Thomas Schachtner

BK virus-specific immunity kinetics: a predictor of recovery from polyomavirus BK-associated nephropathy.

Impaired BKV‐specific immunity is associated with development of BKV‐associated nephropathy. Suitable immunological parameters to identify patients at risk, however, are still debated. We monitored 18 kidney‐transplant recipients through the course of self‐limited BKV‐reactivation (n = 11) and BKV‐associated nephropathy (n = 7). BKV‐specific cellular immunity directed to nonstructural small and Large T‐antigen, and structural VP1–3 was analyzed in an interferon‐γ Elispot assay. BKV‐specific IgM and IgG were measured using an enzyme‐linked immunosorbent assay simultaneously. BKV‐specific cellular immunity directed to five BKV‐proteins increased significantly from diagnosis to resolution of BKV‐reactivation (p < 0.001). Patients with self‐limited BKV‐reactivation developed BKV‐specific T cells without therapeutic interventions, and cleared BKV‐reactivation within a median period of 1 month. Patients with BKV‐associated nephropathy, however, showed BKV‐specific T cells after a median period of 5 months after therapeutic interventions only, and cleared BKV‐reactivation after a median period of 8 months. Anti‐structural T cells were detected earlier than anti‐nonstructural T cells, which coincided with BKV‐clearance. Patients with BKV‐associated nephropathy showed the highest frequencies of BKV‐specific T cells at recovery, the highest increase in BKV‐specific IgG and persistence of increased IgM levels (p < 0.05). Our results suggest prognostic values of BKV‐specific immune monitoring to identify those patients at risk of BKV‐associated nephropathy and to aid in the management of therapeutic interventions.

Novel approach for improved assessment of phenotypic and functional characteristics of BKV-specific T-cell immunity.

Background. BKV-associated nephropathy represents a serious complication of the posttransplant period in kidney transplant recipients. Monitoring BKV-specific immunity is of a special importance for estimation of clinical course in patients with BKV reactivation. Our recent data demonstrated that all five BKV antigens are immunogenic and elicit T-cell responses varying within patients. Therefore, all five BKV proteins should be evaluated for the assessment of BKV-specific immunity. However, analysis of five proteins performed separately is time- and cost-intensive and requires large amount of blood. Methods. Using novel approach of a mixture of overlapping peptide pools encompassing all five BKV antigens (viral protein [VP] 1, VP2, VP3, large tumor antigen, and small tumor antigen) and multiparameter flow cytometry, we evaluate BKV-specific T cells in patients with a previous/present severe long-lasting or transient BKV reactivation. Patients without BKV reactivation were used as control. Results. In this study, we show that using mixture of overlapping peptide pool results in the magnitude of CD4- and CD8-positive BKV-specific T-cell response, which is significantly higher compared with any frequencies detected by previously used single BKV antigen stimulation. Of interest, patients with a history of rapid BKV clearance had significantly higher frequency of multifunctional interferon gamma-&ggr;/interleukin (IL)-2/tumor necrosis factor-&agr; and IL-2/tumor necrosis factor-&agr; CD4-positive T cells, suggesting protective potential of polyfunctional T cells. Furthermore, we did not find IL-17-producing BKV-specific memory T cells in patients recovered from BKV reactivation. Conclusions. Here, we established a fast and sensitive approach allowing the most comprehensive assessment of the total BKV immunity performed to date and offer a new platform for further prospective studies.

The Loss of BKV-specific Immunity From Pretransplantation to Posttransplantation Identifies Kidney Transplant Recipients at Increased Risk of BKV Replication.

Quantification of BKV‐load and BKV‐specific immunity have been evaluated to monitor BKV‐replication and outcomes in kidney transplant recipients (KTRs) with BKV‐infection. However, it remains crucial to better understand how immune markers can predict the risk for later infection. We studied all KTRs between 2008 and 2011. Twenty‐four KTRs were diagnosed with BKV‐replication and a control group of 127 KTRs was used for comparison. Samples were collected before at +1, +2, and +3 months posttransplantation. BKV‐specific and alloreactive T cells were measured using an interferon‐γ Elispot assay. The extent of immunosuppression was quantified by lymphocyte subpopulations and interferon‐gamma levels. KTRs with a loss of BKV‐specific T cells directed to Large T‐antigen from pretransplantation to posttransplantation were at increased risk of BKV‐replication (p < 0.001). In contrast, KTRs with stable/rising BKV‐specific T cells were more likely not to develop BKV‐replication (p < 0.05). KTRs developing BKV‐replication showed significantly lower CD3+, CD4+, CD8+ T cells and interferon‐γ levels posttransplantation, but significantly higher alloreactive T cells (p < 0.05). Monitoring pretransplant and posttransplant BKV‐specific T cells is suggested a sensitive marker to identify KTRs at increased risk of BKV‐replication. Increased susceptibility to immunosuppression predisposes KTRs to a loss of protective BKV‐specific immunity that results in impaired virus control and BKV‐replication.

