CD20-positive infiltrates in renal allograft biopsies with acute cellular rejection are not associated with worse graft survival

Significance of Perivascular Aggregates in Kidney Allografts: Evaluation of 1-Year Protocol Biopsies Using Recent Banff Classification

BACKGROUND

Perivascular aggregates (PVAs) often occur in kidney allografts; however, their significance needs to be re-evaluated in light of changes in the concept and criteria of allograft rejection.

METHODS

We reviewed 1-year protocol biopsies in 258 patients with kidney transplants to identify PVAs and concurrent pathology based on the Banff 2017 classification, including revised criteria for chronic active T-cell mediated rejection (CA-TCMR). We investigated the incidence of PVA, concurrent allograft lesions, diagnosis, and graft survival. No prisoners were used in this study, and no participants were coerced or paid.

RESULTS

We identified PVA in 81 biopsies (31.4%). The incidence of previous rejection (32.1% vs 12.4%, P= .0003) and total inflammation (1.3 ± 0.8 vs 0.6 ± 0.8, P < .0001), inflammation (0.7 ± 0.8 vs 0.2 ± 0.5, P < .0001), inflammation in the area of interstitial fibrosis and tubular atrophy (1.3 ± 1.2 vs 0.7 ± 0.9, P < .0001), tubulitis (1.4 ± 1.1 vs 0.6 ± 0.9, P < .0001), and interstitial fibrosis scores (1.2 ± 0.9 vs 0.9 ± 0.9, P= .01) were higher in PVA-positive compared with patients with PVA-negative. Diagnoses in the PVA-positive group revealed no rejection in 49.4%, CA-TCMR in 21.0%, borderline changes in 18.5%, and acute TCMR in 6.2%. CA-TCMR was more frequent in patients with PVA-positive (21.0% vs 4.0%, P < .0001). Graft survival was similar in both groups among all patients, no-rejection, any type of rejection, and CA-TCMR subgroups.

CONCLUSIONS

PVAs occur heterogeneously and are associated with previous rejection or concurrent CA-TCMR. The prognostic significance of PVAs in kidney transplantation is inconclusive, and further investigations are needed.

The roles of tertiary lymphoid structures in chronic diseases

Tertiary lymphoid structures (TLSs) are ectopic lymphoid tissues that drive antigen-specific immune responses at sites of chronic inflammation. Unlike secondary lymphoid organs such as lymph nodes, TLSs lack capsules and have their own unique characteristics and functions. The presumed influence of TLSs on the disease course has led to widespread interest in obtaining a better understanding of their biology and function. Studies using single-cell analyses have suggested heterogeneity in TLS composition and phenotype, and consequently, functional correlates with disease progression are sometimes conflicting. The presence of TLSs correlates with a favourable disease course in cancer and infection. Conversely, in autoimmune diseases and chronic age-related inflammatory diseases including chronic kidney disease, the presence of TLSs is associated with a more severe disease course. However, the detailed mechanisms that underlie these clinical associations are not fully understood. To what extent the mechanisms of TLS development and maturation are shared across organs and diseases is also still obscure. Improved understanding of TLS development and function at the cellular and molecular levels may enable the exploitation of these structures to improve therapies for chronic diseases, including chronic kidney disease.

Can Gene Expression Analysis in Zero-Time Biopsies Predict Kidney Transplant Rejection?

Zero-time biopsies are taken to determine the quality of the donor organ at the time of transplantation. Histological analyses alone have so far not been able to identify parameters that allow the prediction of subsequent rejection episodes or graft survival. This study investigated whether gene expression analyses of zero-time biopsies might support this prediction. Using a well-characterized cohort of 26 zero-time biopsies from renal transplant patients that include 4 living donor (LD) and 22 deceased donor (DD) biopsies that later developed no rejection (Ctrl, n = 7), delayed graft function (DGF, n = 4), cellular (T-cell mediated rejection; TCMR, n = 8), or antibody-mediated rejection (ABMR, n = 7), we analyzed gene expression profiles for different types of subsequent renal transplant complication. To this end, RNA was isolated from formalin-fixed, paraffin-embedded (FFPE) sections and gene expression profiles were quantified. Results were correlated with transplant data and B-cell, and plasma cell infiltration was assessed by immunofluorescence microscopy. Both principal component analysis and clustering analysis of gene expression data revealed marked separation between LDs and DDs. Differential expression analysis identified 185 significant differentially expressed genes (adjusted p < 0.05). The expression of 68% of these genes significantly correlated with cold ischemia time (CIT). Furthermore, immunoglobulins were differentially expressed in zero-time biopsies from transplants later developing rejection (TCMR + ABMR) compared to non-rejected (Ctrl + DGF) transplants. In addition, immunoglobulin expression did not correlate with CIT but was increased in transplants with previous acute renal failure (ARF). In conclusion, gene expression profiles in zero-time biopsies derived from LDs are markedly different from those of DDs. Pre-transplant ARF increased immunoglobulin expression, which might be involved in triggering later rejection events. However, these findings must be confirmed in larger cohorts and the role of early immunoglobulin upregulation in zero-biopsies needs further clarification.

Advanced Tertiary Lymphoid Tissues in Protocol Biopsies are Associated with Progressive Graft Dysfunction in Kidney Transplant Recipients

BACKGROUND

Tertiary lymphoid tissues (TLTs) are ectopic lymphoid tissues found in chronically inflamed organs. Although studies have documented TLT formation in transplanted kidneys, the clinical relevance of these TLTs remains controversial. We examined the effects of TLTs on future graft function using our histologic TLT maturity stages and the association between TLTs and Banff pathologic scores. We also analyzed the risk factors for the development of TLTs.

METHODS

Serial protocol biopsy samples (0 hour, 1, 6, and 12 months) without rejection were retrospectively analyzed from 214 patients who underwent living donor kidney transplantation. TLTs were defined as lymphocyte aggregates with signs of proliferation and their stages were determined by the absence (stage I) or presence (stage II) of follicular dendritic cells.

RESULTS

Only 4% of patients exhibited TLTs at the 0-hour biopsy. Prevalence increased to almost 50% at the 1-month biopsy, and then slightly further for 12 months. The proportion of advanced stage II TLTs increased gradually, reaching 19% at the 12-month biopsy. Presence of stage II TLTs was associated with higher risk of renal function decline after transplantation compared with patients with no TLT or stage I TLTs. Stage II TLTs were associated with more severe tubulitis and interstitial fibrosis/tubular atrophy at 12 months and predicted poorer graft function independently from the degree of interstitial inflammation. Pretransplantation rituximab treatment dramatically attenuated the development of stage II TLTs.

CONCLUSIONS

TLTs are commonly found in clinically stable transplanted kidneys. Advanced stage II TLTs are associated with progressive graft dysfunction, independent of interstitial inflammation.

