Acute vascular rejection after renal transplantation and isolated v-lesion

Super-resolution ultrasound microvascular imaging: Is it ready for clinical use?

The field of super-resolution ultrasound microvascular imaging has been rapidly growing over the past decade. By leveraging contrast microbubbles as point targets for localization and tracking, super-resolution ultrasound pinpoints the location of microvessels and measures their blood flow velocity. Super-resolution ultrasound is the first in vivo imaging modality that can image micron-scale vessels at a clinically relevant imaging depth without tissue destruction. These unique capabilities of super-resolution ultrasound provide structural (vessel morphology) and functional (vessel blood flow) assessments of tissue microvasculature on a global and local scale, which opens new doors for many enticing preclinical and clinical applications that benefit from microvascular biomarkers. The goal of this short review is to provide an update on recent advancements in super-resolution ultrasound imaging, with a focus on summarizing existing applications and discussing the prospects of translating super-resolution imaging to clinical practice and research. In this review, we also provide brief introductions of how super-resolution ultrasound works, how does it compare with other imaging modalities, and what are the tradeoffs and limitations for an audience who is not familiar with the technology.

Clinicopathological Analyses of Chronic Renal Allograft Arteriopathy after Kidney Transplantation

INTRODUCTION

Herein, we discuss clinicopathological analyses of cases of chronic renal allograft arteriopathy (CRA) after renal transplantation and clarify the mechanisms underlying the development and prognostic significance of CRA.

METHODS

CRA was diagnosed in 34 renal allograft biopsy specimens (BSs) obtained from 27 renal transplant patients who were followed up at the Department of Urology and Transplant Surgery, Toda Chuo General Hospital, between January 2010 and December 2020.

RESULTS

CRA was diagnosed at a median of 33.4 months post-transplantation. Of the 27 patients, 16 had a history of rejection. Among the 34 BSs showing evidence of CRA, CRA was mild (cv1 in Banff's classification) in 22, moderate (cv2) in 7, and severe (cv3) in 5 patients. We then classified the 34 BSs showing evidence of CRA based on their overall histopathological features as follows: cv alone seen in 11 (32%) BSs, cv + antibody-mediated rejection (AMR) in 12 (35%), and cv + T-cell-mediated rejection (TCMR) in 8 (24%). Loss of the renal allograft occurred during the observation period in 3 patients (11%). Of the remaining patients with functioning grafts, deterioration of renal allograft function after biopsies occurred in 7 cases (26%).

CONCLUSIONS

Our study results suggest that AMR contributes to CRA in 30-40% of cases, TCMR in 20-30% of cases, isolated v lesions in 15% of cases, and cv lesions alone in 30%. The intimal arteritis was a prognostic factor in CRA.

The Pathological and Clinical Diversity of Acute Vascular Rejection in Kidney Transplantation

BACKGROUND

Vascular rejection (VR) is characterized by arteritis, steroid resistance, and increased graft loss but is poorly described using modern diagnostics.

METHODS

We screened 3715 consecutive biopsies and retrospectively evaluated clinical and histological phenotypes of VR (n = 100) against rejection without arteritis (v0REJ, n = 540) and normal controls (n = 1108).

RESULTS

Biopsy sample size affected the likelihood of arterial sampling, VR diagnosis, and final Banff v scores (P < 0.001). Local v and cv scores were greatest in larger arteries (n = 258). VR comprised 15.6% of all rejection episodes, presented earlier (median 1.0 mo, interquartile range, 0.4-8 mo) with higher serum creatinine levels and inferior graft survival, versus v0REJ (P < 0.001). Early VR (≤1 mo) was common (54%) and predicted by sensitization, delayed function, and prior corticosteroid use, with associated acute dysfunction and optimal therapeutic response, independent of Banff v score. Late VR followed under-immunosuppression in 71.4% (noncompliance 38.8%, iatrogenic 32.6%), and was associated with chronic interstitial fibrosis, incomplete renal functional recovery and persistent inflammation using sequential histopathology. The etiology was "pure" antibody-mediated VR (n = 21), mixed VR (n = 36), and "pure" T cell-mediated VR (n = 43). Isolated VR (n = 34, Banff i < 1 without tubulitis) comprised 24 T cell-mediated VR and 10 antibody-mediated VR, presenting with mild renal dysfunction, minimal Banff acute scores, and better graft survival compared with inflamed VR. Interstitial inflammation influenced acute renal dysfunction and early treatment response, whereas chronic tubulointerstitial damage determined long-term graft loss.

