Chimeric CLL-1 Antibody Fusion Proteins Containing Granulocyte-Macrophage Colony-Stimulating Factor or Interleukin-2 With Specificity for B-Cell Malignancies Exhibit Enhanced Effector Functions While Retaining Tumor Targeting Properties

Fusion proteins development strategies and their role as cancer therapeutic agents

Cancer continues to be leading cause of morbidity and mortality despite decades of research and advancement in chemotherapy. Most tumors can be reduced via standard oncology treatments, such as chemotherapy, radiotherapy, and surgical resection, and they frequently recur. Significant progress has been made since targeted cancer therapy inception in creation of medications that exhibit improved tumor-selective action. Particularly in preclinical and clinical investigations, fusion proteins have shown strong activity and improved treatment outcomes for a number of human cancers. Synergistically combining many proteins into one complex allows the creation of synthetic fusion proteins with enhanced characteristics or new capabilities. Signal transduction pathways are important for onset, development, and spread of cancer. As result, signaling molecules are desirable targets for cancer therapies, and significant effort has been made into developing fusion proteins that would act as inhibitors of these pathways. A wide range of biotechnological and medicinal applications are made possible by fusion of protein domains that improves bioactivities or creates new functional combinations. Such proteins may function as immune effectors cell recruiters to tumors or as decoy receptors for various ligands. In this review article, we have outlined the standard methods for creating fusion proteins and covered the applications of fusion proteins in treatment of cancer. This article also highlights the role of fusion proteins in targeting the signaling pathways involved in cancer for effective treatment.

Antibody-cytokine fusion proteins: A novel class of biopharmaceuticals for the therapy of cancer and of chronic inflammation

Antibody-cytokine fusion proteins represent a novel class of biopharmaceuticals, with the potential to increase the therapeutic index of cytokine 'payloads' and to promote leukocyte infiltration at the site of disease. In this review, we present a survey of immunocytokines that have been used in preclinical models of cancer and in clinical trials. In particular, we highlight how antibody format, choice of target antigen and cytokine engineering, as well as combination strategies, may have a profound impact on therapeutic performance. Moreover, by using anti-inflammatory cytokines, antibody fusion strategies can conveniently be employed for the treatment of auto-immune and chronic inflammatory conditions.

Antibody-cytokine fusion proteins: Biopharmaceuticals with immunomodulatory properties for cancer therapy

Cytokines have long been used for therapeutic applications in cancer patients. Substantial side effects and unfavorable pharmacokinetics limit their application and may prevent dose escalation to therapeutically active regimens. Antibody-cytokine fusion proteins (often referred to as immunocytokines) may help localize immunomodulatory cytokine payloads to the tumor, thereby activating anticancer immune responses. A variety of formats (e.g., intact IgGs or antibody fragments), molecular targets (e.g., extracellular matrix components and cell membrane antigens) and cytokine payloads have been considered for the development of this novel class of biopharmaceuticals. This review presents the basic concepts on the design and engineering of immunocytokines, reviews their potential limitations, points out emerging opportunities and summarizes key features of preclinical and clinical-stage products.

Immunocytokines and bispecific antibodies: two complementary strategies for the selective activation of immune cells at the tumor site

The activation of the immune system for a selective removal of tumor cells represents an attractive strategy for the treatment of metastatic malignancies, which cannot be cured by existing methodologies. In this review, we examine the design and therapeutic potential of immunocytokines and bispecific antibodies, two classes of bifunctional products which can selectively activate the immune system at the tumor site. Certain protein engineering aspects, such as the choice of the antibody format, are common to both classes of therapeutic agents and can have a profound impact on tumor homing performance in vivo of individual products. However, immunocytokines and bispecific antibodies display different mechanisms of action. Future research activities will reveal whether an additive of even synergistic benefit can be obtained from the judicious combination of these two types of biopharmaceutical agents.

Chimera of IL-2 linked to light chain of anti-IL-2 mAb mimics IL-2/anti-IL-2 mAb complexes both structurally and functionally

IL-2/anti-IL-2 mAb immunocomplexes were described to have dramatically higher activity than free IL-2 in vivo. We designed protein chimera consisting of IL-2 linked to light chain of anti-IL-2 mAb S4B6 through flexible oligopeptide spacer (Gly(4)Ser)(3). This protein chimera mimics the structure of IL-2/S4B6 mAb immunocomplexes but eliminates general disadvantages of immunocomplexes like possible excess of either IL-2 or anti-IL-2 mAb and their dissociation to antibody and IL-2 at low concentrations. This novel kind of protein chimera is characterized by an intramolecular interaction between IL-2 and binding site of S4B6 mAb similarly as in IL-2/S4B6 mAb immunocomplexes. Our protein chimera has biological activity comparable to IL-2/S4B6 mAb immunocomplexes in vitro, as shown by stimulation of proliferation of purified and activated OT-I CD8(+) T cells. The protein chimera exerts higher stimulatory activity to drive expansion of purified CFSE-labeled OT-I CD8(+) T cells activated by an injection of a low dose of SIINFEKL peptide than IL-2/S4B6 mAb immunocomplexes in vivo.

