title: A potential therapeutic strategy to combat leukemia virus infection.
abstract: To test the concept that a replication-competent retrovirus carrying a suicide gene could have potential utility in the control of the natural virus infection in mammalian species, we constructed derivatives of a feline leukemia virus (FeLV) that is commonly associated with leukemia-lymphomas in this species. The FeLV, Rickard strain, subgroup A (FRA) genome contained at the 3' end of the envgene, an insert of an internal ribosomal entry site (IRES) linked to cDNA sequence of either herpes simplex virus thymidine kinase (HSV-TK) or a truncated HSV-TK (HSV-ATK) or yeast cytosine deaminase (CD). These constructs were transfected into feline fibroblast cells (H927). The viruses produced were determined to be replication-competent. The stable propagation of the full-length transgene was, however, dependent on the size of the insert, IRES-CD being the smallest in size (1031 bp) exhibiting maximal stability for at least up to six months. The protein products of the transgenes could be detected, despite the appearance of deleted proviruses at late passages. The transduced cells were susceptible to cytotoxic killing when the appropriate prodrug, ganciclovir (GCV), acyclovir (ACV) or 5-fluorocytosine (5-FC) was added to the culture medium. H927 cells, infected with another subgroup of FeLV, namely, FeLV-B or FeLV-C, could be superinfected by the FRA-suicide gene viruses and thus, subjected to killing. Interestingly, at an early stage of infection by the parental FRA, H927 cells could also be reinfected by the same subgroup FRA constructs to induce the suicide effect. Among the three constructs, the vector with the CD gene was determined to be superior to others in terms of stability, therapeutic index and bystander effect in the cell culture test system. While the in vivo correlates of the therapeutic effect in the feline model remain to be determined, our results do encourage investigation of the same concept in the control of HTLV and, perhaps even, HIV infection in humans.
authors.affiliation: Department of Pathology, Keck School of Medicine, University of Southern California, Los Angeles, California 90033, USA.
authors.forename: Judong
authors.initials: J
authors.lastname: Pan
authors.forename: Chen
authors.initials: C
authors.lastname: Zhong
authors.forename: Zongli
authors.initials: Z
authors.lastname: Chang
authors.forename: Pradip
authors.initials: P
authors.lastname: Roy-Burman
mesh_terms: D000212:Acyclovir / Q000494:pharmacology; D000818:Animals; D015153:Blotting, Western; D002415:Cats; D002478:Cells, Cultured; D043525:Cytosine Deaminase; D017931:DNA Primers / Q000737:chemistry; D005347:Fibroblasts / Q000821:virology; D005437:Flucytosine / Q000494:pharmacology; D015774:Ganciclovir / Q000494:pharmacology; D015967:Gene Expression Regulation, Viral; D005822:Genetic Vectors; D049452:Green Fluorescent Proteins; D006801:Humans; D005256:Leukemia Virus, Feline / Q000502:physiology*; D008164:Luminescent Proteins / Q000378:metabolism; D009700:Nucleoside Deaminases / Q000235:genetics / Q000378:metabolism; D016133:Polymerase Chain Reaction; D011355:Prodrugs; D012192:Retroviridae Infections / Q000235:genetics / Q000628:therapy*; D015682:Retroviridae Proteins, Oncogenic / Q000235:genetics* / Q000378:metabolism; D012270:Ribosomes / Q000235:genetics; D012441:Saccharomyces cerevisiae / Q000201:enzymology; D018139:Simplexvirus / Q000201:enzymology; D013937:Thymidine Kinase / Q000235:genetics / Q000378:metabolism / Q000494:pharmacology; D014162:Transfection; D019076:Transgenes; D014412:Tumor Virus Infections / Q000235:genetics / Q000628:therapy*; D014759:Viral Envelope Proteins / Q000235:genetics* / Q000378:metabolism; D014779:Virus Replication
chemical_list: D017931:DNA Primers; D008164:Luminescent Proteins; D011355:Prodrugs; D015682:Retroviridae Proteins, Oncogenic; D014759:Viral Envelope Proteins; C073723:glycoprotein gp70, Feline leukemia virus; D049452:Green Fluorescent Proteins; D005437:Flucytosine; D013937:Thymidine Kinase; D009700:Nucleoside Deaminases; D043525:Cytosine Deaminase; D015774:Ganciclovir; D000212:Acyclovir