SYNTHETIC RETROTRANSPOSON VECTORS FOR GENE-THERAPY

New gene therapy methods are rapidly being developed to permit the exp ression of tumor suppressor genes, cytotoxins, anticancer antigens, an d immunoregulatory proteins in the treatment of cancer. Large-scale te sting in humans has been delayed by questions concerning the safety an d effectiveness of preferred retroviral vectors and helper cells. Thes e vector systems are limited by their ability to undergo homologous re combination with endogenous retroviruses or helper-viral sequences, re sulting in release of replication-competent retrovirus (RCR). In addit ion, transcriptional inactivation of the retroviral promoter often occ urs, caused in part by methylation of CpG islands in the retroviral lo ng terminal repeats (LTRs). We report the production of highly specifi c retrovectors using gene amplification together with oligonucleotide building blocks. The synthetic vectors were based on mouse VL30 retrot ransposon NVL3, and lacked homology to retroviral helper gene sequence s. Three of four constructs made by gene amplification yielded biologi cally active vectors. These constructs efficiently transmitted and sta bly inserted a neomycin resistance marker gene into the genome of reci pient cells, expressing an abundant RNA species of the expected size i n the absence of detectable replication competent retrovirus. The vect ors and techniques described enable widely applicable expression modes using generic helper cells, and require only approximately 1.3 kb of cis-acting vector RNA sequences for faithful transfer and expression o f genetic material.