Bispecific monoclonal antibodies directed to CD16 and to a tumor-associated antigen induce target-cell lysis by resting NK cells and by a subset of NK clones

Exploiting innate immunity for cancer immunotherapy

Immunotherapies have revolutionized the treatment paradigms of various types of cancers. However, most of these immunomodulatory strategies focus on harnessing adaptive immunity, mainly by inhibiting immunosuppressive signaling with immune checkpoint blockade, or enhancing immunostimulatory signaling with bispecific T cell engager and chimeric antigen receptor (CAR)-T cell. Although these agents have already achieved great success, only a tiny percentage of patients could benefit from immunotherapies. Actually, immunotherapy efficacy is determined by multiple components in the tumor microenvironment beyond adaptive immunity. Cells from the innate arm of the immune system, such as macrophages, dendritic cells, myeloid-derived suppressor cells, neutrophils, natural killer cells, and unconventional T cells, also participate in cancer immune evasion and surveillance. Considering that the innate arm is the cornerstone of the antitumor immune response, utilizing innate immunity provides potential therapeutic options for cancer control. Up to now, strategies exploiting innate immunity, such as agonists of stimulator of interferon genes, CAR-macrophage or -natural killer cell therapies, metabolic regulators, and novel immune checkpoint blockade, have exhibited potent antitumor activities in preclinical and clinical studies. Here, we summarize the latest insights into the potential roles of innate cells in antitumor immunity and discuss the advances in innate arm-targeted therapeutic strategies.

Role of antibody engineering in generation of derivatives starting from MOv19 MAb: 40 years of biological/therapeutic tools against folate receptor alfa

In the 1980s, we developed and characterized numerous murine monoclonal antibodies (MAbs) directed against human tumor-associated antigens. This mini review is focused on the generation of derivatives of an anti-folate receptor α (FRα) MAbs, named MOv19, exploiting the antibody-engineering progresses in the last 40 years. The FRα location on the luminal surface of proliferating epithelial cells, inaccessible to circulation, versus its over-expression in the entire surface of numerous carcinomas suggested a role for anti-FRα MAbs in the diagnosis and/or treatment of solid tumors. Presently, two MOv19 derivatives are in clinical trials: a chimeric resurfaced version in an antibody-drug conjugate format (SORAYA trial, 2022) and the murine scFv in a second generation chimeric antigen receptor, CAR-T (Phase Ia, 2021). MOv19 and its derivatives could be considered a relevant example that well-characterized anti-tumor murine Mabs and antibody engineering could be combined to generate useful therapeutic tools.

Natural Killer Cells in Cancer Immunotherapy

Natural killer (NK) cells have evolved to complement T and B cells in host defense against pathogens and cancer. They recognize infected cells and tumors using a sophisticated array of activating, costimulatory, and inhibitory receptors that are expressed on NK cell subsets to create extensive functional diversity. NK cells can be targeted to kill with exquisite antigen specificity by antibody-dependent cellular cytotoxicity. NK and T cells share many of the costimulatory and inhibitory receptors that are currently under evaluation in the clinic for cancer immunotherapy. As with T cells, genetic engineering is being employed to modify NK cells to specifically target them to tumors and to enhance their effector functions. As the selective pressures exerted by immunotherapies to augment CD8+T cell responses may result in loss of MHC class I, NK cells may provide an important fail-safe to eliminate these tumors by their capacity to eliminate tumors that are “missing self.”

Overcoming Resistance to Natural Killer Cell Based Immunotherapies for Solid Tumors

Despite advances in the diagnostic and therapeutic modalities, the prognosis of several solid tumor malignancies remains poor. Different factors associated with solid tumors including a varied genetic signature, complex molecular signaling pathways, defective cross talk between the tumor cells and immune cells, hypoxic and immunosuppressive effects of tumor microenvironment result in a treatment resistant and metastatic phenotype. Over the past several years, immunotherapy has emerged as an attractive therapeutic option against multiple malignancies. The unique ability of natural killer (NK) cells to target cancer cells without antigen specificity makes them an ideal candidate for use against solid tumors. However, the outcomes of adoptive NK cell infusions into patients with solid tumors have been disappointing. Extensive studies have been done to investigate different strategies to improve the NK cell function, trafficking and tumor targeting. Use of cytokines and cytokine analogs has been well described and utilized to enhance the proliferation, stimulation and persistence of NK cells. Other techniques like blocking the human leukocyte antigen-killer cell receptors (KIR) interactions with anti-KIR monoclonal antibodies, preventing CD16 receptor shedding, increasing the expression of activating NK cell receptors like NKG2D, and use of immunocytokines and immune checkpoint inhibitors can enhance NK cell mediated cytotoxicity. Using genetically modified NK cells with chimeric antigen receptors and bispecific and trispecific NK cell engagers, NK cells can be effectively redirected to the tumor cells improving their cytotoxic potential. In this review, we have described these strategies and highlighted the need to further optimize these strategies to improve the clinical outcome of NK cell based immunotherapy against solid tumors.

