Variables affecting estimated glomerular filtration rate after renal transplantation in children: a NAPRTCS data analysis

Non-invasive biomarkers of acute rejection in pediatric kidney transplantation: New targets and strategies

Kidney transplantation is the preferred treatment for pediatric end-stage renal disease. However, pediatric recipients face unique challenges due to their prolonged need for kidney function to accommodate growth and development. The continual changes in the immune microenvironment during childhood development and the heightened risk of complications from long-term use of immunosuppressive drugs. The overwhelming majority of children may require more than one kidney transplant in their lifetime. Acute rejection (AR) stands as the primary cause of kidney transplant failure in children. While pathologic biopsy remains the "gold standard" for diagnosing renal rejection, its invasive nature raises concerns regarding potential functional impairment and the psychological impact on children due to repeated procedures. In this review, we outline the current research status of novel biomarkers associated with AR in urine and blood after pediatric kidney transplantation. These biomarkers exhibit superior diagnostic and prognostic performance compared to conventional ones, with the added advantages of being less invasive and highly reproducible for long-term graft monitoring. We also integrate the limitations of these novel biomarkers and propose a refined monitoring model to optimize the management of AR in pediatric kidney transplantation.

Rejection markers in kidney transplantation: do new technologies help children?

Recent insights in allorecognition and graft rejection mechanisms revealed a more complex picture than originally considered, involving multiple pathways of both adaptive and innate immune response, supplied by efficient inflammatory synergies. Current pillars of transplant monitoring are serum creatinine, proteinuria, and drug blood levels, which are considered as traditional markers, due to consolidated experience, low cost, and widespread availability. The most diffuse immunological biomarkers are donor-specific antibodies, which are included in routine post-transplant monitoring in many centers, although with some reproducibility issues and interpretation difficulties. Confirmed abnormalities in these traditional biomarkers raise the suspicion for rejection and guide the indication for graft biopsy, which is still considered the gold standard for rejection monitoring. Rapidly evolving new "omic" technologies have led to the identification of several novel biomarkers, which may change the landscape of transplant monitoring should their potential be confirmed. Among them, urinary chemokines and measurement of cell-free DNA of donor origin are perhaps the most promising. However, at the moment, these approaches remain highly expensive and cost-prohibitive in most settings, with limited clinical applicability; approachable costs upon technology investments would speed their integration. In addition, transcriptomics, metabolomics, proteomics, and the study of blood and urinary extracellular vesicles have the potential for early identification of subclinical rejection with high sensitivity and specificity, good reproducibility, and for gaining predictive value in an affordable cost setting. In the near future, information derived from these new biomarkers is expected to integrate traditional tools in routine use, allowing identification of rejection prior to clinical manifestations and timely therapeutic intervention. This review will discuss traditional, novel, and invasive and non-invasive biomarkers, underlining their strengths, limitations, and present or future applications in children.

Changes in graft function after living donor kidney transplantation in children

BACKGROUND

This study aimed to evaluate the change in graft function in two groups stratified by the estimated glomerular filtration rate (eGFR) at 1 month after transplantation (eGFR-1 M) in pediatric living donor kidney transplant recipients.

METHODS

Forty-three pediatric recipients were classified as those with an eGFR-1 M ≥ 90 mL/min/1.73 m² (n = 19; high eGFR group) or those with an eGFR-1 M of 60-89 mL/min/1.73 m² (n = 24; middle eGFR group). In the two groups, changes in the eGFR were retrospectively evaluated for 5 years after kidney transplantation.

RESULTS

The mean recipient age at transplantation in the high/middle eGFR group was 6.1 ± 3.4/7.8 ± 4.0 years (P = 0.14). The mean eGFR-1, -12, and -60 M (mL/min/1.73 m²) in the high/middle eGFR group were 106.8 ± 2.99/78.5 ± 1.52 (P < 0.001), 79.3 ± 3.22/62.7 ± 2.38 (P < 0.001), and 73.1 ± 4.16/59.2 ± 2.79 (P = 0.006), respectively. The change in the mean eGFR remained mostly parallel in the two groups. In both groups, the eGFR significantly decreased only between 1 and 12 months after transplantation (P < 0.0001). Approximately 70% of the patients had an eGFR-60 M ≥ 60 mL/min/1.73 m².

CONCLUSIONS

The high and middle eGFR groups showed a rapid decline in the eGFR by 1 year after transplantation, but the change thereafter was gradual. In pediatric living donor kidney transplant recipients, the eGFR was relatively well maintained up to 5 years after transplantation. A higher resolution version of the Graphical abstract is available as Supplementary information.

