Anti-Tac-H, a humanized antibody to the interleukin 2 receptor, prolongs primate cardiac allograft survival

Cytokines in clinical and experimental transplantation

Allograft rejection is a complex process, which requires interactions between different cell types and a variety of soluble factors, such as cytokines. In this review we discuss the role of cytokines in the induction and effector phases of the rejection process and in the induction and maintenance of allospecific graft tolerance. Furthermore, we discuss the feasibility of clinical graft function monitoring by measuring cytokines and the possibilities for intervention in the cytokine network in order to inhibit graft rejection and eventually obtain graft acceptance.

Long term management of liver transplant rejection in children

The current management of hepatic allograft rejection after liver transplantation in children requires effective baseline immunosuppression to prevent rejection and rapid diagnosis and treatment to manage acute rejection episodes. The subsequent impact on chronic rejection is dependent on the combination of adequate prevention and the treatment of acute rejection. Tacrolimus is a macrolide lactone that inhibits the signal transduction of interleukin-2 (IL-2) via calcineurin inhibition. Introduced in 1989, tacrolimus was first used in the salvage of refractory acute or chronic rejection under cyclosporin or to rescue patients with significant cyclosporin-related complications. The majority of paediatric transplant centres use a combination of steroids with tacrolimus as a basic immunosuppressant regimen following paediatric liver transplantation. This combination has allowed the acute cellular rejection-free rate to increase to between 30 and 60%, while lowering the rate of refractory rejection to less than 5%. Corticosteroid-resistant rejection is commonly treated with monoclonal (muromonab CD3) or polyclonal preparations. Although most episodes of acute cellular rejection occur during the first 6 weeks after liver transplant, the appearance of late acute liver allograft rejection must raise the question of noncompliance, especially in the adolescent population. Chronic rejection is becoming increasingly rare under tacrolimus-based immunosuppression. Tacrolimus is effective in reversing refractory acute cellular rejection or early chronic rejection in patients initially treated with cyclosporin-based regimens. Patients with a history of noncompliance as well as children with autoimmune liver disease are at risk of chronic rejection. Retransplantation therapy for chronic rejection has, fortunately, become more rare in the tacrolimus era with only 3% of retransplants being performed for this indication. Newer immunosuppressive agents are further modifying the long term management of liver allograft rejection. These include mycophenolate mofetil, rapamycin and IL-2 antibodies such as daclizumab. The development of these agents is allowing patient-specific immunosuppressive management to minimise rejection as well as the complications related to immunosuppression.

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.

Safety and pharmacokinetics of daclizumab in pediatric renal transplant recipients

This study examined the safety and pharmacokinetics/pharmacodynamics of daclizumab in combination with mycophenolate mofetil (or azathioprine), corticosteroids, and cyclosporine or tacrolimus, in 61 pediatric renal allograft recipients in three age groups: less than or equal to five yr (n = 18), 6-12 yr (n = 18), and 13-17 yr (n = 25). The dosing regimen was daclizumab 1.0 mg/kg before transplantation, followed by four biweekly doses. The pharmacokinetics of daclizumab were described using NONMEM software. Median (range) estimated trough daclizumab levels achieved on day 56 (before dose 5) were 3.88 microg/mL (2.48-8.78), 4.54 microg/mL (1.79-18.7), and 4.94 microg/mL (0.05-10.6) in the less than or equal to five yr (n = 15), 6-12 yr (n = 17), and 13-17 yr (n = 22) age groups, respectively. Steady-state median (range) daclizumab exposures were 2040 mg x h/mL (1585-3778), 2757 mg x h/mL (1873-3494) and 3297 mg x h/mL (1705-6453), respectively. Saturation of the IL-2R occurred rapidly and was maintained for greater than or equal to three months after transplantation. Daclizumab was generally well-tolerated with no acute allergic or anaphylactic reactions, deaths or malignancies during the study. The proportion of patients who developed acute rejection at six and 12 months was 8.5% and 16.7%, respectively. This study shows that adding daclizumab at 1 mg/kg to standard immunosuppressive therapy provides safe and effective IL-2R blockade.

Suppression of the cell-mediated immune response by a Fas-immunoglobulin fusion protein

INTRODUCTION

Immunosuppressive agents must not only be effective in impairing the host's allo-immune response, but should also be selective in targeting only those elements of the immune system activated by the allograft. The fact that allo-activated T cells express surface protein molecules that are not typically present on resting T cells can be exploited to specifically target this population. Fas ligand is one such molecule whose cell surface expression on T cells is dramatically up-regulated upon activation.

METHODS

We constructed a murine fusion protein by linking the extracellular domain of Fas to the Fc region of IgG2a. The rationale being to selectively target activated T cells via binding of its Fas moiety to cell surface Fas ligand, and then to allow the Fc moiety to invoke its usual effector mechanisms resulting in the destruction of the allo-activated T cell. Here, we describe the design and expression of Fas-IgG2a and characterize several key in vitro and in vivo properties of this fusion protein including its ability to impact on both cell-mediated immune responses and cellular apoptotic activity using a murine model of delayed-type hypersensitivity.

RESULTS

In vitro, our Fas-IgG2a construct bound activated T cells via FasL and invoked cytotoxicity. In vivo, it demonstrated a prolonged half-life characteristic of an immunoglobulin-like molecule. Most significantly, it suppressed the cell-mediated immune response and diminished cellular apoptotic activity in lymphoid tissue in our murine model.

CONCLUSION

Fas-IgG2a is a novel agent for delivering target-specific immunosuppression with potential applicability in the transplant setting.

Antileukemic effect of daclizumab in CD25 high-expressing leukemias and impact of tumor burden on antibody dosing

Humanized anti-CD25 antibody, daclizumab, was applied in a pilot study of 10 patients with CD25(+) leukemias and pharmacokinetic/pharmacodynamic properties were characterized. Two widely held concepts - tumor sink accelerating pharmacokinetics and higher antigen expression correlating with target cell clearance - were supported by this first systematic evaluation of these questions with actual human clinical data. A flexi-dosing regimen was validated for maintaining target drug levels in vivo with a wide range of tumor burdens. Daclizumab induced clearance of peripheral leukemic cells when highly positive for CD25, but durable responses were not obtained. If daclizumab will have a role in antileukemic therapy, it may be in minimal disease settings or as a component of a combination regimen, but only when CD25 expression is high.

