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

Cancer cells under immune attack acquire CD47-mediated adaptive immune resistance independent of the myeloid CD47-SIRPα axis

Cancer cells exploit CD47 overexpression to inhibit phagocytic elimination and neoantigen processing via the myeloid CD47-SIRPα axis and thereby indirectly evade adaptive T cell immunity. Here, we report on a hitherto unrecognized direct immunoinhibitory feature of cancer cell-expressed CD47. We uncovered that in response to IFNγ released during cognate T cell immune attack, cancer cells dynamically enhance CD47 cell surface expression, which coincides with acquiring adaptive immune resistance toward pro-apoptotic effector T cell mechanisms. Indeed, CRISPR/Cas9-mediated CD47-knockout rendered cancer cells more sensitive to cognate T cell immune attack. Subsequently, we developed a cancer-directed strategy to selectively overcome CD47-mediated adaptive immune resistance using bispecific antibody (bsAb) CD47xEGFR-IgG2s that was engineered to induce rapid and prolonged cancer cell surface displacement of CD47 by internalization. Treatment of CD47^pos cancer cells with bsAb CD47xEGFR-IgG2s potently enhanced susceptibility to cognate CD8^pos T cells. Targeting CD47-mediated adaptive immune resistance may open up new avenues in cancer immunotherapy.

Overcoming Challenges for CD3-Bispecific Antibody Therapy in Solid Tumors

Immunotherapy of cancer with CD3-bispecific antibodies is an approved therapeutic option for some hematological malignancies and is under clinical investigation for solid cancers. However, the treatment of solid tumors faces more pronounced hurdles, such as increased on-target off-tumor toxicities, sparse T-cell infiltration and impaired T-cell quality due to the presence of an immunosuppressive tumor microenvironment, which affect the safety and limit efficacy of CD3-bispecific antibody therapy. In this review, we provide a brief status update of the CD3-bispecific antibody therapy field and identify intrinsic hurdles in solid cancers. Furthermore, we describe potential combinatorial approaches to overcome these challenges in order to generate selective and more effective responses.

A novel bispecific antibody for EGFR-directed blockade of the PD-1/PD-L1 immune checkpoint

PD-L1-blocking antibodies produce significant clinical benefit in selected cancer patients by reactivating functionally-impaired antigen-experienced anticancer T cells. However, the efficacy of current PD-L1-blocking antibodies is potentially reduced by ‘on-target/off-tumor’ binding to PD-L1 widely expressed on normal cells. This lack of tumor selectivity may induce a generalized activation of all antigen-experienced T cells which may explain the frequent occurrence of autoimmune-related adverse events during and after treatment.

To address these issues, we constructed a bispecific antibody (bsAb), designated PD-L1xEGFR, to direct PD-L1-blockade to EGFR-expressing cancer cells and to more selectively reactivate anticancer T cells. Indeed, the IC50 of PD-L1xEGFR for blocking PD-L1 on EGFR⁺ cancer cells was ∼140 fold lower compared to that of the analogous PD-L1-blocking bsAb PD-L1xMock with irrelevant target antigen specificity. Importantly, activation status, IFN-γ production, and oncolytic activity of anti-CD3xanti-EpCAM-redirected T cells was enhanced when cocultured with EGFR-expressing carcinoma cells. Similarly, the capacity of PD-L1xEGFR to promote proliferation and IFN-γ production by CMVpp65-directed CD8⁺ effector T cells was enhanced when cocultured with EGFR-expressing CMVpp65-transfected cancer cells. In contrast, the clinically-used PD-L1-blocking antibody MEDI4736 (durvalumab) promoted T cell activation indiscriminate of EGFR expression on cancer cells. Additionally, in mice xenografted with EGFR-expressing cancer cells ¹¹¹In-PD-L1xEGFR showed a significantly higher tumor uptake compared to ¹¹¹In-PD-L1xMock. In conclusion, PD-L1xEGFR blocks the PD-1/PD-L1 immune checkpoint in an EGFR-directed manner, thereby promoting the selective reactivation of anticancer T cells. This novel targeted approach may be useful to enhance efficacy and safety of PD-1/PD-L1 checkpoint blockade in EGFR-overexpressing malignancies.

Liver Metastases from Gastric Carcinoma: Report of a Patient Treated with Adoptive Immunotherapy (Tumor-Infiltrating Lymphocytes plus Interleukin-2 and Subsequently Local-Regional Lymphokine-Activated Killer Cells plus inTerleukin-2)

A 37-year-old patient with liver metastases from gastric cancer was treated with a double adoptive immunotherapy regimen comprising tumor-infiltrating lymphocytes plus interleukin-2 and subsequently local-regional lymphokine-activated killer cells plus interleukin-2 because of an extremely high in vitro cytotoxic specific activity on established gastric cancer cell lines. The necrosis verified in the center of the hepatic metastasis would appear to demonstrate treatment efficacy, but no clinical response was seen. In vitro cytotoxicity data alone are insufficient to predict the clinical efficacy of adoptive immunotherapy.

Targeting T cells with bispecific antibodies for cancer therapy

Bispecific antibodies (BiAbs) offer a unique opportunity to redirect immune effector cells to kill cancer cells. BiAbs combine the benefits of different binding specificities of two monoclonal antibodies (mAbs) into a single construct. This unique feature of BiAbs enables approaches that are not possible with single mAbs. Advances in antibody engineering and antigen profiling of malignant cells have led to the development of a number of BiAb formats and their combinations for redirecting effector cells to tumor targets. There have been significant advances in the design and application of BiAbs for intravenous and local injection.The initial barrier of cytokine storm has been partially overcome by more recent constructs that have improved clinical effectiveness without dose-limiting toxicities. Since the recent revival of BiAbs, there has been multiple, ongoing, phase I/II and III trials, and some promising clinical outcomes have been reported in completed clinical studies. This review focuses on arming T cells with BiAbs to create the 'poor man's cytotoxic lymphocyte'.

