Paramit Chowdhury

Nontransgenic Hyperexpression of a Complement Regulator in Donor Kidney Modulates Transplant Ischemia/Reperfusion Damage, Acute Rejection, and Chronic Nephropathy

Complement activation during ischemia and reperfusion contributes to the development of tissue injury with severe negative impact on outcomes in transplantation. To counter the effect of complement, we present a strategy to deliver a novel complement regulator stabilized on cell surfaces within donor organs. The membrane-bound complement regulator is able to inhibit complement activation when the donor organ is revascularized and exposed to host-circulating complement. Application of this construct to donor kidneys protected transplanted tissues from ischemia/reperfusion injury and reduced the deposition of activated complement and histological signs of damage under conditions in which a nontargeted control construct was ineffective. Treatment of donor organs in this way improved graft performance in the short and long term. An analysis of the immune response in allograft recipients showed that reducing graft damage at the time of transplantation through complement regulation also modulated the alloresponse. Additionally, the results of perfusion studies with human kidneys demonstrated the feasibility of targeting endothelial and epithelial surfaces with this construct, to allow investigation in clinical transplantation.

Pivotal role of CD4+ T cells in renal fibrosis following ureteric obstruction

Tubulointerstitial fibrosis is a common consequence of a diverse range of kidney diseases that lead to end-stage renal failure. The degree of fibrosis is related to leukocyte infiltration. Here, we determined the role of different T cell populations on renal fibrosis in the well-characterized mouse model of unilateral ureteric obstruction. Depletion of CD4(+) T cells in wild-type mice with a monoclonal antibody significantly reduced the amount of interstitial expansion and collagen deposition after 2 weeks of obstruction. Reconstitution of lymphopenic RAG knockout mice with purified CD4(+) but not CD8(+) T cells, prior to ureteric obstruction, resulted in a significant increase in interstitial expansion and collagen deposition. Wild-type mice had significantly greater interstitial expansion and collagen deposition compared with lymphopenic RAG(-/-) mice, following ureteric obstruction; however, macrophage infiltration was equivalent in all groups. Thus, our results suggest that renal injury with subsequent fibrosis is likely to be a multifactorial process, with different arms of the immune system involved at different stages. In this ureteric obstruction model, we found a critical role for CD4(+) T cells in kidney fibrosis. These cells could be a potential target of therapeutic intervention to prevent excessive fibrosis and loss of function due to renal injury.

Role of the complement system in rejection.

The complement system plays a complex role in transplantation, beginning with effects on reperfusion injury and continuing with stimulation of the adaptive immune response. Recent evidence has emphasised the importance of the late components of the complement cascade in the mediation of post-ischaemic damage, which are apparently triggered by the classical, alternative or lectin pathways of complement activation, depending on the organ affected. In studies of renal allograft rejection, the local synthesis of complement component C3 seems to influence the T-cell response more strongly than circulating complement protein, raising the possibility that there is co-operation between locally derived C3 and antigen presentation in the graft. Class switching of alloantibody to a high-affinity IgG response is also highly dependent on C3. In addition, the finding that capillary-bound C4d is a robust marker for humoral rejection has started a new investigation into the significance of alloantibodies in acute and chronic allograft rejection. There are several selective and nonselective inhibitors suitable for clinical development; clearly it is time for more concerted effort to evaluate their role in clinical transplantation.

The use of eculizumab in renal transplantation

The complement system plays a vital role in mediating disease processes within renal allografts. Eculizumab is a humanized monoclonal antibody that targets complement protein C5, inhibiting cleavage into C5a and C5b, and therefore preventing formation of the membrane attack complex (MAC). It has been used primarily within renal transplantation to treat atypical hemolytic‐uremic syndrome (aHUS) and antibody‐mediated rejection (AMR) post‐transplant, and also as prophylaxis in transplants at high risk for these conditions. Eculizumab appears to be effective in protecting renal allografts when post‐transplant aHUS or AMR occur, although the published cases report relatively short follow‐up. It is unclear how long treatment should continue (a particularly important issue given the expense of the drug), or whether eculizumab contributes to the development of accommodation in humans. When used for prophylaxis, eculizumab also appears to be effective. Some highly sensitized patients have developed either acute AMR or features of chronic AMR despite administration of the drug – this suggests that complement activation is not the only mechanism responsible for AMR. All patients should receive vaccination against Neisseria meningitidis prior to receiving eculizumab. Clinical trials, predominantly in antibody‐incompatible renal transplantation, are ongoing to determine the optimal use of C5 inhibition.