Anticorps monoclonaux et thérapeutique

More than 25 years after their discovery, monoclonal antibodies are now the most rapid expanding pharmaceutical viable drugs in clinical trials. The emergence of these antibodies was made possible by the development of genetic recombinant techniques. It is now possible to obtain engineered antibodies: chimearic or humanized or fully human monoclonal antibodies via the use of phage display technology or of transgenic mice. These antibodies are tolerable to the human immune system and eleven have been approved for therapeutic by the US Food and Drug Administration (FDA), the majority of them in the past four years. At least an additional 400 monoclonal antibodies are in clinical trials to treat cancer, transplant rejection or to combat autoimmune or infectious diseases. Important advances have been made in the design of highly specific fragment antibodies, fused or not with drugs or radioisotopes, and in the large industrial scale production with different expression systems (bacteria, yeasts, mammalian cells and transgenic plants and animals). In the next future new molecular promising strategies will enhance affinity, stability and expression levels and reduce the price of these engineering monoclonal to permit their use to treat a large number of diseases.

Comparative in vitro study of the immunomodulatory activity of humanized and chimeric anti-CD25 monoclonal antibodies

Humanized or chimeric monoclonal antibodies (MoAbs) directed against the interleukin-2 (IL-2) receptor alpha-chain, CD25, are promising immunosuppressive agents due to improved pharmacokinetic profiles and less toxicity. These MoAbs have been used effectively in preventing and/or treating rejection in solid organ transplantation and are currently under investigation for prevention/treatment of graft-versus-host disease (GvHD) in stem cell transplantation. We analysed the in vitro activities of the chimeric anti-CD25 MoAb basiliximab and the humanized anti-CD25 MoAb daclizumab in various test systems for alloimmune response and T cell activation in comparison to cyclosporin A (CsA) and prednisolone. Anti-CD3- and alloantigen-induced T cell proliferation were decreased significantly by the anti-CD25 MoAbs in a dose-dependent fashion. At a concentration of 10 ng/ml daclizumab and CsA synergistically decreased T cell proliferation of mixed lymphocyte cultures, whereas basiliximab showed only subadditive activity. Simultaneous addition of the anti-CD25 MoAbs and prednisolone did not result in combined activity. Addition of exogenous IL-2 completely overcame the inhibitory effect on T cell proliferation of both anti-CD25 MoAbs, but not that of CsA and prednisolone. Anti-CD25 MoAbs inhibited the generation of antigen-specific cytotoxic T lymphocytes in a limiting dilution assay, whereas they showed no effect on the cytolytic activity of established antigen-specific T cell clones. This in vitro study demonstrates strong immunosuppressive activity by both chimeric and humanized MoAbs against CD25. The combined activity with CsA justifies their early use for prevention rather than treatment of GvHD.

Stability of murine, chimeric and humanized antibodies against pre-S2 surface antigen of hepatitis B virus

We have constructed a humanized antibody with specificity for the pre-S2 surface antigen of hepatitis B virus (HBV) by grafting the complementarity determining regions (CDRs) of parental murine monoclonal antibody (mAb) into human anti-Sm antibody framework regions. The humanized antibody has a substitution at position 94 in a framework region of the heavy chain variable region, and exhibits the same antigen binding affinity as the parental murine monoclonal and chimeric antibodies. In order to assess the stability of these antibodies, thermal inactivation of the parental, chimeric and humanized antibodies was analyzed. Fifty percent inactivation of the chimeric and humanized antibodies was observed at 63.7 degrees C and 68.7 degrees C, respectively, compared to 55.0 degrees C for murine antibody. The humanized antibody also exhibited increased stability against denaturant. Guanidine-induced unfolding monitored by the changes in fluorescence intensity at 360 nm showed that midpoints of the transition of the chimeric and humanized antibodies were 2.47 M and 2.56 M, respectively, whereas that of the murine antibody was 1.36 M.

The meandering 45-year odyssey of a clinical immunologist

My work on basic and clinical immunology has focused on the regulation of the human immune response and how its dysregulation can lead to immunodeficiency, autoimmune, and malignant disorders. The early focus in our laboratory was on pathogenic mechanisms underlying hypogammaglobulinemia. Our demonstration of active suppression by human suppressor T cells changed thinking about the pathogenesis of certain immunodeficiency disorders. Recently we have focused on the cytokines interleukin-2 (IL-2) and IL-15, which have competitive functions in adaptive immune responses. IL-2 is necessary to destroy self-reactive lymphocytes and thus favors peripheral tolerance to self-antigens, whereas IL-15 favors the persistence of lymphocytes involved in the memory and effector responses to invading pathogens but risks the development of inflammatory autoimmune diseases. Our murine anti-Tac monoclonal antibody exploits these differences, as does a humanized form (daclizumab) now approved for the prevention of renal allograft rejection. New forms of therapy directed at IL-2 and IL-15 receptors may be effective against certain neoplastic diseases and autoimmune disorders and in the prevention of allograft rejection.

Development of a quantitative antigen-specific cell-based ELISA for the 7G7/B6 monoclonal antibody directed toward IL-2Ralpha

Interleukin-2 receptor alpha (IL-2Ralpha, CD25) has been identified as a valuable target for immunotherapy. The 7G7/B6 monoclonal antibody, a mouse IgG2a kappa, recognizes an epitope of the IL-2Ralpha peptide, other than that identified by anti-Tac. This antibody is currently being explored for potential therapeutic and diagnostic applications. Here, we show a cell-based enzyme-linked immunosorbent assay (CbELISA) method for quantitative measurement of the binding activity of the 7G7/B6 antibody to the Kit-225-iG3 cell line expressing IL-2Ralpha antigen on the cell surface. The cell- and antigen-specificity of the assay was established using specific cell lines and irrelevant control antibodies. Satisfactory binding curves were demonstrated with Kit-225-iG3 cells grown between 3 and 25 passages in culture and at seed densities of 2 x 10(5)-4 x 10(6) cells/well. The assay shows reproducible dose-response curves in the concentration range of 10-1000 ng/ml. The assay validation data presented here indicate that this CbELISA assay is quantitative, reproducible, robust, precise, and can be used to test the biological activity, lot to lot comparison, and stability of 7G7/B6 monoclonal antibody.