Immunocytokines: a novel class of potent armed antibodies

Several cytokines have been investigated in clinical trials, based on their potent therapeutic activity observed in animal models of cancer and other diseases. However, substantial toxicities are often reported at low doses, thus preventing escalation to therapeutically active regimens. The use of recombinant antibodies or antibody fragments as delivery vehicles promises to enhance greatly the therapeutic index of pro-inflammatory and anti-inflammatory cytokines. This review surveys preclinical and clinical data published in the field of antibody-cytokine fusions (immunocytokines). Molecular determinants (such as molecular format, valence, target antigen), which crucially contribute to immunocytokine performance in vivo, are discussed in the article, as well as recent trends for the combined use of this novel class of biopharmaceuticals with other therapeutic agents.

Antibody-cytokine fusion proteins: applications in cancer therapy

BACKGROUND

Antibody-cytokine fusion proteins consist of cytokines fused to an antibody to improve antibody-targeted cancer immunotherapy. These molecules have the capacity to enhance the tumoricidal activity of the antibodies and/or activate a secondary antitumor immune response.

OBJECTIVE

To review the strategies used to develop antibody-cytokine fusion proteins and their in vitro and in vivo properties, including preclinical and clinical studies focusing on IL-2, IL-12 and GM-CSF.

METHODS

Articles were found by searching databases such as PubMed and Clinical Trials of the US National Institutes of Health.

RESULTS/CONCLUSION

Multiple antibody-cytokine fusion proteins have demonstrated significant antitumor activity as direct therapeutics or as adjuvants of cancer vaccines in preclinical studies, paving the way for their clinical evaluation.

Efficient growth inhibition of ErbB2-overexpressing tumor cells by anti-ErbB2 ScFv-Fc-IL-2 fusion protein in vitro and in vivo

AIM

To investigate the antitumor activities of an anti-ErbB2 scFv-Fc-interleukin 2 (IL-2) fusion protein (HFI) in vitro and in vivo.

METHODS

Fusion protein HFI was constructed. The efficacy of HFI in mediating tumor cell lysis was determined by colorimetric lactate dehydrogenase release assays. The antitumor activity of HFI was evaluated in tumor xenograft models.

RESULTS

The fusion protein was folded as a homodimer formed by covalently linking Fc portions and it retained ErbB2 specificity and IL-2 biological activity. HFI mediated antibody-dependent cell-mediated cytotoxicity (ADCC) at low effector-to-target ratios in vitro and improved the therapeutic efficacy of IL-2 in experiments in vivo.

CONCLUSION

The genetically-engineered anti-ErbB2 scFv-Fc-IL-2 fusion protein exhibited high efficiency both in mediating ADCC in vitro and significant antitumor activity in tumor xenograft models.

H60/TNT-3 fusion protein activates NK cells in vitro and improves immunotherapeutic outcome in murine syngeneic tumor models

H60 is a murine minor histocompatibility antigen that binds to NKG2D and activates an effector phenotype in NK and T cells. In the present study, H60 was genetically fused to the tumor-targeting murine MAb TNT-3. The resultant fusion protein, named H60/TNT-3, was produced in NS0 cells and determined by ELISA to possess an H60 epitope. The Ka of H60/TNT-3 (2.43 x 10(9) M(-1)) was nearly identical to that of the parental Ab (2.22 x 10(9) M(-1)), demonstrating that addition of the H60 moiety to the N-terminus of TNT-3 heavy chain did not affect antigen affinity. In vitro, H60/TNT-3 bound and activated murine NK cells, eliciting IFN-gamma production in a higher percentage of cells than the activating NKG2D Ab A10. In vivo, H60/TNT-3 possessed a half-life of approximately 12 hours and effectively targeted tumor tissue versus control organs, with nearly 2% injected dose per gram of tumor retained after 48 hours. Finally, H60/TNT-3 was tested for antitumor efficacy in BALB/c and C57BL/6 mice bearing subcutaneous syngeneic carcinomas. Tumor volume reduction was observed in both CT26 and Lewis Lung models (53% and 52%, respectively) relative to untreated control mice. Further, Lewis Lung carcinoma-bearing mice treated with H60/TNT-3 experienced a statistically significant survival advantage. Taken together, these data characterize a new immunotherapeutic MAb with antitumor efficacy that prolonged overall survival in a resistant solid tumor model.

