Advances in Immunosuppression for Renal Transplantation Antoine Durrbach, Helene Francois, Severine Beaudreuil, Antoine Jacquet and Bernard Charpentier

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Advances in immunosuppression for renal transplantation Antoine Durrbach, Helene Francois, Severine Beaudreuil, Antoine Jacquet and Bernard Charpentier

Abstract | The development of immunosuppressants with minimal adverse and nephrotoxic effects is important to improve outcomes, such as acute and chronic antibody-mediated rejection, after organ transplantation. In addition, the application of expanded criteria for donors and transplantation in immunized patients necessitates the development of new therapies. Drug development over the past 10 years has generally been disappointing, but several new promising compounds have been or are being developed to prevent acute and chronic transplant rejection. In this Review, we report on several compounds that have been developed to remove allogenic T cells and/or to inhibit T-cell activation. We also discuss compounds that interfere with antibody-mediated rejection.

Durrbach, A. et al. Nat. Rev. Nephrol. 6, 160–167 (2010); published online 2 February 2010; doi:10.1038/nrneph.2009.233

Introduction Renal transplantation has specific features that make or as a result of previous transplantation, has increased it different from transplantation procedures for other over the past decade. In addition, ABOincompatible organs. For example, outcomes can be affected by grafts are becoming more frequently used. Together, these common states, such as donor and/or recipient age, high factors have led to a rise in the number of ‘immuno logically blood pressure, diabetes mellitus, metabolic disturbances atrisk’ kidney transplantations. Few immunosuppressants (such as high LDL cholesterol) and abnormalities in fluid targeted to B cells have, however, been available to control and electrolyte balance. The kidney is also very sensitive the antibodymediated response. to injury by ischemia and reperfusion and by the use of New immunosuppressants are needed. These should nephrotoxic drugs. ideally be free from any nephrotoxic effects, be strong In the 1970s, immunosuppressants were not nephro enough to act on Tcell and Bcell pathways, interfere toxic (for example, azathioprine, steroids, anti lymphocyte with the immunological components of chronic graft globulins). The 1980s saw the introduction of a new nephropathy, and prevent or treat antibodymediated generation of cyclic molecules that had anticalcineurin rejection. Many molecules have been newly selected for activity (for example, ciclosporin and macrolide anti drug development on the basis of their ability to affect biotics with strong inhibitory properties against Tcell activated Tcell pathways, but over the past 10 years, most activation, such as tacro limus). These drugs, which were of these have failed in clinical development. Agents that included in additive, multidrug, immuno suppressive can address the changing challenges of organ transplanta regimens, reduced acute allograft rejection rates and tion will, however, almost certainly become available. In markedly increased overall graft survival. Use of these this Review, we discuss the different drugs that have been drugs, however, notably increases the risk of chronic dys developed to remove allogenic T cells and other new com function, with immunological (chronic allograft rejec pounds that inhibit Tcell activation. We also report on tion) and nonimmuno logical (nephrotoxic effects from results obtained for agents that interfere with antibody calcineurin inhibitors) compo nents, which can lead to mediated rejection. The different agents are summarized irreversible graft failure and a return to dialysis. in Table 1 and the pathways are described in Figure 1. Nephrology and Transplantation Other phenomena also impact on the success rates of Department, Hopital renal transplantation. For example, organs from deceased Strategies to target T cells Bicetre, UMR U542 donors with extended criteria (that is, age >65 years, renal The use of agents to deplete T cells is only proposed for INSERM/University Paris-Sud XI, 78 Rue du grafts with reduced glomerular filtration rates, donors with the induction phase of transplantation. Although some Général Leclerc, Paris, risk factors for cardiovascular disease) are increasingly studies have highlighted benefits with such treatments, for France (A. Durrbach, H. Francois, transplanted, which has resulted in an increased risk