Age and sex determine conversion from immediate-release to extended-release tacrolimus in a multi-center cohort of Canadian pediatric renal transplant recipients

ER-Tac, taken once per day, is associated with improved adherence. This study examined the potential patient and clinical factors that influence clinicians to convert pediatric patients from immediate-release to ER-Tac. This prospective multi-center observational study followed Canadian pediatric kidney transplant recipients up to 5 years post-transplant. Cox Proportional Hazards Regression was used to examine the influence of factors on conversion to ER-Tac. Sixty-six participants were included in this analysis. For every additional year of age at the time of transplant, the likelihood of conversion was more than doubled (HR 2.54, CI 1.83, 3.54, P < 0.001). The impact of age reduced by three percent for every month after transplant (HR 0.97, CI 0.95, 0.98, P < 0.001). Girls were more likely to be converted than boys (HR 3.78, CI 1.35, 10.6, P 0.01). Adherence measures (MAM-MM and tacrolimus trough variability), individual barriers to adherence, renal function, HLA mismatch, and rejection were not significant predictors of conversion in the final regression model. ER-Tac was preferentially prescribed to older age and female patients. Female sex and adolescence are both associated with worse graft outcomes, but we found no link between individualized markers of adherence/graft risk and conversion. Clinicians appeared to be using demographic features to distinguish patients at perceived higher risk and converted accordingly, without a case-by-case evaluation of who is more susceptible to poor outcomes.

A comparison of post-transplant renal function in pre-emptive and post-dialysis pediatric kidney transplant recipients

PURPOSE

Little is known regarding post-transplant renal function following pediatric pre-emptive KT. Therefore, this study aims to determine whether there is a difference in 1 year post-transplant renal function outcomes between pre-emptive and post-dialysis KT in pediatric transplant recipients.

METHODS

A retrospective review of patients who underwent kidney transplant at our institution between 2000 and 2015 was performed. Kidney transplant recipients were divided into four groups: pre-DD, post-DD, pre-LD, and post-LD. The clinical outcomes, measured in eGFR (mL/min/1.73 m² ), acute rejection episodes within 1 year, and hospitalization within 1 year were compared to between groups in their respective donor types (pre-DD vs post-DD; pre-LD vs post-LD).

RESULTS

The 324 patients were identified (21 pre-DD, 151 post-DD, 54 pre-LD, and 98 post-LD). Post-DD group had more females (P = 0.018) and post-operative complications (P = 0.023), although there was no difference in complications requiring intervention (P = 0.129). Post-LD patients were more likely to be females (P = 0.017) and those with intrinsic renal (non-urological/structural) ESRD etiology (P = 0.003). The 1-year eGFR was similar between pre-DD and post-DD groups (70.3 [IQR 53.5-88.5] vs 74.3 [IQR 62.3-90.5], P = 0.613), as well as pre-LD and post-LD groups (66.6 [IQR 47.8-73.7] vs 63.9 [IQR 55.0-77.1], P = 0.600). There were no significant differences in rates of acute rejection episodes or hospitalization within 1 year of transplantation for in LD/DD groups.

CONCLUSION

There is no significant difference in renal function at 1 year post-transplant in pediatric patients receiving pre-emptive or post-dialysis kidney transplants.

Steroid withdrawal improves blood pressure control and nocturnal dipping in pediatric renal transplant recipients: analysis of a prospective, randomized, controlled trial

BACKGROUND

Variable effects of steroid minimization strategies on blood pressure in pediatric renal transplant recipients have been reported, but data on the effect of steroid withdrawal on ambulatory blood pressure and circadian blood pressure rhythm have not been published so far.

METHODS

In a prospective, randomized, multicenter study on steroid withdrawal in pediatric renal transplant recipients (n = 42) on cyclosporine, mycophenolate mofetil, and methylprednisolone, we performed a substudy in 28 patients, aged 11.2 ± 3.8 years, for whom ambulatory blood pressure monitoring (ABPM) data were available.

RESULTS

In the steroid-withdrawal group, the percentage of patients with arterial hypertension, defined as systolic and/or diastolic blood pressure values recorded by ABPM > 1.64 SDS and/or antihypertensive medication, at month 15 was significantly lower (35.7%, p = 0.002) than in controls (92.9%). The need of antihypertensive medication dropped significantly by 61.2% (p < 0.000 vs. control), while in controls, it even rose by 69.3%. One year after steroid withdrawal, no patient exhibited hypertensive blood pressure values above the 95th percentile, compared to 35.7% at baseline (p = 0.014) and to 14.3% of control (p = 0.142). The beneficial impact of steroid withdrawal was especially pronounced for nocturnal blood pressure, leading to a recovered circadian rhythm in 71.4% of patients vs. 14.3% at baseline (p = 0.002), while the percentage of controls with an abnormal circadian rhythm (35.7%) did not change.