Engineered vascular-targeting antibody-interferon-gamma fusion protein for cancer therapy

A number of cytokines are either approved drugs or are in advanced clinical trials, yet these biopharmaceuticals do not typically localize efficiently in solid tumors and manifest their therapeutic potential at the expense of severe side effects. The targeted delivery of cytokines to solid tumors is a promising avenue for increasing the therapeutic index of these biopharmaceuticals. We engineered a fusion protein between scFv(L19), a human antibody fragment specific to the EDB domain of fibronectin, and a cysteine-free mutant of murine interferon-gamma. The resulting fusion protein was capable of targeting new blood vessels in solid tumors, and the targeting efficiency was strikingly increased in tumor-bearing knockout mice lacking the interferon-gamma receptor. ScFv(L19)-interferon-gamma displayed a strong antitumor effect in both subcutaneous and metastatic murine F9 teratocarcinomas, but was not efficacious as single agent when used to treat C51 and CT26 tumors. The potency of this fusion protein could be substantially enhanced by combination with doxorubicin and other immunocytokines. These findings are of clinical relevance, as the EDB domain is a marker of angiogenesis, with identical sequence in mouse and man, which is abundantly expressed in a variety of aggressive solid tumors but is undetectable in most normal tissues.

Efficient recovery of the functional IP10-scFv fusion protein from inclusion bodies with an on-column refolding system

A functional IP10-scFv fusion protein retaining the antibody specificity for acidic isoferritin and chemokine function was produced at high level in Esherichia coli (E. coli). IP10-scFv gene from the recombinant plasmid pc3IP104c9 was subcloned into pET28a fused to N-terminal His-tag sequence in frame and overexpressed in E. coli BL21(DE3). With an on-column refolding procedure based on Ni-chelating chromatography, the active fusion protein was recovered efficiently from inclusion bodies with a refolding yield of approximate 45% confirmed by spectrophotometer. The activity of refolded IP10-scFv was determined through sodium dodecyl sulfate-polyacrylamide gel electrophoresis, Western blotting and enzyme-linked immunosorbent assay. The results showed the fusion protein retains the specific binding activity to AIF with an affinity constant of 4.48x10(-8) M as well as the chemokine function of IP-10. The overall yield of IP10-scFv with bioactivity in E. coli flask culture was more than 40 mg/L.

In vivo evaluation of an EIAV vector for the systemic genetic delivery of therapeutic antibodies

Lentiviral-based vectors hold great promise as gene delivery vehicles for the treatment of a wide variety of diseases. We have previously reported the development of a nonprimate lentiviral vector system based on the equine infectious anaemia virus (EIAV), which is able to efficiently transduce dividing and nondividing cells both in vitro and in vivo. Here, we report on the application of EIAV vectors for the systemic delivery of an antibody fusion protein designed for the treatment of cancer. The therapeutic potential of a single chain antibody against the tumour-associated antigen, 5T4, fused to immune enhancer moieties has been demonstrated in vitro and here we evaluate the genetic delivery of a 5T4 scFv fused to B7.1 (scFvB7) using an EIAV vector. The kinetics and concentration of protein produced following both intravenous (i.v.) and intramuscular (i.m.) administration was determined in immune competent adult mice. In addition, the immune response to the EIAV vector and the transgene were determined. Here, we show that a single injection of EIAV expressing scFv-B7 can give rise to concentrations of protein in the range of 1-5 microg/ml that persist in the sera for more than 50 days. After a second injection, concentrations of scFv-B7.1 rose as high as 20 microg/ml and levels greater than 2 microg/ml were present in the sera of all mice injected i.v. after 210 days despite the detection of antibodies against both the transgene and viral envelope for the duration of this study. These results demonstrate the potential of EIAV as a gene therapy vector for long-term production of therapeutic recombinant proteins.

chTNT-3/hu IL-12 fusion protein for the immunotherapy of experimental solid tumors

Fusion proteins are emerging as a promising approach for targeting cytokines to the tumor site in order to generate an effective anti-tumor response. In this study, a fusion protein, chTNT-3/huIL-12, consisting of the necrosis targeting antibody, chTNT-3, and human interleukin-12 (IL-12), was constructed and expressed using the glutamine synthetase gene amplification system in NS0 cells. For these studies, IL-12 was chosen since it has been shown to be a powerful anti-tumor cytokine. To generate the fusion protein, an expression vector was prepared by linking the huIL-12 p35 subunit cDNA to the 3' end of the chTNT-3 heavy chain cDNA and the p40 subunit was added to a separate vector. The activity of the expressed chTNT-3/huIL-12 was confirmed by standard IL-12 bioactivity assays which demonstrated that the fusion protein induced similar levels of peripheral blood lymphocyte (PBL) proliferation as free recombinant IL-12. In addition, the lytic activity of the fusion protein was demonstrated in both naive and IL-2-activated lymphocytes using cytotoxicity assays against three human pancreatic and prostatic cancer cell lines (CAPAN, DU145, and PC3-MA). Human PBL incubated with this fusion protein showed an increase in IFN-gamma production which was augmented dramatically by pre-incubation with IL-2. Finally, the immunotherapeutic potential of the fusion protein was demonstrated in the human PBL-SCID mouse model where a 44% reduction in DU145 prostatic tumor growth was obtained compared to control treated mice. These results demonstrate that tumor-targeted human IL-12 may be an effective immunotherapeutic reagent for the treatment of solid tumors in man.

