BLOCKING IMMUNE RESPONSE TO A FOREIGN ANTIGEN USING AN ANTAGONIST WHICH BINDS TO CD20

Abstract: The present application describes methods for blocking immune response to foreign antigens in a mammal using antagonists which bind to CD20.

Description: BLOCKING IMMUNE RESPONSE TO A FOREIGN ANTIGEN USING AN ANTAGONIST WHICH BINDS TO CD20 Field of the Invention The present invention concerns blocking immune response to foreign antigens m a mammal with antagonists which bmd to CD20 Background of the Invention Lymphocytes are one of many types of white blood cells produced m the bone marrow duπng the process of hematopoiesis There are two major populations of lymphocvtes B Ivmphocytes (B cells) and T lymphocytes (T cells) The lymphocytes of particular mterest herem are B cells B cells mature within the bone marrow and leave the marrow expressing an antigen-binding antibody on their cell surface When a naive B cell first encounters the antigen for which its membrane-bound antibody is specific, the cell begins to divide rapidly and its progeny differentiate mto memory B cells and effector cells called "plasma cells" Memory B cells have a longer life span and contmue to express membrane-bound antibody with the same specificity as the oπgmal parent cell Plasma cells do not produce membrane-bound antibody but mstead produce the antibody m a form that can be secreted Secreted antibodies are the major effector molecule of humoral immunity The CD20 antigen (also called human B-lymphocvte-restπcted differentiation antigen. Bp35) is a hydrophobic transmembrane protem with a molecular weight of approximately 35 kD located on pre-B and mature B lymphocytes (Valentine etal J Biol Chem.264(\9) 11282-11287(1989), andEιnfeldefα/ EMBOJ 7(3) 711-717 (1988)) The antigen is also expressed on greater than 90% of B cell non-Hodgkin's lymphomas (NHL) (Anderson etal Blood 63(6).1424-1433 (1984)). but is not found on hematopotetic stem cells, pro-B cells, normal plasma cells or other normal tissues (Tedder et al J Immunol 135(2) 973-979 (1985)). CD20 regulates an early step(s) m the activation process for cell cycle initiation and differentiation (Tedder et al , supra) and possibly functions as a calcium ton channel (Tedder et al J Cell Bwchem 14D 195 (1990)) Given the expression of CD20 in B cell lymphomas, this antigen can serve as a candidate for "targeting" of such lymphomas In essence, such targeting can be generalized as follows annbodies specific to the CD20 surface antigen of B cells are administered to a patient These antι-CD20 antibodies specifically bmd to the CD20 antigen of (ostensibly) both normal and malignant B cells: the antibody bound to the CD20 surface antigen may lead to the destruction and depletion of neoplastic B cells Additionally . chemical agents or radioactive labels having the potential to destroy the tumor can be conjugated to the antι-CD20 antibody such that the agent is specifically "delivered" to the neoplastic B cells Irrespective of the approach, a primary goal is to destroy the tumor, the specific approach can be determined by the particular antι-CD20 antibodv which is utilized and, thus, the available approaches to targeting the CD20 antigen can vary considerably The πtuxunab (RJTUXAN®) antibody is a genetically engmeered chimeric muπne human monoclonal antibody directed agamst the CD20 antigen Rituxrmab is the antibody called "C2B8" in US Patent No 5,736.137 issued Apnl 7. 1998 (Anderson et al ) RJTUXAN® is indicated for the treatment of patients with relapsed or refractory low-grade or folhcular. CD20 positive. B cell non-Hodgkin's lymphoma In vitro mechanism of action studies have demonstrated that RITUXAN® binds human complement and lyses lymphoid B cell lmes through complement-dependent cytotoxicity (CDC) (Reff etal Blood 82(2) 435-445 (1994)). Additionally, it has significant activity in assays for antibody-dependent cellular cytotoxicity ( ADCC) More recently. RITUXAN® has been shown to have anti-prohferative effects m tπtiated thymidine incorporation assays and to mduce apoptosis directly, while other antι-CD20 antibodies do not (Maloney et al Blood 88(10) 637a (1996)) Synergy between RITUXAN® and chemotherapies and toxms has also been observed experimentally In particular. RITUXAN® sensitizes drug- resistant human B cell lymphoma cell lmes to the cytotoxic effects of doxorubicm. CDDP, VP-16. diphtheria toxin andncin(Demidem efa/ Cancer Chemotherapy & Radwpharmaceuticals 12(3) 177-186 (1997)) /« vzvo prechnical studies have shown that RITUXAN® depletes B cells from the peπpheral blood, lymph nodes, and bone marrow of cynomolgus monkeys, presumably through complement and cell-mediated processes (Reff et al Blood 83(2) 435-445 (1994)) Summary of the Invention In a first aspect, the present invention provides a method of blocking an immune response to a foreign antigen in a mammal wherem the mammal is not suffering from a malignancv, compπsmg admmistermg to the mammal a therapeutically effective amount of an antagonist which binds to CD20 In a further aspect, the mvention provides a method of treating a mammal compπsmg administering a therapeutic agent, other than an antagonist which bmds to CD20, to the mammal and further compπsmg administering an antagonist which binds to CD20 to the mammal, wherem the therapeutic agent is lmmunogenic m the mammal and the antagonist blocks an immune response to the therapeutic agent m the mammal The mvention further provides a method of treating graft-versus-host or host-versus-graft disease in a mammal compπsmg administering to the mammal a therapeutically effective amount of an antagonist which bmds to CD20 In addition, a method of desensitizing a mammal awaitmg transplantation is provided which compπses administering to the mammal a therapeutically effective amount of an antagonist which bmds to CD20 The present mvention further relates to articles of manufacture for use m the above methods For example, the article of manufacture may compπse a container and a composition contained therein, wherem the composition compπses an antagonist which bmds to CD20, and further compπsmg a package insert instructing the user of the composition to treat a patient who has been or will be exposed to a foreign antigen The article of manufacture optionally further comprises a second container and a second composition contained therein, wherem the second composition compπses a therapeutic agent Detailed Description of the Preferred Embodiments I. Definitions The "CD20" antigen is a -35 kDa, non-glycosylated phosphoprotem found on the surface of greater than 90% of B cells from peπpheral blood or lymphoid organs CD20 is expressed duπng early pre-B cell development and remams until plasma cell differentiation CD20 is present on both normal B cells as well as malignant B cells Other names for CD20 m the literature include "B-lymphocyte-restπcted antigen" and "Bp35" The CD20 antigen is descπbed in Clark et al PNAS (USA) 82 1766 ( 1985), for example By "foreign antigen" is meant a molecule or molecules which is/are not endogenous or native to a mammal which is exposed to it The foreign antigen may elicit an immune response, e g a humoral and or T cell mediated response m the mammal Generally, the foreign antigen will provoke the production of antibodies thereagainst Examples of foreign antigens contemplated herein mclude lmmunogenic therapeutic agents, e g protems such as antibodies, particularly antibodies compπsing non-human ammo acid residues (e g rodent, chimenc/humamzed, and pπmatized antibodies), toxms (optionally conjugated to a targeting molecule such as an antibody, wherein the targetmg molecule may also be lmmunogenic), gene therapy viral vectors, such as retroviruses and adenoviruses, grafts, mfectious agents (e g bacteπa and virus), alloantigens (i e an antigen that occurs m some, but not m other members of the same species) such as differences m blood types, human lymphocyte antigens (HLA), platelet antigens, antigens expressed on transplanted organs, blood components, pregnancy (Rh), and hemophi c factors (e g Factor VIII and Factor IX) By "blocking an immune response" to a foreign antigen is meant reducing or preventmg at least one immune- mediated response resulting from exposure to a foreign antigen For example, one may dampen a humoral response to the foreign antigen, i e , by preventmg or reducmg the production of antibodies directed agamst the antigen m the mammal Alternatively, or additionally, one may suppress ldiotype, "pacify" the removal of cells coated with alloantibody; and or affect alloantigen presentation through depletion of antigen-presenting cells The mammal to be treated herem is generally one which is "not suffering from a malignancy" and hence has not been diagnosed as having a malignancy or cancer, such as B cell lymphoma, acute lymphoblastic leukemia (ALL), chronic lymphocytic leukemia (CLL), Harry cell leukemia, chronic myeloblastic leukemia, or post-transplant lymphoprohferative disorder (PTLD) The term "therapeutic agent " refers to a compound or composition which is used to treat a disease or disorder m a patient The therapeutic agent may, for example, compπse a polypeptide such as an antibody, a toxin (optionally conjugated to a targeting molecule such as an antibody); a gene therapy viral vector and or a hemophi c factor (e.g Factor VIII or Factor IX) The therapeutic agent is generally admmistered to a mammal m a therapeutically effective amount for treating the disease or disorder of mterest, wherem that amount results m an immune response bemg elicited to the therapeutic agent m the mammal so treated As used herem, "polypeptide" refers generally to peptides and protems having more than about ten ammo acids Examples of mammalian polypeptides mclude molecules such as, e g , rerun, a growth hormone, including human growth hormone, bovme growth hormone; growth hormone releasmg factor, parathyroid hormone; thyroid stimulating hormone; hpoproteins, 1-antιtrypsιn; msulm A-cham, insulin B-cham; proinsuhn; fhrombopoietin; follicle stimulating hormone; calcitomn; luteimzing hormone; glucagon; clotting factors such as factor VfflC, factor IX, tissue factor, and von Willebrands factor, anti-clotting factors such as Protein C; atπal natuπetic factor; lung surfactant; a plasπnnogen activator, such as urokinase or human urine or tissue-type plasminogen activator (t-PA); bombesm, thrombm; hemopoietic growth factor; tumor necrosis factor-alpha and -beta; enkephalinase; a serum albumm such as human serum albumm, mullenan-inhibiting substance; relaxm A-cham; relaxm B-cham; prorelaxm; mouse gonadotropm-associated peptide; a microbial protein, such as beta-lactamase, DNase, inhibin; activin, vascular endothe al growth factor (VEGF), receptors for hormones or growth factors; integπn, protem A or D, rheumatoid factors; a neurotrophic factor such as bram-deπved neurotrophic factor (BDNF), neurotrophm-3, -4, -5, or -6 (NT-3, NT-4, NT-5, or NT-6), or a nerve growth factor such as NGF, cardiotrophins (cardiac hypertrophy factor) such as cardιotroρhιn-1 (CT-1); platelet-deπved growth factor (PDGF), fibroblast growth factor such as aFGF and bFGF, epidermal growth factor (EGF), transforming growth factor (TGF) such as TGF-alpha and TGF-beta, mcludmg TGF- 1 , TGF- 2, TGF- 3 , TGF- 4, or TGF- 5 , insulin-like growth factor-I and -II (IGF-I and IGF-II), des( 1 -3)-IGF-I (bram IGF-I), insulin-like growth factor binding protems; CD protems such as CD3, CD4, CD8. and CD20, erythropoietm; osteomductive factors, lmmunotoxins, a bone morphogenetic protem (BMP), an interferon such as mterferon-alpha, -beta, and -gamma; serum albumm, such as human serum albumm (HSA) or bovme serum albumm (BSA); colony stimulating factors (CSFs), e g , M-CSF, GM-CSF, and G-CSF, mterleukms (ILs), e g , IL-1 to IL-10, cytokines (see below), superoxide dismutase, T-cell receptors, surface membrane protems, decay acceleratmg factor, viral antigen such as, for example, a portion of the AIDS envelope; transport protems; hommg receptors, addressins, regulatory protems; antibodies; and fragments or vaπants of any of the above-listed polypeptides. The term "graft" as used herem refers to biological mateπal deπved from a donor for transplantation mto a recipient Grafts mclude such diverse mateπal as, for example, isolated cells such as islet cells, tissue such as the amniotic membrane of a newborn, bone marrow, hematopoietic precursor cells, and ocular tissue, such as corneal tissue: and organs such as skin, heart, liver, spleen, pancreas, thyroid lobe, lung, kidney, tubular organs (e g , intestine, blood vessels, or esophagus), etc The tubular organs can be used to replace damaged portions of esophagus, blood vessels, or bile duct The skm grafts can be used not only for burns, but also as a dressmg to damaged mtestme or to close certain defects such as diaphragmatic hernia The graft is deπved from any mammalian source, mcludmg human, whether from cadavers or living donors Preferably the graft is bone marrow or an organ such as heart and the donor of the graft and the host are matched for HLA class II antigens The term "mammalian host" as used herem refers to any compatible transplant recipient By "compatible" is meant a mammalian host that will accept the donated graft Preferably, the host is human If both the donor of the graft and the host are human, they are preferably matched for HLA class II antigens so as to improve histocompatibility The term "donor" as used herem refers to the mammalian species, dead or alive, from which the graft is deπved Preferably, the donor is human Human donors are preferably volunteer blood-related donors that are normal on physical exammation and of the same major ABO blood group, because crossing major blood group barπers possibly prejudices survival of the allograft It is, however, possible to transplant, for example, a kidney of a type O donor into an A, B or AB recipient The term "transplant" and vaπations thereof refers to the insertion of a graft mto a host, whether the transplantation is syngeneic (where the donor and recipient are genetically identical), allogeneic (where the donor and recipient are of different genetic oπgms but of the same species), or xenogeneic (where the donor and recipient are from different species) Thus, in a typical scenaπo, the host is human and the graft is an isograft, deπved