Genetically engineered antibodies in gene transfer and gene therapy

Towards Physiologically and Tightly Regulated Vectored Antibody Therapies

Cancers represent highly significant health issues and the options for their treatment are often not efficient to cure the disease. Immunotherapy strategies have been developed to modulate the patient's immune system in order to eradicate cancerous cells. For instance, passive immunization consists in the administration at high doses of exogenously produced monoclonal antibodies directed either against tumor antigen or against immune checkpoint inhibitors. Its main advantage is that it provides immediate immunity, though during a relatively short period, which consequently requires frequent injections. To circumvent this limitation, several approaches, reviewed here, have emerged to induce in vivo antibody secretion at physiological doses. Gene delivery vectors, such as adenoviral vectors or adeno-associated vectors, have been designed to induce antibody secretion in vivo after in situ cell modification, and have driven significant improvements in several cancer models. However, anti-idiotypic antibodies and escape mutants have been detected, probably because of both the continuous expression of antibodies and their expression by unspecialized cell types. To overcome these hurdles, adoptive transfer of genetically modified B cells that secrete antibodies either constitutively or in a regulated manner have been developed by ex vivo transgene insertion with viral vectors. Recently, with the emergence of gene editing technologies, the endogenous B cell receptor loci of B cells have been modified with the clustered regularly interspaced short palindromic repeats (CRISPR)/CRISPR-associated endonuclease (Cas-9) system to change their specificity in order to target a given antigen. The expression of the modified BCR gene hence follows the endogenous regulation mechanisms, which may prevent or at least reduce side effects. Although these approaches seem promising for cancer treatments, major questions, such as the persistence and the re-activation potential of these engineered cells, remain to be addressed in clinically relevant animal models before translation to humans.

Phase I/II clinical trial of encapsulated, cytochrome P450 expressing cells as local activators of cyclophosphamide to treat spontaneous canine tumours

Based upon promising preclinical studies, a clinical trial was performed in which encapsulated cells overexpressing cytochrome P450 enzyme isoform 2B1 were implanted around malignant mammary tumours arising spontaneously in dogs. The dogs were then given cyclophosphamide, one of the standard chemotherapeutic agents used for the treatment of mammary tumours. The dogs were assessed for a number of clinical parameters as well as for reduction in tumour size. The treatment was well tolerated with no evidence of adverse reactions or side effects being associated with the administration of the encapsulated cells. Reductions in tumour size of more than 50% were observed for 6 out of the 11 tumours analysed while 5 tumours showing minor responses, i.e. stable disease. In contrast, the tumours that received cyclophosphamide alone showed only stable disease. Taken together, this data suggests that encapsulated cytochrome P450 expressing cells combined with chemotherapy may be useful in the local treatment of a number of dog mammary tumours and support the performance of further clinical studies to evaluate this new treatment.

Persistent expression of biologically active anti-HER2 antibody by AAVrh.10-mediated gene transfer

Trastuzumab (Herceptin) is a recombinant humanized monoclonal antibody directed against an extracellular region of the HER2 protein. We hypothesized that a single adeno-associated virus mediated genetic delivery of an anti-HER2 antibody should be effective in mediating long term production of anti-HER2 and in suppressing the growth of human tumors in a xenograft model in nude mice. The adeno-associated virus gene transfer vector AAVrh.10αHER2 was constructed based on non-human primate AAV serotype rh.10 to express the cDNAs for the heavy and light chains of monoclonal antibody 4D5, the murine precursor to trastuzumab. The data demonstrates that genetically transferred anti-HER2 selectively bound human HER2 protein and suppressed proliferation of HER2 positive tumor cell lines. A single administration of AAVrh.10αHER2 provided long term therapeutic levels of anti-HER2 antibody expression without inducing anti-idiotype response, suppressed the growth of HER2 positive tumors and increased survival of the tumor-bearing mice. In the context that trastuzumab therapy requires frequent, repeated administration, this strategy might be developed as an alternate platform for delivery anti-HER2 therapy.

