Ibrahim Batal

Deleterious Effect of CTLA4-Ig on a Treg-Dependent Transplant Model

Blockade of the B7:CD28 costimulatory pathway has emerged as a promising therapy to prevent allograft rejection. However, results from the belatacept phase III clinical trial demonstrated a higher rejection rate when compared to cyclosporine, raising concern about potential deleterious effects of this agent. In this study, we investigated the consequences of B7:CD28 blockade by hCTLA4Ig on regulator T cell (Treg) generation in different major histocompatibility complex (MHC) mismatch transplant models. Administration of hCTLA4Ig significantly decreased the amount of Tregs in B6 WT animals and this effect was predominant in thymus‐induced Tregs (Helios+). Although hCTLA4Ig prevented rejection in a fully allogeneic mismatch model, it accelerated rejection in a MHC class‐II mismatch model (MST = 26, p < 0.0001), in which long‐term allograft survival is dependent on Tregs. This accelerated rejection was associated with a marked reduction in thymus‐induced Tregs and led to a higher effector/regulatory T‐cell ratio in secondary lymphoid organs and in the allograft. This study confirms the importance of the B7:CD28 pathway in Treg homeostasis in an in vivo transplant model and suggests that hCTLA4Ig therapy may be deleterious in circumstances where engraftment is dependent on Tregs.

Renal biopsy findings predicting outcome in scleroderma renal crisis

Scleroderma renal crisis is irreversible in some patients despite aggressive treatment. This study was designed to identify pathologic prognostic features in scleroderma renal crisis. We retrospectively reviewed the pathology and the clinical records of 17 patients who underwent kidney biopsies during scleroderma renal crisis (group A, recovered renal function [n = 7]; group B, remained in renal failure or died [n = 10]). Multiple histologic features were assessed semiquantitatively (0-3) or as percentages. C4d staining of peritubular capillaries and small vessels was assessed semiquantitatively (0-3) in patients with scleroderma (n = 11), normotensive (n = 10), and hypertensive (n = 12) nonscleroderma native kidney controls. The percentage of thrombosed vessels (25.1 +/- 21.0 versus 5.6 +/- 12.3, P = .045) and the severity of glomerular ischemic collapse (2.9 +/- 0.3 versus 1.4 +/- 0.8, P = .001) were significantly higher in group B than in group A. Also, group B patients tended to have more severe acute tubular injury and vascular fibrinoid changes. The peritubular capillary C4d score in patients with scleroderma, normotensive controls, and hypertensive controls were 1.1 +/- 0.9, 0.3 +/- 0.7, and 0.3 +/- 0.5, respectively (P = .018, scleroderma versus other controls). Small vessel C4d score was higher in scleroderma compared to normotensive but not hypertensive controls. Within scleroderma samples, a significantly higher peritubular capillary C4d score (1.6 +/- 0.7 versus 0.3 +/- 0.5, P = .024) but not small vessel score was found in group B compared to group A. This tended to be associated with peritubular capillary leukocyte margination. Vascular thrombosis, severe glomerular ischemic collapse, and peritubular capillary C4d deposits in scleroderma renal crisis kidney biopsies correlated with increased risk of failure to recover renal function.

TIM-3 Regulates Innate Immune Cells To Induce Fetomaternal Tolerance

TIM-3 is constitutively expressed on subsets of macrophages and dendritic cells. Its expression on other cells of the innate immune system and its role in fetomaternal tolerance has not yet been explored. In this study, we investigate the role of TIM-3–expressing innate immune cells in the regulation of tolerance at the fetomaternal interface (FMI) using an allogeneic mouse model of pregnancy. Blockade of TIM-3 results in accumulation of inflammatory granulocytes and macrophages at the uteroplacental interface and upregulation of proinflammatory cytokines. Furthermore, TIM-3 blockade inhibits the phagocytic potential of uterine macrophages resulting in a build up of apoptotic bodies at the uteroplacental interface that elicits a local immune response. In response to inflammatory cytokines, Ly-6ChiGneg monocytic myeloid–derived suppressor cells expressing inducible NO synthase and arginase 1 are induced. However, these suppressive cells fail to downregulate the inflammatory cascade induced by inflammatory granulocytes (Ly-6CintGhi) and apoptotic cells; the increased production of IFN-γ and TNF-α by inflammatory granulocytes leads to abrogation of tolerance at the FMI and fetal rejection. These data highlight the interplay between cells of the innate immune system at the FMI and their influence on successful pregnancy in mice.