from a human of the same or different genetic oπgms In another scenaπo, the graft is deπved from a species different from that mto which it is transplanted, such as a baboon heart transplanted mto a human recipient host, and mcludmg annuals from phylogemcally widely separated species, for example, a pig heart valve, or animal beta islet cells or neuronal cells transplanted mto a human host By "gene therapy" is meant the general approach of introducing nucleic acid mto a mammal to be treated therewith The nucleic acid may encode a polypeptide of mterest or may be antisense nucleic acid One or more components of a gene therapy vector or composition may be lmmunogenic m a mammal treated therewith For example, viral vectors (such as adenovirus, Herpes simplex I virus or retrovirus), lipids, and/or targeting molecules m the composition may mduce an immune response m a mammal treated therewith The expression "desensitizing a mammal awaiting transplantation" refers to reducmg or abolishing allergic sensitivity or reactivity to a transplant, pπor to administration of the transplant to the mammal This may be achieved by any mechanism, such as a reduction m anti-donor antibodies in the desensitized mammal, e g where such anti- donor antibodies are directed agamst human lymphocyte antigen (HLA) An "autoimmune disease" herem is a non-malignant disease or disorder aπsmg from and directed agamst an individual's own tissues The autoimmune diseases herem specifically exclude malignant or cancerous diseases or conditions, especially excludmg B cell lymphoma, acute lymphoblastic leukemia (ALL), chronic lymphocytic leukemia (CLL), Hairy cell leukemia and chronic myeloblastic leukemia Examples of autoimmune diseases or disorders mclude, but are not limited to, inflammatory responses such as inflammatory skm diseases mcludmg psonasis and dermatitis (e g atopic dermatitis), systemic scleroderma and sclerosis, responses associated with inflammatory bowel disease (such as Crohn's disease and ulcerative colitis), respiratory distress syndrome (mcludmg adult respiratory distress syndrome, ARDS), dermatitis, meningitis, encephalitis, uveitis, colitis, glomerulonephπtis, allergic conditions such as eczema and asthma and other conditions mvolvmg mfiltration of T cells and chronic inflammatory responses, atherosclerosis, leukocyte adhesion deficiency, rheumatoid arthπtis, systemic lupus erythematosus (SLE), diabetes mellitus (e g Type I diabetes mel tus or msulm dependent diabetes mel tis), multiple sclerosis, Reynaud's syndrome, autoimmune thyroiditis, allergic encephalomye tis, Sjorgen's syndrome, juvenile onset diabetes, and immune responses associated with acute and delayed hypersensitivity mediated by cytokmes and T-lymphocytes typically found m tuberculosis, sarcoidosis, polymyositis, granulomatosis and vasculitis. pernicious anemia (Addison's disease), diseases involving leukocyte diapedesis, central nervous system (CNS) inflammatory disorder, multiple organ injury syndrome, hemolytic anemia (mcludmg, but not limited to cryoglobinemia or Coombs positive anemia) , myasthema gravis, antigen-antibody complex mediated diseases, anti-glomerular basement membrane disease, antiphosphohpid syndrome, allergic neuπtis, Graves' disease, Lambert-Eaton myasthemc syndrome, pemphigoid bullous, pemphigus, autoimmune polyendocπnopathies, Reiter's disease, stiff-man syndrome, Behcet disease, giant cell arteπtis, immune complex nephπtis, IgA nephropathy, IgM polyneuropathies, immune thrombocytopemc purpura (ITP) or autoimmune thrombocytopenia etc An "antagonist" is a molecule which, upon bmdmg to CD20, destroys or depletes B cells in a mammal and/or interferes with one or more B cell functions, e g by reducmg or preventmg a humoral response elicited by the B cell The antagonist preferably is able to deplete B cells (i e reduce circulating B cell levels) m a mammal treated therewith Such depletion may be achieved via vanous mechanisms such antibody-dependent cell-mediated cytotoxicity (ADCC) and/or complement dependent cytotoxicity (CDC), inhibition of B cell proliferation and or induction of B cell death (e g via apoptosis) Antagonists mcluded within the scope of the present mvention mclude antibodies, synthetic or native sequence peptides and small molecule antagonists which bmd to CD20, optionally conjugated with or fused to a cytotoxic agent The preferred antagonist compπses an antibody "Antibody-dependent cell-mediated cytotoxicity" and "ADCC" refer to a cell-mediated reaction m which nonspecific cytotoxic cells that express Fc receptors (FcRs) (e Natural Killer (NK) cells, neutrophils, and macrophages) recognize bound antibody on a target cell and subsequently cause lysis of the target cell The primary cells for mediating ADCC, NK cells, express FcγRIII only, whereas monocytes express FcγRI, FcγRII and FcγRIII FcR expression on hematopoietic cells m summarized is Table 3 on page 464 of Ravetch and Kmet, Annu Rev Immunol 9 457-92 (1991) To assess ADCC activity of a molecule of mterest, an in vitro ADCC assay, such as that descnbed m US Patent No 5,500,362 or 5,821,337 may be performed Useful effector cells for such assays mclude peπpheral blood mononuclear cells (PBMC) and Natural Killer (NK) cells Alternatively, or additionally, ADCC activity of the molecule of mterest may be assessed in vivo, e g , m a animal model such as that disclosed m Clynes etal PNAS (USA) 95 652-656 (1998) "Human effector cells" are leukocytes which express one or more FcRs and perform effector functions Preferably, the cells express at least FcγRIII and carry out ADCC effector function Examples of human leukocytes which mediate ADCC mclude penpheral blood mononuclear cells (PBMC), natural killer (NK) cells, monocytes, cytotoxic T cells and neutrophils, with PBMCs and NK cells being preferred The terms "Fc receptor" or "FcR" are used to descπbe a receptor that bmds to the Fc region of an antibody The preferred FcR is a native sequence human FcR Moreover, a preferred FcR is one which bmds an IgG antibody (a gamma receptor) and mcludes receptors of the FcγRI, FcγRII, and Fcγ RIII subclasses, mcludmg allelic vaπants and alternatively spliced forms of these receptors FcγRII receptors include FcγRIIA (an "activating receptor") and FcγRIIB (an "inhibiting receptor"), which have similar ammo acid sequences that differ pπmaπly in the cytoplasmic domams thereof Activatmg receptor FcγRIIA contains an immunoreceptor tyrosine-based activation motif (IT AM) m its cytoplasmic domam Inhibiting receptor FcγRIIB contains an immunoreceptor tyrosme-based inhibition motif (ITTM) m its cytoplasmic domam (see Daeron, Annu Rev Immunol 15 203-234 (1997)) FcRs are reviewed m Ravetch and Kmet, Annu Rev Immunol 9 457-92 (1991), Capel etal , Immunomethods 4 25-34 (1994), and de Haas et al , J Lab Chn Med 126 330-41 (1995) Other FcRs, including those to be identified in the future, are encompassed by the term "FcR" herem The term also mcludes the neonatal receptor, FcRn, which is responsible for the transfer of maternal IgGs to the fetus (Guyer etal J Immunol 117 587 (1976) and Kim etal , J Immunol 24 249 (1994)) "Complement dependent cytotoxicity" or "CDC" refer to the ability of a molecule to lyse a target m the presence of complement The complement activation pathway is mitiated by the bmdmg of the first component of the complement system (Clq) to a molecule (eg an antibody) complexed with a cognate antigen To assess complement activation a CDC assay, e as descnbed m Gazzano-Santoro et al , J Immunol Methods 202 163 (1996), may be performed "Growth inhibitory" antagonists are those which prevent or reduce proliferation of a cell expressmg an antigen to which the antagonist bmds For example, the antagonist may prevent or reduce proliferation of B cells in vitro and/or in vivo Antagonists which "induce apoptosis" are those which mduce programmed cell death, e g , of a B cell, as determined by standard apoptosis assays, such as bmdmg of annexin V, fragmentation of DNA, cell shrinkage, dilation of endoplasmic reticulum, cell fragmentation, and/or formation of membrane vesicles (called apoptotic bodies) The term "antibody" herem is used m the broadest sense and specifically covers intact monoclonal antibodies, polyclonal antibodies, multispecific antibodies (e g bispecific antibodies) formed from at least two intact antibodies, and antibody fragments so long as they exhibit the desired biological activity "Antibody fragments" compπse a portion of an intact antibody, preferably compπsmg the antigen-bmdmg or vaπable region thereof Examples of antibody fragments mclude Fab, Fab', F(ab') 2 , and Fv fragments, diabodies, linear antibodies, single-chain antibody molecules, and multispecific antibodies formed from antibody fragments "Native antibodies" are usually heterotetrameπc glycoprotems of about 150,000 daltons, composed of two identical light (L) chams and two identical heavy (H) chams Each light cham is linked to a heavy cham by one covalent disulfϊde bond, while the number of disulfide linkages vanes among the heavy chams of different lmmunoglobulin lsotypes Each heavy and light cham also has regularly spaced intrachain disulfide bπdges Each heaw cham has at one end a vaπable domam (V H ) followed by a number of constant domams Each light cham has a vaπable domam at one end (V L ) and a constant domain at its other end. the constant domam of the light cham is aligned with the first constant domam of the heavy cham, and the light-chain vaπable domam is aligned with the vanable domam of the heavy cham Particular ammo acid residues are believed to form an interface between the light cham and heavy cham vaπable domams The term "vanable" refers to the fact that certain portions of the vaπable domams differ extensively in sequence among antibodies and are used m the bmdmg and specificity of each particular antibody for its particular antigen However, the vanability is not evenly distπbuted throughout the vanable domams of antibodies It is concentrated m three segments called hypervanable regions both m the light chain and the heavy cham vanable domams The more highly conserved portions of variable domams are called the framework regions (FRs) The vanable domams of native heavy and light chams each compnse four FRs. largely adoptmg a β-sheet configuration, connected by three hypervanable regions, which form loops connecting, and m some cases forming part of, the β- sheet structure The hypervanable regions m each cham are held together in close proximity by the FRs and, with the hypervanable regions from the other cham, contribute to the formation of the antigen-bmdmg site of antibodies (see Kabat et al , Sequences of Proteins of Immunological Interest, 5th Ed Public Health Service, National Institutes of Health, Bethesda, MD (1991)) The constant domams are not involved directly in bmdmg an antibody to an antigen, but exhibit vanous effector functions, such as participation of the antibody m antibody dependent cellular cytotoxicity (ADCC) Papam digestion of antibodies produces two identical antigen-bmdmg fragments, called "Fab" fragments, each with a smgle antigen-bmdmg site, and a residual "Fc" fragment, whose name reflects its ability to crystallize readily Pepsm treatment yields an F(ab') 2 fragment that has two antigen-bmdmg sites and is still capable of cross- linking antigen "Fv" is the minimum antibody fragment which contains a complete antigen-recognition and antigen-bmdmg site This region consists of a dimer of one heavy cham and one light cham vanable domam in tight, non-covalent association It is m this configuration that the three hypervanable regions of each vaπable domam mteract to define an antigen-bmdmg site on the surface of the V jj -V L dimer Collectively, the six hypervanable regions confer antigen- bmdmg specificity to the antibody However, even a smgle vanable domam (or half of an Fv compnsmg only three hypervanable regions specific for an antigen) has the ability to recogmze and bmd antigen, although at a lower affinity than the entire bmdmg site The Fab fragment also contains the constant domam of the light cham and the first constant domam (CHI) of the heavy cham Fab' fragments differ from Fab fragments by the addition of a few residues at the carboxy terminus of the heavy cham CHI domam mcludmg one or more cystemes from the antibody hmge region Fab'-SH is the designation herem for Fab' m which the cysteme resιdue(s) of the constant domams bear at least one free thiol group F(ab') 2 antibody fragments ongmally were produced as pairs of Fab' fragments which have hmge cystemes between them Other chemical couplmgs of antibody fragments are also known The "light chams" of antibodies (lmmunoglobu ns) from any vertebrate species can be assigned to one of two clearly distmct types, called kappa (K) and lambda (λ), based on the ammo acid sequences of their constant domains Dependmg on the ammo acid sequence of the constant domam of their heavy chains, antibodies can be assigned to different classes There are five major classes of mtact antibodies IgA, IgD, IgE, IgG, and IgM, and several of these may be further divided mto subclasses (lsotypes), e g , IgGl, IgG2, IgG3, IgG4, IgA, andIgA2 The heavy-chain constant domams that correspond to the different classes of antibodies are called α, δ, ε, γ, and μ, respectively The subumt structures and three-dimensional configurations of different classes of lmmunoglobulins are well known " Single-chain Fv" or "scFv" antibody fragments compnse the V H and V L domams of antibody, wherem these domams are present m a smgle polypeptide cham Preferably, the Fv polypeptide further compnses a polypeptide linker between the V H and V L domams which enables the scFv to form the desired structure for antigen bmdmg For a review of scFv see Pluckthun m The Pharmacology of Monoclonal Antibodies, vol 113, Rosenburg and Moore eds , Springer- Verlag, New York, pp 269-315 (1994) The term "diabodies" refers to small antibody fragments with two antigen-bmdmg sites, which fragments compnse a heavy-chain vaπable domam ( V H ) connected to a light-chain vanable domam ( V L ) in the same polypeptide cham (V H - V L ) By usmg a linker that is too short to allow pairing between the two domams on the same cham, the domams are forced to pair with the complementary domams of another cham and create two antigen-bmdmg sites