Current characteristics and outcome of cytomegalovirus infections after kidney transplantation

The clinical course of cytomegalovirus (CMV) infections in the current era is poorly described. We characterized the symptoms and outcome of all CMV infections in a large cohort of kidney transplant recipients. Among 1129 kidney transplant recipients transplanted between 2004 and 2011 in Charité Universitätsmedizin Berlin and Helsinki University Hospital, 297 patients with CMV infection were characterized.

ABO desensitization affects cellular immunity and infection control after renal transplantation

The impact of ABO desensitization on overall immunity, infectious control, and alloreactivity remains unknown. We compared 35 ABO‐incompatible kidney transplant recipients (KTRs) to a control of 62 ABO compatible KTRs. Samples were collected before, at +1, +2, +3, +6, and +12 months post‐transplantation. CMV‐, BKV‐specific, and alloreactive T cells were measured using an interferon‐γ ELISPOT assay. The extent of immunosuppression was quantified by enumeration of lymphocyte subpopulations and cytokines. No differences were observed for 5‐year allograft survival and function between both groups (P > 0.05). However, ABO‐incompatible KTRs were more likely to develop CMV infection, BKV‐associated nephropathy, and severe sepsis (P = 0.001). Interestingly, ABO‐incompatible KTRs with poor HLA‐match showed the highest rates of infections and inferior allograft function (P < 0.05). CD3+, CD4+ T‐cell counts, interferon‐γ and IL‐10 levels were lower in ABO‐incompatible KTRs early post‐transplantation (P < 0.05). Likewise, ABO‐incompatible KTRs showed impaired BKV‐ and CMV‐specific T‐cell immunity (P < 0.05). ABO‐incompatible KTRs showed lower frequencies of alloreactive T cells (P < 0.05). Our data suggest T‐cell depletion due to ABO desensitization, which may contribute to the increased risk of T‐cell‐dependent infections. Elimination of B cells serving as antigen‐presenting cells, thereby causing impaired T‐cell activation, plays a significant role in both impaired infection control and reduced alloreactive T‐cell activation.

Different risk factor profiles distinguish early-onset from late-onset BKV-replication

Two of three reactivations of latent BKV‐infection occur within the first 6 months after renal transplantation. However, a clear differentiation between early‐onset and late‐onset BKV‐replication is lacking. Here, we studied all kidney transplant recipients (KTRs) at our single transplant center between 2004 and 2012. A total of 103 of 862 KTRs were diagnosed with BK viremia (11.9%), among which 24 KTRs (2.8%) showed progression to BKV‐associated nephropathy (BKVN). Sixty‐seven KTRs with early‐onset BKV‐replication (65%) and 36 KTRs with late‐onset BKV‐replication (35%) were identified. A control group of 598 KTRs without BKV‐replication was used for comparison. Lymphocyte‐depleting induction, CMV‐reactivation, and acute rejection increased the risk of early‐onset BKV‐replication (P < 0.05). Presensitized KTRs undergoing renal retransplantation were those at increased risk of late‐onset BKV‐replication (P < 0.05). Among KTRs with BK viremia, higher doses of mycophenolate increased the risk of progression to BKVN (P = 0.004). KTRs with progression to BKVN showed inferior allograft function (P < 0.05). KTRs with late‐onset BK viremia were more likely not to recover to baseline creatinine after BKV‐replication (P = 0.018). Our data suggest different risk factors in the pathogenesis of early‐onset and late‐onset BKV‐reactivation. While a more intensified immunosuppression is associated with early‐onset BKV‐replication, a chronic inflammatory state in presensitized KTRs may contribute to late‐onset BKV‐replication.

Inflammatory activation and recovering BKV-specific immunity correlate with self-limited BKV replication after renal transplantation.

As BKV‐associated nephropathy has emerged as an important cause of allograft failure, it has been of major importance to find immune mechanisms suitable to identify kidney transplant recipients (KTRs) at increased risk of BKV replication. We monitored 29 KTRs with seven measurements during the first year post‐transplantation. BKV‐specific T cells directed to 5 BKV proteins were analyzed in an interferon‐γ ELISPOT assay. BKV‐specific antibodies were measured using an ELISA. The extent of immunosuppression and inflammatory activation were quantified by measures of immune function including lymphocyte subpopulations, IP‐10, and adhesion molecule serum levels. All 5 BKV‐specific T cells increased significantly from diagnosis to resolution of BKV replication (P < 0.001). While antistructural T cells were significantly higher in KTRs with BKV replication (P < 0.05), no differences were observed for antismall t‐ and large T‐antigen‐directed T cells (P > 0.05). Interestingly, 65% of KTRs without BKV replication showed transient appearance of antismall t‐ and large T‐antigen‐directed T cells. Although no significant differences were observed for T‐cell subpopulations and adhesion molecules, IP‐10 levels increased significantly during BKV replication (P < 0.05). Assessment of BKV‐specific T cells identifies recovering BKV‐specific immunity in KTRs with BKV replication and suggests their protective ability in KTRs without BKV replication. Increases in IP‐10 levels stress the importance of infiltrating inflammatory leukocytes in the regulation of BKV replication and point to inflammatory activation in the pathogenesis of BKV replication.

