- Email: [email protected]
Therapeutic monoclonal antibodies
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New drug classes
Therapeutic monoclonal antibodies F C Breedveld The therapeutic potential of monoclonal antibodies (mAb) was quickly realised after the hybridoma technique allowed their development in the mid 1970s. Chimeric humanised and fully humanised mAb can now be made by recombinant engineering. About a quarter of all biotech drugs in development are mAb, and around 30 products are in use or being investigated. Licensed products are available for inhibition of alloimmune and autoimmune reactivity, and for antitumour, antiplatelet, or antiviral therapy. Short-term side-effects are tolerable and as expected, although long-term safety remains to be elucidated. The cost-effectiveness and quality-of-life benefits of the use of mAb in patients who are usually seriously and chronically ill also needs studying. The therapeutic use of mAb is now established, and is perhaps the first example of how the “new biology” and the understanding of underlying molecular mechanisms has benefited patients. Monoclonal antibodies (mAb) are antibodies produced by a single clone of B cells. By contrast with polyclonal antibodies, mAb are monospecific and homogeneous which makes them effective tools in the development of therapies and diagnostics. When the hybridoma technique of Köhler and Milstein was introduced in 1975, its potential clinical use was immediately obvious.1 Yet it took almost a decade before a therapeutic mAb became established in the clinic. The conventional route to derive mAb is to immunise mice. When subsequently the B cells are fused with myeloma cells, a hybridoma is formed and the B cells are immortalised. On selection for the clones that produce the mAb with the desired specificity, hybridomas can produce unlimited quantities of mAb in laboratory animals. For most hybridomas, in-vitro alternatives are now available that eliminate the use of animals in mAb production. Various systems for in-vitro mAb production are available but for the large-scale production of therapeutic mAb the use of hollow fibre systems is required.2 The success of such production systems is dependent on intrinsic characteristics of hybridomas such as cell growth and mAb production activity. Therefore production of large amounts that allow clinical studies is often problematic. Several approaches have been taken to overcome these problems. Developments in the past few years in the fields of phage-display-library technology and expression of recombinant antibodies in heterologous expression systems open up an entirely new perspective for selection and production of mAb. Many new antibodies are being selected and produced in large amounts without animals as an intermediate for the induction of antigen-specific B cells. Recently, recombinant engineering techniques have emerged that permit the construction of mAb customised for the binding site but with possible variations in size, configuration, valence, and effector functions. This design flexibility resulted in the development of chimeric, humanised, and now fully human mAb. mAb-based proteins can also be used to deliver cellular toxins at inflammation or cancer sites. Lancet 2000; 355: 735–40 Department of Rheumatology C4-R, Leiden University Medical Center, PO Box 9600, 2300 RC Leiden, Netherlands (Prof F C Breedveld MD) (e-mail: [email protected])
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Heavy chain
Light chain
CDR 123
Fab IgG Fc
Murine mAb Mouse
Chimeric mAb Human
Humanised mAb
Complementarity determining regions
Structure of mAb and modifications of murine mAb in therapy
mAb structure and function Immunoglobulins consist of two light and two heavy chains composed of different domains (figure). The Fab domain serves as the antigen-binding site; it is made of heavy and light variable chains. The complementaritydetermining regions of the variable chains define the binding site, the structure which is complementary to the epitope on the antigen that can be bound by the antibody. Antibodies achieve diversity due to variations in the aminoacid sequences of the complementaritydetermining regions. The Fc domain structure determines the effector functions of antibodies. Fc domains are necessary for interactions with effector cells or activation of the complement cascade and the different isotypes of immunoglobulins are defined by the structures of immunoglobulin Fc domains. Human IgG1 can in particular trigger the classical complement cascade after binding to cell surfaces. The same isotype is most efficient in promoting antibody-dependent cellular cytotoxity which can be mediated by various leucocytes possessing the appropriate Fc receptors, and this mechanism is a potent mediator of lysis of cells bound by the mAb.
Factors regulating mAb-based targeted therapies Several obstacles to achieving efficacy have been identified for this therapeutic strategy which attempts to
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Monoclonal antibodies registered for therapeutic clinical use Generic name Trade name Company Indication Muromonab Basiliximab
Orthoclone OKT3 Simulect
Janssen-Cilag Novartis
Renal graft rejection Renal graft rejection
Daclizumab
Zenapax
Hoffman-la Roche,
Renal graft rejection
Infliximab Rituzimab Trastuzumab
Remicade Genentech-Roche Herceptin
Centocor Lymphoma* Genentech
Rheumatoid arthritis, Crohn’s disease 375 mg/m2 in four weekly doses Metastatic breast cancer
Abciximab
Reopro
Lilly
Antiplatelet
Synagis
Abbott Laboratories
Antiviral†
Palivizumab
Dose
Route
5 mg per day 20 mg direct before and 4 days after transplantation 1 mg/kg before and 2, 4, 6 and 8 weeks after transplantation 3–10 mg/kg every 4–8 weeks Intravenous 4 mg/kg initially, followed by 2 mg/kg weekly 0·25 mg/kg initially followed by 0·125 g/kg per min 15 mg/kg
Intravenous Intravenous Intravenous Intravenous Intravenous Intravenous Intravenous
*Low-grade and follicular non-Hodgkin lymphoma. †Against respiratory syncytial virus.
induce an unprecedented degree of targeting specificity while using large proteins whose sizes greatly exceed those of conventional drugs. mAb are large proteins and thereby have slower kinetics of distribution than small molecules and more limited tissue-penetration properties. The ability of mAb to penetrate cancers or sites of inflammation is low.3,4 Particularly in the case of antitumour therapy in homogeneous tumours, antigen expression and blood supply limits uniform antibody delivery. The initial clinical trials used murine mAb. The efficacy of these mAb was hampered by three problems: variable ability of the mouse Fc piece to interact with human cellular Fc receptors and accomplish effector function; diminished serum half-life; and the development of human antimouse antibodies (HAMA). The induction of HAMA responses has been postulated to be a major impediment to the success of mAb therapy. There are two types of HAMA responses: antiisotypic and anti-idiotypic. Hence the development of HAMA has two drawbacks: first, retreatment may result in anaphylaxis and allergy; and, second, retreatment may be less effective than previous treatments. These problems can be obviated by combining the variable region of a murine antibody with the constant region of a human antibody (figure) or the production of completely human mAb and the suppression of the immune response by other therapy. Humanised antibodies are less immunogenetic than mouse mAb and more efficient at executing Fc-dependent functions. Fc of a specific immunoglobulin subclass can be chosen to deliver a desirable effect. Hence mAb can be designed to deplete a subset of cells or only to bind to molecules on the cell surface and inhibit their function.5 In addition, chimerisation of mAb will increase persistence of the mAb in the human circulation from 2 days with murine mAb to over 2 weeks with chimeric mAb.
Biological responses Efficacy of any particular mAb depends on several variables. These include the characteristics of the targeted antigen, its function, its cell-surface density and tissue distribution, as well as characteristics of the mAb including fine specificity, avidity, and isotype. The mechanism(s) by which mAb achieve therapeutic effects is often not completely known. Potential mechanisms include: blocking or steric hindrance of the function of the target antigen; cytoxocity to the cell expressing the target antigen, by complement activation or cellular mechanisms; and modulation of the function of the cell by binding to an antigen capable of transducing intracellular signals.
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An additional potential application involves the addition of active compounds to the mAb. mAb used in such immunoconjugates are designed to provide targeting specificity to cytotoxic processes. The toxic payloads used in clinically tested immunoconjugates have included catalytic toxins, chemotherapeutic agents, and radionuclides.4 Another variant of the use of unconjugated mAb is the production of molecules where the Fc region of IgG is linked to a biologically active soluble peptide by molecular biological techniques. Such peptides have the ability to bind and affect the function of a variety of molecules including cytokines or adhesion molecules. The potential mechanisms of action of these immunoglobulin fusion proteins include competitive or non-competitive inhibition for ligand and modulation of ligand function or expression. The best known example is etanercept (Enbrel), an IgG1 fusion protein used for in-vivo blocking of the tumour necrosis factor (TNF) receptor.