The Implications of B-lineage Cells in Kidney Allografts

The majority of cells comprising the inflammatory infiltrates in kidney allografts undergoing acute and/or chronic rejection are typically T cells and monocyte/macrophages with B cells, plasma cells, and eosinophils accounting for <5%. In a significant minority of biopsies, B lineage cells (B cells and/or plasma cells) may be found more abundantly. Although plasma cell infiltrates tend to be more diffuse, B cells tend to aggregate into nodules that may mature into tertiary lymphoid organs. Given the ability to target B cells with anti-CD20 monoclonal antibodies and plasma cells with proteasome inhibitors and anti-CD38 monoclonal antibodies, it is increasingly important to determine the significance of such infiltrates. Both cell types are potential effectors of rejection, but both also have a tolerizing potential. B cell infiltrates have been associated with steroid resistance and reduced graft survival in some studies but not in others, and their presence should not prompt automatic depletional therapy. Plasma cell-rich infiltrates tend to occur later, may be associated with cell-mediated and/or antibody-mediated rejection, and portend an adverse outcome. Viral infection and malignancy must be ruled out. Randomized controlled trials are needed to determine the appropriateness of specific therapy when B cells and/or plasma cells are found. No strong therapeutic recommendations can be made at this time.

Characterizing the B-Cell and Humoral Response in Tertiary Lymphoid Organs in Kidney Allografts

OBJECTIVES

Tertiary lymphoid organs are formed at sites of chronic inflammation and are thought to contribute to the immune response. Here, we aimed to characterize the structure and function of tertiary lymphoid organs in a model of murine kidney allotransplant to understand their role in alloimmunity.

MATERIALS AND METHODS

We transplanted 4 C57BL/6 mouse kidneys (isograft group) and 17 DBA/2 mouse kidneys into C57BL/6 mouse recipients. Three DBA/2-to-C57BL/6 transplant mice that rejected their grafts acutely (before 10 days posttransplant) were excluded from the study. The 14 surviving DAB2 grafts were retrieved at day 45 posttransplant and evaluated histologically. The presence of antibody-secreting cells and circulating levels of donor-specific antibodies were also evaluated.

RESULTS

We found that tertiary lymphoid organs can be associated with a beneficial response in a kidney allotransplant model. Characterization of B-cell subsets within tertiary lymphoid organs in mouse kidney allografts revealed naive, plasma, and memory B cells, which were mostly grouped within or in close proximity of tertiary lymphoid organs. Staining for intracellular immunoglobulin G showed that many of the B cells within tertiary lymphoid organs were capable of producing antibodies. Although allospecific antibodies were found in the serum of recipient mice and were deposited in the transplanted kidneys, graft function was not affected in this model.

CONCLUSIONS

B cells within tertiary lymphoid organs are functional and contribute to the humoral arm of the alloresponse. However, tertiary lymphoid organs are not necessarily associated with graft rejection, suggesting that protective mechanisms are at play.

Presence of intragraft B cells during acute renal allograft rejection is accompanied by changes in peripheral blood B cell subsets

B cells have various functions, besides being plasma cell precursors. We determined the presence of intragraft B cells at time of acute rejection (AR) and looked for correlates of B cell involvement in peripheral blood. Renal biopsies at time of AR or stable graft function were analysed for the presence of B cells and B cell‐related gene expression, as well as C4d staining. Peripheral blood B cell subset distribution was analysed at various time‐points in patients with AR and controls, alongside serum human leucocyte antigen (HLA) antibodies. AR was accompanied by intragraft CD20⁺ B cells, as well as elevated CD20 (MS4A1) and CD19 gene expression compared to controls. B cell infiltrates were proportional to T cells, and accompanied by the chemokine pair C‐X‐C motif chemokine ligand 13 (CXCL13)–C‐X‐C motif chemokine receptor 5 (CXCR5) and B cell activating factor (BAFF). Peripheral blood memory B cells were decreased and naive B cells increased at AR, in contrast to controls. While 22% of patients with AR and 5% of controls showed de‐novo donor‐specific antibodies (DSA), all biopsies were C4d‐negative. These results suggest a role for B cells in AR by infiltrating the graft alongside T cells. We hypothesize that the shift in peripheral blood B cell composition is related to the graft infiltration at time of AR.

Effector B cells in cardiac allograft vasculopathy

PURPOSE OF REVIEW

B cells have recently emerged as important immune players in solid organ rejection, especially in cardiac allograft vasculopathy (CAV), a chronic form of rejection following heart transplantation. B cells can exert either regulatory or effector functions. This review will provide an update on effector B cells in CAV.

RECENT FINDINGS

Independent studies reported the abundance of B cells in graft infiltrates during CAV, especially around coronary arteries. Infiltrates comprise CD20+ CD27+ memory B cells together with differentiated CD20-CD138+ plasma cells, which are almost always associated with T cells and macrophages. The structure of some of these infiltrates evokes that of germinal centers, suggesting the generation of tertiary lymphoid organs in the graft. Remarkably, B-cell infiltrates are most often detected in the absence of circulating donor human leukocyte antigen-specific antibodies, strongly suggesting that the two components are unrelated. Characterization of B-cell clones isolated from explanted human cardiac graft infiltrates revealed the prevalence of polyreactive innate, B1-like B cells. Accumulating evidence suggests that these cells act primarily as antigen-presenting cells in situ. Additional effector functions, such as local antibody secretion and pro-inflammatory cytokine production, promoting T-cell polarization, macrophage activation and fibrosis are also considered.

SUMMARY

Converging observations made through animal and human studies add substantial support for an effector B-cell role in the pathophysiology of CAV. On the basis of these collective findings, a therapeutic strategy targeting B cells could reasonably be envisaged to prevent or treat this complication.

Effects of CD20+ B-cell infiltration into allografts on kidney transplantation outcomes: a systematic review and meta-analysis

The effects of CD20+ B-cell infiltration during acute rejection on graft outcomes are controversial. The objective of this systematic review and meta-analysis was to clarify this issue. We performed a systematic literature search for studies published up to January 14, 2016. A total of 5 studies, with 200 patients, were included. The presence of CD20+ B cells in renal biopsies during allograft rejection was associated with graft loss and steroid resistance. No association of CD20+ B-cell infiltration with C4d-positive staining of the peritubular capillaries in renal biopsies was found in the analysis of patients who experienced kidney graft rejection. In conclusion, CD 20+ B cell infiltration during allograft rejection was associated with an increased risk of graft loss and steroid resistance.