Use of trifunctional bispecific antibodies to prevent graft versus host disease induced by allogeneic lymphocytes

A trifunctional bispecific antibody (BiLu) directed against murine CD3 and human epithelial-cell adhesion molecule (EpCAM) was tested for its ability to improve cell-mediated adoptive immunotherapy in a murine model of B16 melanoma cells transfected with human EpCAM. Intraperitoneal inoculation of naive C57BL/6 (C57) splenocytes induced lethal graft versus host disease (GVHD) in 85% to 97% of sublethally irradiated (BALB/c × C57BL/6) F1 (F1) hosts inoculated intraperitoneally with a sublethal or lethal dose of melanoma cells. BiLu antibodies given intraperitoneally concomitantly with alloreactive C57 cells effectively prevented GVHD-related and tumor-related death in 16 of 25 F1 mice inoculated with a sublethal tumor-cell dose and in 10 of 20 mice inoculated with a lethal tumor-cell dose over a follow-up period of more than 200 days. BiLu treatment also efficiently prevented severe GVHD, which was induced by high doses of BALB/c-derived splenocytes. Trifunctional bispecific antibodies (TbsAbs) capable of cross-linking T lymphocytes, natural killer, and other FcγR-positive effector cells, via their Fc region, to the tumor cells may be applied together with adoptive allogeneic-cell therapy to maximize antitumor responses while acting on GVHD in patients with minimal residual disease.

Immunotherapy of malignant ascites with trifunctional antibodies

A new class of intact bispecific antibodies shows unmet effector qualities by activation of not only T cells but also simultaneous activation of Fcgamma receptor type I/III+ cells (macrophages, NK-cells and DC). These trifunctional antibodies (trAb) lead to efficient specific killing of targeted tumor cells without any pre- or co-stimulation. This concept was investigated in vivo in patients with malignant ascites in a clinical situation that allowed monitoring of tumor cell elimination and correlation with clinical effects. In a prospective study, 8 patients with malignant ascites due to peritoneal carcinomatosis were treated with intraperitoneal application of trAb, which bound either the EpCAM- or Her2/neu-antigen on tumor cells. Treatment consisted of 4-6 applications within 9-23 days with a total amount of 145-940 microg. Seven of eight patients required no further paracentesis during follow-up or until death with a mean paracentesis-free interval of 38 weeks (median = 21.5, range = 4-136). Tumor cell monitoring showed a complete elimination of tumor cells in ascites already at total doses as low as 40-140 microg. Clinical response with disappearance of ascites accumulation was seen in all patients, which was correlated with elimination of tumor cells (p = 0.0014). Severe adverse events were not observed. Clinically relevant side effects were fever, moderate abdominal pain and skin reactions. Intraperitoneal immunotherapy with trAb showed convincing efficacy in patients with malignant ascites. This treatment offers new therapeutic options for patients with peritoneal carcinomatosis.

Retargeting T cells and immune effector cells with bispecific antibodies

The development of BiAbs for therapeutic applications in cancer shows promise. As our understanding of effector cell receptor biology for triggering of cytotoxic functions improves and the behavior of TAA and the targeting antibody engagement is elucidated, customized BiAb reagents can be engineered to optimize in vivo or ex vivo arming of T cells for targeting tumors. Additionally, other variables that require consideration in the equation for successful T cell immunotherapy include: the type of effector cells, their state of activation, the type of effector receptor being activated or tareeted. the presence of Tregs, the affinity of the anti-effector cell antibody and the anti-TAA antibody, the type of BiAb (mouse, humanized, or human), the number of binding sites for the T cells or TAA, the presence or absence of decoy antigen, whether the TAA modulates after being engaged by antibody, the type of tumor, the tumor burden, and last, but not least, the amount of 'immunologic' space available for the adoptively transferred cells to expand and function.

A novel recombinant bispecific single-chain antibody, bscWue-1 × CD3, induces T-cell-mediated cytotoxicity towards human multiple myeloma cells

The development of antibody-based strategies for the treatment of multiple myeloma (MM) has been hampered so far by the fact that suitable plasma cell-specific surface antigens have been missing. However, recently a novel monoclonal antibody, designated Wue-1, has been generated that specifically recognizes normal and malignant human plasma cells. Therefore, Wue-1 is an interesting and promising candidate to develop novel immunotherapeutic strategies for the treatment of MM. One variant for an antibody-based strategy is the bispecific antibody approach. Recombinant bispecific single-chain (bsc) antibodies are especially interesting candidates because they show exceptional biological properties. We have generated a novel MM-directed recombinant bsc antibody, bscWue-1 x CD3, and analyzed the biological properties of this antibody using the MM cell line NCI-H929 and primary cells from the bone marrow of patients with MM. We were able to show that bscWue-1 x CD3 induces efficient and selective T-cell-mediated cell death of NCI-H929 cells and primary myeloma cells in nine out of 11 cases. The bscWue-1 x CD3 Ab is efficacious even at low E:T ratios, and with or without additional T-cell pre- or costimulation. Target cell lyses were specific for Wue-1 antigen-positive cells and could be blocked by the Wue-1 monoclonal antibody.

Bispecific antibody conjugates in therapeutics

Bispecific monoclonal antibodies have drawn considerable attention from the research community due to their unique structure against two different antigens. The two-arm structure of bsMAb allows researchers to place a therapeutic agent on one arm while allowing the other to specifically target the disease site. The therapeutic agent can be a drug, toxin, enzyme, DNA, radionuclide, etc. Furthermore, bsMAb may redirect the cytotoxicity of immune effector cells towards the diseased cells or induce a systemic immune response against the target. BsMAb holds great promise for numerous therapeutic needs in the light of: (1) recent breakthroughs in recombinant DNA technology, (2) the increased number of identified disease targets as the result of the completion of human genomic map project, and (3) a better understanding of the mechanism of human immune system. This review focuses on therapeutic applications and production of bsMAb while providing the up-to-date clinical trial information.

Intraperitoneal bispecific antibody (HEA125xOKT3) therapy inhibits malignant ascites production in advanced ovarian carcinoma

Bispecific antibody HEA125 x OKT3 was shown to redirect T lymphocytes toward carcinoma cells and to induce tumor cell lysis in vitro. Preclinical studies have demonstrated that tumor-associated lymphocytes (TAL) derived from malignant ascites can be used as effector cells with a high efficacy and without prior stimulation. These data provided the rationale for a clinical trial to investigate whether bsAb HEA125 x OKT3 is also able to induce tumor cell lysis in vivo and can be used for local treatment of malignant ascites arising from ovarian carcinoma. Ten ovarian carcinoma patients presenting with malignant ascites resistant to chemotherapy were enrolled in the study. They received weekly intraperitoneal injections of 1 mg bsAb diluted in 500 ml NaCl solution to allow homogeneous antibody distribution within the peritoneal cavity. All patients responded clinically well to the therapy. Eight patients experienced a complete and 2 patients a partial reduction of ascites production. A decrease or stabilization of tumor marker CA125 was detected in the sera of 8 patients. Only WHO Grade I and II toxicity was observed including mild fever, chills and allergic eczema. Thus, intraperitoneal application of bsAb HEA125 x OKT3 appears to be an easy and cost effective palliative treatment for ovarian carcinoma with recurrent ascites that leads to a substantially increased quality of life for the patients. During therapy TNF-alpha concentrations raised markedly in the ascites fluid whereas VEGF and sFLT-1 ascites levels declined. This indicates that not only T cell-mediated tumor cell lysis but also changes in vascular permeability due to downregulation of VEGF and its receptors might be responsible for the beneficial therapeutic effect.

