Identification and synthesis of the epitope for a human monoclonal antibody which can neutralize human T-cell leukemia/lymphotropic virus type I

A monoclonal antibody (mAb), designated 0.5 alpha, derived from a patient with adult T-cell leukemia was found previously to neutralize the human T-cell leukemia/lymphotropic type I (HTLV-I) virus in in vitro assays and bind to the major envelope glycoprotein (gp46) of HTLV-I (Matsushita, S., Guroff, M.R., Trepel, J., Crossman, J., Mitsuya, H., and Broder, S. (1986) Proc. Natl. Acad. Sci. U.S.A. 83, 2671-2676). We have designed experiments to determine the epitope for this mAb. Using simultaneous multiple peptide synthesis, we synthesized 481 overlapping octapeptides which corresponded to the sequence of gp46. We mapped the epitope for mAb 0.5 alpha to lie between residues 186 and 195 of gp46. This result was confirmed by independently synthesizing a peptide containing this epitope which bound specifically to mAb 0.5 alpha with an approximate Ka = 4 x 10(7) M-1. In addition, the peptide inhibited mAb 0.5 alpha binding to gp46 derived from T-cells infected with HTLV-I. This epitope containing peptide may facilitate understanding HTLV-1 infection of T-cells.