Characterization of ectopic lymphoid structures in different types of acute renal allograft rejection

We hypothesize that T cells such as interleukin (IL)-21⁺ B cell lymphoma 6 (BCL6)⁺ T follicular helper cells can regulate B cell-mediated immunity within the allograft during acute T cell-mediated rejection; this process may feed chronic allograft rejection in the long term. To investigate this mechanism, we determined the presence and activation status of organized T and B cells in so-called ectopic lymphoid structures (ELSs) in different types of acute renal allograft rejection. Biopsies showing the following primary diagnosis were included: acute/active antibody-mediated rejection, C4d⁺ (a/aABMR), acute T cell-mediated rejection grade I (aTCMRI) and acute T cell-mediated rejection grade II (aTCMRII). Paraffin sections were stained for T cells (CD3 and CD4), B cells (CD20), follicular dendritic cells (FDCs, CD23), activated B cells (CD79A), immunoglobulin (Ig)D, cell proliferation (Ki67) and double immunofluorescent stainings for IL-21 and BCL6 were performed. Infiltrates of T cells were detected in all biopsies. In aTCMRI, B cells formed aggregates surrounded by T cells. In these aggregates, FDCs, IgD and Ki67 were detected, suggesting the presence of ELSs. In contrast, a/aABMR and aTCMRII showed diffuse infiltrates of T and B cells but no FDCs and IgD. IL-21 was present in all biopsies. However, co-localization with BCL6 was observed mainly in aTCMRI biopsies. In conclusion, ELSs with an activated phenotype are found predominantly in aTCMRI where T cells co-localize with B cells. These findings suggest a direct pathway of B cell alloactivation at the graft site during T cell mediated rejection.

Blood biomarkers of kidney transplant rejection, an endless search?

INTRODUCTION

The tailoring of immunosuppressive treatment is recognized as a promising strategy to improve long-term kidney graft outcome. To guide the standard care of transplant recipients, physicians need objective biomarkers that can identify an ongoing pathology with the graft or low intensity signals that will be later evolved to accelerated transplant rejection. The early identification of 'high-risk /low-risk' patients enables the adjustment of standard of caring, including managing the frequency of clinical visits and the immunosuppression dosing. Given their ease of availability and the compatibility with a large technical array, blood-based biomarkers have been widely scrutinized for use as potential predictive and diagnostic biomarkers. Areas covered: Here, the authors report on non-invasive biomarkers, such as modification of immune cell subsets and mRNA and miRNA profiles, identified in the blood of kidney transplant recipients collected before or after transplantation. Expert commentary: Combined with functional tests, the identification of biomarkers will improve our understanding of pathological processes and will contribute to a global improvement in clinical management.

Kidney Fibrosis: Origins and Interventions

All causes of renal allograft injury, when severe and/or sustained, can result in chronic histological damage of which interstitial fibrosis and tubular atrophy are dominant features. Unless a specific disease process can be identified, what drives interstitial fibrosis and tubular atrophy progression in individual patients is often unclear. In general, clinicopathological factors known to predict and drive allograft fibrosis include graft quality, inflammation (whether "nonspecific" or related to a specific diagnosis), infections, such as polyomavirus-associated nephropathy, calcineurin inhibitors (CNI), and genetic factors. The incidence and severity of chronic histological damage have decreased substantially over the last 3 decades, but it is difficult to disentangle what effects individual innovations (eg, better matching and preservation techniques, lower CNI dosing, BK viremia screening) may have had. There is little evidence that CNI-sparing/minimization strategies, steroid minimization or renin-angiotensin-aldosterone system blockade result in better preservation of intermediate-term histology. Treatment of subclinical rejections has only proven beneficial to histological and functional outcome in studies in which the rate of subclinical rejection in the first 3 months was greater than 10% to 15%. Potential novel antifibrotic strategies include antagonists of transforming growth factor-β, connective tissue growth factor, several tyrosine kinase ligands (epidermal growth factor, platelet-derived growth factor, vascular endothelial growth factor), endothelin and inhibitors of chemotaxis. Although many of these drugs are mainly being developed and marketed for oncological indications and diseases, such as idiopathic pulmonary fibrosis, a number may hold promise in the treatment of diabetic nephropathy, which could eventually lead to applications in renal transplantation.

Absence of Intragraft B Cells in Rejection Biopsies After Rituximab Induction Therapy: Consequences for Clinical Outcome

Background

The pathophysiological role of intragraft B cells during renal allograft rejection is unclear.

Methods

We studied B-cell infiltration during acute rejection in 53 patients who participated in a clinical trial in which adult renal transplant patients were randomized between a single intraoperative dose of rituximab (375 mg/m²) or placebo as induction therapy. Two independent pathologists scored all biopsies in a blinded fashion according to the Banff classification and scored for the presence of B cells and plasma cells using CD79a and CD138 as markers.

Results

The majority of acute rejections were T cell–mediated. The proportion of acute rejections with an antibody-mediated component tended to be lower in rituximab-treated patients (4/23, 17.4%) than in placebo-treated patients (11/30, 36.7%; P = 0.14). Biopsies of rituximab-treated patients had significantly lower scores for B cells (0.00; range, 0.00-0.50 vs 1.70; range, 0.60-3.30; P < 0.0001) and plasma cells (0.10; range, 0.00-1.90 vs 0.40; range, 0.00-7.50; P = 0.006). During acute rejection, intragraft clusters of B cells were not observed after rituximab induction therapy. However, the depletion of intragraft B cells during acute rejection did not affect steroid resistance, proteinuria, graft function at 2 years follow-up, or patient and graft survival at a median follow-up of 4.1 years (range, 2.0-6.2 years).

Conclusions

These data do not support a harmful influence of intragraft B cells present during acute allograft rejection on the clinical course within the first few years after renal transplantation.

B Cell Immunity in Solid Organ Transplantation

The contribution of B cells to alloimmune responses is gradually being understood in more detail. We now know that B cells can perpetuate alloimmune responses in multiple ways: (i) differentiation into antibody-producing plasma cells; (ii) sustaining long-term humoral immune memory; (iii) serving as antigen-presenting cells; (iv) organizing the formation of tertiary lymphoid organs; and (v) secreting pro- as well as anti-inflammatory cytokines. The cross-talk between B cells and T cells in the course of immune responses forms the basis of these diverse functions. In the setting of organ transplantation, focus has gradually shifted from T cells to B cells, with an increased notion that B cells are more than mere precursors of antibody-producing plasma cells. In this review, we discuss the various roles of B cells in the generation of alloimmune responses beyond antibody production, as well as possibilities to specifically interfere with B cell activation.

