Transitional B Cell (TrB) T1/T2 Ratio Is a Marker for Graft Dysfunction in Human Kidney Transplant Recipients (KTRs).

Abstract

Accumulating evidence supports regulatory role for human TrB in KTRs. TrB are heterogeneous with variable cytokine expression. Here we have analysed their functional and clinical significance. The phenotype of TrB as Bregs was established in 15 healthy controls (HC). Compared to other B subsets, TrB expressed relatively higher IL10 and lower TNFα (high IL10/TNFα) and exhibited in vitro regulation by selectively suppressing autologous Th1 cytokines. While neutralizing IL10 blocked TrB mediated regulation, blocking TNFα uncovered regulation by memory B cells, confirming involvement of these cytokines in vitro suppressive activity. Within TrB, we identified phenotypically distinct T1(CD24++CD38++CD20++IgM++CD10+) and T2(CD24+CD38+CD20+IgM+CD10lo) subsets. T1 cells had significantly higher IL10/TNFα and were thereby more polarized towards IL10. Immune regulation by TrB was confirmed in 88 KTRs. Patients with biopsy proven rejection (n=25) had significantly lower absolute B cells, TrBs, and a lower TrB-IL10/TNFα ratio when compared to HC(n=15), patients with stable function (n=41) or graft dysfunction without rejection (n=22). Moreover, lower IL10/TNFα within TrB seen with rejection paralleled a significant fall in T1 cells (lower T1/T2 ratio). Both TrB-IL10/TNFα and T1/T2 ratios effectively distinguished stable patients from those with rejection on ROC analysis (AUC= 0.83&0.88, P<0.001). When divided into tertiles based on either TrB-IL10/TNFα or T1/T2, KTRs in the lowest tertiles of both groups had significantly greater incidence of DSA and deterioration in renal function (ΔeGFR) over 3 yrs from the time of biopsy. Since T1/T2 ratio paralleled IL10/TNFα in its ability to predict graft outcome, its utility as a potential marker of graft dysfunction was validated in two independent samples (n=50, each sample) acquired from a randomized trial comparing alemtuzumab vs. basiliximab induction. All patients from the trial were included and graft dysfunction was calculated as ΔeGFR from 6 mos to 3 yrs post-transplant. In both these sets, patients in the lowest tertile of T1/T2 had worse ΔGFR and DSA. To conclude, we provide evidence for TrB mediated immune regulation which is dependent on both IL10 and TNFα. Within TrB, T1 cells express most IL-10 and the fall in T1/T2 and TrB IL-10/TNFα may be linked. The relative utility of these ratios as biomarkers for allograft dysfunction needs to be determined prospectively.