Intracellular expression of a single-chain antibody directed against type IV collagenase inhibits the growth of lung cancer xenografts in nude mice

It was documented that type IV collagenase with two subtypes of 72 ku/MMP-2 and 92 ku/MMP-9 plays an important role in tumor invasion and metastasis. The endoplasmic reticulum (ER)-retained, single chain Fv antibody fragment (scFv) was used to inhibit the function of type IV collagenase. For expression in mammalian cells, the assembled scFv M97 gene with ER retention signal encoding 6 additional amino acids (SEKDEL) was reamplified by PCR. The amplified fragments were cloned into the pcDNA3.1 vector. The resulting plasmid was sequenced and then introduced into PG cells, a highly metastatic human lung cancer cell line, by lipofectAMINE method. The result of intrabody gene therapy showed that type IV collegenase expression was down regulated significantly as measured by ELISA. The biological behavior of PG cell, such as the ability of in vitro invasion through Matrigel, colony formation on soft agar, was also inhibited by scFv M97 transfection. Animal experiments in a xenograft model of human lung cancer showed that scFv M97 transfection significantly prolonged the survival time of nude mice. The results indicate that intracellular antibody technology represents a novel and efficient way to abrogate selectively the activity of type IV collagenase.

Secreted Antibody/Granzyme B Fusion Protein Stimulates Selective Killing of HER2-overexpressing Tumor Cells

Targeted cell killing is required for effective treatment of cancers. We previously described the generation of a chimeric immunocasp-3 protein and its potent selective antitumor activity (Jia, L. T., Zhang, L. H., Yu, C. J., Zhao, J., Xu, Y. M., Gui, J. H., Jin, M., Ji, Z. L., Wen, W. H., Wang, C. J., Chen, S. Y., and Yang, A. G. (2003) Cancer Res. 63, 3257-3262). Here we extend the repertoire of another chimeric pro-apoptotic protein immunoGrB, which comprises an anti-HER2 single-chain antibody, a Pseudomonas exotoxin A translocation domain and active granzyme B. Human lymphoma Jurkat cells transfected with the immunoGrB gene expression vector were able to produce and secrete the chimeric protein. The immunoGrB molecule selectively recognized and destroyed HER2-overexpressing tumor cells both in vitro and in nude mouse after intramuscular injection of the immunoGrB expression plasmid. Further in vivo study showed that intravenous administration of immunoGrB gene-modified lymphocytes led to suppression of HER2-overexpressing tumor growth and prolonged animal survival because of continuous secretion of immunoGrB molecules into blood and lymph fluid. These results demonstrate that the chimeric immunoGrB molecule, which is capable of antibody-directed targeting and granzyme B-mediated killing, has therapeutic potential against HER2 tumors, especially in cases in which caspase-dependent apoptosis is inhibited.

Monoclonal antibody 667 recognizes the variable region A motif of the ecotropic retrovirus CasBrE envelope glycoprotein and inhibits Env binding to the viral receptor

Monoclonal antibody (MAb) 667 is a neutralizing mouse monoclonal antibody recognizing the envelope glycoprotein (Env) of the ecotropic neurotropic murine retrovirus CasBrE but not that of other murine retroviruses. Since 667 can be used for preclinical studies of antiviral gene therapy as well as for studying the early events of retroviral infection, we have cloned its cDNAs and molecularly characterized it in detail. Spot technique-based experiments showed that 667 recognizes a linear epitope of 12 amino acids located in the variable region A of the receptor binding domain. Alanine scanning experiments showed that six amino acids within the epitope are critical for MAb binding. One of them, D(57), is not present in any other murine retroviral Env, which suggests a critical role for this residue in the selectivity of 667. MAb 667 heavy- and light-chain cDNAs were functionally characterized by transient transfection into Cos-7 cells. Enzyme-linked immunosorbent assays and Biacore studies showed that the specificities as well as the antigen-binding thermodynamic and kinetic properties of the recombinant 667 MAb (r667) produced by Cos-7 cells and those of the parental hybridoma-produced MAb (h667) were similar. However, h667 was shown to contain contaminating retroviral and/or retrovirus-like particles which interfere with both viral binding and neutralization experiments. These contaminants could successfully be removed by a stringent purification protocol. Importantly, this purified 667 could completely prevent retrovirus binding to target cells and was as efficient as the r667 MAb produced by transfected Cos-7 cells in neutralization assays. In conclusion, this study shows that the primary mechanism of virus neutralization by MAb 667 is the blocking of the retroviral receptor binding domain of CasBrE Env. In addition, the findings of this study constitute a warning against the direct use of hybridoma cell culture supernatants for studying the initial events of retroviral cell infection as well as for carrying out in vivo neutralization experiments and suggest that either recombinant antibodies or highly purified antibodies are preferable for these purposes.