Side-effects Potential adverse events may be related to one of three mechanisms: the xenogenetic nature of the mAb used, especially when the mAb is administered without associated immunosuppression; suppression of physiological functions in line with the specificity of the mAb; and activation of inflammatory cells or mediators after binding of the mAb to its target. Sensitisation has been regularly observed in human beings treated with mAb. However, with the mAb so far studied, hypersensitivity reactions leading to clinically evident serum sickness are rare. Suppression of physiological functions with the presently available mAb mainly involves immunosuppression with antilymphocyte mAb and anti-TNF mAb. The exact risk of increased incidence of infections or cancers remains to be determined and has to be compared with the risk of other types of immunosuppression. A common experience in centres that use OKT3 (mAb against CD3 on T cells) and Campath-1H (mAb against CD52 on leucocytes) is that the first injections induce an influenza-like syndrome including chills, headache, pyrexia, vomiting, diarrhoea, tachycardia, respiratory distress, hypotension, and arthralgia. This reaction is spontaneously reversible and is not life-threatening. Such a reaction was also found with other mAb directed against T-cell-surface molecules and to a limited extent also after use of TNF mAb. This reaction was attributed to massive systemic cytokine release resulting from transient activation of T lymphocytes after Fc-receptor-dependent CD3
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cross-linking.6 For Campath-1H the cytokine release seems to be a consequence of ligation of CD16 on natural killer cells. More recent studies have also pointed at the production of complement-activation fragments after OKT3 infusion.7 Complement activation was associated wtih the increased expression of adhesion molecules on neutrophils and with pulmonary haemodynamic changes. This information allows the design of interventions that prevent this reaction, such as the use of mAb that cannot activate complement. In clinical practice, slowing down the infusion rate is often sufficient to allow the treatment to continue.
Current treatments with mAb The potential therapeutic application of mAb created a tremendous interest in the medical and pharamaceutical community. A recent survey suggested that over a quarter of all biotech drugs in development are mAb. Within this group more than 30 chimeric, humanised, or fully human antibodies account for more than 30 products being routinely used or investigated in the clinic for various indications. The most promising and advanced therapeutic strategies include inhibition of alloimmune and autoimmune reactivity, antitumour therapy, antiplatelet therapy, and antiviral therapy. The products that obtained marketing approval by the registration authorities in the USA or Europe will be discussed briefly (panel). Inhibition of alloimmune reactivity After successful clinical trials by multicentre transplant study groups in 1985, the first licence for a mAb was granted by the US Food and Drug Administration for routine use of OKT3 (muromonab CD3), a murine mAb for the prevention of graft rejection in renal transplant patients.8 As first-line or in steroid-resistant rejection therapy, OKT3 has proven efficacious and some studies (but not all) have shown improved graft survival. Because of the risk of infections, reserving OKT3 for steroidresistant rejections is preferred by several centres over first-line use. In the search for more specific immunosuppression with mAb, the interleukin-2 receptor, which is expressed on activated T cells was chosen as a target. Chimeric and humanised mAb, basiliximab (Simulect) and daclizumab (Zenapax) were developed to bind to the interleukin-2 receptor (CD25). These mAb provide immunosuppression by competitive antagonism of interleukin-2 or by elimination of activated T cells. In two large trials, the percentage of patients with biopsy-confirmed acute rejection episodes after renal transplantation was significantly lower with basiliximab 20 mg (administered 2 h before and then 4 days after transplantation surgery, 30 vs 33%, respectively) than placebo (44 vs 46%) at 6 months after surgery.9,10 Daclizumab gave similar results: after 6 months use of two conventional immunosuppressants, acute rejection was 28 and 22% with daclizumab and 47 and 35% with placebo.11,12 Both therapies were well tolerated and not associated with a lymphokine-release syndrome or with an increased frequency of infections. The results of the published trials are encouraging. However, questions on the exact effect of mAb treatment on long-term graft survival and about the cost-effectiveness of mAb treatment for long-term outcome still need to be answered.
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Inhibition of autoimmune reactivity mAb have been investigated as a therapeutic approach for the treatment of autoimmune diseases to target elements of the immune response such as T or B lymphocytes, irrespective of their antigen specificity. This approach seeks to suppress excessive immunopathological responses by removing activated cells, blocking their function, or normalising elevated levels of proinflammatory cytokines. Therapeutic targets with this strategy have included T-cell surface antigens, T-cell activation antigens, molecules involved in T/B cell interaction, adhesion molecules, and cytokines. Recently, the most encouraging clinical results emerged with TNF-blocking therapies in rheumatoid arthritis and Crohn’s disease. TNF is a cytokine produced primarily by activated monocytes and macrophages, with a broad spectrum of biological activities. This enzyme induces vasodilation, increases vascular permeability, activates platelets, and regulates the production of acute phase proteins, other pro-inflammatory cytokines, and mediators of inflammation. TNF is actively produced in various infectious diseases: sepsis, malaria, adult respiratory distress syndrome, and AIDS. TNF is also important in autoimmune inflammatory diseases.13,14 The cytokine is actively produced at the synovial and mucosal sites of inflammation in rheumatoid arthritis and Crohn’s disease. Although soluble TNF receptors are also increasingly detectable, their concentrations are insufficient to neutralise the high levels of TNF present, resulting in persistent TNF bioactivity. Various animal models of arthritis and colitis provide further evidence of a role for TNF in these diseases. mAb against murine TNF prevented the development of collagen-II-induced arthritis and experimental colitis in mice. The chimeric (human-mouse) monoclonal antibody, infliximab (CA2, Remicade), binds to TNF specifically and neutralises its activity. Studies in transgenic mice models that expressed recombinant forms of transmembrane human TNF, which in these animals resulted in polyarthritis or a lethal wasting syndrome, showed that infliximab inhibited the pathological effect mediated by human TNF. Administration of infliximab was of substantial clinical benefit in both rheumatoid arthritis and Crohn’s disease. Preliminary open-label studies in patients with refractory disease led to remarkable clinical improvement and substantial improvement of biochemical and histological measures of disease activity. The first randomised trial of infliximab on rheumatoid arthritis was reported in 1994.15 A single infusion of 1 or 10 mg/kg infliximab was compared with placebo in 73 patients. After 4 weeks 8% of the placebo recipients fulfilled the response criteria compared with 44% and 79% of the low-dose and high-dose treated patients. The major effect of increased dose was on response duration with a median duration of the response in the 1 and 10 mg/kg groups of 3 and 8 weeks, respectively. The duration of response could be directly related to the persistence of circulating infliximab. In a second trial, infliximab in combination with a fixed low-dose of methotrexate in patients with active rheumatoid arthritis, despite methotrexate treatment, showed enhanced degree and duration of efficacy.16 In a recently published, phase III trial 428 patients who had active disease despite treatment with methotrexate were