Natural killer cells unleashed: Checkpoint receptor blockade and BiKE/TriKE utilization in NK-mediated anti-tumor immunotherapy

Natural killer (NK) cells have long been known to mediate anti-tumor responses without prior sensitization or recognition of specific tumor antigens. However, the tumor microenvironment can suppress NK cell function resulting in tumor escape and disease progression. Despite recent advances in cytokine therapy and NK cell adoptive transfer, tumor expression of ligands to NK - expressed checkpoint receptors can still suppress NK mediated tumor lysis. This review will explore many of the checkpoint receptors tumors utilize to manipulate the NK cell response as well as some of the current and upcoming pharmacological solutions to limit tumor suppression of NK cell function. Furthermore, we will discuss the potential to use these drugs in combinational therapies with novel antibody reagents such as bi- and tri-specific killer engagers (BiKEs and TriKEs) against tumor-specific antigens to enhance NK cell-mediated tumor rejection.

Generation of BiKEs and TriKEs to Improve NK Cell-Mediated Targeting of Tumor Cells

Cancer immunotherapies have gained significant momentum over the past decade, particularly with the advent of checkpoint inhibitors and CAR T-cells. While the latter personalized targeted immunotherapy has revolutionized the field, a need for off-the-shelf therapies remains. The ability of NK cells to quickly lyse antibody-coated tumors and potently secrete cytokines without prior priming has made NK cells ideal candidates for antigen-specific immunotherapy. NK cells have been targeted to tumors through two main strategies: mono-specific antibodies and bi/tri-specific antibodies. Mono-specific antibodies drive NK cell antibody-dependent cell-mediated cytotoxicity (ADCC) of tumor cells. Bi/tri-specific antibodies drive re-directed lysis of tumor cells through binding of a tumor antigen and direct binding and crosslinking of the CD16 receptor on NK cells, thus bypassing the need for binding of the Fc portion of mono-specific antibodies. This chapter focuses on the generation of bi- and tri-specific killer engagers (BiKEs and TriKEs) meant to target NK cells to tumors. BiKEs and TriKEs are smaller molecules composed of 2-3 variable portions of antibodies with different specificities, and represent a novel and more versatile strategy compared to traditional bi- and tri-specific antibody platforms.

The biology of NK cells and their receptors affects clinical outcomes after hematopoietic cell transplantation (HCT)

Natural killer (NK) cells were first identified for their capacity to reject bone marrow allografts in lethally irradiated mice without prior sensitization. Subsequently, human NK cells were detected and defined by their non-major histocompatibility complex (MHC)-restricted cytotoxicity toward transformed or virally infected target cells. Karre et al. later proposed 'the missing self hypothesis' to explain the mechanism by which self-tolerant cells could kill targets that had lost self MHC class I. Subsequently, the receptors that recognize MHC class I to mediate tolerance in the host were identified on NK cells. These class I-recognizing receptors contribute to the acquisition of function by a dynamic process known as NK cell education or licensing. In the past, NK cells were assumed to be short lived, but more recently NK cells have been shown to mediate immunologic memory to secondary exposures to cytomegalovirus infection. Because of their ability to lyse tumors with aberrant MHC class I expression and to produce cytokines and chemokines upon activation, NK cells may be primed by many stimuli, including viruses and inflammation, to contribute to a graft-versus-tumor effect. In addition, interactions with other immune cells support the therapeutic potential of NK cells to eradicate tumor and to enhance outcomes after hematopoietic cell transplantation.

The difference of the impacts of surgical approaches on cellular immunity in patients with uterine malignancies: a comparative study of laparoscopy and laparotomy surgery

OBJECTIVE

To explore the impact of laparoscopy and laparotomy surgery on cellular immunity in patients with malignant uterine tumors.

