Chimeric B72.3 mouse/human (IgG1) antibody directs the lysis of tumor cells by lymphokine-activated killer cells

Transient expression of a tumor-specific single-chain fragment and a chimeric antibody in tobacco leaves

To evaluate the expression of different forms of a tumor-specific antibody in plants, we adapted a recently described Agrobacterium-mediated transient expression system. A recombinant single-chain Fv antibody (scFvT84.66) and a full-size mouse/human chimeric antibody (cT84.66) derived from the parental murine mAb T84. 66 specific for the human carcinoembryonic antigen were engineered into a plant expression vector. Chimeric T84.66 heavy and light chain genes were constructed by exchanging the mouse light and heavy chain constant domain sequences with their human counterparts and cloned into two independent plant expression vectors. In vivo assembly of full-size cT84.66 was achieved by simultaneous expression of the light and heavy chains after vacuum infiltration of tobacco leaves with two populations of recombinant Agrobacterium. Upscaling the transient system permitted purification of functional recombinant antibodies from tobacco leaf extracts within a week. His6-tagged scFvT84.66 was purified by immobilized metal affinity chromatography and cT84.66 by protein A affinity chromatography. Sufficient amounts of recombinant antibodies were recovered for detailed characterization by SDS/PAGE, Western blotting, and ELISA.

Macrophage colony-stimulating factor enhancement of antibody-dependent cellular cytotoxicity against human colon carcinoma cells

Antibody-dependent cellular cytotoxicity (ADCC) has been suggested to be an important defense mechanism against tumors. The effects of recombinant human macrophage colony-stimulating factor (rhM-CSF) on ADCC activity of human monocytes were investigated. Human peripheral monocytes were pre-incubated for 72 h with rhM-CSF at various concentrations (50, 100, 200, 400 U/ml) and then used as effector cells in a 24-h 111-Indium release assay. Human carcinoma cell lines LS-174T, CBS, and KLE were used as targets to react with anti-carcinoma monoclonal antibodies (mAbs: murine D612, murine CC49, and chimeric CC49). A significant increase in ADCC activity was observed after monocytes were incubated in 100-400 U/ml of human rhM-CSF. Variation in ADCC activity of monocytes among donors was observed. The enhancement of ADCC activity was blocked by the addition of a neutralizing antibody to rhM-CSF. Less D612 mAb was required for the rhM-CSF-treated monocytes to mediate an equivalent level of ADCC activity as compared to the untreated monocytes. Because of the low levels of rhM-CSF required in these studies to enhance ADCC, treatment of monocytes alone with comparable levels of rhM-CSF did not enhance antibody-independent cytotoxicity. Moreover, it is demonstrated here that recombinant human interleukin-4 (rhIL-4) and rhM-CSF can have a synergistic effect of monocyte-mediated ADCC on human tumor cells. These results thus indicate that rhM-CSF augments ADCC of human peripheral blood monocytes using mAbs to human carcinomas, suggesting a potential role for rhM-CSF in cancer immunotherapy.

Human monoclonal antibody SK1-mediated cytotoxicity against colon cancer cells

PURPOSE

Human monoclonal antibody (HuMAb) SK1, a human monoclonal IgM, has previously been shown to react selectively with a wide range of human carcinomas. In this study, the complement-dependent cytotoxicity (CDC) mediated by the HuMAb SK1 was investigated.

METHODS

The presence of AgSK1 on the two studied cell lines, HT29 and PANC-1, was evaluated by the immunocytochemical staining. The intracellular and surface locations of the targeting antigen of HuMAb SK1 were further characterized by the study of flow cytometry. The specific lysis of target cells by the HuMAb SK1 in the CDC assay was studied.

RESULTS

In the presence of human complement, the HuMAb SK1 was shown to be effective in the lysis of cultured human gastrointestinal cancer cells as well as the fresh colon cancer cells derived from the patient's specimens. In addition, our data suggested that HuMAb SK1 activated the mouse complement in a similar magnitude.

CONCLUSIONS

We concluded that HuMAb SK1 showed some promise for future clinical trials. The in vitro CDC effect of HuMAb SK1 with mouse complement suggested that the antitumor effect of HuMAb SK1 might be successfully studied in the nude mouse model bearing xenografts of human colon cancer as a part of the preclinical evaluation.

Secretion of a single-gene-encoded immunoglobulin from myeloma cells

We describe construction of a single gene encoding a single-chain immunoglobulin-like molecule. This single-gene approach circumvents inefficiencies inherent in delivering two genes into a mammalian cell and in the assembly of a functional immunoglobulin molecule. It would also facilitate ex vivo transfection of cells for gene-therapy protocols. SP2/0 murine myeloma cells transfected with the single gene SG delta CLCH1 expressed a single-chain protein, SC delta CLCH1, comprising approximately 60 kDa of the anti-carcinoma monoclonal antibody (mAb) CC49. The single-chain protein consisted of the heavy- and light-chain variable (VH and VL) domains of the mAb covalently joined through a short linker peptide, while the carboxyl end of the VL domain was linked to the amino terminus of the human gamma 1 Fc region through the hinge region. The single-chain protein assembled into a dimeric molecule, termed SCA delta CLCH1, of approximately 120 kDa and was secreted into the tissue culture fluid. SDS/PAGE analysis of the secreted immunoglobulin purified by protein G affinity chromatography confirmed the size of the molecule. The native mAb CC49 and SCA delta CLCH1 of CC49 showed similar binding to the tumor-associated glycoprotein TAG-72, and the chimeric mAb CC49 and SCA delta CLCH1 showed similar cytotoxic activity. This single-gene construct approach provides a way of generating an immunoglobulin-like molecule which retains the specificity, binding properties, and cytolytic activity of the chimeric mAb CC49. The immunoglobulin-like molecule SCA delta CLCH1 is potentially a therapeutic and diagnostic reagent against a range of human carcinomas.