Diabodies are descnbed more fully m, for example, EP 404,097, WO 93/11161 , and Hollinger etal , Proc Natl Acad Sci USA, 90 6444-6448 (1993) The term "monoclonal antibody" as used herem refers to an antibody obtamed from a population of substantially homogeneous antibodies, i e , the individual antibodies compπsmg the population are identical except for possible naturally occurring mutations that mav be present in mmor amounts Monoclonal antibodies are highly specific, bemg directed agamst a smgle antigenic site Furthermore, m contrast to conventional (polyclonal) antibody preparations which typically mclude different antibodies directed against different determinants (epitopes), each monoclonal antibody is directed agamst a smgle determinant on the antigen In addition to their specificity, the monoclonal antibodies are advantageous m that they are synthesized by the hybndoma culture, uncontammated by other immuno globulins The modifier "monoclonal" mdicates the character of the antibody as bemg obtained from a substantially homogeneous population of antibodies, and is not to be construed as requiring production of the antibody by any particular method For example, the monoclonal antibodies to be used m accordance with the present mvention may be made by the hybndoma method first descπbed by Kohler et al , Nature, 256 495 (1975), or may be made by recombinant DNA methods (see, e g , U S Patent No 4,816,567) The "monoclonal antibodies" may also be isolated from phage antibody branes usmg the techniques descnbed m Clackson et al , Nature, 352 624-628 (1991) and Marks et al , J Mol Biol , 222 581-597 (1991), for example The monoclonal antibodies herem specifically mclude "chimenc" antibodies (immunoglobulins) m which a portion of the heavy and or light cham is identical with or homologous to corresponding sequences m antibodies denved from a particular species or belongmg to a particular antibody class or subclass, while the remamder of the cham(s) is identical with or homologous to corresponding sequences m antibodies denved from another species or belongmg to another antibody class or subclass, as well as fragments of such antibodies, so long as they exhibit the desired biological activity (U S Patent No 4,816,567, Mornson et al , Proc Natl Acad Sci USA, 81 6851-6855 ( 1984)) Chimenc antibodies of mterest herem mclude "pnmatized" antibodies compπsmg vanable domam antigen- bmdmg sequences derived from a non-human pnmate (e g Old World Monkey, such as baboon, rhesus or cynomolgus monkey) and human constant region sequences (US Pat No 5,693,780) "Humanized" forms of non-human (e g , muπne) antibodies are chimenc antibodies that contain minimal sequence denved from non-human immunoglobulin For the most part, humanized antibodies are human immunoglobulins (recipient antibody) m which residues from a hypervanable region of the recipient are replaced by residues from a hypervanable region of a non-human species (donor antibody) such as mouse, rat, rabbit or nonhuman pnmate hav g the desired specificity, affinity, and capacity In some mstances, framework region (FR) residues of the human immunoglobulin are replaced by corresponding non-human residues Furthermore, humanized antibodies may compnse residues that are not found m the recipient antibody or in the donor antibody These modifications are made to further refine antibody performance In general, the humanized antibody will compnse substantially all of at least one, and typically two, vaπable domams, in which all or substantially all of the hypervanable loops correspond to those of a non-human immunoglobulin and all or substantially all of the FRs are those of a human immunoglobulin sequence The humanized antibody optionally also will compnse at least a portion of an immunoglobulin constant region (Fc), typically that of a human immunoglobulin For further details, see Jones et al Nature 321 522-525 (1986), Riechmann et al , Nature 332 323-329 (1988), and Prest , Curr Op Struct Biol 2 593-596 (1992) The term "hypervanable region" when used herein refers to the ammo acid residues of an antibody which are responsible for antigen-bmdmg The hypervanable region compnses ammo acid residues from a "complementanty determining region" or "CDR" (e g residues 24-34 (LI), 50-56 (L2) and 89-97 (L3) in the light cham vanable domam and 31-35 (HI), 50-65 (H2) and 95-102 (H3) m the heavy cham vanable domam, Kabat etal , Sequences of Proteins of Immunological Interest, 5th Ed Public Health Service, National Institutes of Health, Bethesda, MD (1991)) and/or those residues from a "hypervanable loop" (e g residues 26-32 (LI), 50-52 (L2) and 91-96 (L3) m the light cham vaπable domam and 26-32 (HI ), 53-55 (H2) and 96- 101 (H3) m the heavy cham vaπable domam Chothia and Lesk J Mol Biol 196 901-917 (1987)) "Framework" or "FR" residues are those vaπable domam residues other than the hypervanable region residues as herem defined An antagonist "which bmds" an antigen of mterest, e g , CD20, is one capable of bmdmg that antigen with sufficient affinity and/or avidity such that the antagonist is useful as a therapeutic agent for targetmg a cell expressmg the antigen Examples of antibodies which bmd the CD20 antigen mclude "C2B8" which is now called "ntuximab" ("RΓΓUXAN®") (US Patent No 5,736,137, expressly incorporated herein by reference), the yttnum-[90]-labeled2B8 murine antibody designated "Y2B8" (US Patent No 5,736 137, expressly incorporated herem by reference), murine IgG2a "Bl" optionally labeled with 131 I to generate the " 13I I-B1" antibody (BEXXAR™) (US Patent No 5,595,721, expressly incorporated herem by reference), murine monoclonal antibody "1F5" (Press et al Blood 69(2) 584-591 (1987)), "chimenc 2H7" antibody (US Patent No 5,677,180 expressly incorporated herem by reference), and monoclonal antibodies L27, G28-2, 93-1B3, B-Cl or NU-B2 available from the International Leukocyte Typing Workshop (Valentme et al , In Leukocyte Typing III (McMichael, Ed , p 440, Oxford University Press (1987)) The terms "ntuximab" or "RITUXAN®" herem refer to the genetically engmeered chimenc munne/human monoclonal antibody directed agamst the CD20 antigen and designated "C2B8 " in US Patent No 5,736.137, expressly incorporated herem by reference The antibody is an IgG, kappa immunoglobulin containing murine light and heavy cham vanable region sequences and human constant region sequences Rituximab has a bmdmg affinity for the CD20 antigen of approximately 8 OnM An "isolated" antagonist is one which has been identified and separated and/or recovered from a component of its natural environment Contaminant components of its natural environment are matenals which would interfere with diagnostic or therapeutic uses for the antagonist, and may mclude enzymes, hormones, and other protemaceous or nonprotemaceous solutes In preferred embodiments, the antagonist will be puπfied (1) to greater than 95% by weight of antagonist as determmed by the Lowry method, and most preferably more than 99% by weight, (2) to a degree sufficient to obtain at least 15 residues of N-teπninal or internal ammo acid sequence by use of a spinning cup sequenator, or (3) to homogeneity by SDS-PAGE under reducing or nonreducing conditions usmg Coomassie blue or, preferably, silver stam Isolated antagonist mcludes the antagonist in situ within recombmant cells smce at least one component of the antagonist's natural environment will not be present Ordmanly, however, isolated antagonist will be prepared by at least one puπfication step "Mammal" for purposes of treatment refers to any animal classified as a mammal, mcludmg humans, domestic and farm animals, and zoo, sports, or pet animals, such as dogs, horses, cats, cows, etc Preferably, the mammal is human "Treatment" refers to both therapeutic treatment and prophylactic or preventative measures Those m need of treatment mclude those already with the disease or disorder as well as those in which the disease or disorder is to be prevented Hence, the mammal may have been diagnosed as havmg the disease or disorder or may be predisposed or susceptible to the disease The expression "therapeutically effective amount" refers to an amount of the antagonist which is effective for preventmg, ameliorating or treating the disease or condition m question The term "lmmunosuppressive agent" as used herem for adjunct therapy refers to substances that act to suppress or mask the immune system of the mammal bemg treated herein This would include substances that suppress cytokine production, downregulate or suppress self-antigen expression, or mask the MHC antigens Examples of such agents mclude 2-ammo-6-aryl-5-substιtuted pynmidines (see U S Pat No 4 665,077, the disclosure of which is incorporated herem by reference), antipro ferative agents, such as azathiopnne leflunomide or sirolunus: cyclophosphamide: bromocryptme, danazol; dapsone: glutaraldehyde (which masks the MHC antigens, as descnbed inU.S. Pat. No.4, 120,649); anti-idiotypic antibodies for MHC antigens and MHC fragments; cyclosponn A; steroids such as corticosteroids, e g , prednisone, methylprednisolone, and dexamethasone; mycophenolate mofetil, calcmeunn inhibitors (e g tacrolimus); cytokme or cytokine receptor antagomsts mcludmg anti-interferon-γ, -β, or -α antibodies, anti-tumor necrosis factor-α antibodies, anti-tumor necrosis factor-β antibodies, antι-mterleukm-2 antibodies and anti-IL-2 receptor antibodies; antι-LFA-1 antibodies, mcludmg anti-CDl 1 a and anti-CD 18 antibodies; antι-L3T4 antibodies, anti-lymphocyte antibodies, e g. polyclonal anti-lymphocyte antibodies; pan-T antibodies, preferably antι-CD3 or antι-CD4/CD4a antibodies; soluble peptide containing a LFA-3 bmdmg domam (WO 90/08187 published 7/26/90); streptokinase, TGF-β; streptodornase; RNA or DNA from the host, FK506; RS-61443 ; deoxyspergualm; rapamycm. T-cell receptor (Cohen et al , U S . Pat. No 5 , 114.721 ), T-cell receptor fragments (Offner et al , Science, 251: 430-432 (1991); WO 90/11294; Ianeway, Nature, 341: 482 (1989); and WO 91/01133); and T cell receptor antibodies (EP 340,109) such as T10B9 The term "cytotoxic agent" as used herem refers to a substance that inhibits or prevents the function of cells and/or causes destruction of cells. The term is intended to mclude radioactive isotopes (e g At 21 ', I 13 ', I 125 , Y 90 , Re 186 , Re 188 . Sm 153 , Bi 212 . P 32 and radioactive isotopes of Lu), chemotherapeutic agents, and toxms such as small molecule toxms or enzymatically active toxms of bacteπal, fungal, plant or animal oπgm, or fragments thereof. A "chemotherapeutic agent" is a chemical compound useful m the treatment of cancer. Examples of chemotherapeutic agents mclude alkylating agents such as thiotepa and cyclosphosphamide (CYTOXAN™); alkyl sulfonates such as busulfan, improsulfan and piposulfan; azindmes such as benzodopa, carboquone, meturedopa, and uredopa, ethylenimines and methylamelamines mcludmg altretamine, tnethylenemelamine, tπetylenephosphoramide, tπethylenethiophosphaoramide and tnmethylolomelamme; nitrogen mustards such as chlorambucil, chlornaphazine, cholophosphamide, estramustine, lfosfamide, mechlorethamine, mechlorethamine oxide hydrochlonde, melphalan, novembichin, phenestenne, prednimustine, trofosfamide, uracil mustard; mtrosureas such as carmustine, chlorozotocm, fotemustme, lomustme, mmustine, ranmiustme; antibiotics such as aclacinomysins, actmomycm, authramycm, azaseπne, bleomycms, cactmomyc , calicheamicm, carabicm, carminomycin, carzmophilin, chromomycms, dactmomycm, daunorubicm, detorubicin, 6-dιazo-5-oxo-L-norleucme, doxorubicm, epirubicm, esorubicm, ldarubicin, marcellomycm, mitomycms, mycophenohc acid, nogalamycin, o vomycms, peplomycm, potfiromycm, puromycm, quelamycin, rodorubicm, streptomgnn. streptozocm, tubercidm, ubenimex, zmostatm, zorubicm; anti-metabolites such as methotrexate and 5-fluorouracιl (5-FU); fo c acid analogues such as denopteπn, methotrexate, pteroptenn, tπmetrexate; punne analogs such as fludarabme, 6-mercaptopurιne. thiamipnne, thioguanine; pyπmidme analogs such as ancitabine, azacitidme, 6-azaundme, carmofur, cytarabme, dideoxyuπdme, doxiflundme, enocitabme, floxundme, 5-FU; androgens such as calusterone, dromostanolone propionate, epitiostanol, mepitiostane, testolactone, anti-adrenals such as ammoglutethimide, mitotane, tnlostane; fohc acid replemsher such as frolmic acid; aceglatone; aldophosphamide glycoside; aminolevulinic acid; amsacnne; bestrabucil; bisantrene; edatraxate, defofamine, demecolcme. diaziquone, elfornithme; elhptmium acetate; etoglucid, gallium nitrate; hydroxyurea; lentman. lomdamine: mitoguazone; mitoxantrone; mopidamol; mtracnne; pentostatm, phenamet, prrarubicm, podophyllmic acid; 2-ethylhydrazιde; procarbazme, PSK®; razoxane; sizofiran; spirogermanium; tenuazonic acid, tnaziquone, 2, 2',2"-tnchlorotπethylamme, urethan, vmdesme, dacarbazme; mannomustme; mitobronitol, mitolactol; pipobroman, gacytosme; arabinoside ("Ara-C"), cyclophosphamide; thiotepa: taxoids, e g. pachtaxel (TAXOL ® , Bnstol-Myers Squibb Oncology, Prmceton, NJ) and doxetaxel (TAXOTERE * , Rhόne-Poulenc Rorer. Antony, France); chlorambucil; gemcitabme, 6-thιoguanme; mercaptopurme; methotrexate; platmum analogs such as cisplatin and carboplatm, vmblastme; platmum; etoposide ( VP- 16); lfosfamide; mitomycm C, mitoxantrone; vincnstine. vinorelbme. navelbme; novantrone: temposide, daunomycm: ammoptenn; xeloda: lbandronate: CPT- 11. topoisomerase mhibitor RFS 2000; difluoromethylormthme (DMFO): retmoic acid, esperamicms, capecitabme; and pharmaceutically acceptable salts, acids or denvatives of any of the above Also mcluded m this definition are anti- hormonal agents that act to regulate or inhibit hormone action on tumors such as anti-estrogens mcludmg for example tamoxifen. raloxifene, aromatase inhibiting 4(5)-ιmιdazoles, 4-hydroxytamoxιfen, tπoxifene, keoxifene, LY117018, onapnstone, and toremifene (Fareston). and anti-androgens such as flutamide, mlutamide, bicalutamide, leupro de, and goserelm, and pharmaceutically acceptable salts, acids or denvatives of any of the above The term "cytokme" is a genenc term for proteins released by one cell population which act on another cell as intercellular mediators Examples of such cytokmes are lymphokmes, monokines, and traditional polypeptide hormones Included among the cytokmes are growth hormone such as