A novel fusion protein of IP10-scFv retains antibody specificity and chemokine function

We combined the specificity of tumor-specific antibody with the chemokine function of interferon-gamma inducible protein 10 (IP-10) to recruit immune effector cells in the vicinity of tumor cells. A novel fusion protein of IP10-scFv was constructed by fusing mouse IP-10 to V(H) region of single-chain Fv fragment (scFv) against acidic isoferritin (AIF), and expressed in NS0 murine myeloma cells. The IP10-scFv fusion protein was shown to maintain the specificity of the antiAIF scFv with similar affinity constant, and bind to the human hepatocarcinoma SMMC 7721 cells secreting AIF as well as the activated mouse T lymphocytes expressing CXCR3 receptor. Furthermore, the IP10-scFv protein either in solution or bound on the surface of SMMC 7721 cells induced significant chemotaxis of mouse T cells in vitro. The results indicate that the IP10-scFv fusion protein possesses both bioactivities of the tumor-specific antibody and IP-10 chemokine, suggesting its possibility to induce an enhanced immune response against the residual tumor cells in vivo.

Chimeric TNT-3 Antibody/Murine Interferon-γFusion Protein for the Immunotherapy of Solid Malignancies

Interferon-gamma (IFN-gamma) has been used in the experimental treatment of cancer with limited success. Despite direct cytotoxic effects on tumor cells and the ability to stimulate the antitumor activities of a variety of effector cells, IFN-gamma has not been found to produce impressive therapeutic responses partly because of inadequate sustained intratumoral concentrations and systemic toxicity. To overcome these obstacles, we have developed an antibody/murine IFN-gamma fusion protein (chTNT-3/muIFN-gamma), which utilizes the tumor necrosis therapy antibody, chTNT-3, to target murine IFN-gamma to necrotic regions of solid tumors implanted in immunocompetent BALB/c mice. The genetically engineered fusion protein was expressed in NS0 cells using the Glutamine Synthetase Gene Amplification Expression System. After purification, the fusion protein demonstrated both antigen targeting and cytokine activities as assessed by in vitro assays which, when compared to recombinant free IFN-gamma, demonstrated approximately 40-45% biologic activity by two separate assay determinations. Pharmacokinetic and biodistribution studies in mice demonstrated a relatively long whole body half-life of 32 h in vivo and significant intratumoral accretion, respectively. Most importantly, immunotherapeutic studies in the MAD109 syngeneic murine carcinoma of the lung demonstrated significant intratumoral infiltration by leukocytes, primarily by macrophages and CD4(-) CD8(-) Thy-1.2(+) lymphocytes. Additionally, intravenous administration of the fusion protein significantly decreased the number of metastatic foci in an experimental model of pulmonary metastasis without causing any observable toxicity. These studies demonstrate that chTNT3/muIFN-gamma can safely target syngeneic tumor models as part of a promising strategy for the targeted immunotherapy of solid tumors.

LEC/chTNT-3 fusion protein for the immunotherapy of experimental solid tumors

The human chemokine liver-expression chemokine (LEC) was originally found in an expressed sequence tag library, and later the LEC gene was located to chromosome 17q in the ML chemokine gene cluster. LEC has been shown to chemoattract monocytes, lymphocytes, and polymorphonuclear leukocytes (PMNs) by its binding to CCR1 and CCR8 chemokine receptors. Because of its potency as a chemoattractant for immune cells, LEC was used to genetically engineer a fusion protein with chTNT-3, a monoclonal antibody previously shown to target tumors by binding to DNA exposed in necrotic zones. Because the N-terminus of chemokines is important for their activity, the C-terminus of LEC was genetically linked to the chTNT-3 heavy chain variable region and, along with the light chain gene, cotransfected into NSO murine myeloma cells using the glutamine synthetase gene amplification system. The expressed LEC/chTNT-3 fusion protein was purified by tandem protein-A affinity and ion-exchange chromatography and chemotaxis and binding assays confirmed the bioactivity of the purified fusion protein. Pharmacokinetic and biodistribution studies in vivo showed that LEC/chTNT-3 had a biologic half-life of 3 hours and had good uptake in tumor (2.4% injected dose/g), which remained stable at 12 and 24 hours postinjection. Immunotherapy studies performed in three solid tumor models of the BALB/c mouse showed between 37% and 55% tumor reduction at 19 days post-implantation. Immunohistochemical studies using tumor sections obtained at different time points after the administration of control chTNT-3 and LEC/chTNT-3 showed heavy infiltration of CD4+ and CD8+ T cells, PMNs, B cells, and CD11c+CD11b+ dendritic cells in the LEC/chTNT-3 treated groups. The results of these studies demonstrate that this novel fusion protein has potent antitumor activity that is associated with the infiltration of different subpopulations of immune cells. The targeting of LEC to necrotic areas of tumors where the release of tumor antigens is prevalent may be a new approach for the immunotherapy of solid tumors.