METHODS

Thirty-eight women with uterine malignancies were enrolled in a prospective nonrandomized cohort study. Either laparoscopy or laparotomy was performed according to the patients' choice. The frequency of CD3+, CD4+, CD8+ T cells and natural killer cells derived from peripheral venous blood was evaluated by flow cytometry.

RESULTS

(1) Postoperatively, there was a decrease in the number of lymphocyte counts, especially after laparotomy, on the first postoperative day (p < 0.01). (2) Compared with preoperative levels, the frequencies of CD3+ and CD4+ cells and the CD4+/CD8+ ratio were declined both in the laparoscopy and laparotomy groups on postoperative day 1 (p < 0.01). (3) The frequencies of CD3+ and CD4+ cells and the ratio of CD4+ to CD8+ cells were less depressed in the laparoscopy group on the first postoperative day (p < 0.05). (4) The frequency of natural killer cells increased, both in the laparoscopy and laparotomy groups on the first postoperative day (p < 0.01), but there were no significant differences between the two groups (p > 0.05).

CONCLUSION

Cellular immunity was temporally depressed in patients with uterine malignancy after surgical treatment, but laparoscopic surgery depressed the immunity less than laparotomy.

CD16+ gammadelta T cells mediate antibody dependent cellular cytotoxicity: potential mechanism in the pathogenesis of multiple sclerosis

Our overall objective is to understand the role of gammadelta T cells in the pathogenesis of the central nervous system (CNS) autoimmune disease multiple sclerosis (MS). We have demonstrated that gammadelta T cells are directly cytotoxic to CNS cells in vitro. Although the exact mechanism of damage in MS is unknown, recent evidence suggests a role for B cells and antibodies to myelin. We were therefore interested in examining whether gammadelta T cells can injure CNS cells via an indirect mechanism involving antibody dependent cellular cytotoxicity. To study this we developed an in vitro flow cytometric cellular cytotoxicity assay (called "FC(3)A") to quantitate the amount of cytotoxicity. We utilized known target cells (Burkitt's B lymphoma) that express CD20, together with a monoclonal antibody (mAb) to CD20, rituximab, that is being studied as a potential treatment for MS. Target cells are first coated with rituximab followed by co-culture with gammadelta T cells derived from patients with MS. Specific lysis of target cells was determined by quantitation of 7-AAD (which increases only upon nuclear disruption indicating cell death). We determined that this lysis was due to gammadelta T cells that express CD16 (Fc gamma receptor) and were therefore capable of binding the rituximab and mediating cytolysis via ADCC. This specific cell lysis correlated with rituximab concentration, E:T ratio, and the surface expression of CD16 on gammadelta T cells. These findings provide a new perspective with regards to the role of gammadelta T cells in the immunopathogenesis of MS and an insight into one of the potential therapeutic effects of rituximab in the treatment of MS. In addition, this new FC(3)A method we developed could readily be adapted to study other types of immune cells suspected of ADCC-type killing.

Active antiviral T-lymphocyte response can be redirected against tumor cells by antitumor antibody x MHC/viral peptide conjugates

PURPOSE

To redirect an ongoing antiviral T-cell response against tumor cells in vivo, we evaluated conjugates consisting of antitumor antibody fragments coupled to class I MHC molecules loaded with immunodominant viral peptides.

EXPERIMENTAL DESIGN

First, lymphochoriomeningitis virus (LCMV)-infected C57BL/6 mice were s.c. grafted on the right flank with carcinoembryonic antigen (CEA)-transfected MC38 colon carcinoma cells precoated with anti-CEA x H-2D(b)/GP33 LCMV peptide conjugate and on the left flank with the same cells precoated with control anti-CEA F(ab')(2) fragments. Second, influenza virus-infected mice were injected i.v., to induce lung metastases, with HER2-transfected B16F10 cells, coated with either anti-HER2 x H-2D(b)/NP366 influenza peptide conjugates, or anti-HER2 F(ab')(2) fragments alone, or intact anti-HER2 monoclonal antibody. Third, systemic injections of anti-CEA x H-2D(b) conjugates with covalently cross-linked GP33 peptides were tested for the growth inhibition of MC38-CEA(+) cells, s.c. grafted in LCMV-infected mice.

