Prolongation of primate renal allograft survival by anti-Tac, an anti-human IL-2 receptor monoclonal antibody

Small-molecule inhibitors of IL-2/IL-2R: lessons learned and applied

The IL-2:IL-2R protein-protein interaction is of central importance to both healthy and diseased immune responses, and is one of the earliest examples of successful small-molecule inhibitor discovery against this target class. Drug-like inhibitors of IL-2 have been identified through a combination of fragment discovery, structure-based design, and medicinal chemistry; this discovery approach illustrates the importance of using a diverse range of complementary screening methods and analytical tools to achieve a comprehensive understanding of molecular recognition. The IL-2 story also provides insight into the dynamic nature of protein-protein interaction surfaces, their potential druggability, and the physical and chemical properties of effective small-molecule ligands. These lessons, from IL-2 and similar discovery programs, underscore an increasing awareness of the principles governing the development of drugs for protein-protein interactions.

Anti-interleukin-2 receptor antibodies-basiliximab and daclizumab-for the prevention of acute rejection in renal transplantation

The use of antibody induction after kidney transplantation has increased from 25% to 63% in the past decade and roughly one half of the induction agent used is anti-interleukin-2 receptor antibody (IL-2RA, ie, basiliximab or daclizumab). When combined with calcineurin inhibitor (CNI)-based immunosuppression, IL-2RAs have been shown to reduce the incidence of acute rejection, one of the predictors of poor graft survival, without increasing risks of infections and malignancies in kidney transplantation. For low-immunological-risk patients, IL-2RAs, as compared with lymphocyte-depleting antibodies, are equally efficacious and have better safety profiles. For high-risk patients, however, IL-2RAs may be inferior to lymphocyte-depleting antibodies for the prophylaxis of acute rejection. In an effort to reduce toxicities of other immunosuppressive medications without increasing the risk of acute rejection and chronic graft loss, IL-2RAs have often been combined with steroid- and CNI-sparing immunosuppression protocols. More data support the benefits of early steroid withdrawal with IL-2RA in low-risk patients, but preferred induction therapy for high-risk patients has yet to be determined. Although CNI-sparing protocols with IL-2RA may preserve renal function and improve long-term survival in selected patients, further studies are needed to identify those who benefit most from this strategy.

Pharmacologic strategies in the prevention and treatment of corneal transplant rejection

Corneal transplantation remains one of the most successful organ transplantation procedures in humans. The unique structure of the cornea, with its absence of blood vessels and corneal lymphatic, allows the survival of corneal allograft. Recent advances in sutures, storage media, microsurgical instrumentation, and new pharmacological strategies have greatly improved the success of corneal transplantation and the prevention of corneal allograft rejection. Our strategies in the management and prevention of corneal graft rejection can modify and improve the survival of corneal allografts. Preoperative evaluation, understanding the risk factors, and management of ocular surface disorders may greatly improve the survival of the corneal transplant. Early recognition of corneal allograft rejection and aggressive treatment may improve the survival of the corneal graft. Furthermore, patients who undergo corneal transplantation should be maintained under close ophthalmic surveillance and patients should be informed to report immediately whenever symptoms of corneal graft rejection occur. The mainstay of therapy is topical corticosteroids. In severe cases, periocular, intravenous, and oral corticosteroids therapy can be rendered. New therapeutic modalities such as cyclosporine, tacrolimus, daclizumab, mycophenolate mofetil, leflunomide, rapamycin, and others may prove to be of help in the prevention and treatment of corneal graft rejection. Early recognition of corneal graft rejection and prompt treatment are mandatory for the successful survival of the corneal allograft.

Pharmacologic approaches to composite tissue allograft

This article discusses the pharmacologic approaches and the most promising new compounds for composite tissue allograft tolerance. Although some approaches rely on a combination of immunosuppressive agents that act synergistically against rejection, other strategies use immunologic manipulation, including major histocompatibility complex matching, induction of chimerism, and use of monoclonal antibodies to abrogate the immune response. There is still a need, however, to reproduce these findings in species phylogenetically closer to humans. This may be the target of future research efforts, which may overcome the challenge of limb and face transplant rejection.

IL-2 pathway blocking in combination with anti-CD154 synergistically establishes mixed macrochimerism with limited dose of bone marrow cells and prolongs skin graft survival in mice

To facilitate the establishment of mixed chimerism with limited dose of bone marrow (BM) cells, and to achieve tolerance in skin graft model, combined blocking of costimulatory pathway and IL-2 pathway was used in minimally myeloablative model using busulfan. BM cells (2.5x10(7)) of BALB/c were injected into C57BL/6 mice at day 0 with full thickness skin graft after single dose injection of busulfan (25 mg/kg) on day-1. Recipients were grouped and injected the anti-CD154, CTLA4-Ig, anti-IL-2R at days 0, 2, 4, and 6 according to protocol. Mixed macrochimerism were induced in groups treated with anti-CD154+anti-CTLA4-Ig, anti-CD154+anti-IL-2R, and anti-CD154+anti-CTLA4 Ig+anti-IL-2R. Three groups having chimerism enjoyed prolonged graft survival more than 6 months. Superantigen deletion study revealed deletion of alloreactive T cells in combined blockade treated groups. In graft versus host disease model using CFSE staining, CD4+ T cell and CD8+ T cell proliferation were reduced in groups treated with CTLA4-Ig or anti-IL-2R or both in combination with anti-CD154. However, anti-IL-2R was not so strong as CTLA4-Ig in terms of inhibition of T cell proliferation. In conclusion, IL-2 pathway blocking combined with anti-CD154 can establish macrochimerism with limited dose of BM transplantation and induce specific tolerance to allograft.