CONCLUSIONS

VR is a heterogenous entity influenced by time-of-onset, pathophysiology, accompanying interstitial inflammation and fibrosis. Adequate histological sampling is essential for its accurate diagnostic classification and treatment.

Clinical Significance of Isolated V1 Arteritis in Renal Transplantation

BACKGROUND

The presence of intimal arteritis (v) in renal allograft biopsy specimens establishes the presence of acute T-cell mediated rejection (TCMR), Grade IIa-III, according to the Banff classification of rejection. The clinical significance of isolated v1 lesions (v1), characterized by arteritis alone, compared with lesions of arteritis with tubulointerstitial inflammation (i-t-v) has been controversial.

METHODS

We performed a retrospective review of 280 patients undergoing renal transplantation between 2005 and 2015 who received a "for cause" transplant biopsy using the Banff 2013 classification. Patients with TCMR grade IIa (n = 83) were subdivided into groups with isolated v1 arteritis and i-t-v. Pre- and postoperative renal function, graft survival, and overall survival were evaluated in all patients.

RESULTS

Donor and recipient demographics were similar between groups. One month following treatment of rejection, patients with v1 disease had superior recovery of glomerular filtration rate vs patients with i-t-v (P < .002). At a median follow-up of 41 months from transplant, death-censored graft survival was 92% vs 79% (P = .04), and overall survival was 98% vs 79% (P < .004) in the isolated v1 and i-t-v groups, respectively.

CONCLUSION

Despite having identical Banff classification of TCMR IIa, our results indicate that graft survival in patients with isolated v1 rejection is superior to those with i-t-v. Following corroboration with data from other centers, modification of the Banff classification scheme should be considered.

Clinicopathologic Analyses of Chronic Vascular Rejection After Kidney Transplantation

AIM

We discuss the clinicopathologic analyses of cases of biopsy specimens (BS) after renal transplantation and clarify the mechanisms underlying the development and prognostic significance of chronic vascular rejection (CVR).

PATIENTS

CVR was diagnosed in 30 renal allograft BS obtained from 23 renal transplant patients being followed up at the Department of Urology and Transplant Surgery, Toda Chuo General Hospital, between January 2010 and August 2017.

RESULTS

CVR was diagnosed at a median of 33.1 months post-transplantation. Among the 23 patients, 14 had a history of rejection. Among the 30 BS showing evidence of CVR, the CVR was mild (cv1 on Banff's classification) in 19, moderate (cv2) in 6, and severe (cv3) in 5. We then classified the 30 BS showing evidence of CVR by their overall histopathologic features as follows: cv alone was seen in 9 (30%), cv + antibody-mediated rejection (AMR) in 11 (37%), and cv + T-cell-mediated rejection (TCMR) in 8 (27%). Loss of the renal allograft occurred during the observation period in 2 patients (9%). Of the remaining patients with functioning grafts, deterioration of the renal allograft function after the biopsies occurred in 6 (26%).

CONCLUSIONS

Our study results suggest that AMR contributes to CVR in 30% to 40% of cases, TCMR in 20% to 30% of cases, isolated v lesions in 10% of cases, and cv lesions alone in 30%. The prognosis of the graft exhibiting CVR was not too poor even under the present immunosuppressive protocol.