The Effect of Histological CD20-Positive B Cell Infiltration in Acute Cellular Rejection on Kidney Transplant Allograft Survival

Background. It is controversial whether lymphocyte infiltration exhibited in biopsy specimens is associated with transplant outcomes. This study focused on the effect of CD20-positive B cell infiltration in biopsy specimens from allografts with acute cellular rejection (ACR) in a Chinese population. Methods. Altogether, 216 patients transplanted from Sep. 2001 to Dec. 2014 with biopsy-proved ACR (Banff I or Banff II) were included in the analysis. Biopsies were immunostained for CD20 and C4d. Baseline information, serum creatinine and GFR before and after treatment, steroid resistance, response to treatment, graft loss, and survival were analyzed. Results. Eighty-three patients were classified into CD20-negative group, and 133 patients were classified into CD20-positive group. Significantly more CD20-negative patients (49/83, 59.0%) received steroid plus antibody therapy compared with the CD20-positive group (52/133, 39.1%) (P = 0.004). The response to treatment for ACR did not differ between these two groups. The CD20-positive group had less graft loss (18.8% versus 32.5%, P = 0.022) and a better graft survival rate. Further exploration of the infiltration degree suggested that it tended to be positively related to graft survival, but this did not reach statistical significance. Conclusion. CD20-positive B cell infiltration in renal allograft biopsies with ACR is associated with less steroid resistance and better graft survival. The presence of CD20-positive B cells is protective for renal allografts.

Lymphoid Neogenesis and Tertiary Lymphoid Organs in Transplanted Organs

The progressive organization of immune effectors into functional ectopic lymphoid structures, named tertiary lymphoid organs (TLO), has been observed in many conditions in which target antigens fail to be eliminated by the immune system. Not surprisingly, TLO have been recurrently identified in chronically rejected allografts. Although significant progress has been made over the last decades in understanding the molecular mechanisms involved in TLO development (a process named lymphoid neogenesis), the role of intragraft TLO (if any) in chronic rejection remains elusive. The prevailing dogma is that TLO contribute to graft rejection by generating and propagating local humoral and cellular alloimmune responses. However, TLO have been recently observed in long-term accepting allografts, suggesting that they might also be able to regulate alloimmune responses. In this review, we discuss our current understanding of how TLO are induced and propose a unified model in which TLO can play deleterious or regulatory roles and therefore actively modulate the kinetics of chronic rejection.

Presentation and Outcomes of C4d-Negative Antibody-Mediated Rejection After Kidney Transplantation

The updated Banff classification allows for the diagnosis of antibody-mediated rejection (AMR) in the absence of peritubular capillary C4d staining. Our objective was to quantify allograft loss risk in patients with consistently C4d-negative AMR (n = 51) compared with C4d-positive AMR patients (n = 156) and matched control subjects without AMR. All first-year posttransplant biopsy results from January 2004 through June 2014 were reviewed and correlated with the presence of donor-specific antibody (DSA). C4d-negative AMR patients were not different from C4d-positive AMR patients on any baseline characteristics, including immunologic risk factors (panel reactive antibody, prior transplant, HLA mismatch, donor type, DSA class, and anti-HLA/ABO-incompatibility). C4d-positive AMR patients were significantly more likely to have a clinical presentation (85.3% vs. 54.9%, p < 0.001), and those patients presented substantially earlier posttransplantation (median 14 [interquartile range 8-32] days vs. 46 [interquartile range 20-191], p < 0.001) and were three times more common (7.8% vs 2.5%). One- and 2-year post-AMR-defining biopsy graft survival in C4d-negative AMR patients was 93.4% and 90.2% versus 86.8% and 82.6% in C4d-positive AMR patients, respectively (p = 0.4). C4d-negative AMR was associated with a 2.56-fold (95% confidence interval, 1.08-6.05, p = 0.033) increased risk of graft loss compared with AMR-free matched controls. No clinical characteristics were identified that reliably distinguished C4d-negative from C4d-positive AMR. However, both phenotypes are associated with increased graft loss and thus warrant consideration for intervention.

Monitoring B cell subsets and alloreactivity in kidney transplantation

B cells are the precursors of antibody producing plasma cells that can give rise to the formation of donor-specific antibodies. However, recent data suggest that besides their role in antibody production, B cells participate in antibody-independent responses, potentially leading to allograft rejection or allograft tolerance. The presence of CD20(+) B cells in kidney graft biopsies has been shown during severe acute rejection episodes and during chronic rejection. Furthermore, operationally tolerant kidney transplant recipients showed a clear B cell dominated fingerprint of tolerance. Several techniques exist to study B cells on different levels. Numerous classification schemes allow for the distinction of many different B cell subsets using flow cytometry. Regardless, data on B cell subsets during stable graft function, rejection or tolerance remain scarce. To obtain a complete picture of the role of B cells during transplantation, antigen specific B cell assays may be required. Therefore, techniques have now been developed that allow for studying the specificity and frequency of HLA specific B cells. Here, we present an overview of the existent assays, panels and techniques intended to characterize peripheral B cells, and the currently available HLA specific B cell functional assays that may allow for monitoring the humoral alloimmune response in transplant recipients.

Quantifying renal allograft loss following early antibody-mediated rejection

Unlike antibody-mediated rejection (AMR) with clinical features, it remains unclear whether subclinical AMR should be treated, as its effect on allograft loss is unknown. It is also uncertain if AMR's effect is homogeneous across donor (deceased/live) and (HLA/ABO) antibody types. We compared 219 patients with AMR (77 subclinical, 142 clinical) to controls matched on HLA/ABO-compatibility, donor type, prior transplant, panel reactive antibody (PRA), age and year. One and 5-year graft survival in subclinical AMR was 95.9% and 75.7%, compared to 96.8% and 88.4% in matched controls (p = 0.0097). Subclinical AMR was independently associated with a 2.15-fold increased risk of graft loss (95% CI: 1.19-3.91; p = 0.012) compared to matched controls, but not different from clinical AMR (p = 0.13). Fifty three point two percent of subclinical AMR patients were treated with plasmapheresis within 3 days of their AMR-defining biopsy. Treated subclinical AMR patients had no difference in graft loss compared to matched controls (HR 1.73; 95% CI: 0.73-4.05; p = 0.21), but untreated subclinical AMR patients did (HR 3.34; 95% CI: 1.37-8.11; p = 0.008). AMR's effect on graft loss was heterogeneous when stratified by compatible deceased donor (HR = 4.73; 95% CI: 1.57-14.26; p = 0.006), HLA-incompatible deceased donor (HR = 2.39; 95% CI: 1.10-5.19; p = 0.028), compatible live donor (no AMR patients experienced graft loss), ABO-incompatible live donor (HR = 6.13; 95% CI: 0.55-67.70; p = 0.14) and HLA-incompatible live donor (HR = 6.29; 95% CI: 3.81-10.39; p < 0.001) transplant. Subclinical AMR substantially increases graft loss, and treatment seems warranted.