Physiological Mechanisms of Regulating Alloimmunity: Cytokines, CTLA-4, CD25+ Cells, and the Alloreactive T Cell Clone Size

The mechanisms underlying physiological regulation of alloimmune responses remain poorly defined. We investigated the roles of cytokines, CTLA-4, CD25(+) T cells, and apoptosis in regulating alloimmune responses in vivo. Two murine cardiac transplant models were used, B10.D2 (minor mismatch) and C57BL/6 (major mismatch), into BALB/c recipients. Recipients were wild type, STAT4(-/-) (Th1 deficient), or STAT6(-/-) (Th2 deficient) mice. Minor mismatched allografts were accepted spontaneously in approximately 70% of wild type and STAT4(-/-) mice. By contrast, there was significantly shorter graft survival in minor mismatched STAT6(-/-) mice. Either the adoptive transfer of STAT4(-/-) splenocytes or the administration of IL-4Fc fusion protein into STAT6(-/-) mice resulted in long term graft survival. Blocking CTLA-4 signaling accelerated the rejection in all recipients, but was more pronounced in the minor combination. This was accompanied by an increased frequency of alloreactive T cells. Furthermore, CTLA-4 blockade regulated CD4(+) or CD8(+) as well as Th1 or Th2 alloreactive T cells. Finally, while anti-CD25 treatment prolonged graft survival in the major mismatched combination, the same treatment accelerated graft rejection in the minor mismatched group. The latter was associated with an increased frequency of alloreactive T cells and inhibition of T cell apoptosis. These data demonstrate that cytokine regulation, CTLA-4 negative signaling, and T cell apoptosis play critical roles in regulating alloimmunity, especially under conditions where the alloreactive T cell clone size is relatively small.

Drug treatment of clinical problems related to cardiac transplantation

In recent years, several new immunosuppressive agents have become available for the treatment of cardiac transplant recipients. Use of these agents and their potential side effects are reviewed.

Therapeutic applications of monoclonal antibodies

Researchers have sought therapeutic applications for monoclonal antibodies since their development in 1975. However, murine-derived monoclonal antibodies may cause an immunogenic response in human patients, reducing their therapeutic efficacy. Chimeric and humanized antibodies have been developed that are less likely to provoke an immune reaction in human patients than are murine-derived antibodies. Antibody fragments, bispecific antibodies, and antibodies produced through the use of phage display systems and genetically modified plants and animals may aid researchers in developing new uses for monoclonal antibodies in the treatment of disease. Monoclonal antibodies may have a number of promising potential therapeutic applications in the treatment of asthma, autoimmune diseases, cancer, poisoning, septicemia, substance abuse, viral infections, and other diseases.

In vivo pharmacodynamic effects of Hu1D10 (remitogen), a humanized antibody reactive against a polymorphic determinant of HLA-DR expressed on B cells

The humanized monoclonal antibody Hu1D10 (Remitogen, Protein Design Labs, Fremont, CA) recognizes a polymorphic determinant of human leukocyte antigen-DR expressed on the majority of B-cell lymphomas and on normal B cells of most individuals. Hu1D10 mediates complement-mediated cytotoxicity, antibody-dependent cell-mediated cytotoxicity, and apoptosis of 1D10 antigen (Ag)-positive B cells in vitro. The 1D10 Ag is expressed on a variety of tissues but is restricted primarily to lymphocytes, macrophages, and mesenchymal dendritic cells. The safety and pharmacology of Hu1D10 were investigated in rhesus macaques. Animals were prescreened for 1D10 Ag expression on circulating B cells. Sixteen animals received either placebo (4 Ag+ animals), 1 mg/kg Hu1D10 (4 Ag+ animals), or 10 mg/kg Hu1D10 (4 Ag+ animals and 4 Ag- animals) daily via intravenous (i.v.) bolus-injection for 5 consecutive days, and 4 Ag+ animals received 10 mg/kg Hu1D10 via 90 min i.v. infusion x 5 days. Bolus-injection of Hu1D10 resulted in type 1 hypersensitivity reactions in the majority of Ag+ animals and one death due to anaphylaxis. Slow infusion of Hu1D10 was associated with only mild hypersensitivity reactions after the first dose but not subsequent doses. In animals treated with 10 mg/kg Hu1D10 via bolus-injection, the median terminal elimination half-life of Hu1D10 was 2.6 and 8.4 days in Ag+ and Ag- animals, respectively. Administration of Hu1D10 to Ag+ animals resulted in rapid and profound depletion of circulating B cells for 7-10 days following the last dose. No B-cell depletion was observed in Ag- animals, despite slower elimination of Hu1D10. These studies demonstrate that Hu1D10 reacts with antigen-presenting cells in rhesus macaques. It can be safely administered as a slow i.v. infusion but causes severe toxicity when given as a bolus. This study provides the foundation for testing Hu1D10 for the treatment of B-cell malignancies in humans.

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.