Isolated Vascular Lesions (IVL) in Early Allograft Biopsies: A Case Series

This case series includes five patients diagnosed as isolated vascular lesion (IVL) on allograft biopsy in an early post-transplant period. These patients presented with graft dysfunction. The biopsies satisfied the criteria for IVL as laid down by Banff 2009. Four of these patients were treated with corticosteroids and other anti rejection measures. C4d and DSA were negative in all. The patients showed good response to treatment with stable graft function at the longest follow-up of one year. We have also reviewed the literature about IVL as a specific entity. There are differences between the molecular and clinical data of IVL. It is difficult to differentiate whether IVL is a rejection or non-rejection process. This study aims to highlight the importance of a rare entity.

Isolated v-lesion represents a benign phenotype of vascular rejection of the kidney allograft - a retrospective study

While the detrimental impact of the humoral acute vascular rejection (AVR) phenotype is recognized, the prognostic significance of isolated v-lesion (IV) remains unclear. In this retrospective single-centre study, AVR was found in 98 of 1015 patients (9.7%) who had undergone kidney transplantation in 2010-2014, with donor-specific antibodies (DSA) evaluated in all of them. The outcome of four AVR phenotypes was evaluated during median follow-up of 59 months; in 25 patients with IV, 18 with T-cell-mediated vascular rejection (TCMVR), 19 with antibody-mediated vascular rejection (AMVR) and 36 with suspected antibody-mediated rejection (sAMVR). AVR was diagnosed mainly by for-cause biopsy (81%) early after transplantation (median 19 POD) and appeared as mild-grade intimal arteritis. IV occurred in low-sensitized patients after the first transplantation (96%) in the absence of DSA. IV responded satisfactorily to treatment (88%), showed no persistence of rejection in surveillance biopsy, and had stable graft function, minimal proteinuria and excellent DCGS (96%). Contrary to that, Kaplan-Meier estimate of 3-year DCGS of AMVR was 66% (log-rank = 0.0004). Early IV represents a benign phenotype of AVR with a favourable outcome. This study prompts further research to evaluate the nature of IV before considering any change in the classification and management.

Clinical and Pathological Analyses of Cases of Acute Vascular Rejection After Kidney Transplantation

BACKGROUND

We performed a clinical and pathological analysis of cases of acute vascular rejection (AVR), characterized by intimal arteritis and transmural arteritis (Banff v score) after kidney transplantation, in an attempt to clarify the mechanisms underlying the development and prognostic significance of AVR.

METHODS

AVR (Banff score: v >0) was diagnosed in 31 renal allograft biopsy specimens (BS) obtained from 31 renal transplant patients receiving follow-up care at the Department of Urology, Tokyo Women's Medical University, between January 2010 and April 2016.

RESULTS

AVR was diagnosed at a median of 124.6 days after transplantation. Among the 31 BS showing evidence of AVR, AVR was mild (v1 in Banff's classification) in 25 cases, moderate (v2) in 6, and severe (v3) in none. We classified the 31 BS with evidence of AVR by their overall histopathological features as follows: isolated v lesions were observed in 6 BS, acute antibody-mediated rejection (AAMR) in 7, acute T-cell-mediated rejection (ATCMR) in 12, and both ATCR and AAMR in 6. Loss of the renal allograft occurred during the observation period in 3 patients, and, of the remaining cases with functioning grafts, deterioration of renal allograft function after biopsy occurred in only 2 patients.

CONCLUSIONS

The results of our study suggest that ATCMR contributes to AVR in 40% to 60% of cases, AAMR in 20% to 40% of cases, and isolated v lesions in 20% of cases. The prognosis of the patient with the graft that had AVR was relatively good under the present immunosuppression protocol and current anti-rejection therapies.

