Graft Growth and Podocyte Dedifferentiation in Donor-Recipient Size Mismatch Kidney Transplants

Establishment of a rat model of pediatric-to-adult kidney transplantation to study the early rapid compensatory growth of the grafts

Pediatric donor kidneys show rapid compensatory development in morphology and function after being transplanted into adult recipients. Establishing an animal model that can simulate clinical pediatric-to-adult (P→A) kidney transplantation is important for studying the characteristics and potential mechanisms related to this rapid graft growth. In the P→A group, kidneys harvested from 3- to 4-week-old Sprague-Dawley (SD) rats weighing <50 g were transplanted into adult SD rats (300-400 g). Novel techniques were employed using recipient common iliac vessels for vascular anastomosis and ureter graft drag-in connection to the recipient bladder. As a control group, conventional kidney transplantation was performed between adult SD rats (A→A group). A total of 11 transplants were performed in the P→A group. Eight recipients survived to 28 days without obvious complications and were euthanized for graft harvesting and analysis. Ultrasonography showed that the renal grafts grew significantly faster in the P→A group than in the A→A group during the first 7 days after transplantation, and the size of the renal grafts in the two groups was similar on day 28. Histology revealed significant glomerular enlargement and cell proliferation in the pediatric donor kidneys, with signs of hyperfiltration injury but without podocyte proliferation. Proximal tubular epithelial cells (PTECs) in the P→A group showed significant cell proliferation and hypertrophy. This study has successfully established an animal model in rats with similar characteristics to clinical P→A kidney transplantation, providing a new tool for studying the pathophysiological changes and potential mechanisms of early rapid compensatory growth of the grafts after small pediatric donor kidneys were transplanted into size-mismatched large adult recipients.

Recognition of intraglomerular histological features with deep learning in protocol transplant biopsies and their association with kidney function and prognosis

Background

The Banff Classification may not adequately address protocol transplant biopsies categorized as normal in patients experiencing unexplained graft function deterioration. This study seeks to employ convolutional neural networks to automate the segmentation of glomerular cells and capillaries and assess their correlation with transplant function.

Methods

A total of 215 patients were categorized into three groups. In the Training cohort, glomerular cells and capillaries from 37 patients were manually annotated to train the networks. The Test cohort (24 patients) compared manual annotations vs automated predictions, while the Application cohort (154 protocol transplant biopsies) examined predicted factors in relation to kidney function and prognosis.

Results

In the Test cohort, the networks recognized histological structures with Precision, Recall, F-score and Intersection Over Union exceeding 0.92, 0.85, 0.89 and 0.74, respectively. Univariate analysis revealed associations between the estimated glomerular filtration rate (eGFR) at biopsy and relative endothelial area (r = 0.19, P = .027), endothelial cell density (r = 0.20, P = .017), mean parietal epithelial cell area (r = -0.38, P < .001), parietal epithelial cell density (r = 0.29, P < .001) and mesangial cell density (r = 0.22, P = .010). Multivariate analysis retained only endothelial cell density as associated with eGFR (Beta = 0.13, P = .040). Endothelial cell density (r = -0.22, P = .010) and mean podocyte area (r = 0.21, P = .016) were linked to proteinuria at biopsy. Over 44 ± 29 months, 25 patients (16%) reached the primary composite endpoint (dialysis initiation, or 30% eGFR sustained decline), with relative endothelial area, mean endothelial cell area and parietal epithelial cell density below medians linked to this endpoint [hazard ratios, respectively, of 2.63 (P = .048), 2.60 (P = .039) and 3.23 (P = .019)].

Conclusion

This study automated the measurement of intraglomerular cells and capillaries. Our results suggest that the precise segmentation of endothelial and epithelial cells may serve as a potential future marker for the risk of graft loss.

Pediatric renal transplantation-A UNOS database analysis of donor-recipient size mismatch

BACKGROUND

We used the BSAi (Donor BSA/Recipient BSA) to assess whether transplanting a small or large kidney into a pediatric recipient relative to his/her size influences renal transplant outcomes.

METHODS

We included 14 322 single-kidney transplants in pediatric recipients (0-17 years old) (01/2000-02/2020) from the United Network for Organ Sharing database. We divided cases into four BSAi groups (BSAi ≤ 1, 1 < BSAi ≤ 2, 2 < BSAi ≤ 3, BSAi > 3).