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randomised to placebo or one of four regimens of infiliximab given every 4 or 8 weeks on a background of the stable dose of methotrexate. At 30 weeks response criteria were achieved in 52–58% of patients receiving infliximab compared with 20% of patients receiving placebo plus methotrexate (p<0·001 for each of the four infliximab regimens versus placebo).17 The analysis of joint radiographs after 1 year of treatment was most remarkable. The scores for joint-space narrowing and bone erosions of hands and feet progressed in the placebo and methotrexate group, an effect that was completely blocked in the infliximab groups.18 Similar anti-inflammatory activity in rheumatoid arthritis was reported for a TNF-receptor IgG-1 fusion protein (etanercept).19 The efficacy of infliximab in Crohn’s disease is based on two placebo-controlled dose-response studies. In the first trial, 108 patients with active disease received either 0, 5, 10, or 20 mg/kg infliximab intravenously.20 The combined response among all infliximab treatment groups (a drop in the CDI by 肁70 points) was 65%, which was significantly (p<0·001) more frequent than the 17% in the placebo group. Most patients reached the response at the second week after the infusion. In another study 94 patients with Crohn’s disease and draining fistulae were given three infusions of placebo or infliximab 5 or 10 mg/kg at weeks 0, 2, and 6.21 Closure of at least 50% of the fistulae was obtained in 67% and 56% of the patients in the 5 and 10 mg/kg groups, respectively, compared with 15% in the placebo group. The median time to response was 14 days in the infliximab group versus 42 days after placebo. In all the infliximab trials active treatment was well tolerated. Withdrawals for adverse events as well as the occurrence of serious adverse events or serious infections did not exceed those in the placebo group. The trials show a favourable efficacy-safety balance of TNFblocking mAb in rheumatoid arthritis and Crohn’s disease. However, observations after long-term treatment are still needed. Experimental evidence suggests that TNF does have a role in host-defence mechanisms against certain infections with organisms such as mycobacteria. Long-term observations in the clinic will be required to establish whether other molecular defence mechanisms can compensate for TNF during long-term blockage. The results of preliminary trials on TNF blockage in other diseases are awaited. These include other autoimmune and inflammatory conditions but also diseases where inflammation is not the dominant clinical feature, such as congestive heart failure. mAb against cancers Many therapeutic strategies have been explored that use mAb or their derivatives in the treatment of cancer, and some promising therapeutic possibilities have already emerged. Rituximab (Mabthera) is the first mAb approved for the treatment of cancer. It is a chimeric IgG-1 mAb directed against CD20 which is a transmembrane protein on pre-B and mature B lymphocytes. This is not strictly specific therapy, but rather the abilation of a specific lineage of malignant and corresponding normal cells with the anticipation that normal cells will be regenerated from normal stem cells. Multicentre studies have demonstrated its efficacy against relapsed low-grade and follicular non-Hodgkin
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lymphoma. In-vitro experiments with rituximab showed its ability to mediate complement-dependent cellular cytotoxicity after binding to human C1q and to activate antibody-dependent cellular cytokines with human effector cells, and, recently, to possess direct antiproliferative and apoptotic activity in some CD20positive cell lines. 166 patients received 375 mg/m2 rituximab in four weekly doses. The overall response rate was 50% in the 161 evaluable patients who had previously received chemotherapy.22 Most adverse events were infusion-related and included low-grade fever and nausea. In addition, combination therapy trials of rituximab and CHOP (cyclophosphamide, doxorubicin, vincristine, prednisone) suggest that rituximab adds therapeutic benefit without causing significant additional toxicity. These trials included both refractory and newly diagnosed patients. PCR can detect the chromosomal translocation BCL-2, which occurs in up to 85% of the follicular lymphomas.23 Conversion of BCL-2-positive peripheral blood to negativity is not seen with CHOP alone, but was seen in patients on CHOP and rituximab. This finding suggests that rituximab may have a role in eradicating residual disease. The combination of CHOP with rituximab appears to be a viable treatment option for relapsed low-grade non-Hodgkin lymphoma. A large number of trials with rituximab for CD20positive neoplasms are currently underway worldwide to determine the optimum conditions in which the mAb exerts its maximal effect. CD52 mAb (Campath-1H) have also been extensively evaluated for their capacity to lyse malignant lymphopoietic cells.24 CD52 mAb provide effective therapy for chronic leukaemias of T-cell or Bcell origin that may be resistant to conventional chemotherapy. For example, most patients with T-cell polylymphocytic leukaemia, including those with a large tumour burden and high peripheral-blood-cell counts, will enter complete remission after using the Campath1H mAb. Another strategy for antitumour therapy with mAb targets growth-factor receptors. Antibodies directed against epidermal-growth-factor receptors directly inhibit the growth of tumours bearing such receptors, in vitro and in vivo. Trastuzumab (Herceptin), a humanised IgG1 mAb targeting the extracellular domain of the HER2 receptor has been investigated in the treatment of breast cancer. In-vitro and in-vivo preclinical studies showed that administration of trastuzumab alone or in combination with cytostatic drugs inhibits the growth of breast-tumour-derived cells. In a single-arm clinical study of 222 patients, treatment with a loading dose of trastuzumab 4 mg/kg intravenously followed by weekly doses of 2 mg/kg produced an overall response rate of 14%.25 In another clinical study 469 women with metastatic breast carcinoma were randomised to a cytostatic regimen with or without trastuzumab.26,27 The overall response rate was significantly greater in the trastuzumab plus chemotherapy group. These promising results represent the most advanced clinical therapy programmes with unconjugated mAb, but a wealth of innovative strategies with recombinant prepared molecules with novel effector functions are in earlier stages of clinical evaluation. Thus far, studies with mAb conjugated to an isotope, drug, or toxin are mostly early and therefore it is too soon to determine the efficacy of these agents. mAb therapy will have a
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significant impact in the management of patients with cancer. The unique specificity of mAb in being able to reach microscopic tumour deposits, outside the reach of surgical intervention, makes them ideal reagents in this regard. Antiplatelet therapy Acute coronary syndromes and percutaneous coronary interventions share a common pathophysiological mechanism of intimal disruption and platelet aggregation. Glycoprotein IIb/IIIa receptor antagonists, which interrupt the final common pathway of platelet activation and aggregation, have clear benefit as acute therapy. Abciximab (Reo-Pro) was the first antagonist to be evaluated in clinical studies. The EPIC trial examined whether an abciximab or placebo bolus combined with a 12-h infusion of abciximab or placebo would reduce ischaemic complications in high-risk patients undergoing angioplasty.28 At 30 days there was a 35% reduction of composite death, myocardial infarction, and urgent revascularisation compared with placebo (8·3 vs 12·8%, p=0·008). Two subsequent studies were stopped because of highly significant benefit with abciximab.29–31 The side-effect spectrum is favourable. Haemorrhagic complications can be prevented by adjustments in the heparin dosage immediately after the procedure. Longterm follow-up of more than 6500 patients treated with abciximab suggests that the mortality benefit increases over a 3-year period. The short-term benefit stems from prevention of fatal myocardial infarctions; the late benefit may result from reductions in early myocardial damage. These unique pharmacological characteristics might also provide benefits in other disabling thrombocytic conditions such as stroke, unstable angina, and acute myocardial infarction. mAb in infectious diseases Many strategies have been explored in the treatment of infectious diseases, particularly in sepsis. At present only palivizumab (Synagis), a humanised mAb directed against respiratory syncytial virus (RSC) has been approved in the treatment of premature infants and infants with bronchopulmonary dysplasia. RSV replication was inhibited by palivizumab both in vitro and ex vivo in tracheal aspirates from infants receiving palivizumab 15 mg/kg.32 In a large multicentre trial in 1502 infants at high risk of RSV infection, palivizumb 15 mg/kg intravenously more than halved the frequency of RSV-attributable admissions to 4·8% compared with 10·6% in placebo recipients.33 The frequency of adverse events was similar in placebo and palivizumab groups. Ongoing studies are planned to allow a more clear definition of the place of palivizumab in the prevention of RSV infections.
accumulate at tumour sites also stimulated studies on the diagnostic use of mAb. In this respect four mAb have been approved for localisation of cancer: Igorvomab for ovarium carcinoma, tecnemab-K-1 for melanoma, and votumab and arcilumomab for colorectal cancer. Sulemab is for detection of the infection. These technical development and the promising results in phase III studies will initiate other studies. Studies on long-term safety will be first. Only properly designed case-control studies supported by international collaboration will show the long-term risks of mAb therapy. Furthermore, the costly long-term administration of mAb awaits data which evaluates the cost of this therapy and the improvement in the quality of life that might follow, set against the cumulative social and health-care costs of current therapies. Such studies will allow an optimum introduction of mAb therapy in clinical practice. The author has been an investigator in trials with infliximab and etanercept.