Comparison of recombinant derivatives of chimeric TNT-3 antibody for the radioimaging of solid tumors

Although intact monoclonal antibodies (MAbs) are well suited as therapeutic reagents, their relatively slow clearance rates render them less useful for imaging applications. Over the last several years, our laboratory has developed a unique targeting approach to solid tumors that utilizes MAbs directed against DNA and its components to bind to degenerating cells and necrotic regions of tumors in a specific manner. Because these MAbs have considerable potential for the early diagnosis of cancer and for the monitoring of cytoreductive therapies, the availability of an effective imaging agent is highly desirable. To accomplish this goal, a series of genetically engineered derivatives of MAb chTNT-3 including the single-chain Fv, diabody, triabody, Fab, and F(ab')(2) were generated and expressed in NS0 myeloma cells using the Glutamine Synthetase Amplification System. Initial in vitro studies demonstrated that each of the antibody derivatives maintained its antigen binding in a stable manner. In vivo analyses after radiolabeling were then performed to evaluate their pharmacokinetic, biodistribution, and tumor-imaging properties in solid tumor-bearing mice. The results of these studies showed that compared with intact parental chTNT-3, which has a half-life of 134.2 h, the smaller derivatives were eliminated more rapidly (4.9-8.1 h). Importantly, the smaller derivatives were found to have significantly higher tumor-to-organ ratios, but lower overall uptake levels compared with parental (125)I-chTNT-3 in two different tumor models. A comparison of the five derivatives showed that the F(ab')(2) reagent consistently gave the best results in imaging and biodistribution studies. Based upon these results, further studies are warranted to demonstrate the potential of this reagent for the diagnosis and monitoring of solid tumors using noninvasive imaging techniques such as immunoscintigraphy and positron emission tomography (PET).

Generation of human interferon gamma and tumor Necrosis factor alpha chimeric TNT-3 fusion proteins

Studies have shown that cytokines can effectively treat solid tumors by a direct cytotoxic effect as well as by immunomodulation. Both human interferon gamma (IFNgamma) and tumor necrosis factor alpha (TNFalpha) have been used to treat a variety of colon carcinoma cell lines and tumors in patients. These cytokines, however, are dose limited by their toxicity and fast clearance rates when given intravenously. To improve their therapeutic value, we now report on the generation of two new fusion proteins consisting of human IFNgamma and TNFalpha genetically linked to the C-terminal portion of chTNT-3, a monoclonal antibody (MAb), which targets human solid tumors by binding to intracellular antigens exposed in degenerating cells associated with tumor necrosis. In vitro characterization studies demonstrate that both the IFNgamma and TNFalpha fusion proteins are able to maintain their binding affinity to antigen as well as their direct cytotoxic effect and immunomodulatory functions. When both fusion proteins are combined at optimal doses, they demonstrate a 30% direct cellular cytotoxicity of human colon carcinoma cells of which approximately 14% can be attributed to apoptosis. In vivo, these agents were studied for their pharmakocinetic clearance rates and their ability to target human colon carcinomas heterotransplanted in nude mice. The results of these studies show that, compared with chTNT-3 parental antibody, both fusion proteins have a substantially shorter whole body half-life, yet are able to target tumor in a similar manner. As each of these fusion proteins are cleared from the circulation and normal tissues, tumor-to-normal-tissues ratios rise demonstrating the retention of these reagents in tumor. The generation of long-acting and targeted human IFNgamma and TNFalpha antibody fusion proteins will enable investigators to study the role of these potent immunostimulatory cytokines in the treatment of human solid tumors.

Pharmacokinetic characteristics and biodistribution of radioiodinated chimeric TNT-1, -2, and -3 monoclonal antibodies after chemical modification with biotin

To improve the clinical potential of monoclonal antibodies (MAbs), new methods are required to augment antibody uptake in the tumor while minimizing binding in normal tissues. Our laboratory has pioneered the use of chemical modification to accomplish this goal. Using three chimeric MAbs, chTNT-1, chTNT-2, and chTNT-3, which target solid tumors by binding to common antigens found in the central necrotic core, we now demonstrate the potential of chemical modification to improve the pharmacokinetic characteristics of these unique MAbs. To identify optimal modification conditions, TNT MAbs were reacted with biotin at various ratios and tested by clearance and biodistribution analyses. The biodistribution results revealed that the numbers of biotin molecules per MAb yielding optimal tumor uptake were 3:1 for chTNT-1, 5:1 for chTNT-2, and 8:1 for chTNT-3. Biotinylated MAbs were found to have faster whole body clearance times and better biodistribution profiles compared to unmodified antibodies. Although chTNT-2 showed only a modest improvement after biotinylation, biodistribution results indicated that this MAb had the highest uptake in tumor. By reducing the charge of the antibody molecule, chemical modification appears to be a useful method for improving the pharmacokinetics and biodistribution of TNT antibodies directed to the necrotic region of solid tumors.