Isolated v-lesion in kidney transplant recipients: Characteristics, association with DSA, and histological follow-up

Isolated v-lesion (IvL) represents a rare and challenging situation in renal allograft biopsies because it is unknown whether IvL truly represents rejection, antibody- or T cell-mediated, or not. This multicentric retrospective study describes the clinicopathological features of IvL with an emphasis on the donor-specific antibody (DSA) status, histological follow-up, and graft survival. Inclusion criteria were the presence of v-lesion with minimal interstitial (i ≤ 1) and microvascular inflammation (g + ptc≤1). C4d-positive biopsies were excluded. We retrospectively found 33 IvL biopsies in 33 patients, mainly performed in the early posttransplantation period (median time 27 days) and clinically indicated in 66.7%. A minority of recipients (5/33, 15.2%) had DSA at the time of biopsy. IvL was treated by anti-rejection therapy in 21 cases (63.6%), whereas 12 (36.4%) were untreated. Seventy percent of untreated patients and 66% of treated patients showed favorable histological evolution on subsequent biopsy. Kidney graft survival in IvL was significantly higher than in a matched cohort of antibody-mediated rejection with arteritis. In conclusion, IvL is not primarily antibody-mediated and may show a favorable evolution. The heterogeneity of IvL pathophysiology on early biopsies should prompt DSA testing as well as close clinical and histological follow-up in all patients with IvL.

Early Posttransplant Isolated v1 Lesion Does Not Need to Be Treated and Does Not Lead to Increased Fibrosis

Acute vascular rejection (AVR) is characterized by intimal arteritis in addition to tubulitis and interstitial inflammation. It is associated with a poorer prognosis compared to tubulointerstitial rejection (AIR) and AVR is associated with a higher rate of graft loss than AIR. The prognosis and treatment of arteritis without tubulitis and interstitial inflammation (isolated v1 lesion) are still controversial. We report a case of a patient who had a biopsy of the kidney allograft for evaluation of slow graft function. The biopsy revealed an isolated v1 lesion. However, we chose not to augment immunosuppression. The patient's kidney allograft function improved over time with close monitoring. Repeat biopsy a year later showed no evidence of endothelialitis and relatively unchanged fibrosis and no other abnormalities. Although it is suggested that most cases of isolated v1 lesions will respond to corticosteroids or T cell depleting therapies, some cases will improve with conservative management. Further studies are needed to determine which cases could be managed conservatively.

Banff 2013 update: Pearls and pitfalls in transplant renal pathology

The pathological classification of rejection in renal allografts (Banff classification) has undergone substantial evolution for more than 20 years, and has been the diagnostic gold standard in clinical practice. The 2013 updated Banff classification encompasses a revised scheme of antibody-mediated rejection (ABMR) that consists of donor-specific antibody (DSA) positivity, characteristic histological manifestations for both acute and chronic ABMR, and DSA-induced endothelial cell injury which is represented by either C4d positivity, microvascular inflammation or expression of activated endothelial gene transcripts. Other modified criteria include a C4d positivity threshold, and histological definition of transplant glomerulitis and transplant glomerulopathy. Morphologically, glomerulonephritis, either recurrent or de novo, can be challenging to differentiate from ABMR-mediated transplant glomerulitis. Endothelial arteritis by itself does not warrant the diagnosis of acute T-cell mediated rejection; ABMR should also be considered based on the DSA test results. With regard to polyomavirus BK-associated nephropathy, immunohistochemical examination using anti-simian virus (SV) 40 antibody can be a promising method to assess the quantitative viral load of polyomavirus BK and graft survival. In summary, the 2013 updated Banff classification strictly defines ABMR with histopathological and serological criteria irrespective of C4d positivity. Inclusion of gene expression data relevant to ABMR highlights that the Banff criteria have entered the era of 'Seeing the Unseen' schemes, reflecting recent advances in understanding the molecular events in allograft injury.

The Relationship of the Severity and Category of Acute Rejection With Intimal Arteritis Defined in Banff Classification to Clinical Outcomes

BACKGROUND

It is unclear if the category of acute rejection with intimal arteritis (ARV) is relevant to short- and long-term clinical outcomes and if the graft outcomes are affected by the severity of intimal arteritis.

