Monitoring after renal transplantation: recommendations and caveats

CXCL13 Is an Indicator of Germinal Center Activity and Alloantibody Formation Following Transplantation

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Donor-specific antibodies (DSA) are a recognized cause of allograft injury, yet biomarkers that indicate their development posttransplant or guide management are not available. CXCL13 (chemokine [C-X-C motif] ligand 1) is a chemoattractant produced within secondary lymphoid organs necessary for germinal center (GC) and alloantibody formation. Perturbations in serum CXCL13 levels have been associated with humoral immune activity. Therefore, CXCL13 may correlate with the formation of HLA antibodies following transplantation.

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

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

[New faces of acute rejection in 2008]

Along the time, the definition of acute rejection has been modified according to the successive Banff classifications, the use of C4d and the identification of anti- HLA antibodies. Both cellular and humoral acute rejection are nowadays considered to be different with regard to definition, pathogenesis and hence treatment. The Banffclassification remains a very useful tool to improve the precision of these definitions. The new technologies such as microarrays should help to identify new aspects of acute rejection.