RESULTS

In the LCMV-infected mice, five of the six grafts with conjugate-precoated MC38-CEA(+) cells did not develop into tumors, whereas all grafts with F(ab')(2)-precoated MC38-CEA(+) cells did so (P = 0.0022). In influenza virus-infected mice, the group injected with cells precoated with specific conjugate had seven times less lung metastases than control groups (P = 0.0022 and P = 0.013). Most importantly, systemic injection in LCMV-infected mice of anti-CEA x H-2D(b)/cross-linked GP33 conjugates completely abolished tumor growth in four of five mice, whereas the same tumor grew in all five control mice (P = 0.016).

CONCLUSION

The results show that a physiologic T-cell antiviral response in immunocompetent mice can be redirected against tumor cells by the use of antitumor antibody x MHC/viral peptide conjugates.

The assembly of single domain antibodies into bispecific decavalent molecules

Bispecific antibodies present unique opportunities in terms of new applications for engineered antibodies. However, designing ideal bispecific antibodies remains a challenge. Here we describe a novel bispecific antibody model in which five single domain antibodies (sdAbs) are fused via a linker sequence to the N-terminus of the verotoxin B (VTB) subunit, a pentamerization domain, and five sdAbs are fused via a linker sequence to the VTB C-terminus. Fifteen such decavalent bispecific molecules, termed decabodies, were constructed and characterized for the purpose of identifying an optimal decabody design. One of the fifteen molecules existed in a non-aggregated decavalent form. In conjunction with the isolation of sdAbs with the desired specificities from non-immune phage display libraries, the decabody strategy provides a means of generating high avidity bispecific antibody reagents, with good physical properties, relatively quickly.

Antibody-conjugated MHC class I tetramers can target tumor cells for specific lysis by T lymphocytes

To demonstrate that antibody-guided targeting of antigenic MHC class I-peptide tetramer on tumor cells can render them susceptible to lysis by relevant cytotoxic T lymphocytes (CTL), biotinylated HLA-A*0201/Flu matrix peptide complexes were tetramerized on streptavidin molecules previously coupled to Fab' fragments from monoclonal antibodies (mAb) specific for cell surface markers such as carcinoembryonic antigen (CEA), ErbB-2 or CD20. Flow cytometry analysis showed that coating of the HLA-A2-peptide complexes on the four HLA-A2-negative human cancer lines tested (including a CEA-positive colon carcinoma, an ErbB-2(+) breast carcinoma and two CD20(+) B lymphomas) was entirely dependent upon the specificity of the conjugated antibody fragments. More importantly, HLA-A2-restricted Flu matrix peptide-specific CTL were then found to lyse specifically and efficiently the MHC-coated target cells. These results open the way to the development of new immunotherapy strategies based on antibody targeting of MHC class I-peptide complexes.

Bispecific antibodies for treatment of cancer in experimental animal models and man

Immunotherapy is a powerful anti-cancer treatment modality. However, despite numerous encouraging results obtained in pre-clinical studies, a definite breakthrough towards an established clinical treatment modality has as yet not occurred. Antibodies against tumor antigens have been shown to localise at the site of the tumor, but inadequate triggering of immune effector mechanisms have thwarted clinical efficacy thus far. Cellular immunotherapy has been hampered by limitations such as lack of specificity, down-regulation of major histocompatibility complex (MHC)-expression or Fas ligand up-regulation on tumor cells. This review focuses on the use of bispecific antibodies (BsAbs) for immunotherapy of cancer. Using BsAbs, it is possible to take advantage of the highly specific binding characteristics of antibodies and combine these with the powerful effector functions of cytotoxic immune effector cells. BsAbs share two different, monoclonal antibody-derived, antigen-recognizing moieties within one molecule. By dual binding, BsAbs reactive with a trigger molecule on an immune effector cell on the one hand and a surface antigen on a tumor target cell on the other are thus able to functionally focus the lytic activity of the immune effector cell towards the target cell. Over the last few years, the concept of BsAb-mediated tumor cell killing has been studied extensively both in preclinical models and in a number of phase I clinical trials. Promising pre-clinical results have been reported using tumor models in which diverse immune effector cell populations have been used. Despite this pre-clinical in vivo efficacy, the first clinical trials indicate that we are still not in a position to successfully treat human malignancies. This review discusses the production of BsAbs, the choice of trigger molecules in combination with potential effector cells and the preclinical models that have led to the current use of BsAbs in experimental clinical trials. It has become clear that appropriate immune cell activation and establishing a favourable effector-to-target cell ratio will have direct impact on the efficacy of the therapeutic approaches using BsAbs. New directions are discussed, i.e. finding appropriate dosage schemes by which immune effector cells become redirected without inducing hyporesponsiveness, defining possibilities for combining different immune effector cell populations and creating an in situ tumor environment that allows maximal tumoricidal activity

