What's in the pipeline? New immunosuppressive drugs in transplantation

Correction of murine sickle cell disease by allogeneic haematopoietic cell transplantation with anti-3rd party veto cells

Despite advances in gene therapy allogeneic hematopoietic stem cell transplants (HSCT) remains the most effective way to cure sickle cell disease (SCD). However, there are substantial challenges including lack of suitable donors, therapy-related toxicity (TRM) and risk of graft-versus-host disease (GvHD). Perhaps the most critical question is when to do a transplant for SCD. Safer transplant protocols for HLA-disparate HSCT is needed before transplants are widely accepted for SCD. Although risk of GvHD and TRM are less with T-cell-deplete HSCT and reduced-intensity conditioning (RIC), transplant rejection is a challenge. We have reported graft rejection of T cell-depleted non-myeloablative HSCT can be overcome in wild type fully mis-matched recipient mice, using donor-derived anti-3rd party central memory CD8-positive veto cells combined with short-term low-dose rapamycin. Here, we report safety and efficacy of this approach in a murine model for SCD. Durable donor-derived chimerism was achieved using this strategy with reversal of pathological parameters of SCD, including complete conversion to normal donor-derived red cells, and correction of splenomegaly and the levels of circulating reticulocytes, hematocrit, and hemoglobin.

Immunosuppressive Agents on the Horizon

The evolution of immunosuppression in organ transplantation has resulted in decreasing rates of rejection and improved allograft survival. The current successes, however, comes at the price of intense drug monitoring, frequent adverse affects, and long-term toxicity. New immunosuppressive agents offer the hope for decreased toxicity and improved long-term results. This article highlights those novel agents that are currently in late-stage clinical studies including new calcineurin inhibitor analogs and formulations, mycophenolate acid sodium, everolimus, FK-778, FTY720, and various monoclonal antibodies. The diverse mechanisms of action of these agents, coupled with promising efficacy and adverse effect profiles, may land each of them a unique niche for immunosuppression in organ transplantation.

Evaluation of Immunosuppressive Activity of Demethylzeylasteral in a Beagle Dog Kidney Transplantation Model

Several monomers isolated from Tripterygium wilfordii Hook f. (Celastraceae) have attracted worldwide interest. In this study, we established a simple and reliable kidney transplantation model in beagle dog to evaluate the immunosuppressive activity of demethylzeylasteral (T-96), an immunosuppressive monomer isolated from the root xylem of T. wilfordii. Recipient and donor male beagle dogs were obtained from two different breeders to ensure MHC mismatching. All dogs were randomly divided into six groups following kidney transplantation, and different doses of T-96 or cyclosporine A (CsA) were administered to each group during 14 days of observation. The results showed that T-96 alone at a dosage of 10 or 20 mg/kg/day prolonged graft survival up to 10.83 ± 1.47 or 11.17 ± 1.47 days. A combination of T-96 and CsA significantly prolonged the survival time to 13.33 ± 1.75 days. The results demonstrated that T-96 can inhibit acute rejection in kidney transplantation, and the inhibitory effect of T-96 was enhanced when combined with CsA, which suggests the possible use in organ transplantation to prevent immune rejection.

Cost-effectiveness of modern mTOR inhibitor based immunosuppression compared to the standard of care after renal transplantation in Germany

OBJECTIVES

Standards of immunosuppression in renal transplantation have changed dynamically in recent years. We here provide a refined advanced pharmacoeconomic model which uses state-of-the-art methods including a mixed treatment comparison (MTC) analysis. The aim was to assess the cost-effectiveness of current immunosuppressive therapy regimens (TR): "sirolimus + early withdrawal of cyclosporine + steroids" (TR1), "sirolimus-early transition" (TR2), "everolimus-early transition" (TR3) and "tacrolimus low dose + mycophenolate mofetil (MMF) + steroids" (TR4).

METHODS

An up-to-date Markov model with current source data was employed to assess the cost-effectiveness of modern immunosuppressive regimens over 12-month and 10-year time periods. Transition probabilities for the occurrence of events for the first year were based on an MTC analysis. The robustness of the model was tested in extensive sensitivity analyses.

RESULTS

Within the 12-month time period TR2 yields the highest life years (0.987 LY), generating costs of 17,500 <euro>. In terms of years with functioning graft (FG), TR4 yields the best efficacy over the 12-month model duration (0.970 years with FG). For the 10-year time period, TR2 yields the lowest costs (107,246 <euro>) and dominates both TR3 and TR1, as it is simultaneously more effective. Within the 10-year model duration, TR4 reaches slightly higher effects compared with TR2 (6.493 vs. 6.474 LY) resulting in an incremental cost-effectiveness ratio of 387,684 <euro> per LY gained.

CONCLUSIONS

The early transition to sirolimus provides long-term efficiency results comparable with a tacrolimus-based regimen, which represents a common treatment standard after kidney transplantation. Both are superior to other investigated immunosuppressive regimens.

Characterization of ASKP1240, a fully human antibody targeting human CD40 with potent immunosuppressive effects

Blocking the CD40-CD154 interaction is reported to be effective for transplantation management and autoimmune disease models in rodents and nonhuman primates. However, clinical trials with anti-CD154 mAbs were halted because of high incidence of thromboembolic complications. Thus, we generated and characterized a fully human anti-CD40 mAb ASKP1240, as an alternative to anti-CD154 mAb. In vitro ASKP1240 concentration-dependently inhibited human peripheral blood mononuclear cell proliferation induced by soluble CD154. In addition, ASKP1240 did not destabilize platelet thrombi under physiological high shear conditions while mouse anti-human CD154 mAb (mu5C8) did. And ASKP1240 itself did not activate platelet and endothelial cells. In vivo administration of ASKP1240 (1 or 10 mg/kg, intravenously) to cynomolgus monkeys, weekly for 3 weeks, significantly attenuated both delayed-type hypersensitivity and specific antibody formation evoked by tetanus toxoid. The immunosuppressive effect was well correlated with the CD40 receptor saturation. Thus, these results suggest that ASKP1240 is immunosuppressive but not prothromboembolic, and as such appears to be a promising therapeutic candidate for the management of solid organ transplant rejection and autoimmune diseases therapy.

