Sequence variations in LTR and env regions of HTLV-I do not discriminate between the virus from patients with HTLV-I-associated myelopathy and adult T-cell leukemia.

For detailed comparison of human T-cell leukemia virus type I (HTLV-I) in adult T-cell leukemia (ATL) and HTLV-I-associated myelopathy (HAM), the nucleotide sequences of parts of the long terminal repeat (LTR) and env regions of the HTLV-I proviruses from 12 patients with HAM, 8 patients with ATL and one with both diseases were analyzed. About 340 bp of the LTR U3 region, about 450 bp of the 5' region and about 280 bp of the 3' region of env were sequenced directly in DNAs amplified by the polymerase chain reaction (PCR) with 2 or 3 sets of primers for each region. Nucleotide insertions, deletions or point mutations were observed at 50 positions in these regions of about 1,000 nucleotides length. None of these changes was specific to either HAM or ATL, and some changes were observed in proviruses from both cases of HAM and ATL. Moreover, the sequences of proviruses isolated from pairs of cell lines established from cerebrospinal fluid (CSF) and peripheral blood mononuclear cells (PBMCs) of the 4 patients with HAM also had different sequences. These results indicate that the proviruses from HAM and ATL are indistinguishable in these sequenced regions, suggesting that these 2 diseases are caused by infection with genetically indistinguishable HTLV-I. Therefore, the reason why these two distinct diseases, HAM and ATL, develop in HTLV-I carriers may be based on a host factor(s) or some other factor(s) rather than variation in the virus itself.