of example prolonging survival of transplanted organs, their S. Beaudreuil, recipients developing chronic renal dysfunction. Moreover, longterm use is not recommended. Immunodepletion of A. Jacquet, B. Charpentier) the number of recipients who are immunized before trans alloreactive T cells during sequential immunosuppression plantation, such as through pregnancy, blood transfusions may be beneficial for graft outcome by avoiding initial Correspondence to: acute rejection. Noncontrolled use of Tcelldepleting B. Charpentier bernard.charpentier@ Competing interests agents is associated with several complica tions, such bct.aphp.fr The authors declare no competing interests. as infections and tumor development. For instance,

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increasing numbers of tumors are reported in registries.1 Key points The development of tumors is a multifactorial event: ■ Allogenic organ transplantation is limited by drug-associated toxicity and the longterm exposure to immunosuppressants, the dura occurrence of antibody-mediated or chronic rejection tion of the trans plantation, patient’s age, the number of ■ Improved understanding of the molecular mechanisms of rejection has led to transplantations and genetic predisposition or epigenetic the development of agents that regulate T-cell function, complement activation factors can all influence the occurrence of tumors. The and/or the survival of plasma and B cells in immunized or naive patients use of depleting agents can, however, lower this risk and ■ These new agents may control acute, antibody-mediated rejection and chronic improve management. rejection to increase long-term renal transplantation outcomes ■ The safety of these new agents remains to be evaluated to ensure that they do Clonal deletion with alefacept not increase the risk of infections or tumor formation in transplanted patients Depletion of allogenic T cells by inducing apoptosis of activated T cells (clonal deletion) has emerged as a useful immunomodulatory strategy. Alefacept is a fusion protein Table 1 | Immunological effects of promising new immunosuppressants that binds to the immunological synapseassociated Inhibitory Target Molecule type Method of Main function protein CD2. CD2 is expressed on T cells and normally molecule administration interacts with lymphocytefunctionassociated antigen3 Alefacept CD2 Fusion protein Intravenous Deletion of activated (LFA3) on antigenpresenting cells to participate in the T cells formation and stabilization of the immune synapse. Belatacept CD80 Fusion protein Intravenous Inhibition of the second LFA3–CD2 signaling has important roles in the activa and signal of activation tion of memory–effector T cells, increased proliferative CD86 responses, and cytotoxic Tcell effector functions.2,3 By Sotrastaurin PKC Small molecule Oral Inhibition of PKC contrast, the use of paired antibodies or monoclonal anti CP-690,550 JAK-3 Small molecule Oral JAK-3 inhibitor bodies (mAbs) against CD2 prevents interaction with LFA Eculizumab C5 Antibody Intravenous Inhibition of complement and induces caspasedependent and caspaseindependent activation 4–9 apoptosis of alloreactive T cells. Use of monoclonal Bortezomib NFκB Small molecule Intravenous Depletion of plasmocytes 9 antibodies in mice prevents and treats acute rejection. and inhibition of NFκB

similarly, a human fusion protein, comprising the first Abbreviations: JAK, Janus kinase 3; NFκB, nuclear factor κB; PKC, protein kinase C. extracellular domain of LFA3 fused to two constant domains of human IgG1, has been designed to prevent interaction between LFA3 and CD2, and thus to interfere LFA3–Ig. The modest decrease in lymphocyte count is with the activation of T cells.10–12 In addition, the IgG1 attributable to the selective depletion of memory Tcell domain can activate the complement cascade and inter levels without altering the number of naive T cells. acts with CD16 (Fc γ receptor type III) on natural killer Alefacept has also been used to treat chronic exten cells to induce granzymemediated apoptosis of memory sive graftversushost disease (cGvHD) in humans.16,17 T cells and/or, preferentially, alloreactive T cells.11 Among 12 patients with steroidresistant cGvHD, Alefacept was initially developed to treat psoriasis, a eight (75%) responded to alefacept therapy. six of the lymphocytedependent disease. In animal models this 12 patients were still alive more than 30 months after drug prevents psoriasislike lesions. A randomized, therapy; the others died from progression