Molecular cloning and characterization of a transmembrane surface antigen in human cells

The mouse mAb 6C6, raised against a plasma-membrane preparation from human breast-cancer cells, reacts with an antigen that appears to be overexpressed in human breast cancers and other human tumors. Here we describe the cDNA cloning and characterization of the antigen recognized by the 6C6 mAb. The isolated cDNA clone encodes a protein of 246 amino acids, with a predicted molecular mass of 27 991 Da. The protein contains three amino-terminal hydrophobic regions, which could represent transmembrane domains, and a hydrophilic carboxy-terminal region, which we show to be extracellular. The identity of the protein encoded by the cloned cDNA as the 6C6 antigen was confirmed by in vitro translation and immunoprecipitation experiments, and by transfection into cell lines that do not react with the 6C6 mAb, which resulted in the expression of a 28-kDa surface protein that was recognized by the antibody. The 6C6 antigen appears to be a type II transmembrane protein, with multiple membrane-spanning domains and a long extracellular non-glycosylated carboxy-terminal domain, to which the 6C6 epitope has been mapped. The overall structure of the protein and weak amino acid similarities with a family of multiple-transmembrane-spanning-domain proteins that includes some antigens (such as L6, CD63/ME491 and CO-029) that are overexpressed in tumor cells, suggest that the 6C6 antigen may belong to this family of proteins.

Phase I study of intravenously applied bispecific antibody in renal cell cancer patients receiving subcutaneous interleukin 2

In a phase I trial the toxicity and immunomodulatory effects of combined treatment with intravenous (i.v.) bispecific monoclonal antibody BIS-1 and subcutaneous (s.c.) interleukin 2 (IL-2) was studied in renal cell cancer patients. BIS-1 combines a specificity against CD3 on T lymphocytes with a specificity against a 40 kDa pancarcinoma-associated antigen, EGP-2. Patients received BIS-1 F(ab')2 fragments intravenously at doses of 1, 3 and 5 micrograms kg-1 body weight during a concomitantly given standard s.c. IL-2 treatment. For each dose, four patients were treated with a 2 h BIS-1 infusion in the second and fourth week of IL-2 therapy. Acute BIS-1 F(ab')2-related toxicity with symptoms of chills, peripheral vasoconstriction and temporary dyspnoea was observed in 2/4 and 5/5 patients at the 3 and 5 micrograms kg-1 dose level respectively. The maximum tolerated dose (MTD) of BIS-1 F(ab')2 was 5 micrograms kg-1. Elevated plasma levels of tumour necrosis factor alpha (TNF-alpha) and interferon gamma (IFN-gamma) were detected at the MTD. Flow cytometric analysis showed a dose-dependent binding of BIS-1 F(ab')2 to circulating T lymphocytes. Peripheral blood mononuclear cells (PBMCs), isolated after treatment with 3 and 5 micrograms kg-1 BIS-1, showed increased specific cytolytic capacity against EGP-2+ tumour cells as tested in an ex vivo performed assay. Maximal killing capacity of the PBMCs, as assessed by adding excess BIS-1 to the assay, was shown to be decreased after BIS-1 infusion at 5 micrograms kg-1 BIS-1 F(ab')2. A BIS-1 F(ab')2 dose-dependent disappearance of circulating mononuclear cells from the peripheral blood was observed. Within the circulating CD3+ CD8+ lymphocyte population. LFA-1 alpha-bright and HLA-DR+ T-cell numbers decreased preferentially. It is concluded that i.v. BIS-1 F(ab')2, when combined with s.c. IL-2, has a MTD of 5 micrograms kg-1. The treatment endows the T lymphocytes with a specific anti-EGP-2-directed cytotoxic potential.