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Conclusions The initial clinical studies with mAb identified several areas that promise to make significant contributions to the management of patients with various diseases. The promising results of the mAb discussed here represent the most advanced clinical antibody therapy programmes, but a large number of innovative strategies with recombinantly prepared mAb with novel effector functions are in earlier stages of clinical evaluation. Such studies are being done in most clinical disciplines. The ability of mAb to
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Köhler G, Milstein C. Continuous cultures of fused cells secreting antibody of predefined specificity. Nature 1975; 256: 495–97. de Geus B, Hendriksen CFM. In vivo and in vitro production of monoclonal antibodies: current possibilities and future perspectives. Res Immunol 1998; 149: 533–620. Choy EH, Pitzalis C, Cauli A, et al. Percentage of anti-CD4 monoclonal antibody-coated lymphocytes in the rheumatoid joint is associated with clinical improvement: implications for the development of immunotherapeutic dosing regimens. Arthritis Rheum 1996; 39: 52–56. Weiner LM. An overview of monoclonal antibody therapy of cancer. Semin Oncol 1999; 26: 41–50. Waldmann H, Cobbold S. How do monoclonal antibodies induce tolerance? A role for infectious tolerance? Annu Rev Immunol 1998; 16: 619–44. Alegre M-L, Collins AM, Pulito VL, et al. Effect of a single amino acid mutation on the activating and immunosuppressive properties of a “humanised” OKT3 monoclonal antibody. J Immunol 1992; 148: 3461–68. Vallhonrat H, Williams WW, Cosimi AB, et al. In vivo generation of C4d, Bb, iC3v, and SC5b-9 after OKT3 administration in kidney and lung transplant recipients. Transplantation 1999; 67: 253–58. Ortho Multicenter Transplant Study Group. A randomized clinical trial of OKT3 monoclonal antibody for acute rejection of cadaveric renal transplants. N Engl J Med 1985; 313: 337–42. Nashan B, Moore R, Amlot P, et al. Randomised trial of basiliximab versus placebo for control of acute cellular rejection in renal allograft recipients. Lancet 1997; 350: 1193–98. Kahan BD, Rajagopalan PR, Hall M. Reduction of the occurrence of acute cellular rejection among renal allograft recipients treated with basiliximab, a chimeric anti-interleukin-2 receptor monoclonal antibody. Transplantation 1999; 67: 276–84. Vincenti F, Lantz M, Birnbaum J, et al. A phase I trial of humanized anti-interleukin 2 receptor antibody in renal transplantation. Transplantation 1997; 63: 33–38. Nashan B, Light S, Hardie IR, et al. Reduction of acute renal allograft rejection by daclizumab: Daclizumab Double Therapy Study Group. Transplantation 1999; 67: 110–15. Feldmann M, Elliot MJ, Woody JN, Maini RN. Anti-tumor necrosis factor-␣ therapy in rheumatoid arthritis. Adv Immunol 1997; 64: 283–351. van Deventer SJH. Tumor necrosis factor and CD. Gut 1997; 40: 443–48. Elliot MJ, Maini RN, Feldmann M, et al. Randomised double-blind comparison of chimeric monoclonal antibody to tumour necrosis factor ␣ (cA2) versus placebo in rheumatoid arthritis. Lancet 1994; 344: 1105–40. Maini RN, Breedveld FC, Kalden JR, et al. Therapeutic efficacy of multiple intravenous infusions of anti-tumor necrosis factor ␣ monoclonal antibody combined with low-dose weekly methotrexate in rheumatoid arthritis. Arthritis Rheum 1998; 41: 1552–63. Maini RN, St Clair EW, Breedveld FC, et al. Infliximab (chimeric anti-tumour necrosis factor ␣ monoclonal antibody) versus placebo in rheumatoid arthritis patients receiving concomitant methotrexate: a randomised phase III trial. Lancet 1999; 354: 1932–39.
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NEW DRUG CLASSES 18 Lipsky P, St Clair EW, Furst D, et al. 54-week clinical and radiographic results from the ATTRACT trial: a phase III study of infliximab (Remicade™) in patients with active RA despite methotrexate. Arthritis Rheum 1999; 42: S401. 19 Breedveld FC. New tumor necrosis factor-alpha biologic therapies for rheumatoid arthritis. Eur Cytokine Netw 1998; 9: 233–38. 20 Targan SR, Hanauer SB, van Deventer SJH, et al. A short term study of chimeric monoclonal antibody cA2 to tumor necrosis factor ␣ for Crohn’s disease. N Engl J Med 1997; 337: 1029–35. 21 Present DH, Rutgeerts P, Targan S, et al. Infliximab for the treatment of fistulas in patients with Crohn’s disease. N Engl J Med 1999; 340: 1398–405. 22 Laughlin P, Grillo-Lopez AJ, Link BK, et al. Rituximab chimeric anti-CD20 monoclonal antibody therapy for relapsed indolent lymphoma: half of patients respond to a 4-dose treatment programme. J Clin Oncol 1998; 16: 2824–33. 23 Czuczman MS, Grillo-Lopez AJ, White CA, et al. Treatment of patients with low grade B-cell lymphoma with the combination of chimeric anti-CD20 monoclonal antibody and CHOP chemotherapy. J Clin Oncol 1999; 17: 268–76. 24 Dyer MJS. The role of CAMPATH-1 antibodies in the treatment of lymphoid malignancies. Semin Oncol 1999; 26: 52–57. 25 Baselga J, Tripathy D, Mendelsohn J, et al. Phase II study of weekly intravenous recombinant humanized anti-p185HER2 monoclonal antibody in patients with HER2/neu-overexpressing metastatic breast cancer. J Clin Oncol 1996; 14: 737–44. 26 Slamon DJ, Leyland-Jones B, Shak S, et al. Addition of Herceptin (humanized anti-HER2 overexpressing metastatic breast cancer
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(HER2+/MBC) markedly increases anticancer activity: a randomized multinational controlled phase III trial. Proc ASCO 1998; 17: 98 (abstr). Baselga J, Tripathy D, Mendelsohn J, et al. Phase II study of weekly intravenous trastuzumab (Herceptin) in patients with HER2/neuoverexpressing metastatic breast cancer. Semin Oncol 1999; 26: 78–83. Topol EJ, Califf RM, Weisman HF, et al. Randomised trial of coronary intervention with antibody against platelet IIb/IIIa integrin for reduction of clinical restenosis: results at 6 months. Lancet 1994; 343: 881–86. EPILOG Investigators. Platelet glycoprotein IIb/IIIa receptor blockade and low-dose heparin during percutaneous coronary revascularisation. N Engl J Med 1997; 336: 1689–96. CAPTURE Investigators. Randomised placebo-controlled trial of abciximab before and during coronary intervention in refractory unstable angina: the CAPTURE study. Lancet 1997; 349: 1429–35. Hamm CW, Heeschen C, Goldmann B, et al. Benefit of abciximab in patients with refractory unstable angina in relation to serum troponin T levels. c7E3 Fab Antiplatelet Therapy in Unstable Refractory Angina (CAPTURE) Study Investigators. N Engl J Med 1999; 340: 1623–29. Malley R, De Vincenzo J, Ramilo O, et al. Reduction of respiratory syncytial virus (RSV) in tracheal aspirates in intubated infants by use of humanized monoclonal antibody to RSV F protein. J Infect Dis 1998; 178: 1555–61. Impact-RSV Study Group. Palivizumab, a humanized respiratory syncytial virus monoclonal antibody, reduces hospitalization from respiratory syncytial virus infection in high-risk infants. Pediatrics 1998; 102: 531–37.