of cGvHD. doubleblind, placebocontrolled, multicenter, phase III Alefacept has also been shown to control cGvHD that study demonstrated that, compared with placebo, occurs after liver transplantation.17 These findings indi intravenous alefacept improved cutaneous lesions.13 cate that alefacept could be useful in the control of allo Intramuscular administration of this agent was also genic lymphocytes in transplantation and could be used associ ated with a dosedependent reduction in memory as an induction therapy, or to treat cellular rejection. T cells (CD4+CD45RO+ and CD8+CD45RO+), whereas levels of naive CD4+CD45RA+ and CD8+CD45RA+CD19+ regulation of T‑cell activation with belatacept B cells, and CD16+CD56+ natural killer cells were unaf secondsignal activation has an important role in the fected.14 After 12 weeks, total CD4+ lymphocyte counts activa tion of T cells. The secondsignal family is com returned to within the normal range. Currently available posed of two subfamilies—CD28 and tumor necrosis co stimulation, blockadebased immunosuppression regi factor receptors.18,19 These subfamilies induce positive and mens do not prevent allograft rejection driven by memory negative signals in activated T cells. The CD28 pathway T cells, therefore, alefacept has been evaluated in associa has been extensively studied. Blockade of this pathway has tion with CTLA4–Ig recombinant molecules and siro limus been evaluated in human transplantation.20 to prevent allograft rejection in a nonhuman primate CD28 is a disulfidebound molecule that belongs to model of heart transplantation.15 This regimen was associ the immunoglobulin superfamily and is constitutively ated with prolonged graft survival in 50% of cases when expressed on T cells. CD28 interacts with B7.1 (CD80) compared with other combinations, a greater reduction in and B7.2 (CD86) molecules expressed on the surface of CD8+ cells, and an increase in the CD4+:CD8+ ratio when antigenpresenting cells and induces full Tcell activa compared with other regimens . In macaques treated with tion.19 The molecule shares 20% sequence identity with the LFA3–Ig, these results were reversed after this therapy inhibitory receptor CTLA4 (CD152), which is upregulated was withdrawn, compared with that in those not receiving during Tcell activation. CD28 and CTLA4 both bind to

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■ Alefacept: T-cell apoptosis longer periods of kidney graft survival (up to 6 months) Belatacept: T-cell activation ■ with humanized CD80 and CD86 antibodies than did ■ Sotrastaurin: T-cell activation untreated monkeys.27,31 All the monkeys that received LFA-3 ■ Eculizumab: Complement activation ■ Bortezomib: B-cell survival treatment developed donorspecific antibodies and had renal infiltrates, which indicates that CD28 blockade CD2 has to be used in combination. The agent belatacept was Alefa cept T cell improved by the introduction of two point mutations to APC increase its avidity for CD80 and CD86. This drug has been evaluated in a clinical trial of human renal transplant Sotrastaurin 20 IL-2 recipients. This phase II, multicenter study included CD80 IL-2 or CD86 PKC 218 adults who were randomly assigned to either an intensive regimen of belatacept (without ciclosporin), a CTLA4 lessintensive regimen of belatacept without ciclosporin, JAK-3 Belatacept or ciclosporin alone (control). All patients received a Fc (IgG1) basiliximabbased induction therapy, mycophenolate mofetil and steroids. The incidence of acute rejection at

CP-690,550 6 months was similar in the three groups: 7% for intensive belatacept, 6% for lessintensive belatacept, and 8% for ciclosporin alone. subclinical rejection at 12 months (as Complement assessed by routine biopsy) was more common with less intensive belatacept therapy (20%) than with intensive Eculizumab Bortezomib IL-6 production Anti-HLA antibodies belatacept (9%) or ciclosporin (11%). Glomerular filtra Figure 1 | Intracellular signaling and inhibition by novel compounds. The JAK3 tion rate at 12 months was markedly elevated in patients inhibitor (CP-690,550), PKC inhibitor (sotrastaurin) and CD28 inhibitor receiving belatacept compared with those treated with (belatacept) inhibit T-cell activation whereas LFA-3–Ig depletes allogenic T cells. ciclosporin (66.3 and 62.1 ml/min/1.73 m2 in patients Bortezomib impairs plasma cell production of anti-HLA antibodies and eculizumab receiving intensive and nonintensive belatacept, respec inhibits complement activation mediated by anti-HLA antibodies. Abbreviations: