Persistently Human Immunodeficiency Virus Type 1‐infected T Cell Clone Expressing Only Doubly Spliced mRNA Exhibits Reduced Cell Surface CD4 Expression

Several cell clones possessing the human immunodeficiency virus type 1 (HIV‐1) genome, consisting of an almost full‐length DNA sequence, were isolated by limiting dilution of the clonal cell line M10 derived from MT‐4 that survived infection with HIV‐1 vpr mutant (M10/vpr(−)). One of the isolated clones (termed Vpr‐1) expressed only doubly spliced mRNA, but not unspliced or singly spliced mRNA. Western blots of Vpr‐1 revealed the presence of the nef translation product, although no expression of major structural genes such as gag, pol, and env was detected by indirect immunofluorescence and assay of reverse transcriptase activity. These HIV‐1 phenotypes differed greatly from those of the original M10/vpr(−), most of which expressed major structural HIV‐1 proteins. Despite undetectable levels of env expression in Vpr‐1, CD4 antigens were greatly down‐modulated on the surface without alteration of steady‐state levels of CD4 mRNA expression, similar to M10/vpr(−). These HIV‐1 phenotypes in Vpr‐1 did not change after the treatment of the cells with both phorbol 12‐myristate 13‐acetate and phytohemagglutinin. Therefore, the abnormal HIV‐1 life cycle in Vpr‐1 seems to be due to some viral factor(s), as well as cellular factors. Thus, Vpr‐1 could be a useful model for understanding one HIV‐1 latent form.