Costimulatory pathways in kidney transplantation: pathogenetic role, clinical significance and new therapeutic opportunities

Costimulatory pathways play a key role in immunity, providing the second signal required for a full activation of adaptive immune response. Different costimulatory families (CD28, TNF-related, adhesion and TIM molecules), characterized by structural and functional analogies, have been described. Costimulatory molecules modulate T cell activation, B cell function, Ig production, cytokine release and many other processes, including atherosclerosis. Patients suffering from renal diseases present significant alterations of the costimulatory pathways, which might make them particularly liable to infections. These alterations are further pronounced in patients undergoing kidney transplantation. In these patients, different costimulatory patterns have been related to distinct clinical features. The importance that costimulation has gained during the last years has led to development of several pharmacological approaches to modulate this critical step in the immune activation. Different drugs, mainly monoclonal antibodies targeting various costimulatory molecules (i.e. anti-CD80, CTLA-4 fusion proteins, anti-CD154, anti-CD40, etc.) were designed and tested in both experimental and clinical studies. The results of these studies highlighted some criticisms, but also some promising findings and now costimulatory blockade is considered a suitable strategy, with belatacept (a CTLA-4 fusion protein) being approved as the first costimulatory blocker for use in renal transplantation. In this review, we summarize the current knowledge on costimulatory pathways in the setting of kidney transplantation. We describe the principal costimulatory molecule families, their role and clinical significance in patients undergoing renal transplantation and the new therapeutic approaches that have been developed to modulate the costimulatory pathways.

Prolonged, low-dose anti-thymocyte globulin, combined with CTLA4-Ig, promotes engraftment in a stringent transplant model

BACKGROUND

Despite significant nephrotoxicity, calcineurin inhibitors (CNIs) remain the cornerstone of immunosuppression in solid organ transplantation. We, along with others, have reported tolerogenic properties of anti-thymocyte globulin (ATG, Thymoglobulin®), evinced by its ability both to spare Tregs from depletion in vivo and, when administered at low, non-depleting doses, to expand Tregs ex vivo. Clinical trials investigating B7/CD28 blockade (LEA29Y, Belatacept) in kidney transplant recipients have proven that the replacement of toxic CNI use is feasible in selected populations.

METHODS

Rabbit polyclonal anti-murine thymocyte globulin (mATG) was administered as induction and/or prolonged, low-dose therapy, in combination with CTLA4-Ig, in a stringent, fully MHC-mismatched murine skin transplant model to assess graft survival and mechanisms of action.

RESULTS

Prolonged, low-dose mATG, combined with CTLA4-Ig, effectively promotes engraftment in a stringent transplant model. Our data demonstrate that mATG achieves graft acceptance primarily by promoting Tregs, while CTLA4-Ig enhances mATG function by limiting activation of the effector T cell pool in the early stages of treatment, and by inhibiting production of anti-rabbit antibodies in the maintenance phase, thereby promoting regulation of alloreactivity.

CONCLUSION

These data provide the rationale for development of novel, CNI-free clinical protocols in human transplant recipients.

CD28 family and chronic rejection: "to belatacept...And beyond!"

Kidneys are one of the most frequently transplanted human organs. Immunosuppressive agents may prevent or reverse most acute rejection episodes; however, the graft may still succumb to chronic rejection. The immunological response involved in the chronic rejection process depends on both innate and adaptive immune response. T lymphocytes have a pivotal role in chronic rejection in adaptive immune response. Meanwhile, we aim to present a general overview on the state-of-the-art knowledge of the strategies used for manipulating the lymphocyte activation mechanisms involved in allografts, with emphasis on T-lymphocyte costimulatory and coinhibitory molecules of the B7-CD28 superfamily. A deeper understanding of the structure and function of these molecules improves both the knowledge of the immune system itself and their potential action as rejection inducers or tolerance promoters. In this context, the central role played by CD28 family, especially the relationship between CD28 and CTLA-4, becomes an interesting target for the development of immune-based therapies aiming to increase the survival rate of allografts and to decrease autoimmune phenomena. Good results obtained by the recent development of abatacept and belatacept with potential clinical use aroused better expectations concerning the outcome of transplanted patients.

Costimulatory pathways in transplantation

Secondary, so-called costimulatory, signals are critically required for the process of T cell activation. Since landmark studies defined that T cells receiving a T cell receptor signal without a costimulatory signal, are tolerized in vitro, the investigation of T cell costimulation has attracted intense interest. Early studies demonstrated that interrupting T cell costimulation allows attenuation of the alloresponse, which is particularly difficult to modulate due to the clone size of alloreactive T cells. The understanding of costimulation has since evolved substantially and now encompasses not only positive signals involved in T cell activation but also negative signals inhibiting T cell activation and promoting T cell tolerance. Costimulation blockade has been used effectively for the induction of tolerance in rodent models of transplantation, but turned out to be less potent in large animals and humans. In this overview we will discuss the evolution of the concept of T cell costimulation, the potential of 'classical' and newly identified costimulation pathways as therapeutic targets for organ transplantation as well as progress towards clinical application of the first costimulation blocking compound.

Past, present, and future prospects for inducing donor-specific transplantation tolerance for composite tissue allotransplantation

Composite tissue allotransplantation (CTA) is among the most immunologically complex and newest transplant fields. Although the field has made considerable advances, there are still concerns that these procedures are performed to enhance quality-of-life issues and are not lifesaving procedures that restore physiologic function. Two challenges limit the widespread application of CTA; the first is chronic rejection, the most prevailing cause of organ allograft failure after transplantation; the second barrier is the numerous health complications associated with lifelong immunosuppressive therapy. Several tolerance-inducing strategies, including costimulatory blockade, T-cell depletion, mixed chimerism, and gene targeting of transplanted organs, have the potential to induce lifelong tolerance to organ allografts without chronic immunosuppression. Effective clinical tolerance protocols that improve CTA acceptance and offer an alternative to the requirement for chronic immunosuppressive therapy could be a major advance in the field. Tolerance would allow allotransplantation to provide a currently unmet need for reconstruction of large tissue defects. This article reviews the history of CTA, current challenges and complications, and offers future directions for CTA research in strategies to induce tolerance.