A Critical Appraisal of Methods to Grade Transplant Glomerulitis in Renal Allograft Biopsies

Transplant glomerulitis is an increasingly recognized lesion in renal transplant biopsies. To develop a refined grading system, we defined glomerulitis by the presence of ≥5 leukocytes/glomerulus and evaluated 111 biopsies using three different grading systems: (i) percentage of glomerular involvement, (ii) peak inflammation in the most severely affected glomerulus and (iii) presence/absence of endocapillary occlusion by inflammatory cells. Endocapillary occlusion had no impact on graft survival, but was associated with increased serum creatinine, proteinuria and subsequent transplant glomerulopathy. Grading based on either percent or peak glomerular involvement correlated with graft failure and peritubular capillaritis. However, the percent glomerular involvement method had the additional advantage of displaying associations with: concurrent proteinuria, focal or diffuse immunoperoxidase peritubular capillary C4d staining, 1‐year postbiopsy serum creatinine, subsequent detection of donor‐specific antibody and development of transplant glomerulopathy. Patients with >75% glomerular involvement also revealed persistent high‐grade glomerulitis on follow‐up biopsies despite antirejection treatment. In conclusion, grading of glomerulitis is a meaningful exercise, and a quantification system based on percentage of glomerular involvement shows the most robust associations with clinical parameters and prognosis.

Scleroderma renal crisis: a pathology perspective.

Scleroderma renal crisis (SRC) is an infrequent but serious complication of systemic sclerosis (SSc). It is associated with increased vascular permeability, activation of coagulation cascade, and renin secretion, which may lead to the acute renal failure typically associated with accelerated hypertension. The histologic picture of SRC is that of a thrombotic microangiopathy process with prominent small vessel involvement manifesting as myxoid intimal changes, thrombi, onion skin lesions, and/or fibrointimal sclerosis. Renal biopsies play an important role in confirming the clinical diagnosis, excluding overlapping/superimposed diseases that might lead to acute renal failure in SSc patients, helping to predict the clinical outcome and optimizing patient management. Kidney transplantation may be the only treatment option available for a subset of SRC patients who develop end-stage renal failure despite aggressive angiotensin-converting enzyme inhibitor therapy. However, the posttransplant outcome for SSc patients is currently suboptimal compared to the general renal transplant population.

Measurements of global cell-mediated immunity in renal transplant recipients with BK virus reactivation

The Cylex ImmuKnow Test (Cylex, Columbia, MD) measures immune cell function (ICF) and is based on the amount of adenosine triphosphate (ATP) released when T cells are stimulated by phytohemagglutinin. This preliminary study sought to determine if ICF measurements can be used to stratify kidney transplant recipients according to the risk for developing BK virus infection. ICF measurements were done in 15 samples from 8 patients with BK viremia, 38 samples from 25 patients with BK viruria, and 243 samples from 148 patients with no BK viruria or viremia. The mean+/-SD amounts of ATP released in these 3 groups were 102.9+/-58.6, 227.2+/-146.4, and 231.8+/-150.8 ng/mL, respectively (P= .002, viremia vs all other samples). Within the viruria group, lower ICF values were associated with higher urinary viral load (P= .037). These results show that a decreased ICF test result correlates with active viral replication in kidney transplant recipients.

Clinical significance of the distribution of C4d deposits in different anatomic compartments of the allograft kidney

Diffuse C4d deposition in peritubular capillaries is a well-recognized marker of antibody-mediated rejection. The significance of staining patterns that are focal or affect non-peritubular capillary compartments is less well defined. Paired frozen section and paraffin-embedded tissue stains were performed in 52 kidney allograft biopsies, and correlated with clinicopathologic parameters. Diffuse peritubular capillary C4d deposits were more often seen in frozen sections (22/52, 43% frozen tissue vs 10/52, 19% paraffin-embedded tissue), whereas focal staining was observed more frequently within paraffin sections (13/52, 25% paraffin-embedded tissue vs 7/52, 14% frozen tissue). In biopsies taken from patients with a history of donor-specific antibodies, diffuse, focal and negative peritubular capillary C4d staining patterns were seen in 11/14 (79%), 1/14 (7%) and 2/14 (14%) of frozen biopsies vs 5/14 (36%), 6/14 (43%) and 3/14 (21%) of paraffin-embedded biopsies. Transplant glomerulopathy score in paraffin-embedded biopsies was higher in specimens with vs without glomerular basement membrane C4d staining (1.5±0.8 vs 1.0±0.6, P=0.03). Tubular basement membrane staining was present in 4% paraffin-embedded and 48% frozen specimens independent of tubular atrophy. Arteriolar hyalinosis score in paraffin-embedded specimens was higher in biopsies with vs those without arteriolar C4d deposits (1.3±0.9 vs 0.9±0.8, P=0.04). Arterial staining was unrelated to the degree of intimal thickening. In conclusion, peritubular capillary deposits correlate well with circulating donor-specific antibody. For paraffin-embedded tissue, combining the results of focal and diffuse staining allows a diagnostic sensitivity comparable to diffuse staining in frozen tissue. Finally, C4d deposits preferentially in lesions of chronic transplant glomerulopathy and arteriolar hyalinosis.