tively, versus 53.5 ml/min/1.73 m2 in ciclosporintreated APC, antigen-presenting cell; IL, interleukin; JAK-3, Janus kinase 3; LFA-3, patients). By month 12, the incidence of chronic allograft lymphocyte-function-associated antigen-3; PKC, protein kinase C. nephropathy was lower in both belatacept groups (20% for the intensive group and 29% for the lessintensive CD80+ and CD86+ molecules, although the latter does so group) than in the control group (44%). The incidence of with higher kinetic energy than the former and induces a infections or tumors did not differ between groups. positive signal.21 By contrast, CTLA4 exerts a negative effect Two additional phase III studies have been developed on T cells, which leads to a decrease in the signal trans with standard donors (BeNeFIT study) or with donors with mitted by Tcell receptors. Belatacept was created by fusing extended criteria (BeNeFIT extended study).32,33 These the ecto domain of CTLA4 with two constant domains of trials showed that, compared with ciclosporin, belata human IgG1 (CTLA4–Ig), enabling dissociation of CD28 cept was associated with improved renal function and a from CD80+CD86+ molecules, thus impairing Tcell decreased risk of cardiovascular risk factors in recipients. activa tion. This effect is also associ ated with modifica A trend towards more acute rejections, however, was seen tion of the activa tion status of the target cells. The binding in patients receiving belatacept than in those receiving of CTLA4–Ig induces tryptophan cata bolism through ciclosporin. In addition, more cases of posttransplant the stimulation of indoleamine 2,3dioxygenase, which lymphoma were reported in patients treated with belata degrades tryptophan and, therefore, impairs Tcell prolifera cept than in the controls, although the overall number tion and promotes the extension of CD4+CD25+FOXP3+ was low and most cases occurred in patients who had 22,23 Tregulatory (TReG) cells. In addition, CTLA4–Ig wellknown risk factors for lymphoma, such as a negative binding favors the synthesis of the regulatory human status for epstein–Barr virus before transplantation and leuko cyte antigen (HLA) G molecule by antigen the use of Tcelldepleting agents. presenting cells. Furthermore, in vivo allogenic regulation In a trial of belatacept in renal transplant recipients, + + + + + by TReG cells (CD4 CD25 FOXP3 ) that express CTLA4 patients did not exhibit expansion of TReG (CD4 CD25 requires B7 expression on antigenpresenting cells.24 bright) cells or upregulation of FOXP3+ T cells.24 Prolonged graft survival and donorspecific tolerance Moreover, two patients in this trial in whom belatacept has been induced by CTLA4–Ig in a human pancreatic treatment was stopped, developed chronic rejection, sug islet cell xenograft in rats, in a heterotopic cardiac allograft gesting that in humans shortterm administration of this model in rats and mice, in a rat renal allograft model and in drug does not induce longterm tolerance. a mouse skin allograft model.25–29 In addition, CTLA4–Ig reduced the incidence of GvHD induced by allogeneic Inhibition of protein kinase C with sotrastaurin bone marrow transplantation and its related mortality. Protein kinase C (PKC) isoforms have a pivotal role Costimulation blockade in nonhuman primate models in signal transmission in Tcellreceptor engagement has bridged the gap between smallanimal models and (signal 1) and CD28 coactivation (signal 2); inhibition of clinical protocols.30 Adolescent rhesus monkeys displayed PKC blocks early Tcell activation.34,35 The PKC family is

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very large and is separated into three subfamilies accord of sotrastaurin so far seems acceptable for each of the ing to the needs of their cofactors.36–38 Based on findings combinations tested.49,50 from animal studies—mostly in PKC isoenzymespecific several phase II trials have been started in the past 2 years knockout mice—at least three isoforms (PKCα, β and to evaluate calcineurin inhibitor withdrawal at 3 months θ), have assigned importance in Tcell and Bcell signal after transplantation in patients receiving tacro limus plus ing.39–43 PKCθ is mostly found in T cells and is a trans sotrastaurin.49,50 At 3 months after trans plantation, tacro mission factor between nuclear factor κB (NFκB) and limus was replaced with mycophenolic acid. However, the transcription factor activator protein 1, and has an both these trials were stopped because of marked increases important role in inducing the production of