CD40-specific costimulation blockade enhances neonatal porcine islet survival in nonhuman primates

The widespread clinical implementation of alloislet transplantation as therapy for type 1 diabetes has been hindered by the lack of suitable islet donors. Pig-to-human islet xenotransplantation is one strategy with potential to alleviate this shortage. Long-term survival of porcine islets has been achieved using CD154-specific antibodies to interrupt the CD40/CD154 costimulation pathway; however, CD154-specific antibodies seem unlikely candidates for clinical translation. An alternative strategy for CD40/CD154 pathway interruption is use of CD40-specific antibodies. Herein, we evaluate the ability of a chimeric CD40-specific monoclonal antibody (Chi220) to protect islet xenografts. Neonatal porcine islets (~50,000 IEQ/kg) were transplanted intraportally into pancreatectomized diabetic macaques. Immunosuppression consisted of induction therapy with Chi220 and the IL-2 receptor-specific antibody basiliximab, and maintenance therapy with sirolimus and the B7-specific fusion protein belatacept. Chi220 effectively promoted xenoislet engraftment and survival, with five of six treated recipients achieving insulin-independent normoglycemia (median rejection-free survival 59 days; mean 90.8 days, maximum 203 days). No thromboembolic phenomena were observed. CD40 represents a promising alternative to CD154 as a therapeutic target, and the efficacy of CD40-specific antibodies in islet xenotransplantation warrants further investigation.

Co-stimulation blockade as a new strategy in kidney transplantation: benefits and limits

New immunosuppressive drugs have greatly decreased the frequency of graft failure due to acute rejection but have had little impact on long-term graft survival. This is due, at least in part, to the broad non-immune effects of the current immunosuppressive drugs, which are involved in the death of patients and in chronic allograft dysfunction, particularly due to their nephrotoxicity. Recent progress in the development of biologicals, i.e. antibodies and fusion proteins, allows precise targeting of the immune system, preventing the non-immune side effects encountered with current protocols. In particular, targeting of the two most important co-stimulation pathways critical for T-cell activation, i.e. B7/CD28 and CD40/CD40L, has provided excellent results in many experimental models of organ transplantation. This has led to the clinical development of belatacept, a cytotoxic T-lymphocyte-associated antigen 4 immunoglobulin (CTLA4-Ig) fusion protein, which has proved to be efficient in preventing acute rejection in kidney transplant recipients. Its use is associated with improved renal function and a better metabolic profile than calcineurin inhibitors. However, because belatacept does not selectively target alloreactive T lymphocytes and must be combined with classical immunosuppressive drugs, infectious and neoplastic complications may occur, particularly post-transplantation lymphoproliferative disorders. We also address the current development of molecules targeting other co-stimulatory pathways (CD40/CD40L, leukocyte function-associated antigen [LFA]-1/intercellular adhesion molecule [ICAM], CD2/LFA-3). Many unresolved issues regarding the use of co-stimulation blocking agents are also discussed, e.g. their long half-life, which can be problematic in cases of serious adverse events, their long-term safety and efficacy, and the lack of monitoring tools to allow modulation of their use over time.

Biomarkers in renal transplantation

Identifying surrogate markers of renal allograft outcome and biomarkers of acute and chronic graft injury is a critical issue for the transplant community. Measurement of serum creatinine and biopsy remain the current gold standards for the evaluation of renal allografts. These tests have significant limitations in predicting which patients are destined for immune tolerance or immune-mediated graft loss, and aiding in the management of long-term immunosuppression. The goal of biomarkers is to diagnose rejection early, determine prognosis and tailor immunosuppressive therapy in a noninvasive, cost-effective manner. Biomarker research has focused on primary areas of kidney injury, the tubules and the cells that infiltrate them. This article reviews biomarkers currently under investigation in the setting of renal allograft transplantation.

Impact of immunosuppressants on the therapeutic efficacy of in vitro-expanded CD4+CD25+Foxp3+ regulatory T cells in allotransplantation

BACKGROUND

Although the therapeutic potential of regulatory T lymphocytes (Tregs) in preventing allograft rejection has been well documented, accumulating evidence indicates that supplemental measures, such as concomitant use of immunosuppressive agents, are essential for effective application of Treg cell therapy in clinical transplantation. Thus, it is important to know the effect of immunosuppressive agents on Treg cell therapy.

METHODS

We examined the impact of various immunosuppressive agents on the in vivo proliferation and therapeutic efficacy of in vitro-expanded Tregs using the murine graft-versus-host reaction and skin allograft model (BDF1 [H-2] to C57BL/6 [H-2]), respectively.

RESULTS

All six immunosuppressive agents tested inhibited the alloantigen-stimulated proliferation of Tregs as efficiently as they inhibited the proliferative response of conventional CD3 T cells. We further show that blockade of the CD40-CD40L interaction by treatment with a MR-1 antibody significantly increased the therapeutic efficacy of Tregs, a synergistic effect that seemed to be related to the strong regulatory activity of adoptively transferred Tregs together with effector T-cell hyporesponsiveness. Although concomitant use of rapamycin marginally augmented the therapeutic effectiveness of Tregs, mycophenolate mofetil and cyclosporine A at their full therapeutic doses exerted an antagonistic effect on Treg cell therapy.

CONCLUSION

These results demonstrate that inhibition of CD40-CD40L interaction or treatment with rapamycin could be successfully combined with in vitro-expanded Treg cell therapy, but the concomitant use of mycophenolate mofetil or cyclosporine A in this type of Treg cell therapy should be carefully considered.

Cost-effectiveness of immunosuppressive regimens in renal transplant recipients in Germany: a model approach

BACKGROUND

The choice of immunosuppression regimen is of paramount importance for outcomes and cost of renal transplantation. We compared the cost-effectiveness of triple immunosuppressive regimens in Germany.

METHODS

A strong micro-simulation model was built comparing regimens based on cyclosporine, everolimus, sirolimus, and tacrolimus. Mean cost per patient, incremental cost per life year gained, and incremental cost per additional year with functioning graft were assessed from the perspective of the German statutory health insurance (SHI) after 2 and 10 years.

RESULTS

Over the 2-year period, the model predicted mean total costs per patient of 26,732, 29,352, 33,415, and 49,978 euro for sirolimus, cyclosporine, everolimus, and tacrolimus, respectively. Focusing on the cost per life year gained, the sirolimus-based regimen compared favorably with those based on everolimus and tacrolimus. The incremental cost-effectiveness ratio (ICER) of cyclosporine versus sirolimus is 524,000 euro per life year gained. Regarding the cost per year with functioning graft gained, sirolimus dominated cyclosporine and everolimus, while the ICER for tacrolimus compared to sirolimus amounts to 1,788,154 euro. Over the 10-year time frame, mean total costs per patient were 100,758, 108,300, 120,316, and 183,802 euro for sirolimus, cyclosporine, everolimus, and tacrolimus, respectively. With regard to life years gained, sirolimus dominated both cyclosporine and everolimus. The ICER of tacrolimus versus sirolimus was 1,766,894 euro. Considering the years with functioning graft gained, sirolimus dominated cyclosporine and everolimus, while the ICER for tacrolimus compared to sirolimus amounted to 1,339,419 euro.

