A Deletion in the Proximal Untranslated pX Region of Human T-cell Leukemia Virus Type I1 Decreases Viral Replication But Not Infectivity In Vivo

The function of untranslated (UT) nucleotide sequences in the proximal portion of the pX region of the human T-cell leukemia virus (HTLV) family of retroviruses remains enigmatic. Previous studies have shown that these sequences are not necessary for the expression of viral proteins or for the induction, transmission, or maintenance of the transformed cell type in vitro. To determine the effect of the UT region in vivo, separate groups of rabbits were inoculated with lethally irradiated, stable clones of the human Blymphoblastoid cell line, 729, transfected with either a fulllength wild-type HTLV-II clone (pH6neo) or a mutant clone containing a 324-bp deletion in the proximal UT portion of pX (pH6neoAUl'l6661-69841). or nontransfected 729 cells. All rabbits inoculated with either wild-type or pX-deleted HTLV-II developed a similar profile and titer of serum antibodies against HTLV-II antigens, as determined by Western immunoblots, by 4 weeks postinoculation (PI). Antibody titers, as determined by enzyme immunoassay, were similar between the two groups of rabbits and increased over the