Construction and purification of domain-deleted immunoglobulin variants of the recombinant/chimeric B72.3 (y1) monoclonal antibody

Chimeric antibodies have been produced against a pancarcinomic tumor associated antigen, TAG-72, by fusing the genes for the variable region of mouse MAb B72.3 to the genes for the constant region of human IgG. In our efforts to optimize the pharmacokinetics of plasma clearance and the efficiency of tumor localization and penetrance of cB72.3, we have now developed truncated versions of immunoglobulin heavy chains. The domain-deleted antibodies are produced by transfecting cells that produce chimeric kappa chains with expression vectors that encode chimeric heavy chains lacking the sequences that encode the CH2 domain, CH3 domain, or both. Despite the absence of these domains, the transfectomas secrete H2L2 tetramers with appropriate antigenic specificity. All the domain-deleted immunoglobulins can be purified by chromatography on Protein G Sepharose which binds to a site on the Fab region that is retained in the domain-deleted antibodies. The CH2CH3 domain-deleted immunoglobulin produced in cell culture is analogous in size to enzymatically produced F(ab')2.

A single amino acid substitution abolishes the heterogeneity of chimeric mouse/human (IgG4) antibody

Human immunoglobulin G4 (IgG4) exists in two molecular forms due to the heterogeneity of the inter-heavy chain disulphide bridges in the hinge region in a proportion of secreted human IgG4. This heterogeneity is only revealed under denaturing, non-reducing conditions in which an HL "half antibody" is detected, a phenomenon not seen in other human IgG isotypes. In native conditions noncovalent interactions hold the antibody together as the H2L2 tetramer. Analysis of the hinge sequences of human IgG heavy chains suggested that the presence of serine at residue 241 might be the cause of this heterogeneity. We therefore changed the serine at 241 to proline (found at that position in IgG1 and IgG2) in a mouse/human chimeric heavy chain. This single residue substitution leads to the production of a homogeneous antibody. Further, the variant IgG4 has significantly extended serum half-life and shows an improved tissue distribution compared to the original chimeric IgG4.

Engineering antibodies for therapy

Success in the generation of an antibody-based therapeutic requires careful consideration of the binding site, to achieve specificity and high affinity; of the effector, to produce the desired therapeutic effect; of the means of attachment of the effector to the binding site; production of the end product; and the response made by the patient to the administered compound. Each of these areas is receiving attention by antibody-engineering techniques. The number of potentially useful monoclonal antibodies developed over the last 10 years, and currently in clinical trials or preregistration, is now being increased by these engineered newcomers. It will be interesting to see over the next few years how many of these antibodies, and of which kind, emerge as products.

Immunotherapy of colorectal cancer

Specific and nonspecific stimulation of the host immune system to reject cancer is an attractive concept that is just beginning to mature. Results with crude extracts and nonspecific immune stimulation have been variable. However, the recent observations of improved survival after administration of levamisole plus 5-fluorouracil in the adjuvant setting have made an impact on the treatment of colorectal cancer. Animal studies consistently show that immune therapies are most effective for disease that is not advanced. Thus, the small benefit seen with levamisole, a low toxicity immunomodulator, suggests that much more impressive results can be anticipated with more potent and specific agents. Postsurgical autologous tumor cell vaccine has been effective in some prospective randomized trials; in others, no benefit was found. The identification and purification of allogeneic tumor-associated antigens has lead to enhanced antigen-specific host cell-mediated immunity; this may result in more consistent antitumor effects. The current development of chemically defined immune adjuvants of low toxicity allows tumor-specific immune stimulation to be tested in high-risk apparently healthy patients after resection of colorectal cancer (Stages II and III). The influx of information regarding immune cell populations, cell-surface markers, and cytokines has fostered extensive exploration of lymphocyte stimulation, in vitro cell growth and expansion, and in vivo evaluation in patients with advanced cancer. Modest tumor response rates have been documented with adoptive transfer of lymphokine-activated killer cells and interleukin-2. Improved results are anticipated with the more potent tumor-infiltrating lymphocytes and specific in vitro sensitization of draining lymph node cells to autologous and allogeneic tumor antigens. Murine monoclonal antibodies specific for cell-surface markers, such as carcinoembryonic antigen, have been tested for their value in the diagnosis and therapy of colorectal cancer. A small response rate has been seen with single and multiple injections of C017-1A, a monoclonal antibody specific for colonic and pancreatic cancer. The development of antiidiotypic antibodies in these patients may have been important in those that responded to this type of therapy. However, laboratory evidence suggests that monoclonal antibody conjugated to a cytotoxic agent (i.e., radionuclide, drug, or toxin) should be much more effective. Radioimmunotherapy trials in the nude mouse model bearing human colon cancer xenografts showed good tumor incorporation of the radionuclide (yttrium 90 or iodine 131), inhibition of tumor growth, and long-term survival.(ABSTRACT TRUNCATED AT 400 WORDS)