CONCLUSIONS

Over both the 2-year and the 10-year time horizon, sirolimus-based immunosuppression represents a cost-effective option in renal transplantation in Germany.

Translating costimulation blockade to the clinic: lessons learned from three pathways

SUMMARY

As the recognition that costimulatory signals are critical for optimal T-cell activation, proliferation, and differentiation, there has been an explosion in the study of costimulatory molecules and their roles in enhancing anti-donor T-cell responses following transplantation. Here, we focus on the bench-to-beside translation of blocking agents designed to target three critical costimulatory pathways: the CD28/CD80/CD86 pathway, the CD154/CD40 pathway, and the lymphocyte function associated antigen-1/intercellular adhesion molecule pathway. While blockade of each of these pathways proved promising in inhibiting donor-reactive T-cell responses and promoting long-term graft survival in murine models of transplantation, the progression of development of therapeutic agents to block these pathways has each taken a slightly different course. Both logistical and biological pitfalls have accompanied the translation of blockers of all three pathways into clinically applicable therapies, and the development of costimulatory blockade as a substitute for current standard-of-care calcineurin inhibitors has by no means reached completion. Collaboration between both the basic and clinical arenas will further propel the development of costimulation blockers currently in the pipeline, as well as of novel methods to target these critical pathways during transplantation.

What's next in the pipeline

The first decade of the new millennium has been disappointing for transplant therapeutics: no new immunosuppression agents have been approved. Several high profile drugs and biologics failed the rigors of clinical trials or had disappointing preclinical results (FTY720, FK778, anti-CDI54, anti-IL15, anti-CD28, R3421). Several challenges face the industry and clinical investigators in bringing novel drugs to the clinic including the difficulty in targeting new endpoints for toxicities or chronic allograft disease since acute rejection has been reduced to below 15% as well as the Food and Drug Administration insistence of excluding the use of immunosuppression regimens embraced by the transplant community in control arms of clinical trials. Currently six new agents, 3 small molecules (ISA247, a semisynthetic analogue of cyclosporine; AEB071, a protein kinase C isoforms inhibitor; CP 690,550, a selective Janus kinase inhibitor) are in phase II trials and 3 biologics (belatacept, a second generation CTLA4Ig; efalizumab, a humanized antiCD11a [LFA1] monoclonal antibody; and alefacept, a LFA3-IgG1 fusion receptor protein) are in phase II/III clinical trials. The preclinical pipeline is not only full but promises to address previously neglected targets and fulfill unmet medical needs in transplant therapeutics.

Transplant acceptance following anti-CD4 versus anti-CD40L therapy: evidence for differential maintenance of graft-reactive T cells

Inductive therapy with anti-CD4 or anti-CD40L monoclonal antibodies (mAb) leads to long-term allograft acceptance but the immune parameters responsible for graft maintenance are not well understood. This study employed an adoptive transfer system in which cells from mice bearing long-term cardiac allografts following inductive anti-CD4 or anti-CD40L therapy were transferred into severe combined immunodeficiency (SCID) allograft recipients. SCID recipients of cells from anti-CD4-treated mice (anti-CD4 cells) did not reject allografts while those receiving cells from anti-CD40L-treated mice (anti-CD40L cells) did reject allografts. Carboxyfluorescein succinimidyl ester (CFSE) labeling of transferred cells revealed that this difference was not associated with differential proliferative capacities of these cells in SCID recipients. Like cells from naïve mice, anti-CD40L cells mounted a Th1 response following transfer while anti-CD4 cells mounted a dominant Th2 response. Early (day 10) T-cell priming was detectable in both groups of primary allograft recipients but persisted to day 30 only in recipients treated with anti-CD4 mAb. Thus, anti-CD40L therapy appears to result in graft-reactive T cells with a naïve phenotype while anti-CD4 therapy allows progression to an altered state of differentiation. Additional data herein support the notion that anti-CD40L mAb targets activated, but not memory, cells for removal or functional silencing.

A novel fully human anti-CD40 monoclonal antibody, 4D11, for kidney transplantation in cynomolgus monkeys

BACKGROUND

CD40-CD154 pathway blockade by anti-CD154 monoclonal antibodies (mAbs) significantly prolongs allograft survival in nonhuman primates. However, thromboembolic complications have prevented clinical application. Thus, blockade of the counter molecule by a novel fully human anti-CD40 mAb, 4D11, is an attractive alternative.

METHODS

Kidney transplantations were performed between outbred cynomolgus monkeys (stimulation index >3 in a mixed lymphocyte reaction). The animals were divided into five groups: nontreatment control (Group 1, n=3), 10-week treatment with either 10 mg/kg (Group 2, n=3), 20 mg/kg (Group 3, n=3), or 40 mg/kg (Group 4, n=1), and 4-week treatment (Group 5, n=1 each) with 10 mg/kg, 20 mg/kg, or 40 mg/kg followed by monthly administration. Graft survival, biochemistry, complete blood counts, lymphocyte phenotypes, blood drug levels, antidonor and antidrug antibodies, and renal histology were examined.

RESULTS

Survival (days) was as follows: Group 1 (5, 6, 7), Group 2 (150, 108, 108), Group 3 (84, 108, 379), Group 4 (147), and Group 5 (147, 102, 112). Two animals in Group 3 with normal graft function were killed upon development of hydronephrosis and cerebral infarction. B lymphocytes fell to one-third of the preoperative value at 4 weeks after transplantation in all animals. Antidonor antibodies developed in most of the animals after stopping drug treatment or at the time of death. No animals except for one formed anti-4D11 antibody.

CONCLUSION

4D11 appears to be a promising agent for antirejection treatment in clinical organ transplantation.

Adhesion molecules in cutaneous immunity

Skin serves a vital role, providing protection from the broad array of pathogens present in our environment. In addition to the passive barrier functions of the skin, mammals have evolved a robust and versatile surveillance and rapid response system for recognition and elimination of invading organisms. This immune surveillance network directs the movement of immune cells, regulating homeostatic populations of immune cells in the skin, as well as recruitment to sites of inflammation. In this review, we discuss current understanding of the regulation and function of adhesion molecules in cutaneous immune surveillance and their relevance to the immunopathology of inflammatory skin disease.

