B cells play an important role in the immune responses which affect the outcomes of kidney allografts. Dynamic changes of B-cell compartments in clinical kidney transplantation are still poorly understood. B-cell subsets were prospectively monitored using flow cytometry for 1 year in 98 kidney transplant recipients. Data were correlated with immunosuppression and clinical outcomes. An increase in the total population of B lymphocytes was observed during the first week after transplantation. The level of IgM(high) CD38(high) CD24(high) transitional B cells reduced significantly up until the third month, with partial repopulation in the first year. Lower numbers of transitional B cells in the third month were associated with higher risk of graft rejection. IgM(+) IgD(+) CD27(-) naive B cells did not change within follow-up. IgM(+) CD27(+) nonswitched memory B cells and IgM(-) CD27(+) switched memory B cells increased on post-operative day 7. IgM(-) CD38(high) CD27(high) plasmablasts showed similar kinetics during the first post-transplant year, similar to transitional B cells. In conclusion, sensitized kidney transplant recipients as well as those with either acute or chronic rejection within the first post-transplant year exhibited lower levels of transitional B cells. Therefore, these data further support the hypothesis that transitional B cells have a protective role in kidney transplantation.

Most kidney transplant patients who undergo biopsies are classified as having no rejection based on consensus thresholds. However, we hypothesized that because these patients have normal adaptive immune systems, T cell-mediated rejection (TCMR) and antibody-mediated rejection (ABMR) may exist as subthreshold activity in some transplants currently classified as no rejection. To examine this question, we studied genome-wide microarray results from 5086 kidney transplant biopsies (4170 patients). An updated archetypal analysis designated 56% of biopsies as no rejection. Subthreshold molecular TCMR and/or ABMR activity molecular activity was detectable as elevated classifier scores in many biopsies classified as no rejection, with ABMR activity in many TCMR biopsies and TCMR activity in many ABMR biopsies. In biopsies classified as no rejection histologically and molecularly, molecular TCMR classifier scores correlated with increases in histologic TCMR features and molecular injury, lower eGFR, and higher risk of graft loss, and molecular ABMR activity correlated with increased glomerulitis and donor-specific antibody. No rejection biopsies with high subthreshold TCMR or ABMR activity had a higher probability of having TCMR or ABMR respectively diagnosed in a future biopsy. We conclude that many kidney transplant recipients have unrecognized subthreshold TCMR or ABMR activity, with significant implications for future problems.

Background: Asymptomatic cytomegalovirus (CMV) infection is associated with graft dysfunction and failure. However, no study assessed CMV viral load in terms of the risk for graft failure. Methods: In a prospective cohort of kidney transplant recipients, we assessed the impact of CMV DNAemia on the overall graft survival and the incidence of moderate-to-severe interstitial fibrosis and tubular atrophy (IF/TA) in protocol biopsy at 36 months. CMV DNAemia was stratified by viral load in whole blood. Results: A total of 180 patients transplanted from October 2003 through January 2011 were included and followed for 4 years; 87 (48%) patients received 3-month prophylaxis with valacyclovir and 45 (25%) with valganciclovir; 48 (27%) were managed by pre-emptive therapy. Within 12 months of transplantation, CMV DNAemia developed in 102 (57%) patients with 36 (20%) having a viral load of ≥2,000 copies/ml. Multivariate Cox analysis identified CMV DNAemia as an independent risk factor for graft loss (hazard ratio 3.42; P=0.020); however, after stratification by viral load, only CMV DNAemia ≥2,000 copies/ml (hazard ratio 7.62; P<0.001) remained significant. Both early-onset (3 months; P<0.001) CMV DNAemia ≥2,000 copies/ml were risk factors for graft loss. The incidence of moderate-to-severe IF/TA was not significantly influenced by CMV DNAemia. Conclusions: Kidney transplant recipients having CMV DNAemia with a higher viral load irrespective of the time to onset are at increased risk for graft loss.

The aim of the study was to characterize by molecular profiling two glomerular diseases: IgA nephropathy (IgAN) and focal segmental glomerulosclerosis (FSGS) and to identify potential molecular markers of IgAN and FSGS progression. The expressions of 90 immune-related genes were compared in biopsies of patients with IgAN (n=33), FSGS (n=17) and in controls (n=11) using RT-qPCR. To identify markers of disease progression, gene expression was compared between progressors and non-progressors in 1 year follow-up. The results were verified on validation cohort of patients with IgAN (n=8) and in controls (n=6) using laser-capture microdissection, that enables to analyze gene expression separately for glomeruli and interstitium. In comparison to controls, patients with both IgAN and FSGS, had lower expression of BAX (apoptotic molecule BCL2-associated protein) and HMOX-1 (heme oxygenase 1) and higher expression of SELP (selectin P). Furthermore, in IgAN higher expression of PTPRC (protein-tyrosine phosphatase, receptor-type C) and in FSGS higher expression of BCL2L1 (regulator of apoptosis BCL2-like 1) and IL18 compared to control was observed. Validation of differentially expressed genes between IgAN and controls on another cohort using laser-capture microdissection confirmed higher expression of PTPRC in glomeruli of patients with IgAN. The risk of progression in IgAN was associated with higher expression EDN1 (endothelin 1) (AUC=0.77) and FASLG (Fas ligand) (AUC=0.82) and lower expression of VEGF (vascular endothelial growth factor) (AUC=0.8) and in FSGS with lower expression of CCL19 (chemokine (C-C motif) ligand 19) (AUC=0.86). Higher expression of EDN1 and FASLG along with lower expression of VEGF in IgAN and lower expression of CCL19 in FSGS at the time of biopsy can help to identify patients at risk of future disease progression.