Construction and characterization of efficient, stable and safe replication-deficient foamy virus vectors

Abstract

As serious side effects affected recent virus-mediated gene transfer studies, novel vectors with improved safety profiles are urgently needed. In the present study, replicationdeficient retroviral vectors based on feline foamy virus (FFV) were constructed and analyzed. The novel FFV vectors are devoid of almost the complete env gene plus the internal promoter -accessory bel gene cassette including the gene for the viral transcriptional transactivator Bel1/Tas. In these Bel1/Tas-independent vectors, expression of the lacZ (b-galactosidase) marker gene is directed by the heterologous, constitutively active human ubiquitin C promoter (ubi). Env-transcomplemented vectors have unconcentrated titers of more than 10 5 transducing units/ml.The vectors allow efficient transduction of a broad array of diverse target cells, which can be increased by repeated vector exposure. However, the number of lacZ marker gene expressing cells decreased slightly upon serial passages of the transduced cells. Vectors carrying a self-inactivating (SIN) deletion of the TATA box and most parts of the viral promoter were not rescued by wt FFV whereas those with the intact or a partially deleted promoter were readily reactivated. This finding indicates that the viral promoters are in fact non-functional, pointing to a highly advantageous safety profile of these new FFV-ubi-lacZ-SIN vectors.

Development of Foamy Virus Vectors for Gene Therapy for Neurological Disorders and Other Diseases

“…In addition to the prototypic PFV (Trobridge et al, 1998;Heinkelein et al, 1998;Trobridge et al, 2002;Schmidt et al, 1995;Nestler et al, 1997;Heinkelein et al, 2002), a variety of FV vectors have been developed, including simian foamy virus type 1 (SFV-1, macaque) (Wu et al, 1998;Park et al, 2002) and feline foamy virus (FFV) (Bastone et al, 2006;Bastone et al, 2007). A series of vectors and helper plasmids derived from SFV-1 have been constructed, and the minimum vector sequence required for efficient gene transduction has been established.…”

“…The use of viral mediated gene transfer is challenged by serious defects, yet they remain a potential tool of gene therapy for various diseases (Bastone et al, 2007). Therefore, it is critical to find a refined vector that is efficient and safe for treatment of the diseases, especially for nervous system therapy.…”

New Vectors for Stable and Safe Gene Modification

“…These properties make them a very attractive tool for gene therapy. Novel FVV vectors are devoid of the env gene and the internal promoter (Bel1/Tas-independent vectors) and the expression is directed by a heterologous human promoter (Trobridge et al, 2002;Bastone et al, 2007). For a long time, the low FVV titers have been a major hurdle for FVV clinical applications.…”

Progress and prospects: Foamy virus vectors enter a new age

“…Similar self-inactivating feline foamy virus virus vectors have been produced that are capable of longterm transduction in cell lines. 23 Foamy virus vectors are more efficient than gammaretroviral vectors in transducing quiescent cells, but unlike lentiviral vectors, they fail to transduce truly resting cells in which foamy viruses accumulate close to the centrosome, but uncoating is impaired. On stimulation, however, disassembly and viral infection proceeds, indicating that uncoating is the rate-limiting step for productive foamy virus infection of growth-arrested cells.…”

“…22 There is an additional risk with ORV vectors of a read-through into host sequences, resulting in fusion proteins with unforeseen characteristics, if the termination of transcription at the 3 0 end of the viral genome is not tightly controlled. In feline foamy virus the read-through from the 3 0 LTR into neighbouring genes is a more stringent process, resulting in termination at the 3 0 end 23 and this may hold for PFV as discussed by Rethwilm. 13 Once integration is complete, subsequent gene expression from the integrated genes transported by the vector can be silenced by host factors, switching off continuous expression.…”