Emerging role of cell-free DNA in kidney transplantation

Monitoring kidney transplants for rejection conventionally includes serum creatinine, immunosuppressive drug levels, proteinuria, and donor-specific antibody (DSA). Serum creatinine is a late marker of allograft injury, and the predictive ability of DSA regarding risk of rejection is variable. Histological analysis of an allograft biopsy is the standard method for diagnosing rejection but is invasive, inconvenient, and carries risk of complications. There has been a long quest to find a perfect biomarker that noninvasively predicts tissue injury caused by rejection at an early stage, so that diagnosis and treatment could be pursued without delay in order to minimize irreversible damage to the allograft. In this review, we discuss relatively novel research on identifying biomarkers of tissue injury, specifically elaborating on donor-derived cell-free DNA, and its clinical utility.

Vaccinations in kidney transplant recipients: Clearing the muddy waters

Vaccine preventable diseases account for a significant proportion of morbidity and mortality in transplant recipients and cause adverse outcomes to the patient and allograft. Patients should be screened for vaccination history at the time of pre-transplant evaluation and vaccinated at least four weeks prior to transplantation. For non-immune patients, dead-vaccines can be administered starting at six months post-transplant. Live attenuated vaccines are contraindicated after transplant due to concern for infectious complications from the vaccine and every effort should be made to vaccinate prior to transplant. Since transplant recipients are on life-long immunosuppression, these patients may have lower rates of serological conversion, lower mean antibody titers and waning of protective immunity over shorter period as compared to general population. Recommendations regarding booster dose in kidney transplant recipients with sub-optimal serological response are lacking. Travel plans should be part of routine post-transplant assessment and pre-travel vaccines and counseling should be provided. More studies are needed on vaccination schedules, serological response, need for booster doses and safety of live attenuated vaccines in this special population.

Kidney transplantation in older recipients: Preemptive high KDPI kidney vs lower KDPI kidney after varying dialysis vintage

AIM

To evaluate the outcomes of transplanting marginal kidneys preemptively compared to better-quality kidneys after varying dialysis vintage in older recipients.

METHODS

Using OPTN/United Network for Organ Sharing database from 2001-2015, we identified deceased donor kidney (DDK) transplant recipients > 60 years of age who either underwent preemptive transplantation of kidneys with kidney donor profile index (KDPI) ≥ 85% (marginal kidneys) or received kidneys with KDPI of 35%-84% (better quality kidneys that older wait-listed patients would likely receive if waited longer) after being on dialysis for either 1-4 or 4-8 years. Using a multivariate Cox model adjusting for donor, recipient and transplant related factors- overall and death-censored graft failure risks along with patient death risk of preemptive transplant recipients were compared to transplant recipients in the 1-4 and 4-8 year dialysis vintage groups.

RESUTLS

The median follow up for the whole group was 37 mo (interquartile range of 57 mo). A total of 6110 DDK transplant recipients above the age of 60 years identified during the study period were found to be eligible to be included in the analysis. Among these patients 350 received preemptive transplantation of kidneys with KDPI ≥ 85. The remaining patients underwent transplantation of better quality kidneys with KDPI 35-84% after being on maintenance dialysis for either 1-4 years (n = 3300) or 4-8 years (n = 2460). Adjusted overall graft failure risk and death-censored graft failure risk in preemptive high KDPI kidney recipients were similar when compared to group that received lower KDPI kidney after being on maintenance dialysis for either 1-4 years (HR 1.01, 95%CI: 0.90-1.14, P = 0.84 and HR 0.96, 95%CI: 0.79-1.16, P = 0.66 respectively) or 4-8 years (HR 0.82, 95%CI: 0.63-1.07, P = 0.15 and HR 0.81, 95%CI: 0.52-1.25, P = 0.33 respectively). Adjusted patient death risk in preemptive high KDPI kidney recipients were similar when compared to groups that received lower KDPI kidney after being on maintenance dialysis for 1-4 years (HR 0.99, 95%CI: 0.87-1.12, P = 0.89) but lower compared to patients who were on dialysis for 4-8 years (HR 0.74, 95%CI: 0.56-0.98, P = 0.037).