METHODS

One hundred forty-eight ARV episodes were reviewed and categorized according to the 2013 Banff criteria of AMR: T cell-mediated rejection with intimal arteritis (v) lesion (TCMRV; n = 78), total antibody-mediated rejection with v lesion (AMRV), which were further divided into suspicious AMRV (n = 37) and AMRV (n = 33). The Banff scores of intimal arteritis (v1, v2 and v3) represented low, moderate, and high ARV severity.

RESULTS

The grafts with TCMRV, suspicious AMRV (sAMRV), and AMRV showed similar responses to antirejection therapy, whereas the grafts with v2- or v3-ARV responded significantly poorer compared to those with v1-ARV. The 8-year death-censored graft survival (DCGS) rate was 56.8% of TCMRV versus 34.1% of total AMRV (Log rank, P = 0.03), but the 1- and 5-year DCGS rates were comparable between the 2 groups; moreover, the 1-, 5-, and 8-year DCGS rates of v1-ARV were evidently higher than v2- and v3-ARV (each pairwise comparison to v1-AVR yields P < 0.01); in contrast, the DCGS rates were similar between sAMRV and AMRV. The existing donor-specific antibodies or moderate microvascular inflammation or C4d-positive staining or intensive tubulointerstitial inflammation played a less significant role on the long-term graft survival.

CONCLUSIONS

Compared to the category, the ARV severity is more closely associated with the initial response to antirejection therapy and long-term graft failure. The sAMRV and AMRV might represent a spectrum of the same disorder.

External Iliac Arterial Obstruction Caused by Satinsky Atrauma Forceps in Renal Transplantation

External iliac arterial obstruction is relatively rare in renal transplantation, and may cause surgical failure and ipsilateral leg ischaemia. Prompt diagnosis and management of this kind of complication is essential to rescue the patient and allograft. Four patients with external iliac arterial obstruction caused by Satinsky atrauma forceps in renal transplantation were analysed and summarized. In case one, the obstruction of the external iliac artery distal to the renal allograft caused ipsilateral leg ischaemia. After surgical fixation of the endarterium, the patient recovered from the lower limb ischaemia. In case two, the obstruction of the external iliac artery was located proximal to the renal allograft. Since the endarterial rupture was not found and fixed in time, the renal allograft was lost. The third case was similar to the second. Based on the previous experience, we fixed the endarterium promptly and transplanted the kidney back successfully. In case four, there was endarterial rupture with atherosclerosis located around the anastomosis stoma. After taking out the atherosclerotic plaque and fixing the endarterium, the blood supply of kidney and lower limb was good. External iliac arterial rupture and obstruction caused by Satinsky atrauma forceps in renal transplantation is rare, but may cause severe and depressing outcome. The critical step is to find and fix the impaired endarterium as early as possible.

Intimal arteritis in renal allografts: new takes on an old lesion

PURPOSE OF REVIEW

Inflammation of the arterial wall has been recognized as a key element of rejection since the early studies of pathologic changes in transplanted organs. Better elucidation of the mechanisms involved in endothelial injury has brought increasing complexity to the diagnostic classification of this lesion in the context of transplantation, and has affected the clinical management of patients with allograft rejection. Here, we examine how our understanding of the significance of intimal arteritis in renal graft biopsies has evolved in the past decades.

RECENT FINDINGS

Recognition that antidonor antibody may cause intimal arteritis has prompted revision of histologic classifications of transplant rejection. Although molecular signatures/biomarkers are being developed and proposed as new tools for aiding in the identification of cell-mediated and antibody-mediated types of rejection, histological examination is still needed to identify intimal arteritis in allograft biopsies. Outcome studies are contributing to clarify the prognostic significance of intimal arteritis in transplant rejection.

SUMMARY

Intimal arteritis remains an important histologic feature of allograft rejection, which comes in different nuances requiring tailored therapeutic approaches.