Sarcoidosis in native and transplanted kidneys: incidence, pathologic findings, and clinical course

Renal involvement by sarcoidosis in native and transplanted kidneys classically presents as non caseating granulomatous interstitial nephritis. However, the incidence of sarcoidosis in native and transplant kidney biopsies, its frequency as a cause of end stage renal disease and its recurrence in renal allograft are not well defined, which prompted this study. The electronic medical records and the pathology findings in native and transplant kidney biopsies reviewed at the Johns Hopkins Hospital from 1/1/2000 to 6/30/2011 were searched. A total of 51 patients with a diagnosis of sarcoidosis and renal abnormalities requiring a native kidney biopsy were identified. Granulomatous interstitial nephritis, consistent with renal sarcoidosis was identified in kidney biopsies from 19 of these subjects (37%). This is equivalent to a frequency of 0.18% of this diagnosis in a total of 10,023 biopsies from native kidney reviewed at our institution. Follow-up information was available in 10 patients with biopsy-proven renal sarcoidosis: 6 responded to treatment with prednisone, one progressed to end stage renal disease. Renal sarcoidosis was the primary cause of end stage renal disease in only 2 out of 2,331 transplants performed. Only one biopsy-proven recurrence of sarcoidosis granulomatous interstitial nephritis was identified.

Conclusions

Renal involvement by sarcoidosis in the form of granulomatous interstitial nephritis was a rare finding in biopsies from native kidneys reviewed at our center, and was found to be a rare cause of end stage renal disease. However, our observations indicate that recurrence of sarcoid granulomatous inflammation may occur in the transplanted kidney of patients with sarcoidosis as the original kidney disease.

Histopathological diagnosis of acute and chronic rejection in pediatric kidney transplantation

ABO-compatible as well as ABO-incompatible kidney transplantation are well established in the pediatric population. There are particularities in the histopathological evaluation of pediatric kidney transplant biopsies as for example the recurrence of certain diseases different from the adult population. Furthermore, the challenging transition of pediatric renal transplant recipients to adulthood is associated with an increased rate of non-adherence triggered rejection episodes. With modern immunosuppressive drugs, T-cell-mediated rejection of renal allografts is well controlled. In contrast, antibody-mediated rejection (AMR) is increasingly recognized as one of the major reasons for allograft loss. However, the 2001 diagnostic Banff criteria for antibody-mediated rejection require further refinement, as the morphological spectrum of AMR expands while effective therapeutic strategies are lacking. For example, endarteritis, which traditionally has been attributed to T-cell-mediated rejection, has recently been shown to be part of the AMR spectrum in some cases. Many findings in transplant renal biopsies are not specific for a certain disease but need consideration of differential diagnoses. To use the term "chronic allograft nephropathy" as a diagnostic entity is no longer appropriate. Therefore, the precise identification of specific diseases is paramount in the assessment of transplant renal biopsies in order to enable tailored therapeutic management.

Histologic phenotype on 1-year posttransplantation biopsy and allograft survival in HLA-incompatible kidney transplants

BACKGROUND

The correlation between histopathologic phenotypes and allograft outcomes among patients desensitized for donor-specific antibody (HLA-incompatible) is unknown.

METHODS

We analyzed 1-year biopsies from desensitized recipients transplanted between 1999 and 2010 and estimated graft survival for each histologic phenotype identified. Median time posttransplant for the 1-year biopsy was 367 days (interquartile range 357-388 days) and median follow-up of all patients post-1-year biopsy was 42 months (interquartile range 19.5-65 months).

RESULTS

Transplant glomerulopathy was present in 25.0% of biopsies and resulted in worse graft survival (66.7% vs. 96.7%, P<0.001). C4d positivity and transplant glomerulopathy together portended exceptionally poor graft survival (33.3% vs. 97.2%, P<0.001). Microcirculation inflammation was prevalent, with glomerulitis and peritubular capillaritis found in 60.0% and 47.6% of 1-year biopsies, respectively. Glomerulitis was associated with worse graft survival (82.1% vs. 98.1%, P=0.004), whereas capillaritis was not (88.1% vs. 97.7% respectively, P=0.091). Among C4d-negative HLA-incompatible recipients (82.6% of biopsies), no difference in graft survival was observed between patients with or without microcirculation inflammation in contrast to previous reports by other investigators. Patients who had no C4d deposition, transplant glomerulopathy, or microcirculation inflammation had a 100.0% graft survival. On Cox regression analysis, no independent histopathological parameter was associated with graft survival.

CONCLUSIONS

We have identified several histopathologic phenotypes in HLA-incompatible kidney recipients that correlate with allograft outcomes. Characterization of these phenotypes is the first step towards better understanding the pathophysiologic basis of chronic antibody-mediated allograft injury and individualizing therapeutic intervention.

Time course of pathologic changes in kidney allografts of positive crossmatch HLA-incompatible transplant recipients

BACKGROUND

Recipients of incompatible allografts are at increased risk of graft loss. We hypothesized that analysis of sequential biopsies from these grafts could define progression of graft lesions and identify features predictive of progression.

METHODS

We studied the time course of histologic injury in 745 kidney graft biopsies from 129 patients transplanted with a positive crossmatch human leukocyte antigen-incompatible kidney between 2000 and 2010 (follow-up of 1-9 years).

RESULTS

Graft survival was 98% at 1 year and 80% at 5 years after transplantation. Throughout follow-up, 70% of patients experienced rejection, with 52% showing subclinical rejection in the first year. Cell-mediated rejection was more frequent than antibody-mediated rejection throughout follow-up. Transplant glomerulopathy (TxGN; cg≥1) developed in 47% of patients over the period of the study, as early as 3 months in a few patients. TxGN was preceded by glomerulitis in more than 90% of cases, with a median time interval of 12 months. Glomerulitis and detectable posttransplantation donor-specific antibodies were risk factors for TxGN (P<0.0001 and P<0.05). C4d-negative antibody-mediated rejection manifesting as capillaritis (g≥1 and ptc≥1) with detectable donor-specific antibodies was observed in some recipients (<20%). There was progressively higher average tubulointerstitial scarring (ci+ct) from 3 to 6 to 12 months (P<0.001).

CONCLUSIONS

Despite good graft survival, a significant incidence of biopsy-proven rejection occurred in this subset of closely monitored human leukocyte antigen-incompatible recipients throughout follow-up. Microcirculation inflammation, particularly glomerulitis, irrespective of C4d, is associated with a high risk of development of TxGN at 1 year.

Participation of functionally active plasma cells in acute rejection and response to therapy in renal allografts

Acute rejection (AR) includes T-cell-mediated and antibody-mediated rejection. The inflammatory infiltrate comprised not only T cells but also varying amounts of B cells (CD20(+)) and plasma cells (CD138(+)). The latter are associated with poor clinical outcomes, but their functional status is not clear. The phosphorylation of the S6 ribosomal protein (p-S6RP) is present in cells that are metabolically active, thus identifying functionally active antibody-secreting plasma cells. This study was designed to evaluate the clinical significance of functionally active p-S6RP plasma cells in AR in renal allografts. Renal allografts with biopsy evidence of AR during 2006-2009 were included. Immunohistochemistry staining for CD20, CD138, and p-S6RP was performed on paraffin-embedded slides and scaled as 0-6. The response to antirejection treatment was assessed by the serum creatinine ratio (CrR) at rejection episode (time 0) and following treatment (4 and 12 weeks). Patients with lower scores (0-2) were compared with a higher scored group (3-6). The T-test was conducted using statistical significance of p<0.05. A total of 28 patients (40.7 ± 14.3 year; M:F=15:13) were diagnosed with acute T-cell-mediated rejection (I and II). The p-S6RP staining in the high-score group had a significantly higher CrR (p<0.05) than the low-score group at the time of biopsy, 4 and 12 weeks following treatment. There was no significant difference in the CrR between groups for CD20 or CD138 staining. Functional antibody-secreting p-S6RP plasma cells are actively participating in AR and associated with poor response to treatment in renal allografts.

