EVALUATION OF CATIONIC LIPOSOMES FOR DELIVERY OF DIPHTHERIA-TOXIN A-CHAIN GENE TO CELLS INFECTED WITH BOVINE LEUKEMIA-VIRUS

We investigated whether cationic liposomes are efficient at delivering the gene for diphtheria toxin A-chain (DT-A) under the control of the long terminal repeat (LTR) of bovine leukemia virus (BLV) (pLTR-DT) i nto BLV-infected cells and are also suitable for in vivo use. The tran sfection activity of the cationic liposomes composed of lpha-trimethyl ammonioacetyl)-didodecyl-D-glutamate chloride (TMAG), dioleoyl phospha tidylethanolamine (DOPE) and dilauroyl phosphatidylcholine (DLPC) (1:2 :2, molar ratio) (TMAG-liposome) and liposomes composed of phosphatidy lserine (PS) (PS-liposome) was evaluated by the luciferase assay using a plasmid which contains the coding sequence of firefly luciferase un der the control of the SR alpha: promoter (pSR alpha/L-A Delta 5). The TMAG-liposome gave highly efficient transfection in the presence of s erum. On the other hand, PS-liposome showed inferior efficiency. When BLV-infected cells were co-transfected with a fixed amount of pSR alph a/L-A Delta 5-entrapped TMAG-liposome and various amount of pLTR-DT-co ntaining TMAG-liposome, the luciferase activity in the BLV-infected ce lls was inhibited by the addition of pLTR-DT-entrapped TMAG-liposome d ose-dependently. The cationic TMAG-liposome containing pLTR-DT was suc cessively added to BLV-infected cells in culture. The number of viable cells was markedly reduced by the cationic TMAG-liposome containing p LTR-DT. On the other hand, TMAG-liposome containing pSR alpha L-A Delt a 5 showed no such effect. pLTR-DT entrapped by the cationic TMAG-lipo some was not digested by the treatment with DNase I and with serum. Th ese results suggest that the cationic liposomes, such as TMAG-liposome , may be efficient transfection reagent for the BLV-infected cells and can be utilized for DT-A gene delivery into the BLV-infected cells in vivo.