RESULTS

There were no differences concerning delayed graft function (DGF) or primary non-function (PNF) rates, whether the grafts were from living or brain-dead donors. In both transplants coming from living donors and brain-dead donors, cases with BSAi > 3 and cases with 2 < BSAi ≤ 3 had similar graft survival (p = .13 for transplants from living donors, p = .413 for transplants from brain-dead donors), and both groups had longer graft survival than cases with 1 < BSAi ≤ 2 and cases with BSAi ≤ 1 (p < .001). The difference in 10-year graft survival rates between cases with BSAi > 3 and cases with BSAi ≤ 1 reached around 25% in both donor types. The better graft survival in transplants with BSAi > 2 was confirmed in multivariable analysis.

CONCLUSIONS

There is no significant impact of donor-recipient size mismatch on DGF and PNF rates in pediatric renal transplants. However, graft survival is significantly improved when the donor's size is more than twice the pediatric recipient's size.

Excellent Clinical Long-Term Outcomes of Kidney Transplantation From Small Pediatric Donors (Age ≤ 5 Years) Despite Early Hyperfiltration Injury

Background:

The use of small pediatric donors (age ≤ 5 years and body weight < 20kg) for adult transplant recipients is still regarded controversially in terms of early complications, long-term outcomes, and development of hyperfiltration injury due to body size mismatch.

Objective:

To investigate long-term outcomes of adult renal allograft recipients receiving a kidney from small pediatric donor (SPD) in terms of kidney function and early features of hyperfiltration injury such as histological changes and proteinuria.

Design:

Retrospective, single center study.

Settings:

Transplant center of the University Hospital of Basel, Switzerland.

Patients:

Adult renal allograft recipients receiving a kidney from a small pediatric donor at our center between 2005 and 2017.

Methods:

The outcome of 47 transplants from SPD were compared with 153 kidney transplants from deceased-standard criteria donors (SCD) occurring during the same time period. Incidence of clinical signs of hyperfiltration injury (eg, proteinuria) was investigated. According to our policy, surveillance biopsies were taken at 3 and 6 months post-transplant and were evaluated in terms of signs of hyperfiltration injury.

Results:

At a median follow-up of 2.3 years post-transplant, death-censored graft survival of SPD was comparable to transplants from SCD (94% vs 93%; P = .54). Furthermore, allograft function at last follow-up (estimated glomerular filtration rate–Modification of Diet in Renal Disease) was significantly higher in pediatric transplant (80 vs 55 ml/min/1.73 m2, P = .002). We found histological signs of early hyperfiltration injury in 55% of SPD. There was an equally low proteinuria in both groups during follow-up.

Limitations:

It is a single center and retrospective observational study with small sample size. The outcomes were investigated in a well-selected population of recipients with low body mass index, low immunological risk, and well-controlled hypertension and was not compared with equal selected group of recipients.

Conclusions:

Early histological and clinical signs of hyperfiltration injury in SPD is frequent. Despite the hyperfiltration injury, there is an equal allograft survival and even superior allograft function in SPD compared with SCD during follow-up. This observation supports the concept of high adaptive capacity of pediatric donor kidneys.

Encouraging outcomes of using a small-donor single graft in pediatric kidney transplantation

BACKGROUND

The use of small pediatric kidneys as single grafts for transplantation is controversial, due to the potential risk for graft thrombosis and insufficient nephron mass.

METHODS

Aiming to test the benefits of transplanting these kidneys, 375 children who underwent kidney transplantation in a single center were evaluated: 49 (13.1%) received a single graft from a small pediatric donor (≤ 15 kg, SPD group), 244 (65.1%) from a bigger pediatric donor (> 15 kg, BPD group), and 82 (21.9%) from adult living donors (group ALD).

RESULTS

Groups had similar baseline main characteristics. After 5 years of follow-up, children from the SPD group were comparable to children from BPD and ALD in patient survival (94%, 96%, and 98%, respectively, p = 0.423); graft survival (89%, 88%, and 93%, respectively, p = 0.426); the frequency of acute rejection (p = 0.998); the incidence of post-transplant lymphoproliferative disease (p = 0.671); the odds ratio for severely increased proteinuria (p = 0.357); the rates of vascular thrombosis (p = 0.846); and the necessity for post-transplant surgical intervention prior to discharge (p = 0.905). The longitudinal evolution of eGFR was not uniform among groups. The three groups presented a decrease in eGFR, but the slope of the curve was steeper in ALD children. At 5 years, the eGFR of the ALD group was 10 ml/min/1.73m² inferior to the others. At that time, the eGFR from the SPD group was statistically similar to the BPD group (p = 0.952).