Reassessing the Significance of Intimal Arteritis in Kidney Transplant Biopsy Specimens

Intimal arteritis (the presence of v-lesions) in kidney transplant biopsy specimens is believed to have major prognostic and diagnostic significance. We assessed the relationship of v-lesions to prognosis in 703 indication biopsy specimens and used microarray-based molecular tests to re-examine the relationship of v-lesions to rejection. v-Lesions were noted in 49 specimens (7%) and were usually mild (v1). The presence of v-lesions had no effect on graft survival compared with the absence of v-lesions. Pathologists using current conventions almost always interpreted v-lesions as reflecting T cell-mediated rejection (TCMR), either pure or mixed with antibody-mediated rejection (ABMR). The molecular scores questioned the conventional diagnoses in 29 of 49 specimens (59%), including ten that were conventional TCMR with no molecular rejection and nine that were conventional TCMR mixed with pure ABMR molecularly. The presence of tubulointerstitial inflammation (i-t) meeting TCMR criteria allowed subclassification of v-lesion specimens into 21 i-t-v-lesion specimens and 28 isolated v-lesion specimens. Molecular TCMR scores were positive in 95% of i-t-v-lesion specimens but only 21% of isolated v-lesion specimens. Molecular ABMR scores were often positive in isolated v-lesion biopsies (46%). Time of biopsy after transplantation was critical for understanding isolated v-lesions: most early isolated v-lesion specimens had no molecular rejection and were DSA negative, whereas most isolated >1 year after transplantation had positive DSA and ABMR scores. Therefore, v-lesions in indication biopsy specimens do not affect prognosis and can reflect TCMR, ABMR, or no rejection. Time after transplantation, DSA, and accompanying inflammation provide probabilistic basis for interpreting v-lesions.

Isolated endarteritis and kidney transplant survival: a multicenter collaborative study

Isolated endarteritis of kidney transplants is increasingly recognized. Notably, microarray studies revealed absence of immunologic signatures of rejection in most isolated endarteritis biopsy samples. We investigated if isolated endarteritis responds to rejection treatment and affects kidney transplant survival. We retrospectively enrolled recipients of kidney transplant who underwent biopsies between 1999 and 2011 at seven American and Canadian centers. Exclusion criteria were recipients were blood group-incompatible or crossmatch-positive or had C4d-positive biopsy samples. After biopsy confirmation, patients were divided into three groups: isolated endarteritis (n=103), positive controls (type I acute T cell-mediated rejection with endarteritis; n=101), and negative controls (no diagnostic rejection; n=103). Primary end points were improved kidney function after rejection treatment and transplant failure. Mean decrease in serum creatinine from biopsy to 1 month after rejection treatment was 132.6 µmol/L (95% confidence interval [95% CI], 78.7 to 186.5) in patients with isolated endarteritis, 96.4 µmol/L (95% CI, 48.6 to 143.2) in positive controls (P=0.32), and 18.6 µmol/L (95% CI, 1.8 to 35.4) in untreated negative controls (P<0.001). Functional improvement after rejection treatment occurred in 80% of patients with isolated endarteritis and 81% of positive controls (P=0.72). Over the median 3.2-year follow-up period, kidney transplant survival rates were 79% in patients with isolated endarteritis, 79% in positive controls, and 91% in negative controls (P=0.01). In multivariate analysis, isolated endarteritis was associated with an adjusted 3.51-fold (95% CI, 1.16 to 10.67; P=0.03) risk for transplant failure. These data indicate that isolated endarteritis is an independent risk factor for kidney transplant failure.

The severity of acute cellular rejection defined by Banff classification is associated with kidney allograft outcomes

BACKGROUND

It is unclear if the severity or the timing of acute cellular rejection (ACR) defined by Banff classification 2009 is associated with graft survival.

METHODS

Borderline changes, TCMR I (interstitial rejection), and TCMR II/III (vascular rejection) were defined as low, moderate, and high ACR severity, respectively. Approximately 270 patients who had at least one episode of ACR were enrolled, 270 biopsies were chosen which showed the highest ACR severity of each patient and were negative for donor-specific antibodies (DSA), C4d, and microcirculation changes (MC). Six months were used as the cutoff to define early and late ACR; 370 patients without biopsy posttransplantation were recruited in the control group.