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Therapeutic monoclonal antibodies F C Breedveld The therapeutic potential of monoclonal antibodies (mAb) was quickly realised after the hybridoma technique allowed their development in the mid 1970s. Chimeric humanised and fully humanised mAb can now be made by recombinant engineering. About a quarter of all biotech drugs in development are mAb, and around 30 products are in use or being investigated. Licensed products are available for inhibition of alloimmune and autoimmune reactivity, and for antitumour, antiplatelet, or antiviral therapy. Short-term side-effects are tolerable and as expected, although long-term safety remains to be elucidated. The cost-effectiveness and quality-of-life benefits of the use of mAb in patients who are usually seriously and chronically ill also needs studying. The therapeutic use of mAb is now established, and is perhaps the first example of how the “new biology” and the understanding of underlying molecular mechanisms has benefited patients. Monoclonal antibodies (mAb) are antibodies produced by a single clone of B cells. By contrast with polyclonal antibodies, mAb are monospecific and homogeneous which makes them effective tools in the development of therapies and diagnostics. When the hybridoma technique of Köhler and Milstein was introduced in 1975, its potential clinical use was immediately obvious.1 Yet it took almost a decade before a therapeutic mAb became established in the clinic. The conventional route to derive mAb is to immunise mice. When subsequently the B cells are fused with myeloma cells, a hybridoma is formed and the B cells are immortalised. On selection for the clones that produce the mAb with the desired specificity, hybridomas can produce unlimited quantities of mAb in laboratory animals. For most hybridomas, in-vitro alternatives are now available that eliminate the use of animals in mAb production. Various systems for in-vitro mAb production are available but for the large-scale production of therapeutic mAb the use of hollow fibre systems is required.2 The success of such production systems is dependent on intrinsic characteristics of hybridomas such as cell growth and mAb production activity. Therefore production of large amounts that allow clinical studies is often problematic. Several approaches have been taken to overcome these problems. Developments in the past few years in the fields of phage-display-library technology and expression of recombinant antibodies in heterologous expression systems open up an entirely new perspective for selection and production of mAb. Many new antibodies are being selected and produced in large amounts without animals as an intermediate for the induction of antigen-specific B cells. Recently, recombinant engineering techniques have emerged that permit the construction of mAb customised for the binding site but with possible variations in size, configuration, valence, and effector functions. This design flexibility resulted in the development of chimeric, humanised, and now fully human mAb. mAb-based proteins can also be used to deliver cellular toxins at inflammation or cancer sites. Lancet 2000; 355: 735–40 Department of Rheumatology C4-R, Leiden University Medical Center, PO Box 9600, 2300 RC Leiden, Netherlands (Prof F C Breedveld MD) (e-mail: [email protected])
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Heavy chain
Light chain
CDR 123
Fab IgG Fc
Murine mAb Mouse
Chimeric mAb Human
Humanised mAb
Complementarity determining regions
Structure of mAb and modifications of murine mAb in therapy
mAb structure and function Immunoglobulins consist of two light and two heavy chains composed of different domains (figure). The Fab domain serves as the antigen-binding site; it is made of heavy and light variable chains. The complementaritydetermining regions of the variable chains define the binding site, the structure which is complementary to the epitope on the antigen that can be bound by the antibody. Antibodies achieve diversity due to variations in the aminoacid sequences of the complementaritydetermining regions. The Fc domain structure determines the effector functions of antibodies. Fc domains are necessary for interactions with effector cells or activation of the complement cascade and the different isotypes of immunoglobulins are defined by the structures of immunoglobulin Fc domains. Human IgG1 can in particular trigger the classical complement cascade after binding to cell surfaces. The same isotype is most efficient in promoting antibody-dependent cellular cytotoxity which can be mediated by various leucocytes possessing the appropriate Fc receptors, and this mechanism is a potent mediator of lysis of cells bound by the mAb.
Factors regulating mAb-based targeted therapies Several obstacles to achieving efficacy have been identified for this therapeutic strategy which attempts to
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Monoclonal antibodies registered for therapeutic clinical use Generic name Trade name Company Indication Muromonab Basiliximab
Orthoclone OKT3 Simulect
Janssen-Cilag Novartis
Renal graft rejection Renal graft rejection
Daclizumab
Zenapax
Hoffman-la Roche,
Renal graft rejection
Infliximab Rituzimab Trastuzumab
Remicade Genentech-Roche Herceptin
Centocor Lymphoma* Genentech
Rheumatoid arthritis, Crohn’s disease 375 mg/m2 in four weekly doses Metastatic breast cancer
Abciximab
Reopro
Lilly
Antiplatelet
Synagis
Abbott Laboratories
Antiviral†
Palivizumab
Dose
Route
5 mg per day 20 mg direct before and 4 days after transplantation 1 mg/kg before and 2, 4, 6 and 8 weeks after transplantation 3–10 mg/kg every 4–8 weeks Intravenous 4 mg/kg initially, followed by 2 mg/kg weekly 0·25 mg/kg initially followed by 0·125 g/kg per min 15 mg/kg
Intravenous Intravenous Intravenous Intravenous Intravenous Intravenous Intravenous
*Low-grade and follicular non-Hodgkin lymphoma. †Against respiratory syncytial virus.
induce an unprecedented degree of targeting specificity while using large proteins whose sizes greatly exceed those of conventional drugs. mAb are large proteins and thereby have slower kinetics of distribution than small molecules and more limited tissue-penetration properties. The ability of mAb to penetrate cancers or sites of inflammation is low.3,4 Particularly in the case of antitumour therapy in homogeneous tumours, antigen expression and blood supply limits uniform antibody delivery. The initial clinical trials used murine mAb. The efficacy of these mAb was hampered by three problems: variable ability of the mouse Fc piece to interact with human cellular Fc receptors and accomplish effector function; diminished serum half-life; and the development of human antimouse antibodies (HAMA). The induction of HAMA responses has been postulated to be a major impediment to the success of mAb therapy. There are two types of HAMA responses: antiisotypic and anti-idiotypic. Hence the development of HAMA has two drawbacks: first, retreatment may result in anaphylaxis and allergy; and, second, retreatment may be less effective than previous treatments. These problems can be obviated by combining the variable region of a murine antibody with the constant region of a human antibody (figure) or the production of completely human mAb and the suppression of the immune response by other therapy. Humanised antibodies are less immunogenetic than mouse mAb and more efficient at executing Fc-dependent functions. Fc of a specific immunoglobulin subclass can be chosen to deliver a desirable effect. Hence mAb can be designed to deplete a subset of cells or only to bind to molecules on the cell surface and inhibit their function.5 In addition, chimerisation of mAb will increase persistence of the mAb in the human circulation from 2 days with murine mAb to over 2 weeks with chimeric mAb.
Biological responses Efficacy of any particular mAb depends on several variables. These include the characteristics of the targeted antigen, its function, its cell-surface density and tissue distribution, as well as characteristics of the mAb including fine specificity, avidity, and isotype. The mechanism(s) by which mAb achieve therapeutic effects is often not completely known. Potential mechanisms include: blocking or steric hindrance of the function of the target antigen; cytoxocity to the cell expressing the target antigen, by complement activation or cellular mechanisms; and modulation of the function of the cell by binding to an antigen capable of transducing intracellular signals.
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An additional potential application involves the addition of active compounds to the mAb. mAb used in such immunoconjugates are designed to provide targeting specificity to cytotoxic processes. The toxic payloads used in clinically tested immunoconjugates have included catalytic toxins, chemotherapeutic agents, and radionuclides.4 Another variant of the use of unconjugated mAb is the production of molecules where the Fc region of IgG is linked to a biologically active soluble peptide by molecular biological techniques. Such peptides have the ability to bind and affect the function of a variety of molecules including cytokines or adhesion molecules. The potential mechanisms of action of these immunoglobulin fusion proteins include competitive or non-competitive inhibition for ligand and modulation of ligand function or expression. The best known example is etanercept (Enbrel), an IgG1 fusion protein used for in-vivo blocking of the tumour necrosis factor (TNF) receptor.