CCR5 and CXCR3 are dispensable for liver infiltration, but CCR5 protects against virus-induced T-cell-mediated hepatic steatosis

CCR5 and CXCR3 are important molecules in regulating the migration of activated lymphocytes. Thus, the majority of tissue-infiltrating T cells found in the context of autoimmune conditions and viral infections express CCR5 and CXCR3, and the principal chemokine ligands are expressed within inflamed tissues. Accordingly, intervention studies have pointed to nonredundant roles of these receptors in models of allograft rejection, viral infection, and autoimmunity. In spite of this, considerable controversy exists, with many studies failing to support a role for CCR5 or CXCR3 in disease pathogenesis. One possible explanation is that different chemokine receptors may take over in the absence of any individual receptor, thus rendering individual receptors redundant. We have attempted to address this issue by analyzing CCR5(-/-), CXCR3(-/-), and CCR5/CXCR3(-/-) mice with regard to virus-induced liver inflammation, generation and recruitment of effector cells, virus control, and immunopathology. Our results indicate that CCR5 and CXCR3 are largely dispensable for tissue infiltration and virus control. In contrast, the T-cell response is accelerated in CCR5(-/-) and CCR5/CXCR3(-/-) mice and the absence of CCR5 is associated with the induction of CD8(+) T-cell-mediated immunopathology consisting of marked hepatic microvesicular steatosis.

A phase I/II randomized open-label multicenter trial of efalizumab, a humanized anti-CD11a, anti-LFA-1 in renal transplantation

Leukocyte function associated antigen-1 (LFA-1) has a multifaceted role in the immune response, including adhesion and trafficking of leukocytes, stabilizing the immune synapse of the MHC-TCR complex and providing costimulation signals. Monoclonal antibodies to the CD11a chain of LFA-1 have been seen to result in effective immunosuppression in experimental models. Efalizumab, a humanized IgG1 anti-CD11a, is approved for use in psoriasis and may provide effective immunosuppression in organ transplantation. Thirty-eight patients undergoing their first living donor or deceased renal transplant were randomized to receive efalizumab 0.5 or 2 mg/kg weekly subcutaneously for 12 weeks. Patients were maintained on full dose cyclosporine, mycophenolate mofetil and steroids or half dose cyclosporine, sirolimus and prednisone. At 6 months following transplant patient survival was 97% and graft survival was 95%. Clinical biopsy-proven acute rejection in the first 6 months after transplantation was confirmed in 4 of 38 patients (11%). Three patients (8%) developed post transplant lymphoproliferative disease, all treated with the higher dose efalizumab and full dose cyclosporine. The two doses of efalizumab resulted in comparable saturation and modulation of CD11a. This phase II trial suggests that efalizumab may warrant further investigation in transplantation.

Anti–LFA-1 Monotherapy Prevents Neointimal Formation in a Murine Model of Transplant Intimal Hyperplasia

BACKGROUND

Cardiac allograft vasculopathy (CAV) is the pre-eminent cause of late cardiac allograft failure. It is characterized by a concentric intimal hyperplasia, which we designate transplant intimal hyperplasia (TIH). To date, blockade of the adhesion molecule lymphocyte function-associated antigen-1 (LFA-1) has been shown to be effective in preventing TIH in experimental models of transplantation, but only when combined with other immunosuppressants. In this study we explored the impact of monotherapy against LFA-1 in a carotid artery allograft model of TIH.

METHODS

B10A(2R) (H-2(h2)) mice were used as donors and C57BL/6 (H-2(b)) mice used as recipients. The recipients were treated with a monoclonal antibody against LFA-1alpha (M17/4) or isotype-matched control immunoglobulin. Grafts were harvested after 35 days and analyzed by histomorphometry and immunohistochemistry. Blood samples were taken and analyzed by differential cell count and alloantibody levels.

RESULTS

We found that treatment with M17/4 resulted in a significant reduction in TIH compared with controls. Immunostaining revealed that LFA-1alpha blockade inhibited CD45+ leukocyte infiltration, prevented intimal smooth muscle cell (SMC) proliferation, and preserved the medial SMC population. Finally, we demonstrated a reduction in the serum alloantibody titer in the group treated with anti-LFA-1alpha when compared with controls.

CONCLUSIONS

We have demonstrated for the first time that LFA-1alpha blockade on its own can prevent development of TIH in an experimental model. The concept of modulating LFA-1alpha-mediated leukocyte migration and T-cell activation may therefore be of relevance to clinical cardiac transplantation and, as such, represents a potential target for therapeutic intervention against clinical CAV.

Novel Immunosuppression: Small Molecules and Biologics

Kidney transplantation today has excellent short-term outcomes that have paralleled the use of new immunosuppressive agents introduced in the 1990s. In addition to reducing acute rejection, the goals for developing new agents is to improve long-term outcome, minimize nephrotoxicity, and reduce infectious, cardiovascular, and malignancy-related complications. Novel small molecules and biological agents currently in clinical development may help to minimize the use of calcineurin inhibitors and steroids. These small molecules include FTY720, a sphingosine phosphate-receptor modulator, FK778, an inhibitor of pyrimidine synthesis, CP-690550, a JAK3 inhibitor, and AEB-071, a protein kinase C inhibitor. The biological agents include drugs targeting interleukin-15, anti-CD40, belatacept (LEA29Y), a second-generation CTLY4Ig that blocks the interaction between CD80/86 and CD28 costimulatory pathways, and efalizumab, a humanized anti-LFA1 monoclonal antibody. These new agents currently in preclinical and clinical trials appear promising and may represent the emergence of novel immunosuppressive agents that can deliver immunosuppression without long-term toxicity.

Recent Progress in Tolerance Induction through Mixed Chimerism

Organ transplant recipients require life-long treatment with immunosuppressive drugs. Currently available immunosuppression is associated with substantial morbidity and mortality, and is ineffective in inhibiting chronic rejection and graft loss. Therefore, a permanent state of donor-specific tolerance remains a primary goal for transplantation research. The induction of mixed hematopoietic chimerism is an attractive concept in this regard. Hematopoietic chimerism modulates the immunologic repertoire by extending the mechanisms of self-tolerance to donor-specific allotolerance. Despite recent progress in developing nontoxic bone marrow transplantation protocols for rodents, translation to large animals has remained difficult. Here, we outline the concept of tolerance via mixed chimerism, and review recent progress and remaining challenges in bringing this approach to the clinical setting.