Peripheral blood biomarkers for the characterization of alloimmune reactivity after pediatric liver transplantation

Individualization of immunosuppressive medications is an important objective in transplantation medicine. Reliable biomarkers to distinguish between patients dependent from intensive immunosuppressive therapy and those where therapy can be minimized among pediatric transplant recipients receiving immunosuppressive medications are still not established. We evaluated the potential of cross-sectional quantification of regulatory T cells, lymphocyte subsets, and cytokine concentrations as biomarkers in 60 pediatric liver transplant recipients with AR, CR, or normal graft function and in 11 non-transplanted patients. Transplant recipients presenting with AR had significantly higher CD8+ T-cell counts, significantly higher concentrations of IL-2, and increased levels of IFN-γ compared with asymptomatic patients or controls. Regulatory T-cell numbers did not differ between children with rejection and children with good graft function. A tendency toward increased concentrations of IL-4 and TGF-β was detected in transplant recipients with good graft function. Cross-sectional parameters of peripheral regulatory T cells in pediatric liver transplant recipients do not seem to be valuable biomarkers for individualizing immunosuppressive therapy prior to the weaning process. Lymphocyte subsets, IL-2, IFN-γ, IL-4, and TGF-β serum concentrations may be helpful to identify children in whom immunosuppression can be reduced or discontinued.

Molecular markers of rejection and tolerance: lessons from clinical research

In terms of finding specific molecular markers associated with graft outcome, attempts have been made to study whole genome transcripts using microarray assays or to study the effect of number of genes of interest using quantitative real-time polymerase chain reaction. Using these techniques, molecular phenotypes of rejection have been characterized, and the variability of the clinical outcome besides similar morphology explained in part. Recently, several specific transcripts including naïve B cell regulation have been identified in the peripheral blood of operationally tolerant kidney transplant recipients. The decrease in immature B cell-related transcripts in the peripheral blood in patients with immunosuppression was shown to be associated with acute rejection. Similarly, tolerance-associated antigen 1 transcripts were identified in biopsies and regulatory T cell transcripts in urine and biopsies in patients without rejection. Better understanding of molecular processes associated with allograft rejection or alloantigen hyporesponsiveness/tolerance may help to improve our knowledge about graft pathology and identify novel markers suitable for future monitoring and guided therapy and finally improve the outcome of kidney transplantation.

CD20+ B-cell infiltration is related to the time after transplant and poor prognosis of acute cellular rejection in renal transplant

OBJECTIVES

This study sought to determine the relation between CD20+ B-cell infiltration and time after transplant and outcome of acute cellular rejection in renal allografts.

MATERIALS AND METHODS

Fifty-five patients with acute cellular rejection were categorized into 3 groups: very early, early, and late rejection. The density of CD4+, CD8+, CD20+, and CD68+ cells and HLA-DR expression were characterized and quantified using immunohistochemical staining. Histologic changes were compared between high-density and low-density CD20+ B-cell groups. Poor prognosis factors were analyzed with Cox proportional regression.

RESULTS

Density of CD20+ cells in the very-early rejection group was lower than it was in the early- and late-acute rejection groups (P = .03); the density of CD4+, CD8+, and CD68+ cells and HLA-DR expression did not differ between the groups. Mesangial matrix increase, tubular atrophy, arteriolar hyaline thickening, and tubulitis were more prevalent in the high CD20+ density group. Cox regression analysis demonstrated that HLA-DR expression on the tubules, arteriolar hyaline thickening, and CD20+ cell density were associated with an elevated risk of acute cellular rejection.

CONCLUSIONS

Expansion aggregation of CD20+ B cells occurred mostly after 2 weeks. When combined with HLA-DR expression and arteriolar hyaline thickening, these influence the outcome of acute cellular rejection in renal allograft.

Application of systems biology principles to protein biomarker discovery: urinary exosomal proteome in renal transplantation

PURPOSE

In mass spectrometry (MS)-based studies to discover urinary protein biomarkers, an important question is how to analyze the data to find the most promising potential biomarkers to be advanced to large-scale validation studies. Here, we describe a "systems biology-based" approach to address this question.

EXPERIMENTAL DESIGN

We analyzed large-scale liquid chromatography-tandem mass spectrometry (LC-MS/MS) data of urinary exosomes from renal allograft recipients with biopsy-proven evidence of immunological rejection or tubular injury (TI). We asked whether bioinformatic analysis of urinary exosomal proteins can identify biological-process based protein groups that correlate with biopsy findings and whether the protein groups fit with general knowledge of the pathophysiological mechanisms involved.

RESULTS

LC-MS/MS analysis of urinary exosomal proteomes identified more than 1000 proteins in each pathologic group. These protein lists were analyzed computationally to identify the Biological Process and Kyoto Encyclopedia of Genes and Genomes (KEGG) Pathway terms that are significantly associated with each pathological group. Among the most informative terms for each group were: "sodium ion transport" for TI; "immune response" for all rejection; "epithelial cell differentiation" for cell-mediated rejection; and "acute inflammatory response" for antibody-mediated rejection. Based on these terms, candidate biomarkers were identified using a novel strategy to allow a dichotomous classification between different pathologic categories.

CONCLUSIONS AND CLINICAL RELEVANCE

The terms and candidate biomarkers identified make rational connections to pathophysiological mechanisms, suggesting that the described bioinformatic approach will be useful in advancing large-scale biomarker identification studies toward a validation phase.

Plasma cell densities and glomerular filtration rates predict renal allograft outcomes following acute rejection

The contribution of T cells and graft-reactive antibodies to acute allograft rejection is widely accepted, but the role of graft-infiltrating B and plasma cells is controversial. We examined 56 consecutive human renal transplant biopsies classified by Banff schema into T-cell-mediated (N = 21), antibody-mediated (N = 18), and mixed (N = 17) acute rejection, using standard immunohistochemistry for CD3, CD20, CD138, and CD45. In a predominantly African-American population (75%), neither Banff classification nor C4d deposition predicted the return to dialysis. Immunohistochemical analysis revealed CD3(+) T cells as the dominant cell type, followed by CD20(+) B cells and CD138(+) plasma cells in all acute rejection types. Using univariate Cox Proportional Hazard analysis, plasma cell density significantly predicted graft failure while B-cell density trended toward significance. Surprisingly T-cell density did not predict graft failure. The estimated glomerular filtration rate (eGFR) at diagnosis of acute rejection also predicted graft failure, while baseline eGFR ≥6 months prior to biopsy did not. Using multivariate analysis, a model including eGFR at biopsy and plasma cell density was most predictive of graft loss. These observations suggest that plasma cells may be a critical mediator and/or an independently sensitive marker of steroid-resistant acute rejection.

