The long terminal repeat is not a major determinant of the cellular tropism of human immunodeficiency virus type 1

The long terminal repeats (LTRs) of human immunodeficiency virus type 1 (HIV-1) strains from the central nervous systems of four patients with AIDS and of an HIV-1 isolate which is highly macrophage-tropic were isolated by using the polymerase chain reaction. In transient transfection assays, these LTRs demonstrated no significant difference in basal or stimulated levels of transcription in any of a variety of cell lines tested, compared with expression directed from the LTR of a T-lymphocyte-tropic strain of HIV-1. Chimeric viruses were created with the LTRs of the macrophage-tropic and brain-derived viruses ligated to the viral backbone from a T-lymphocyte-tropic strain. No change in cellular tropism was demonstrated with these chimeric viruses. Thus, unlike the LTRs of some murine retroviruses, the LTR of HIV-1 does not appear to play a major role in determining cellular tropism.