Routes to Transplant Tolerance versus Rejection

The alloimmune response can be divided into specific junctures where critical decisions between tolerance and immunity are made which define the outcome of the transplant. At these "decision nodes" various cytokines direct alloresponsive T cells to develop either a proinflammatory response aimed at graft destruction or an immunoregulatory response facilitating graft acceptance. This review will focus on the role of these cytokines in influencing the progression of an alloimmune response leading ultimately to either allograft survival or rejection.

Humanized anti-interleukin-2 (IL-2) receptor alpha therapy: long-term results in uveitis patients and preliminary safety and activity data for establishing parameters for subcutaneous administration

Therapy for severe uveitis is frequently long-term immunosuppression using systemic corticosteroids and cytotoxic agents, but side effects make long-term therapy difficult. A long-term (>4 year) Phase I/II single armed interventional study using intravenous anti-IL-2 receptor alpha treatments (daclizumab) and a short-term Phase II study evaluating the use of a subcutaneous daclizumab formulation were conducted. Patients were tapered off their systemic immunosuppressive therapy and received daclizumab infusions or subcutaneous injections at intervals varying from 2 to 6 weeks. In the long-term study, seven of ten enrolled patients were tapered from their original immunosuppressive medications and maintained exclusively on repeated daclizumab infusions for control of their uveitis for over 4 years. No patient was permanently removed from therapy for an adverse event ascribed to the medication. The use of 6-week infusion intervals led to recurrence of uveitis, while 2- to 4-week intervals did not. Only one patient developed measurable anti-daclizumab antibodies but this disappeared when subcutaneous therapy was begun. In the short-term study, four of the five patients receiving the subcutaneous formulation met the study endpoints for success within the first 12 weeks. All five were successful by 26 weeks. These studies provide preliminary evidence that regularly administered long-term daclizumab therapy can be given in lieu of standard immunosuppression for years to treat severe uveitis and that subcutaneously administered daclizumab appeared to be a clinically viable treatment strategy. These studies suggest that anti-IL-2 receptor blockade could be useful in the treatment of Th1-mediated autoimmune conditions.

Effects of combined treatment with CD25- and CD154-specific monoclonal antibodies in non-human primate allotransplantation

The CD154-specific monoclonal antibody (Mab) hu5c8 greatly prolongs allograft survival in primates. The CD25-specific Mab daclizumab has not, to date, been paired with hu5c8. We evaluated the effects of hu5c8 in vitro, alone and in combination with daclizumab on rhesus-mixed lymphocyte reactions (MLRs). We then evaluated therapy with hu5c8 and daclizumab in four monkey renal allograft recipients compared with monkeys untreated or contemporaneously treated with hu5c8 alone. Lymphocyte proliferation in MLR was reduced by both daclizumab and hu5c8, and their combined effects were additive. Rejection-free allograft survival in monkeys treated with both hu5c8 and daclizumab (74-479 days) was not significantly better than animals treated with hu5c8 alone (257-587 days), and one combined therapy animal rejected while still on hu5c8 therapy, a condition not typically seen with hu5c8 monotherapy. Although daclizumab and hu5c8 are additively effective in MLR, they do not appear to be synergistic in vivo in rhesus monkeys.

Limited dose monoclonal IL-2R antibody induction protocol after primary kidney transplantation

This study prospectively compared immunoprophylaxis with a single intraoperative dose (2 mg/kg) of monoclonal interleukin-2 receptor (IL-2R) antibody vs. noninduction in kidney transplant recipients treated with tacrolimus (FK 506), mycophenolate mofetil (MMF) and a prednisone-based immunosuppression regimen. One hundred recipients of first-kidney transplant were enrolled into the study to receive either anti-IL-2R monoclonal antibody, daclizumab (2 mg/kg intraoperatively, limited anti-IL-2R) or no induction (control). Each patient also received oral tacrolimus (dosed to target trough level 10-15 ng/mL), MMF (500 mg bid) and prednisone. The primary efficacy end-point was the incidence of biopsy proven acute rejection during the first 6 months post-transplant. The patients were also followed for 12-month graft function, and graft and patient survival rates. Other than the donor's age being significantly lower in the control group, both groups were comparable with respect to age, weight, gender, race, human leukocyte antigen (HLA)-DR mismatch, panel reactive antibody (%PRA), cold ischemic time, cytomegalovirus (CMV) status, causes of renal failure, and duration and modes of renal replacement therapy (RRT). During the first 6 months, episodes of first biopsy confirmed acute rejection was 3/50 (6%) in the limited anti-IL-2R group and 8/50 (16%) in the controls (p < 0.05). Twelve-month patient 100/98 (%) and graft survival 100/96 (%) were not statistically different. The group receiving limited anti-IL-2R did not have any adverse reactions. Our study demonstrates that a limited (single) 2 mg/kg immunoprophylaxis dose with monoclonal IL-2R antibody (daclizumab) when combined with tacrolimus/MMF/steroid allows significant reduction in early renal allograft rejection to the single digit level. The therapy with anti-IL-2R antibody is simple and is well tolerated.