interleukin in episodes of acute rejection. A third phase II trial was (IL)2.42–45 For example, notable impairment of Tcell conducted as a multicenter, openlabel study to assess activation is seen in PKCθ knockout mice.46 use of a calcineurinfree regimen of 300 mg sotras taurin sotrastaurin is a novel immunosuppressant that blocks and 720 mg mycophenolic acid twice daily (n = 44) in early Tcell activation via inhibition of PKC. This agent comparison with a control regimen of tacro limus and is a highly potent and selective inhibitor of the classical mycophenolic acid (n = 81).49,50 All patients also received (isoforms α and β) and novel (isoforms δ, ε, η and θ) PKC basiliximab and steroids. The primary end points were subfamilies. At the cellular level, early Tcell activa tion, acute rejection (assessed by biopsy), graft loss, death, or but not Tcell proliferation, is strongly inhibited by sotras loss to followup at 3 months. At 1 month, the sotras taurin taurin, which is reflected in raised IL2 secretion.34 By regimen seemed as efficacious as the control regimen, by contrast, Tcell proliferation driven by IL2 is not affected. 3 months, efficacy had fallen by 26% in the sotrastaurin sotrastaurin potently inhibits allogenic stimulated Tcell group for the composite end point compared with a decline proliferation in mixed lymphocyte reactions, but does of only 5% in the control group. Although sotrastaurin not exhibit hematological cytotoxic effects. sotrastaurin was associ ated with benefits to renal function and had blocks alloantigenstimulated proliferation of effector acceptable tolerability, this result led to the early termina T cells, while leaving intact the regulatory functions and tion of the study. Treatment was discontinued in 12 of phenotype of CD4+CD25+FOXP3+CD127+ cells. This 81 patients who received sotrastaurin compared with two finding suggests that sotrastaurin does not abrogate the of 44 patients who received tacrolimus. The main reason + functions of tolerogenic CD4 TReG cells in patients after for discontinuation was graft rejection. 26% of patients in organ transplantation. the sotrastaurintreatment group met the composite effi Investigation of the pharmacokinetics and exposure– cacy endpoint of biopsyproven acute rejection, death, or efficacy relationship in de novo kidney transplant recipi graft loss at 3 months, versus 5% in the control group. ents showed that 1 week after transplantation, sotrastaurin exposure (defined by the area under the curve) after Inhibition of JAK‑3 daily treatment was stable in all patients (n = 152) and The development of sirolimus has focused on the inhibi remained similar in the presence of tacrolimus or myco tion of ubiquitously expressed serine–threonine kinases phenolic acid.47 In addition, in contrast to the effects to prevent immunological responses driven by IL2,51,52 of myco phenolic acid, the pharmacokinetic interactions of as cytokines have an important role in acute and chronic sotrastaurin generally increases tacrolimus blood levels by rejection, favoring clonal expansion and survival of naive less than twofold.47 sotrastaurin, is primarily metabolized and memory alloreactive T cells.53,54 Blockade of IL2 alone by the liver, with metabolites being excreted via the bile,47 is not sufficient to impair the allogenic response owing to bound to the acute phase protein α1acid glycoprotein. the involvement and redundancy of cytokines that share Levels of the drug in plasma should, therefore, be carefully some common poly peptide chains in the structure of their monitored after the transplantation. receptors.55 For example, the γchain of the IL2 receptor Oral sotrastaurin is efficacious in rodents and non (IL2R) is shared by IL2, IL7, and IL15.56 The specificity primate humans in preventing graft rejection. In a rat of the different IL interactions with the receptor is, there heart transplantation model and a monkey kidney fore, achieved through another associated chain, which transplantation model, 30–50 mg/kg sotrastaurin mono is frequently the αchain.56,57 In most cases, intracellular therapy or combined subtherapeutic doses of sotrastaurin trans duction is achieved through the activation of Janus (10–20 mg/kg) with ciclosporin or the sirolimus deriva kinase 3 (JAK3). This tyrosine protein kinase is one of the tive everolimus resulted in significantly prolonged graft four known members of the Janus kinase family (JAK1, survival compared with that in control animals. JAK2, JAK3, and TYK2), and has a key role in mediating A phase II study of