CONCLUSION

In a specialized transplant center, the use of a single small pediatric donor kidney for transplantation is as successful as bigger pediatric or adult living donors, after 5 years of follow-up. A higher resolution version of the Graphical abstract is available as Supplementary information.

The implications of donor-recipient size mismatch in renal transplantation

INTRODUCTION

Transplanting kidneys small for recipient's size results in inferior graft function. Body surface area (BSA) is related to kidney size. We used the BSA index (BSAi) (Donor BSA/Recipient BSA) to assess whether the renal graft size is sufficient for the recipient.

METHODS

We included 26,223 adult single kidney transplants (01/01/2007-31/12/2019) from the UK Transplant Registry. We divided renal transplants into groups: BSAi ≤ 0.75, 0.75 < BSA ≤ 1, 1 < BSAi ≤ 1.25, BSAi > 1.25. We compared delayed graft function rates, primary non-function rates and graft survival among them. (Reference category: BSAi ≤ 0.75).

RESULTS

Cases with BSAi ≤ 0.75 had the highest delayed graft function rates in living-donor renal transplants (11.1%) (0.75 < BSAi ≤ 1: OR = 0.59, 95% CI = 0.32-1.1, p = 0.095, 1 < BSAi ≤ 1.25: OR = 0.46, 95% CI = 0.23-0.89, p = 0.022, BSAi > 1.25: OR = 0.32, 95% CI = 0.13-0.77, p = 0.011) and in renal transplants from donors after brain death (26.2%) (0.75 < BSAi ≤ 1: OR = 0.72, 95% CI = 0.55-0.96, p = 0.024, 1 < BSAi ≤ 1.25: OR = 0.62, 95% CI = 0.47-0.83, p = 0.001, BSAi > 1.25: OR = 0.65, 95% CI = 0.47-0.9, p = 0.01). There were no significant differences in renal transplants from donors after circulatory death regarding delayed graft function rates (~ 40% in all groups). Graft survival was similar among BSAi groups in renal transplants from living donors and donors after brain death. Renal transplants from donors after circulatory death with BSAi ≤ 0.75 had the shortest graft survival (0.75 < BSAi ≤ 1: HR = 0.55, 95% CI = 0.41-0.74, p < 0.001, 1 < BSAi ≤ 1.25: HR = 0.48, 95% CI = 0.35-0.66, p < 0.001, BSAi > 1.25: HR = 0.45, 95% CI = 0.31-0.66, p < 0.001). Ten-year graft survival rate was 58.4% for renal transplants from donors after circulatory death with BSAi ≤ 0.75.

CONCLUSIONS

Delayed graft function risk is higher in renal transplants with BSAi ≤ 0.75 coming from living donors and donors after brain death. Graft survival is greatly reduced in renal transplants from donors after circulatory death with BSAi ≤ 0.75.

Renal cell markers: lighthouses for managing renal diseases

Kidneys, one of the vital organs in our body, are responsible for maintaining whole body homeostasis. The complexity of renal function (e.g., filtration, reabsorption, fluid and electrolyte regulation, and urine production) demands diversity not only at the level of cell types but also in their overall distribution and structural framework within the kidney. To gain an in depth molecular-level understanding of the renal system, it is imperative to discern the components of kidney and the types of cells residing in each of the subregions. Recent developments in labeling, tracing, and imaging techniques have enabled us to mark, monitor, and identify these cells in vivo with high efficiency in a minimally invasive manner. In this review, we summarize different cell types, specific markers that are uniquely associated with those cell types, and their distribution in the kidney, which altogether make kidneys so special and different. Cellular sorting based on the presence of certain proteins on the cell surface allowed for the assignment of multiple markers for each cell type. However, different studies using different techniques have found contradictions in cell type-specific markers. Thus, the term "cell marker" might be imprecise and suboptimal, leading to uncertainty when interpreting the data. Therefore, we strongly believe that there is an unmet need to define the best cell markers for a cell type. Although the compendium of renal-selective marker proteins presented in this review is a resource that may be useful to researchers, we acknowledge that the list may not be necessarily exhaustive.