Long-term survival of transplanted allogeneic cells engineered to express a T cell chemorepellent

BACKGROUND

Alloantigen specific T cells have been shown to be required for allograft rejection. The chemokine, stromal cell derived factor-1 (SDF-1) at high concentration, has been shown to act as a T-cell chemorepellent and abrogate T-cell infiltration into a site of antigen challenge in vivo via a mechanism termed fugetaxis or chemorepulsion. We postulated that this mechanism could be exploited therapeutically and that allogeneic cells engineered to express a chemorepellent protein would not be rejected.

METHODS

Allogeneic murine insulinoma beta-TC3 cells and primary islets from BALB/C mice were engineered to constitutively secrete differential levels of SDF-1 and transplanted into allogeneic diabetic C57BL/6 mice. Rejection was defined as the permanent return of hyperglycemia and was correlated with the level of T-cell infiltration. The migratory response of T-cells to SDF-1 was also analyzed by transwell migration assay and time-lapse videomicroscopy. The cytotoxicity of cytotoxic T cell (CTLs) against beta-TC3 cells expressing high levels of SDF-1 was measured in standard and modified chromium-release assays in order to determine the effect of CTL migration on killing efficacy.

RESULTS

Control animals rejected allogeneic cells and remained diabetic. In contrast, high level SDF-1 production by transplanted cells resulted in increased survival of the allograft and a significant reduction in blood glucose levels and T-cell infiltration into the transplanted tissue.

CONCLUSIONS

This is the first demonstration of a novel approach that exploits T-cell chemorepulsion to induce site specific immune isolation and thereby overcomes allograft rejection without the use of systemic immunosuppression.

Is the Malononitrilamide FK778 Better for the Prevention of Acute or Chronic Rejection?

OBJECTIVE

The aim of this study was to assess the efficacy of FK778 to prevent acute and chronic allograft rejection compared with other immunosuppressive agents.

MATERIALS AND METHODS

Heterotopic Brown-Norway (BN)-to-Lewis rat cardiac transplantations and heterotopic BN-to-Lewis tracheal transplantations were performed to study acute heart rejection and the development of chronic obliterative airway disease (OAD), respectively. Recipients were treated with FK778, tacrolimus, MMF, or sirolimus for 10 days (acute rejection study) or 28 days (chronic OAD study) at varying doses.

RESULTS

In untreated recipients, cardiac allograft survival was 6.2 +/- 0.4 days. FK778 (20 mg/kg), tacrolimus (2 or 8 mg/kg), mycophenolate mofetil (MMF; 40 mg/kg), or sirolimus (0.5 or 2 mg/kg) significantly prolonged graft survival to 17.0 +/- 2.8, 18.5 +/- 2.7, 25.0 +/- 2.5, 20.7 +/- 3.8, 14.5 +/- 2.2, and 23.2 +/- 1.5 days, respectively (P < .05). Tracheal grafts in untreated recipients showed intense infiltration and complete luminal obliteration by day 28. FK778 (20 mg/kg), tacrolimus (1 or 4 mg/kg), MMF (10 or 40 mg/kg), or sirolimus (0.5 or 2 mg/kg) significantly inhibited tracheal luminal obliteration (19.5% +/- 16.4%, 44.2% +/- 33.6%, 12.3% +/- 3.3%, 61.7% +/- 18.6%, 18.3% +/- 11.3%, 55.0% +/- 30.9%, and 8.5% +/- 3.5% (P < .05). All 4 high-dose groups showed similar efficacy.

CONCLUSIONS

When used in therapeutic doses, tacrolimus and sirolimus were more effective than FK778 to prolong cardiac allograft survival. However, with its antiproliferative effects on smooth muscle cells, its good tolerability, and its blockade of cytomegalovirus replication, FK778 proved effective to prevent chronic OAD development. Thus, FK778 may acquire an important role in maintenance therapy for the prevention of long-term fibroproliferative complications.

[Efalizumab]

Efalizumab (Raptiva, Serono) is a humanised monoclonal antibody (IgG1) produced by biotechnology. This antibody has a novel place among biotherapies for psoriasis. It is bound to the CD11a subunit of a surface molecule of the T lymphocyte LFA-1 (Leucocyte Function-associated Antigen-1). This molecule is essential for binding of T lymphocytes to the ICAM-1 molecule (Intercellular Adhesion Molecule-1) found on antigen-presenting cells, endothelial cells and keratinocytes. Binding of efalizumab to CD11a prevents binding of LFA-1 to ICAM-1, thus inhibiting several steps in the immunological process responsible for formation of psoriatic plaque (activation of naive T lymphocytes to memory T lymphocytes, lymphocyte migration and reactivation of T lymphocytes in skin). Efalizumab was approved in the United States by the FDA (Food and Drug Administration) in 2003 for the treatment of moderate-to-severe psoriasis requiring systemic therapy. It may be used as first-line therapy in the United States in this indication. In France, marketing authorisation (MA) was granted more recently in September 2005. The indications are moderate-to-severe cutaneous plaque psoriasis in adults in cases of failure, intolerance or contraindication of at least two systemic treatments including phototherapy, methotrexate and cyclosporine. Current clinical trial data is available for 3500 patients with plaque psoriasis. A 75% improvement in PASI score was seen in between 22 and 39% of patients treated with efalizumab (vs. 2 to 5% for patients on placebo) in a single weekly subcutaneous injection (1 mg/kg). A study in good responders confirms the continuing long-term efficacy of prescription of the drug up to 36 months (with at least a 75% improvement in PASI score in 53% of patients). However, it is not effective against joint involvement in psoriasis. The most common side-effects (incidence >1/100) are influenza-like syndrome, risk of outbreak of cutaneous psoriasis during or after discontinuation of treatment, worsening of arthralgia, minor hypersensitivity reactions, reversible changes in laboratory values (hyperlymphocytosis, elevated alkaline phosphatases and transaminases). Because of rare cases of thrombocytopenia (incidence<1/100), reversible on discontinuation of treatment, monthly monitoring of platelet counts is required over the first 3 months of therapy. There are currently no randomised studies comparing the various systemic treatments (standard therapy and biotherapy) for psoriasis. However, on extrapolation of the available results concerning efficacy (PASI-75 after 12 weeks of treatment), efalizumab appears to be less efficacious than anti-TNF alpha agents. This drug constitutes an additional treatment option and its position in the therapeutic arsenal will depend upon its long-term benefit/risk ratio in relation to other biotherapies.