CONCLUSIONS

Steroid withdrawal in pediatric renal transplant recipients with well-preserved allograft function is associated with less arterial hypertension recorded by ABPM and recovery of circadian blood pressure rhythm by restoration of nocturnal blood pressure dipping.

When does vesicoureteral reflux in pediatric kidney transplant patients need treatment?

PURPOSE

The treatment of VUR in children with UTI has changed significantly, due to studies showing that antibiotic prophylaxis does not decrease renal scarring. As children with kidney transplants are at higher risk for UTI, we investigated if select patients with renal transplant VUR could be managed without surgery.

MATERIALS AND METHODS

A total of 18 patients with VUR into their renal grafts were identified, and 319 patients underwent transplantation from 2006 to 2016. The cause for the detection of the VUR, treatment, and graft function was reviewed.

RESULTS

Six boys and 12 girls were identified, 13 of whom had grade 3 or 4 VUR into the renal graft. Nine patients presented with hydronephrosis or abnormal renal biopsy: eight were successfully managed with antibiotic prophylaxis and bladder training, one developed UTI and underwent Dx/HA subureteric injection. Nine patients presented with recurrent febrile UTI, only one was successfully managed without surgery. Only 2 of 9 (22%) patients who underwent Dx/HA injection had resolution of their reflux. Of the remaining seven, five required open ureteral reimplantation (two for obstruction), one lost the graft due to rejection, and one had significant hydronephrosis. eGFR was similar between the hydronephrosis, UTI, and abnormal renal biopsy groups at all times.

CONCLUSION

Patients with transplant VUR and recurrent febrile UTI are more likely to require surgical therapy, but the complication and failure rate for Dx/HA injection is significant. Patients with transplant VUR without febrile UTI can be successfully managed with bladder training and temporary antibiotic prophylaxis.

Clinical implication of renal allograft volume to recipient body surface area ratio in pediatric renal transplant

Our study aims to assess the clinical implication of RAV/rBSA ratio in PRT as a predictor for attained renal function at 1 year post-transplantation and its association with surgical complications. A retrospective cohort was performed for PRT cases from January 2000 to December 2015 in our institution. Extracted clinical information includes the recipient's demographics, donor type, renal allograft characteristics, arterial, venous and ureteral anastomoses, vascular anastomosis time while kidney off ice, overall operative time, and estimated blood loss. The RAV/rBSA was extrapolated and assessed for its association with renal graft function attained in 1 year post-transplantation and surgical complications within 30-day post-transplantation. A total of 324 PRTs cases were analyzed. The cohort consisted of 187 (52.4%) male and 137 (42.3%) female recipients, with 152 (46.9%) living donor and 172 (53.1%) deceased donor renal transplants, and an overall median age of 155.26 months (IQR 76.70-186.98) at time of renal transplantation. The receiver operating characteristic identified that a RAV/rBSA ratio of 135 was the optimal cutoff in determining the renal graft function outcome. Univariate and multivariate analyses revealed the relative OR for RAV/rBSA ≥ 135 ratio in predicting an eGFR ≥ 90 attained within 1 year post-transplant was highest among younger pediatric recipients (<142.5 months) of deceased kidney donors (OR = 11.143, 95% CI = 3.156-39.34). Conversely, Kaplan-Meier analysis revealed that RAV/rBSA ratio ≥ 135 is associated with lower odds of having eGFR <60 (OR = 0.417, 95% CI = 0.203-0.856). The RAV/rBSA ratio was not associated nor predictive of transplant-related surgical complications. Our study determined that the RAV/rBSA ratio is predictive of renal graft function at 1-year PRT, but not associated with any increased surgical complications.