Side-effects Potential adverse events may be related to one of three mechanisms: the xenogenetic nature of the mAb used, especially when the mAb is administered without associated immunosuppression; suppression of physiological functions in line with the specificity of the mAb; and activation of inflammatory cells or mediators after binding of the mAb to its target. Sensitisation has been regularly observed in human beings treated with mAb. However, with the mAb so far studied, hypersensitivity reactions leading to clinically evident serum sickness are rare. Suppression of physiological functions with the presently available mAb mainly involves immunosuppression with antilymphocyte mAb and anti-TNF mAb. The exact risk of increased incidence of infections or cancers remains to be determined and has to be compared with the risk of other types of immunosuppression. A common experience in centres that use OKT3 (mAb against CD3 on T cells) and Campath-1H (mAb against CD52 on leucocytes) is that the first injections induce an influenza-like syndrome including chills, headache, pyrexia, vomiting, diarrhoea, tachycardia, respiratory distress, hypotension, and arthralgia. This reaction is spontaneously reversible and is not life-threatening. Such a reaction was also found with other mAb directed against T-cell-surface molecules and to a limited extent also after use of TNF mAb. This reaction was attributed to massive systemic cytokine release resulting from transient activation of T lymphocytes after Fc-receptor-dependent CD3
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cross-linking.6 For Campath-1H the cytokine release seems to be a consequence of ligation of CD16 on natural killer cells. More recent studies have also pointed at the production of complement-activation fragments after OKT3 infusion.7 Complement activation was associated wtih the increased expression of adhesion molecules on neutrophils and with pulmonary haemodynamic changes. This information allows the design of interventions that prevent this reaction, such as the use of mAb that cannot activate complement. In clinical practice, slowing down the infusion rate is often sufficient to allow the treatment to continue.
Current treatments with mAb The potential therapeutic application of mAb created a tremendous interest in the medical and pharamaceutical community. A recent survey suggested that over a quarter of all biotech drugs in development are mAb. Within this group more than 30 chimeric, humanised, or fully human antibodies account for more than 30 products being routinely used or investigated in the clinic for various indications. The most promising and advanced therapeutic strategies include inhibition of alloimmune and autoimmune reactivity, antitumour therapy, antiplatelet therapy, and antiviral therapy. The products that obtained marketing approval by the registration authorities in the USA or Europe will be discussed briefly (panel). Inhibition of alloimmune reactivity After successful clinical trials by multicentre transplant study groups in 1985, the first licence for a mAb was granted by the US Food and Drug Administration for routine use of OKT3 (muromonab CD3), a murine mAb for the prevention of graft rejection in renal transplant patients.8 As first-line or in steroid-resistant rejection therapy, OKT3 has proven efficacious and some studies (but not all) have shown improved graft survival. Because of the risk of infections, reserving OKT3 for steroidresistant rejections is preferred by several centres over first-line use. In the search for more specific immunosuppression with mAb, the interleukin-2 receptor, which is expressed on activated T cells was chosen as a target. Chimeric and humanised mAb, basiliximab (Simulect) and daclizumab (Zenapax) were developed to bind to the interleukin-2 receptor (CD25). These mAb provide immunosuppression by competitive antagonism of interleukin-2 or by elimination of activated T cells. In two large trials, the percentage of patients with biopsy-confirmed acute rejection episodes after renal transplantation was significantly lower with basiliximab 20 mg (administered 2 h before and then 4 days after transplantation surgery, 30 vs 33%, respectively) than placebo (44 vs 46%) at 6 months after surgery.9,10 Daclizumab gave similar results: after 6 months use of two conventional immunosuppressants, acute rejection was 28 and 22% with daclizumab and 47 and 35% with placebo.11,12 Both therapies were well tolerated and not associated with a lymphokine-release syndrome or with an increased frequency of infections. The results of the published trials are encouraging. However, questions on the exact effect of mAb treatment on long-term graft survival and about the cost-effectiveness of mAb treatment for long-term outcome still need to be answered.
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Inhibition of autoimmune reactivity mAb have been investigated as a therapeutic approach for the treatment of autoimmune diseases to target elements of the immune response such as T or B lymphocytes, irrespective of their antigen specificity. This approach seeks to suppress excessive immunopathological responses by removing activated cells, blocking their function, or normalising elevated levels of proinflammatory cytokines. Therapeutic targets with this strategy have included T-cell surface antigens, T-cell activation antigens, molecules involved in T/B cell interaction, adhesion molecules, and cytokines. Recently, the most encouraging clinical results emerged with TNF-blocking therapies in rheumatoid arthritis and Crohn’s disease. TNF is a cytokine produced primarily by activated monocytes and macrophages, with a broad spectrum of biological activities. This enzyme induces vasodilation, increases vascular permeability, activates platelets, and regulates the production of acute phase proteins, other pro-inflammatory cytokines, and mediators of inflammation. TNF is actively produced in various infectious diseases: sepsis, malaria, adult respiratory distress syndrome, and AIDS. TNF is also important in autoimmune inflammatory diseases.13,14 The cytokine is actively produced at the synovial and mucosal sites of inflammation in rheumatoid arthritis and Crohn’s disease. Although soluble TNF receptors are also increasingly detectable, their concentrations are insufficient to neutralise the high levels of TNF present, resulting in persistent TNF bioactivity. Various animal models of arthritis and colitis provide further evidence of a role for TNF in these diseases. mAb against murine TNF prevented the development of collagen-II-induced arthritis and experimental colitis in mice. The chimeric (human-mouse) monoclonal antibody, infliximab (CA2, Remicade), binds to TNF specifically and neutralises its activity. Studies in transgenic mice models that expressed recombinant forms of transmembrane human TNF, which in these animals resulted in polyarthritis or a lethal wasting syndrome, showed that infliximab inhibited the pathological effect mediated by human TNF. Administration of infliximab was of substantial clinical benefit in both rheumatoid arthritis and Crohn’s disease. Preliminary open-label studies in patients with refractory disease led to remarkable clinical improvement and substantial improvement of biochemical and histological measures of disease activity. The first randomised trial of infliximab on rheumatoid arthritis was reported in 1994.15 A single infusion of 1 or 10 mg/kg infliximab was compared with placebo in 73 patients. After 4 weeks 8% of the placebo recipients fulfilled the response criteria compared with 44% and 79% of the low-dose and high-dose treated patients. The major effect of increased dose was on response duration with a median duration of the response in the 1 and 10 mg/kg groups of 3 and 8 weeks, respectively. The duration of response could be directly related to the persistence of circulating infliximab. In a second trial, infliximab in combination with a fixed low-dose of methotrexate in patients with active rheumatoid arthritis, despite methotrexate treatment, showed enhanced degree and duration of efficacy.16 In a recently published, phase III trial 428 patients who had active disease despite treatment with methotrexate were