Cytokines as therapeutic drugs

Cytokines are a growing group of proteins that are responsible for the communication of cells of the immune system, hematopoietic cells, and other cell types. They play a dominant role in various diseases, particularly in promoting and perpetuating inflammation. Cytokine production is a reaction of the body to a pathologic state to restore homeostasis. In such cases, the therapeutic intervention should support the reaction of the body by giving the cytokine itself (agonistic therapeutics). In other cases, manifestation of a disease results from an overproduction of cytokines, making cytokine antagonists desirable therapeutic drugs. Furthermore, cytokines may be good candidates as cancer therapeutics, especially to support the restoration of blood cell populations after chemotherapy or radiation.

Myeloma expression systems

Myeloma expression systems have been utilized successfully for the production of various recombinant proteins. In particular, myeloma cell lines have been exploited to express a variety of different antibodies for diagnostic applications as well as in the treatment of various human diseases. The use of myeloma cells for antibody production is advantageous because they are professional immunoglobulin-secreting cells and are able to make proper post-translational modifications. Proper glycosylation has been shown to be important for antibody function. Advances in genetic engineering and molecular biology techniques have made it possible to isolate murine and human variable regions of almost any desired specificity. Antibodies and antibody variants produced in myeloma cells have been extremely helpful in elucidating the amino acid residues and structural motifs that contribute to antibody function. Because of their domain nature, immunoglobulin genes can be easily manipulated to produce chimeric or humanized antibodies. These antibodies are less immunogenic in humans and also retain their specificity for antigen and biologic properties. In addition, novel proteins in which antibodies are fused to non-immunoglobulin sequences as well as secretory IgA have been produced in myeloma cells.

Stable, genetically engineered F(ab')(2) fragments of chimeric TNT-3 expressed in mammalian cells

F(ab')(2) fragments are desirable structural derivatives of monoclonal antibodies (MAbs) because of their pharmacokinetic properties and bivalent binding to antigen. Production of these fragments, however, has proven difficult because of the variable sensitivity of intact antibodies to proteolytic enzymes, which can result in very low yields and unstable product. To circumvent these problems, we attempted to apply genetic engineering methods to generate stable F(ab')(2) fragments in NSO murine myeloma cells using the glutamine synthase expression system. For these studies, the chimeric MAb, chTNT-3, directed against necrotic regions of solid tumors, was used to generate several F(ab')(2) variants, which contained between one and three cysteine residues at the end of the hinge region. In addition, two different affinity tags (his tag, streptactin tag) were used with each variant to determine the best tag for purification procedures. Stability was measured by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and by antigen binding studies and the constructs were tested in vivo to measure their pharmacokinetic properties and biodistribution in normal organs and tumor. The results of these studies show that 3 cysteine residues are required to produce stable F(ab')(2) fragments and that either purification tag can be used with this variant to produce suitable reagents for in vivo studies. Those constructs containing one or two cysteines were found to be unstable and broke down to Fab fragments regardless of the purification tag used. These studies demonstrate that stable, clinically useful F(ab')(2) fragments of chTNT-3 can be produced in mammalian cells by genetic engineering methods.

Antibody-cytokine fusion proteins for the therapy of cancer

Advances in genetic engineering and expression systems have led to rapid progress in the development of antibodies fused to other proteins. These 'antibody fusion proteins' have novel properties and include antibodies with specificity for tumor associated antigens fused to cytokines such as interleukin-2 (IL2), granulocyte/macrophage colony-stimulating factor (GM-CSF), and interleukin-12 (IL12). The goal of this approach to cancer therapy is to concentrate the cytokine in the tumor microenvironment and in so doing directly enhance the tumoricidal effect of the antibody and/or enhance the host immune response (T-cell, B-cell or NK) against the tumor. In the past decade, multiple antibody-cytokine fusion proteins have been developed with different specificities targeting a broad variety of tumors. These novel molecules retain both antibody and cytokine associated functions. In addition, in animals bearing tumors, antibody-cytokine fusion proteins are able to target the tumor and to elicit a significant anti-tumor response that in some cases results in a complete elimination of the tumor. These results suggest that antibody-cytokine fusion proteins have potential for use in the treatment of human cancer. In the present review, we describe strategies for construction of antibody-cytokine fusion proteins and discuss the properties of several antibody-cytokine fusion proteins with IgG genetically fused to the cytokines IL2, GM-CSF or IL12.

Recombinant anti-human HER2/neu IgG3-(GM-CSF) fusion protein retains antigen specificity and cytokine function and demonstrates antitumor activity

