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

Sequential affinity purification of peroxidase tagged bispecific anti-SARS-CoV antibodies on phenylboronic acid agarose

Hybrid hybridomas (quadromas) are derived by fusing at least two hybridomas, each producing a different antibody of predefined specificity. The resulting cell secretes not only the immunoglobulins of both parents but also hybrid molecules manifesting the binding characteristics of the individual fusion partners. Purification of the desired bispecific immunoprobe with high specific activity from a mixture of bispecific and monospecific monoclonal antibodies requires special strategies. Using a dual, sequential affinity chromatography (Protein-G chromatography followed by m-aminophenyleboronic acid agarose column), we have purified bispecific monoclonal antibodies (BsMAb) as a preformed HRPO (Horseradish Peroxidase) complex (BsMAb-HRPO). The quadroma culture supernatant was initially processed on a Protein-G column to isolate all the species of immunoglobulins. This pre-enriched fraction was subsequently passed through the aminophenyleboronic acid column super saturated with HRPO. The column matrix has the ability to bind to proteins such as HRPO with vicinal diols. The enzyme loaded column captures the desired bispecific anti-SARS-CoVxanti-HRPO species with the elimination of the monospecific anti-SARS-CoV MAb to result in a high specific activity diagnostic probe. The presence of anti-HRPO MAb is an acceptable impurity as it will not bind to the target SARS-CoV NP antigen and will get washed out during the ELISA procedure.

Affinity chromatography and co-chromatography of bispecific monoclonal antibody immunoconjugates

Bispecific monoclonal antibodies (bsMAb) are unique macromolecules functioning as cross-linkers with two different predetermined binding specificities. A wide range of potential applications employing these probes can be envisioned in immunodiagnostics and immunotherapy. One of the major limitations for the use of bsMAbs produced by hybrid-hybridomas is the production of parental monospecific antibodies along with bsMAbs. Hence, the purification of desired bsMAb free from both parental mAbs and other possible promiscuous combinations is essential. Purification of antibodies is the single greatest obstacle in obtaining an immunoprobe with high specific activity. This review describes the affinity purification and affinity co-purification techniques for the separation of bsMAb as a pre-formed immune complex or as a pure species. The use of immobilized ligands is the basis of affinity chromatography. Affinity chromatography can be classified into three different categories depending on the properties of the immobilized ligand. The ligand-specific affinity chromatography is based on the extremely specific immobilized ligand, directed towards the protein or antibody of interest. Using a dual, sequential affinity chromatography, bsMAb can be purified from a mixture of bispecific and monospecific monoclonal antibodies with a ligand specific for each antibody. Thiophilic adsorption is a group-specific affinity method that can be successfully used to separate monospecific forms from bispecific species by salt gradient elution. Affinity co-chromatography offers a convenient one-step method for purification of bulk amounts of immunoconjugates for diagnostic applications by exploiting several dye-ligands known to bind certain enzymes. The same method could be potentially used for quality control and quality assurance purposes in industrial biotechnology.

Bispecific antibody-mediated lysis of primary cultures of ovarian carcinoma cells using multiple target antigens

We have shown previously that a bispecific antibody (BsAb) directed against both germ-cell alkaline phosphatase (GCAP) and the CD3 complex on mouse T cells could effectively eliminate GCAP-positive tumor cells in vivo using an immunocompetent mouse model. However, some GCAP-negative tumor cells were still able to grow, suggesting that BsAb therapy, when used in a clinical setting, could benefit from targeting several tumor markers to prevent outgrowth of tumor cells lacking a targeted marker. To test this hypothesis, we developed an in vitro model based on primary human ovarian carcinoma (OC) cultures and BsAbs directed against human T cells and several tumor markers [placental alkaline phosphatase (PLAP), GCAP, folate-binding protein (FBP) and CA19.9]. OC cells, isolated from primary tumors, were co-cultured with human peripheral blood mononuclear cells in the presence or absence of various concentrations of BsAbs against PLAP/GCAP, FBP and CA19.9 administered separately or in combination. Results derived from 18 primary OC samples showed that the combination treatment was better than or equally effective as the best single BsAB treatment in 60% of cases. Sometimes targeting FBP, PLAP/GCAP or CA19.9 alone was superior to targeting all simultaneously. Combining each BsAb with a low dose of IL-2 was always beneficial. These results indicate that before using a specific BsAb in the clinic, it is important to determine the optimal BsAb for each patient using this in vitro assay on cells from the removed tumor mass.