Differentiation of cytotoxicity using target cells labelled with europium and samarium by electroporation

We report the simultaneous use of europium-DTPA (Eu-DTPA) and samarium-DTPA (Sm-DTPA) in cytotoxicity experiments to analyze simultaneously LAK and NK cell lysis and to differentiate between specific target lysis and bystander killing. The target cells were either labelled with Eu-DTPA or Sm-DTPA chelates by electroporation, which permits the use of target cell lines or primary leukemic B cells (B-CLL) that cannot be labelled by the conventional dextran-sulphate method. The release of europium and samarium reaches a maximum at comparable time intervals (2-3 h). Due to the shorter counting interval within the samarium window the labelling efficiency is about ten times less efficient compared to europium. Using europium as label for the LAK target Daudi and samarium as label for the NK sensitive cell line K562 the differentiation of LAK versus NK activity can be performed in a single culture assay. Also, the killing of B cells and bystander cells by cytotoxic T cells was analyzed in a system where T cells were redirected to B cells through CD3 x CD19 bispecific antibodies. In fact, no bystander killing was noted when bispecific antibodies were used to bridge cytotoxic T cells to the B cells. This approach provides a simple non-radioactive method for evaluating cytotoxicity against two different cells in a single culture well.

Targeting of T lymphocytes against EGF-receptor+ tumor cells by bispecific monoclonal antibodies: requirement of CD3 molecule cross-linking for T-cell activation

Targeting of T lymphocytes against epidermal growth-factor-receptor (EGF-R)+ tumor cells was achieved by constructing a hybrid hybridoma which secretes an anti-EGF-R/anti-CD3 bispecific monoclonal antibody (biMAb) of hybrid isotype (IgG1/IgG2a). Purification of biMAb molecules from parental anti-EGF-R and anti-CD3 MAbs was performed by protein-A chromatography. The purified biMAb was able to trigger the lysis of EGF-R+ tumor cell lines (A431, IGROV-1, MDA-468 and U-87) and of NIH-3T3 transfectants expressing human EGF-R by cytolytic T lymphocytes, but it was ineffective in the case of EGF-R-negative tumor targets. Normal EGF-R+ cells (keratinocytes and endometrial cells) were also susceptible to biMAb-targeted cytolysis. However, the amount of biMAb required to induce half-maximal cytolysis of tumor cells over-expressing the EGF-R molecule (A431) was considerably lower than that required to induce lysis of EGF-R+ tumor or normal cells which express EGF-R at considerably lower density. The ability of such biMAbs to deliver activation signals to T cells was evaluated by Ca++ mobilization and lymphokine production experiments. The soluble anti-EGF-R/anti-CD3 biMAb failed to induce intracellular Ca++ increases, which occurred only after cross-linking induced by an anti-mouse IgG antibody. Secretion of lymphokines (IFN-gamma, TNF-alpha and GM-CSF) was induced by contact of the biMAb-coated effector cells with the relevant tumor target, whereas the soluble biMAb was virtually ineffective. In addition, biMAb-coated effector cells retained the ability to recognize and to lyse EGF-R+ tumor cells for a prolonged period of time. Our data indicate that activation of effector cells targeted by biMAbs can only occur at the tumor site, where cross-linking of surface CD3 molecules is induced by contact with the tumor cells.

A CD16/CD30 bispecific monoclonal antibody induces lysis of Hodgkin's cells by unstimulated natural killer cells in vitro and in vivo

In order to target NK cells against the Hodgkin's-derived cell line L540, we developed bispecific monoclonal antibodies (Bi-MAbs) by somatic hybridization of the 2 mouse hybridoma cell line HRS-3 and A9 which produce monoclonal antibodies (MAbs) with reactivity against the Hodgkin and Reed-Sternberg cell-associated CD30 antigen and the CD16 antigen (Fc gamma III receptor), respectively. The CD16 MAb-producing cell line A9 was selected as a partner for HRS-3 because of its efficiency in inducing lysis of the A9 hybridoma cells by resting NK cells. The hybrid hybridoma cell line HRS-3/A9 produced the supernatant with the strongest bispecific reactivity and was repeatedly subcloned and used for ascites production. Crude supernatant and purified HRS-3/A9 Bi-MAb triggered specific lysis of the CD30+ Hodgkin's-derived cell line L540, but not of the CD30- cell line HPB-ALL by unstimulated peripheral-blood lymphocytes and NK-cell-enriched populations. Moreover, treatment of SCID mice bearing heterotransplanted human Hodgkin's tumors with HRS-3/A9 and human peripheral blood lymphocytes induced specific complete tumor regression in 10/10 animals. We thus report successful tumor treatment in an in vivo model using NK-cell-associated Bi-MAbs and show that the Bi-MAb HRS-3/A9 is an efficient promoter of the anti-tumor effects of NK cells in vitro and in vivo.

