The human immune response to the OKT3 monoclonal antibody is oligoclonal

Single-domain antibodies as therapeutics for solid tumor treatment

Single-domain antibodies (sdAbs), initially identified in camelids or sharks and commonly referred to as nanobodies or VNARs, have emerged as a promising alternative to conventional therapeutic antibodies. These sdAbs have many superior physicochemical and pharmacological properties, including small size, good solubility and thermostability, easier accessible epitopes, and strong tissue penetration. However, the inherent challenges associated with the animal origin of sdAbs limit their clinical use. In recent years, various innovative humanization technologies, including complementarity-determining region (CDR) grafting or complete engineering of fully human sdAbs, have been developed to mitigate potential immunogenicity issues and enhance their compatibility. This review provides a comprehensive exploration of sdAbs, emphasizing their distinctive features and the progress in humanization methodologies. In addition, we provide an overview of the recent progress in developing drugs and therapeutic strategies based on sdAbs and their potential in solid tumor treatment, such as sdAb-drug conjugates, multispecific sdAbs, sdAb-based delivery systems, and sdAb-based cell therapy.

Half-Life Extended Nanobody-Based CD38-Specific Bispecific Killercell Engagers Induce Killing of Multiple Myeloma Cells

CD38 is a target for immunotherapy of multiple myeloma. Llama-derived CD38-specific nanobodies allow easy reformatting into mono-, bi- and multispecific proteins. To evaluate the utility of nanobodies for constructing CD38-specific nanobody-based killer cell engagers (nano-BiKEs), we generated half-life extended nano-BiKEs (HLE-nano-BiKEs) by fusing a CD38-specific nanobody to a CD16-specific nanobody for binding to the Fc-receptor on NK cells and further to an albumin-specific nanobody to extend the half-life in vivo. HLE-nano-BiKEs targeting three different epitopes (E1, E2, E3) of CD38 were expressed in transiently transfected HEK-6E cells. We verified specific and simultaneous binding to CD38 on myeloma cells, CD16 on NK cells, and to albumin. We tested the capacity of these HLE-nano-BiKEs to mediate cytotoxicity against CD38-expressing multiple myeloma cell lines and primary myeloma cells from human bone marrow biopsies in bioluminescence and flowcytometry assays with NK92 cells as effector cells. The results revealed specific time- and dose-dependent cytolysis of CD38+ myeloma cell lines and effective depletion of CD38-expressing multiple myeloma cells from primary human bone marrow samples. Our results demonstrate the efficacy of CD38-specific HLE-nano-BiKEs in vitro and ex vivo, warranting further preclinical evaluation in vivo of their therapeutic potential for the treatment of multiple myeloma.

Immunotherapy with oral administration of humanized anti-CD3 monoclonal antibody: a novel gut-immune system-based therapy for metaflammation and NASH

The immune system plays a role in the pathogenesis of non-alcoholic steatohepatitis (NASH) underlying hepatocyte injury and fibrosis progression at all disease stages. Oral administration of anti-CD3 monoclonal antibody (mAb) has been shown in preclinical studies to be an effective method for systemic immune modulation and alleviates immune-mediated disorders without T cell depletion. In the present review, we summarize the concept of the oral administration of humanized anti-CD3 mAb in patients with NASH and discuss the potential of this treatment to address the current requirements of treatments for NASH. Recently published preclinical and clinical data on oral administration of anti CD3 are discussed. Human trials have shown that the oral administration of anti-CD3 in healthy volunteers, patients with chronic hepatitis C virus (HCV) infection and patients with NASH and type 2 diabetes is safe and well tolerated, as well as biologically active. Oral anti-CD3 induces regulatory T cells, suppresses the chronic inflammatory state associated with NASH and exerts a beneficial effect on clinically relevant parameters. Foralumab is a fully human anti-CD3 mAb that has recently been shown to exert a potent anti-inflammatory effect in humanized mice. It is being developed for treatment of NASH and primary biliary cholangitis (PBC). Oral administration of anti CD3 may provide an effective therapy for patients with NASH.