A new look at blockade of T-cell costimulation: a therapeutic strategy for long-term maintenance immunosuppression

Activated T cells orchestrate the immune response that results in graft rejection; therefore, a common goal among current immunosuppressive therapies is to block T-cell activation, proliferation and function. Current immunosuppressive regimens that inhibit T cells and immune cells have greatly reduced the incidence of acute rejection following solid-organ transplant. However, the expected improvements in long-term outcomes have not been realized. This may be related to the non-immune side effects of current maintenance immunosuppressants, which target ubiquitously expressed molecules. The focus in transplantation research is shifting in search of maintenance immunosuppressive regimens that might offer improved long-term outcomes by providing efficacy in prevention of acute rejection combined with reduced toxicities. An emerging therapeutic strategy involves an immunoselective maintenance immunosuppressant that inhibits full T-cell activation by blocking the interaction between costimulatory receptor-ligand pairs. This review describes costimulatory pathways and the development of molecules, which inhibit them in the context of transplantation research. Recent clinical data using the selective costimulation blocker, belatacept (LEA29Y), as a part of a CNI-free maintenance immunosuppressive regimen in renal transplantation is highlighted.

FTY720, a novel immunomodulator in de novo kidney transplant patients: pharmacokinetics and exposure-response relationship

The pharmacokinetics, safety, and preliminary efficacy of FTY720, a novel immunomodulator, were examined in de novo renal transplant patients. Both noncompartmental and population methods were used to estimate pharmacokinetic estimates in the patients. The steady-state plasma concentrations of FTY720 increased in accordance with maintenance dose level, indicating linearity in clearance and volume of distribution over the 0.25- to 2.5-mg dose range. The pharmacokinetics of FTY720 in de novo renal transplant patients were characterized by the long terminal phase half-life of approximately 200 hours across doses, high volume of distribution (>3000 L), and low clearance (10.8 L/h). The intersubject variation of clearance was 55%, and the intrasubject variation of FTY720 concentrations was 28%. The population analysis revealed significant positive relationships between baseline alkaline phosphatase and clearance, as well as between baseline body weight on apparent volume of distribution. There was no relationship between FTY720 concentrations within a given FTY720 dose cohort and the rate of allograft rejection.

Novel therapies in transplantation

Immunosuppressant drugs are crucial in order to protect transplanted kidney, heart or liver against the body's natural defence mechanisms. These drugs are used to prevent both acute rejection of the organ as well as chronic deterioration of the graft over longer periods of time. Currently used immunosuppressant drugs are calcineurin inhibitors (cyclosporin and tacrolimus), steroids (prednisolone and methylprednisolone), antimetabolites (azathioprine and mycophenolate mofetil), antiproliferatives (sirolimus) and monoclonal antibodies that are used as an induction therapy (basilximab, daclizumab and muromonab). Over time, we have learnt more about existing immunosuppressive choices and the ways to monitor these drugs, and the current trend in immunosuppression therapy is towards tailoring the therapy according to an individual patient. The major issue that is now emerging is not how to prevent acute rejection, as current drugs are all efficacious, but rather how to avoid the long-term side effects that can harm both the graft and host, and negatively influence compliance. The market in transplantation is considerable and still growing; the whole market including the immuno-suppressants used in autoimmune diseases had sales of approximately pound 1.5 billion in 2001. There are currently 23 new drugs in advanced clinical development intended to be used in either organ transplantation or as treatment of autoimmune diseases. The new drugs that are intended to be used in transplantation are mostly analogues of currently used drugs with improved safety and pharmaceutical profiles.

A synergistic effect between PG490-88 and tacrolimus prolongs renal allograft survival in monkeys

This study was undertaken to determine if PG490-88 and tacrolimus (Tac) act synergistically to prevent renal allograft rejection in monkeys and to explore possible mechanisms of synergy between these agents. MHC-mismatched renal allografts were transplanted into cynomolgus monkeys after bilateral nephrectomy. Recipients were divided into the following groups: (i) no treatment; (ii) PG490-88 (0.03 mg/kg); (iii) Tac (1 mg/kg); (iv) PG490-88 (0.01 mg/kg) + Tac (1 mg/kg) and (v) PG490-88 (0.03 mg/kg) + Tac (1 mg/kg). Through synergy PG490-88 and Tac inhibited anti-CD3/PMA-induced T-cell proliferation and IFN-gamma expression in vitro. Tac monotherapy only marginally prolonged survival (27 +/- 3.2 days), while the combination of PG490-88 and Tac significantly prolonged graft survival to a median of 99 days (PG490-88 at 0.03 mg) and 38.5 days (PG490-88 at 0.01 mg/kg). Prolonged survival correlated with inhibited IgM production as well as reduced T-cell infiltration, IL-2 protein expression and NF-AT/NF-kappaB activity. We conclude that PG490-88 and a subtherapeutic dose of Tac significantly prolong renal allograft survival in monkeys through the synergistic inhibition of T-cell activation and a decrease in IFN-gamma production and NF-AT/NF-kappaB activity.

LFA-1 (CD11a) as a therapeutic target

Leukocyte function associated antigen-1 (LFA-1) was one of the earliest of cell-surface molecules identified by monoclonal antibodies generated against leukocyte immunogens. This integrin heterodimer is perhaps best known as a classic adhesion molecule facilitating the interaction between T cells and antigen-presenting cells. However, varied studies indicate that LFA-1 has multi-faceted roles in the immune response including adhesion, activation and trafficking of leukocyte populations. While there has been long-standing interest in LFA-1 as a therapeutic target for regulating immunity, anti-LFA-1 therapy is still not a first-line indication for any clinical condition. Antagonism of LFA-1 with monoclonal antibodies, either alone or in combination with other agents, can result in regulatory tolerance in vivo. Furthermore, new generation humanized anti-LFA-1 monoclonal antibodies (Efalizumab) show at least modest promise for continued application in clinical trials. Thus, anti-LFA-1 forms a potential, but still largely unexploited, immunotherapy which may find its greatest application as an agent which augments other therapies.

