INHIBITION OF MOLONEY MURINE LEUKEMIA VIRUS-INDUCED LEUKEMIA IN TRANSGENIC MICE EXPRESSING ANTISENSE RNA COMPLEMENTARY TO THE RETROVIRAL PACKAGING SEQUENCES

Recombinant plasmids pLP-psi-as and pCP-psi-as were constructed by positioning the Moloney murine leukemia virus (M-MuLV) proviral packaging (psi) sequences in reverse orientation under the transcriptional regulation of lymphotropic promoter/regulatory elements from the M-MuLV long terminal repeat or the cytomegalovirus immediate-early region. Linear fragments containing the antisense-psi and the appropriate transcriptional regulatory sequences from these plasmids were introduced into the mouse germ line by zygote microinjection. The chromosomal integration, germ-line transmission, and lymphocyte-directed expression of the antisense-psi RNA were confirmed. Control (nontransgenic) and transgenic mice containing either the pLP-psi-as or the pCP-psi-as sequences were infected with M-MuLV on the day of birth and assayed for signs of leukemia between 12 and 14 weeks of age with standard assay procedures. While 31% (11 of 36) of the control, nontransgenic, mice developed leukemia, none of the antisense-psi transgenic mice developed any symptoms of leukemia. The pCP-psi-as sequences were also introduced into mouse NIH 3T3 cells and stably transformed cell lines were isolated. When infected with M-MuLV these cells were shown to produce virus devoid of packaged viral RNA.