Anti-HER2/neu therapy of human HER2/neu-expressing malignancies such as breast cancer has shown only partial success in clinical trials. To expand the clinical potential of this approach, we have genetically engineered an anti-HER2/neu IgG3 fusion protein containing GM-CSF. Anti-HER2/neu IgG3-(GM-CSF) expressed in myeloma cells was correctly assembled and secreted. It was able to target HER2/neu-expressing cells and to support growth of a GM-CSF-dependent murine myeloid cell line, FDC-P1. The Ab fusion protein activated J774.2 macrophage cells so that they exhibit an enhanced cytotoxic activity and was comparable to the parental Ab in its ability to effect Ab-dependent cellular cytotoxicity-mediated tumor cell lysis. Pharmacokinetic studies showed that anti-HER2/neu IgG3-(GM-CSF) is stable in the blood. Interestingly, the half-life of anti-HER2/neu IgG3-(GM-CSF) depended on the injected dose with longer in vivo persistence observed at higher doses. Biodistribution studies showed that anti-HER2/neu IgG3-(GM-CSF) is mainly localized in the spleen. In addition, anti-HER2/neu IgG3-(GM-CSF) was able to target the HER2/neu-expressing murine tumor CT26-HER2/neu and enhance the immune response against the targeted Ag HER2/neu. Anti-HER2/neu IgG3-(GM-CSF) is able to enhance both Th1- and Th2-mediated immune responses and treatment with this Ab fusion protein resulted in significant retardation in the growth of s.c. CT26-HER2/neu tumors. Our results suggest that anti-HER2/neu IgG3-(GM-CSF) fusion protein is useful in the treatment of HER2/neu-expressing tumors.

Feasibility of antibody production in plants for human therapeutic use

From the description above, the diversity of antibodies as a class of potential therapeutic agents is weighed against the constraints of developing any therapeutic molecule. Although much of this limit is specific to the antibody design, plant-based production systems have a potential to impact commercialization by making larger volume products manageable, with lower up-front capital requirements. Due to their novel glycosylation pattern (Faye et al. 1989), plants at present may not create antibodies with all the functions of mammalian-glycosylated antibodies (Wright and Morrison 1994). This is not a limit for all current products. Success is dependent on fusing the efficient agriculture infrastructure with the narrow tolerances required for a drug production system. Further validation of plants as a production system will come as more therapeutics from plants follow the corn-produced material through human clinical trials.

Immunocytokines: a promising approach to cancer immunotherapy

Recombinant antibody-cytokine fusion proteins are immunocytokines that achieve high cytokine concentrations in the tumor microenvironment and thereby effectively stimulate cellular immune responses against malignancies. The activation and expansion of immune effector cells, such as CD8+ T lymphocytes, by interleukin-2 immunocytokines resulted in the eradication of established pulmonary and hepatic metastases of murine melanoma and colorectal carcinoma in syngeneic mouse models. These immunocytokines were equally effective in eliminating established bone marrow and liver metastases of murine neuroblastoma by activating natural killer cells. The effective eradication of metastases by immunocytokines resulted in significant prolongation in life span of mice over that of controls receiving equivalent mixtures of antibody and interleukin-2, which failed to reduce the growth of disseminated metastases. Proof of concept was established, indicating that immunocytokine-induced activation and expansion of immune effector cells in the tumor microenvironment can effectively eradicate established tumor metastases. This promising new approach to cancer immunotherapy may lead to clinical applications that improve treatment of cancer patients with minimal residual disease in an adjuvant setting.

Treatment of B-Cell Lymphoma With Chimeric IgG and Single-Chain Fv Antibody–Interleukin-2 Fusion Proteins

Anti-idiotype (Id) antibodies (Abs) have been shown to be effective in treatment of B-cell lymphoma in animal models and in clinical trials. The combination of interleukin-2 (IL-2) can augment the therapeutic effect of anti-Id Abs. To further improve the power of the combined therapy, a monoclonal anti-Id Ab, S5A8, specifically recognizing a murine B-cell lymphoma 38C13, was genetically modified to contain the IL-2 domain and thus use the unique targeting ability of Abs to direct IL-2 to the tumor site. Two forms of the anti-Id–IL-2 fusion proteins were constructed: one configuration consisting of mouse-human chimeric IgG (chS5A8–IL-2) and the other containing only the variable light (VL) and variable heavy (VH) Ab domains covalently connected by a peptide linker (scFvS5A8-IL-2). Both forms of the anti-Id–IL-2 fusion proteins retained IL-2 biological activities and were equivalent in potentiating tumor cell lysis in vitro. In contrast, the antigen-binding ability of scFvS5A8–IL-2 was 30- to 40-fold lower than that of the bivalent chS5A8–IL-2. Pharmacokinetic analysis showed that scFvS5A8–IL-2 was eliminated about 20 times faster than chS5A8–IL-2. Finally, it was shown that chS5A8–IL-2 was very proficient in inhibiting 38C13 tumor growth in vivo, more effectively than a combined therapy with anti-Id Abs and IL-2, whereas scFvS5A8–IL-2 did not show any therapeutic effect. These results demonstrate that the anti-Id–IL-2 fusion protein represents a potent reagent for treatment for B-cell lymphoma and that the intact IgG fusion protein is far more effective than its single-chain counterpart.

© 1998 by The American Society of Hematology.