A review of modifications to recombinant antibodies: attempt to increase efficacy in oncology applications

Although monoclonal antibodies have high specificity, their usefulness in the clinic, especially against solid tumors, has been limited. This arises in part from the inability of antibody molecules to penetrate into the tumor and kill the tumor cells. In addition, natural cytotoxic effects of antibodies, mediated through complement or Fc receptors, may not be sufficient to kill malignant cells. This review will present some of the antibody modifications used to increase efficacy. Modified recombinant antibodies have been designed to be more cytotoxic (immunotoxins), to increase natural effector functions (bivalent antibodies, antibody-fusion molecules, multimeric antibodies, directed mutations in Fc region), or to pretarget cells for concentration of cytotoxic drugs. This review will also focus on engineering of smaller versions of antibodies that retain specificity (single chain Fvs, Fabs, Fab(2)s, minibodies, domain deleted antibodies) and have increased penetrability of solid tumors. Many of these antibody modifications may result in antigenic compounds which can limit repeat administration. Clinical experiences will be highlighted if information is available.

Preparation and in vivo evaluation of linkers for 211At labeling of humanized anti-Tac

The syntheses, radiolabeling, antibody conjugation, and in vivo evaluation of new linkers for 211At labeling of humanized anti-Tac (Hu-anti-Tac), an antibody to the alpha-chain of the IL-2 receptor (IL-2Ralpha) shown to be a useful target for radioimmunotherapy are described. Synthesis of the organometallic linker precursors is accomplished by reaction of the corresponding bromo- or iodoaryl esters with bis(tributyltin) in the presence of a palladium catalyst. Subsequent conversion to the corresponding N-succinimidyl ester and labeling with 211At of two new linkers, N-succinimidyl 4-[211At]astato-3-methylbenzoate and N-succinimidyl N-(4-[211At]astatophenethyl)succinamate (SAPS), together with the previously reported N-succinimidyl 4-[211At]astatobenzoate and N-succinimidyl 3-[211At]astato-4-methylbenzoate, are each conjugated to Hu-anti-Tac. The plasma survival times of these conjugates are compared to those of directly iodinated (125I) Hu-anti-Tac. The N-succinimidyl N-(4-[211At]astatophenethyl)succinamate compound (SAPS) emerged from this assay as the most viable candidate for 211At-labeling of Hu-anti-Tac. SAPS, along with the directly analogous radio-iodinated reagent, N-succinimidyl N-(4-[125I]astatophenethyl)succinamate (SIPS), are evaluated in a biodistribution study along with directly iodinated (125I) Hu-anti-Tac. Blood clearance and biological accretion results indicate that SAPS is a viable candidate for further evaluation for radioimmunotherapy of cancer.

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.

Advances in interleukin 2 receptor targeted treatment

T cell activation and cellular immune responses are modulated by interleukin 2 (IL2) through binding to its corresponding cell surface receptor. Three forms of the receptor are recognised based on IL2 binding affinity. The high affinity receptor is a heterotrimer composed of alpha, beta, and gamma(c)-polypeptide chains. The 55 kDa alpha-chain also known as the Tac (T cell activation) antigen or CD-25 is a unique subunit of the high affinity IL2 receptor (IL2Ralpha). Resting T cells express few IL2Ralpha, however, when activated, the expression of ILR2alpha rapidly increases. The IL2Ralpha is shed from the cell surface and is measurable in the serum as a 45 kDa soluble form (s-Tac or s-IL2Ralpha). Serum concentrations of s-Tac can be used as a surrogate marker for T cell activation and IL2Ralpha expression. IL2Ralpha is over expressed by T cells in a number of autoimmune diseases, allograft rejection and a variety of lymphoid neoplasms. IL2 induced proliferation of T cells can be inhibited by the murine monoclonal antibody (anti-Tac) directed against the alpha-chain of the IL2R. Through molecular engineering, murine anti-Tac has been humanised reducing its immunogenicity without changing its specificity. Humanised anti-Tac (HAT) has been shown to reduce the incidence of renal and cardiac allograft rejection as well as decrease the severity of graft versus host disease in patients undergoing HLA matched allogeneic bone marrow transplantation. IL2Ralpha targeted treatment with radioimmunoconjugates of anti-Tac and immunotoxins has shown promise in the treatment of CD25 expressing lymphomas.

Successful in vivo blockade of CD25 (high-affinity interleukin 2 receptor) on T cells by administration of humanized anti-Tac antibody to patients with psoriasis

BACKGROUND

Daclizumab is a humanized antibody to the alpha-subunit (CD25) of the interleukin 2 (IL-2) receptor that blocks normal IL-2 binding to this receptor. Because IL-2 is a major stimulus for T-cell growth, blockade of the IL-2 receptor could be useful in treating T-cell-mediated (autoimmune) diseases.

OBJECTIVE

Our purpose was to determine whether adequate concentrations of antibody were achieved in circulating blood and in psoriatic skin lesions to saturate CD25 receptors. We also intended to measure clinical effect and safety of this agent when used alone (without other immunosuppressive drugs) in psoriasis.

METHODS

Nineteen patients with psoriasis in two centers received daclizumab at an initial dose of 2 mg/kg, then 1 mg/kg at weeks 2, 4, 8, and 12. To determine whether CD25 was blocked in vivo, flow cytometric studies measured (1) expression of CD25 on CD3(+) T cells derived from blood and (2) immuno-histochemistry measures of CD25(+) cells done on pretreatment and posttreatment biopsy specimens. Patients were followed up clinically with photographs and Psoriasis Area and Severity Index scores.

RESULTS

This study showed a consistent blockade of CD25 in peripheral blood and tissue during the first 4 weeks of therapy while the dosing was every 2 weeks. Variable desaturation of receptors began after 4 weeks, which correlated with a reversal in disease improvement. Patients with a pretreatment Psoriasis Area and Severity Index score of less than 36 showed a mean reduction in severity by 30% at 8 weeks (P =.02). During the 16 weeks of treatment, a 44.8% decrease in expression of the IL-2 receptor alpha-subunit was found. The absolute T-cell counts were calculated and showed no significant changes during the course of the study. No significant adverse events were produced by daclizumab during this study.

CONCLUSION

We therefore conclude that daclizumab is a well-tolerated agent that blocks CD25 expression in peripheral blood and skin. Furthermore, it may be useful in treating psoriasis in some patients.