Small donors for small recipients - excellent growth and long-term function of single kidney grafts

Small-donor kidneys (≤20 kg donor weight, SDK) are preferably transplanted en bloc in adults. Concerns about thrombotic complications or hyperfiltration hinder their use in children, particularly as single grafts. Low centre experience and donor-to-recipient size are rated critical regarding outcomes. We evaluated SDK transplantation (SDTx) in paediatric recipients at a specialized transplant centre. Between 2008 and 2018, SDTx was performed in 40 children (mean age 5.4 ± 1.4 years, single grafts n = 38, donor weight ≤10 kg: n = 10). Perioperative complications were rare (n = 3), mainly thromboses despite immediate heparinization and resulted in graft loss in one patient. Overall, early and long-term GFR were excellent (76 ± 21 and 100 ± 11 ml/min/1.73 m² , first month and year 5, respectively). Three patients presented with delayed graft function. Graft volume increased significantly (69 ± 38 vs. 111 ± 33 ml within 5 years; P < 0.0001). Patients showed catch-up growth to normal range (SDS for height -2.06 ± 1.6 to -1.60 ± 1.5). Stratification by recipient age and donor weight revealed superior results in young recipients (≤3 years) and ≤10 kg donors, respectively. Outcome of single SDK grafts was excellent. Gain of GFR and graft volume was even higher in patients with very small donor or recipient size, regardless of a reduced donor-to-recipient weight ratio. Therefore, SDTx should be considered favouring small paediatric recipients.

Pediatric Donor Glomerulopathy Is a Possible Cause of Abnormal Urinalysis in Adults Receiving Small Pediatric Donor Kidneys

Background.

Reports about prognosis of adults receiving small pediatric-donor kidneys (PDK) as compared to those receiving elder pediatric or adult donor kidneys (ADKs) are controversial. This study aimed to examine the outcomes of adults receiving small PDK and possible prognostic factors.

Methods.

The records of adults who received kidneys from donors < 10 years old at our center from July 1, 2011 to June 30, 2018 were reviewed.

Results.

A total of 121 adults were small PDK recipients. Twenty-three patients received 29 biopsies or nephrectomy between 6 and 896 days posttransplantation days. Seven patients (30.4%) had pediatric donor glomerulopathy (PDG), which developed from 113 to 615 days posttransplantation. The incidence of proteinuria and hematuria was significantly higher in the PDG group. The characteristic pathological finding in PDG was irregular lamination and splintering of the glomerular basement membrane (GBM). Donor age, donor weight, and donor kidney volume were significantly less in PDG cases compared with the non-PDG cases. For the risk factors of PDG, increasing urinary RBC count during follow-up was an independent predictor, while increasing donor age and body weight were protective factors. PDG was not a significant risk factor for Scr increasing of PDKs.

Conclusions.

PDG is a potential cause of abnormal urinalysis in adults receiving small PDKs. The pathological characteristic change of PDG is splitting and lamination of GBM. Persistent hematuria after transplantation in recipients of PDK is a predictor of PDG development.

Single kidney transplantation from donors with acute kidney injury: A single-center experience

INTRODUCTION

Despite a severe shortage of organ supply, patients are reluctant to accept organs from deceased donors with AKI, let alone from pediatric AKI donors.

METHODS

We assessed 70 patients who received kidneys from donors with AKI (10 with pediatric and 60 with adult donors) and 176 contemporaneous patients who received kidneys from non-AKI donors (41 with pediatric and 135 with adult donors) between March 2012 and February 2017 for retrospectively evaluating the clinical outcomes.

RESULTS

AKI was defined and staging by the RIFLE criteria and pediatric-modified RIFLE criteria. Median age was 11.00 years IQR (4.50-14.00 years), and median weight was 25.00 kg (IQR, 17.00-45.00 kg) for all pediatric donors. Median follow-up was 8 months (range, 1-49 months). Adult AKI group had the highest incidence of DGF (35.0% vs 10%, 9.8%, and 19.3%, P = 0.011). There was a significant increase in DGF in higher AKI stages (Risk: 20.7%, Injury: 46.7%, Failure: 50.0%; P = 0.014) among patients with adult donors. No significant differences were noted in 1-year (100.0%, 95.1%, 98.3%, and 97.8%; P = 0.751) and 3-year (100.0%, 95.1%, 98.3%, and 97.8%; P = 0.751) patient survival, and 1-year (90.0%, 97.6%, 98.3%, and 95.6%; P = 0.535) and 3-year (90.0%, 97.6%, 98.3%, and 95.6%; P = 0.535) graft survival.

CONCLUSION

Transplants procured from donors with AKI, particularly pediatric ones, could achieve excellent intermediate-term clinical outcomes and thus potentially expand the donor pool.