Nanobodies and Nanobody-Based Human Heavy Chain Antibodies As Antitumor Therapeutics

Monoclonal antibodies have revolutionized cancer therapy. However, delivery to tumor cells in vivo is hampered by the large size (150 kDa) of conventional antibodies. The minimal target recognition module of a conventional antibody is composed of two non-covalently associated variable domains (VH and VL). The proper orientation of these domains is mediated by their hydrophobic interface and is stabilized by their linkage to disulfide-linked constant domains (CH1 and CL). VH and VL domains can be fused via a genetic linker into a single-chain variable fragment (scFv). scFv modules in turn can be fused to one another, e.g., to generate a bispecific T-cell engager, or they can be fused in various orientations to antibody hinge and Fc domains to generate bi- and multispecific antibodies. However, the inherent hydrophobic interaction of VH and VL domains limits the stability and solubility of engineered antibodies, often causing aggregation and/or mispairing of V-domains. Nanobodies (15 kDa) and nanobody-based human heavy chain antibodies (75 kDa) can overcome these limitations. Camelids naturally produce antibodies composed only of heavy chains in which the target recognition module is composed of a single variable domain (VHH or Nb). Advantageous features of nanobodies include their small size, high solubility, high stability, and excellent tissue penetration in vivo. Nanobodies can readily be linked genetically to Fc-domains, other nanobodies, peptide tags, or toxins and can be conjugated chemically at a specific site to drugs, radionuclides, photosensitizers, and nanoparticles. These properties make them particularly suited for specific and efficient targeting of tumors in vivo. Chimeric nanobody-heavy chain antibodies combine advantageous features of nanobodies and human Fc domains in about half the size of a conventional antibody. In this review, we discuss recent developments and perspectives for applications of nanobodies and nanobody-based human heavy chain antibodies as antitumor therapeutics.

From rabbit antibody repertoires to rabbit monoclonal antibodies

In this review, we explain why and how rabbit monoclonal antibodies have become outstanding reagents for laboratory research and increasingly for diagnostic and therapeutic applications. Starting with the unique ontogeny of rabbit B cells that affords highly distinctive antibody repertoires rich in in vivo pruned binders of high diversity, affinity and specificity, we describe the generation of rabbit monoclonal antibodies by hybridoma technology, phage display and alternative methods, along with an account of successful humanization strategies.

Expression of an anti-Pseudomonas aeruginosa lipopolysaccharide core recombinant antibody in Escherichia coli

Antibodies against Pseudomonas aeruginosa LPS are generally protective, however, this protection is usually serotype-specific. Thus the generation of antibodies against the more conserved core-lipid A epitopes has a potential for being more broadly cross reactive. Our laboratory has previously produced several monoclonal antibodies (mAb) against the core region and lipid A region of P. aeruginosa LPS. In this study, we cloned the immunoglobulin genes from mAb 7-4, an antibody with specificity for the inner core region of P. aeruginosa LPS. VH and VL genes of 7-4 were cloned into both of the M13-derived phagemid vectors, pComb3 and pComb8. 14 pComb3/VH/VL and 6 pComb8/VH/VLrecombinant clones were isolated. The presence of recombinant F(ab) molecules in the periplasmic extracts of Escherichia coli was confirmed by Western immunoblots of these extracts with goat anti-mouse F(ab')2 and goat anti-mouse kappa light chain antibodies under non-reduced conditions. Recombinant 7-4 antibody also interacted with LPS prepared from a rough mutant P. aeruginosa strain AK43 in Western immunoblotting, and ELISA as well as with whole cells of AK43 in immunofluorescence. Thus, recombinant 7-4 antibodies expressed in E. coli are structurally and functionally correct.

Cross-reactive and pre-existing antibodies to therapeutic antibodies--Effects on treatment and immunogenicity

The potential for immunogenicity is an ever-present concern during the development of biopharmaceuticals. Therapeutic antibodies occasionally elicit an antibody response in patients, which can result in loss of response or adverse effects. However, antibodies that bind a drug are sometimes found in pre-treatment serum samples, with the amount depending on drug, assay, and patient population. This review summarizes published data on pre-existing antibodies to therapeutic antibodies, including rheumatoid factors, anti-allotype antibodies, anti-hinge antibodies, and anti-glycan antibodies. Unlike anti-idiotype antibodies elicited by the drug, pre-formed antibodies in general appear to have little consequences during treatment. In the few cases where (potential) clinical consequences were encountered, antibodies were characterized and found to bind a distinct, unusual epitope of the therapeutic. Immunogenicity testing strategies should therefore always include a proper level of antibody characterization, especially when pre-formed antibodies are present. This minimizes false-positives, particularly due to rheumatoid factors, and helps to judge the potential threat in case a genuine pre-dose antibody reactivity is identified.