human growth hormone, N-methionyl human growth hormone, and bovme growth hormone; parathyroid hormone, thyroxme, msulm; promsulm; relaxm, prorelaxm; glycoprotem hormones such as follicle stimulating hormone (FSH), thyroid stimulating hormone (TSH), and luteinizing hormone (LH), hepatic growth factor; fibroblast growth factor, prolactm, placental lactogen; tumor necrosis factor-α and -β; mullenan-inhibiting substance; mouse gonadotropm-associated peptide; lnhibin; activm, vascular endothe al growth factor; mtegπn; thrombopoietin (TPO), nerve growth factors such as NGF-β; platelet- growth factor; transforming growth factors (TGFs) such as TGF-α and TGF-β, insulin-like growth factor-I and -II, erythropoietm (EPO); osteomductive factors; interferons such as interferon-α, -β, and -γ; colony stimulating factors (CSFs) such as macrophage-CSF (M-CSF); granulocyte-macrophage-CSF (GM-CSF); and granulocyte-CSF (G-CSF), interleukins (ILs) such as IL-1, IL-lα, IL-2, IL-3, IL-4, IL-5, IL-6, IL-7, IL-8, IL-9, IL-11, IL-12, IL-15, a tumor necrosis factor such as TNF-α or TNF-β; and other polypeptide factors mcludmg LIF and kit gand (KL). As used herem, the term cytokme mcludes protems from natural sources or from recombmant cell culture and biologically active equivalents of the native sequence cytokmes The term "prodrug" as used m this application refers to a precursor or deπvative form of a pharmaceutically active substance that is less cytotoxic to tumor cells compared to the parent drug and is capable of bemg enzymatically activated or converted mto the more active parent form. See, e g , Wilman, "Prodrugs in Cancer Chemotherapy" Biochemical Society Transactions, 14, pp 375-382, 615th Meeting Belfast (1986) and Stella et al., "Prodrugs. A Chemical Approach to Targeted Drug Delivery," Directed Drug Delivery, Borchardt et al , (ed ), pp. 247-267, Humana Press ( 1985) The prodrugs of this mvention mclude, but are not limited to, phosphate-contammg prodrugs, fhiophosphate-containing prodrugs. sulfate-containmg prodrugs, peptide-containing prodrugs, D-amino acid-modified prodrugs, glycosylated prodrugs, β-lactam-containing prodrugs, optionally substituted phenoxyacetamide-containing prodrugs or optionally substituted phenylacetamide-contaimng prodrugs, 5-fluorocytosme and other 5-fluorouπdme prodrugs which can be converted mto the more active cytotoxic free drug. Examples of cytotoxic drugs that can be deπvatized mto a prodrug form for use m this mvention mclude, but are not limited to, those chemotherapeutic agents descnbed above A "hposome" is a small vesicle composed of vanous types of hpids, phospho pids and/or surfactant which is useful for delivery of a drug (such as the antagonists disclosed herem and, optionally, a chemotherapeutic agent) to a mammal. The components of the hposome are commonly arranged m a bilayer formation, similar to the pid arrangement of biological membranes The term "package insert" is used to refer to instructions customanly mcluded in commercial packages of therapeutic products, that contain information about the indications, usage, dosage, administration, contraindications and/or warnings concerning the use of such therapeutic products II. Production of Antagonists The methods and articles of manufacture of the present invention use, or incorporate, an antagonist which bmds to CD20 Accordmgly, methods for generatmg such antagonists will be descπbed here The CD20 antigen to be used for production of or screenmg for, antagonιst(s) may be, e g , a soluble form of the antigen or a portion thereof, containing the desired epitope Alternatively, or additionally, cells expressing CD20 at their cell surface can be used to generate or screen for, antagonιst(s) Other forms of CD20 useful for generatmg antagonists will be apparent to those skilled m the art While the preferred antagonist is an antibody, antagonists other than antibodies are contemplated herem For example, the antagonist may compnse a small molecule antagonist optionally fused to, or conjugated with, a cytotoxic agent (such as those descnbed herem) Libranes of small molecules may be screened agamst CD20 in order to identify a small molecule which bmds to that antigen The small molecule may further be screened for its antagonistic properties and/or conjugated with a cytotoxic agent The antagonist may also be a peptide generated by rational design or by phage display (see, e g , WO98/35036 published 13 August 1998) In one embodiment, the molecule of choice may be a "CDR mimic" or antibody analogue designed based on the CDRs of an antibody While such peptides may be antagonistic by themselves, the peptide may optionally be fused to a cytotoxic agent so as to add or enhance antagonistic properties of the peptide A descnption follows as to exemplary techniques for the production of the antibody antagonists used m accordance with the present mvention (i) Polyclonal antibodies Polyclonal antibodies are preferably raised m animals by multiple subcutaneous (sc) or mtrapentoneal (lp) injections of the relevant antigen and an adjuvant It may be useful to conjugate the relevant antigen to a protem that is lmmunogenic in the species to be immunized, e g , keyhole limpet hemocyanin, serum albumm, bovme thyroglobulm, or soybean trypsm inhibitor usmg a bifunctional or denvatizmg agent, for example, maleimidobenzoyl sulfosuccmimide ester (conjugation through cysteme residues), N-hydroxysuccimmide (through lysme residues), glutaraldehyde, succmic anhydride, SOCl 2 . or R'N=C=NR, where R and R 1 are different alkyl groups Animals are immunized agamst the antigen, lmmunogenic conjugates, or denvatives by combining, e g , 100 μg or 5 μg of the protem or conjugate (for rabbits or mice, respectively) with 3 volumes of Freund's complete adjuvant and mjectmg the solution lntradermally at multiple sites One month later the animals are boosted with 1/5 to 1/10 the oπgmal amount of peptide or conjugate m Freund's complete adjuvant by subcutaneous injection at multiple sites Seven to 14 days later the animals are bled and the serum is assayed for antibody titer Animals are boosted until the titer plateaus Preferably, the animal is boosted with the conjugate of the same antigen, but conjugated to a different protem and/or through a different cross-linking reagent Conjugates also can be made m recombinant cell culture as protem fusions Also, aggregatmg agents such as alum are suitably used to enhance the immune response (u) Monoclonal antibodies Monoclonal antibodies are obtained from a population of substantially homogeneous antibodies, i e , the individual antibodies compnsmg the population are identical except for possible naturally occurring mutations that may be present m mmor amounts Thus, the modifier "monoclonal" indicates the character of the antibody as not bemg a mixture of discrete antibodies For example, the monoclonal antibodies may be made usmg the hybndoma method first descπbed by Kohler et al Nature, 256495 (1975) or may be made by recombmant DNA methods (U S Patent No 4,816,567) In the hybndoma method, a mouse or other appropnate host animal, such as a hamster, is immunized as heremabove descnbed to elicit lymphocytes that produce or are capable of producing antibodies that will specifically bmd to the protem used for immunization Alternatively, lymphocytes may be immunized in vitro Lymphocytes then are fused with myeloma cells usmg a suitable fusing agent, such as polyethylene glycol. to form a hvbndoma cell (Godmg, Monoclonal Antibodies Principles and Pi actice, pp 59-103 (Academic Press. 1986)) The hybndoma cells thus prepared are seeded and grown in a suitable culture medium that preferably contains one or more substances that inhibit the growth or survival of the unfused, parental myeloma cells For example, if the parental myeloma cells lack the enzyme hypoxanthine guanme phosphoπbosyl transferase (HGPRT or HPRT), the culture medium for the hybndomas typically will mclude hypoxanthine. ammopteπn. and thymidine (HAT medium), which substances prevent the growth of HGPRT-deficient cells Preferred myeloma cells are those that fuse efficiently, support stable high-level production of antibody by the selected antibody-producing cells, and are sensitive to a medium such as HAT medium Among these, preferred myeloma cell lmes are murine myeloma lmes, such as those derived from MOPC-21 and MPC-11 mouse tumors available from the Salk Institute Cell Distπbution Center, San Diego, California USA, and SP-2 or X63- Ag8-653 cells available from the Amencan Type Culture Collection, Rockville, Maryland USA Human myeloma and mouse- human heteromyeloma cell lmes also have been descπbed for the production of human monoclonal antibodies (Kozbor, / Immunol , 133 3001 (1984), Brodeur et al , Monoclonal Antibody Production Techniques and Applications, pp 51-63 (Marcel Dekker, Inc , New York, 1987)) Culture medium m which hybndoma cells are growmg is assayed for production of monoclonal antibodies directed agamst the antigen Preferably, the bmdmg specificity of monoclonal antibodies produced by hybndoma cells is determmed by lmmunoprecipitation or by an in vitro bmdmg assay, such as radioimmunoassay (RIA) or enzyme- linked immunoabsorbent assay (ELISA) The bmdmg affinity of the monoclonal antibody can, for example, be determmed by the Scatchard analysis of Munson et al , Anal Biochem , 107 220 (1980) After hybndoma cells are identified thatproduce antibodies of the desired specificity, affinity, and or activity, the clones may be subcloned by limiting dilution procedures and grown by standard methods (Godmg. Monoclonal Antibodies Principles and Practice, pp 59-103 (Academic Press, 1986)) Suitable culture media for this purpose mclude, for example, D-MEM or RPMI-1640 medium In addition, the hybndoma cells may be grown in vno as ascites tumors m an animal The monoclonal antibodies secreted by the subclones are suitably separated from the culture medium, ascites fluid, or serum by conventional immunoglobulin punfication procedures such as, for example, protein A-Sepharose, hydroxylapatite chromatography, gel electrophoresis, dialysis, or affinity chromatography DNA encodmg the monoclonal antibodies is readily isolated and sequenced usmg conventional procedures (e g , by usmg ohgonucleotide probes that are capable of bmdmg specifically to genes encodmg the heavy and light chams of muπne antibodies) The hybndoma cells serve as a preferred source of such DNA Once isolated, the DNA may be placed mto expression vectors, which are then transfected mto host cells such as E coh cells, simian COS cells, Chmese Hamster Ovary (CHO) cells, or myeloma cells that do not otherwise produce immunoglobulin protem. to obtam the synthesis of monoclonal antibodies m the recombmant host cells Review articles on recombmant expression in bactena of DNA encodmg the antibody mclude Skerra et al , Curr Opinion in Immunol . 5 256-262 (1993) and Pluckthun, /7n/n«no/ Revs , 130 151-188 (1992) In a further embodiment, antibodies or antibody fragments can be isolated from antibody phage braπes generated usmg the techniques descπbed m McCafferty et al Nature, 348 552-554 (1990) Clackson efα/ Nature 352 624-628 (1991) and Marks etal , J Mol Biol , 222 581-597 (1991) descnbe the isolation of murine and human antibodies, respectively, usmg phage branes Subsequent publications descnbe the production of high affinity (nM range) human antibodies by cham shuffling (Marks et al , Bio/Technology, 10 779-783 (1992)), as well as combmatoπal mfection and m vivo recombmation as a strategy for constructing very large phage hbranes (Waterhouse etal , Nuc Acids Res .21 2265-2266(1993)) Thus, these techniques are viable alternatives to traditional monoclonal antibody hybndoma techniques for isolation of monoclonal antibodies The DNA also may be modified, for example, by substituting the coding sequence for human heavy- and light-chain constant domams m place of the homologous murine sequences (U S Patent No 4,816,567, Mornson, etal, Proc NatlAcad Sci USA. 81 6851 (1984)), or by covalently joining to the lπimunoglobulin coding sequence all or part of the codmg sequence for a non- immunoglobulin polypeptide Typically such non- immunoglobulin polypeptides are substituted for the constant domams of an antibody, or they are substituted for the vaπable domams of one antigen-combmmg site of an antibody to create a chimenc bivalent antibody compnsmg one antigen-combmmg site havmg specificity for an antigen and another antigen- combining site havmg specificity for a different antigen (in) Humanized antibodies Methods for human izmg non-human antibodies have been descπbed m the art Preferably, a humanized antibody has one or more ammo acid residues introduced mto it from a source which is non-human These non-human ammo acid residues are often refened to as "import" residues, which are typically taken from an "import" vanable domam Humanization can be essentially performed following the method of Wmter and co-workers (Jones et al , Nature, 321 522-525 (1986), Riechmann et al , Nature, 332.323-327 (1988), Verhoeyen et al , Science, 239 1534- 1536 (1988)), by substituting hypervanable region sequences for the corresponding sequences of a human antibody Accordmgly, such "humanized" antibodies are chimenc antibodies (U S Patent No 4,816,567) wherem substantially less than an mtact human vanable domam has been substituted by the corresponding sequence from a non-human species In practice, humanized antibodies are typically human antibodies m which some hypervanable region residues and possibly some FR residues are substituted by residues from analogous sites m rodent antibodies The choice of human vanable domams, both light and heavy, to be used m making the humanized antibodies is very important to reduce antigenicity Accordmg to the so-called "best-fit" method, the sequence of the vaπable domam of a rodent antibody is screened agamst the entire library of known human vanable-domam sequences The human sequence which is closest to that of the rodent is then accepted as the human framework region (FR) for the humanized antibody (Sims et al , J Immunol , 151 2296 (1993), Chothia et al , J Mol Biol , 196 901 (1987)) Another method uses a particular framework region denved from the consensus sequence of all human antibodies of a particular subgroup of light or heavy chams The same