Antihuman Leukocyte Antigen-Specific Antibody Strength Determined by Complement-Dependent or Solid-Phase Assays Can Predict Positive Donor-Specific Crossmatches

CONTEXT The association of circulating donor-specific antibody (DSA) strength with crossmatch results is of potential interest to predict allograft outcome. OBJECTIVES To systematically investigate the aforementioned association and to attempt to define a cutoff value for DSA strength that can predict a positive crossmatch result. DESIGN We analyzed DSA strength and crossmatch results from the 2006 to 2008 proficiency testing samples of the American Society of Histocompatibility and Immunogenetics (n  =  50). We further validated our findings in candidates for potential kidney transplant (n  =  19). RESULTS Proficiency test samples with positive antihuman globulin T-cell crossmatch results had significantly higher DSA strength, as assessed by Luminex (Austin, Texas) mean fluorescent intensity (MFI; MFI [SD], 7860 [4770]), compared with samples with negative crossmatch results (MFI [SD], 2900 [1820]; P  =  .001). Similarly, higher Luminex values were observed in samples from candidates for transplant with positive antihuman globulin T-cell crossmatch results (MFI [SD], 7910 [2370] versus 2840 [1960]; P < .001). The MFI value of 6540 had 61% and 75% sensitivity and 92% and 94% specificity for predicting positive antihuman globulin T-cell crossmatches in proficiency test samples and in candidates for transplant, respectively. CONCLUSIONS The DSA strength correlates well with crossmatch results. An MFI of 6540 predicted a positive antihuman globulin T-cell crossmatch.

Blockade of Notch Ligand Delta1 Promotes Allograft Survival by Inhibiting Alloreactive Th1 Cells and Cytotoxic T Cell Generation

The Notch signaling pathway has been recently shown to contribute to T cell differentiation in vitro. However, the in vivo function of Notch signaling in transplantation remains unknown. In this study, we investigated the importance of Delta1 in regulating the alloimmune response in vivo. Delta1 expression was upregulated on dendritic cells and monocytes/macrophages upon transplantation in a BALB/c into B6 vascularized cardiac transplant model. Whereas administration of anti-Delta1 mAb only slightly delayed survival of cardiac allografts in this fully MHC-mismatched model, it significantly prolonged graft survival in combination with single-dose CTLA4-Ig or in CD28 knockout recipients. The prolongation of allograft survival was associated with Th2 polarization and a decrease in Th1 and granzyme B-producing cytotoxic T cells. The survival benefit of Delta1 blockade was abrogated after IL-4 neutralization and in STAT6KO recipients, but was maintained in STAT4KO recipients, reinforcing the key role of Th2 cell development in its graft-prolonging effects. To our knowledge, these data demonstrate for the first time an important role of Delta1 in alloimmunity, identifying Delta1 ligand as a potential novel target for immunomodulation in transplantation.

Eculizumab for drug-induced de novo posttransplantation thrombotic microangiopathy: A case report.

De novo thrombotic microangiopathy (TMA) following renal transplantation is a severe complication associated with high rates of allograft failure. Several immunosuppressive agents are associated with TMA. Conventional approaches to managing this entity, such as withdrawal of the offending agent and/or plasmapheresis, often offer limited help, with high rates of treatment failure and graft loss. We herein report a case of drug induced de novo TMA successfully treated using the C5a inhibitor eculizumab in a renal transplant patient. This report highlights a potentially important role for eculizumab in settings where drug-induced de novo TMA is refractory to conventional therapies.