Immunogenicity of anti-TNF biologic therapies for rheumatoid arthritis

Currently, five anti-TNF biologic agents are approved for the treatment of rheumatoid arthritis (RA): adalimumab, infliximab, etanercept, golimumab and certolizumab pegol. Formation of anti-drug antibodies (ADA) has been associated with all five agents. In the case of adalimumab and infliximab, immunogenicity is strongly linked to subtherapeutic serum drug levels and a lack of clinical response, but for the other three agents, data on immunogenicity are scarce, suggesting that further research would be valuable. Low ADA levels might not influence the efficacy of anti-TNF therapy, whereas high ADA levels impair treatment efficacy by considerably reducing unbound drug levels. Immunogenicity is not only an issue in patients treated with anti-TNF biologic agents; the immunogenicity of other therapeutic proteins, such as factor VIII and interferons, is well known and has been investigated for many years. The results of such studies suggest that investigations to determine the optimal treatment regimen (drug dosing, treatment schedule and co-medication) required to minimize the likelihood of ADA formation might be an effective and practical way to deal with the immunogenicity of anti-TNF biologic agents for RA.

Otelixizumab in the treatment of Type 1 diabetes mellitus

Anti-CD3 antibodies have been demonstrated in both animal and human studies to be able to reverse autoimmune diseases; for example Type 1 diabetes. Not only does treatment with anti-CD3 antibodies result in the removal of pathogenic T cells but evidence suggests that a state of operational tolerance can be induced through the effects on regulatory T cells. The clinical use of anti-CD3 antibodies has been hampered by their safety profile. However, the introduction of humanized, nonmitogenic, aglycosylated anti-CD3 antibodies, such as otelixizumab, and promising results reported in newly-diagnosed patients with Type 1 diabetes, have renewed the interest for these antibodies in the treatment of autoimmune diseases.

Human CD3 transgenic mice: preclinical testing of antibodies promoting immune tolerance

Monoclonal antibodies have proven to be potent agents to promote immunological tolerance in animal models of autoimmune disease and transplantation. However, optimal clinical application and pharmaceutical development have been limited by the species specificity of therapeutic antibodies, as well exemplified in the case of anti-CD3 antibodies. Compelling evidence in the nonobese diabetic (NOD) mouse, recently translated to clinical autoimmune insulin-dependent diabetes, demonstrates that a short CD3 antibody treatment effectively and durably controls disease progression. We established transgenic mice expressing the human ε chain of the CD3 complex bred onto the NOD background. These mice developed a high incidence of spontaneous autoimmune diabetes and harbored T cells sensitive both in vitro and in vivo to anti-human CD3 antibodies. Treatment of diabetic transgenic mice with otelixizumab, an anti-human CD3 antibody that has proven effective in the clinic, resulted in durable disease remission dependent on transferable T cell-mediated tolerance. This model should enable the evaluation of anti-human CD3 antibodies to determine their potential clinical utility.

An extreme strategy for the production of hybridoma

The ethical issues surrounding human immunization hamper the production of human monoclonal antibody through scarcity of immunized B cells in peripheral blood. This defect can be compensated in part by improvement of hybridoma production techniques. We have developed a new strategy to bypass the toxic effects of polyethylene glycol (PEG) as fusogenic reagent and hypoxanthine aminoptrin thymidine (HAT) as selective medium on newly fused cells. The Epstein-Barr virus (EBV) transformed peripheral blood mononuclear cells (PBMC) of accidentally Rh antigen sensitized persons were fused using cephalin as fugenic reagent, with emetine and actinomycin D pretreated heteromyeloma cells. Our results showed that 19-34% of EBV-transformed B cells were grown as hybridoma clones following selection. This extreme improvement in hybridoma production rate may end the fusion efficiency problem and make hybridoma production a plug-and-play technology.

CD3-specific antibody-induced active tolerance: from bench to bedside

Although they were used initially as non-specific immunosuppressants in transplantation, CD3-specific monoclonal antibodies have elicited renewed interest owing to their capacity to induce immune tolerance. In mouse models of autoimmune diabetes, CD3-specific antibodies induce stable disease remission by restoring tolerance to pancreatic beta-cells. This phenomenon was extended recently to the clinic--preservation of beta-cell function in recently diagnosed patients with diabetes was achieved by short-term administration of a CD3-specific antibody. CD3-specific antibodies arrest ongoing disease by rapidly clearing pathogenic T cells from the target. Subsequently, they promote long-term T-cell-mediated active tolerance. Recent data indicate that transforming growth factor-beta-dependent CD4+CD25+ regulatory T cells might have a central role in this effect.