sotrastaurin has been started in signals from the γc receptors, including IL2R. JAK3 is recipients of kidney allografts. Patients in this study activated via several cytokines (IL2, IL4, IL7, IL9, IL15 receive 200 mg or 300 mg sotrastaurin twice daily in and IL21).58–60 This protein has restricted and regulated combination with tacrolimus (0.1 mg/kg daily) or expression in lymphoid and myeloid cells; it is expressed entericcoated mycophenolic acid (1,440 mg daily).48 at high levels in natural killer cells and thymocytes, In combination with tacrolimus, sotrastaurin has so far and is inducible in T cells, B cells and myeloid cells.61–63 shown excellent efficacy, whereas, when combined with Receptor oligomerization by IL2 binding induces cross mycophenolic acid or everolimus, efficacy seems lower phosphoryla tion and trans activation of JAK3 and JAK1, than that achieved with the control regimen (tacrolimus which in turn results in tyrosine phosphorylation of and mycophenolic acid). Overall, the clinical tolerability multiple target molecules. As a consequence, the latent

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transcription factors, signal transducer and trans cription Antibody-mediated rejection activator (sTAT) 3 and 5, bind to IL2R via newly created Over the past 15 years, important progress has been docking sites, where they are tyrosine phosphorylated. made to prevent acute rejection. However, the rate of sTAT dimers are trans located to the nucleus where severe and/or steroidresistant rejection has increased. they bind to specific regulatory sequences within target The reported incidence of antibodymediated rejection is genes.58–60,64–66 An indispensable role for JAK3 in cytokine variable, ranging from 5.6% to 23% in unselected popula receptor signal transduction is reinforced by observations tions,81–83 and from 30% to 60% in patients undergoing of Jak3 knockout mice64–66 and of humans with autosomal preconditioning for ABOincompatible transplantation severe combined immunodeficiency syndrome caused by or transplantation across a positive donorspecific cross mutations in JAK3.64–68 JAK3 deficiency is associated with match.84–88 Over the past 5 years, the development of a severe deficit in the immune system that leads to sub sensi tive methods to detect antibodies and to find markers stantial alterations in lymphocyte development, functional for antibody injury, such as C4dA staining, made on the incompetence and susceptibility to apoptosis in peripheral basis of a careful analysis of biopsy samples, has empha T and B cells, and a reduced number or a lack of natural sized the role of HLA and nonHLA allo antibodies as killer cells.60 effectors of acute and chronic immune allograft injury.89,90 several inhibitors of JAK3 have been developed. This action has become the predominant focus of the AG490 has been developed as a JAK2 inhibitor but also complement pathway in the rejection process. impairs JAK3 signaling. This compound blocks the effect The current strategies to cure antibodymediated rejec of γc cytokines, which prevents activation of JAK3 in tion are based on the use of plasma exchange, intravenous T cells.69–71 By contrast, AG490 does not affect antigen immunoglobulin, and agents that deplete B and T cells, induced activation of tetanus toxoidresponsive human including antilymphocyte globulins or rituximab. The Tcell clones, stimulation of Zap70 or p56Lck tyrosine overall outcomes, however, have not been as good as phosphorylation by monoclonal antibodies to CD3, was expected. or expression of αchains, βchains, or γchains in the The persistence of donorspecific antibodies can arise IL2R.70–73 In a rat study, AG490 was shown to substan from memory B cells or longlived plasma cells,91,92 such tially prolong allograft survival when acting synergisti as CD20– and CD138+ cells. These cells are not targeted by cally with ciclosporin, a firstsignal inhibitor, but not with a rituximab regimen and, therefore, new strategies need the thirdsignal inhibitor sirolimus.67 Graft infiltration to be explored to inhibit their functions. by mononuclear cells was minimal, and ex vivo stat5a/b DNAbinding activity stimulated by IL2 was inhibited, plasma‑cell‑directed therapy with bortezomib but failed to affect the expression of IL2Rα.74 The Rel/NFκB pathway is critical for the survival of CP690,550 is an orally administered JAK3 inhibitor memory B cells and longlived plasma cells.93 For with nanomolar potency against JAK3. Both in vitro and example, mice lacking transcription factors