Immunotherapy for De Novo Renal Transplantation

Immunosuppressive drugs have been traditionally developed to prevent acute rejection and to improve short-term kidney transplant outcomes. There is still a medical need to improve outcomes among subgroups of patients at higher risk for graft loss and to reduce cardiovascular, infectious and malignancy-associated morbidity and mortality, and improve long-term adherence. Several new immunosuppressive agents and formulations are undergoing clinical investigation and are discussed in this review.A modified release tacrolimus formulation (MR4) for once-daily administration is undergoing phase III trials. It has been developed to be administered de novo or for maintenance using the same therapeutic target tacrolimus trough concentrations as for the original formulation. Belatacept (LEA29Y), a second generation cytotoxic-T-lymphocyte-associated antigen immunoglobulin (CTLA4-Ig), blocks the interaction between CD80/86 and CD28 costimulatory pathways. In phase II trials, belatacept was as effective as ciclosporin (cyclosporine) when administered in combination with basiliximab, mycophenolate mofetil (MMF) and corticosteroids. Currently, belatacept is undergoing phase III trials including one study in recipients of organs from expanded criteria donors. Inhibitors of the Janus protein tyrosine kinase (JAK)-3 show some selectivity for cells of the lymphoid lineage and have been shown to be effective in late preclinical transplant models. The most frequent adverse effects have been related to nonspecific binding to JAK2 kinases. CP-690550, a JAK3 inhibitor is currently in phase II clinical trials.FK778, is a synthetic malononitrilamide that targets the critical enzyme of the de novo pyrimidine synthesis, dihydroorotic acid dehydrogenase, and receptor-associated tyrosine kinases has completed phase II trials. FK778 also shows antiviral activities that have been tested in patients with polyomavirus nephropathy. Fingolimod (FTY720), a synthetic sphingosine phosphate receptor modulator that reduces the recirculation of lymphocytes to blood and peripheral tissues including inflammatory lesions and graft sites is undergoing phase III trials. Although the efficacy of fingolimod is similar to MMF in patients receiving full doses of ciclosporin, safety issues such as a negative chronotropic effect, macular oedema, pulmonary adverse reactions and graft function resulted in premature discontinuation of the development programme for kidney transplantation. Because there was no clear clinical benefit over treatment options, the clinical development programme of FK778 was discontinued.Finally, a new evolving strategy with powerful induction-induced prolonged T-cell depletion followed by low-dose immunosuppressive monotherapy is showing promising results.

New Strategies in Immunosuppression

New immunosuppressive strategies that can prevent both acute and chronic rejection are being investigated to achieve graft tolerance and to minimize side effects and toxicity that may lead to graft loss. Drug pharmacokinetics and pharmacodynamics, as well as pharmacogenetics, all play a role in customizing treatment to the individual patient. To improve patient compliance, new drug formulations are on trial, such as the modified- release oral form of tacrolimus MR4 for once daily administration, which seems to be equivalent to bid administration in terms of steady-state exposure. Monoclonal/polyclonal antibodies are increasingly used in the induction phase in protocols where steroids are discontinued early. However, discontinuing steroids carries a high risk of acute rejection or organ failure in some subgroups of patients. The supposed benefit of steroid discontinuation may not be enjoyed by all patients. Minimizing anticalcineurin agents may prove to be similarly or even more advantageous. The use of new drugs and new combinations has greatly improved short-term transplant outcomes. The new goal is, therefore, to improve long-term results and particularly to prevent chronic rejection, thus increasing patient and organ survival.

New insights into the pathogenesis and the therapy of recurrent focal glomerulosclerosis

Recurrent focal glomerulosclerosis (FSGS) in renal allografts has remained a frustrating and enigmatic disease. Recent studies on gene mutations encoding podocin and other components of the slit-diaphragm in patients with native kidney nephrotic syndrome have underscored the heterogenecity of the idiopathic form of FSGS. While familial FSGS rarely recurs following transplantation, the sporadic variety of FSGS is associated with a 30% recurrence rate. The patients with the sporadic variety of FSGS who have homozygous or complex heterozygous podocin mutations have a low recurrence rate. In the other patients with sporadic FSGS, a more complex and likely multifactorial etiology accounts for the recurrence of FSGS. The role of CD80 expression on podocytes is intriguing but requires confirmation in kidney biopsies of patients with recurrent FSGS. Recent findings on podocin genomics, the permeability factor and CD80 expression may ultimately lead to a better understanding of recurrent FSGS as well as a more effective approach to its prevention and treatment.

Antibodies in the prevention of renal allograft rejection

The rejection of renal allografts is mediated largely by the intragraft accumulation of alloreactive T lymphocytes. Current immunosuppressive drugs impair lymphocyte function, but also have specific toxicities and lead to nonspecific impairment of immune responses, resulting in an increased risk of infections and malignancy. Initial studies examined the usefulness of antibodies that depleted lymphocytes in preventing rejection. More recently, antibodies that impair lymphocyte function by blocking the interleukin-2 receptor-alpha (IL-2Ralpha), thereby reducing IL-2-mediated activation of T cells, were shown to reduce the risk of rejection. As an additional strategy, antibodies that impair lymphocyte trafficking have been investigated for their effect on acute rejection. This review describes the results of clinical trials of depleting antilymphocyte antibodies, IL-2Ralpha blockers and antibodies to intercellular adhesion molecule-1, lymphocyte function-associated antigen-1, CD154 and CD52 in the prevention of allograft rejection. Particular emphasis has been placed on therapies for which there is evidence obtained from good, randomised, controlled trials or registry data.

Lessons learned from anti-CD40L treatment in systemic lupus erythematosus patients

The CD40-CD40L system has pleiotropic effects in a variety of cells and biological processes including immune response, thrombosis and atherogenesis. Within the immune system, these molecules represent a critical link between its humoral and cellular arms. As a result of these attributes and based on preclinical data in animals, anti-CD40L antibodies were tested in a variety of immunologic diseases including idiopathic thrombocytopenic purpura, psoriasis, Crohn's disease, systemic lupus erythematosus and transplantation. Phase I/II studies in humans with lupus nephritis demonstrated reduction of anti-double-stranded DNA (anti-dsDNA) antibodies but not of protective antibodies. Reduction of anti-DNA was associated with increased serum complement levels and reduced glomerular inflammation. As a result of thrombotic effects, observed even in patients negative for anti-cardiolipin antibodies, there is a temporary halt on further human studies. The reasons for the prothrombotic effects are not clear at present but may represent effects on platelets and/or the endothelium. In view of the significant immunomodulatory effects of anti-CD40L treatment in patients with lupus nephritis, the increasing realization of the importance of premature atherosclerosis in lupus and an increasing amount of data supporting a role for the CD40-CD40L interactions in this process, inhibition of this pathway deserves further exploration in lupus.