[Cancer genetic immunotherapy]

The concept of cancer immunotherapy and the resulting technical advances have evolved considerably during the last decade. However, cancer treatment by recombinant IL-2 or IFN-alpha still represents today the best therapeutic way for the treatment of renal carcinoma, melanoma and in some cases lymphoma. The immunotherapy approaches such as vaccination, gene and cellular therapy, have not yet demonstrated a sufficient clinical efficacy for the treatment of solid tumors. The goal of this review is to summarize the different approaches to cancer immunotherapy developed today. Specific approaches such as antigenic vaccination will be first described, then non-specific approaches such as gene transfer on the tumor site of immuno-stimulating genes will be discussed.

Genetically engineered intracellular single-chain antibodies in gene therapy

The delineation of the molecular basis of cancer allows for the possibility of specific intervention at the molecular level for therapeutic purposes. To a large extent, the genetic lesions associated with malignant transformation and progression are being identified. Thus, not only in the context of inherited genetic diseases, but also for many acquired disorders, characteristic aberrancies of patterns of gene expression may be precisely defined. It is therefore clear that elucidation of the genetic basis of inherited and acquired diseases has rendered gene therapy both a novel and rational approach for these disorders. To this end, three main strategies have been developed: mutation compensation, molecular chemotherapy, and genetic immunopotentiation. Mutation compensation relies on strategies to ablate activated oncogenes at the level of DNA (triplex), messenger RNA (antisense or ribozyme), or protein (intracellular single-chain antibodies), and augment tumor suppressor gene expression. This article will review in detail practical procedures to generate a single-chain intracellular antibody (scFv). We will emphasize in this article the different steps in our protocol that we have employed to develop scFvs to a variety of target proteins.

High in vivo production of a model monoclonal antibody on adenoviral gene transfer

The therapeutic potential of monoclonal antibodies (MAbs) for treating a variety of severe or life-threatening diseases is high. Although intravenous infusion appears to be the simplest and most obvious mode of administration, it is not applicable in many long-term treatments. It might, however, be advantageously replaced by gene/cell therapies, rendering treatments cost-effective and eliminating the short- and long-term side effects associated with injection of massive doses of antibodies. Grafting of ex vivo genetically modified cells of various types has already been used for in vivo production and systemic delivery of MAbs in mice. However, although sustained for long periods of time, serum levels of ectopic MAbs were low. We show here that in vivo administration to mice of a first-generation adenoviral vector expressing a model MAb also permits achievement of the same goal, but with 100 to 200 times better efficiency that in any other case of gene transfer described thus far. We also investigated for possible anti-idiotypic response against the ectopic MAb. None was detected in the animals expressing the lowest levels of ectopic MAb production; a response was detected among the highest producers. In the latter case, however, the response was low and could not exert any significant neutralizing activity. In conclusion, our work indicates that high levels of circulating ectopic MAb can be obtained on direct in vivo gene transfer without inducing an anti-idiotypic response sufficiently robust to exert a neutralizing effect. This observation is encouraging in the perspective of clinical applications of this technology.

Skin as a potential organ for ectopic monoclonal antibody production

The therapeutic potential of monoclonal antibodies for treating a variety of severe or life-threatening diseases is high. Although intravenous infusion appears the simplest and most obvious mode of administration, it is not applicable to many long-term treatments. It might be advantageously replaced by gene/cell therapies, however, rendering treatments cost-effective and eliminating the short- and long-term side-effects associated with injection of massive doses of antibodies. We have tested whether skin can potentially be used as an organ for production and systemic delivery of ectopic antibodies. Normal human primary keratinocytes were shown to be capable of synthesis and secretion of a model monoclonal antibody directed against human thyroglobulin upon retroviral gene transduction in vitro. Neo- epidermis reconstructed in vitro, either in cell culture inserts or on dermal substrates, from such modified keratinocytes also produced the monoclonal antibody. Interestingly, the latter could cross the epidermis basal layer and be released in culture fluids. Finally, grafting of epidermis reconstituted in vitro on dermal substrates to SCID mice permitted sustained monoclonal antibody delivery into the bloodstream to be achieved. Our data thus show that genetically engineered keratinocytes can potentially be used for genetic antibody-based immunotherapies. They also indicate that proteins as big as 150 kDa, after release by engineered keratinocytes into skin intercellular spaces, can migrate to the general circulation, which is potentially important for a number of other gene-based therapies.