Tumor-targeted immune complex formation: effects on myeloid cell activation and tumor-directed immune cell migration

The effectiveness of cellular immunotherapy of solid tumors is often hampered by the lack of specific infiltration of immune effector cells into the tumor mass. Therefore, we studied the potential of tumor antigen-specific antibodies to elicit tumor-specific myeloid cell activation, to induce or enhance tumor infiltration by immune cells. To this end, we developed an in vitro model system using the human myeloid cell line MonoMac-6. Incubation of IFN-gamma-primed MonoMac-6 cells with serum-opsonized zymosan or EGP-2-directed, mouse IgG2a-opsonized, EGP-2-positive tumor cells resulted in the production of ROS and TNF-alpha and induced E-selectin and ICAM-1 expression on HUVECs. FcR-mediated MonoMac-6 cell activation was strictly dependent on the activation of MonoMac-6 cells with IFN-gamma. In addition, no myeloid cell activation was observed in the presence of human serum or using tumor antigen-specific mouse antibody subclasses other than IgG2a, suggesting the crucial involvement of CD64 (FcgammaR1) in the effects observed. However, serum-inhibited myeloid cell activation was completely restored employing a 2-step targeting approach in which tumor cell opsonization with mouse anti-EGP-2 antibodies was followed by incubation with human antimouse Ig antibodies. Moreover, using this 2-step approach, not only anti-EGP-2-directed mouse IgG2a but also mouse IgG1 antibodies effectively induced tumor-specific myeloid cell activation. In conclusion, we describe a method to induce efficient and tumor-specific activation of myeloid cells based on the sequential use of mouse tumor antigen-specific and human antimouse Ig antibodies. Targeted myeloid cell activation may provide a means to aid in the induction of a tumor-directed immune response and as such, the method described here could be of clinical significance.

Cancer immunotherapy: insights from transgenic animal models

A wide range of strategies in cancer immunotherapy has been developed in the last decade, some of which are currently being used in clinical settings. The development of these immunotherapeutical strategies has been facilitated by the generation of relevant transgenic animal models. Since the different strategies in experimental immunotherapy of cancer each aim to activate different immune system components, a variety of transgenic animals have been generated either expressing tumor associated, HLA, oncogenic or immune effector cell molecule proteins. This review aims to discuss the existing transgenic mouse models generated to study and develop cancer immunotherapy strategies and the variable results obtained. The potential of the various transgenic animal models regarding the development of anti-cancer immunotherapeutical strategies is evaluated.

Use of anti-CD3 x anti-HER2/neu bispecific antibody for redirecting cytotoxicity of activated T cells toward HER2/neu+ tumors

Relapse after adjuvant chemotherapy or high-dose chemotherapy with stem cell transplant for high-risk breast cancer remains high and new strategies that provide additional antitumor effects are needed. This report describes methods to generate highly effective HER2/neu-specific cytotoxic T cells by arming activated T cells with anti-CD3 x anti-HER2/neu bispecific antibody (BsAb). OKT3 and 9184 (anti-HER2) monoclonal antibodies (mAb) were conjugated and used to arm T cells that were subsequently tested in binding, cytotoxicity, and cytokine secretion assays. Armed T cells aggregated and specifically killed HER2/neu(+) breast cancer cells. Cytotoxicity emerged after 6 days of culture, was higher in armed T cells than unarmed T cells at all effector to target ratios (E/T) tested, and increased as the arming dose was increased. At an E/T of 20:1, the mean cytotoxicity of armed activated T cells (ATC) from 10 normal subjects increased by 59 +/- 11% (+/-SD) over that seen in unarmed ATC (p < 0.001) and the mean cytotoxicity of armed ATC from 6 cancer patients increased by 32 +/- 9% above that seen for unarmed ATC (p < 0.0004). After arming, the BsAb persisted on ATC up to 72 h and armed ATC continued to be cytotoxic up to 54 h. The amount of interferon-gamma (IFN-gamma), tumor necrosis factor-alpha (TNF-alpha), and granulocyte-macrophage colony-stimulating factor (GM-CSF) secreted was 1699, 922, and 3092 pg/ml/10(6) cells per 24 h, respectively, when armed T cells were exposed to a HER2/neu(+) breast carcinoma cell line. These studies show the feasibility and clinical adaptability of this approach for generating large numbers of anti-HER2-specific, cytotoxic T cells for clinical trials.

Characterization of BIS20x3, a bi-specific antibody activating and retargeting T-cells to CD20-positive B-cells

This paper describes a bi-specific antibody, which was called BIS20x3. It retargets CD3varepsilon-positive cells (T-cells) to CD20-positive cells and was obtained by hybrid-hybridoma fusion. BIS20x3 could be isolated readily from quadroma culture supernatant and retained all the signalling characteristics associated with both of its chains. Cross-linking of BIS20x3 on Ramos cells leads to DNA fragmentation percentages similar to those obtained after Rituximab-cross-linking. Cross-linking of BIS20x3 on T-cells using cross-linking F(ab')2-fragments induced T-cell activation. Indirect cross-linking of T-cell-bound BIS20x3 via Ramos cells hyper-activated the T-cells. Furthermore, it was demonstrated that BIS20x3 effectively re-targets T-cells to B-cells, leading to high B-cell cytotoxicity. The results presented in this paper show that BIS20x3 is fully functional in retargeting T-cells to B-cells and suggest that B-cell lymphomas may represent ideal targets for T-cell retargeting bi-specific antibodies, because the retargeted T-cell is maximally stimulated in the presence of B-cells. Additionally, since B-cells may up-regulate CD95/ Fas expression upon binding of CD20-directed antibodies, B-cells will become even more sensitive for T-cell mediated killing via CD95L/ Fas L, and therefore supports the intention to use T-cell retargeting bi-specific antibodies recognizing CD20 on B-cell malignancies as a treatment modality for these diseases.