framework may be used for several different humanized antibodies (Carter et al , Proc Natl Acad Sci USA, 89 4285 (1992), Presta et al , J Immunol , 151 2623 (1993)) It is further important that antibodies be humanized with retention of high affinity for the antigen and other favorable biological properties To achieve this goal, accordmg to a preferred method, humanized antibodies are prepared by a process of analysis of the parental sequences and vanous conceptual humanized products usmg three- dimensional models of the parental and humamzed sequences Three-dimensional immunoglobulin models are commonly available and are familiar to those skilled m the art Computer programs are available which illustrate and display probable three-dimensional conformational structures of selected candidate immunoglobulin sequences Inspection of these displays permits analysis of the likely role of the residues in the functioning of the candidate immunoglobulin sequence, I e , the analysis of residues that influence the ability of the candidate immunoglobulin to bmd its antigen In this way, FR residues can be selected and combmed from the recipient and import sequences so that the desired antibody charactenstic. such as mcreased affinity for the target antigen(s), is achieved In general, the hypervanable region residues are directly and most substantially mvolved m influencing antigen bmdmg (iv) Human antibodies As an alternative to humamzation, human antibodies can be generated For example, it is now possible to produce transgenic animals (e g , mice) that are capable, upon immunization, of producmg a full repertoire of human antibodies m the absence of endogenous immunoglobulin production For example, it has been descnbed that the homozygous deletion of the antibody heavy-chain joining region (J H ) gene m chimenc and germ-line mutant mice results m complete inhibition of endogenous antibody production Transfer of the human germ-line immunoglobulin gene array in such germ- line mutant mice will result m the production of human antibodies upon antigen challenge See, e g , Jakobovits et al , Proc Natl Acad Sci USA. 90 2551 (1993), Jakobovits et al , Nature, 362 255-258 (1993), Bruggermann e/α/ Yearmlmmuno , 1 33 (1993), and US PatentNos 5,591,669, 5,589,369 and 5,545,807 Alternatively, phage display technology (McCafferty et al , Nature 348 552-553 (1990)) can be used to produce human antibodies and antibody fragments in vitro, from immunoglobulin vanable (V) domam gene repertoires from unimmunized donors Accordmg to this technique, antibody V domam genes are cloned in-frame mto either a major or mmor coat protem gene of a filamentous bactenophage, such as M13 or fd, and displayed as functional antibody fragments on the surface of the phage particle Because the filamentous particle contains a single- stranded DNA copy of the phage genome, selections based on the functional properties of the antibody also result in selection of the gene encodmg the antibody exhibiting those properties Thus, the phage mimics some of the properties of the B cell Phage display can be performed in a vanety of formats, for their review see, e , Johnson, KevmS and Chiswell, David J , Current Opinion in Structural Biology 3 564-571 (1993) Several sources of V-gene segments can be used for phage display Clackson et al , Nature, 352 624-628 ( 1991 ) isolated a diverse array of anti- oxazolone antibodies from a small random combmatonal library of V genes deπved from the spleens of immunized mice A repertoire of V genes from unimmunized human donors can be constructed and antibodies to a diverse array of antigens (including self-antigens) can be isolated essentially following the techniques descπbed by Marks et al , J Mol Biol 222 581-597 (1991), oτ Griffith, et al , EMBO J 12 725-734 (1993) See, also, US Patent Nos 5,565,332 and 5,573.905 Human antibodies may also be generated by in vitro activated B cells (see US Patents 5,567,610 and 5,229,275) (v) Antibody fragments Vaπous techniques have been developed for the production of antibody fragments Traditionally, these fragments were denved via proteolytic digestion of intact antibodies (see, e g , Monmoto et al , Journal of Biochemical and Biophysical Methods 24 107-117 (1992) and Brennan et al , Science, 229 81 (1985)) However, these fragments can now be produced directly by recombmant host cells For example, the antibody fragments can be isolated from the antibody phage hbranes discussed above Alternatively, Fab'-SH fragments can be directly recovered from E coh and chemically coup led to form F(ab') 2 fragments (Carter etal , Bio/Technology 10 163-167 ( 1992)) Accordmg to another approach, F(ab') 2 fragments can be isolated directly from recombmant host cell culture Other techniques for the production of antibody fragments will be apparent to the skilled practitioner In other embodiments, the antibody of choice is a smgle cham Fv fragment (scFv) See WO 93/16185, US Patent No 5,571 ,894, and US Patent No 5,587,458 The antibody fragment may also be a "linear antibody", e , as descnbed in US Patent 5,641,870 for example Such lmear antibody fragments may be monospecific or bispecific (vi) Bispecific antibodies Bispecific antibodies are antibodies that have binding specificities for at least two different epitopes Exemplary bispecific antibodies may bmd to two different epitopes of CD20 Alternatively, an antι-CD20 bmdmg arm may be combmed with an arm which bmds to a tnggenng molecule on a leukocyte such as a T-cell receptor molecule (e g CD2 or CD3), or Fc receptors for IgG (FcγR), such as FcγRI (CD64), FcγRII (CD32) and FcγRIII (CD 16) so as to focus cellular defense mechanisms to the B cell Bispecific antibodies may also be used to localize cytotoxic agents to the B cell These antibodies possess a CD20-bιndιng arm and an arm which bmds the cytotoxic agent (e g saponn, anti-interferon-α. vinca alkaloid, ncm A chain, methotrexate or radioactive isotope hapten) Bispecific antibodies can be prepared as full length antibodies or antibody fragments (e F(ab') ? bispecific antibodies) Methods for making bispecific antibodies are known m the art Traditional production of full length bispecific antibodies is based on the coexpression of two immunoglobulm heavy chain-light cham parrs, where the two chams have different specificities (Millstein et al , Nature, 305 537-539 (1983)) Because of the random assortment of immunoglobulm heavy and light chams, these hybndomas (quadromas) produce a potential mixture of 10 different antibody molecules, of which only one has the correct bispecific structure Punfication of the correct molecule, which is usually done by affinity chromatography steps, is rather cumbersome, and the product yields are low Similar procedures are disclosed m WO 93/08829, and m Traunecker et al , EMBO J , 10 3655-3659 (1991) Accordmg to a different approach, antibody vaπable domams with the desired bmdmg specificities (antibody-antigen combining sites) are fused to immunoglobulm constant domam sequences The fusion preferably is with an immunoglobulin heavy cham constant domam, compπsmg at least part of the hmge, CH2, and CH3 regions It is preferred to have the first heavy-chain constant region (CH 1 ) containing the site necessary for light cham bmdmg, present m at least one of the fusions DNAs encodmg the immunoglobulm heavy cham fusions and, if desired, the immunoglobulm light cham, are inserted mto separate expression vectors, and are co-transfected mto a suitable host organism This provides for great flexibility m adjustmg the mutual proportions of the three polypeptide fragments m embodiments when unequal ratios of the three polypeptide chams used m the construction provide the optimum yields It is, however, possible to insert the codmg sequences for two or all three polypeptide chams m one expression vector when the expression of at least two polypeptide chams m equal ratios results m high yields or when the ratios are of no particular significance In a preferred embodiment of this approach, the bispecific antibodies are composed of a hybnd immunoglobulm heavy cham with a first bmdmg specificity m one arm. and a hybnd immunoglobulm heavy chain- light cham pair (providing a second bmdmg specificity) in the other arm It was found that this asymmetnc structure facilitates the separation of the desired bispecific compound from unwanted immunoglobulin cham combmations, as the presence of an immunoglobulm light cham m only one half of the bispecific molecule provides for a facile way of separation This approach is disclosed m WO 94/04690 For further details of generatmg bispecific antibodies see, for example, Suresh et al , Methods in Enzvmology, 121 210 (1986) Accordmg to another approach descnbed m US Patent No 5,731,168, the mterface between a pair of antibody molecules can be engmeered to maximize the percentage of heterodimers which are recovered from recombinant cell culture The prefened mterface compnses at least a part of the C H 3 domam of an antibody constant domam In this method, one or more small ammo acid side chams from the mterface of the first antibody molecule are replaced with larger side chams (e g tyrosme or tryptophan) Compensatory "cavities" of identical or similar size to the large side cham(s) are created on the mterface of the second antibody molecule by replacmg large amino acid side chams with smaller ones (e g alanme or fhreonine) This provides a mechanism for mcreasmg the vield of the heterodimer over other unwanted end-products such as homodimers Bispecific antibodies include cross-linked or "heteroconjugate" antibodies For example, one of the antibodies in the heteroconjugate can be coupled to avidin, the other to biotm Such antibodies have for example, been proposed to target immune system cells to unwanted cells (US Patent No 4,676,980), and for treatment of HIV mfection (WO 91/00360, WO 92/200373. and EP 03089) Heteroconjugate antibodies may be made usmg any convenient cross-linking methods Suitable cross-linking agents are well known m the art, and are disclosed in US Patent No 4,676,980, along with a number of cross-linking techniques Techniques for generatmg bispecific antibodies from antibody fragments have also been descnbed m the literature For example, bispecific antibodies can be prepared usmg chemical linkage Brennan et al Science, 229 81 (1985) descnbe a procedure wherem mtact antibodies are proteolytically cleaved to generate F(ab')- > fragments These fragments are reduced m the presence of the dithiol complexmg agent sodium arsemte to stabilize vicmal dithiols and prevent intermolecular disulfide formation The Fab' fragments generated are then converted to thionitrobenzoate (TNB) denvatives One of the Fab'-TNB denvatives is then reconverted to the Fab'-thiol by reduction with mercaptoethylamine and is mixed with an equimolar amount of the other Fab'-TNB denvative to form the bispecific antibody The bispecific antibodies produced can be used as agents for the selective immobilization of enzymes Recent progress has facilitated the direct recovery of Fab'-SH fragments from E coll which can be chemically coupled to form bispecific antibodies Shalaby et al , J Exp Med , 175 217-225 (1992) descnbe the production of a fully humanized bispecific antibody F(ab') 2 molecule Each Fab' fragment was separately secreted from E coli and subjected to directed chemical coupling in vitro to form the bispecific antibody The bispecific antibody thus formed was able to bmd to cells overexpressmg the ErbB2 receptor and normal human T cells, as well as tngger the lytic activity of human cytotoxic lymphocytes agamst human breast tumor targets Vanous techniques for makmg and isolating bispecific antibody fragments directly from recombmant cell culture have also been descπbed For example, bispecific antibodies have been produced usmg leucine zippers Kostelny et al , J Immunol , 148(5) 1547-1553 (1992) The leucine zipper peptides from the Fos and Jun protems were linked to the Fab' portions of two different antibodies by gene fusion The antibody homodimers were reduced at the hmge region to form monomers and then re-oxidized to form the antibody heterodimers This method can also be utilized for the production of antibody homodimers The "diabody" technology descπbed by Hollinger et al Proc Natl Acad Sci USA, 90 6444-6448 (1993) has provided an alternative mechanism for makmg bispecific antibody fragments The fragments compnse a heavy-chain vanable domam (V H ) connected to a light-chain vanable domam (V L ) by a linker which is too short to allow pairing between the two domams on the same cham Accordmgly, the V H and V L domams of one fragment are forced to pair with the complementary V L and V H domams of another fragment, thereby forming two antigen-bmdmg sites Another strategy for makmg bispecific antibody fragments by the use of smgle-cham Fv (sFv) dimers has also been reported See Gruber et al J Immunol , 152 5368 (1994) Antibodies with more than two valencies are contemplated For example, tπspecific antibodies can be prepared Tutt et al J Immunol 147 60 (1991) III. Conjugates and Other Modifications of the Antagonist The antagonist used m the methods or mcluded m the articles of manufacture herem is optionally conjugated to a cytotoxic agent Chemotherapeutic agents useful in the generation of such antagonist-cvtotoxic agent conjugates have been descnbed above Conjugates of an antagonist and one or more small molecule toxms, such as a calicheamicm, a maytansme (US Patent No 5,208,020), a tnchothene, and CC1065 are also contemplated herem In one embodiment of the mvention, the antagonist is conjugated to one or more maytansme molecules (e g about 1 to about 10 maytansme molecules per antagonist molecule) Maytansme may, for example, be converted to May-SS-Me which may be reduced to May-SH3 and reacted with modified antagonist (Chan et al Cancer Research 52 127-131 (1992)) to generate a maytansmoid-antagonist conjugate Alternatively, the antagonist is conjugated to one or more calicheamicm molecules The calicheamicm family of antibiotics are capable of producmg double-stranded DNA breaks at sub-picomolar concentrations Structural analogues of calicheamicm which may be used mclude, but are not limited to, γ, 1 , α 2 , α 3 , N-acetyl-γ, , PSAG and θ [ , (Hmman e/ α/ Cancer Research 53 3336-3342 (1993) and Lode et al Cancer Research 