Non-invasive staging of chronic kidney allograft damage using urine metabolomic profiling

Chronic kidney allograft damage is characterized by IFTA and GS. We sought to identify urinary metabolite signatures associated with severity of IFTA and GS in pediatric kidney transplant recipients. Urine samples (n = 396) from 60 pediatric transplant recipients were obtained at the time of kidney biopsy and assayed for 133 metabolites by mass spectrometry. Metabolite profiles were quantified via PLS-DA. We used mixed-effects regression to identify laboratory and clinical predictors of histopathology. Urine samples (n = 174) without rejection or AKI were divided into training/validation sets (75:25%). Metabolite classifiers trained on IFTA severity and %GS showed strong statistical correlation (r = .73, P < .001 and r = .72; P < .001, respectively) and remained significant on the validation sets. Regression analysis identified additional clinical features that improved prediction: months post-transplant (GS, IFTA); and proteinuria, GFR, and age (GS only). Addition of clinical variables improved performance of the %GS classifier (AUC = 0.9; 95% CI = 0.85-0.96) but not for IFTA (AUC = 0.82; 95% CI = 0.71-0.92). Despite the presence of potentially confounding phenotypes, these findings were further validated in samples withheld for rejection or AKI. We identify urine metabolite classifiers for IFTA and GS, which may prove useful for non-invasive assessment of histopathological damage.

The prognostic value of urinary chemokines at 6 months after pediatric kidney transplantation

Pediatric kidney transplantation is lifesaving, but long-term allograft survival is still limited by injury processes mediated by alloimmune inflammation that may otherwise be clinically silent. Chemokines associated with alloimmune inflammation may offer prognostic value early post-transplant by identifying patients at increased risk of poor graft outcomes. We conducted a single-center prospective cohort study of consecutive pediatric kidney transplant recipients (<19 years). Urinary CCL2 and CXCL10 measured at 6 months post-transplant were evaluated for association with long-term eGFR decline, allograft survival, and concomitant acute cellular rejection histology. Thirty-eight patients with a mean age of 12.4 ± 4.6 years were evaluated. Urinary CCL2 was associated with eGFR decline until 6 months (ρ -0.43; P < .01), but not at later time points. Urinary CXCL10 was associated with eGFR decline at 36 months (ρ -0.49; P < .01), risk of 50% eGFR decline (HR = 1.04; P = .02), risk of allograft loss (HR = 1.05; P = .01), borderline rejection or rejection episodes 6-12 months post-transplant (r .41; P = .02), and Banff i + t score (r .47, P < .01). CCL2 and CXCL10 were also correlated with one another (ρ 0.54; P < .01). CCL2 and CXCL10 provide differing, but complementary, information that may be useful for early non-invasive prognostic testing in pediatric kidney transplant recipients.

Serum Endocan Levels Associated with Hypertension and Loss of Renal Function in Pediatric Patients after Two Years from Renal Transplant

Endocan is an important biomarker of inflammation and endothelial dysfunction that increases in association with several chronic diseases. Few published data have described the role of endocan in pediatric renal transplant (RT) patients. We evaluated the endocan concentrations in 62 children who underwent renal transplantation and assessed their relationships with the patients' blood pressure and loss of renal function. The endocan levels were significantly elevated in the pediatric RT patients who had hypertension and a loss of renal function. We determined positive correlations between the endocan concentrations and the hemodynamic variables (systolic blood pressure: r = 0.416; P = 0.001; pulse pressure: r = 0.412; P = 0.003). The endocan levels were inversely correlated with the estimated glomerular filtration rate (r = −0.388; P = 0.003). An endocan cutoff concentration of 7.0 ng/mL identified pediatric RT patients who had hypertension and a loss of renal function with 100% sensitivity and 75% specificity. In conclusion, the endocan concentrations were significantly elevated in pediatric RT patients who had both hypertension and a loss of renal function. The correlations between the endocan levels and the hemodynamic variables and the markers of renal function strengthen the hypothesis that it is an important marker of cardiorenal risk.

An observational cohort study of the effect of hypertension on the loss of renal function in pediatric kidney recipients

BACKGROUND

Post-transplant hypertension impacts negatively on renal graft survival. Our primary objective was to analyze the effect of hypertension on the glomerular filtration rate (GFR) slope.

METHODS

All clinical charts of children who underwent renal transplantation since the introduction of the routine use of ambulatory blood pressure monitoring (ABPM) were reviewed. Eligibility criteria for inclusion were measurement of GFR at 3 months, at 1 year post-transplant, and thereafter at yearly intervals; ABPM performed annually after transplantation; and functioning graft for a minimum of 2 years.

