A recombinant IgG3-(IL-2) fusion protein for the treatment of human HER2/neu expressing tumors.

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 human IgG3 fusion protein containing interleukin-2 (IL-2) fused at its carboxyl terminus. Anti-Her2/neu IgG3-(IL-2) retained antibody and cytokine related activity. Treatment of immunocompentent mice with this antibody fusion protein resulted in significant retardation in the subcutaneous (s.c.) growth of CT26-HER2/neu tumors suggesting that anti-HER2/neu IgG3-(IL-2) fusion protein will be useful in the treatment of HER2/neu expressing tumors. We also found that fusing IL-2 to human IgG3 results in a significant enhancement of the murine anti-human antibody (MAHA) response.

An antibody-avidin fusion protein specific for the transferrin receptor serves as a delivery vehicle for effective brain targeting: initial applications in anti-HIV antisense drug delivery to the brain.

In the present study a novel Ab-avidin fusion protein has been constructed to deliver biotinylated compounds across the blood brain barrier. This fusion molecule consists of an Ab specific for the transferrin receptor genetically fused to avidin. The Ab-avidin fusion protein (anti-TfR IgG3-CH3-Av) expressed in murine myeloma cells was correctly assembled and secreted and showed both Ab- and avidin-related activities. In animal models, it showed much longer serum half-life than the chemical conjugate between OX-26 and avidin. Most importantly, this fusion protein demonstrated superior [3H]biotin uptake into brain parenchyma in comparison with the chemical conjugate. We also delivered a biotinylated 18-mer antisense peptide-nucleic acid specific for the rev gene of HIV-1 to the brain. Brain uptake of the HIV antisense drug was increased at least 15-fold when it was bound to the anti-TfR IgG3-CH3-Av, suggesting its potential use in neurologic AIDS. This novel Ab fusion protein should have general utility as a universal vehicle to effectively deliver biotinylated compounds across the blood-brain barrier for diagnosis and/or therapy of a broad range of CNS disorders such as infectious diseases, brain tumors as well as Parkinson's and Huntington's diseases.

In vivo properties of three human HER2/neu-expressing murine cell lines in immunocompetent mice.

BACKGROUND AND PURPOSE: Expression of the HER2/neu proto-oncogene, a receptor-like transmembrane protein expressed at low levels on some normal cells, is markedly increased in a subset of human breast, colon, lung, and ovarian cancers. A humanized HER2/neu antibody has been tested as a therapeutic agent in several clinical trials, with promising results. We have developed a family of anti-HER2/neu fusion proteins. To evaluate the immunologic efficacy of these proteins, it is critical that tumors expressing the target antigen can grow in immunologically intact mice. METHOD: To produce murine tumors expressing human HER2/neu on the surface, CT26, MC38, and EL4 murine cell lines were transduced by use of a retroviral construct containing the cDNA encoding the human HER2/neu gene. RESULTS: Histologic features and kinetics of tumor growth in subcutaneous space of the human HER2/neu-expressing cells were similar to those of the respective parental cell lines. Intravenous inoculation with these cells induced disseminated malignant disease. Flow cytometric and immmunohistochemical analyses of freshly isolated tumors revealed in vivo expression of human HER2/neu. Secretion of antigen was not detected by use of an ELISA. CONCLUSION: Although an antibody response against the human HER2/neu antigen was observed, this response does not affect the growth rate of the HER2/neu-expressing cells. These murine models may be useful tools for evaluation of anti-cancer therapeutic approaches that target human HER2/neu.

A B7.1-antibody fusion protein retains antibody specificity and ability to activate via the T cell costimulatory pathway.

We describe the construction and characterization of an Ab fusion protein specific for the tumor-associated Ag HER2/neu linked to sequences encoding the extracellular domain of the B7.1 T cell costimulatory ligand. The Ab domain of the fusion molecule will specifically target HER2/neu-expressing tumor cells, while the B7.1 domain is designed to activate a specific immune response. We show that the B7.1 fusion Ab retained ability to selectively bind to the HER2/neu Ag and to the CTLA4/CD28 counter-receptors for B7.1. Specific T cell activation was observed when the B7.1 Ab fusion protein was bound to HER2/neu-expressing cells. The use of the B7.1 Ab fusion protein may overcome limitations of gene transfer and/or standard Ab therapy and represents a novel approach to the eradication of minimal residual disease.

Functional and pharmacokinetic properties of antibody-avidin fusion proteins.

In an attempt to produce broadly useful targeting agents, genetic engineering and expression techniques have been used to produce Ab-avidin fusion proteins. Chicken avidin has been fused to mouse-human chimeric IgG3 at the end of C(H)1 (C(H)1-Av), immediately after the hinge (H-Av), and at the end of C(H)3 (C(H)3-Av). Fusion heavy chains of the expected molecular mass were expressed, assembled with a co-expressed light chain, and secreted. The resulting molecules continued to bind Ag. They also bound biotinylated human serum albumin; C(H)3-Av had reduced affinity (K(A) = 5.13 x 10(9) M(-1)) compared with the tetrameric avidin (K(A) = 1 x 10(15) M(-1)), but greater affinity than monomeric avidin (K(A) = 1 x 10(7) M(-1)). Importantly, the avidin-IgG fusion proteins had a longer serum t1/2 in rats than avidin. The favorable pharmacokinetic parameters suggest that these avidin fusion proteins can be used effectively to deliver biotinylated ligands such as drugs and peptides to locales expressing any Ag recognized by the associated Ab.