58 2925-2928 (1998)) Enzymatically active toxms and fragments thereof which can be used mclude diphthena A cham, nonbmdmg active fragments of diphthena toxm, exotoxm A cham (from Pseudomonas aeruginosa), ncin A cham, abnn A cham, modeccm A cham, alpha-sarcrn, Aleuntes fordu protems, dianthin protems, Phytolaca americana proteins (PAPI, PAP II. and P AP-S), momordica charantia inhibitor, curcin, crotm, sapaonana offϊcinalis inhibitor, gelonm. mitogellm, restnctocm, phenomycm, enomycm and the tπcothecenes See, for example, WO 93/21232 published October 28, 1993 The present mvention further contemplates antagonist conjugated with a compound with nucleolytic activity (e g a πbonuclease or a DNA endonuclease such as a deoxynbonuclease, DNase) A vaπety of radioactive isotopes are available for the production of radioconjugated antagonists Examples mclude At 211 , 1 131 , 1 125 , Y 90 , Re 186 , Re 188 , Sm 153 , Bi 212 , P 32 and radioactive isotopes of Lu Conjugates of the antagonist and cytotoxic agent may be made usmg a vanety of bifunctional protem coupling agents such as N-succιnιmιdyl-3-(2-pyndyldιthιol) propionate (SPDP), succmιmιdyl-4-(N-maleιmιdomethyl) cyclohexane- 1 -carboxylate, lminothiolane (IT), bifunctional denvatives of lmidoesters (such as dimethyl adipunidate HCL). active esters (such as disuccinimidyl suberate), aldehydes (such as glutareldehyde), bis-azido compounds (such as bis (p-azidobenzoyl) hexanediamine), bis-diazonium denvatives (such as bιs-(p-dιazonιumbenzoyl)- ethylenediamine), dusocyanates (such as tolyene 2.6-dιιsocyanate), and bis-active fluorine compounds (such as 1 ,5- dιfluoro-2,4-dιmtrobenzene) For example, a πcm lmmunotoxin can be prepared as descnbed m Vitetta et al Science 238 1098 (1987) Carbon- 14-labeled l-isothiocyanatobenzyl-3-methyldiethylene tnammepentaacetic acid (MX- DTP A) is an exemplary chelatmg agent for conjugation of radionucleotide to the antagonist See W094/11026 The linker may be a "cleavable linker" facilitating release of the cytotoxic drug m the cell For example, an acid-labile linker, peptidase-sensitive linker, dimethyl linker or disulfide-contaimng linker (Chan etal Cancer Research 52 127- 131 (1992)) may be used Alternatively, a fusion protein compnsing the antagonist and cytotoxic agent may be made, e g by recombmant techniques or peptide synthesis In yet another embodiment, the antagonist may be conjugated to a "receptor" (such streptavidm) for utilization in tumor pretargeting wherem the antagonist-receptor conjugate is administered to the patient, followed by removal of unbound conjugate from the circulation using a clearing agent and then administration of a "ligand" (e g avidm) which is conjugated to a cytotoxic agent (e g a radionucleotide) The antagonists of the present mvention may also be conjugated with a prodrug-activating enzyme which converts a prodrug (e g a peptidyl chemotherapeutic agent, see W081 /01145) to an active anti-cancer drug See, for example, WO 88/07378 and U S Patent No 4,975,278 The enzyme component of such conjugates mcludes any enzyme capable of acting on a prodrug m such a way so as to covert it mto its more active, cytotoxic form Enzymes that are useful m the method of this mvention mclude, but are not limited to, alkaline phosphatase useful for converting phosphate-contammg prodrugs mto free drugs, arvlsulfatase useful for converting sulfate- contaimng prodrugs mto free drugs, cytosine deaminase useful for converting non-toxic 5-fluorocytosιne mto the anti- cancer drug, 5-fluorouracιl, proteases, such as senatia protease, thermolysin. subtihsm, carboxypeptidases and cathepsins (such as cathepsins B and L), that are useful for converting peptide-containing prodrugs mto free drugs, D-alanylcarboxypeptidases, useful for converting prodrugs that contain D-ammo acid substituents, carbohydrate- cleaving enzymes such as β-galactosidase and neurammidase useful for converting glycosylated prodrugs mto free drugs, β-lactamase useful for converting drugs deπvatized with β-lactams mto free drugs, and penicillin amidases, such as penicillin V amidase or penicillin G amidase, useful for converting drugs denvatized at their amme nitrogens with phenoxyacetyl or phenylacetyl groups, respectively, mto free drugs Alternatively, antibodies with enzymatic activity, also known m the art as "abzymes", can be used to convert the prodrugs of the mvention mto free active drugs (see, e g , Massey, Nature 328 457-458 (1987)) Antagonist-abzyme conjugates can be prepared as descnbed herem for delivery of the abzyme to a tumor cell population The enzymes of this mvention can be covalently bound to the antagonist by techniques well known m the art such as the use of the heterobifunctional crosslinking reagents discussed above Alternatively, fusion protems compnsmg at least the antigen bmdmg region of an antagonist of the invention linked to at least a functionally active portion of an enzyme of the mvention can be constructed usmg recombmant DNA techmques well known m the art (see, e g , Neuberger et al , Nature, 312 604-608 (1984)) Other modifications of the antagonist are contemplated herem For example, the antagonist may be linked to one of a vanety of nonprotemaceous polymers, e g , polyethylene glycol, polypropylene glycol, polyoxyalkylenes, or copolymers of polyethylene glycol and polypropylene glycol The antagonists disclosed herem may also be formulated as liposomes Liposomes containing the antagonist are prepared by methods known m the art, such as descπbed in Epstem et al , Proc Natl Acad Sci USA, 82 3688 (1985), Hwang et al , Proc Natl Acad Sci USA, 11 4030 (1980), U S Pat Nos 4,485,045 and 4,544,545, and W097/38731 published October 23 1997 Liposomes with enhanced circulation time are disclosed m U S Patent No 5,013,556 Particularly useful liposomes can be generated by the reverse phase evaporation method with a pid composition compπsmg phosphatidylcholine, cholesterol and PEG-denvatized phosphatidylethanolamine (PEG-PE) Liposomes are extruded through filters of defined pore size to yield liposomes with the desired diameter Fab' fragments of an antibody of the present mvention can be conjugated to the liposomes as descnbed in Martin et al J Biol Chem 257 286-288 (1982) via a disulfide interchange reaction A chemotherapeutic agent is optionally contained within the hposome See Gabizon et al J National Cancer Inst 81(19)1484 (1989) Ammo acid sequence modιficatιon(s) of protem or peptide antagonists descnbed herein are contemplated For example, it may be desirable to improve the bmdmg affinity and/or other biological properties of the antagonist Ammo acid sequence vanants of the antagonist are prepared by introducing appropnate nucleotide changes mto the antagonist nucleic acid, or by peptide synthesis Such modifications mclude. for example, deletions from, and/or insertions mto and/or substitutions ot. residues within the ammo acid sequences of the antagonist Any combination of deletion, insertion, and substitution is made to arnve at the final construct, provided that the final construct possesses the desired charactenstics The ammo acid changes also may alter post-translational processes of the antagonist, such as changing the number or position of glycosylation sites A useful method for identification of certain residues or regions of the antagonist that are prefeπed locations for mutagenesis is called " alamne scannmg mutagenesis" as descπbed by Cunningham and Wells Science, 244.1081- 1085 ( 1989) Here, a residue or group of target residues are identified (e g , charged residues such as arg, asp, his, lys, and glu) and replaced by a neutral or negatively charged ammo acid (most preferably alanine or polyalanine) to affect the interaction of the ammo acids with antigen Those ammo acid locations demonstrating functional sensitivity to the substitutions then are refined by introducing further or other vanants at, or for, the sites of substitution. Thus, while the site for introducing an ammo acid sequence vaπation is predetermmed, the nature of the mutation pe se need not be predetermmed For example, to analyze the performance of a mutation at a given site, ala scannmg or random mutagenesis is conducted at the target codon or region and the expressed antagonist vanants are screened for the desired activity Ammo acid sequence insertions mclude ammo- and/or carboxyl-terminal fusions rangmg m length from one residue to polypeptides containing a hundred or more residues, as well as lntrasequence insertions of smgle or multiple ammo acid residues. Examples of terminal insertions mclude an antagonist with an N-teπmnal methionyl residue or the antagonist fused to a cytotoxic polypeptide. Other lnsertional vanants of the antagonist molecule mclude the fusion to the N- or C-terminus of the antagonist of an enzyme, or a polypeptide which mcreases the serum half-life of the antagonist. Another type of vanant is an ammo acid substitution vanant. These vanants have at least one ammo acid residue in the antagonist molecule replaced by different residue. The sites of greatest mterest for substitutional mutagenesis of antibody antagonists mclude the hypervanable regions, but FR alterations are also contemplated. Conservative substitutions are shown m Table 1 under the heading of "preferred substitutions". If such substitutions result m a change m biological activity, then more substantial changes, denommated "exemplary substitutions" m Table 1, or as further descnbed below in reference to ammo acid classes, may be introduced and the products screened Table 1 Substantial modifications m the biological properties of the antagonist are accomplished by selecting substitutions that differ significantly in their effect on maintaining (a) the structure of the polypeptide backbone m the area of the substitution, for example, as a sheet or helical conformation, (b) the charge or hydrophobicity of the molecule at the target site, or (c) the bulk of the side cham. Naturally occurring residues are divided mto groups based on common side-cham properties: (1) hydrophobic: norleucme, met, ala, val, leu, lie; (2) neutral hydrophihc cys, ser, thr; (3) acidic: asp, glu, (4) basic: asn, gin, his, lys, arg; (5) residues that influence cham onentation: gly, pro. and (6) aromatic: trp, tyr, phe Non-conservative substitutions will entail exchangmg a member of one of these classes for another class Any cysteme residue not mvolved m maintaining the proper conformation of the antagonist also may be substituted, generally with senne, to improve the oxidative stability of the molecule and prevent abeπant crosshnking Conversely, cysteme bond(s) may be added to the antagonist to improve its stability (particularly where the antagomst is an antibody fragment such as an Fv fragment) A particularly preferred type of substitutional vanant mvolves substituting one or more hypervanable region residues of a parent antibody. Generally, the resultmg vanant(s) selected for further development will have improved biological properties relative to the parent antibody from which they are generated A convenient way for generatmg such substitutional vanants is affinity maturation usmg phage display. Bπefly, several hypervanable region sites (e 6-7 sites) are mutated to generate all possible ammo substitutions at each site. The antibody vanants thus generated are displayed in a monovalent fashion from filamentous phage particles as fusions to the gene III product of Ml 3 packaged within each particle The phage-displayed vanants are then screened for their biological activity (e g bmdmg affinity) as herem disclosed In order to identify candidate hypervanable region sites for modification, alanine scannmg mutagenesis can be performed to identify hypervanable region residues contnbuting significantly to antigen bmdmg Alternatively or m additionally, it may be beneficial to analyze a crystal structure of the antigen-antibody complex to identify contact points between the antibody and antigen Such contact residues and neighboring residues are candidates for substitution accordmg to the techmques elaborated herem Once such vanants are generated, the panel of vanants is subjected to screenmg as descπbed herem and antibodies with supenor properties m one or more relevant assays mav be selected for further development Another type of ammo acid vanant of the antagonist alters the oπgmal glycosylation pattern of the antagomst By altering is meant deleting one or more carbohydrate moieties found m the antagonist, and/or addmg one or more glycosylation sites that are not present m the antagonist Glycosylation of polypeptides is typically either N-lmked or O-linked N-linked refers to the attachment of the carbohydrate moiety to the side cham of an asparagme residue The tnpeptide sequences asparagme-X-senne and asparagine-X-threomne, where X is any ammo acid except prolme, are the recognition sequences for enzymatic attachment of the carbohydrate moiety to the asparagme side cham Thus, the presence of either of these tnpeptide sequences m a polypeptide creates a potential glycosylation site O-linked glycosylation refers to the attachment of one of the sugars N-aceylgalactosamrne, galactose, or xylose to a hydroxyamino acid, most commonly seπne or threomne, although 5-hydroxyprolιne or 5-hydroxylysme may also be used Addition of glycosylation sites to the antagonist is conveniently accomplished by altering the ammo acid sequence such that it contains one or more of the above-descnbed tnpeptide sequences (for N-lmked glycosylation sites) The alteration may also be made by the addition of, or substitution by, one or more seπne or threomne residues to the sequence of the ongmal antagonist (for O- linked glycosylation sites) Nucleic acid molecules encodmg ammo acid sequence vanants of the antagonist are prepared by a vanety of methods known m the art These methods mclude, but are not limited to, isolation from a natural source (m the case of naturally occurring ammo acid sequence vanants) or preparation by ohgonucleotide-mediated (or site-directed) mutagenesis, PCR mutagenesis, and cassette mutagenesis of an earlier prepared vanant or a non- vanant version of the antagonist It may be desirable to modify the antagonist of the invention with respect to effector function g so as to enhance antigen-dependent cell-mediated cyotoxicity (ADCC) and/or complement dependent