Identification of lesions indicating rejection in kidney transplant biopsies: tubulitis is severely under-detected by conventional microscopy

Renal MRI: From Nephron to NMR Signal

Renal diseases pose a significant socio-economic burden on healthcare systems. The development of better diagnostics and prognostics is well-recognized as a key strategy to resolve these challenges. Central to these developments are MRI biomarkers, due to their potential for monitoring of early pathophysiological changes, renal disease progression or treatment effects. The surge in renal MRI involves major cross-domain initiatives, large clinical studies, and educational programs. In parallel with these translational efforts, the need for greater (patho)physiological specificity remains, to enable engagement with clinical nephrologists and increase the associated health impact. The ISMRM 2022 Member Initiated Symposium (MIS) on renal MRI spotlighted this issue with the goal of inspiring more solutions from the ISMRM community. This work is a summary of the MIS presentations devoted to: 1) educating imaging scientists and clinicians on renal (patho)physiology and demands from clinical nephrologists, 2) elucidating the connection of MRI parameters with renal physiology, 3) presenting the current state of leading MR surrogates in assessing renal structure and functions as well as their next generation of innovation, and 4) describing the potential of these imaging markers for providing clinically meaningful renal characterization to guide or supplement clinical decision making. We hope to continue momentum of recent years and introduce new entrants to the development process, connecting (patho)physiology with (bio)physics, and conceiving new clinical applications. We envision this process to benefit from cross-disciplinary collaboration and analogous efforts in other body organs, but also to maximally leverage the unique opportunities of renal physiology. LEVEL OF EVIDENCE: 1 TECHNICAL EFFICACY STAGE: 2.

Evaluation of Early Renal Allograft Dysfunction from Living Donors among Egyptian Patients (Histopathological and Immunohistochemical Study)

BACKGROUND: Early renal graft dysfunction is a major problem in the early post-transplantation period and is considered a major cause of graft loss. Clinical diagnosis based on the clinical criteria alone is unreliable; therefore, biopsy remains the gold standard to differentiate between rejection and non-rejection causes. AIM: This study was designed to identify and differentiate between causes of early graft dysfunction during the first post-transplantation month and to correlate between histological lesions and immunohistochemistry (IHC) for accurate diagnosis and a better outcome. MATERIALS AND METHODS: A total of 163 renal allograft biopsies, performed in the first post-transplantation month over 6 years, were included in the study. New sections were prepared from the paraffin blocks and stained with conventional stains. Additional sections were prepared and treated by complement fragment 4d (C4d) and cluster differentiation 3 (CD3) antibodies for IHC evaluation. RESULTS: All the studied cases were from living donors. The mean patient age was 39 years with predominant males. The clinical indication for most biopsies (94.5%) was impaired graft function. Acute rejection (AR) was the main diagnostic category observed in (98/163, 60.1%); out of which, T cell-mediated rejection (TCMR) was observed in (62/98, 63.2%). Drug toxicity was suspected in (53/163, 32.5%), acute tubular injury (ATI) not otherwise specified (nos) in (21/163, 12.9%), and other lesions including thrombotic microangiopathy were observed in the remaining biopsies. The most common cause of graft dysfunction in the 1st and 2nd weeks was AR representing. A significant correlation was seen between mild glomerulitis (g1) and mild peritubular capillaritis (PTC) 1, on the one side, and negative C4d staining, on the other side. No significant correlation was seen between moderate glomerulitis (g2) and moderate ptc2 at one side and positive C4d staining at the other side reflecting the poor association between the microvascular inflammation (“g” and “ptc” scores) and C4d positivity (r = 0.2). Missed mild tubulitis (t1) was found in a single case and missed moderate tubulitis (t2) was found in a single case detected by CD3 IHC. CONCLUSION: AR and drug toxicity account for the majority of early graft dysfunction, however, other pathological lesions, per se or coincide with them may be the cause. The significance of g2 per se as a marker for diagnosis of antibody-mediated rejection requires further study. Considering C4d score 1 (by IHC) positive; also requires further study with follow-up.