Experimental utility of rabies virus-neutralizing human monoclonal antibodies in post-exposure prophylaxis

Rabies immune globulin (RIG) is essential for post-exposure prophylaxis but is expensive and not widely available. Rabies virus-neutralizing human monoclonal antibodies (Mabs) were evaluated in vitro and in a Syrian hamster model as a potential future alternative. Seven Mabs neutralized representative rabies virus variants. However, a European bat lyssavirus was not neutralized by either Mabs or RIG. Moreover, Duvenhage virus was neutralized by RIG, but not by Mabs, and Lagos bat and Mokola viruses were neutralized by one Mab but not by RIG. In hamsters, one Mab resulted in protection that was comparable to human RIG. These results suggest that Mabs may provide a promising alternative to RIG.

Targeted macrophage cytotoxicity using a nonreplicative live vector expressing a tumor-specific single-chain variable region fragment

Antigen-specific recognition and subsequent destruction of tumor cells is the goal of vaccine-based immunotherapy of cancer. Often, however, tumor antigen-specific cytotoxic T lymphocytes (CTLs) are either not available or in a state of anergy. In addition, MHCI expression on tumor cells is often downregulated. Either or both of these situations can allow tumor growth to proceed unchecked by CTL control. We have shown previously that tumor antigen-specific monoclonal antibodies can be expressed in vaccinia virus and that activated macrophages infected with this virus acquire the ability to kill tumor cells expressing that antigen. Here we show that a membrane-anchored form of the scFv portion of the MUC1 tumor antigen-specific monoclonal antibody, SM3, can be expressed on activated macrophages with the highly attenuated poxvirus, modified vaccinia Ankara (MVA), as a gene transfer vector. Cells infected with the MVA-scFv construct were shown to express the membrane-bound scFv by Western blot and FACS analysis. That cells expressing the membrane-anchored scFv specifically bind antigen was shown by FACS and by BIAcore analysis. GM-CSF-activated macrophages were infected with the construct and shown to recognize specifically MUC1-expressing tumor cells as measured by IL-12 release. Furthermore, activated macrophages expressing the membrane-bound scFv specifically lyse target cells expressing the MUC1 antigen but not cells that do not express MUC1.

Antiviral activity of an intracellularly expressed single-chain antibody fragment directed against the murine leukemia virus capsid protein

We have addressed the possibility that intracellularly expressed miniantibodies directed against the viral capsid protein can be used as antiretroviral agents in gene transfer experiments. R187 is a rat monoclonal antibody that has been reported to recognize the MuLV p30gag capsid polypeptide. We report here that it also binds to the Pr65gag precursor polyprotein. R187 has been cloned and expressed in the form of a single-chain variable fragment (scFv) that shows the same binding specificity as the parental antibody. When expressed intracellularly, the R187 scFv favors the production of viral particles showing reduced infectivity. It, however, exerts no detectable protective effect against infection. This was observed both when using replication-incompetent MuLV-derived vector and replication-competent wild-type MuLV. Although the intimate mechanism of the inhibition is not clear, this work raises the possibility that gene engineering of anti-capsid protein scFvs may offer an additional lead for gene therapy of severe retrovirus-linked diseases.

Extended half-life and elevated steady-state level of a single-chain Fv intrabody are critical for specific intracellular retargeting of its antigen, caspase-7

8 h) and high steady-state levels of protein accumulation, while the H2 intrabodies had a half-life of 2 h and less protein at steady state. These results suggest that the choice of sFv as an intrabody depends critically on the intracellular sFv protein having an extended half-life and elevated steady-state level. Thus, extended half-life must be considered together with sFv antibody specificity and affinity when choosing an optimal sFv intrabody for functional studies of cellular proteins.

Strategy of liver-directed gene therapy: present status and future prospects

The liver is particularly amenable to gene therapy as it is the site of many metabolic diseases and malignancies. Thus, liver-directed gene therapy is being actively pursued and developed as a method of treatment for various liver diseases. Strategies of liver-directed gene therapy include drug delivery to the liver, compensation of the defective gene(s), anti-tumor activity, anti-viral therapy, and immunomodulation. The strategy chosen for liver-directed gene therapy depends on the genetic basis of the disease. Many aspects are key factors to the success of the chosen strategy: intervention of genes, efficient gene delivery system, stable transgene expression, transgene regulation, target cell transfection, and timing of transgene expression. Several tactics can be used to overcome problems in the above, and these include the use of a gene switch to exogenously regulate transgene expression, targeting at the transcriptional level, circumvention of the immune response (as in the use of adenovirus vector to achieve long-term correction of genetic diseases), and genetically engineered antibodies in gene transfer. At the present rate of research activity and development, gene therapies may soon be more efficient than current standard treatments for some liver diseases.