A recombinant bispecific single-chain antibody, CD19 × CD3, induces rapid and high lymphoma-directed cytotoxicity by unstimulated T lymphocytes

Although bispecific antibodies directed against malignant lymphoma have been shown to be effective in vitro and in vivo, extended clinical trials so far have been hampered by the fact that conventional approaches to produce these antibodies suffer from low yields, ill-defined byproducts, or laborious purification procedures. To overcome this problem, we have generated a small, recombinant, lymphoma-directed, bispecific single-chain (bsc) antibody according to a novel technique recently described. The antibody consists of 2 different single-chain Fv fragments joined by a glycine-serine linker. One specificity is directed against the CD3 antigen of human T cells, and the other antigen-binding site engages the pan–B-cell marker CD19, uniformly expressed on the vast majority of B-cell malignancies. The construct was expressed in Chinese hamster ovary cells and purified by its C-terminal histioline tag. Specific binding to CD19 and CD3 was demonstrated by fluorescence-activated cell sorter analysis. By redirecting unstimulated primary human T cells derived from the peripheral blood against CD19-positive lymphoma cells, the bscCD19 × CD3 antibody showed significant cytotoxic activity at very low concentrations of 10 to 100 pg/mL and at effector to target cell ratios as low as 2:1. Moreover, strong lymphoma-directed cytotoxicity at low antibody concentrations was rapidly induced during 4 hours even in experiments without any T-cell prestimulation. Thus, this particular antibody proves to be much more efficacious than the bispecific antibodies described until now. Therefore, the described bscCD19 × CD3 molecule should be a suitable candidate to prove the therapeutic benefit of bispecific antibodies in the treatment of non-Hodgkin lymphoma.

The use of bispecific antibodies in tumor cell and tumor vasculature directed immunotherapy

To overcome dose limiting toxicities and to increase efficacy of immunotherapy of cancer, a number of strategies are under development for selectively redirecting effector cells/molecules towards tumor cells. Many of these strategies exploit the specificity of tumor associated antigen recognition by monoclonal antibodies. Using either hybridoma fusion, chemical derivatization or molecular biology technology, antibodies with dual specificity can be constructed. These so called biospecific antibodies (BsAbs) have been used to redirect the cytolytic activity of a variety of immune effector cells such as cytotoxic T lymphocytes, natural killer cells, neutrophils and monocytes/macrophages to tumor cells. Local administration of BsAbs, either alone or in combination with autologous effector cells, is highly effective in eradicating tumor cells. In contrast, systemic application of BsAb at present is only suitable for adjuvant treatment of minimal residual disease due to poor tumor cell accessibility. As an alternative, angiogenesis related determinants on tumor blood vessels can be exploited for the selective delivery of effector cells/molecules apart from being used to inhibit angiogenesis. Important advantages of this strategy is that the endothelial cell associated target epitope(s) are easy accessible. The dependence of tumor growth on the tumor's blood supply also renders tumor endothelial cells an attractive target for therapy. Although still in its infancy, attacking the tumor's blood supply for example by delivering coagulation factors or toxins, or by BsAb directed immunotherapies holds great promise for antineoplastic therapy.

Development and characterization of a bispecific single-chain antibody directed against T cells and ovarian carcinoma

Bispecific antibodies with specificity for tumor antigen and CD3 have been shown to redirect the cytotoxicity of T cells against relevant tumor. Our objective was to generate single-chain bispecific antibodies (bsSCA) that could retarget mouse cytotoxic T lymphocytes (CTL) to destroy human ovarian carcinoma in a xenogeneic setting. A bsSCA, 2C11 x B43.13, was constructed by genetic engineering and expressed in mammalian cells. Molecular characteristics, binding properties, and ability to retarget CTL were studied. Western blot analysis showed that the product is a 65-kDa protein. Purification of antibodies could be done by single-step affinity chromatography using protein L-agarose with an unoptimized yield of 200 microg/L. BsSCA 2C11 x B43.13 was capable of binding to mouse CD3 and human CA125 as detected by FACS analysis of EL4 and OVCAR Nu3H2 cells, respectively. It could also bridge activated splenic T cells and human ovarian carcinoma as demonstrated by a bridge FACS assay. Redirected mouse CTL could mediate human target cell lysis in a 20-h 51Cr release assay despite that they are xenogeneic. Prolonged incubation of redirected CTL and tumor targets resulted in a dramatic reduction in tumor cell number. CD28 co-stimulation enhanced redirected CTL function in both types of assays. BsSCA 2C11 x B43.13 thus can be used as a preclinical immunotherapeutic model for human ovarian cancer in a xenogeneic setting.

CD3 directed bispecific antibodies induce increased lymphocyte-endothelial cell interactions in vitro

Bispecific antibody (BsMAb) BIS-1 has been developed to redirect the cytolytic activity of cytotoxic T lymphocytes (CTL) to epithelial glycoprotein-2 (EGP-2) expressing tumour cells. Intravenous administration of BIS-1 F(ab')2 to carcinoma patients in a phase I/II clinical trial, caused immunomodulation as demonstrated by a rapid lymphopenia prior to a rise in plasma tumour necrosis factor-alpha and interferon-gamma levels. Yet, no lymphocyte accumulation in the tumour tissue and no anti-tumour effect could be observed. These data suggest a BsMAb-induced lymphocyte adhesion to blood vessel walls and/or generalized redistribution of the lymphocytes into tissues. In this study, we describe the effects of BIS-1 F(ab')2 binding to peripheral blood mononuclear cells (PBMC) on their capacity to interact with resting endothelial cells in vitro. Resting and pre-activated PBMC exhibited a significant increase in adhesive interaction with endothelial cells when preincubated with BIS-1 F(ab')2, followed by an increase in transendothelial migration (tem). Binding of BIS-1 F(ab')2 to PBMC affected the expression of a number of adhesion molecules involved in lymphocyte adhesion/migration. Furthermore, PBMC preincubated with BIS-1 F(ab')2 induced the expression of endothelial cell adhesion molecules E-selectin, VCAM-1 and ICAM-1 during adhesion/tem. These phenomena were related to the CD3 recognizing antibody fragment of the BsMAb and dependent on lymphocyte-endothelial cell contact. Possibly, in patients, the BIS-1 F(ab')2 infusion induced lymphopenia is a result of generalized activation of endothelial cells, leading to the formation of a temporary sink for lymphocytes. This process may distract the lymphocytes from homing to the tumour cells, and hence prevent the occurrence of BIS-1 F(ab')2 - CTL-mediated tumour cell lysis.