Transferrin-antibody fusion proteins are effective in brain targeting.

In the present study, the receptor binding potential of transferrin (Tf) was linked to an antibody binding specificity. Human Tf was fused to mouse-human chimeric IgG3 at three positions: at the end of heavy chain constant region 1 (CH1), after the hinge, and after CH3. The resulting Tf-antibody fusion proteins were able to bind antigen and the Tf receptor. The CH3-Tf fusion protein showed no complement-mediated cytolysis but possessed IgG receptor I (Fc gamma RI) binding activity. Most importantly, all of the fusion proteins demonstrated significant uptake into brain parenchyma, with 0.3% of the injected dose of the hinge-Tf fusion protein rapidly targeted to the brain. Recovery of iodinated CH3-Tf fusion protein from the brain parenchyma demonstrated that the fusion proteins can cross the blood-brain barrier intact. The binding specificity of these fusion proteins can be used for brain delivery of noncovalently bound ligands, such as drugs and peptides, or for targeting antigens present within the brain.

Functional properties of antibody insulin-like growth factor fusion proteins.

Genetic engineering and expression techniques have been used to produce antibody growth factor fusion proteins. Insulin-like growth factors (IGFs) 1 and 2 have been fused to mouse-human chimeric IgG3 at the end of CH1, immediately after the hinge, and at the end of CH3. Fusion heavy chains of the expected molecular weight were expressed, assembled with a co-expressed light chain, and secreted. The resulting molecules continued to bind antigen; they also bound the growth factor receptors, albeit with decreased affinity. The molecule with IGF1 attached after CH3 (CH3-IGF1) had reduced ability to carry out complement-mediated cytolysis. In contrast the molecule with IGF2 attached after CH3 (CH3-IGF2) showed an approximately 50-fold increase in its ability to effect complement-mediated cytolysis and so should be an effective cytolytic agent. Both CH3-IGF1 and CH3-IGF2 bound Fc gamma RI with affinity similar to that of IgG3. The growth factor fusion proteins showed small but significant uptake into the brain parenchyma.

Hybrid antibodies.

One of the major advantages of genetic engineering is the ability to produce novel, hybrid antibodies. Hybrid antibodies can be assembled using fragments from different antibodies with the objective of assembling novel combinations of antibody-related effector functions. To efficiently achieve this goal it is necessary to have a precise understanding of the structure-function relationships within the antibody molecule. Secondly, it is possible to produce hybrids of antibodies with non-immunoglobulin proteins thereby achieving unique combination of functional properties. In this case it is necessary to consider both the desired functional properties and the means of assembling the protein components so as to maintain these properties. In all cases it is necessary to have the cloned gene segments, appropriate vectors and expression systems.

Structural and functional properties of mouse-human chimeric IgD.

A gene encoding mouse-human chimeric secreted IgD was constructed using the rearranged murine variable region specific for the hapten dansyl and the genomic gene sequences for the constant region of the heavy (H) chain of human IgD. When expressed with the dansyl-specific chimeric light (L) chain, chimeric IgD specific for the hapten dansyl was synthesized and secreted as an H2L2 molecule. The pathway of assembly was H + L----HL----H2L2. The chimeric IgD heavy chain contains three N-linked carbohydrate moieties; one of these appears to be added co-translationally, and the other two appear to be added post-translationally. In secreted chimeric IgD some of the N-linked carbohydrate remains in the high mannose form. The chimeric IgD heavy chain also contains O-linked carbohydrate, which is added at the time of secretion. Inhibition of N-linked glycosylation with tunicamycin halts assembly at the HL half-molecule stage and prevents secretion. Like natural human IgD, the chimeric IgD binds to and upregulates the IgD receptor (IgD-R) on human peripheral blood T cells, and it is equivalent to human myeloma IgD in the competitive inhibition of rosette formation between IgD-R-bearing cells and IgD-coated Ox-RBC, Cross-linking by dansyl-BSA is needed for the chimeric IgD in soluble form to cause IgD-R upregulation.

Genetically engineered antibodies: progress and prospects.

Techniques of genetic engineering and expression have been applied to the production of antibodies in a variety of expression systems. Novel antibodies have been produced with a variety of modifications: as chimeric antibodies, as "humanized" antibodies, with catalytic groups, as bifunctional or fusion proteins, and as functional fragments such as Fabs or Fvs. The domain structure of the antibody is favorable to such manipulation; the novel proteins often retain their antibody-derived activity and acquire new properties as well. Chimeric and complementarity-determining region (CDR)-grafted antibodies have been effective in immunotherapy, but problems of immunogenicity remain. Combinatorial libraries produced in bacteriophage may present an alternative to animal immunization as a source of antigen-binding specificities. Structural and mutational analysis of variable regions is providing useful information about the requirements of the variable region for antigen binding. Careful analysis and comparison of effector functions among immunoglobulin isotypes may be applied to the design of effective therapeutic antibodies.