Level of anti-mouse-antibody response induced by bi-specific monoclonal antibody OC/TR in ovarian-carcinoma patients is associated with longer survival

More than 60% of cancer patients injected with intact murine monoclonal antibody (MAb) develop a humoral response against the antigen even after a single dose. Analysis of a series of 35 ovarian-cancer patients entered in phase-I and -II clinical studies of T-cells retargeted with the bi-specific F(ab')2 OC/TR revealed: (i) a detectable human anti-mouse antibody (HAMA) response in 31/35 (88%) patients, with high HAMA levels (> or = 150 ng/ml) in 18/31 (58%) cases by the end of the treatment; (ii) no correlation between HAMA levels and the form of delivery of the mAb (OC/TR bound to T cells or bound plus soluble), time schedule or cumulative dose; (iii) an association between high HAMA levels and favorable clinical parameters and response to immunotherapy; and (iv) a significantly longer median survival probability in patients with high HAMA levels than in patients with lower HAMA levels, even when the sub-group of non-responder patients was considered. Evaluation of the anti-idiotypic response in HAMA-positive sera indicated that 11/17 sera showed high-titer (>6000) binding of OC/TR, as evaluated by a specific radioimmunoassay, and 15/18 and 16/16 sera specifically inhibited the binding of the MOv18 and anti-CD3 parental MAbs to ovarian-carcinoma cells and T lymphocytes respectively. Of 7 patients evaluated for duration of the HAMA response, 5 showed stable or even increased HAMA levels. The long-lasting HAMA response maintained an anti-idiotypic component, directed mainly against the alphaCD3 idiotype of bi-MAb OC/TR in 2 out of 3 cases tested.

Efficient bispecific monoclonal antibody purification using gradient thiophilic affinity chromatography

Bispecific monoclonal antibodies (bsMAbs), due their unique design, have a wide range of potential applications in immunodiagnostics and immunotherapy. One of the major limitations for the use of bsMAbs produced by hybrid-hybridomas is the concomitant production of parental monospecific antibodies. The relative amount of bsMAb secreted may vary between different hybrid-hybridomas. Hence, the purification of the desired bispecific molecule from other forms is crucial. Current purification methods include anion-exchange, HPLC on different matrices, and dual affinity methods. Most of those methods include multiple steps and have limitations on the purity or yield of the desired species. We report here a simple single-step purification method, using inexpensive thiophilic chromatography. This new method can potentially be scaled up, for industrial proposes. Finally, based on the amino acid sequences and assembly of the two heavy chains we attempt to explain the possible mechanism by which thiophilic chromatography was able to resolve the bsMAbs from the monospecific species.

Single-step purification of bispecific monoclonal antibodies for immunotherapeutic use by hydrophobic interaction chromatography

A method for large scale production and single-step purification of bispecific antibodies is described. Hybrid-hybridomas were grown in hollow-fibre bioreactors with an average yield of 8 to 12 g of immunoglobulin per month. Bispecific antibodies were purified from the bioreactor supernatant by hydrophobic interaction chromatography which resolves bispecific antibodies, monospecific immunoglobulins, and culture medium supplements in one single chromatographic step. Proteins were analyzed by ELISA, SDS-PAGE, isoelectric focussing, indirect fluorescence staining, CTL-stimulation and T-cell proliferation assays. Finally, antibody preparations were checked for the presence of endotoxin and mouse DNA. Our results suggest that functional bispecific antibodies for use in therapeutic applications can be batch purified from bioreactor harvest by hydrophobic interaction chromatography in a single step. Compared to other methods such as affinity chromatography (protein A/G), ion-exchange or hydroxyapatite chromatography, our protocol offers a substantial reduction in labor time, cost, protein loss, and risk of contamination.

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.

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.

Bispecific antibody targeted T cell therapy of ovarian cancer: clinical results and future directions

The high frequency of relapse after induction chemotherapy in advanced ovarian carcinoma patients calls for new therapeutic modalities. Retargeted T cell-mediated lysis can be achieved using the bispecific antibody (BsmAb) OCTR, directed to CD3 on T cells and to the folate receptor on ovarian carcinoma cells. Twenty-eight patients with limited intraperitoneal disease after first-line therapy entered a phase II study. They received two i.p. 5 day cycles of activated PBMC retargeted with OCTR. Despite unfavorable tumor characteristics, 7 of 26 patients (27%) showed complete or partial intraperitoneal responses with strict surgicopathologic evaluation. In most cases, the disease relapsed outside the peritoneal cavity, and in 1 case complete intraperitoneal response was accompanied by progression in retroperitoneal lymph nodes. The morbidity was mild to moderate and transient. Combination of i.v. and i.p. administration of OCTR-retargeted lymphocytes will possibly lead to extraperitoneal cure. Ongoing clinical studies indicate that the i.v. infusion of up to 8 x 10(8) OCTR-retargeted T lymphocytes does not induce a higher toxicity than the i.p. treatment. To avoid PBMC preactivation, new approaches for delivering accessory signals are under investigation. Preliminary results indicate that nonactivated PBMC retargeted by OCTR in the presence of an anti-CD28 monoclonal antibody (mAb) are able to significantly inhibit tumor growth.