CONCLUSION

In summary, our study supports accepting a “marginal” quality high KDPI kidney preemptively in older wait-listed patients thus avoiding dialysis exposure.

Does Induction Type Influence Outcomes in Kidney Transplant Recipients at Different Phases of Hepatitis B Infection?

OBJECTIVES

Immunosuppressive therapy in kidney transplant recipients with hepatitis B virus infection may increase the risk of disease progression. Here, we compared outcomes of depleting (antithymocyte globulin/alemtuzumab) versus nondepleting (basiliximab/daclizumab) antibody induction in kidney transplant recipients at different serologic phases of hepatitis B virus infection.

MATERIALS AND METHODS

We used the Organ Procurement and Transplantation Network/United Network for Organ Sharing database to identify adult kidney transplant recipients at different serologic phases of hepatitis B virus infection (transplants received from 2001-2011 after patients received perioperative induction with discharge on calcineurin inhibitors/mycophenolate mofetil with/without steroids). We used a Cox model to compare outcomes among patient groups.

RESULTS

Median follow-up was 50.7 months (range, 28.6 to 82.6 mo). Serologic phase for the 7681 study patients were as follows: 1098 at HBsAg+/anti-HBc- (depleting = 652, nondepleting = 446), 446 at HBsAg+/anti-HBc+ (depleting = 250, nondepleting = 216), and 6117 at HBsAg-/anti-HBc+ (depleting = 3562, nondepleting = 2555) (where anti-HBc denotes hepatitis B core antibody, HBsAg denotes hepatitis B surface antigen, and +/- denote positive/negative). When we compared those with depleting versus nondepleting agents, hazard ratios (95% confidence intervals) for adjusted overall graft, death-censored graft, and patient survival were 0.97 (0.78-1.26; P = .86), 1.20 (0.83-1.60; P = .44), and 0.92 (0.66-1.30; P = .51) in the HBsAg+/anti-HBc-; 0.81 (0.55-1.18; P = .27), 0.59 (0.32-1.12; P = .11), and 0.95 (0.60-1.49; P = .83) in the HBsAg+/anti-HBc+; and 0.96 (0.86-1.05; P = .37), 0.95 (0.60-1.49; P = .97), and 0.92 (0.80-1.05; P = 0.22) in the HBsAg-/anti-HBc+ groups.

CONCLUSIONS

Our study did not show adverse graft and patient outcomes associated with depleting versus nondepleting antibody induction in kidney transplant recipients at different phases of hepatitis B virus infection. This supports the selection and use of induction agents based on immunologic risk in such patients.

Limitation of Terminal Serum Creatinine as a Kidney Donor Profile Index Variable in Predicting Long-Term Kidney Transplant Outcomes

BACKGROUND

Donor final serum creatinine (SCr) is a dynamic variable and is 1 of 10 factors used in calculating kidney donor profile index (KDPI). We hypothesize that deceased-donor kidneys (DDKs) with higher SCr were likely accepted for transplantation if procurement biopsy findings were favorable and with long-term outcomes no worse than kidneys with lower final SCr within a KDPI group.

METHODS

Using the Organ Procurement and Transplant Network/United Network for Organ Sharing database, we identified DDK transplant recipients from 2000 to 2015 who received induction and calcineurin inhibitor/mycophenolate mofetil maintenance. Patients were divided into 4 KDPI groups: 0-20%, 21%-50%, 51%-85%, and >85%. In each KDPI category, long-term outcomes were compared, with the use of Cox models, between patients who received kidneys with final SCr >2 versus ≤2 mg/dL.

RESULTS

A total of 59,644 patients were divided into KDPI groups 0-20% (SCr >2 mg/dL, n = 478; SCr ≤2 mg/dL, n = 14,769), 21%-50% (SCr >2 mg/dL, n = 1,592; SCr ≤2 mg/dL, n = 17,762), 51%-85% (SCr >2 mg/dL; n = 1,388, SCr ≤2 mg/dL, n = 18,024), and >85% (SCr >2 mg/dL, n = 349; SCr ≤2 mg/dL, n = 5,282). Adjusted overall graft failure risks (hazard ratio [HR] 0.88, P = .04; HR, 0.86, P = .007) and patient death risks (HR, 0.86, P = .04; HR, 0.84, P = .01) for final SCr >2 versus ≤2 mg/dL groups were lower in KDPI categories 21%-50% and 51%-85%, respectively, with similar death-censored graft failure risks.