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randomised to placebo or one of four regimens of infiliximab given every 4 or 8 weeks on a background of the stable dose of methotrexate. At 30 weeks response criteria were achieved in 52–58% of patients receiving infliximab compared with 20% of patients receiving placebo plus methotrexate (p<0·001 for each of the four infliximab regimens versus placebo).17 The analysis of joint radiographs after 1 year of treatment was most remarkable. The scores for joint-space narrowing and bone erosions of hands and feet progressed in the placebo and methotrexate group, an effect that was completely blocked in the infliximab groups.18 Similar anti-inflammatory activity in rheumatoid arthritis was reported for a TNF-receptor IgG-1 fusion protein (etanercept).19 The efficacy of infliximab in Crohn’s disease is based on two placebo-controlled dose-response studies. In the first trial, 108 patients with active disease received either 0, 5, 10, or 20 mg/kg infliximab intravenously.20 The combined response among all infliximab treatment groups (a drop in the CDI by 肁70 points) was 65%, which was significantly (p<0·001) more frequent than the 17% in the placebo group. Most patients reached the response at the second week after the infusion. In another study 94 patients with Crohn’s disease and draining fistulae were given three infusions of placebo or infliximab 5 or 10 mg/kg at weeks 0, 2, and 6.21 Closure of at least 50% of the fistulae was obtained in 67% and 56% of the patients in the 5 and 10 mg/kg groups, respectively, compared with 15% in the placebo group. The median time to response was 14 days in the infliximab group versus 42 days after placebo. In all the infliximab trials active treatment was well tolerated. Withdrawals for adverse events as well as the occurrence of serious adverse events or serious infections did not exceed those in the placebo group. The trials show a favourable efficacy-safety balance of TNFblocking mAb in rheumatoid arthritis and Crohn’s disease. However, observations after long-term treatment are still needed. Experimental evidence suggests that TNF does have a role in host-defence mechanisms against certain infections with organisms such as mycobacteria. Long-term observations in the clinic will be required to establish whether other molecular defence mechanisms can compensate for TNF during long-term blockage. The results of preliminary trials on TNF blockage in other diseases are awaited. These include other autoimmune and inflammatory conditions but also diseases where inflammation is not the dominant clinical feature, such as congestive heart failure. mAb against cancers Many therapeutic strategies have been explored that use mAb or their derivatives in the treatment of cancer, and some promising therapeutic possibilities have already emerged. Rituximab (Mabthera) is the first mAb approved for the treatment of cancer. It is a chimeric IgG-1 mAb directed against CD20 which is a transmembrane protein on pre-B and mature B lymphocytes. This is not strictly specific therapy, but rather the abilation of a specific lineage of malignant and corresponding normal cells with the anticipation that normal cells will be regenerated from normal stem cells. Multicentre studies have demonstrated its efficacy against relapsed low-grade and follicular non-Hodgkin
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lymphoma. In-vitro experiments with rituximab showed its ability to mediate complement-dependent cellular cytotoxicity after binding to human C1q and to activate antibody-dependent cellular cytokines with human effector cells, and, recently, to possess direct antiproliferative and apoptotic activity in some CD20positive cell lines. 166 patients received 375 mg/m2 rituximab in four weekly doses. The overall response rate was 50% in the 161 evaluable patients who had previously received chemotherapy.22 Most adverse events were infusion-related and included low-grade fever and nausea. In addition, combination therapy trials of rituximab and CHOP (cyclophosphamide, doxorubicin, vincristine, prednisone) suggest that rituximab adds therapeutic benefit without causing significant additional toxicity. These trials included both refractory and newly diagnosed patients. PCR can detect the chromosomal translocation BCL-2, which occurs in up to 85% of the follicular lymphomas.23 Conversion of BCL-2-positive peripheral blood to negativity is not seen with CHOP alone, but was seen in patients on CHOP and rituximab. This finding suggests that rituximab may have a role in eradicating residual disease. The combination of CHOP with rituximab appears to be a viable treatment option for relapsed low-grade non-Hodgkin lymphoma. A large number of trials with rituximab for CD20positive neoplasms are currently underway worldwide to determine the optimum conditions in which the mAb exerts its maximal effect. CD52 mAb (Campath-1H) have also been extensively evaluated for their capacity to lyse malignant lymphopoietic cells.24 CD52 mAb provide effective therapy for chronic leukaemias of T-cell or Bcell origin that may be resistant to conventional chemotherapy. For example, most patients with T-cell polylymphocytic leukaemia, including those with a large tumour burden and high peripheral-blood-cell counts, will enter complete remission after using the Campath1H mAb. Another strategy for antitumour therapy with mAb targets growth-factor receptors. Antibodies directed against epidermal-growth-factor receptors directly inhibit the growth of tumours bearing such receptors, in vitro and in vivo. Trastuzumab (Herceptin), a humanised IgG1 mAb targeting the extracellular domain of the HER2 receptor has been investigated in the treatment of breast cancer. In-vitro and in-vivo preclinical studies showed that administration of trastuzumab alone or in combination with cytostatic drugs inhibits the growth of breast-tumour-derived cells. In a single-arm clinical study of 222 patients, treatment with a loading dose of trastuzumab 4 mg/kg intravenously followed by weekly doses of 2 mg/kg produced an overall response rate of 14%.25 In another clinical study 469 women with metastatic breast carcinoma were randomised to a cytostatic regimen with or without trastuzumab.26,27 The overall response rate was significantly greater in the trastuzumab plus chemotherapy group. These promising results represent the most advanced clinical therapy programmes with unconjugated mAb, but a wealth of innovative strategies with recombinant prepared molecules with novel effector functions are in earlier stages of clinical evaluation. Thus far, studies with mAb conjugated to an isotope, drug, or toxin are mostly early and therefore it is too soon to determine the efficacy of these agents. mAb therapy will have a
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significant impact in the management of patients with cancer. The unique specificity of mAb in being able to reach microscopic tumour deposits, outside the reach of surgical intervention, makes them ideal reagents in this regard. Antiplatelet therapy Acute coronary syndromes and percutaneous coronary interventions share a common pathophysiological mechanism of intimal disruption and platelet aggregation. Glycoprotein IIb/IIIa receptor antagonists, which interrupt the final common pathway of platelet activation and aggregation, have clear benefit as acute therapy. Abciximab (Reo-Pro) was the first antagonist to be evaluated in clinical studies. The EPIC trial examined whether an abciximab or placebo bolus combined with a 12-h infusion of abciximab or placebo would reduce ischaemic complications in high-risk patients undergoing angioplasty.28 At 30 days there was a 35% reduction of composite death, myocardial infarction, and urgent revascularisation compared with placebo (8·3 vs 12·8%, p=0·008). Two subsequent studies were stopped because of highly significant benefit with abciximab.29–31 The side-effect spectrum is favourable. Haemorrhagic complications can be prevented by adjustments in the heparin dosage immediately after the procedure. Longterm follow-up of more than 6500 patients treated with abciximab suggests that the mortality benefit increases over a 3-year period. The short-term benefit stems from prevention of fatal myocardial infarctions; the late benefit may result from reductions in early myocardial damage. These unique pharmacological characteristics might also provide benefits in other disabling thrombocytic conditions such as stroke, unstable angina, and acute myocardial infarction. mAb in infectious diseases Many strategies have been explored in the treatment of infectious diseases, particularly in sepsis. At present only palivizumab (Synagis), a humanised mAb directed against respiratory syncytial virus (RSC) has been approved in the treatment of premature infants and infants with bronchopulmonary dysplasia. RSV replication was inhibited by palivizumab both in vitro and ex vivo in tracheal aspirates from infants receiving palivizumab 15 mg/kg.32 In a large multicentre trial in 1502 infants at high risk of RSV infection, palivizumb 15 mg/kg intravenously more than halved the frequency of RSV-attributable admissions to 4·8% compared with 10·6% in placebo recipients.33 The frequency of adverse events was similar in placebo and palivizumab groups. Ongoing studies are planned to allow a more clear definition of the place of palivizumab in the prevention of RSV infections.
accumulate at tumour sites also stimulated studies on the diagnostic use of mAb. In this respect four mAb have been approved for localisation of cancer: Igorvomab for ovarium carcinoma, tecnemab-K-1 for melanoma, and votumab and arcilumomab for colorectal cancer. Sulemab is for detection of the infection. These technical development and the promising results in phase III studies will initiate other studies. Studies on long-term safety will be first. Only properly designed case-control studies supported by international collaboration will show the long-term risks of mAb therapy. Furthermore, the costly long-term administration of mAb awaits data which evaluates the cost of this therapy and the improvement in the quality of life that might follow, set against the cumulative social and health-care costs of current therapies. Such studies will allow an optimum introduction of mAb therapy in clinical practice. The author has been an investigator in trials with infliximab and etanercept.