CD20 Expression in the Transplanted Kidney of Patients with Graft Loss and Transient Allograft Dysfunction

This study aimed to explore the relationship between the infiltration of CD20+ B cells and the survival time of a renal allograft and to investigate the role of infiltrated B cells in the rejection of the renal allograft. A total of 40 patients with renal allograft loss due to refractory rejection and 20 patients with transient renal allograft dysfunction were recruited. Renal biopsy was done and CD20 expression was detected by immunohistochemistry. In addition, the survival time of the renal allograft was also obtained. The relationships between the CD20 expression and the survival time of the renal allograft and graft loss due to rejection were analyzed. The associations of gender, age and clinicopathogical types with the CD20 expression were also investigated. The proportion of patients positive for CD20 in the transplanted kidney was higher in patients receiving nephrectomy of the allograft due to rejection than in those with transient allograft dysfunction. The diffuse infiltration of CD20+ B cells was considered as positive staining. In 40 samples from patients with graft loss, 19 had diffuse infiltration of CD20+ B cells (47.5%). In 19 patients positive for CD20, hyperacute rejection was found in 1 patient, acute rejection in 5 and chronic rejection in 13. Statistical analysis showed the CD20 expression was not associated with the age and gender of donors and recipients, regimen for immunosuppressive treatment, cold/warm ischemia time and secondary transplantation. CD20+ B cell infiltration predicts a poor prognosis of patients with kidney transplantation and is one of the risk factors of graft loss.

Gene expression profiling in acute allograft rejection: challenging the immunologic constant of rejection hypothesis

In humans, the role and relationship between molecular pathways that lead to tissue destruction during acute allograft rejection are not fully understood. Based on studies conducted in humans, we recently hypothesized that different immune-mediated tissue destruction processes (i.e. cancer, infection, autoimmunity) share common convergent final mechanisms. We called this phenomenon the "Immunologic Constant of Rejection (ICR)." The elements of the ICR include molecular pathways that are consistently described through different immune-mediated tissue destruction processes and demonstrate the activation of interferon-stimulated genes (ISGs), the recruitment of cytotoxic immune cells (primarily through CXCR3/CCR5 ligand pathways), and the activation of immune effector function genes (IEF genes; granzymes A/B, perforin, etc.). Here, we challenge the ICR hypothesis by using a meta-analytical approach and systematically reviewing microarray studies evaluating gene expression on tissue biopsies during acute allograft rejection. We found the pillars of the ICR consistently present among the studies reviewed, despite implicit heterogeneity. Additionally, we provide a descriptive mechanistic overview of acute allograft rejection by describing those molecular pathways most frequently encountered and thereby thought to be most significant. The biological role of the following molecular pathways is described: IFN-γ, CXCR3/CCR5 ligand, IEF genes, TNF-α, IL-10, IRF-1/STAT-1, and complement pathways. The role of NK cell, B cell and T-regulatory cell signatures are also addressed.

Significance of intragraft CD138+ lymphocytes and p-S6RP in pediatric kidney transplant biopsies

BACKGROUND

We have previously shown that intragraft CD20+ B cells are associated with acute cellular rejection (ACR) and allograft loss. Phosphorylation of S6 ribosomal protein, a downstream target of the PI3K/Akt/mTOR pathway, promotes growth and proliferation of cells and could identify metabolically active cells such as alloantibody secreting plasma cells. Because CD20+ lymphocytes can differentiate into CD138+ plasma cells, we aimed to identify functionally active plasma cells by using intragraft CD138 quantification and p-S6RP staining and correlate these results with allograft rejection, function, and survival.

METHODS

We examined 46 renal transplant biopsies from 32 pediatric patients who were biopsied for clinical suspicion of rejection. Immunohistochemical staining for C4d, CD20, CD138, and p-S6RP was performed. Patient creatinine clearance and graft status was followed up postbiopsy.

RESULTS

Patients with greater than or equal to six CD138+ cells/high power field (hpf) had worse graft survival with a hazard ratio of 3.4 (95% CI 1.3-9.2) 2 years postbiopsy compared with those with 0 to 5 cells/hpf (P=0.016). CD138+ cells were stained for p-S6RP, indicating functionally active plasma cells. They were associated with ACR (P=0.004) and deteriorating graft function (R=0.22, P=0.001). Intragraft CD20+ and CD138+ cells found together in ACR were associated with poorer graft survival than either marker alone, hazard ratio 1.5 (95% CI 1.1-2.2, P=0.01).

CONCLUSIONS

A threshold of greater than or equal to six CD138+ metabolically active plasma cells per hpf, coexisting with CD20+ B cells, was associated with poor allograft function and survival. This may represent an additional antibody-mediated process present in the setting of ACR and could play an important role in characterization and treatment of transplant rejection.

Clinical impacts of CD38+ B cells on acute cellular rejection with CD20+ B cells in renal allograft

BACKGROUND

There is an increasing evidence that the presence of CD20 B cells is associated with poor clinical outcomes in acute cellular rejection (ACR), but clinical significance of CD38 B cells is undetermined. We attempted to examine the clinical significance of the CD38 B cells alone or in combination with CD20 B cells in renal transplant recipients with ACR.

METHODS

Fifty-four patients with ACR were included. Biopsy specimens were stained for CD20 and CD38. The clinical outcomes of CD20 or CD38 B cells were evaluated with late-onset and repeated ACR, steroid resistance, incomplete recovery after rejection treatment, and allograft survival.

RESULTS

Twenty-three patients (42.6%) had CD20 and 25 (46.3%) patients had CD38 B cells. Of these, 15 patients (27.8%) were positive for both CD20 and CD38 (CD20CD38). CD38 patients had higher rates of late-onset or repeated ACR and incomplete recovery compared with CD38 patients (P<0.05). The patients with CD20CD38 had a higher incomplete recovery rate than did patients with only CD20 or CD38 (P<0.05). The 5-year allograft survival was lower in CD20 and CD38 patients than in CD20 or CD38 patients (P<0.05 for each). CD20CD38 patients had lower graft survival than did patients with CD20 or CD38 alone (P<0.05).

CONCLUSION

Infiltration of CD38 B cells alone or in combination with CD20 B cells is a predictor for poor clinical outcomes of ACR in renal allograft.

