Int J Cancer 1986 Apr 15;37(4):601-6
HTLV-I propagated in IMR90 human diploid fibroblasts was transmitted to human myeloid leukemia HL60 cells at a low efficiency. After co-cultivation for 3 months, the viral genome was detected in 14/48 HL60 cell clones. Among the 14 HTLV-I-infected clones, 8 contained subgenomic fragments alone or in addition to the complete HTLV-I genome. The frequency of deleted proviruses (9/24 total proviruses) was unexpectedly high. Hirt's supernatant of some of the clones harboring complete HTLV-I genome(s) in the chromosome contained both linear and circular HTLV-I proviral DNAs. The circular DNAs were composed of one LTR and 2 LTR closed circular proviruses. These clones produced infectious HTLV-I constitutively, which was proved by transmission of the viral genome into fresh IMR90 cells by co-cultivation. However, in these clones, re-integration of extrachromosomal provirus into their own chromosomes was not observed.