Pharmacokinetics, pharmacodynamics, and immunodynamics of daclizumab in a two-dose regimen in liver transplantation

BACKGROUND

The humanized anti-interleukin 2 receptor (IL-2R) monoclonal antibody daclizumab (Zenapax) has been shown to be safe and effective for preventing acute allograft rejection in renal transplantation. The aim of this study was to evaluate pharmacokinetics and pharmacodynamics of daclizumab in a two-dose regimen (1.5 mg/kg total) after liver transplantation.

METHODS

Twenty-eight patients were enrolled in this study. Patients were evaluated for outcome, postoperative blood and ascites loss, serum levels of daclizumab, and corresponding changes in peripheral blood. Patients were also checked for development of anti-daclizumab antibodies.

RESULTS

CD25+ cells in patients' blood were significantly reduced for 28 days after daclizumab application. Elimination half-life of the antibody was 99 hr with a total body clearance of 57 ml/hr. Blood loss was not statistically significant and loss of ascites was weakly correlated to the monoclonal antibody clearance. One episode of mild acute rejection occurred. Although there was no significant decrease in absolute counts of CD3+, CD4+, and CD8+ lymphocytes, we were not able to show constant coating of IL-2Ralpha with daclizumab. IL-2Ralpha was not detectable on cell surface with two different antibodies and IL-2Rbeta was clearly reduced. Low titers of neutralizing anti-daclizumab antibodies in 3 of 13 patients were not of clinical significance and without influence on the pharmacokinetics.

CONCLUSIONS

A two-dose regimen with daclizumab in liver transplantation leads to effective blockade of the IL-2Ralpha for at least 14 days after transplantation. Daclizumab seems to affect not only IL-2Ralpha but also IL-2Rbeta and may lead to an impairment of other cytokine pathways, such as the IL-15 pathway.

Long-term safety, tolerability and efficacy of daclizumab (Zenapax) in a two-dose regimen in liver transplant recipients

A major thrust of transplantation research is to find more effective and less broadly toxic immunosuppressive agents. One potential way is the use of monoclonal antibodies directed to IL-2R alpha. Immunoprophylaxis with daclizumab, a humanized anti-IL-2R alpha monoclonal antibody, has been shown to be effective in the prevention of acute rejection in kidney transplant patients. These results encouraged us to initiate a pilot study in 28 liver transplant patients in 1997. Daclizumab was administered intravenously approximately 6 h after reperfusion (1 mg/kg) and on day 4 post-transplant (0.5 mg/kg). Additional immunosuppression consisted of cyclosporine A as well as of corticosteroids. Administration of daclizumab was not associated with any side-effects. We only experienced one acute rejection in a patient on day 17 post-transplant. It resolved immediately under therapy with prednisolone. The rate of opportunistic infections did not differ from results with conventional immunosuppressive regimens. At 4 years post-transplant no lymphoproliferative disease was observed. Patient survival at 12, 24, 36 and 48 months post-transplant was 88.5, 84.6, 80.8 and 73.1%, respectively. Immunoprophylaxis with a two-dose daclizumab regimen is safe, effective and well tolerated, and does not lead to increased opportunistic infections.

Bench to bedside: new approaches to the immunotherapy of uveitic disease

Intraocular inflammatory disease, or uveitis, appears to be due in large part to non-infectious, cell-mediated mechanisms. Experimental autoimmune uveitis (EAU) has been a valuable tool to better understand underlying mechanisms of this disorder, and it provides the possibility to evaluate new approaches to immunotherapy as well. Two approaches described here are oral tolerance and anti-IL2 receptor therapy. Both therapies were evaluated in the animal model and showed positive therapeutic effects. Based on these observations, both approaches were used in the treatment of patients with uveitis. Oral tolerance showed initial promising results. Anti-IL2 receptor therapy has been used for over 4 years in uveitis patients with an additional study evaluating this therapy in Behçet's disease. Future plans are to expand this approach to a larger number of patients. The use of animal models has been very useful in better understanding mechanisms of ocular disease and bringing new therapeutic approaches to the clinic.

Prophylactic and therapeutic effects of a humanized monoclonal antibody against the IL-2 receptor (DACLIZUMAB) on collagen-induced arthritis (CIA) in rhesus monkeys

CIA in the rhesus monkey is an autoimmune-based polyarthritis with inflammation and erosion of synovial joints that shares various features with human rheumatoid arthritis (RA). The close phylogenetic relationship between man and rhesus monkey makes the model very suitable for preclinical safety and efficacy testing of new therapeutics with exclusive reactivity in primates. In this study we have investigated the prophylactic and therapeutic effects of a humanized monoclonal antibody (Daclizumab) against the alpha-chain of the IL-2 receptor (CD25). When Daclizumab treatment was started well after immunization but before the expected onset of CIA a significant reduction of joint-inflammation and joint-erosion was observed. A therapeutic treatment, initiated as soon as the first clinical signs of CIA were observed, proved also effective since joint-degradation was abrogated. The results of this study indicate that Daclizumab has clinical potential for the treatment of RA during periods of active inflammation and suppression of the destruction of the joint tissues.