Local antitumour treatment in carcinoma patients with bispecific-monoclonal-antibody-redirected T cells

In a pilot clinical study carcinoma patients with malignant ascites or pleural exudates have been treated locally with autologous lymphocytes activated ex vivo and redirected towards tumour cells with bispecific monoclonal antibodies. BIS-1, the bispecific monoclonal antibody used in this study, combines specificity against a tumour-associated antigen, AMOC-31, present on carcinomas, with a specificity against the CD3 complex on T lymphocytes. Patients selected for treatment had malignant pleural or peritoneal effusions. Treatment consisted of isolating autologous peripheral blood lymphocytes, ex vivo activation, incubation with bispecific monoclonal antibodies and injection at the effusion site of these BIS-1-redirected lymphocytes. To evaluate the effects of the bispecific monoclonal antibody, five patients received treatments with activated lymphocytes without bispecific antibodies. Effusion samples taken before and at various times after treatment were analysed by immunocytology and for the presence of the soluble factors carcinoembryonic antigen (CEA), interleukin-6 (IL-6), tumour necrosis factor (TNF), C-reactive protein and soluble CD8. In this way both immune activation and anti-tumour activity could be monitored. Conjugate formation between tumour cells and activated lymphocytes was seen as soon as 4 h after injection of BIS-1-redirected activated lymphocytes, followed by a disappearance or reduction of tumour cells after 24-48 h. In parallel with this, the soluble tumour marker CEA decreased in the effusion fluid following injection with the BIS-1-redirected lymphocytes. Furthermore, a steep increase in local granulocyte numbers was observed in the effusion fluid, which reached a maximum 24-48 h after the start of the treatment. Also levels of IL-6 and TNF were greatly elevated. The data suggest that the treatment induces both antitumour activity and a strong local inflammatory reaction. This is accompanied by no or only minor local and systemic toxicity, i.e. mild fever, which disappeared as the local inflammatory reaction diminished 48-72 h after treatment.

Purification of monoclonal antibodies with light-chain heterogeneity produced by mouse hybridomas raised with NS-1 myelomas: application of hydrophobic interaction high-performance liquid chromatography

Monoclonal antibodies (mAbs) of IgG1 class produced by hybridomas raised with NS-1 myelomas, which were purified homogeneously by anion-exchange high-performance liquid chromatography (HPLC), contained two types of immunoglobulin light (kappa) chain. Since NS-1 myeloma synthesizes the light (kappa) chain, the mAb was presumed to be the mixture of hybrid mAbs formed by the random association of heavy (gamma l) and light chains from antigen-immunized spleen cells and light chain from NS-1 cells. Hydrophobic interaction HPLC using TSKgel Phenyl-5PW was applicable to separate 3 species of hybrid mAb from mAb fractions obtained by anion-exchange HPLC. mAbs in the fractions were adsorbed onto the gel equilibrated with phosphate-buffered saline containing 1 M ammonium sulfate and eluted by reducing the concentration to 0 M. The hybrid mAbs were purified separately. The hydrophobic interaction HPLC could discriminate a small difference in hydrophobicity between kappa chains from spleen and NS-1 cells. The immunoreactivities of hybrid mAb bearing light chains only from spleen cells and that bearing those from both spleen and NS-1 cells were almost the same, and hybrid mAb bearing light chains derived only from NS-1 cells showed a relatively lower immunoreactivity than the others. The method described here could be useful for purification of hybrid mAbs.