DISCUSSION

Outcomes of transplanting DDKs with elevated final SCr are no worse than transplanting kidneys with lower final SCr, highlighting the limitation of the single value of final SCr as a variable for calculating KDPI.

Impact of cold ischemia time on the outcomes of kidneys with Kidney Donor Profile Index ≥85%: mate kidney analysis - a retrospective study

The new kidney allocation system recommends local and regional sharing of deceased donor kidneys (DDK) with 86-100% Kidney Donor Profile Index (KDPI) to minimize discard. Regional sharing can increase cold ischemia time (CIT) which may negatively impact transplant outcomes. Using a same donor mate kidney model, we aimed to define a CIT that should be targeted to optimize outcomes. Using Organ Procurement and Transplant Network/United Network for Organ Sharing database, we identified recipients of DDK from 2000 to 2013 with ≥85% KDPI. From this cohort, three groups of mate kidney recipients were identified based on CIT: group 1 (≥24 vs. ≥12 to <24 h), group 2 (≥24 vs. <12 h), and group 3 (≥12 to <24 vs. <12 h). Adjusted delayed graft function (DGF), and graft and patient survivals were compared for mate kidneys. DGF risk was significantly lower for patients with CIT <12 vs. ≥24 h in group 2 (adjusted OR: 0.25, 95% CI: 0.12-0.57, P < 0.001) while trending lower for CIT ≥12 to <24 vs. ≥24 h in group 1 (adjusted OR: 0.78, 95% CI: 0.59-1.03, P = 0.08) and CIT <12 vs. ≥12 to <24 h in group 3 (adjusted OR: 0.74, 95% CI: 0.55-1.0, P = 0.05). Adjusted graft and patient survivals were similar between mate kidneys in all groups. Minimizing CIT improves outcomes with regional sharing of marginal kidneys.

Outcomes of Kidney Transplantation in Patients Exposed to Hepatitis B Virus: Analysis by Phase of Infection

BACKGROUND

In kidney transplant recipients (KTRs) with hepatitis B virus (HBV) infection, immunosuppression may increase viral replication with increased risk for liver disease progression and HBV-related kidney diseases, factors that could adversely influence graft and patient outcomes. We aimed to analyze the impact of different phases of HBV infection on the outcomes in KTRs.

METHODS

Using the Organ Procurement and Transplant Network/United Network for Organ Sharing database, we selected adult KTRs from 2001 to 2011 who received peri-operative antibody induction followed by calcineurin inhibitor/mycophenolate mofetil maintenance with/without steroid. The cohort was divided into 4 groups, based on the presence/absence of hepatitis B surface antigen (HBsAg) and core antibody (HBcAb) at the time of transplantation: group 1: HBsAg+/HBcAb- (acute infection); group 2: HBsAg+/HBcAb+ (developing immune response); group 3; HBsAg-/HBcAb+ (resolving infection); and group 4: HBsAg-/HBcAb- (HBV-naive). Graft and patient survivals were compared among the groups in a multivariate Cox model.

RESULTS

Adjusted overall graft (hazard ratio [HR], 0.97; 95% confidence interval [CI], 0.90-1.10; P = .58) and patient (HR, 0.95; 95% CI, 0.83-1.09; P = .52) survival rates were similar between groups 1 and 2, with inferior death-censored graft survival in group 1 (HR, 0.83; 95% CI, 0.71-0.98; P = .02). Adjusted over all graft (HR, 1.0; 95% CI, 0.90-1.00; P = .46) and patient (HR, 1.03; 95% CI, 0.90-1.10; P = .10) survival rates were similar between groups 3 and 4, and death-censored graft survival trended inferior in group 3 (HR, 0.97; 95% CI, 0.90-1.00; P = .05).

CONCLUSIONS

Our analysis supports a practice of delaying kidney transplantation in HBV-infected patients until they develop an immune response and preferably until the infection is cleared.