Anti-CD16/CD30 bispecific antibodies as possible treatment for refractory Hodgkin's disease

Fifteen patients with refractory Hodgkin's disease were treated in a phase I/II dose escalation trial with the NK-cell activating bispecific monoclonal antibody HRS-3/A9 which is directed against the Fcgamma-receptor III (CD16 antigen) and the Hodgkin's associated CD30 antigen, respectively. HRS-3/A9 was given four times every 3-4 days starting with 1 mg/m2. The treatment was well tolerated and the maximum tolerated dose was not reached at 64 mg/m2, the highest dose given due to limited amounts of HRS-3/A9 available. Mild to moderate side effects occured in six patients and consisted of fever, pain in involved lymph nodes, and a maculopapulous rash. Median counts of NK-cells and of all lymphocyte subsets were considerably decreased in the patients before therapy and showed no consistent changes under therapy. Eight patients developed human anti-mouse immunoglobulin antibodies, and five patients showed an allergic reaction after attempted retreatment. One complete and one partial remission (lasting 6 and 3 months, respectively), three minor responses (lasting 1 to 15 months), two disease stabilizations (for 2 and 17 months, respectively), and one mixed response were achieved. There was no clearcut dose-side effect or dose-response correlation. Our results encourage further clinical trials with this novel immunotherapeutic approach and emphasize the necessity to reduce the immunogenicity of the murine bispecific antibodies.

Tumor vasculature targeted therapies: getting the players organized

Based on their location and central role in solid tumor growth, tumor vascular endothelial cells may present an attractive target for the delivery of therapeutic drugs or cells. The potency of blocking the tumor blood supply in eradicating solid tumors was demonstrated recently in a mouse model of tumor vasculature targeting (Huang et al., Science 275: 547-550, 1997). For clinical application of such strategies, tumor endothelium specific target epitopes need to be identified. Recent studies on angiogenesis have identified angiogenesis-related molecules as potential target epitopes. Among these are vascular endothelial growth factor (VEGF)/VEGF-receptor complex, alpha(v) integrins, and Tie receptor tyrosine kinases. Besides blockade of their signalling cascades leading to inhibition of angiogenesis, these epitopes may also be instrumental in tumor vessel specific delivery of therapeutics. Data on the efficacy of therapeutic modalities aimed at these, mostly heterogeneously distributed tumor endothelial epitopes are scarce, and sophisticated experimentation is required to rationalize the development of new therapeutic strategies. Importantly, only detailed evaluations in cancer patients will provide the blueprint for the development of clinically effective tumor vascular targeted therapies.

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

Local but no systemic immunomodulation by intraperitoneal treatment of advanced ovarian cancer with autologous T lymphocytes re-targeted by a bi-specific monoclonal antibody

We have reported a 27% overall anti-tumor response using i.p. immunotherapy of advanced ovarian carcinoma with autologous, ex vivo expanded, T lymphocytes re-targeted with bi-specific monoclonal antibody OC/TR, combined with soluble OC/TR and low-dose recombinant interleukin-2 (IL-2). This treatment had no effect on extraperitoneal disease. Therefore we studied in 13 patients whether this immunotherapeutic protocol resulted only in local or also in systemic immunomodulation. The phenotype of the ex vivo expanded lymphocytes was mainly CD3+, 4-, 8+, 16-, 56-. Their OC/TR-re-targeted cytolytic activity against Igrov-1 ovarian-carcinoma cells was approximately as high in responders as in non-responders. Following most therapeutic cycles, the immunophenotype of lymphocytes recovered from the peritoneal fluid was similar to that of the infused T cells (i.e., mainly CD3+, 4-, 8+) and they were coated with OC/TR. However, cytolytic activity of the recovered lymphocytes against Igrov- 1 cells was low in direct assays, and only slightly increased after additional in vitro re-targeting with OC/TR. Systemically, the i.p. immunotherapy resulted in a transient lymphopenia lasting for about 7 days, low (i.e., 5 to 13 ng/ml) serum concentrations of free, functional OC/TR, and very weak coating of circulating T lymphocytes with OC/TR. These peripheral-blood T lymphocytes did not exert OC/TR-re-targeted cytolytic activity. Thus, locoregional OC/TR-re-targeted cellular immunotherapy resulted in substantial local immunomodulation and anti-tumor effects but virtually no systemic immunomodulation.

Treatment of Refractory Hodgkin's Disease With an Anti-CD16/CD30 Bispecific Antibody

Fifteen patients with refractory Hodgkin's disease were treated in a phase I/II trial with the natural killer (NK)-cell–activating bispecific monoclonal antibody HRS-3/A9, which is directed against the Fcγ-receptor III (CD16 antigen) and the Hodgkin's-associated CD30 antigen, respectively. Median counts of NK cells and of all lymphocyte subsets were considerably decreased in the patients before therapy. HRS-3/A9 was administered 4 times every 3 to 4 days, starting with 1 mg/m2. The treatment was well tolerated, and the maximum tolerated dose was not reached at 64 mg/m2, the highest dose administered because of the limited amounts of HRS-3/A9 available. Side effects were rare and consisted of fever, pain in involved lymph nodes, and a maculopapulous rash. A total of 9 patients developed human antimouse Ig antibodies, and 4 patients developed an allergic reaction after attempted retreatment. A total of 1 complete and 1 partial remission (lasting 16 and 3 months, respectively), 3 minor responses (1 to 11+ months), and 1 mixed response were achieved. There was no clear-cut dose-side effect or dose-response correlation. Our results encourage further clinical trials with this novel immunotherapeutic approach and emphasize the necessity to reduce the immunogenicity of the murine bispecific antibodies.

A quantitative reverse transcriptase polymerase chain reaction-based assay to detect carcinoma cells in peripheral blood

The presence of tumour cells in the circulation may predict disease recurrence and metastasis. To improve on existing methods of cytological or immunocytological detection, we have developed a sensitive and quantitative technique for the detection of carcinoma cells in blood, using the reverse transcriptase polymerase chain reaction (RT-PCR) identifying transcripts of the pancarcinoma-associated tumour marker EGP-2 (KSA or 17-1A antigen). The amount of EGP2 mRNA was quantified using an internal recombinant competitor RNA standard with known concentration and which is both reversely transcribed and co-amplified in the same reaction, allowing for a reliable assessment of the initial amount of EGP2 mRNA in the sample. Calibration studies, seeding blood with MCF-7 breast carcinoma cells, showed that the assay can detect ten tumour cells among 1.0 x 10(6) leucocytes. The PCR assay revealed that normal bone marrow expresses low levels of EGP2 mRNA, although immunocytochemistry with the anti-EGP2 MAb MOC31 could not identify any positively stained cell. Analyses using this RT-PCR assay may prove to have applications to the assessment of circulating tumour cells in clinical samples.