The use of monoclonal antibodies to restore self-tolerance in established autoimmunity

The author hopes to convince the reader that the data presented argue for a stage during the development of IDDM when beta-cell destruction can be counteracted and tolerance to beta cells restored, provided the immune aggression is arrested. This argument constitutes a solid rationale for immunointervention in established IDDM, especially by using potent agents such as CD3. The future for the application of monoclonal antibodies not only in autoimmunity but also in transplantation is exiting. With the development of humanized monoclonal antibodies, therapeutic uses for them are likely to expand. Enormous progress has been made in the last 15 years, and it is likely that before a similar time period has elapsed, monoclonal antibodies will have become standard tools that will dispense the need for long-term immunosuppression and its inherent dangers in various clinical arenas.

CDR substitutions of a humanized monoclonal antibody (CC49): contributions of individual CDRs to antigen binding and immunogenicity

One of the major obstacles in the successful clinical application of monoclonal antibodies has been the development of host immune responses to murine Ig constant and variable regions. While the CDR grafting of MAbs may alleviate many of these problems, the potential remains that one or more murine CDRs on the human Ig backbone of a "humanized" MAb may still be immunogenic. Studies were undertaken employing a MAb of potential clinical utility, CC49, to define those CDRs that are essential for antigen binding and those that may be immunogenic in humans. We previously developed a humanized CC49 (HuCC49) by grafting the MAb CC49 hypervariable regions onto frameworks of human MAbs. To identify those CDRs essential for binding, a panel of variant HuCC49 MAbs was generated here by systematically replacing each of the murine CDRs with their human counterparts. The relative affinity constant of each variant was determined. Serum from a patient who received murine CC49 was used to determine the potential immunogenicity of each CDR in humans. The serum was shown to react with the anti-CC49 variable region. Results showed that patients' anti-idiotypic responses are directed mainly against LCDR3 and moderately against LCDR1 and HCDR2. These studies demonstrate for the first time that variants containing individual CDR substitutions of a humanized MAb can be constructed, and each CDR can be defined for the two most important properties for potential clinical utility: antigen binding and immunogenicity.

Inhibition of arteriosclerosis by T-cell depletion in normocholesterolemic rabbits immunized with heat shock protein 65

Previous studies in our laboratory have shown that arteriosclerotic changes can be induced in normocholesterolemic rabbits by immunization with mycobacterial heat shock protein (hsp) 65. To further investigate the immunologic mechanisms underlying such vascular lesions, 39 male New Zealand White rabbits were treated by triple immunization with fortified Freund's complete adjuvant containing 5 mg/mL Mycobacterium tuberculosis as a source of hsp65 and simultaneous immunosuppressive therapy twice per week with either anti-CD3 monoclonal antibody (1 mg/kg) and prednisolone (1 mg/kg) or prednisolone (1 mg/kg) alone. Sixteen weeks after the first immunization the animals were killed, and as expected, severe arteriosclerotic lesions in the intima of the aortic arch were found in 9 of 10 immunized rabbits. However, only 1 of 10 rabbits immunized and immunosuppressed with the combined anti-CD3 monoclonal antibody and prednisolone treatment showed a single moderate lesion in the aorta, whereas 5 of 9 rabbits immunized and immunosuppressed by prednisolone treatment alone showed lesions, albeit mild. In conclusion, the early inflammatory stages of arteriosclerotic lesions induced by immunization with hsp65 can be inhibited by immunosuppressive therapy with anti-CD3 monoclonal antibody.

Tolerogenic antibodies and fusion proteins to prevent graft rejection and treat autoimmunity

The immune mechanisms underlying autoimmune diseases and allograft rejection are similar, and T cells play a major role in both processes. Current therapeutic strategies rely on the application of nonspecific immunosuppression using chemicals such as corticosteroids, azathioprine, methotrexate, cyclophosphamide and cyclosporin. One major drawback of these drugs is their relative ineffectiveness over the long term; withdrawal leads to recurrence of the disease, but chronic administration puts patients at risk of being overimmunosuppressed, which can result in an increased incidence of infections and tumors. This review describes the advantages of developing biological agents that target immune receptors on T cells. In some cases, these agents can induce a state of durable, antigen-specific unresponsiveness in the absence of generalized immunosuppression, which could be useful in transplantation and autoimmunity.