Efficacy and toxicity of sunitinib in patients with metastatic renal cell carcinoma with severe renal impairment or on haemodialysis.

Study Type – Therapy (case series)

Endogenous ligands for TLR2 and TLR4 are not involved in renal injury following ureteric obstruction.

Background: Toll-like receptors (TLRs) are a recently described arm of innate immunity. As well as responding to conserved molecular patterns found on pathogens, TLRs can also respond to endogenous ligands. Those described for TLR2 and TLR4 include molecules released following tissue injury including heat shock proteins and matrix proteins. We hypothesised that following injury, TLRs on renal tubular cells are activated by these endogenous ligands, resulting in cytokine production and cellular infiltration which propagate the fibrotic process. Methods: We performed unilateral ureteric obstruction (UUO) in wild-type C57BL/6, TLR2 knockout and TLR4 knockout mice. Gene expression of TGF-β and TNF-α within renal tissue was analysed by real-time PCR. Kidneys were also scored for the level of tubulointerstitial fibrosis, collagen type IV deposition and macrophage infiltration. Results: No significant difference was found in the degree of tubulointerstitial fibrosis, collagen type IV deposition or macrophage infiltration 14 days after UUO between the 3 groups. Renal TNF-α and TGF-β gene expression was also similar in all groups 3 days after UUO. Conclusions: TLR2 and TLR4 do not play a significant role in the development of tubulointerstitial fibrosis following obstruction.

Complement in renal transplantation

Previous research and therapy in renal transplantation largely focused on the cellular arm of the adaptive immune response. Evidence is emerging that innate immune mechanisms, particularly complement, play a greater role in inflammatory and immune responses against the graft than has been previously recognized. Alternative complement pathway activation appears to mediate renal ischaemia/reperfusion injury, and proximal tubular cells may be both the source and the site of attack of complement components in this setting. Locally produced complement also plays a role in the development of both cellular and antibody-mediated immune responses against the graft. C4d staining has emerged as a useful marker of humoral rejection both in the acute and in the chronic setting and led to renewed interest in the significance of anti-donor antibody formation. A number of therapies are in development which inhibit complement or reduce local synthesis, and may lead to an improved clinical outcome following renal transplantation.

Pregnancy in pancreas–kidney transplant recipients: report of three cases and review of the literature

Seventy-three pregnancies in 43 women with SPK have now been described by the US National Transplantation Pregnancy Registry (NTPR) (established in 1991), which contains self-reported data from questionnaires and hospital records. These women have high rates of complications despite normoglycaemia and restoration of renal function. We describe the pregnancies of three SPK recipients in the UK managed in joint renal obstetric clinics and discuss the antenatal and postnatal complications specific to SPK transplants.

Systematic assessment of the influence of complement gene polymorphisms on kidney transplant outcome

The importance of the innate immune system, including complement, in causing transplant injury and augmenting adaptive immune responses is increasingly recognized. Therefore variability in graft outcome may in part be due to genetic polymorphism in genes encoding proteins of the immune system. This study assessed the relationship between single nucleotide polymorphisms (SNPs) in complement genes and outcome after transplantation. Analysis was performed on two patient cohorts of 650 and 520 transplant recipients. 505 tagged SNPs in 47 genes were typed in both donor and recipient. The relationships between SNPs and graft survival, serum creatinine, delayed graft function and acute rejection were analyzed. One recipient SNP in the gene encoding mannose binding lectin was associated with graft outcome after correction for analysis of multiple SNPs (p=6.41 × 10(-5)). When further correction was applied to account for analysis of the effect of SNPs in both donor and recipient this lost significance. Despite association p values of <0.001 no SNP was significantly associated with clinical phenotypes after Bonferroni correction. In conclusion, the variability seen in transplant outcome in this patient cohort cannot be explained by variation in complement genes. If causal genetic effects exist in these genes, they are too small to be detected by this study.