Daclizumab: a review of its use in the prevention of acute rejection in renal transplant recipients

The humanised monoclonal antibody daclizumab is an immunosuppressive agent that reduces acute rejection in renal transplant recipients. It is specific for the alpha subunit (Tac/CD25) of the interleukin-2 (IL-2) receptor on activated T cells and achieves immunosuppression by competitive antagonism of IL-2-induced T cell proliferation. Daclizumab has advantages over murine antibodies to the IL-2 receptor, including improved effector function, a low potential for immunogenicity and long elimination half-life. When added to standard cyclosporin-based immunosuppressive therapy with or without azathioprine, daclizumab (1 mg/kg prior to surgery and once every 2 weeks thereafter for a total of 5 doses) significantly reduced the 6-month rate of acute rejection compared with placebo in 2 phase III studies. The mean number of rejection episodes was significantly reduced and the time to first acute rejection significantly increased in daclizumab versus placebo recipients. Patient survival at 1 year after transplantation was significantly higher with daclizumab than placebo in 1 study and showed a trend in favour of the drug in the other study. The 1-year graft survival rate tended to be greater in daclizumab than in placebo recipients in both studies, In a phase II study, acute rejection rates in patients treated with both daclizumab and mycophenolate mofetil (plus standard cyclosporin-based immunosuppression) were lower than those achieved with mycophenolate mofetil alone. Preliminary results indicate that daclizumab is also a useful agent in paediatric renal transplant recipients. Further investigation of the efficacy and tolerability of the drug in this patient group is clearly warranted. Daclizumab does not increase the incidence of adverse events when added to standard cyclosporin-based therapy. The incidence of opportunistic infections, lymphoproliferative disorders and malignancies was not increased above that seen with placebo.

CONCLUSIONS

Although the effects of daclizumab on long term graft and patient survival require further investigation, available data indicate that daclizumab is an important advance in renal transplant immunosuppression, reducing acute graft rejection without affecting the tolerability of standard cyclosporin-based immunosuppression.

Newer immunosuppressive drugs: a review

In recent years, many new immunosuppressive drugs have been discovered and developed for clinical use in transplantation. This review focuses on those drugs (leflunomide, mycophenolate mofetil, sirolimus, tacrolimus) that have been shown to have immunosuppressive activity in patients. Different anti-interleukin-2 receptor antibodies are also reviewed as an example of a resurgence of development in the area of monoclonal antibodies. The price for reducing the incidence of allograft rejection by improved immunosuppression was thought to be a proportional increase in the incidence of infection and malignancy. Data from Phase III clinical trials of new immunosuppressants, however, show a statistically significant reduction in the incidence of acute rejection produced by these new drugs, which has not been accompanied by increases in infection and malignancy rates. The wide array of new drugs offers the opportunity to use combinations that block different pathways of immune activation while at the same time selecting drug combinations with nonoverlapping toxicity profiles so that doses of each single drug can be reduced below toxicity levels. The immunosuppressive therapy for patients can be tailored according to their individual needs.

Reduction of the occurrence of acute cellular rejection among renal allograft recipients treated with basiliximab, a chimeric anti-interleukin-2-receptor monoclonal antibody. United States Simulect Renal Study Group

BACKGROUND

A double-blind, placebo-controlled phase III study was performed to assess whether basiliximab, a chimeric anti-interleukin-2 receptor monoclonal antibody, reduced the incidence of acute rejection episodes in renal allograft recipients.

METHODS

A total of 348 patients were randomized into two demographically matched, equally sized groups treated with either basiliximab or placebo. The dose of basiliximab-20-mg infusions on day 0 and day 4-was selected to block detection of interleukin-2 receptor on 97% of peripheral blood lymphocytes for 30-45 days. All patients received immunosuppressive therapy with cyclosporine microemulsion (Neoral) and steroids. An intent-to-treat analysis of 1-year data assessed the incidence of posttransplant acute rejection episodes, patient and graft survival rates, and the safety and tolerability of basiliximab.

RESULTS

Among the eligible 346 patients equally divided into the two treatment groups, basiliximab reduced the proportion of patients who experienced biopsy-confirmed acute rejection episodes by 28%: 61 (35.3%) basiliximab vs. 85 (49.1%) placebo (P=0.009). Graft losses occurred in 9 (5.2%) basiliximab-treated and 12 (6.9%) placebo-treated patients. Five (2.9%) deaths in the basiliximab group and seven (4.0%) in the placebo group occurred. Compared with placebo, a higher fraction of basiliximab patients produced urine in the operating room, and a significantly lower fraction had renal dysfunction in the first month (serum creatinine > or =5 mg(dl) and between 1 and 12 months (serum creatinine > or =3 mg/dl). During the first 12 months, 94 (54%) basiliximab-treated patients experienced serious adverse events, compared with 106 (61%) who received placebo.

CONCLUSIONS

Prophylactic basiliximab therapy is well tolerated, has an adverse event profile comparable to placebo, and significantly reduces the number of acute rejection episodes in renal allograft patients within the first year after transplantation.

The use of antibodies against the IL-2 receptor in transplantation

Humanized monoclonal antibodies that recognize the alpha chain of the IL-2 receptor (e.g. daclizumab) have been used to prevent allograft rejection, since this chain is expressed by T cells participating in allograft rejection but not by resting T cells. In a randomized trial, when added to standard cyclosporin-based immunosuppression, daclizumab significantly reduced the frequency of acute rejection of renal transplants.

