Abstract: Chimeric retroviral vectors were constructed containing the long terminal repeats (LTRs) from a simple retrovirus (e.g. spleen necrosis virus (SNV); murine leukemia virus (MLV)) devoid of the integration site (att) and more complex retroviral (e.g. bovine leukemia virus (BLV); human immunodeficiency virus (HIV)) cis-acting regulatory sequences (e.g. att; primer binding site (PBS); encapsidation site (E), and polypurine tract (ppt)) and coding regions. Cells transfected with these constructs produce replication competent retrovirus particles. These retroviral particles provide a source of viral antigens that can be employed in both diagnostic assays and as immunogens for the production of high-titer specific antisera.

Abstract: An improved helper cell for growing up stocks of replication incompetent retrovirus vectors is disclosed. The helper cell resists recombination events due to the fact that natural promoters and poly(A) sequences in the helper sequences have been replaced with foreign promoters and poly(A) sequences bearing little or no homology to the vectors. Plasmids containing these modified sequences can still create a helper cell with resulting expression of the needed helper proteins, yet there is much less risk of recombination events in the helper cell. Also disclosed are vectors produced by such helper cells, target cells infected by such vectors, and helper cells which convert vectors so that they can be used with hosts from different species.

Abstract: A recombinant retrovirus vector is disclosed. It is of the type having a normally replication incompetent retrovirus gene sequence with a foreign eukaryotic gene to be expressed. The retrovirus gene sequence is designed so as to be promoter deficient in the right side LTR. The vector can produce progeny virus from helper cells, which progeny can infect a eukaryotic host cell, form a provirus, and express the eukaryotic gene in the host cell. However, the provirus will then be defective in the retrovirus promoter, such that retrovirus RNA is not expressed from the provirus.

Abstract: A helper cell for providing retrovirus protein which is required by a normally replication incompetent recombinant retrovirus gene sequence in order to replicate is disclosed. In one embodiment there is a eukaryotic host cell, a first retrovirus gene sequence in the cell which has a helper portion coding for a retrovirus protein and which is capable of expressing the retrovirus protein, and a defective portion which renders the gene sequence replication imcompetent. In this embodiment, there is also a second retrovirus gene sequence in the cell having a defective retrovirus portThis invention was made with Government support under NIH Grant Nos. P01 CA 22443, P30 CA0 7175 and T32 CA0 9075 awarded by the Department of Health and Human Services. The Government has certain rights in this invention.