Review article: the clinical role of anti-TNFalpha antibody treatment in Crohn's disease

The recent licensing of anti-TNFalpha antibody treatment offers the potential to radically alter the course of severe Crohn's disease using genetically-engineered drugs directed against a specific inflammatory mediator. Controlled randomized trials have demonstrated clinical benefit associated with tissue healing in patients with active intestinal disease and fistulae, often when conventional therapies were unsuccessful. This therapy is expensive, however, and long-term efficacy and safety data are still awaited. This review considers the nature of this therapy and the current evidence for its clinical benefit and adverse effects. The treatment is also considered in the context of available immunosuppressive agents, with suggestions about its practical application.

Prevention of rejection in cardiac transplantation by blockade of the interleukin-2 receptor with a monoclonal antibody

BACKGROUND

Alloantigen-activated T cells express the high-affinity interleukin-2 receptor. Specific blockade of this receptor with the human IgG1 monoclonal antibody daclizumab may prevent rejection of allografts after cardiac transplantation without inducing global immunosuppression.

METHODS

We randomly assigned 55 nonsensitized patients undergoing a first cardiac transplantation to receive either induction therapy with daclizumab (1.0 mg per kilogram of body weight), given intravenously within 24 hours after cardiac-transplantation surgery and every two weeks thereafter, for a total of five doses, or generalized immunosuppressive therapy. Concomitant immunosuppression was achieved in both groups with cyclosporine, mycophenolate mofetil, and prednisone. The primary end points were the incidence and severity of acute rejection, and the length of time to a first episode of biopsy-confirmed rejection.

RESULTS

Of the 55 patients in the study, 28 were randomly assigned to receive daclizumab and 27 served as the control group. During induction therapy, the mean frequency of acute rejection episodes (defined as a histologic grade of 2 or higher according to the classification of the International Society of Heart and Lung Transplants) was 0.64 per patient in the control group and 0.19 per patient in the daclizumab group (P=0.02). Acute rejection developed in 17 of 27 patients in the control group (63 percent), as compared with 5 of 28 patients in the daclizumab group (18 percent; relative risk, 2.8; 95 percent confidence interval, 1.1 to 7.4; P=0.04). Throughout follow-up, there were nine patients with episodes of acute rejection of histologic grade 3 in the control group, as compared with two in the daclizumab group (P= 0.03), and the time to a first episode of rejection was significantly longer in the daclizumab group (P=0.04). There were no adverse reactions to daclizumab and no significant differences between the groups in the incidence of infection or cancer during follow-up.

CONCLUSIONS

Induction therapy with daclizumab safely reduces the frequency and severity of cardiac-allograft rejection during the induction period.

Daclizumab, a humanized anti-interleukin-2 receptor alpha chain antibody, for treatment of acute graft-versus-host disease

Daclizumab, a humanized monoclonal IgG1 directed against the  chain of the interleukin-2 receptor (IL-2R), is a competitive inhibitor of IL-2 on activated lymphocytes. To test the hypothesis that specific inhibition of activated lymphocytes in patients with ongoing acute graft-versus-host disease (GVHD) might ameliorate the process, we treated 43 patients with advanced or steroid-refractory GVHD with daclizumab. The first cohort of 24 patients was treated with daclizumab 1 mg/kg on days 1, 8, 15, 22, and 29. On day 43, the complete response (CR) rate was 29% (95% confidence interval [CI], 13%-51%). Survival on day 120 was 29% (95% CI, 13%-51%). A second cohort of 19 patients was treated with daclizumab 1 mg/kg on days 1, 4, 8, 15, and 22. For these patients, the CR rate on day 43 was 47% (95% CI, 24%-71%), and survival on day 120 was 53% (95% CI, 29%-76%). There were no infusion-related reactions and no serious side effects related to daclizumab. Following treatment, there was a reduction in serum concentrations of soluble IL-2R and peripheral blood CD3 + 25+ lymphocytes, but these changes were not predictive of response. Daclizumab has substantial activity for the treatment of acute GVHD, and the second regimen evaluated is recommended for a controlled study. (Blood, 2000; 95:83-89)

Daclizumab, a humanized anti-interleukin-2 receptor alpha chain antibody, for treatment of acute graft-versus-host disease

Daclizumab, a humanized monoclonal IgG1 directed against the  chain of the interleukin-2 receptor (IL-2R), is a competitive inhibitor of IL-2 on activated lymphocytes. To test the hypothesis that specific inhibition of activated lymphocytes in patients with ongoing acute graft-versus-host disease (GVHD) might ameliorate the process, we treated 43 patients with advanced or steroid-refractory GVHD with daclizumab. The first cohort of 24 patients was treated with daclizumab 1 mg/kg on days 1, 8, 15, 22, and 29. On day 43, the complete response (CR) rate was 29% (95% confidence interval [CI], 13%-51%). Survival on day 120 was 29% (95% CI, 13%-51%). A second cohort of 19 patients was treated with daclizumab 1 mg/kg on days 1, 4, 8, 15, and 22. For these patients, the CR rate on day 43 was 47% (95% CI, 24%-71%), and survival on day 120 was 53% (95% CI, 29%-76%). There were no infusion-related reactions and no serious side effects related to daclizumab. Following treatment, there was a reduction in serum concentrations of soluble IL-2R and peripheral blood CD3 + 25+ lymphocytes, but these changes were not predictive of response. Daclizumab has substantial activity for the treatment of acute GVHD, and the second regimen evaluated is recommended for a controlled study. (Blood, 2000; 95:83-89)

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.

Reduction of acute renal allograft rejection by daclizumab. Daclizumab Double Therapy Study Group

BACKGROUND

Acute rejection is still a major problem in renal transplantation and is one of the most important causes of chronic graft dysfunction and late graft loss. Selective immunosuppression with a humanized antibody against the alpha-chain of the interleukin (IL)-2 receptor (CD25) was evaluated to demonstrate the efficacy of this type of immunoprophylaxis in combination with dual immunosuppression.