Persistent long-term changes in lymphocyte subsets induced by polyclonal antibodies

BACKGROUND

Clinicians are well aware of the short-term effects of immunosuppression by mono- or polyclonal antibodies. Little is known about long-term changes induced by these therapies.

METHODS

Forty-three renal allograft recipients were selected according to their initial postoperative immunosuppression: (1) BI group=basic immunosuppression with steroids and cyclosporine, n=16; (2) ATG group=basic immunosuppression plus polyclonal antibody antithymocyte globulin (ATG), n=11; and (3) OKT3 group=basic immunosuppression plus monoclonal antibody OKT3, n=16 patients. At intervals of 6 months, the following parameters were measured prospectively: lymphocyte surface antigens (HLA-DR, CD3, CD4, CD8, CD16, CD19, CD56, and CD57); serum and urine neopterin; serum amyloid A; and indirect and direct tests for herpes viruses.

RESULTS

The mean period of observation was 58.4 months. The most significant differences between the groups occurred for CD4+ and CD8+ T cells. The ratios of CD4+ to CD8+ cells (n=278 measurements) were significantly and persistently lower in the ATG group (P<0.001, Brown-Mood test). Five years after transplantation, the ATG group had a CD4+ to CD8+ cell ratio of x=0.6 versus x=1.7 in the OKT3 group and x=2.0 in the BI group. This inversion was due to a persistent depletion of the CD4+ cells and an increased regeneration of the CD8+ cells, in particular of the CD8+brightCD57+ subpopulation. Extent and duration of CD4+ depletion correlated with the cumulative ATG dose (r=0.7, P<0.05, Spearman rank correlation test).

CONCLUSION

Therapy with polyclonal antibody ATG induces dose-dependent long-term changes in T-cell lymphocyte subsets, which persist over a period of years.

Induction of selective cell death targeting on mature T-lymphocytes in rats by a novel immunosuppressant, FTY720

A novel immunosuppressant, FTY720, induces a rapid and marked decrease of peripheral lymphocytes, and prolong allograft survival in rats. Its mechanism of action is mediated by apoptotic cell death. In this study, we determined the time-related changes in the numbers of total lymphocytes, and the ratios of lymphocyte subpopulations in peripheral blood and lymphomyeloid organs in rats after the single oral administration of FTY720 (10 mg/kg), comparing with the effects of cyclophosphamide (80 mg/kg, ip). Total number of peripheral lymphocytes decreased significantly 3 h after the administration of the drug, while that of polymorphonuclear cells increased. T-cells were markedly decreased in number and reached a minimum of 2.3% of the control 3 days after the treatment, while B-cells reached 19.7%. T-cells decreased in spleen and liver but there was no notable change in thymus, lymph nodes, and bone marrow. The susceptibility of the cells against the drug was variant based on the type and the source of cells in vitro. Polymorphonuclear cells were the most resistant and lymph node cells the most sensitive to FTY720 after 3 h incubation with different concentration of the drug (1, 10,100 mumol/l). When incubated with 10 mumol/l of FTY720, B-cells were significantly higher in viability than the whole T- or CD4-cells. These results demonstrated that FTY720 induces cell death selectively in mature T-lymphocytes, especially CD4-lymphocytes, in peripheral blood without the depression of bone marrow.

Immunosuppression by Fc region-mismatched anti-T cell antibody treatment

Formation of anti-antibodies (anti-Ab) is known to counteract immunotherapy with anti-T cell antibodies. Our previously described immunological approach prevented anti-Ab with the consequence of prolonged survival of fully mismatched skin grafts in C57BL/6 mice. These mice were treated with a single priming injection of a monoclonal anti-T cell Ab followed by repeated injections of anti-T cell mAb differing in species origin from the priming mAb. We now show prolonged tolerance to discordant xenogeneic, to bispecific, and even to polyclonal Ab, and demonstrate that the underlying immunosuppressive principle is due to a difference in heavy chain constant region between first and second antibodies, independent of whether or not they share the same idiotype. To examine this phenomenon, a panel of mAb was generated which share the same mouse anti-Thy-1.2 idiotype, but carry a human IgG1(T23), IgG3(T212C8), or mouse IgG2a(MmT1) constant heavy chain region. We found that sequential injection of MmT1 and T23 according to the above treatment schedule induced huIgG1 isotype-specific tolerance to T23, which was similar to that seen when using a primary mAb (MmT5) that was, instead, fully mismatched with T23 in both idiotype and constant region. Thus, differences of idiotype between primary and booster Ab were inconsequential for their ability to inhibit anti-Ab formation. This novel form of induced specific tolerance to anti-T cell Ig survived graft rejection and was still evident 230 days after termination of the T cell depletion protocol. Taken together, these results demonstrate that rechallenge with Fc region-mismatched Ab opens an immunological window that allows for induction of tolerance to immunogenic anti-T cell Ab and prolonged immunosuppression.