Mechanism of tolerance to class I-mismatched renal allografts in miniature swine: regulation of interleukin-2 receptor alpha-chain expression on CD8 peripheral blood lymphocytes of tolerant animals

BACKGROUND

Donor-specific tolerance to renal allografts in miniature swine is uniformly induced across a two-haplotype class I plus minor histocompatibility antigen disparity by a 12-day course of cyclosporine. Recent studies have demonstrated that the thymus is essential for rapid and stable tolerance induction, because either prior thymectomy or a series of thymic biopsies induce a spontaneously reversible rejection crisis after the 12-day course of cyclosporine. The present study examined the peripheral cellular mechanisms of tolerance by analyzing cytotoxic effector pathways in peripheral blood lymphocytes (PBL) of tolerant animals.

METHODS

The phenotype and cytotoxic T lymphocyte response of alloantigen-activated PBL cultures using cells from a series of tolerant animals with stable renal function (no thymic manipulation), or during a rejection crisis (induced by thymic biopsies), were studied. The in vitro findings were correlated with the in vivo clinical course of experimental animals.

RESULTS

The data demonstrated that in vivo and in vitro tolerance was associated with a specific deficiency of interleukin-2 receptor (IL-2R) alpha-chain up-regulation on CD8 single-positive (SP) T cells expressing high levels of CD8 (CD8high) when PBL from tolerant animals are stimulated with donor class I alloantigen. Stimulation by third party class I alloantigen, or by donor antigen during a rejection crisis, produced efficient cytotoxic T lymphocyte responses and expression of IL-2Ralpha on CD8high SP cells.

CONCLUSION

Antigen-specific regulation of the IL-2Ralpha expression on CD8high SP PBL is a principal event associated with and potentially involved in the mechanism of tolerance in this preclinical large animal model.

Interleukin-2-receptor blockade with daclizumab to prevent acute rejection in renal transplantation. Daclizumab Triple Therapy Study Group

BACKGROUND

Monoclonal antibodies that block the high-affinity interleukin-2 receptor expressed on alloantigen-reactive T lymphocytes may cause selective immunosuppression. Daclizumab is a genetically engineered human IgG1 monoclonal antibody that binds specifically to the alpha chain of the interleukin-2 receptor and may thus reduce the risk of rejection after renal transplantation.

METHODS

We administered daclizumab (1.0 mg per kilogram of body weight) or placebo intravenously before transplantation and once every other week afterward, for a total of five doses, to 260 patients receiving first cadaveric kidney grafts and immunosuppressive therapy with cyclosporine, azathioprine, and prednisone. The patients were followed at regular intervals for 12 months. The primary end point was the incidence of biopsy-confirmed acute rejection within six months after transplantation.

RESULTS

Of the 126 patients given daclizumab, 28 (22 percent) had biopsy-confirmed episodes of acute rejection, as compared with 47 of the 134 patients (35 percent) who received placebo (P=0.03). Graft survival at 12 months was 95 percent in the daclizumab-treated patients, as compared with 90 percent in the patients given placebo (P=0.08). The patients given daclizumab did not have any adverse reactions to the drug, and at six months, there were no significant differences between the two groups with respect to infectious complications or cancers. The serum half-life of daclizumab was 20 days, and its administration resulted in prolonged saturation of interleukin-2alpha receptors on circulating lymphocytes.

CONCLUSIONS

Daclizumab reduces the frequency of acute rejection in kidney-transplant recipients.

A phase I trial of humanized anti-interleukin 2 receptor antibody in renal transplantation

The efficacy of murine monoclonal anti-interleukin 2 alpha chain receptor (Tac) antibodies is limited by a short half-life and the development of antibodies to the heterologous protein. The safety, pharmacokinetics-dynamics, and immunosuppressive effect of a humanized anti-Tac antibody (HAT) was evaluated in 12 renal transplant recipients. Ten patients received living related transplants (three HLA-identical matches and seven one-haplotype or zero-haplotype matches) and two patients received cadaver organs. The patients were divided into four HAT treatment arms: 0.5 mg/kg/week (n=4), 1 mg/kg/week (n=2), 0.5 mg/kg every other week (n=3), and 1 mg/kg every other week (n=3). The first dose of HAT was given within 12 hr before transplantation, and four additional doses were given after transplantation. Patients were also placed on cyclosporine, steroids, and azathioprine. Only one patient, a recipient of a cadaver kidney in the lowest HAT treatment arm, had a reversible rejection episode. The 10 recipients of living related transplants were compared with 17 historical controls treated with an identical immunosuppressive regimen except for HAT. Whereas none of the HAT-treated living related donor recipients had a rejection episode, 6 of 17 (41%) of the historical controls had a rejection episode in the first year after transplantation. There were no first-dose reactions after HAT therapy or other subsequent side effects. None of the patients experienced opportunistic infections or malignancies. One patient developed low-titer anti-HAT antibodies, although the patient maintained high serum HAT concentrations throughout the study. Immune monitoring showed that there were no changes in the percentage or absolute counts of CD3 cells or T-cell subsets after HAT therapy. However, there was a significant decrease in the number of circulating lymphocytes that expressed free Tac. The overall harmonic mean half-life of HAT was 273 hr. The results of this study indicate that HAT given at 1 mg/kg every other week for a total of five doses may provide therapeutic HAT concentration levels and result in good saturation of Tac receptors for at least 12 weeks after transplantation. In summary, HAT is safe and is well tolerated by patients. Its long half-life and lack of immunization could make it a very useful immunosuppressive drug.