METHODS

We studied the effect of daclizumab, a humanized monoclonal antibody against the alpha-chain of the IL-2 receptor, in a randomized double-blind, prospective phase III clinical trial in 275 patients receiving a first cadaveric renal allograft. Among them 111 (83%) in the placebo arm and 116 (82%) in the daclizumab arm received the full regimen of five doses (1.0 mg/kg) every other week. Baseline immunosuppression consisted of cyclosporine and corticosteroids.

RESULTS

At 6 months, 39 (28%) of the patients in the daclizumab group had biopsy-proven rejections, as compared with 63 (47%) in the placebo group (P=0.001). The need for additional antilymphocyte therapy, antithymocyte globulin, antilymphocyte globulin (ATG, ALG, OKT3) was also lower in the daclizumab group (8% vs. 16%, P=0.02), and they required significantly lower mean (+/- SD) cumulative doses of prednisone (3750+/-1981 mg vs. 4438+/-2667 mg in the placebo group, P=0.01). Graft function was significantly better (P=0.02) in the daclizumab group (graft function rate: 58 vs. 51 ml/min, mean) as was patient survival (P=0.01, 99% vs. 94%). No specific adverse events were observed in daclizumab-treated patients. Patients receiving daclizumab experienced fewer cytomegalovirus infections (18% vs. 25%), and none died from severe infectious complications, compared to four patients in the placebo arm. No patient in the daclizumab group had a lymphoproliferative disorder or any other form of immunosuppression-related tumor during the first year after transplant.

CONCLUSIONS

Administration of daclizumab in addition to dual immunosuppression therapy significantly reduced biopsy-proven acute rejection after renal transplantation, improved patient survival, and did not add to the toxicity of the immunosuppressive regimen.

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.

Humanized antibodies as potential therapeutic drugs

BACKGROUND

Antibodies have been used therapeutically to treat a variety of clinical conditions. The introduction of monoclonal antibodies and more recently, engineered humanized antibodies has greatly refined and expanded the therapeutic potential of this modality of treatment.

LEARNING OBJECTIVES

To reinforce the reader's knowledge of the therapeutic application of antibody in the treatment for different diseases. More specifically, to enhance reader's understanding of basic methods employed in the production and clinical use of humanized antibodies.

DATA SOURCE

The MEDLINE database was used to review the humanized antibody related literature.

CONCLUSION

Humanized antibodies provide a novel approach for the treatment of a broad range of diseases. Expanded use will depend on improvement in their efficacy (avidity and specificity), demonstration of their safety, and reduction of their immunogenicity.

IL-6 functions in cynomolgus monkeys blocked by a humanized antibody to human IL-6 receptor

A humanized antibody to the human interleukin-6 receptor (IL-6R), hPM-1, blocked the interleukin-6 (IL-6) functions in normal cynomolgus monkey lymphocytes in vitro. The binding activity of hPM-1 to non-human primate IL-6R was examined in peripheral blood lymphocytes by flow cytometry. PM-1 recognized the IL-6R on T lymphocytes of cynomolgus and rhesus monkeys, but did not on those of marmosets. The homology between human IL-6R and its cynomolgus monkey counterpart was 97.3% in the extracellular domain of the amino acid sequence, as determined by DNA sequencing of the PCR product from peripheral blood mononuclear cells. PM-1 inhibited two functional parameters in vitro in cynomolgus monkeys: (1), T-cell proliferation stimulated by phytohemaglutinin and human IL-6; (2), Immunoglobulin G-production evoked by Staphylococcus aureus Cowan-1- and human IL-6-stimulated B lymphocytes. These data show that hPM-1 binds to and functionally blocks the cynomolgus monkey IL-6 receptors.

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.

Generation and characterization of a humanized antibody with specificity for preS2 surface antigen of hepatitis B virus

For the prevention of hepatitis B virus (HBV) infection, monoclonal antibodies (mAbs) against the surface antigens of HBV would offer several advantages over the current human polyclonal antibody. We have developed a humanized antibody with specificity for the preS2 surface antigen of HBV and evaluated the neutralizing activity of the humanized antibody. The complementarity-determining regions of the heavy and light chains of a murine monoclonal antibody (H8) were grafted onto the variable regions of a highly homologous human anti-Sm antibody, which were then combined with the constant regions of human gamma 1 and kappa, respectively. The affinity of the resulting humanized antibody (Z6B) was about one tenth that of the chimeric antibody. The new version (ZP39) of the humanized antibody, which was constructed by substituting the heavy-chain framework residue at position 94 of the Z6B with original mouse residue, showed almost the same affinity as that of the chimeric antibody. The evaluation of the HBV neutralizing activity of ZP39 using in vitro infection of adult human hepatocyte primary culture by HBV showed that it had a specific activity that was approximately 1000 times higher than commercially available polyclonal hepatitis B immune globulin. We expect that the present humanized antibody will be useful in the prevention of HBV infection.

The promiscuous IL-2/IL-15 receptor: a target for immunotherapy of HTLV-I-associated disorders

Human T-cell lymphotrophic virus I (HTLV-I)-encoded tax plays a role in the early phases of HTLV-I-induced disease by deregulating the expression of the genes that encode interleukin-2 (IL-2) and the multisubunit (IL-2R alpha, IL-2R beta, and IL-2R gamma) IL-2 receptor (IL-2R). However, later in the course of the disease adult T-cell leukemia (ATL), cells no longer produce IL-2 yet continue to express the IL-2R. During studies to define the pathogenic mechanisms that underlie this IL-2-independent proliferation, we defined a cytokine designated IL-T/IL-15 that stimulates T-cell proliferation and requires the expression of IL-2R beta and IL-2R gamma for its action. To exploit the fact that IL-2Rs are present on abnormal T cells in patients with tropical parasitic paraparesis/HTLV-I-associated myelopathy (TSP/HAM) and ATL but not on normal resting cells, different forms of IL-2R-directed therapy have been initiated. Unmodified humanized anti-Tac is being used to treat patient with TSP/HAM. To enhance its effector function for the treatment of ATL anti-Tac was armed with alpha- and beta-emitting radionuclides. In a clinical trial with 90Y-anti-Tac at the doses used (5, 10, and 15 mCi), 9 of the 18 patients with ATL underwent a partial or sustained complete remission. Thus the clinical application of IL-2R-directed therapy using a humanized monoclonal antibody or that antibody armed with radionuclides provides a new perspective for the treatment of autoimmune disorders such as TSP/HAM and certain neoplastic diseases including ATL.