RESULTS

Up to 8-year posttransplantation, death-censored graft survival (DCGS) rates of control, borderline, TCMR I, and TCMR II/III groups were 97.6%, 93.3%, 79.6%, and 73.6% (log rank test, P<0.001); the control group had significantly higher DCGS rate than the three ACR groups (each pairwise comparison yields P<0.05). The DCGS rate of late ACR was significantly lower compared with early ACR (63.6% vs. 87.4%, P<0.001). Intimal arteritis (Banff v-lesion) was an independent histologic risk factor correlated with long-term graft loss regardless of the timing of ACR. The v-lesions with minimal or high-grade tubulitis displayed similar graft survival (72.7% vs. 72.9%, P=0.96).

CONCLUSION

All types of ACR affect long-term graft survival. Vascular or late ACR predict poorer graft survival; the extent of tubulointerstitial inflammation (TI) is of no prognostic significance for vascular rejection.

Histopathological and clinical findings in renal transplants with Banff type II and III acute cellular rejection without tubulointerstitial infiltrates

According to the Banff guidelines for renal transplants, pure endothelialitis without any tubulointerstitial infiltrates (with the Banff components v ≥ 1, i0, t0) has to be called acute cellular rejection (ACR). The pathophysiology of this rare lesion abbreviated as v_only is currently unclear, as well as its clinical, serological, and prognostic implications. Therefore, we conducted this retrospective comparative study. We compared all 23 biopsies with v_only from Hannover Medical School between 2003 and 2010 with 23 matched biopsies with the Banff components v ≥ 1, i ≥ 1, and t ≥ 1 (v_plus) and 23 biopsies with v0, i0, and t0 (v0i0t0). Serological (available in 10, 11, and 14 patients, respectively), histological, and clinical data were compared. Of all biopsies, 0.4 % had findings of v_only. v_only, v_plus, and v0i0t0 only showed minimal differences in the Banff components apart from the cohort-defining components. Endothelialitis in v_only more frequently involved the arcuate arteries than the smaller preglomerular vessels compared to v_plus and vice versa. Combining histopathological data and serological data, v_only more frequently showed criteria for acute humoral rejection than v0i0t0 (albeit not persistent after the Bonferroni-Holm correction in pairwise comparisons), while there was no difference between v_only and v_plus. No difference could be demonstrated regarding clinical presentation at biopsy or outcome. Our results show minimal differences regarding clinical presentation, outcome, and histological features between v_only and v_plus. Patients with v_only should be thoroughly investigated for evidence of acute humoral rejection.

Clinical significance of isolated v lesions in paediatric renal transplant biopsies: muscular arteries required to refute the diagnosis of acute rejection

Intimal vascular lesions are considered features of acute T-cell-mediated rejection yet can occur in the absence of tubulointerstitial inflammation, termed isolated 'v' lesions. The clinical significance of these lesions is unclear. The diagnosis requires a biopsy with the presence of arteries. The frequency of adequate biopsies was analysed in 89 renal transplant biopsies from 57 paediatric renal allograft recipients, and the incidence of isolated endarteritis was determined. 60 (67%) biopsies contained an artery and of these, isolated 'v' lesions occurred in 6 (10%). 5 (83%) biopsies with isolated 'v' lesions were associated with positive DSA, suggesting that these lesions may represent acute antibody-mediated rejection. Patients with vessel-negative biopsies had an increased decline in eGFR (median -20.5, IQR -24.4 to 1.2 ml/min/1.73 m(2) vs. -9.6, IQR -78.7 to -6.8 ml/min/1.73 m(2) ; P = 0.01). Patients with vessel-negative biopsies were more likely to have repeat biopsy for ongoing allograft dysfunction, (25.0% vs. 2.4%; P < 0.01). The data suggest that isolated 'v' lesions are more common than previously thought. A significant proportion of biopsies classified as 'normal' or 'borderline change' in the absence of a large vessel may represent undiagnosed acute rejection. This may result in suboptimal therapy with possible adverse effects on renal outcome.