Local character of readthrough activation in adenovirus type 5 early region 1 transcription control

Strong foreign promoters contribute to innate inflammatory responses induced by adenovirus transducing vectors

E1-deleted adenovirus (FG Ad) transducing vectors are limited for use in vivo by their induction of strong innate and adaptive inflammatory responses. We have examined the contribution of the transgene cassette, particularly the foreign promoter driving transgene expression, in the induction of innate inflammation using a mouse ear model in which swelling is measured as a sensitive surrogate marker of the total innate inflammatory response. The commonly used cytomegalovirus major immediate early (CMV) promoter led to high-level swelling that was independent of transgene expression, while the Rous sarcoma virus and human ubiquitin C promoters led to intermediate levels of swelling and the Ad E1A promoter or no promoter led to equally low levels of swelling. Significant swelling was induced by a virus in which the E1A promoter directed pIX expression, supporting the possibility that activation of expression of Ad genes retained in the vector plays an important role in the inflammatory response. Taken together, our findings support the idea that strong foreign promoters likely play the limiting role in the induction of innate and adaptive immune responses that limit the duration of transgene expression after transduction by FG Ad vectors.

Read-through activation of transcription in a cellular genomic context

Read-through transcription from the adjacent E1a gene region is required for wild-type (wt) activity of the downstream adenovirus E1b promoter early after infection (read-through activation). However, whether a cellular chromosomal template can support read-through activation is not known. To address this issue, read-through activation was evaluated in the context of stably expressed templates in transfected cells. Inhibition of read-through transcription by insertion of a transcription termination sequence between the E1a and E1b promoters reduced downstream gene expression from stably integrated templates. The results indicate that the mechanism of read-through activation does not depend on the structure of early adenovirus nucleoprotein complexes, a structure that is likely to be different from that of cellular chromatin. Accordingly, this regulatory interaction could participate in the coordinated control of the expression of closely linked cellular genes.

An inducible system for highly efficient production of recombinant adeno-associated virus (rAAV) vectors in insect Sf9 cells

Production of clinical-grade gene therapy vectors for human trials remains a major hurdle in advancing cures for a number of otherwise incurable diseases. We describe a system based on a stably transformed insect cell lines harboring helper genes required for vector production. Integrated genes remain silent until the cell is infected with a single baculovirus expression vector (BEV). The induction of expression results from a combination of the amplification of integrated resident genes (up to 1,200 copies per cell) and the enhancement of the expression mediated by the immediate-early trans-regulator 1 (IE-1) encoded by BEV. The integration cassette incorporates an IE-1 binding target sequence from wild-type Autographa californica multiple nuclear polyhedrosis virus, a homologous region 2 (hr2). A feed-forward loop is initiated by one of the induced proteins, Rep78, boosting the amplification of the integrated genes. The system was tested for the coordinated expression of 7 proteins required to package recombinant adeno-associated virus (rAAV)2 and rAAV1. The described arrangement provided high levels of Rep and Cap proteins, thus improving rAAV yield by 10-fold as compared with the previously described baculovirus/rAAV production system.