Horse gammaglobulin-induced thrombocytopenia in anaphylaxis involving sequestration and activation of platelets

Thrombocytopenia as well as hemoconcentration and leukopenia followed by leukocytosis were induced after HoGG challenge on HoGG-sensitized mice. Thrombocytopenia was induced within 2 min and sustained for 1 day. HoGG-induced thrombocytopenia was not observed until day 10 after sensitization; mice challenged with HoGG dose > or = 10 micrograms developed thrombocytopenia. Two types of thrombocytopenia were observed in appropriately sensitized mice. HoGG induced thrombocytopenia at 2 min and 60 min, whereas, alpha-macroglobulin induced thrombocytopenia at 2 min, the platelet count of which returned to normal within 60 min. Poly (Glu60Ala30Tyr10) did not induce thrombocytopenia at 2 min or 60 min. The tracing study by 3H-serotonin labelled platelets demonstrated the 2 min-sequestration of platelets in lungs or livers. The HoGG-induced sequestration of platelets at 2 min was blocked by high dose heparin or Cobra Venom factor. Platelet activation at 60 min was partially inhibited by dexamethasone, rhodostomin synthetic peptide 45-59, or platelet activation factor antagonist (WEB 2086). Furthermore, the thrombocytopenia could be transferred by heat (56 degrees C, 4h) treated immune sera. This suggests that HoGG-induced, non-IgE-mediated thrombocytopenia in anaphylaxis involves sequestration and activation of platelets. The sequestion in lungs occurs within 2 min and can be inhibited by high dose heparin or Cobra Venom factor. The activation of platelets involves platelet activation factor, and fibrinogen receptor.

Immunomodulating IL-6 activity by murine monoclonal antibodies

The human anti-mouse immunoglobulin antibody (HAMA) response, which occurs frequently after injection of murine monoclonal antibodies (MAb) directed against cellular targets, has been reported extensively in several studies. We analysed here HAMA in 12 patients (six with multiple myeloma, MM, and six with metastatic renal cell carcinoma, MRCC) who were treated with B-E8, an IgG1 MAb against interleukin-6 (IL-6). Efficiency of the treatment was evidenced by the drop in the serum levels of C reactive protein (CRP), of which the in vivo production is under the control of IL-6. Three patients with MM and the six patients with MRCC became immunized to the injected MAb. HAMA appeared between days 7 and 15 after the beginning of the treatment. The nine patients made IgG antibodies; four also made IgM. All of immunized patients made anti-idiotype antibodies specific to B-E8. Two of them also developed HAMA directed to murine IgG1 isotype; in these two patients B-E8 MAb cleared rapidly from the circulation with loss of treatment efficiency. In the patients who developed only anti-idiotype antibodies, serum levels of B-E8 remained unchanged and CRP production remained inhibited, indicating that treatment efficiency was not affected by the presence of HAMA. Circulating B-E8 MAb were still able to bind to IL-6 and to inhibit IL-6-independent proliferation despite the presence of anti-idiotypic HAMA. Therefore, in contrast to HAMA against MAb directed against cellular targets, HAMA against anti-IL-6 MAb idiotopes led neither to clearance nor to functional inactivation of the injected MAb.(ABSTRACT TRUNCATED AT 250 WORDS)

Human anti-mouse antibody response to the injection of murine monoclonal antibodies against IL-6