Generation of chimeric bispecific G250/anti-CD3 monoclonal antibody, a tool to combat renal cell carcinoma

The monoclonal antibody (MAb) G250 binds to a tumour-associated antigen, expressed in renal cell carcinoma (RCC), which has been demonstrated to be a suitable target for antibody-mediated immunotherapy. A bispecific antibody having both G250 and anti-CD3 specificity can cross-link G250 antigen-expressing RCC target cells with T cells and can mediate lysis of such targets. Therapy studies with murine antibodies are limited by immune responses to the antibodies injected (HAMA response), which can be decreased by using chimeric antibodies. We generated a chimeric bispecific G250/anti CD3 MAb by transfecting chimeric genes of heavy and light chains for both the G250 MAb and the anti-CD3 MAb into a myeloma cell line. Cytotoxicity assays revealed that the chimeric bispecific MAb was capable of mediating lysis of RCC cell lines by cloned human CD8+T cells or by IL-2-stimulated peripheral blood lymphocytes (PBLs). Lysis mediated by the MAb was specific for target cells that expressed the G250 antigen and was effective at concentrations as low as 0.01 microgram ml-1. The chimeric bispecific G250/anti-CD3 MAb produced may be an effective adjuvant to the currently used IL-2-based therapy of advanced renal cell arcinoma.

Pharmacokinetics, biodistribution and biological effects of intravenously administered bispecific monoclonal antibody OC/TR F(ab')2 in ovarian carcinoma patients

The bispecific monoclonal antibody (biMAb) OC/TR combines the anti-ovarian-cancer reactivity of the MOv18 monoclonal antibody (MAb) with the reactivity of an anti-CD3 MAb. Pre-clinical studies have indicated that this biMAb is able to redirect the cytolytic activity of T cells towards tumour cells, resulting in efficient tumour-cell lysis. To assess the clinical potential of systemic biMAb-based cancer therapy we initiated a study in ovarian-cancer patients. Five patients suspected of ovarian cancer received 123I-OC/TR F(ab')2 i.v. Unexpectedly, the first patient developed side effects (grade III-IV toxicity) starting 30 min after infusion (p.i.) of 1 mg of OC/TR F(ab')2. After approval of the Ethical Committee, the study was continued at lower dose levels (0.1 mg; 0.2 mg). However, at the 0.2-mg dose level similar side effects were observed. FACS analysis indicated that all peripheral T cells were coated with biMAb immediately following the infusion. The cytokines tumour necrosis factor-alpha, interferon-gamma and interleukin-2 showed maximum serum concentrations 2 h p.i. Tumour uptake ranged from 0.8 to 1.9% ID/kg, resulting in tumour/background ratios of 3 to 8. Our results suggest that at higher antibody dose levels OC/TR F(ab')2 causes T-cell activation with acute release of cytokines. Only low doses of biMAb can be administered safely. Despite the interaction with T cells, OC/TR F(ab')2 preferentially localizes in tumours following i.v. administration, thus offering therapeutic perspectives.

The role of apoptosis in bispecific antibody-mediated T-cell cytotoxicity

In this report we describe the role of apoptosis in the process of tumour cell killing by bispecific monoclonal antibody (BsMAb)-redirected cytolytic T cells. The BsMAb used, BIS-1, has dual specificity for the CD3 complex on T cells and the pancarcinoma-associated 38 kDa transmembrane antigen EGP-2. BIS-1 allows activated T cells to specifically recognise and kill EGP-2-positive but not EGP-2-negative target cells. An assay was developed to quantify apoptosis in cells by separation of 3H-thymidine-labelled low-molecular, i.e. fragmented, from high-molecular, i.e. non-fragmented DNA. The presence of low molecular weight DNA was measured both within the target cells and in the cell-free supernatant. After exposure to BIS-1-redirected, -activated T cells, apoptosis was observed in EGP-2-positive target cells but not in EGP-2-negative target cells. Also no DNA fragmentation proved to be induced in the activated effector cells during assay. The degree of EGP-2-positive target DNA fragmentation depended on the concentration of BsMAb, the E/T ratio and the incubation time. Using a low E/T ratio (1/1), DNA fragmentation in and 51Cr release from target cells showed similar characteristics and kinetics. At higher E/T ratio (20/1), the 51Cr release from the target cells increased to a greater extent than the percentage fragmented target cell DNA. Inhibitors of DNA fragmentation added to the cytotoxicity assay inhibited not only DNA fragmentation, but also the release of chromium-51 from the target cells, suggesting that apoptosis and cell lysis are closely related in BsMAb-mediated cell killing.

A single-chain bispecific Fv2 molecule produced in mammalian cells redirects lysis by activated CTL

Single-chain Fv (sFv) molecules consist of the two variable domains of an antibody (Ab) connected by a polypeptide spacer and contain the binding activities of their parental antibodies (Abs). In this paper we have attached the C-terminus of 2C11-sFv (anti-mouse CD3 epsilon-chain) to the N-terminus of OKT9-sFv (anti-human transferrin receptor [TfR]) through a 23 amino acid inter-sFv linker consisting primarily of CH1 region residues from 2C11, to form a single-chain bispecific Fv2 [bs(sFv)2] molecule. The bs(sFv)2 was expressed in COS-7 cells, and was secreted at the same rate as the two parental sFvs. The secreted protein had both anti-CD3 and anti-TfR binding activities. Essentially all of the secreted bs(sFv)2 molecules bound TfR and the binding affinity of the bs(sFv)2 was comparable to that of OKT9 sFv and Fab. Thus, the attachment of the inter-sFv linker to the N-terminus of OKT9-sFv did not impair its binding function. The bs(sFv)2 retained both binding specificities after long-term storage at 4 degrees C or overnight incubation at 37 degrees C. It redirected activated mouse CTL to specifically lyse human TfR+ target cells at low (ng/ml) concentrations and was much more active than a chemically cross-linked heteroconjugate prepared from the same parental mAbs. Because bs(sFv)2 molecules secreted by mammalian cells are homogeneous proteins containing two binding sites in a single polypeptide chain, they hold great promise as an easily obtainable, economic source of a bispecific molecule suitable for in vivo use.