B cells and plasma cells in coronaries of chronically rejected cardiac transplants

BACKGROUND.: Previously, we reported that transcripts of immunoglobulins were increased in coronary arteries dissected from cardiac transplants with arteriopathy, but the prevelance and patterns of B cell and plasma cell infiltration in cardiac allografts has not been documented. METHODS.: In this study, we documented the frequency and distribution of B cells and plasma cells in 16 cardiac transplants with advanced chronic rejection that were explanted during a second transplant procedure. Coronary arteries with pathologically confirmed allograft vasculopathy and controls with native atherosclerosis were immunohistologically stained for markers of T cells, B cells, plasma cells, IgG subclasses, C4d, CD21, and CXCL13. RESULTS.: We found that B cells and plasma cells were prevalent in most of the samples analyzed (14 of 16) and were distributed in three patterns: adventitial nodules, diffuse adventitial infiltrates, and neointimal infiltrates. These cells were found most frequently in nodules, some of which had distinct compartmentalization and granular C4d deposits on follicular dendritic cells (FDCs) that typify tertiary lymphoid nodules. FDCs also stained for CD21 and CXCL13. Diffuse infiltrates of B cells and plasma cells were found in fibrotic areas of the neointima and adventitia. Only a minority of control coronaries with atherosclerosis contained B cells. CONCLUSIONS.: B cells and plasma cell infiltrates are consistent findings in and around coronary arteries with allograft vasculopathy and are significantly more frequent than in coronaries with native atherosclerosis. The presence of C4d on FDCs in tertiary lymphoid nodules suggests active antigen presentation.

B cells limit repair after ischemic acute kidney injury

There is no established modality to repair kidney damage resulting from ischemia-reperfusion injury (IRI). Early responses to IRI involve lymphocytes, but the role of B cells in tissue repair after IRI is unknown. Here, we examined B cell trafficking into postischemic mouse kidneys and compared the repair response between control (wild-type) and muMT (B cell-deficient) mice with and without adoptive transfer of B cells. B cells infiltrated postischemic kidneys and subsequently activated and differentiated to plasma cells during the repair phase. Plasma cells expressing CD126 increased and B-1 B cells trafficked into postischemic kidneys with distinct kinetics. An increase in B lymphocyte chemoattractant in the kidney preceded B cell trafficking. Postischemic kidneys of muMT mice expressed higher IL-10 and vascular endothelial growth factor and exhibited more tubular proliferation and less tubular atrophy. Adoptive transfer of B cells into muMT mice reduced tubular proliferation and increased tubular atrophy. Treatment with anti-CD126 antibody increased tubular proliferation and reduced tubular atrophy in the late repair phase. These results demonstrate that B cells may limit the repair process after kidney IRI. Targeting B cells could have therapeutic potential to improve repair after IRI.

Molecular phenotypes of acute rejection predict kidney graft prognosis

Earlier detection of antibody-mediated rejection of kidney allografts may improve graft outcomes. Profiling of gene expression holds promise for the diagnosis and prognosis of antibody-mediated rejection. Here, we identified 730 patients who received kidney transplants during 2002-2005, including 21 patients (2.9%) who experienced early acute antibody-mediated rejection. We also identified a matched group of 43 patients with early acute T cell-mediated rejection to serve as controls. Compared with patients with T cell-mediated rejection, those with antibody-mediated rejection had significantly higher intrarenal mRNA expression of the cytoprotective heme oxygenase-1 but had lower expression of the regulatory T cell marker forkhead box P3 (FoxP3), the B cell marker CD20, and the chemokine regulated upon activation, normal T cell expressed and secreted (RANTES). T cell infiltration was similar in both groups of patients. Compared with grafts that had a favorable course, those that failed as a result of antibody-mediated rejection had expression profiles suggesting a lack of regulation (less FoxP3, TGF-beta1, RANTES, and CD20). Grafts that failed as a result of T cell-mediated rejection only revealed lower expression of CD20 mRNA. In summary, these data suggest that severe antibody-mediated rejection and T cell-mediated rejection result in graft loss by distinct mechanisms. Molecular phenotypes of early acute rejection might help to identify grafts with poor prognosis, allowing earlier application of additional therapies.

Urinary CD20 mRNA as a surrogate of CD20-positive cells infiltration during allograft dysfunction in renal transplant patients

B lymphocyte infiltration in renal acute allograft rejection has been associated with steroid resistance and poor outcomes. We aimed to measure CD20 mRNA in urine of renal transplant patients with graft dysfunction and correlate with the histological diagnosis and immunohistochemical (IH) staining for CD20. A total of 48 urine samples were analyzed (21 with acute rejection, 10 with chronic allograft nephropathy, 11 with unspecific tubular lesions, 3 with acute pyelonephritis and 3 with polyomavirus nephropathy). Higher urinary CD20 levels associated with a positive IH staining for CD20 (>50 positive cells/HPF) in renal tissue (p=0.04), with a sensitivity of 83.3% and a specificity of 51.6%. Within the acute rejection group, a positive staining for CD20 was not associated with graft loss, steroid resistance or lack of return to basal creatinine after treatment, but was associated with higher serum creatinine at 3 and 6 months, 1 and 2 years after the acute episode (p<0.05). In conclusion, we showed that urinary levels of CD20 detected by RT-PCR had a high sensitivity for CD20+ staining in the corresponding renal tissue, but with a low specificity. Patients with clusters of CD20+ cells >50/HPF had higher serum creatinine after 2 years of follow up.

Differential effects of donor-specific alloantibody

Alloantigen exposure typically provokes an adaptive immune response that can foster rejection of transplanted organs, and these responses present the most formidable biological barrier to kidney transplantation. Although most cellular alloimmune responses can be therapeutically controlled with T-cell-specific immunosuppressants, humoral alloimmune responses remain relatively untamed. Importantly, humoral immunity, typically manifesting as allospecific antibody production, is increasingly recognized for its variable appearance after kidney transplantation. Indeed, the appearance of alloantibody can herald the onset of rapid and destructive antibody-mediated rejection or have no demonstrable acute effects. The factors determining the end result of alloantibody formation remain poorly understood. This review will discuss the breadth of alloantibody responses seen in clinical kidney transplantation and provide an overview of potential factors explaining the phenotypic variability associated with humoral alloimmunity. We propose several avenues ripe for future investigation including the influence of innate immune components and the potential influence of heterologous immune responses in determining the ultimate clinical import of an alloantibody response.

"To B or not to B?" B-cells and graft rejection

There is increasing evidence that various maturational stages of B-cells infiltrate various solid organ transplants undergoing acute rejection. The presence of immature CD20 and mature CD138 plasma cells associate with more aggressive and steroid-recalcitrant graft rejection and portend poor graft outcomes. Though associative, the causal role of B-cells in graft rejection remains to be better understood. This review discusses the possible roles of B-cells in graft rejection, whether involved as antigen presenting, as indirect effector, or antibody producing cells.