We analysed human anti-mouse antibodies (HAMA) in 12 patients (six with multiple myeloma (MM) and six with metastatic renal cell carcinoma (MRCC) who were treated with B-E8, an IgG1 MoAb against IL-6. Efficiency of the treatment was evidenced by the drop in the serum levels of C-reactive protein (CRP), the in vivo production of which is under the control of IL-6. Three patients with MM and the six patients with MRCC became immunized to the injected MoAb. HAMA appeared between days 7 and 15 after the beginning of the treatment. The nine patients made IgG antibodies; four also made IgM. All immunized patients made anti-idiotype antibodies specific to B-E8. Two of them also developed HAMA directed to murine IgG1 isotype; in these two patients B-E8 MoAb cleared rapidly from the circulation with loss of treatment efficiency. In the patients who developed only anti-idiotype antibodies, serum levels of B-E8 remained unchanged and CRP production remained inhibited, indicating that treatment remained efficient in the presence of HAMA. Circulating B-E8 MoAbs were still able to bind to IL-6 and to inhibit IL-6-dependent proliferation despite the presence of anti-idiotypic HAMA. Therefore, in contrast to HAMA produced against MoAb directed against cellular targets, HAMA against anti-IL-6 MoAb idiotopes led neither to clearance nor to functional inactivation of the injected MoAb. This was further shown by resuming the B-E8 treatment with success in a patient who still had anti-idiotypic HAMA.

Diphtheria toxin-related cytokine fusion proteins: elongation factor 2 as a target for the treatment of neoplastic disease

We have used protein engineering and recombinant DNA methodologies in order to construct a fusion protein in which human interleukin-2 (IL-2) is genetically linked to the catalytic and transmembrane domains of diphtheria toxin. The fusion toxin, DAB486IL-2, is highly cytotoxic for only those cells which display the high affinity interleukin-2 receptor (IL-2R) on their surface. In phase I/II clinical studies the intravenous administration of DAB486IL-2 has been found to be safe, well tolerated and may lead to the induction of durable remissions in patients presenting with a variety of IL-2R positive lymphomas.

Murine anti-mouse T cell monoclonal antibodies elicit anti-antibodies in mice: intra-species immunization model for estimating potential patient sensitization against humanized anti-T cell antibodies

Humanization of immunosuppressive anti-T cell monoclonal antibodies (mAb) raises the question as to how completely it helps to avoid formation of neutralizing anti-antibodies (anti-Ab) in patients. To get more information on intra-species sensitization against anti-T cell mAb, we produced two immunosuppressive mouse IgG2a anti-mouse Thy-1.2 mAb (MmT1 and MmT5) in AKR/J mice and measured the potential of MmT1 to elicit inhibitory anti-Ab in AKR/J (H-2k), C57BL/6 (H-2b), congenic B10.BR (H-2k) and DBA/2 (H-2d) mice. After one injection once weekly for 4 weeks of 5 micrograms MmT1 (200 micrograms/kg) in C57BL/6 mice, without the use of any adjuvants, high concentrations of anti-Ab directed against MmT1 (300 micrograms/ml) and MmT5 (100 micrograms/ml) were measured by enzyme-linked immunosorbent assay. Similar concentrations of anti-Ab were found in immunized DBA/2 and less in B10.BR mice. No syngeneic anti-Ab could be produced in AKR/J. From the C57BL/6 mice, we raised anti-MmT1+, MmT5- idiotype (IDIO1) and anti-MmT1+, MmT5+ allotype (ALLO1) mAb. An in vivo test system was adapted to measure the inhibitory effects of circulating poly- or monoclonal anti-Ab. It revealed a reduction of in vivo depletion capacity not only of the sensitizing mAb (MmT1), but also of another anti-Thy-1.2 mAb (MmT5), with identical allotype but different idiotype. From this we conclude that intra-species immunization following injection of anti-T cell mAb can produce high titer inhibitory anti-idiotype and anti-allotype antibodies. Implications for hyperchimeric or fully human anti-T cell mAb are discussed.