Single nucleotide variant counts computed from RNA sequencing and cellular traffic into human kidney allografts

Advances in bioinformatics allow identification of single nucleotide polymorphisms (variants) from RNA sequence data. In an allograft biopsy, 2 genomes contribute to the RNA pool, 1 from the donor organ and the other from the infiltrating recipient's cells. We hypothesize that imbalances in genetic variants of RNA sequence data of kidney allograft biopsies provide an objective measure of cellular infiltration of the allograft. We performed mRNA sequencing of 40 kidney allograft biopsies, selected to represent a comprehensive range of diagnostic categories. We analyzed the sequencing reads of these biopsies and of 462 lymphoblastoid cell lines from the 1000 Genomes Project, for RNA variants. The ratio of heterozygous to nonreference genome homozygous variants (Het/Hom ratio) on all autosomes was determined for each sample, and the estimation of stromal and immune cells in malignant tumors using expression data (ESTIMATE) score was computed as a complementary estimate of the degree of cellular infiltration into biopsies. The Het/Hom ratios (P = .02) and the ESTIMATE scores (P < .001) were associated with the biopsy diagnosis. Both measures correlated significantly (r = .67, P < .0001), even though the Het/Hom ratio is based on mRNA sequence variation, while the ESTIMATE score uses mRNA expression. Het/Hom ratio and the ESTIMATE score may offer unbiased and quantitative parameters for characterizing cellular traffic into human kidney allografts.

Moving Biomarkers toward Clinical Implementation in Kidney Transplantation

Long-term kidney transplant outcomes remain suboptimal, delineating an unmet medical need. Although current immunosuppressive therapy in kidney transplant recipients is effective, dosing is conventionally adjusted empirically on the basis of time after transplant or altered in response to detection of kidney dysfunction, histologic evidence of allograft damage, or infection. Such strategies tend to detect allograft rejection after significant injury has already occurred, fail to detect chronic subclinical inflammation that can negatively affect graft survival, and ignore specific risks and immune mechanisms that differentially contribute to allograft damage among transplant recipients. Assays and biomarkers that reliably quantify and/or predict the risk of allograft injury have the potential to overcome these deficits and thereby, aid clinicians in optimizing immunosuppressive regimens. Herein, we review the data on candidate biomarkers that we contend have the highest potential to become clinically useful surrogates in kidney transplant recipients, including functional T cell assays, urinary gene and protein assays, peripheral blood cell gene expression profiles, and allograft gene expression profiles. We identify barriers to clinical biomarker adoption in the transplant field and suggest strategies for moving biomarker-based individualization of transplant care from a research hypothesis to clinical implementation.

Capillary deposition of complement C4d and C3d in Chinese renal allograft biopsies

BACKGROUND

C3d is a product of both the classic and the alternative complement cascades; however, few studies have addressed the role of C3d in renal biopsies and its relationship with long-term graft survival rate is not very clear.

METHODS

94 patients with biopsy-proven acute rejection episodes were included in the study. We investigated the associations between histological findings, clinical examinations, and outcome.

RESULTS

The overall prevalence for C4dPTC and C3dPTC was 42.6% and 29.8%. There was a significant association between C3dPTC and C4dPTC (P < 0.001). C3dPTC and C4dPTC were related with histological types (P = 0.024 and P < 0.001, resp.). The long-term survival rate for C4dPTC positive transplants was lower than that of C4dPTC negative transplants, but it was not statistic significant in our study (P = 0.150). The survival rate of C3dPTC positive group was much lower than the negative group (P = 0.014). Patients with double positives for C4dPTC and C3dPTC exhibited the lowest survival rate significantly different from those of the C3dPTC only and C4dPTC only groups (P = 0.01 and P = 0.0037).

CONCLUSIONS

This longitudinal cohort study has demonstrated that C3d deposition in the PTC was closely related to renal dysfunction and pathological changes.

Pseudorejection and true rejection after kidney transplantation: classification and clinical significance

OBJECTIVES

Multiple factors may result in an elevation in serum creatinine level after kidney transplantation, mimicking rejection. It is crucial to differentiate between a true rejection and other conditions inducing a 'pseudorejection', in order to avoid overtreatment, or worse, mistreatment. Our goal was to review and classify true rejections and pseudorejections and their clinical significance.

MATERIAL AND METHODS

This was a retrospective review of articles published in the USA and Europe, from 1976 to the present. The sites from which information was retrieved included PubMed, Clinical Imaging, Histopathology, Archives of Surgery, JACS, the American Urological Association, Medline and Springer Link. The importance of the resistive index will also be emphasized.

RESULTS

We reviewed 61 articles regarding the causes of renal graft dysfunction, which may be classified into true rejections and pseudorejections, the latter including the following 6 factors: hyperglycemia, ureteral obstruction, lymphocele, arterial stenosis, infection and recurrence of primary pathology.

CONCLUSIONS

'Pseudorejection' has been described only once, for the first time in 1976 in the USA, and there have been no other reports since then. Multiple factors, mainly hyperglycemia, may induce a pseudorejection, presenting with an elevation of serum creatinine level and leading the clinician to an erroneous diagnosis of true rejection initially, resulting in inappropriate management.