS + cTfhs in blood preceded the appearance of DSA, followed by a contraction phase (23). By contrast, we did not observe an increase of these cTfhs but a decrease level associated with dnDSA which may be explained by different kinetics between mice and human (days compared to months or years).…”

“…Several studies in animal models suggest a beneficial effect of blocking the differentiation of cTfhs in transplantation (9, 19–23). In Humans, recent reports have shown an association of Tfhs with anti-HLA antibodies and/or DSA (10, 24–29).…”

“…Examining their presence/clearance in blood from transplanted patients, particularly activated cTfh subsets linked to antibody production, may thus predict the genesis of antibody-mediated rejection as suggested in mouse model (23). Thus, herein, we measured the frequency of total CD4 + CD45RA − CXCR5 + cTfhs and activated CXCR5 + PD1 + , CXCR5 + PD1 + ICOS + and CXCR5 + PD1 + CXCR3 − subsets at the time of transplantation (day 0) and after 1 year (M12) in peripheral blood mononuclear cells (PBMCs) from a prospective cohort of 237 patients without DSA before renal transplantation and without any occurrence of dnDSA during the first year post-transplantation.…”

Superior inhibition of alloantibody responses with selective CD28 blockade is CTLA-4 dependent and T follicular helper cell specific

“…Thus, CTLA‐4 antagonism reversed selective CD28 blockade‐mediated inhibition of alloantibody formation. Because peak Tfh response precedes antibody formation by 4 days, 32 we next examined the GC response in graft‐DLNs 24 days posttransplant. The addition of anti‐CTLA‐4 mAb significantly increased CXCR5 + PD‐1 hi Tfh and Bcl6 hi PD‐1 hi+ GC Tfh cells over that observed in animals treated with anti‐CD28 dAb alone (Figure 3D,E).…”