Targeting of saporin to CD25-positive normal and neoplastic lymphocytes by an anti-saporin/anti-CD25 bispecific monoclonal antibody: in vitro evaluation

This study has been designed to verify the specific toxicity of saporin, a type 1 ribosome-inactivating protein (RIP), with the same activity as ricin A chain, targeted by a bispecific monoclonal antibody (bimAb) recognising both the CD25 antigen and the RIP. The CD25 antigen is expressed by lymphoid populations upon activation and by leukaemias and lymphomas with an activated membrane phenotype (Hodgkin's lymphoma, anaplastic large cell lymphoma, adult T cell leukaemia). The bimAb-saporin mixture was tested on CD25+ targets at different bimAb and saporin concentrations. Saporin, in the presence of a bimAb concentration of 10(-9) M, inhibited protein synthesis by CD25+ neoplastic lymphocytes (L540 and MT2 cell lines) with IC50S (concentrations giving 50% of inhibition) ranging from 8 x 10(-12) M to 3 x 10(-11) M. The saporin-bimAb mixture was also effective in blocking the phytohaemagglutinin-driven proliferation of normal lymphocytes, whereas it displayed the same level of toxicity exerted by saporin alone on an irrelevant CD25-negative cell line (EBV-infected B lymphoblastoid cell line). From these results it is possible to envisage a clinical use of this bimAb as a cytotoxic agent for CD25+ leukaemias and lymphomas, as well as an immunosuppressive agent for severe immune disorders such as graft-vs-host disease (GVHD) and transplanted organ rejection.

The development and purification of a bispecific antibody for lymphokine-activated killer cell targeting against the rat colon carcinoma CC531

In vivo targeting of lymphokine-activated killer (LAK) cells to tumour deposits by bispecific monoclonal antibodies (bimAb) may be a way to improve adoptive immunotherapy. We developed a bimAb against adherent LAK (ALAK) cells and colon tumour CC531 in Wag rats. The bimAb was produced by somatic hybridization of two mouse hybridomas, one producing monoclonal antibodies (mAb) against CD8 (IgG2b, OX8), and the other producing mAb against a CC531-associated antigen (IgG1, CC52). A bimAb-producing clone was selected by an enzyme-linked immunosorbent assay with CC531 tumour cells. BimAb were purified from ascitic fluid by protein A affinity chromatography. Each of five pooled peak fractions was analysed by flow cytometry for the presence of bimAb. Most bimAb were found in a fraction that was eluted at pH 4.5 from protein A. FPLC analysis of this fraction revealed that no parental antibodies were present. The OX8 x CC52 bimAb greatly increased conjugate formation in vitro between ALAK cells and CC531. Results of 51Cr-release assays with CC531 as target cells and ALAK cells as effector cells were not significantly different in the presence or in the absence of the bimAb. The methods we used here, a cell enzyme-linked immunosorbent assay and flow cytometry, are simple methods for development and purification of a bimAb when a functional selection method is not a priori available. The OX8 x CC52 bimAb we developed this way may increase in vivo tumour targeting of ALAK cells and thus augment antitumour effect in vivo.

Targeted immunotherapy. An update with special emphasis on ovarian cancer

An overview of antibody-guided immunotherapy for neoplasia is presented. The diversity of the antibody molecule is highlighted, through the many sophisticated strategies proposed and employed, to overcome a number of problems impeding successful targeting. An update of radioimmunotherapy of ovarian cancer is presented and the exciting concepts that are introduced to the field of targeted cancer therapy by molecular biology and genetic engineering are addressed.

Ber-H2 (anti-CD30)-saporin immunotoxin: a new tool for the treatment of Hodgkin's disease and CD30+ lymphoma: in vitro evaluation

An immunotoxin containing an anti-CD30 monoclonal antibody (Ber-H2) and saporin, a ribosome-inactivating protein type 1, is described. It specifically inhibits protein synthesis by Hodgkin derived target cell lines with a very high efficiency (IC50 ranging from 5 x 10(-12) M to 5 x 10(-14) M, as saporin), while irrelevant immunotoxins do not. Present results suggest that this immunotoxin could be used for in vivo therapy as well as for ex vivo bone marrow purging in Hodgkin's disease and CD30+ lymphomas.

Bifunctional antibodies and their potential clinical applications

Bifunctional antibodies are monovalent, bispecific, antibody-derived molecules. They have been produced by both chemical and biological means. They are thought to have several advantages over monoclonal antibodies in both immunotherapy and immunodiagnosis. Bifunctional antibodies have been shown to be efficient in the targeting of drugs, toxins, radiolabelled haptens and effector cells on to diseased tissues, primarily cancer cells. In addition, bifunctional antibodies have been used to develop novel immunoassays. The full potential of bifunctional antibodies has yet to be realised.