Treatment of B-Cell Lymphoma With Chimeric IgG and Single-Chain Fv Antibody–Interleukin-2 Fusion Proteins

Anti-idiotype (Id) antibodies (Abs) have been shown to be effective in treatment of B-cell lymphoma in animal models and in clinical trials. The combination of interleukin-2 (IL-2) can augment the therapeutic effect of anti-Id Abs. To further improve the power of the combined therapy, a monoclonal anti-Id Ab, S5A8, specifically recognizing a murine B-cell lymphoma 38C13, was genetically modified to contain the IL-2 domain and thus use the unique targeting ability of Abs to direct IL-2 to the tumor site. Two forms of the anti-Id–IL-2 fusion proteins were constructed: one configuration consisting of mouse-human chimeric IgG (chS5A8–IL-2) and the other containing only the variable light (VL) and variable heavy (VH) Ab domains covalently connected by a peptide linker (scFvS5A8-IL-2). Both forms of the anti-Id–IL-2 fusion proteins retained IL-2 biological activities and were equivalent in potentiating tumor cell lysis in vitro. In contrast, the antigen-binding ability of scFvS5A8–IL-2 was 30- to 40-fold lower than that of the bivalent chS5A8–IL-2. Pharmacokinetic analysis showed that scFvS5A8–IL-2 was eliminated about 20 times faster than chS5A8–IL-2. Finally, it was shown that chS5A8–IL-2 was very proficient in inhibiting 38C13 tumor growth in vivo, more effectively than a combined therapy with anti-Id Abs and IL-2, whereas scFvS5A8–IL-2 did not show any therapeutic effect. These results demonstrate that the anti-Id–IL-2 fusion protein represents a potent reagent for treatment for B-cell lymphoma and that the intact IgG fusion protein is far more effective than its single-chain counterpart.

© 1998 by The American Society of Hematology.

A new chemically modified chimeric TNT-3 monoclonal antibody directed against DNA for the radioimmunotherapy of solid tumors

In the last several years, our laboratory has developed a new approach to the radioimmunotherapy of solid tumors, designated Tumor Necrosis Treatment (TNT), that exploits the presence of degenerating and necrotic cells within tumors by utilizing MAbs directed against universal, intracellular antigens. The first TNT MAb developed by our laboratory, designated TNT-1, was directed against nucleosomal determinants consisting of histone H1 and DNA. Since absolute tumor accretion of MAb is a critical determinant of antitumor efficacy in radioimmunotherapy, we sought to identify new antinuclear antibodies that displayed high tumor localization properties. In the present study, we describe a murine antinuclear antibody, TNT-3, which demonstrates 3-fold higher tumor uptake than TNT-1. Because of this characteristic, a chimeric derivative designated chTNT-3 was developed and evaluated for antigen binding and tumor targeting. ELISA studies using a series of nuclear antigens confirmed that TNT-3 is directed against single-stranded DNA and does not cross react with TNT-1. Immunohistology reveals predominantly nuclear staining reactivity in human tissues and tumors. Since it was shown by our laboratory that charge modification can significantly improve the pharmacokinetic performance of monoclonal antibodies, chTNT-3 was chemically modified with biotin to generate an improved therapeutic reagent designated chTNT-3/B. Comparative studies with unmodified MAb demonstrated that biotinylation significantly shortened its clearance time in mice and produced lower normal tissue levels, while maintaining an equal amount of uptake in tumor xenografts for up to 10 days. These in vivo characteristics suggest that chTNT-3/B is an improved TNT reagent for the radioimmunotherapy of solid tumors.

Recombinant immunocytokines targeting the mouse transferrin receptor: construction and biological activities

Localized cytokine therapies with recombinant monoclonal antibody-cytokine fusion proteins, designated immunocytokines, have become of increasing interest for tumor immunotherapy, since they direct immunomodulatory cytokines into the tumor microenvironment. To investigate their mechanisms of action in a variety of syngeneic tumor models, recombinant mouse cytokines IL2 and GM-CSF were engineered as fusion proteins to the carboxyl terminus of a chimeric rat/mouse antitransferrin receptor antibody, ch17217 and expressed in stable-transfected Chinese hamster ovary cells. The recombinant immunocytokines were readily purified by affinity chromatography and their binding characteristics were identical to those shown for the ch17217 antibody. The IL2 immunocytokine had an activity similar to recombinant mouse IL2, whereas the GM-CSF immunocytokine had enhanced cytokine activity relative to recombinant mouse GM-CSF. The clearance rates of ch17217 and the GM-CSF and IL2 immunocytokines were relatively similar with elimination phases (t1/2alpha) of 1.8 h and distribution phases (t1/2beta) of 83, 88, and 91 h, respectively. Both immunocytokines demonstrated effective antitumor activity by suppressing the growth of hepatic metastases of mouse neuroblastoma and pulmonary metastases of mouse colon carcinoma in syngeneic A/J and BALB/c mice, respectively. These results indicate that biologically effective IL2 and GM-CSF immunocytokines combine the targeting ability of an antitransferrin receptor monoclonal antibody with the immunomodulatory functions of each cytokine. Because of the universal expression of the transferrin receptor on mouse tumor cell lines, these constructs should prove useful to determine their efficacy in a wide variety of syngeneic mouse tumor models and to perform detailed studies of their modes of action.