Longitudinal Studies of a B-Cell-Derived Signature of Tolerance in Renal Transplantation

The development of reliable biomarkers of transplant tolerance would enhance the safety and feasibility of clinical trials and potentially also facilitate management of patients on standard immunosuppressive therapies. To this end, we examined peripheral blood samples of spontaneously tolerant renal transplant recipients, as well as patients enrolled in two interventional tolerance trials, using multiparameter flow cytometry and gene expression analysis. Repeat analysis of samples from a previously reported tolerant cohort, as well as newly identified tolerant patients, confirmed that tolerance was associated with increased expression of B cell-associated genes relative to immunosuppressed patients with stable renal function. This was not accounted for merely by an increase in total B cell numbers, but appeared to be the result of increased frequencies of transitional and naïve B cells. Moreover, serial measurements demonstrated that this pattern persisted over several years. Importantly, patients rendered tolerant via induction of transient mixed chimerism, and those weaned to low levels of immunosuppression, showed similar increases in the expression of selected B cell genes as did spontaneously tolerant individuals. Collectively, these findings support the notion that alterations in B cells may be a common theme for tolerant kidney transplant recipients, and a useful immune monitoring tool in prospective trials. The MassARRAY QGE (Sequenom) multiplexed primer and competitive template designs and analysis were reported previously. Total of 25 TOL (Tolerant), 7 New TOL (New Tolerant), 34 SI (Standard Immunosuppression) in cohort ITN507; 7 Sirolimus Monotherapy, 2 SI Multiagent in cohort ITN013; and 7 TOL and 1 Return to SI in cohorts ITN010 and ITN036.