CMV-Specific T Cell Monitoring Offers Superior Risk Stratification of CMV-Seronegative Kidney Transplant Recipients of a CMV-Seropositive Donor

Background Detectable cytomegalovirus (CMV)-specific T cells in CMV-seronegative kidney transplant recipients (KTRs) have been attributed to an absence of circulating antibodies despite CMV sensitization. The diagnostic value of CMV-specific T cells, however, needs to be implemented in risk stratification for CMV replication. Methods Three hundred twenty-six KTRs were studied and classified with respect to CMV serostatus and presence of CMV-specific T cells. Samples were collected pretransplantation, at +1, +2, and +3 months posttransplantation. CMV-specific T cells directed to CMV-IE1 and CMV-pp65 were measured by interferon-&ggr; Elispot assay. Results Nineteen (28%) of 67 D+R− KTRs showed pretransplant CMV-specific T cells. Although no differences were observed for CMV replication, KTRs with CMV-specific T cells presented with lower initial and peak CMV loads (P < 0.05). KTRs with decreasing/undetectable CMV-IE1–specific T cells pretransplantation and posttransplantation were at greatest risk of CMV replication. KTRs with stable/increasing CMV-IE1–specific T cells from pretransplantation to posttransplantation, however, showed low risk of CMV replication (P < 0.001). One hundred sixty-two (80%) of 203 R+ KTRs showed pretransplant CMV-specific T cells. Decreasing/undetectable CMV-IE1–specific T cells from pretransplantation and posttransplantation identified those R+ KTRs at increased risk of CMV replication (65/80 KTRs; 81%; P < 0.001). Conclusions Despite CMV prophylaxis, D+R− KTRs are at greatest risk of CMV disease. Our data suggest that monitoring CMV-specific T cell kinetics from pretransplantation to posttransplantation, particularly directed to CMV-IE1, offers superior risk stratification compared with CMV serostatus alone.

Estimated nephron number of the remaining donor kidney: impact on living kidney donor outcomes

BACKGROUND It has been demonstrated that low birth weight gives rise to a reduction in nephron number with increased risks for hypertension and renal disease. Its impact on renal function in kidney donors, however, has not been addressed. METHODS To investigate the impact of birth weight, kidney weight, kidney volume and estimated nephron number on kidney function, we collected data from 91 living kidney donors before nephrectomy, at +12, +36 and +60 months after nephrectomy. RESULTS Birth weight showed a positive correlation with estimated glomerular filtration rate (eGFR) at +12, +36 and +60 months after nephrectomy (P < 0.05). The strongest link was observed in donors >50 years old (R = 0.535, P < 0.001 at +12 months). Estimated nephron number and eGFR showed a strong positive correlation at +12, +36 and +60 months after nephrectomy (R = 0.540; R = 0.459; R = 0.506, P < 0.05). Daily proteinuria at +12 months showed a negative correlation with birth weight (P = 0.009). Donors with new-onset hypertension showed significantly lower birth weights and higher uric acid levels (P < 0.05). Kidney weight and volume did not show any impact on donor outcomes (P > 0.05). CONCLUSIONS Low nephron number predisposes donors to inferior remaining eGFR, hypertension and proteinuria. The strong correlation in elderly donors may be attributed to reduced renal functional reserve due to the decline of renal function with age.

Simultaneous pancreas/kidney transplant recipients present with late-onset BK polyomavirus-associated nephropathy

BACKGROUND Infections have increased in simultaneous pancreas/kidney transplant recipients (SPKTRs) with BK polyomavirus (BKV)-associated nephropathy (BKVN) being the most important infectious cause of allograft loss. Comparisons of BKVN with kidney transplant recipients (KTRs), however, are lacking. METHODS We studied all SPKTRs and KTRs at our transplant centre between 2003 and 2012. Eleven of 106 SPKTs (10.4%) and 21 of 1062 KTRs (2.0%) were diagnosed with BKVN with allograft loss in 1 SPKTR (9.1%) and 2 KTRs (9.5%). A control of 95 SPKTRs without BKVN was used for comparison. RESULTS SPKTRs showed an increased incidence of BKVN compared with KTRs (P < 0.001). Onset of BKVN in SPKTRs was significantly later compared with KTRs (P = 0.033). While 67% of KTRs showed early-onset BKVN, 64% of SPKTRs developed late-onset BKVN. Older recipient age and male gender increased the risk of BKVN in SPKTRs (P < 0.05). No differences were observed for patient and allograft survival (P > 0.05). However, SPKTRs with BKVN showed inferior estimated glomerular filtration rate and a higher incidence of de novo donor-specific antibodies compared with SPKTRs without BKVN in long-term follow-up (P < 0.05). SPKTRs showed higher peak BKV loads, a need for more intense therapeutic intervention and were more likely not to recover to baseline creatinine after BKVN (P < 0.05). CONCLUSIONS Our results suggest a higher incidence, more severe course and inferior outcome of BKVN in SPKTRs. An increased vulnerability of the allograft kidney due to inferior organ quality may predispose KTRs to early-onset BKVN. In contrast, SPKTRs present with late-onset BKVN in the presence of high-dose immunosuppression.