Characterization of HTLV envelope seroreactivity in large granular lymphocyte leukemia

T-cell large granular lymphocyte (T-LGL) leukemia is a rare chronic lymphoproliferative disorder of unknown etiology. We have previously reported that patients with T-LGL leukemia were seroreactive against BA21, a 34 amino acid peptide derived from HTLV-I envelope protein p21. We tested sera from 70 patients with T-LGL leukemia and found that 21/70 (30%) of them were seroreactive against fusion peptide GST-BA21. In control group of healthy blood donors 3/30 (10%) were seroreactive. We synthesized a set of overlapping peptides derived from BA21 and tested them against sera from patients. Only a single peptide (p21 env 417-430) showed reactivity. We then generated multiple fusion peptides consisting of 5-14 amino acid residues derived from this peptide and tested them against patient and control sera. Shortest peptide giving positive seroreactivity was octapeptide P8 (p21 env 418-425). Competitive Western blot assay with use of fusion peptides revealed that the minimal HTLV-I epitope responsible for seroreactivity found in patients with T-LGL leukemia is a decapeptide PP10 (p21 env 417-426). Protein Bank (NCBI) search did not reveal any significant homology between PP10 epitope and known human proteins. These results further define the epitope responsible for HTLV env seroreactivity observed in LGL leukemia.