The induction of cytotoxicity by a bispecific antibody against CEA positive cell line, in vitro

A mouse anti-human carcinoembryonic antigen (CEA) x anti-human CD3 bispecific antibody, AB5C10*UCHT1, was developed. This antibody-heteroconjugate was chemically prepared by cross-linking the AB5C10 monoclonal antibody reactive with human CEA with the monoclonal antibody, UCHT1, which binds to CD3 on human T-lymphocytes. The AB5C10*UCHT1 recognized both CEA expressed on the KATOIII cell line and CD3 expressed on T-lymphocytes, as determined using flowcytometry. Next, AB5C10*UCHT1-mediated cytolysis was analyzed by 51Cr-release assay. When 51Cr-labeled target KATOIII cells were incubated for 6 h with effector cells that had been pretreated with AB5C10*UCHT1 for 60 min at 4 degrees C, the percentage specific lysis was significantly increased compared to that of untreated effector cells. Using peripheral blood mononuclear cells (PBMC) and lymphokine-activated killer (LAK) cells pretreated with AB5C10*UCHT1 for effector cells, the percentage specific lysis was determined to be 16.3% and 57.4% at effector: target (E:T) ratios of 100:1 and 12.5:1, respectively. On the other hand, the percentage specific lysis of untreated PBMC and LAK cells determined to be 3.0% and 35.8% at E:T ratios of 100:1 and 12.5:1, respectively. The minimum effective dose of AB5C10*UCHT1 required for antibody-mediated cytotoxicity was 0.1 mu g/ml. The results of this study suggest that AB5C10*UCHT1 could be useful for augmenting the cytotoxicity of CD3-positive T-cells against CEA-positive target cells in vitro.

Bifunctional antibody retargeting in vivo-activated T lymphocytes: simplifying clinical application

For antitumor x anti-CD3 bifunctional antibody (BFA) therapy to be clinically relevant in solid tumors, activated lymphocytes must be present within tumors. Toward that end, three uniquely different in vivo activation approaches were investigated in a p97 human antigen expressing syngeneic murine melanoma model. beta-Glucan (200 micrograms), staphylococcal enterotoxin B (SEB) (50 micrograms), and F(ab')2 BFA (10 micrograms) were tested for their ability to activate lymphocytes, neutralize pulmonary metastases, and treat established tumors. Systemic activation, measured as the ability of splenocytes to lyse tumor cells in vitro in the presence of BFA, was enhanced by the in vivo administration of SEB but not by beta-glucan or F(ab')2 BFA. Despite lacking a systemic effect, F(ab')2 BFA increased both direct and BFA-mediated cytotoxicity in fresh tumor infiltrating lymphocytes. beta-Glucan did not increase systemic or intratumor T cell activation. However, it significantly enhanced the ability of splenocytes to lyse NK-sensitive YAC-1 cells. When tested in a pulmonary metastases model, all three forms of immune modulation combined with F(ab')2 BFA significantly reduced the number of metastases. BFA were more effective at tumor neutralization when combined with SEB compared with adoptively transferred, in vitro-activated splenocytes. These studies demonstrate that immune modulators when combined with F(ab')2 BFA can provide effective antitumor therapy. Several clinical obstacles may be overcome by the application of these reagents.

Performance of CD3xCD19 bispecific monoclonal antibodies in B cell malignancy

Bispecific monoclonal antibodies, with a dual specificity for tumor associated antigens on target cells and for surface markers on immune effector cells, have been shown (in vitro) to be effective in directing and triggering effector cells to kill target cells resulting in target cell lysis. Bispecific monoclonal antibodies (BsAb) against the CD3 antigen on T cells and the CD19 antigen on B cell were developed. Data obtained by in vitro experiments might indicate that clinical responses in BsAb immunotherapy, will only be obtained in patients with minimal tumor load, and may need additional T cell stimulation via cytokines such as IL-2. Although these experiments have shown us their limitations, they also include the promise of BsAb-directed immunotherapy in B cell malignancy as further demonstrated during a Phase I trail, showing little toxicity. Clearly, much remains to be done before this BsAb is routinely used for therapy, but, the results presented show that the CD3xCD19 BsAb has a potential as a therapeutic agent in B cell malignancy. This report describes the experiments performed to test a new immunotherapeutic approach for the treatment of B cell malignancy. Bispecific antibodies are described that can target cytotoxic T cells to tumor cells and elicit a cytolytic action towards these cancer cells.

Bispecific monoclonal antibodies for intravenous treatment of carcinoma patients: immunobiologic aspects

Immunobiologic parameters measured during a phase I trial of intravenously (i.v.) administered bispecific monoclonal antibodies (BsmAb) in renal cell carcinoma (RCC) patients are described. The BsmAb used, BIS-1, is reactive with a pancarcinoma-associated 38 kDa transmembrane glycoprotein, EGP-2, as well with the CD3 complex. Patients received during a 2 h i.v. infusion F(ab')2 fragments of BIS-1 at doses of 1, 3, or 5 micrograms/kg body weight during concomitantly applied subcutaneous (s.c.) IL-2 treatment. Acute but transient BIS-1 F(ab')2-related toxicity was observed at the 3 and 5 micrograms/kg dose level, and the maximum tolerated dose (MTD) was set at 5 micrograms/kg. A dose-dependent binding of BIS-1 F(ab')2 to circulating T lymphocytes was found. The in vivo occupancy of CD3 molecules on T lymphocytes was highest at teh end of the infusion period and then rapidly decreased, as shown by flow cytometry. A much slower decrease of BIS-1 F(ab')2 binding was observed in vitro, suggesting migration of BIS-1 F(ab')2-loaded T lymphocytes from the circulation. A strong but transitory leukopenia was observed, in which LFA-1 alpha bright, CD3/CD8 double positive T cells left the circulation preferentially. This phenomenon was most likely induced by elevated TNF-alpha and IFN-gamma plasma levels, which were at a maximum shortly after the end of the infusion. Isolated peripheral blood mononuclear cells obtained from patients directly after treatment with BIS-1 F(ab')2 at the 3 and 5 micrograms/kg dose level showed increased EGP-2-directed antitumor activity.

Toward the production of bispecific antibody fragments for clinical applications

The clinical potential of bispecific antibodies (BsAb) has been hindered by the difficulty of obtaining clinical grade material, together with the immunogenicity of rodent-derived BsAb in patients. The supply issue is being directly addressed by recombinant methods for BsAb fragment production reviewed here. The immunogenicity issue will likely be overcome by the use of humanized or human antibodies. Currently, three technologies appear suitable for the production of BsAb fragments for clinical applications: BsF(ab')2 assembled from Fab' fragments expressed in Escherichia coli, BsF(ab')2 assembled using leucine zippers, and diabodies.