Instability of immunoglobulin genes in S107 cell line.

Somatic mutation occurs frequently in rearranged and expressed immunoglobulin variable region genes in vivo. In contrast, V region hypermutation seldom occurs in antibody-forming cells in culture. The S107 mouse myeloma cell line is one of the few cell lines that has been observed to generate V region mutations frequently and spontaneously in vitro. Detailed examination reveals that both the S107 tumor and the cell line derived from it contain and express a duplicated heavy-chain gene. In culture, only one of the two heavy-chain genes undergoes both V and C region mutation, and variants with complex phenotypes and genotypes arise as a result of mutation and segregation of these duplicated genes.

Chimeric antibody: potential applications for drug delivery and immunotherapy.

Antibodies, because of their inherent specificity, seem ideal agents for recognizing and destroying malignant cells. When monoclonal antibodies became available, they appeared ideal candidates for use as anti-cancer drugs. However, monoclonal antibodies as currently constituted still have certain inherent limitations. Transfectomas provide an approach to overcoming some of these limitations. Genetically engineered antibodies can be expressed following gene transfection into lymphoid cells. One of the major advantages of expressing genetically engineered antibodies, is that one is not limited to using antibodies as they occur in nature. In particular, non-immunoglobulin sequences can be joined to antibody sequences creating multi-functional chimeric antibodies. Creation of a family of multi-functional chimeric antibodies with a growth factor joined to a combining specificity may be useful in targeting therapy to malignant cells and delivering drugs into specific locales in the human body. Presence of the growth factor may facilitate transcytosis of chimeric antibody across the blood-brain barrier using growth factor receptors. These novel chimeric antibodies constitute a new family of immunotherapeutic molecules for cancer therapy.

Expression and characterization of an antibody binding specificity joined to insulin-like growth factor 1: potential applications for cellular targeting.

To create antibody molecules with improved functional properties, a growth factor (insulin-like growth factor 1, IGF1) was used to replace the constant region of a chimeric mouse-human IgG3 anti-dansyl antibody. The chimeric heavy chain was expressed with an anti-dansyl-specific chimeric kappa light chain. The IgG3-IGF1 chimeric protein retained its specificity for the antigen dansyl. The chimeric proteins bound to the IGF1 receptors of the human lymphoblast IM-9, albeit with reduced affinity, and elicited some of the same biologic effects (increased glucose and amino acid uptake) in human KB cells as did human IGF1, but with reduced specific activity. The reduced affinity and biologic activity may result from several things: the presence of the unprocessed IGF1 moiety, the large size of the IgG3-IGF1 chimeric protein (160 kDa) compared with IGF1 (7 kDa), and three amino acid substitutions in rat IGF1 compared with human IGF1, which may lead to decreased affinity for the human IGF1 receptor. The chimeric proteins show that it is feasible to produce a new family of immunotherapeutic molecules targeted to growth factor receptors.

Somatic diversification of S107 from an antiphosphocholine to an anti-DNA autoantibody is due to a single base change in its heavy chain variable region.

The S107 myeloma cell line expresses the germ-line sequence of the T15 antiphosphocholine (P-Cho) antibody, which is the major antibody made by BALB/c mice in response to P-Cho, either on a variety of bacterial polysaccharides or when attached to a protein carrier. We have previously reported that a somatic mutant of the S107 cell line produces an antibody that has lost the ability to bind P-Cho and has acquired binding for double-stranded DNA. This antibody has a substitution of an alanine for a glutamic acid at residue 35 in the heavy chain variable region. We now show that this amino acid substitution is due to a single A-C transversion, which is the only nucleotide change in the heavy and light chain variable regions. Further, it appears that this change is due to somatic mutation rather than to gene conversion.

Studies on the somatic instability of immunoglobulin genes in vivo and in cultured cells.

We have examined the molecular mechanism and impact of somatic diversification on the T15 heavy chain variable region gene in vivo and in vitro. Somatic point mutation appears to be responsible for the changes we have observed in both hybridomas from early and late in the immune response and in the S107 myeloma cell line in culture. By identifying S107 mutants with decreases in antigen binding, we have shown that a single point mutation can cause the loss of binding to the eliciting antigen and the acquisition of binding to another antigen. Furthermore, in this case a point mutation of the T15 heavy chain variable region gene caused the conversion of an important protective antibody to an autoantibody. While the S107 cell line frequently generates both constant and variable region mutants, hybridomas appear to have relatively stable variable region genes and unstable constant region genes which in some cases result in mutants with increased binding.

The role of monoclonal antibodies and the recombinant DNA technology in studying autoantibody production.

The hybridoma technology has made it possible to sample the B-cell repertoire and to generate monoclonal antibodies which can be analyzed for their specificity and idiotypy. Using the recombinant DNA technology, the structure of the genes which encode those antibodies can be analyzed. The knowledge gained from the application of these techniques has made it possible to pose specific questions about the origins of autoantibodies.