Pharmacokinetics of reshaped MAb 425 in three animal species

The murine monoclonal antibody (MAb) 425 (mMAb 425) directed against the human EGFR (epidermal growth factor receptor) was reshaped (rMAb 425) in order to improve its therapeutical potential in humans. The pharmacokinetic properties of [125I]-mMAb and [125I]-rMAb 425 were compared in three animal species. Whereas the clearance curves of both antibodies decreased biphasically in rats and nude mice bearing human mammary carcinoma, a monophasic decline was observed in Cynomolgus monkeys. Plasma elimination half-lives of murine and reshaped MAb 425 were similar, short in the monkey (26 h for mMAb 425 and 31 h for rMAb 425) and long in rats (240 h for mMAb 425 and 225 h for rMAb 425). In xenografted nude mice however, the half-life of mMAb 425 (203 h) was about twice as long as that of rMAb 425 (124 h). The half-lives of intact rMAb 425 in the three species obtained by ELISA differed at most by a factor of two from those obtained by radioactivity measurements. Biodistribution studies of [125I]-rMAb 425 revealed a tumor/blood ratio of 1.2 on d 1 and 5.1 on d 18, respectively. Fifty-four and thirty-eight percent of the radioactive dose were excreted with urine in nude mice (within 12 d) and rats (within 11 d), respectively. Specific localization of [125I]-rMAb 425 in human mammary carcinoma xenografted to nude mice was demonstrated.

Characterization of murine and humanized anti-CD33, gelonin immunotoxins reactive against myeloid leukemias

M195 antibodies recognize CD33, an antigen present on acute myeloid leukemia blasts as well as some myeloid progenitor cells, but not on the ultimate hematopoietic progenitor stem cell. Immunotoxins (IT) reactive with human myeloid leukemias were constructed by conjugating gelonin, a single-chain ribosome-inactivating protein, to murine and genetically engineered, humanized M195 antibodies via an N-succinimidyl-3-(2-pyridyl-dithio)-propionate linkage. No losses of gelonin cytotoxic activity or M195 binding activity were observed after conjugation of up to two toxin molecules per antibody. Toxin conjugates displayed specific, potent toxicity for CD33+ cells. The murine and humanized IT were not toxic to CD33- cells and were 600 and 4500 times more potent, respectively, than free gelonin in inhibiting CD33+ HL60 cells. Treatment of HL60 cells with 1 micrograms/ml HuM195-gelonin resulted in more than 1000 times lower colony formation; normal bone marrow mononuclear cell colony-forming units treated with HuM195-IT were reduced by a factor of 10. HL60 leukemia cells could be effectively purged from an excess of normal bone marrow cells. Exposure of target cells to IT for as little as 30 min was as effective as continuous exposure of IT for up to 6 days. However, measures of the efficacy of the immunotoxin were directly related to the length of time of observation after IT exposure and were inversely related to cell concentration. M195-gelonin immunoconjugates are potential candidates for therapeutic use in in vivo or ex vivo bone marrow purging for myeloid leukemias.

An assessment of serum and urine soluble interleukin-2 receptor concentrations during renal transplant rejection

During rejection, renal transplant recipients have increased concentrations of soluble interleukin-2 receptors (sIL-2R) in their serum and urine. However, the clinical application of this measurement in the diagnosis of rejection or the assessment of treatment efficacy is limited by the variance of the measurement in sample populations. We examined the serum and urine sIL-2R concentrations in 20 renal transplant recipients, 12 of whom experienced 13 episodes of allograft rejection. There was no statistical difference in the mean serum sIL-2R concentration at the time of rejection compared with the baseline value (2,817 +/- 801 v 1,943 +/- 255 U/mL). By contrast, the urinary excretion rate, expressed as units of sIL-2R per milligram creatinine, was 26.2 +/- 6.4 compared with 14.2 +/- 2.5 (P < 0.05). Furthermore, when urinary sIL-2R was expressed as a fractional excretion (FE), both the absolute measurement (4.4% +/- 1.7%) and the percent increase (+245%) at the time of rejection provided the greatest degree of discrimination of rejection from those values during allograft stability (1.2% +/- .2% and +2.5%, respectively; P < 0.005). We conclude that (1) serum and urine sIL-2R concentrations are affected by a number of factors during rejection; (2) FE calculations of sIL-2R improve discrimination of rejection from graft stability; and (3) serial measurement of sIL-2R excretion may be a useful adjunct to the diagnosis of rejection and, possibly, the subsequent assessment of response to immunotherapy.

Lymphokine receptors: a target for immunotherapy of lymphomas

Lymphoma cells often express lymphokine receptors that provide a target for therapy. For example, malignant cells of patients with HTLV-1-associated adult T-cell leukemia/lymphoma (ATL) express IL-2 receptors. In contrast, normal resting cells do not express the IL-2 receptors identified by the anti-Tac monoclonal antibody. Using the unmodified anti-Tac monoclonal antibody, one-third of the 19 patients treated with ATL have undergone a remission. However, unmodified murine monoclonal antibodies are limited by their immunogenicity and their poor effector functions. To address these issues, we used genetic engineering to produce humanized anti-Tac that contains the complementarity-determining regions from the mouse with the remainder of the antibody derived from human IgG1-kappa. Humanized anti-Tac is dramatically less immunogenic than the murine versions and, in contrast to the parent antibody, manifests antibody-dependent cellular cytotoxicity with human mononuclear cells. To enhance its effector function, anti-Tac was armed with toxins or with alpha- and beta-emitting radionuclides. In a clinical trial with 90Y-anti-Tac, 11 of the 17 patients with ATL underwent a partial or sustained complete remission. Thus, the clinical application of lymphokine-receptor-directed therapy provides a new perspective for treatment of certain lymphomas, including HTLV-1-associated ATL.