The role of T-cell subsets in the response to anti-CD3 monoclonal antibodies

Administration of monoclonal antibodies (mAb) to CD3 elicits an immune response to the mAb and an acute toxic syndrome that has been attributed to the release of cytokines from activated T cells. To clarify the cellular basis for these effects, we used anti-lymphocyte mAb to deplete selected T-cell subsets from BALB/c mice prior to administration of anti-CD3. In our first series of experiments, anti-CD4 repeatedly blocked the immune response to anti-CD3, but did not prevent severe toxicity. This observation suggested that other T-cell subsets might contribute to anti-CD3 induced toxicity. Therefore, we treated mice with mAb to CD8 as well as mAb to CD4 prior to administration of anti-CD3. Despite depletion of > 95% of CD8+ and CD4+ T cells, toxicity was not suppressed. This finding cast doubt on the belief that toxicity is due to activation of either CD4+ or CD8+ T cells by anti-CD3. Therefore, we assessed the role of thymocytes (which are not deleted by the mAb) and gamma delta + T cells. Thymectomy did not prevent toxicity in CD4/CD8-depleted mice, demonstrating that thymocytes are not responsible for toxicity. Anti-alpha beta TCR mAb produced a toxic reaction similar to anti-CD3 whereas anti-gamma delta TCR mAb did not, suggesting that gamma delta+ T cells are not the source of toxic cytokines. In addition, we proved that anti-CD3-induced toxicity was not due to direct effects on macrophages or to other nonspecific factors associated with the hamster mAb. These findings imply that a few residual mature T cells in mice treated with mAb to CD4 and CD8 are sufficient for the full expression of the anti-CD3-induced toxic syndrome. To confirm that both CD4+ and CD8+ T cells can mediate toxicity, we showed that:(i) SCID mice, which normally do not develop anti-CD3-induced toxicity, can be rendered susceptible by reconstitution with purified CD4+ T cells; and (ii) CD4-knockout mice that lack CD4+ T cells but have normal CD8+ T cells are susceptible to anti-CD3-induced toxicity. These findings establish that both CD4+ and CD8+ cells contribute to the toxic effects of anti-CD3, and that relatively few cells are required to mediate the full effect.

Monoclonal antibodies in organ transplantation

Monoclonal antibody (mAb) technology has made possible the production of designer proteins, specifically reactive with almost any conceivable biological molecule. Using these reagents, the surface molecules on cells crucial for allograft rejection have been identified and described in detail. These structures can now be selectively targeted by mAb-based therapy in order to prevent rejection. For instance, the CD3 molecule, expressed on all mature T lymphocytes, triggers T cell activation, a key event in rejection. OKT3, an anti-CD3 mAb, disrupts T cell function and is now the agent of choice for the treatment of severe rejection episodes. MAbs targeting other T cell molecules are currently being investigated. Some of the most promising, the anti-CD4, anti-ICAM-1, and anti-interleukin 2 receptor mAbs, have already induced donor-specific tolerance in rodent models. These hosts accept permanently a genetically incompatible graft after only a limited period of mAb therapy. Interestingly, anti-ICAM-1 also diminishes the ischemic injury of preservation. The development of these new molecular agents, effectively directed to specific cellular targets, will likely play an increasingly important role in future clinical protocols, and perhaps finally provide a means to achieve long-term tolerance in human allograft recipients.

Monoclonal antibodies in renal transplantation: a review

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

Use of monoclonal antibodies in human transplantation

Monoclonal antibodies are of growing importance in human organ transplantation in the prophylatic and curative treatment of cellular rejection. Among the pan T-lymphocyte monoclonal antibodies, OKT3 has been much studied, although clinical research is engaged with more selective targets of allorecognition and/or their consequences, for example monoclonal antibodies directed against the interleukin-2 receptor, adhesion molecules and CD4 molecules. We summarize the use of these monoclonal antibodies and bioreagents in clinical transplantation.

The role of OKT3 in clinical transplantation

OKT3 is a murine monoclonal anti-T cell antibody that is directed to CD3, a five-chain molecular complex found in association with the T cell receptor for antigen. OKT3 was the first monoclonal antibody to be used in organ transplantation and during the past 10 years there has been extensive experience of its use both for preventing and treating rejection in organ transplantation. OKT3 blocks T cell function by modulating CD3 and the T cell receptor from the T cell surface. A reaction to OKT3 results from cytokines released when OKT3 first reacts with T cells. This reaction is generally mild but can be severe. First rejections following kidney transplantation are reversed in approximately 95% of cases. Steroid-resistant rejections are also susceptible to OKT3 but in only approximately 75% of cases. When used for prophylaxis, OKT3 completely blocks rejection in 95% of patients and significantly delays the onset of rejection in those who do reject. Antibodies to OKT3 are produced in approximately 75% of patients receiving it. However, seldom are the antibodies to OKT3 present in high titer and only in those cases is successful re-use of OKT3 prevented. As is the case with all potent immunosuppressive drugs, the use of OKT3 is associated with increased viral, specifically cytomegalovirus, infections. However, it appears that reduction of concomitant immunosuppression decreases the incidence of severe infections. Unquestionably, OKT3 has been a useful addition to the immunosuppression used for organ transplantation. In addition, its use has stimulated research on other monoclonal antibodies for use in organ transplantation.

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

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