Reduction of EGP-2-positive pulmonary metastases by bispecific-antibody-redirected T cells in an immunocompetent rat model

Effectiveness of bispecific-monoclonal-antibody (BsMAb)-mediated cellular anti-tumour activity was evaluated in vitro and in vivo in relation to the additional need for T-cell activation in a new immunocompetent rat tumour model. L37 tumour cells, derived from a squamous-cell carcinoma of the lung of Wag/Rij rats, were transfected with the cDNA coding for the human 38-kDa transmembrane pan-carcinoma-associated antigen EGP-2. Intravenous inoculation of EGP-2-positive L37 cells resulted in a rapid outgrowth of EGP-2-positive tumour nodules in the lungs. A BsMAb BIS-19, recognizing EGP-2 on the transfected tumour cells and the T-cell receptor of the rat, was made and allowed specific lysis of EGP-2-transfected L37 tumour cells by activated rat T lymphocytes in vitro. In vivo T-cell activation, assessed by up-regulation of IL-2-receptor expression, could be induced by daily injection of rat rIL-2. Intravenous treatment of tumour-bearing EGP-2-positive L37 tumour with BIS-19 together with rat rIL-2 resulted in almost complete disappearance of established tumour. In contrast, animals treated with BIS-19 alone, IL-2 alone or a combination of anti-EGP-2, anti-TcR and IL-2 showed much less or no tumour reduction. These results show effectiveness of systemic treatment with BsMAbs to induce anti-tumour activity in established tumours. Immune activation prior to or during treatment with BsMAbs, as achieved with IL-2, appears to be a prerequisite for successful treatment.

Tumor therapy by immune recruitment with bispecific antibodies

Many strategies for experimental immunotherapy of cancers aim at inducing and expanding tumor-specific cytotoxic T-lymphocytes. One of the most promising approaches uses bispecific monoclonal antibodies (Bi-MAbs) which are able to accumulate and activate human effector cells at the tumor site. Human resting peripheral NK- or T cells targeted by appropriate Bi-MAbs to tumor cells expressing a tumor-associated antigen display multiple signs of activation including proliferation, cytokine secretion, upregulation of cytotoxic peptides and enzymes and induce an efficient tumor cell lysis in vivo. Moreover, tumor-bearing SCID which were treated by effector cell-triggering Bi-MAbs and human peripheral blood lymphocytes had complete regressions of established tumors and most or all animals were cured by human NK-cell or T-cell cytotoxicity, respectively. Local tumor site-specific activation of T-cells was demonstrated, and enhanced granzyme and perforin expression together with the results of inhibition experiments suggest both mechanisms as the major contributors to the cytolytic machinery of Bi-MAb-mediated T-cell cytotoxicity in vivo. The encouraging results of this approach, which is able to cure animals with even advanced disseminated tumors, together with the local site-specific effector cell activation, which suggests minimal side effects, warrant the clinical evaluation of this Bi-MAb approach. As lymphocytes from tumor patients can be adequately activated by the respective Bi-MAbs, the clinical application of Bi-MAbs promises to become a safe, efficient and simple approach which should be readily applicable to the treatment of human malignancies that cannot be cured by standard regimens.

Bispecific monoclonal antibody therapy of B-cell malignancy

Bispecific monoclonal antibodies (bsAbs) that recognize CD3 with one arm and a tumor associated antigen with the other arm can retarget T-cells toward tumor cells in an MHC independent manner, thereby combining the specificity of monoclonal antibodies with the power of the cellular immune system. B-cell malignancies are particularly attractive as targets for anti-CD3-based bsAb therapy because of their sensitivity to other forms of antibody therapy, and the extent to which B-cells and T-cells communicate at the molecular level. BsAbs that recognize CD3 and a number of antigens on malignant B-cells have been shown in vitro to be capable of retargeting T-cells. In animal models of B-cell malignancy, bsAb can eliminate tumor loads that are resistant to unmodified monoclonal antibody therapy. Ongoing early clinical trials in advanced B-cell lymphoma indicate CD3-based bsAbs have significant biologic effects, and suggest they have anti-tumor activity as well. A number of significant questions relating to bsAb therapy of B-cell malignancies remain. It is unclear what role both endogenously produced and exogenously administered cytokines are likely to play. Further exploration of whether bsAb can induce T-cells to target to tumor will also be required before the true promise of this novel form of immunotherapy can be determined.

Purification of bispecific F(ab')2 from murine trinoma OC/TR with specificity for CD3 and ovarian cancer

A study was made of the stability of the murine bispecific trinoma OC/TR with respect to secretion of both types of parental heavy and light chains. OC/TR is a cell line producing bispecific antibody that reacts with the CD3 antigen on T cells and the folate-binding receptor--frequently found to be overexpressed on ovarian carcinoma cells. Of the 10 different IgG combinations theoretically possible with 2 heavy and 2 light chains, 6 combinations were secreted. Subclones varied considerably in relative production of the two parental heavy and light chains. A detailed analysis was made of the binding characteristics and retargeting activity of each of the IgGs produced. From a clone producing a relatively high quantity of bispecific IgG, a large-scale production was initiated. The purification of clinical grade bispecific F(ab')2 from harvest fluids is described. The yield from this purification process was found to be comparable to the yield of bispecific F(ab')2 after chemical cross-linking of two different Fab'.

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.

SCLC-cluster-2 antibodies detect the pancarcinoma/epithelial glycoprotein EGP-2

Analysis of the antibodies submitted to the 3 International Workshops on Small Cell Lung Cancer Antigens has resulted in the identification of 15 clusters of antibody reactivity. One of these clusters, named SCLC cluster 2, is characterized by reactivity against an epithelium-associated 38 kDa membrane glycoprotein. SCLC cluster 2, and a number of other antibodies with reportedly similar reactivities, were shown to recognize a protein encoded by the GA733-2 gene, whereas the newly defined SCLC cluster 13 antibodies react with the GA733-1 gene product. We propose to call the antigen detected by SCLC-cluster-2 antibodies "epithelial glycoprotein 2" (EGP-2), and the epithelium-associated glycoprotein recognized by antibodies clustered in SCLC cluster 13 (see elsewhere in this volume) "epithelial glycoprotein 1" (EGP-1). A short overview of the characteristics of both proteins and the applications of anti-EGP-2 antibodies is presented.