A heavy-chain grafted antibody that recognizes the tumor-associated TAG72 antigen

Murine anti-TAG72 antibodies react with more than 85% of human colorectal, gastric and ovarian carcinomas. However, the therapeutic utility of murine antibodies in human is severely restricted by their immunogenicity. The construction of humanized antibodies can potentially circumvent this problem. The latter antibodies can be generated by grafting CDRs from a murine antibody onto human immunoglobulin FRs followed by combining the resultant product with human immunoglobulin constant regions. In this study, we constructed a heavy-chain humanized anti-TAG72 antibody that we designated hmM4. This was achieved by the transplantation of CDRs from the murine VH of the ccM4 antibody into FRs of the human myeloma protein NEWM. The humanized antibody hmM4 retained its binding reactivity for the TAG72 antigen as measured by ELISA and Western blotting analysis respectively. However, it showed considerably less immunoreactivity for the TAG72 antigen than the original chimeric antibody ccM4. These results indicate that the murine anti-TAG72 specificity can be grafted to human immunoglobulin, and that the choice of the human immunoglobulin framework for the grafted antibody may be critical in maintenance of the immunoreactivity.

Pharmacokinetics of an HIV-1 gp120-specific chimeric antibody in patients with HIV-1 disease

The pharmacokinetics of mouse V/human C (gamma 1, kappa) chimeric monoclonal antibody CGP 47 439 specific for the principal neutralizing determinant of human immunodeficiency virus type 1 (HIV-1) was studied in patients with stage IV HIV-1 disease in an open-labeled phase I/IIA trial. Twelve male patients were enrolled and nine completed the study. Patients were divided into three groups according to the extent of CGP 47 439 to bind to gp120 from their viral isolates: undetectable for group 1, modestly reactive for group 2, and strongly reactive for group 3. A first dose of 1, 10, or 25 mg was administered by intravenous infusion to group 1, group 2 and group 3 patients, respectively. The patients then received seven doses of 50, 100, or 200 mg, respectively, every three weeks. CGP 47 439 serum concentrations were determined by an ELISA using monoclonal antibody AB19-4 specific for the idiotope of CGP 47 439. Half an hour after infusion only 25.5-36.1% of the administered antibody was found in the serum, reflecting its rapid distribution in the extravascular space and possibly binding to gp120 antigen in some of the patients. The terminal elimination half-life (T1/2) was 16.2 days in group 1 patients, 9.7 days in group 2 and in group 3 patients 7.5 days and 9.1 days. An antibody response to CGP 47 439 was not a factor in determining elimination rates, because only very low and transient responses were found in three patients. These results suggest that the reactivity of CGP 47 439 with HIV-1 gp120 contributed to its elimination in HIV-1 infected patients.

Influence of syngeneic monoclonal anti-idiotypic antibodies to murine monoclonal antibodies against tumour-associated antigens on the biodistribution of their target antibodies and their fragments

The effect of syngeneic anti-idiotypic (anti-id) antibodies on the biodistribution of three murine monoclonal antibodies (mAb) against human tumour-associated antigens, and also on that of their fragments, has been examined in mice using, as a model system, purified anti-id mAb against three different target mAb. With the IgG2b mAb NCRC-2, pretreatment of mice 24 h previously with its IgG1 anti-id mAb NCRC-60 caused clearance of subsequently administered NCRC-2. With the univalent Fab/c fragment of NCRC-2 there was little effect, even with anti-id to Fab/c pretreatment ratios of 20:1, although immune complexes were present in the circulation. With Fab of NCRC-2, anti-id mAb prolonged blood survival by reducing renal clearance, immune complexes surviving in the circulation. With the IgG1 mAb NCRC-23, immune complexes formed in vivo with the IgG2b anti-id mAb NCRC-59, but with only little hepatic clearance. With the Fab and F(ab')2 fragments of NCRC-23, blood survival was increased in mice pretreated with anti-id mAb, and with Fab this was clearly due to reduced renal clearance. The third mAb, the IgG3 NCRC-48, formed complexes with its IgG2a anti-id mAb NCRC-62, but these survived in the circulation with no accelerated clearance of the target mAb. These results are different from those previously seen with endogenous anti-id responses. They indicate the diversity of effects that anti-id mAb can have on the biodistribution of their target mAb, and emphasise the difficulty of using such anti-id mAb to modulate the pharmacokinetics of target mAb.

Interleukin-4 bypass of the immunosuppressive effect mediated by interleukin-2 receptor antibodies

Numerous studies have demonstrated that the generation of alloreactive effector cells depends on cytokines. Conversely, there is evidence that cytokine metabolism is altered at the clonal level in tolerant chimaeras. This has led to preclinical and clinical studies using antibodies that antagonize interleukin-2 (IL-2), with the hope of achieving immunosuppression and inducing tolerance. Monoclonal antibodies against the alpha-chain (p55) of the human IL-2 receptor are being applied to prevent transplant rejection and graft-versus-host disease in several clinical trials. The antibodies that have been applied clinically so far antagonize the binding of IL-2 to the IL-2 receptor alpha-chain which is part of the high affinity IL-2 receptor, but they do not deplete the receptor-bearing cells. Our study investigates the immunosuppressive effect of monoclonal antibodies against the alpha-chain (p55) and beta-chain (p75). In mixed lymphocyte cultures the p55 antibody causes a reduction in T-cell proliferation to about 50%. The generation of cytotoxic T cells is reduced more effectively (up to 80%). By additional blocking of the IL-2 receptor beta-chain we achieved an additional but still incomplete immunosuppressive effect. Moreover we show that IL-2 receptor-blocked alloreactive T cells escape suppression by using IL-4 as an alternative stimulating signal. To prevent T lymphocytes benefiting from this alternative and thwarting the immunosuppressive effect, cytotoxic IL-2 receptor antibodies that deplete the high affinity receptor-bearing cells are needed.