Immunoprophylaxis with a monoclonal anti-IL-2 receptor antibody in liver transplant patients

The immunosuppressive effect of a monoclonal antibody (moAb), BT563, directed to the alpha-chain of the IL-2R (CD25), was analyzed in a prospective nonrandomized trial and a prospective randomized trial. Primary objectives were evaluation of the incidence of acute rejections and infections; secondary objectives were safety and tolerability of the moAb. A total of 28 patients were enrolled (phase II) to receive 10 mg/day of BT563 (12 days) as immunoprophylaxis in combination with cyclosporine, azathioprine, and low-dose steroids. Subsequently 32 patients were randomly assigned (phase III) to receive BT563 (10 mg/day) for 12 days or ATG (5 mg/kg/day) for 7 days in addition to cyclosporine and low-dose steroids. No side effects of the BT563 treatment were noted. The actuarial survival was 82% at 12 months in the phase II trial and 92% at 12 months in both arms of the phase III trial. There was one acute rejection in the phase II trial. No acute rejections were noted in the BT arm of the phase III trial and 5 acute rejections were treated in the ATG arm. In the phase II trial 7 infectious episodes were observed, while one infection was seen in the BT arm and 7 in the ATG arm of the triple immunosuppression phase III trial. In all patients circulation of coated CD25+ lymphocytes was observed during BT563 treatment; there was no evidence of depletion or modulation of CD25+ cells. Mean serum levels of BT563 ranged from 1.6 to 7.6 microgram/ml throughout the therapy. An antimurine response was seen in 82% (phase II) and 100% (phase III) of the patients. Antirabbit antibodies were found in 56% of the patients treated with ATG. Analysis of the antimurine response specificity revealed in 56% blocking anti-isotypic antibodies and only in 3% of the patients an anti-idiotypic response. The data of the study presented suggest that therapy with an anti IL-2R moAb is at least equal to ATG application according to the incidence of acute rejections and infections.

Development and functional characterization of a murine/human chimeric antibody with specificity for the human interleukin-2 receptor

A murine/human chimeric antibody, with specificity for the human interleukin-2 receptor, was developed by genetic engineering. For this purpose, the light and heavy chain variable region exons encoding the murine monoclonal antibody 2C8 were isolated and inserted into expression vectors containing the human kappa and gamma-1 constant regions. After transfection by electroporation of the chimeric genes into murine Sp 2/0 hybridoma cells, transfectomas secreting the complete chimeric antibody were selected. The chimeric antibody has similar binding properties as the original murine antibody. The in vitro cytotoxic effects of the murine and the chimeric antibodies were compared.

Monoclonal antibodies in renal transplantation: a review

OKT3 is the first anti-CD3 monoclonal antibody available for treatment in humans. Over the last few years it has proven to be a very powerful immunosuppressive agent in renal transplantation. Clinical studies have shown that OKT3 is superior to high-dose steroids as first-line treatment for acute renal allograft rejection. Furthermore, it is comparable to antithymocyte globulin (ATG) in treating steroid-resistant rejection and is also effective as rescue treatment in ATG- and antilymphocyte globulin-(ALG-) resistant rejection. Despite its excellent rejection-reversal rate, OKT3 treatment is followed by a substantial percentage of re-rejections, most of which respond well to steroids. In the early post-transplantation period, a prophylactic course of OKT3 is very effective in preventing acute rejections, and in this respect it is probably equivalent to ATG. Indirect evidence exists that a prophylactic course of OKT3 may be beneficial in immunologically high-risk patients and in patients with delayed graft function. However, more clinical studies are required to answer the question whether OKT3 should be given as induction treatment, as first-line treatment, or as rescue treatment. To answer this question, the side effects of OKT3 should also be taken into account. First-dose-related side effects, although frequent and disturbing, are usually transient and seldom life-threatening, provided overhydration has been corrected and steroids have been given before the first administration. These side effects are attributed to the release of cytokines as a result of T-cell activation or lysis. After exposure of patients to OKT3 an increased incidence of infections and malignancies has been reported. However, it is not yet clear whether this is due to OKT3 as such, or whether it merely reflects the total burden of immunosuppression. Xeno-sensitization represents an important limitation to OKT3 treatment, although a second or third course can still be effective in patients with low antibody titers. The precise immunosuppressive mechanism of anti-CD3 monoclonal antibodies is yet unknown. Monitoring of patients treated with OKT3 revealed CD3 and/or T-cell antigen receptor depletion and immunological incompetence of remaining T cells. More clinical data are required to establish the correct dose and duration of OKT3 treatment. In conclusion, OKT3 is a powerful immunosuppressive agent but its real value in renal transplantation remains to be determined. A practical approach may be to reserve it for the treatment of steroid-resistant rejections.(ABSTRACT TRUNCATED AT 400 WORDS)

Renal graft rejection or cyclosporin toxicity? Early diagnosis by a combination of Papanicolaou and immunocytochemical staining of urinary cytology specimens

A method is described for distinguishing between graft rejection and cyclosporin nephrotoxicity in renal allograft recipients by analyzing fresh morning urine samples. The technique combines classic Papanicolaou with immunocytochemical staining and was performed in urine specimens from a series of 42 patients. Early-stage cyclosporin toxicity was usually associated with increased numbers of proximal tubular cells only, whereas in rejection and late-stage toxicity there were increases in both tubular cells and in lymphocytes and monocytes (greater than 2000 cells/ml urine). Differentiation between these two clinical conditions was achieved by immunostaining, which revealed that increased numbers of CD25+ and CD8+ cells, as well as an increase in the HLA-DR/Lu5 ratio, were typical of rejection. CD25 positivity proved to be the best indicator of rejection, with a sensitivity and specificity of more than 90%. A cytodiagnostic algorithm is presented that is based on cell numbers and types, including immunophenotypes. The proposed method has the advantage of being noninvasive and appears to represent a reliable and rapid adjunct for the monitoring of graft function, especially in high-risk patients on cyclosporin immunosuppression.