belonging in vivo, CP690,550 causes a marked reduction of IL2 to the Rel/NFκB family exhibit defects in their ability to and cytokine production by T cells, and reduces Tcell develop effective Bcell responses in terms of prolifera tion proliferation.75 In animal models of transplantation, and differentiation. In addition, mice deficient in NFκB CP690,550 significantly reduces numbers of natural have defects in the formation of their germinative centers killer cells and T cells, but not CD8effector memory involved in the development of memory B cells.94–96 Tcell populations.75,76 Furthermore, NFκB has an important role in controlling In nonhuman primate models of transplantation, cell cycle progression, the action of celladhesion mol CP690,550, alone or in combination with myco phenolic ecules, and cytokine secretion.97 Activation of NFκB is acid, caused prominent delays in allogenic kidney rejec controlled by the degradation of its inhibitor, IκB via the tion and reduced intimal hyperplasia in an allogenic proteasome complex.98,99 Proteasome inhibitors are impli rat aorta transplantation model.77–79 In addition, the cated in the inhibition of NFκB100 by maintaining a high researchers of those studies observed a sizeable reduc level of IκB, and are linked with direct growth inhibition tion in the production of donorspecific IgG. A phase II and apoptosis of plasma cells. trial included 61 renal transplant recipients who were ran The proteasome inhibitor bortezomib exerts numerous domly assigned to receive CP690,550 at doses of either biological effects, including blockade of Tcell cycling, 15 mg or 30 mg twice daily, or tacrolimus in combination inhibition of the upregulation of CD25 or adhesion mol with an IL2R antagonist, mycophenolic acid, and ster ecules, decreasing Thelper1 responses101–103 and the oids. The incidence of biopsyproven acute rejection and subsequent apoptosis of activated T cells. Proteosomal renal function at 6 months was similar in all three groups, inhibition also affects the function of dendritic cells (by and no graft loss, deaths, or malig nancies were reported.78 reducing costimulatory molecule expression and cytokine However, patients receiving 30 mg CP690,550 twice daily production and by inducing apoptosis).98,104 Proteosomal developed more infections, including cytomegalovirus inhibitors also affect Bcell survival by reducing the infection, and BKvirusassociated nephropathy, than production of IL6 by bone marrow stromal cells.105 patients in the other groups. Bortezomib is a boronic acid dipeptide derivative Finally, a novel JAK3 and sYK inhibitor, R348, that effectively treats multiple myeloma.106 Owing to reduces allogenic heart rejection in animal models of its effect on plasma tumor cells, bortezomib has been transplantation.80 tested in vitro on CD138+ cells from patients sensitized

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to HLA.93 In contrast to rituximab and antilymphocyte without inhibiting the forma tion of complement C3b globulins, bortezomib induces apoptosis of CD138+ cells which participates in the opsonization process. and in vitro substantially reduces the production of class I The role of eculizumab in acute or chronic antibody and II antibodies. Bortezomib has also been successfully mediated rejection has yet to be defined. Prevention used to treat six kidney transplant patients with antibody has been reported in patients who had undergone renal mediated rejection who were refractory to standard transplantation with a Bcellpositive or Tcellpositive therapies.107 Treatment with bortezomib is associated flow cytometry crossmatched donor organ, in whom with a decrease in donor alloantibodies.108 Investigation donorspecific antibody levels remained low. No cases into its use to control the production of donorspecific of antibodymediated rejection developed, whereas anti bodies could, therefore, be of interest, especially in in historical control groups, frequency ranged from patients who are highly sensitized, and this drug could 61% to 92%.115 eculizumab has been reported to cure have a role in controlling the allogenic response, although steroid resistant and thymoglobulinresistant antibody a sustained response needs to be obtained to reduce the mediated rejection.115 In another patient, eculizumab risk of antibodymediated rejection. therapy, in combination with plasmapheresis and intra venous immunoglobulin, led to a substantial reduction eculizumab for complement‑associated rejection of MAC deposition and salvage of a kidney allograft