cytotoxicity (CDC) of the antagonist This may be achieved by introducing one or more ammo acid substitutions in an Fc region of an antibody antagomst Alternatively or additionally, cysteme resιdue(s) may be introduced m the Fc region, thereby allowing mtercham disulfide bond formation m this region The homodimenc antibody thus generated may have improved lnternalization capability and/or mcreased complement-mediated cell killing and antibody-dependent cellular cytotoxicity (ADCC) See Caron et al , J Exp Med 176 1191-1195 (1992) and Shopes, B J Immunol 148 2918-2922 (1992) Homodimenc antibodies with enhanced anti-tumor activity may also be prepared usmg heterobifunctional cross-linkers as descnbed in Wolff et al Cancer Research 53 2560-2565 (1993) Alternatively, an antibody can be engineered which has dual Fc regions and may thereby have enhanced complement lysis and ADCC capabilities See Stevenson et al Anti-Cancer Drug Design 3 219-230 (1989) To mcrease the serum half life of the antagonist, one may incorporate a salvage receptor binding epitope mto the antagonist (especially an antibody fragment) as descπbed in US Patent 5.739,277, for example As used herem, the term "salvage receptor bmdmg epitope" refers to an epitope of the Fc region of an IgG molecule (e g , IgG,, IgG 2 , IgG-,, or IgG 4 ) that is responsible for increasing the in vivo serum half- life of the IgG molecule IV. Pharmaceutical Formulations Therapeutic formulations of the antagonists used m accordance with the present mvention are prepared for storage by mixing an antagonist havmg the desired degree of puπty with optional pharmaceutically acceptable earners, excipients or stabilizers (Remington 's Pharmaceutical Sciences 16th edition. Osol, A. Ed (1980)), m the form of lyophihzed formulations or aqueous solutions. Acceptable earners, excipients. or stabilizers are nontoxic to recipients at the dosages and concentrations employed, and mclude buffers such as phosphate, citrate, and other organic acids; antioxidants mcludmg ascorbic acid and methionine; preservatives (such as octadecyldimethylbenzyl ammonium chlonde, hexamethonium chlonde; benzalkonium chlonde, benzethonium chloπde, phenol, butyl or benzyl alcohol; alkyl parabens such as methyl or propyl paraben; catechol: resorcrnol. cyclohexanol, 3-pentanol; and m-cresol); low molecular weight (less than about 10 residues) polypeptides; protems, such as serum albumm, gelatm, or immunoglobulins; hydrophilic polymers such as polyvmylpyrro done: ammo acids such as glycme, glutamine, asparagme, histidme, arginine, or lysme; monosacchaπdes, disacchaπdes, and other carbohydrates mcludmg glucose, mannose, or dextπns; chelatmg agents such as EDTA; sugars such as sucrose, manmtol, trehalose or sorbitol; salt- forming counter-ions such as sodium; metal complexes (e g Zn-protem complexes): and or non-iomc surfactants such as TWEEN™, PLURONICS™ or polyethylene glycol (PEG). Exemplary antι-CD20 antibody formulations are descnbed m W098/56418, expressly incorporated herem by reference. This publication descnbes a liquid multidose formulation compnsing 40 mg/mL ntuximab, 25 mM acetate, 150 mM trehalose, 0.9% benzyl alcohol, 0.02% polysorbate 20 at pH 5.0 that has a minimum shelf life of two years storage at 2-8°C Another antι-CD20 formulation of interest compnses lOmg mL ntuximab m 9.0 mg/mL sodium chlonde, 7.35 mg/mL sodium citrate dihydrate, 0.7mg mL polysorbate 80, and Stenle Water for Injection, pH 6.5. Lyophilized formulations adapted for subcutaneous administration are descnbed m WO97/04801. Such lyophilized formulations may be reconstituted with a suitable diluent to a high protem concentration and the reconstituted formulation may be admmistered subcutaneously to the mammal to be treated herem. The formulation herem may also contain more than one active compound as necessary for the particular indication bemg treated, preferably those with complementary activities that do not adversely affect each other. For example, it may be desirable to further provide a cytotoxic agent, chemotherapeutic agent, cytokme or immunosuppressive agent (e g one which acts on T cells, such as cyclosponn or an antibody that bmds T cells, e g one which bmds LFA- 1 ). The effective amount of such other agents depends on the amount of antagonist present m the formulation, the type of disease or disorder or treatment, and other factors discussed above. These are generally used m the same dosages and with administration routes as used herembefore or about from 1 to 99% of the heretofore employed dosages The active mgredients may also be entrapped m microcapsules prepared, for example, by coacervation techniques or by mterfacial polymeπzation, for example, hydroxymethylcellulose or gelatin-microcapsules and poly- (methylmethacylate) microcapsules, respectively, m colloidal drug delivery systems (for example, liposomes, albumm microspheres, microemulsions, nano-particles and nanocapsules) or m macroemulsions Such techniques are disclosed in Remington's Pharmaceutical Sciences 16th edition, Osol, A Ed. (1980) Sustained-release preparations may be prepared. Suitable examples of sustained-release preparations mclude semipermeable matnces of solid hydrophobic polymers contammg the antagonist, which matnces are in the form of shaped articles, e g films, or microcapsules. Examples of sustained-release matπces mclude polyesters, hydrogels (for example, poly(2-hydroxyethyl-methacrylate), or poly(vιnylalcohol)), polylactides (U.S. Pat. No. 3,773,919), copolymers of L-glutamic acid and γ ethyl-L-glutamate. non-degradable ethylene- vmyl acetate, degradable lactic acid- glyco c acid copolymers such as the LUPRON DEPOT™ (injectable microspheres composed of lactic acid-glyco c acid copolymer and leupro de acetate), and poly-D-(-)-3-hydroxybutyπc acid The formulations to be used for in vivo administration must be stenle This is readily accomplished by filtration through stenle filtration membranes V. Treatment with the Antagomst The antagonist which binds to CD20 may be used to block an immune response to a foreign antigen m a mammal (preferably a human), wherein the mammal is not suffenng from a malignancy Preferably, the antagonist compπses an antι-CD20 antibody The antibody m one embodiment is not conjugated with a cytotoxic agent, m another, the antibody is conjugated with a cytotoxic agent (e g Y2B8 or 131 I-B1) The mammal to be treated herem may be exposed to both the antagonist which bmds to CD20 and a further different therapeutic agent, e g , where the therapeutic agent is lmmunogenic m the mammal In this embodiment, the antagonist may block an immune response to the therapeutic agent m the mammal treated therewith The therapeutic benefit may also mclude blocking removal of antibody coated cells by the spleen The therapeutic agent is admmistered to the mammal in a therapeutically effective amount to treat a disease or disorder which could benefit from administration of the therapeutic agent In this embodiment, one may administer the therapeutic agent and the antagonist essentially simultaneously or separately m either order to the mammal Hence, the antagomst may be admmistered to the mammal pπor to the therapeutic agent, or the therapeutic agent may be administered to the mammal pnor to the antagonist The antagonist which binds to CD20 may thus be used to treat graft- versus-host or host-versus-graft disease m a mammal and/or to desensitize a mammal awaitmg transplantation For the vaπous indications disclosed herem, a composition compnsmg an antagomst which bmds to CD20 will be formulated, dosed, and admmistered m a fashion consistent with good medical practice Factors for consideration m this context mclude the particular disease or condition bemg treated, the particular mammal bemg treated, the clinical condition of the individual patient, the cause of the disease or condition, the site of delivery of the agent, the method of administration, the schedulmg of administration, and other factors known to medical practitioners The therapeutically effective amount of the antagonist to be admmistered will be governed by such considerations As a general proposition, the therapeutically effective amount of the antagonist admmistered parenterally per dose will be in the range of about 0 1 to 20 mg/kg of patient body weight per day, with the typical mitial range of antagonist used bemg m the range of about 2 to 10 mg/kg The preferred antagonist is an antibody, e g an antibody such as RITUXAN®, which is not conjugated to a cytotoxic agent Suitable dosages for an unconjugated antibody are, for example, in the range from about 20mg/πr to about 1000mg/m 2 In one embodiment, the dosage of the antibody differs from that presently recommended for RITUXAN® For example, one may administer to the patient one or more doses of substantially less than 375mg/πr of the antibody, e g where the dose is in the range from about 20mg/m 2 to about 250mg/m 2 , for example from about 50mg/m 2 to about 200mg/m ' ' Moreover, one may administer one or more mitial dose(s) of the antibody followed by one or more subsequent dose(s), wherem the mg/m 2 dose of the antibody in the subsequent dose(s) exceeds the mg/m 2 dose of the antibody in the mitial dose(s) For example, the mitial dose may be in the range from about 20mg/m 2 to about 250mg/m 2 (e g from about 50mg/nr to about 200mg/m 2 ) and the subsequent dose may be m the range from about 250mg/m 2 to about 1000mg/m' As noted above, however, these suggested amounts of antagonist are subject to a great deal of therapeutic discretion The key factor in selecting an appropnate dose and schedulmg is the result obtamed, as mdicated above For example, relatively higher doses may be needed initially for the treatment of ongomg and acute diseases To obtam the most efficacious results, dependmg on the disease or condition, the antagonist is admmistered as close to the first sign, diagnosis, appearance, or occuπence of the disease or condition as possible or duπng remissions of the disease or condition The antagonist is admmistered by any suitable means mcludmg parenteral, subcutaneous, lntrapentoneal, rntrapulmonary, and mtranasal. and, if desired for local lmmunosuppressive treatment, intralesional administration Parenteral infusions mclude intramuscular, intravenous, mtraartenal, lntrapentoneal. or subcutaneous administration In addition, the antagonist may suitably be admmistered by pulse infusion, e g , with declining doses of the antagonist Preferably the dosmg is given by injections, most preferably intravenous or subcutaneous injections, dependmg m part on whether the administration is bπef or chronic One may administer other compounds such as cytotoxic agents, chemotherapeutic agents lmmunosuppressive agents and or cytokmes with the antagonists herein The combmed administration mcludes coadministration, usmg separate formulations or a smgle pharmaceutical formulation, and consecutive administration m either order, wherem preferably there is a time peπod while both (or all) active agents simultaneously exert their biological activities Aside from administration of protem antagonists to the patient the present application contemplates administration of antagonists by gene therapy Such administration of nucleic acid encoding the antagonist is encompassed by the expression "admmistermg a therapeutically effective amount of an antagonist" See. tor example, WO96/07321 published March 14, 1996 concerning the use of gene therapy to generate mtracellular antibodies There are two major approaches to getting the nucleic acid (optionally contained m a vector) mto the patient's cells, in vivo and ex vivo For in vivo delivery the nucleic acid is mjected directly mto the patient, usually at the site where the antagonist is required For ex vivo treatment, the patient's cells are removed, the nucleic acid is introduced mto these isolated cells and the modified cells are admmistered to the patient either directly or, for example, encapsulated within porous membranes which are implanted mto the patient (see, eg U S Patent Nos 4 892, 538 and 5,283.187) There are a vaπety of techmques available for introducing nucleic acids mto viable cells The techniques vary dependmg upon whether the nucleic acid is transferred into cultured cells in vitro, or in vivo m the cells of the mtended host Techmques suitable for the transfer of nucleic acid into mammalian cells in vitro include the use of liposomes, electroporation, microinjection. cell fusion, DEAE-dextran, the calcium phosphate precipitation method, etc A commonly used vector for ex vivo delivery of the gene is a retrovirus The cuπently prefened in vivo nucleic acid transfer techniques mclude transfection with viral \ ectors (such as adenovirus. Herpes simplex I virus, or adeno-associated virus) and pid-based systems (useful hpids for pid- mediated transfer of the gene are DOTMA, DOPE and DC-Choi, for example) In some situations it is desirable to provide the nucleic acid source with an agent that targets the target cells, such as an antibody specific for a cell surface membrane protem or the target cell, a hgand for a receptor on the target cell, etc Where liposomes are employed, protems which bind to a cell surface membrane protein associated with endocytosis may be used for targetmg and/or to facilitate uptake, e g capsid proteins or fragments thereof tropic for a particular cell type, antibodies for protems which undergo internalization in cycling, and protems that target mtracellular localization and enhance mtracellular half-life The technique of receptor-mediated endocytosis is descnbed, for example, by Wu et al . J Biol Chem 262 4429-4432 (1987), and Wagner et al , Proc Natl Acad Sci USA 87 3410-3414 (1990) For review of the cunentlv known gene marking and gene therapy protocols see Anderson et al . Science 256 808-813 (1992) See also WO 93/25673 and the references cited therem VI. Articles of Manufacture In another embodiment of the mvention. an article of manufacture contammg matenals useful for the treatment of the diseases or conditions descnbed above is provided The article of manufacture compnses a container and a label or package insert on or associated with the contamer Suitable contamers mclude. for example, bottles, vials, syringes, etc The contamers may be formed from a vanety of matenals such as glass or plastic