Rejection prophylaxis with interleukin-2 receptor antibody BT 563: mechanisms of action on human cells

We investigated the in vitro immunosuppressive effect of BT 563, a monoclonal antibody, against the alpha-chain of the human interleukin-2 (IL-2) receptor (p 55), which has been used to prevent transplant rejection in several clinical trials. We also measured the proliferative T cell alloresponse and pCTL frequencies of BT563-treated kidney transplant patients. In mixed lymphocyte cultures BT 563 caused a reduction of T cell proliferation to about 50%. This could not be reversed by the addition of exogenous IL-2. A more effective reduction (80%) was seen in the generation of cytotoxic T cells from CML cultures and at the clonal level. The specific T cell response after preincubation with antigen and BT 563 was not reduced so that BT 563 did not induce tolerance. The in vitro findings indicated that BT 563 had a significant but incomplete immunosuppressive effect. This correlated with the clinical course and ex vivo analysis of PBL from BT 563-treated patients after kidney transplantation.

Effects of interleukin 2 receptor b chain (P75)-specific monoclonal antibody on the generation of cytotoxic T lymphocytes and suppressor T cells in mixed lymphocyte culture

The interaction of interleukin 2 (IL-2) with its receptor (IL-2R) plays an essential role in the proliferation and differentiation of T cells. The IL-2R beta-chain is considered to function directly in the intracellular signal transduction. In this study, we investigated using a newly established IL-2R beta-chain-specific monoclonal antibody (MAb) (TU-25) and an IL-2R alpha-chain-specific MAb (H-31). The IL-2-induced proliferation of concanavalin blasts and the mixed lymphocyte reaction (MLR) were suppressed by TU-25 in combination with H-31. This combination had a greater suppressive effect than each of them alone. The generation of cytotoxic T lymphocytes (CTL) using a cell-mediated lympholysis (CML) assay, was not inhibited by TU-25 alone. TU-25 in combination with H-31 suppressed the generation of CTL completely in this assay even if recombinant IL-2 (rIL-2) was added. Although the CTL generation was inhibited, cells that suppressed a fresh MLR were preserved. Our study suggests that the combination of TU-25 with H-31 completely blocks the functional high-affinity binding site of IL-2 but does not inhibit the generation of suppressor cells. This may lead to immunosuppressive therapy using an IL-2R beta-chain-specific MAb in combination with an IL-2R alpha-chain-specific MAb in clinical organ transplantation.

Suppressor cells and T cell synergy in the primary MLR: interleukin-2 is required for the maintenance of rat CD8+ suppressor cells

The requirements for maintenance of allospecific CD8+ Ts cells generated in the rat primary MLR were investigated. Allospecific CD8+ Ts cells rapidly lose their activity over 72 hr in secondary culture with media alone, whereas low concentrations of rIL-2 (less than 1 U/ml) are able to maintain potent CD8+ Ts cell activity. This Ts cell activity is maintained at rIL-2 concentrations which do not result in significant cell proliferation. Therefore, cell proliferation per se is not a requirement to maintain Ts cell activity, although the CD8+ Ts cells can proliferate to rIL2 in a concentration-dependent manner. An anti-IL-2 receptor monoclonal antibody significantly inhibited the maintenance of Ts cell activity. Two-color flow cytometric analysis demonstrated that Ts cells cultured in rIL-2 maintain upregulation of their high-affinity IL-2 receptor. Although allospecific Ts cells maintained in secondary culture with rIL-2 for 48 hr maintained antigen specificity, there is also the induction of an antigen-nonspecific population. After 168 hr in secondary culture the Ts cells have lost allospecificity, although Ts activity can be maintained with rIL2 in continuous culture for up to 4 weeks.

Biochemical analysis of class I and class II MHC antigens in cynomolgus macaques by one-dimensional isoelectric focusing

To obtain a better estimate of major histocompatibility complex (MHC) polymorphism in the Old World macaque, Macaca fascicularis, class I and class II MHC proteins from 42 animals were analyzed by sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) and one-dimensional isoelectric focusing (1D-IEF). The panel represented both related and unrelated animals with a total of at least 30 serologically distinct haplotypes. Cells were sequentially immunoprecipitated with monoclonal antibody (mAb) W6/32 for class I and with mAb L243 for class II molecules, followed by neuraminidase treatment. Both sets of immunoprecipitates yielded 5-7 major bands on IEF. All bands present in offspring were present in at least 1 parent. Siblings which were serologically identical for class I and which were non-stimulatory in mixed lymphocyte culture (MLC) yielded identical IEF patterns for both class I and class II; in other sibling pairs which were serologically identical for class I antigens (Ag), IEF produced convincing evidence that the siblings were indeed nonidentical, or helped to verify that recombination had occurred within the MHC. Specific bands were found which correlated with class I specificities A8, A24, and B25 previously defined by serology. Comparison of serological and biochemical data will broaden our understanding of the MHC in Macaca fascicularis and will increase the potential use of this species in transplantation research, as a model of disease, and for comparative studies.