in During antibodymediated rejection, complement one patient.107 The use of this antibody may, therefore, activa tion is observed via the classical pathway, which modulate antibodymediated rejection and might have leads to capillary deposition of C4dA.88 The presence roles in the preventive and therapeutic management of of this complement protein has been used as a marker this complication. for antibody mediated rejection. In addition, it is a marker for production of C3a and b, C5a and b, and, Conclusions consequently, the membraneattack complex associated The current aim of treatment development in renal with endo thelial cell injury, which leads to the release of transplantation is to enable the reduction or avoidance of chemo attractants, procoagulant factors and/or to cell drugs with renal toxic effects while lessening the risk death.109,110 The activation of C3 convertase is associated of allograft rejection. New molecules have been devel with the production of C5a anaphylatoxin, which favors oped to inhibit specific pathways activated during the poly nuclear and macrophage recruitment, and of comple allogenic response or with roles in antibody production. ment C5b, which lead to synthesis of the membrane attack These compounds have been evaluated to complement complex. Different grades of comple ment activation are current validated strategies. The capacity of these agents present in the various stages of antibodymediated rejec to prevent acute rejection, however, needs to be defined to tion. In addition, protocol biopsies of ABOincompatible determine the target populations (that is, immunized or allografts have shown that, despite the reappearance of new patients). Compounds that can impair long living ABO antibodies, accommoda tion occurs, mostly enabled B cells or plasma cells, and inhibit the complement by cellular mechanisms that control activation of the activating pathway, offer new opportunities for the treat complement pathway.109 In a xenogenic model of cardiac ment of antibodymediated rejection to prevent rejection trans plantation (pig to baboon), accommodation corre and prolong allograft survival. Important aspects of post lated with the overexpression in endothelial cells of CD59, transplantation therapy are maintaining the patient’s a complement regulatory molecule that prevents the ability to deal with infections and avoiding tumor synthesis of C5a anaphylatoxin and complement C5b.111 develop ment. An increase in immuno suppression needs Modulation of the complement cascade is, therefore, to be integrated sequentially and for a short period of becoming of interest as a treatment target in association time, after which standard maintenance therapy should with current available therapies, such as plasma exchange, be employed. Thus, understanding the impact of these intravenous immunoglobulin infusion, and Tcell and agents on the immune system and on patient survival Bcell depletion with antithymoglobulin or rituximab. needs to be a major objective for the future. eculizumab is a humanized antibody in which the constant domains of the parental IgG1 have been Review criteria replaced by the constant domain of human IgG4 and IgG2 to avoid complement and Fcγ receptor binding, Most articles were selected by searching the PubMed respectively.112 The drug acts against complement database using the search terms “alefacept”, C5 and was developed to treat paroxysmal nocturnal “LFA-3”, “CD2”, “BTI”, “apoptosis”, “transplantation”, hemoglobinuria, which is related to the deficiency of “belatacept”, “CTLA4-Ig”, “PKC”, “sotrastaurin”, “AEB”, “T-cell activation”, “CD80/86”, “Jak3 inhibitors”, “IL-2 glycosylphosphatidylinositollinked surface proteins, receptor”, “IL-15 receptor”, “mTOR pathway”, “T-cell 112,113 including the terminal complement inhibitor CD59. regulation”, “bortezomib”, “plasma cell”, “memory B cell”, Recurrent hemolytic uremic syndrome is associated with “NFκB inhibitor”, “eculizumab”, “complement activation”, a heterozygous missense mutation of the gene encod “complement regulation”, “anti-C5 antibody”, “humoral ing the regulatory complement factor H.114 eculizumab rejection”, “C4d deposition”. The PubMed search was blocks the proinflammatory and cytolytic effects of ter performed between 1995 and 2009. Abstracts from minal complement activation.113 This effect reduces the the most recent ESOT and AST congresses were also searched for information on very new agents. chronic complementmediated intravascular hemolysis

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