Gene Transfer of a Chimeric Trans-Activator Is Immunogenic and Results in Short-Lived Transgene Expression

Abstract

Pharmacologic gene regulation is a key technology, necessary to achieve safe, long-term gene transfer. The approaches described in the scientific literature all share in common the creation of artificial transcription factors by fusing a DNA-binding domain, a drug-binding domain and a transcription activation domain. These transcription factors activate the transgene expression upon binding of the pharmacologic agent (antibiotics of the tetracycline family, insect hormone, progesterone antagonist, or immunosuppressor drug) to the drug-binding domain. The major limitations to the use of these systems for human gene and cell therapies are the toxicity of the inducer molecule and the immunogenicity of the chimeric transcription factor. Thus, the gene regulation systems should operate with clinically approved drugs with safety records that do not conflict with the therapeutic gene expression regimen. This work focuses on the characterization of the immunogenicity of a tetracycline-activated transcription factor commonly used in preclinical gene therapy, rtTA2-M2, and its impact on reporter gene expression. We demonstrate that intramuscular injection of plasmid or adenoviral vectors encoding rtTA-M2 in outbred primates generates a cellular and humoral immune response to this transcription factor. The immune response to rtTA2-M2 blunts the duration of the expression the rtTA2-M2-controlled transgene in primates, presumably by destruction of the cells that coexpress rtTA2-M2 and the reporter or therapeutic gene. This immune response may result directly from the vectors used in this study, which prompts the development of new gene transfer vectors enabling safe and efficient pharmacologic gene regulation in clinic.

Skeletal muscle cells: from local inflammatory response to active immunity

“…Most importantly, the toxicity of the inducer molecule and the immunogenicity of the chimeric transcription factor are the major limitations to the use of this system for human gene and cell therapies: a strong cellular and humoral immune response to the transactivator leads to the loss of transgene expression, probably by the destruction of transgene expressing cells. 6,7 Gene therapy application would be broadened by developing systems that can finely reduce the potential of eliciting an immune response.…”

How not to be seen: immune-evasion strategies in gene therapy

“…Simple intramuscular injection of plasmid or adenoviral vectors encoding rtTA in primates generates a cellular and humoral immune response against the transactivator protein and results in the destruction of the genemodified cells. 11 Although extensive evolution yielded improved transactivator proteins, which require lower amounts of the activator, the transactivator proteins remain very immunogenic.…”

Gene therapy progress and prospects: transcription regulatory systems

“…10 The Tet-system is apparently not immunogenic in several mouse strains; in contrast, recent studies indicate that intramuscularly delivered Tet-ON activators may elicit a cellular and humoral response in non-human primates. 11,12 More studies will be required to clarify the potential for immunogenicity in humans.…”