The contamer holds or contams a composition which is effective for treating the disease or condition of choice and may have a stenle access port (for example the contamer may be an intravenous solution bag or a vial havmg a stopper pierceable by a hypodermic injection needle) At least one active agent m the composition is the antagonist which bmds CD20 The label or package insert mdicates that the composition is used for blocking an immune response to a foreign antigen and or treating the vaπous diseases or conditions as heremdescnbed The article of manufacture may further compnse a second contamer compπsmg a pharmaceutically-acceptable diluent buffer, such as bactenostatic water for injection (BWFI), phosphate-buffered salme. Ringer's solution and dextrose solution In one embodiment, the second contamer holds or contams a composition wherem the active agent m that composition is a therapeutic agent The package insert may indicate that the patient is to be treated with both compositions m this embodiment of the invention The article of manufacture may further mclude other matenals desirable from a commercial and user standpoint, mcludmg other buffers, diluents, filters, needles, and syringes Further details of the mvention are illustrated by the following non-limiting Examples The disclosures of all citations m the specification are expressly incorporated herem by reference Example 1 Blocking an Immune Response to a Therapeutic Protein In the present example, an antι-CD20 antibody is used to block an immune response to the therapeutic protem. megakaryocyte growth and development factor (MGDF, also known as thrombopoietm or Mpl gand) In particular, a pegylated form of recombmant human MGDF (PEG-rHuMGDF) has been reported to develop neutralizing antibodies m cancer patients and platelet donors Admmistration of an antι-CD20 antibody as disclosed herem will ameliorate an immune response, especially the humoral response, directed against PEG-rHuMGDF PEG-rHuMGDF is prepared as descnbed m US Patent No 5,795,569 issued August 18, 1998, expressly incorporated herein by reference PEG-rHuMGDF consists of ammo acids 1 - 163 (numbermg from the beginning of the mature protem) of human E coli denved MGDF with a single polyethylene glycol (PEG) attached to the α-amino group at the N-terminus of the polypeptide MGDF is admmistered to patients suffering from thrombocytopenia, e g as a result of chemotherapy or radiation therapy, m dosages appropπate for mcreasmg platelet counts m the patients, e g m the range of 0 1 to 1000 micrograms of MGDF per kilogram of body weight MGDF therapy is optionally combmed with admmistration of one or more additional cytokmes, such as erythropoietin (EPO), ιnterleuktn-3 (IL-3) and granulocvte megakaryocyte colonv stimulating factor (GM-CSF) Anti-MGDF antibody titers in the patient so treated are monitored by a suitable assay, such as an antibody titer enzyme linked immunosorbent assay (ELISA) Those patients demonstrating a low titer immune response to MGDF are then candidates for treatment with an antι-CD20 antibody, such as RITUXAN® The antι-CD20 antibody may be admmistered subsequent to, simultaneously with, or following further treatment with MGDF A suitable dosage of the antι-CD20 antibody is 375mg/m ~ by four weekly infusions However, lesser doses, e g . m the range from about 50 to about 250mg/m : may also be admmistered Admmistration of the antι-CD20 antibodv to the patient will prevent, or reduce to an acceptable level, the formation of anti-MGDF antibodies in patients treated with both MGDF and antι-CD20 as descnbed above Hence, for a protein drug of great therapeutic value and known immunogenicity, co-admimstration of an antι-CD20 antibody as herem-descnbed will treat the lmmunogenic side- effects) associated with admmistration of that protem drug to a patient Example 2 Blocking an Immune Response to a Gene Therapy Viral Vector El, E3-deleted, replication-deficient recombmant adenoviruses have been evaluated for their capability to transfer therapeutic genes in vivo New vectors with additional deletions in the E2a or the E4 regions have been developed Chnsterα/ Immunol Let 57 19-25 (1997) Despite the deletion of these viral regions, low levels of early and late viral genes are expressed in vivo Production of anti-adenovirus antibodies, the cellular immune response as well as the early non-specific clearance of the vectors constitute barners to successful gene therapy In order to inhibit, or reduce to an acceptable level, the production of neutralizing antibodies to adenovirus, an antι-CD20 antibody (e g RITUXAN®) is admmistered to the gene therapy patient as herem descnbed For example, cystic fϊbrosis patients are treated with a replication-deficient adenovirus expressmg the human cystic fibrosis transmembrane conductance regulator (CFTR) (Bellon et al Human Gene Therapy 8 15-25 (1997)) Suitable dosages of the CFTR gene therapy vector (defined in terms of viral plaque forming units, pfu) are admmistered via aerosohzation m order to achieve expression of CFTR m the lungs (e g from about 10 to about 10 9 pfu) Anti-adenovirus antibodies in the patient may be detected by ELIS A. immuno fluorescence, and/or complement fixation In those patients demonstrating anti-adenovirus antibodies, an antι-CD20 antibody (e g chimenc 2H7, US Patent No 5,677,180), optionally m combmation with other lmmunosuppressive drugs (eg cyclophosphamide, FK506, or monoclonal antibodies that block either the T cell receptor or costimulation pathways), is admmistered to the patient pnor to, simultaneously with, or following re-administration of the gene therapy vector. A suitable dosage of the antι-CD20 antibody is 375mg m 2 by four weekly infusions Admmistration of the antι-CD20 antibody will reduce or eliminate an immune response in the patients (e g by reducmg anti-adenovirus antibody production), and thereby facilitate successful gene therapy retreatments Example 3 Blocking an Immune Response to a Transplant An antι-CD20 antibody is used as part of combmation lmmunosuppressive regimens for prophylaxis of acute rejection In this settmg, an antι-CD20 antibody, such as RITUXAN®, is administered in the pen-transplant penod as part of a sequential combmation regimen that mcludes T cell directed agents such as cyclosponne, corticosteroids, mycophenolate mofetil, with or without an antι-IL2 receptor antibody Hence, the antι-CD20 antibody would be considered part of an mduction regimen, to be used m conjunction with chronic lmmunosuppressive therapies The antι-CD20 antibody may contnbute to prevention of an allorejection response by inhibiting alloantibody production and/or affecting alloantigen presentation through depletion of antigen-presentmg cells The treatment regimen may entail four weekly infusions (375mg/m 2 ) of RITUXAN® admmistered pnor to, or around, transplant Suitable dosages of the further lmmunosuppressive agents are as follows cyclosponne (5mg/kg/day), corticosteroids (1 mg/kg, gradually tapered off), mycophenolate mofetil (1 gram given twice a day), and antι-IL2 receptor antibody (1 mg kg, five infusions given weekly) The antι-CD20 antibody may also be combmed with other mduction lmmunosuppressive drugs, such as polyclonal anti-lymphocyte antibodies or monoclonal antι-CD3 antibodies, maintenance lmmunosuppressive drugs, such as calcmeunn inhibitors (e g , tacrolimus) and antipro ferative agents (such as azathiopnne. leflunomide or srrolimus), or combmation regimens that mclude blockade of T cell costimulation blockade of T cell adhesion molecules of blockade of T cell accessory molecules Aside from prophylaxis of acute rejection. antι-CD20 antibodies may be used to treat acute rejection Suitable dosages of the antι-CD20 are as descnbed above The antι-CD20 antibody is optionally combmed with an antι-CD3 monoclonal antibody and/or corticosteroids m the treatment of acute rejection Antι-CD20 antibodies may also be used (a) later in the post-transplant penod alone, or m combmation with other lmmunosuppressive agents and/or costimulatory blockade, for treatment or prophylaxis of "chrome" allograft rejection, (b) as part of a tolerance- mducmg regimen, or (c) m the settmg of xenotransplantation Example 4 Blocking an Immune Response to a Hemophilic Factor A patient with hereditary deficiency of Factor VIII has received multiple transfusions of Factor VIII preparation and developed high titers of anti-Factor VIII antibodies An antι-CD20 antibody, such as RITUXAN®, is admmistered to such a patient with anti-Factor VIII antibodies, e g , m dosages such as those descnbed above The antι-CD20 antibody may block an immune response to the Factor VIII, by affecting the production of antibodies thereagamst or by other mechanisms such as ldiotype suppression Example 5 Blocking an Immune Response to Platelets A patient has received multiple platelet transfusions and is makmg alloantibodies agamst platelets The patient has failed steroid therapy and may have received other treatments (e g cyclosponne, Staph protem A column etc) An antι-CD20 antibody (e g RITUXAN®) is administered to the patient in dosages, e g , as descnbed above The antι-CD20 antibody may block or ameliorate the immune response by affectmg the production of antibodies or by other mechanisms such as ldiotype suppression or inhibition of removal of coated platelets by the spleen

Claims: What is claimed is 1 A method of blocking an immune response to a foreign antigen in a mammal, wherem the mammal is not suffering from a malignancy, compnsmg admmistenng to the mammal a therapeutically effective amount of an antagonist which bmds to CD20 2 The method of claim 1 wherem the antagonist compπses an antibody 3 The method of claim 1 wherem the foreign antigen compnses a therapeutic agent 4 The method of claim 1 wherem the foreign antigen is selected from the group consisting of an antibody, a toxin, a gene therapy viral vector, a graft, an mfectious agent, and an alloantigen 5 The method of claim 1 wherem the mammal is human 6 The method of claim 2 wherem the antibody is not conjugated with a cytotoxic agent 7 The method of claim 2 wherem the antibody compπses ntuximab (RITUXAN®) 8 The method of claim 2 wherem the antibody is conjugated with a cytotoxic agent 9 The method of claim 8 wherem the cytotoxic agent is a radioactive compound 10 The method of claim 9 wherem the antibody compnses Y2B8 or 131 I-B1 (BEXXAR™) 11 The method of claim 1 compπsmg admmistenng the antagonist intravenously 12 The method of claim 1 compnsmg admmistenng the antagonist subcutaneously 13 The method of claim 2 compnsmg admmistenng a dose of substantially less than 375mg m 2 of the antibody to the mammal 14 The method of claim 13 wherem the dose is m the range from about 20mg/m 2 to about 250mg/m 2 15 The method of claim 14 wherem the dose is m the range from about 50mg/m 2 to about 200mg/m 2 16 The method of claim 2 compnsmg admmistermg an mitial dose of the antibody followed by a subsequent dose, wherem the mg/m 2 dose of the antibody m the subsequent dose exceeds the mg/m 2 dose of the antibody m the mitial dose 17 The method of claim 4 wherem the foreign antigen is an antibody 18 The method of claim 17 wherem the antibody is a murine antibody 19 The method of claim 4 wherem the foreign antigen is a gene therapy viral vector 20 The method of claim 4 wherem the foreign antigen is a graft 21 The method of claim 4 wherem the foreign antigen is an alloantigen 22 The method of claim 1 compπsmg admmistenng the antagonist to the mammal before the mammal is exposed to the foreign antigen 23 The method of claim 22 wherem the foreign antigen compnses a graft 24 A method of treating a mammal compnsmg admmistenng a therapeutic agent, other than an antagonist which bmds to CD20, to the mammal and further compnsmg admmistenng an antagomst which bmds to CD20 to the mammal, wherem the therapeutic agent is lmmunogenic m the mammal and the antagonist blocks an immune response to the therapeutic agent in the mammal 25 The method of claim 24 compnsmg admmistenng the therapeutic agent and the antagomst essentially simultaneously to the mammal 26 The method of claim 24 compnsmg admmistenng the antagonist to the mammal pnor to the therapeutic agent 27 The method of claim 24 compnsmg admmistenng the therapeutic agent to the mammal pnor to the antagonist A method of treating graft-versus-host or host-versus-graft disease m a mammal compπsmg admmistermg to the mammal a therapeutically effective amount of an antagomst which bmds to CD20 A method of desensitizing a mammal awaitmg transplantation compnsmg admmistermg to the mammal a therapeutically effective amount of an antagomst which bmds to CD20 An article of manufacture compnsmg a contamer and a composition contained therein, wherein the composition compnses an antagonist which bmds to CD20, and further compnsmg a package msert instructmg the user of the composition to treat a patient who has been or will be exposed to a foreign antigen The article of manufacture of claim 30 further compπsmg a second contamer and a second composition contained therein, wherem the second composition compnses a therapeutic agent AMENDED CLAIMS [received by the International Bureau on 7 November 2000 (07.11.00); original claim 29 cancelled; claims 30 31 renumbered as claims 29-30; other claims unchanged (1 page)] 28. A method of treating graft-versus-host or host-versus-graft disease in a mammal comprising administering to the mammal a therapeutically effective amount of an antagonist which binds to CD20. 29. An article of manufacture comprising a container and a composition contained therein, wherein the composition comprises an antagonist which binds to CD20, and further comprising a package insert instructing the user of the composition to treat a patient who has been or will be exposed to a foreign antigen. 30. The article of manufacture of claim 29 further comprising a second container and a second composition contained therein, wherein the second composition comprises a therapeutic agent.

Inventors: GRILLO-LOPEZ ANTONIO J, KUNKEL LORI A, STEWART TIMOTHY A, GRILLO-LOPEZ, ANTONIO, J., KUNKEL, LORI, A., STEWART, TIMOTHY, A.
Applicants: GENENTECH INC, IDEC PHARMACEUTICALS INC, GENENTECH, INC., IDEC PHARMACEUTICALS, INC.
Application year: 2000
Main classification: A61K39
IPC codes: A61K39, A61K45, A61K51, A61P37, C07K16