RESULTS

Sixty-eight (39 males) of 79 patients, aged 9.1±5.3 years, met the inclusion criteria. The mean follow-up was 6.2±2.8 years. Twenty-four patients had normotension or controlled hypertension throughout their follow-up (normotensive group). Forty-four patients had hypertension or noncontrolled hypertension at some point(s) during the follow-up period (hypertensive group). GFR slope was -1.6ml/min/1.73 m(2) per year (95% confidence interval (CI = -3.7 to 0.4) in the normotensive group and -2ml/min/1.73 m(2) per year (95% CI = -3 to -1.1) in the hypertensive group (P = 0.42). There was no difference between groups with regard to the change in GFR values from 3 months to 1 year and to last control (P = 0.87). At most recent control, the overall prevalence of controlled hypertension was 78.2% (95% CI = 63.6-89.1).

CONCLUSIONS

Although the results of our study are encouraging, they need to be confirmed in a larger prospective study using the same post-transplant follow-up protocol.

Serum soluble interleukin 2 receptor (sIL-2R) as a marker of acute rejection in renal transplant children

The aim of the study was to evaluate whether or not serum levels of soluble interleukin 2 receptor (sIL-2R) predict acute rejection in pediatric recipients. We studied 51 pediatric renal transplant recipients divided into three groups: Group 1) Biopsy-proven cellular acute rejection (n = 19), Group 2) Graft dysfunction with histological diagnosis other than acute rejection (n = 8) and Group 3) Patients with stable graft function, no biopsy (n = 24). Serum samples for sIL-2R measurement by sandwich ELISA were obtained at the time of renal transplant and at the time of renal biopsy due to graft dysfunction (Groups 1 and 2) or at six months post-transplant in the case of Group 3. The mean ± s.e. serum values of sIL-2R were higher in patients during acute rejection (6539 ± 1802 pg/mL) compared to patients with other causes of graft dysfunction (2217 ± 256 pg/mL) or stable graft function at six months (2183 ± 283 pg/mL) (Kruskal-Wallis p = 0.004). When the sIL2-R levels at the time of transplant were compared to those at the time of biopsy (Groups 1 and 2) or at six months post-transplant in Group 3, there was no significant difference between baseline and biopsy in the acute rejection group (paired t-test = 0.07), whereas there was a significant reduction in Groups 2 and 3.

Intraindividual variability of the modified Schwartz and novel CKiD GFR equations in pediatric renal transplant patients

GFR in children can be obtained from a formula using SCr and height or various formulas including serum CysC. Recently, two new GFR formulas have been developed: (i) height and SCr-mSchwartz GFR and (ii) height, SCr, CysC, and serum urea (CKiD GFR). While these formulas proved to be accurate when compared to the gold standard, their use in children post-kidney Tx is yet to be assessed. A total of 1174 blood samples (urea, SCr and CysC) were analyzed from the post-Tx period in 24 Tx children (12 boys, median age = 8.6 yr) currently followed at our institution. CKiD GFR and mSchwartz GFR were compared using Bland-Altman analysis and the CV. The mSchwartz GFR overestimated the CKiD GFR (mean bias = 1.09 ± 0.14; 95% limits of agreements from 0.82 to 1.36). Median CV of CKiD GFR (10.3%) was significantly lower than that of mSchwartz GFR (15.0%), p = 0.04, and negatively correlated with the slope of GFR (r(2) = 0.34, p = 0.0026). In conclusion, CKiD GFR has a significantly lower intraindividual variation than mSchwartz GFR and may be better suited for longitudinal follow-up of patients post-Tx.

Histological progression of chronic renal allograft injury comparing sirolimus and mycophenolate mofetil-based protocols. A single-center, prospective, randomized, controlled study

In an effort to mitigate progression of IF/TA associated with chronic renal allograft injury, we hypothesize that adjuvant immunosuppression with sirolimus (SRL) will delay progression compared with MMF. Subjects 5-17 yr old, >1-yr post-transplant with mild or moderate IF/TA (Banff criteria) and tacrolimus dose minimization were randomized to continue MMF or convert to SRL and followed for two yr. For the entire cohort (n = 20), there was significant progression of %GGS, ci, ct, cv, and ah scores over the follow-up period (p < 0.05). There was no difference in rates of progression of Banff scores, %GGS, or % IF over two yr between the two groups, though power was low. Both groups exhibited similar rates of eGFR decline (MMF: -12.3 vs. SRL: -11.8 mL/min/1.73 m²/yr), which was correlated with ct score (p < 0.05). The SRL group had more episodes of acute allograft dysfunction and oral ulcers. Proteinuria at 24 months was significantly increased in the SRL group (6/9 subjects) but was not correlated with eGFR or %GGS. We conclude that neither MMF nor SRL, combined with low-dose tacrolimus, was effective at mitigating progressive histological changes or functional decline associated with chronic renal allograft injury.