Pretreatment with cyclosporine and anti-interleukin 2 receptor antibody abrogates the anti-idiotype response in rat recipients of cardiac allografts

A 10-day course with ART-18, a mouse monoclonal antibody (mAb) directed against the rat interleukin 2 receptor (IL-2R), prolongs the survival of (LEW x BN)F1 cardiac allografts in LEW recipients to approximately 3 weeks (acute rejection = 8 days, P less than 0.001). We examined host responses against ART-18 idiotype (Id) and mouse immunoglobulin in recipients immunomodulated with ART-18 mAb. Treatment with ART-18 elicited high titers of anti-Id antibodies 14 days after transplantation. However, naive rats given ART-18 before transplantation showed strong anti-Id responses as early as day 4 after engraftment, coinciding with abrogation of the treatment effect (graft survival, approximately 10 days). Preimmunization with irrelevant mouse IgG, which elicited high titers of anti-IgG, did not influence the efficacy of ART-18 upon graft survival (17 days). The use of cyclosporin A (CsA) in conjunction with ART-18 prior to transplantation suppressed the anti-Id response and led to dramatic graft prolongation (greater than 58 days), with two of five grafts surviving indefinitely. This striking effect of CsA plus ART-18 pretreatment did not depend upon CsA per se, as grafts were rejected within 12 days in animals pretreated with CsA alone; in both groups CsA trough levels were comparable. Moreover, administration of CsA before transplantation in concert with control IgG (instead of ART-18) prompted rejection within 2-4 weeks. Thus, discrete interaction(s) between anti-IL-2R mAb and CsA prior to engraftment induces partial host unresponsiveness/tolerance to anti-IL-2R mAb treatment following transplantation and suppresses the neutralizing anti-Id responses, which results in long-term/permanent graft acceptance. This study provides a strategy to overcome the anti-Id response mounted by graft recipients that otherwise limits the efficacy of anti-IL-2R mAb treatment.

Sequential measurement of the murine acute-phase protein serum amyloid P component (SAP) as an indicator of graft-versus-host disease following allogeneic bone marrow transplantation in mice

Murine models of bone marrow transplantation (BMT) are used commonly for studies of the pathogenesis and treatment of graft-versus-host disease (GVHD). We report here that the sequential measurement of the mouse acute-phase protein SAP can be used to provide a sensitive, quantitative index of the severity of GVHD. Thirty mice underwent allogeneic, and a further 30 syngeneic BMT. GVHD was assessed in vivo by clinical appearances and weight change, and post mortem by histology and calculation of splenic indices. Blood was obtained twice/week for SAP measurement and blood culture. In all mice an initial rise in SAP levels due to irradiation was followed by a return to baseline. Thereafter in syngeneic marrow recipients levels remained low. In contrast, after allogeneic BMT SAP levels rose progressively as mice developed GVHD, reaching a peak of 135 micrograms/ml prior to death, from a nadir at day 20 of 15 micrograms/ml. Mice with high splenic indices and histological evidence of severe GVHD had significantly higher SAP levels than mice with mild GVHD (P = 0.0002). Elevation in SAP levels occurred independently of bacteraemia. We conclude that in murine BMT sequential measurement of SAP provides an objective means of assessing GVHD in vivo.

RO 23-6457 prolongs survival of vascularized allografts in rodents and primates

The ability of RO 23-6457, a retinoid compound with marked in vitro immunosuppressive properties, to prolong vascularized allografts was examined in several in vivo transplantation models. In the murine heterotopic heart model, efficacy was shown in two H-2 incompatible strain combinations, with indefinite graft survival at some doses. In the rat heterotopic heart model, oral administration prolonged Wistar-Furth grafts in Lewis hosts an average of 1 week, with no long-term survivors at a variety of doses. Given subcutaneously, grafts were further prolonged, but the compound proved toxic. In a bilaterally nephrectomized renal transplant model in cynomolgus monkeys treated intravenously at a dose of 2 mg/kg/day, host survival was prolonged to 18, 32, 33, and 74 days, compared with 11, 11, 12, 13, and 26 days in untreated controls (P less than 0.05 by rank-sum testing). The three shorter surviving recipients died from anorexia and weight loss with normal renal function, while the longest survivor rejected its kidney when exhaustion of iv sites precluded further treatment. The toxic effects of the compound resemble the syndrome of hypervitaminosis A. RO 23-6457 will prolong graft survival as a single agent, justifying further preclinical testing and efforts to reduce toxicity.

A humanized antibody that binds to the interleukin 2 receptor

The anti-Tac monoclonal antibody is known to bind to the p55 chain of the human interleukin 2 receptor and to inhibit proliferation of T cells by blocking interleukin 2 binding. However, use of anti-Tac as an immunosuppressant drug would be impaired by the human immune response against this murine antibody. We have therefore constructed a "humanized" antibody by combining the complementarity-determining regions (CDRs) of the anti-Tac antibody with human framework and constant regions. The human framework regions were chosen to maximize homology with the anti-Tac antibody sequence. In addition, a computer model of murine anti-Tac was used to identify several amino acids which, while outside the CDRs, are likely to interact with the CDRs or antigen. These mouse amino acids were also retained in the humanized antibody. The humanized anti-Tac antibody has an affinity for p55 of 3 x 10(9) M-1, about 1/3 that of murine anti-Tac.