References 1 2
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Conclusions The initial clinical studies with mAb identified several areas that promise to make significant contributions to the management of patients with various diseases. The promising results of the mAb discussed here represent the most advanced clinical antibody therapy programmes, but a large number of innovative strategies with recombinantly prepared mAb with novel effector functions are in earlier stages of clinical evaluation. Such studies are being done in most clinical disciplines. The ability of mAb to
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Köhler G, Milstein C. Continuous cultures of fused cells secreting antibody of predefined specificity. Nature 1975; 256: 495–97. de Geus B, Hendriksen CFM. In vivo and in vitro production of monoclonal antibodies: current possibilities and future perspectives. Res Immunol 1998; 149: 533–620. Choy EH, Pitzalis C, Cauli A, et al. Percentage of anti-CD4 monoclonal antibody-coated lymphocytes in the rheumatoid joint is associated with clinical improvement: implications for the development of immunotherapeutic dosing regimens. Arthritis Rheum 1996; 39: 52–56. Weiner LM. An overview of monoclonal antibody therapy of cancer. Semin Oncol 1999; 26: 41–50. Waldmann H, Cobbold S. How do monoclonal antibodies induce tolerance? A role for infectious tolerance? Annu Rev Immunol 1998; 16: 619–44. Alegre M-L, Collins AM, Pulito VL, et al. Effect of a single amino acid mutation on the activating and immunosuppressive properties of a “humanised” OKT3 monoclonal antibody. J Immunol 1992; 148: 3461–68. Vallhonrat H, Williams WW, Cosimi AB, et al. In vivo generation of C4d, Bb, iC3v, and SC5b-9 after OKT3 administration in kidney and lung transplant recipients. Transplantation 1999; 67: 253–58. Ortho Multicenter Transplant Study Group. A randomized clinical trial of OKT3 monoclonal antibody for acute rejection of cadaveric renal transplants. N Engl J Med 1985; 313: 337–42. Nashan B, Moore R, Amlot P, et al. Randomised trial of basiliximab versus placebo for control of acute cellular rejection in renal allograft recipients. Lancet 1997; 350: 1193–98. Kahan BD, Rajagopalan PR, Hall M. Reduction of the occurrence of acute cellular rejection among renal allograft recipients treated with basiliximab, a chimeric anti-interleukin-2 receptor monoclonal antibody. Transplantation 1999; 67: 276–84. Vincenti F, Lantz M, Birnbaum J, et al. A phase I trial of humanized anti-interleukin 2 receptor antibody in renal transplantation. Transplantation 1997; 63: 33–38. Nashan B, Light S, Hardie IR, et al. Reduction of acute renal allograft rejection by daclizumab: Daclizumab Double Therapy Study Group. Transplantation 1999; 67: 110–15. Feldmann M, Elliot MJ, Woody JN, Maini RN. Anti-tumor necrosis factor-␣ therapy in rheumatoid arthritis. Adv Immunol 1997; 64: 283–351. van Deventer SJH. Tumor necrosis factor and CD. Gut 1997; 40: 443–48. Elliot MJ, Maini RN, Feldmann M, et al. Randomised double-blind comparison of chimeric monoclonal antibody to tumour necrosis factor ␣ (cA2) versus placebo in rheumatoid arthritis. Lancet 1994; 344: 1105–40. Maini RN, Breedveld FC, Kalden JR, et al. Therapeutic efficacy of multiple intravenous infusions of anti-tumor necrosis factor ␣ monoclonal antibody combined with low-dose weekly methotrexate in rheumatoid arthritis. Arthritis Rheum 1998; 41: 1552–63. Maini RN, St Clair EW, Breedveld FC, et al. Infliximab (chimeric anti-tumour necrosis factor ␣ monoclonal antibody) versus placebo in rheumatoid arthritis patients receiving concomitant methotrexate: a randomised phase III trial. Lancet 1999; 354: 1932–39.
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NEW DRUG CLASSES 18 Lipsky P, St Clair EW, Furst D, et al. 54-week clinical and radiographic results from the ATTRACT trial: a phase III study of infliximab (Remicade™) in patients with active RA despite methotrexate. Arthritis Rheum 1999; 42: S401. 19 Breedveld FC. New tumor necrosis factor-alpha biologic therapies for rheumatoid arthritis. Eur Cytokine Netw 1998; 9: 233–38. 20 Targan SR, Hanauer SB, van Deventer SJH, et al. A short term study of chimeric monoclonal antibody cA2 to tumor necrosis factor ␣ for Crohn’s disease. N Engl J Med 1997; 337: 1029–35. 21 Present DH, Rutgeerts P, Targan S, et al. Infliximab for the treatment of fistulas in patients with Crohn’s disease. N Engl J Med 1999; 340: 1398–405. 22 Laughlin P, Grillo-Lopez AJ, Link BK, et al. Rituximab chimeric anti-CD20 monoclonal antibody therapy for relapsed indolent lymphoma: half of patients respond to a 4-dose treatment programme. J Clin Oncol 1998; 16: 2824–33. 23 Czuczman MS, Grillo-Lopez AJ, White CA, et al. Treatment of patients with low grade B-cell lymphoma with the combination of chimeric anti-CD20 monoclonal antibody and CHOP chemotherapy. J Clin Oncol 1999; 17: 268–76. 24 Dyer MJS. The role of CAMPATH-1 antibodies in the treatment of lymphoid malignancies. Semin Oncol 1999; 26: 52–57. 25 Baselga J, Tripathy D, Mendelsohn J, et al. Phase II study of weekly intravenous recombinant humanized anti-p185HER2 monoclonal antibody in patients with HER2/neu-overexpressing metastatic breast cancer. J Clin Oncol 1996; 14: 737–44. 26 Slamon DJ, Leyland-Jones B, Shak S, et al. Addition of Herceptin (humanized anti-HER2 overexpressing metastatic breast cancer
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(HER2+/MBC) markedly increases anticancer activity: a randomized multinational controlled phase III trial. Proc ASCO 1998; 17: 98 (abstr). Baselga J, Tripathy D, Mendelsohn J, et al. Phase II study of weekly intravenous trastuzumab (Herceptin) in patients with HER2/neuoverexpressing metastatic breast cancer. Semin Oncol 1999; 26: 78–83. Topol EJ, Califf RM, Weisman HF, et al. Randomised trial of coronary intervention with antibody against platelet IIb/IIIa integrin for reduction of clinical restenosis: results at 6 months. Lancet 1994; 343: 881–86. EPILOG Investigators. Platelet glycoprotein IIb/IIIa receptor blockade and low-dose heparin during percutaneous coronary revascularisation. N Engl J Med 1997; 336: 1689–96. CAPTURE Investigators. Randomised placebo-controlled trial of abciximab before and during coronary intervention in refractory unstable angina: the CAPTURE study. Lancet 1997; 349: 1429–35. Hamm CW, Heeschen C, Goldmann B, et al. Benefit of abciximab in patients with refractory unstable angina in relation to serum troponin T levels. c7E3 Fab Antiplatelet Therapy in Unstable Refractory Angina (CAPTURE) Study Investigators. N Engl J Med 1999; 340: 1623–29. Malley R, De Vincenzo J, Ramilo O, et al. Reduction of respiratory syncytial virus (RSV) in tracheal aspirates in intubated infants by use of humanized monoclonal antibody to RSV F protein. J Infect Dis 1998; 178: 1555–61. Impact-RSV Study Group. Palivizumab, a humanized respiratory syncytial virus monoclonal antibody, reduces hospitalization from respiratory syncytial virus infection in high-risk infants. Pediatrics 1998; 102: 531–37.
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