Approximately one-tenth of the 10 million individuals living with human
T-cell leukemia virus type-1 (HTLV-1) worldwide live in Japan. Most of these infected individuals live in the southwest region of Japan, including Okinawa prefecture; however, currently no prophylactic
vaccine against HTLV-1
infection is available. For preventing the HTLV-1 spread, we previously generated a humanized
monoclonal antibody (hu-LAT-27) that mediates both neutralization and antibody-dependent cellular cytotoxicity (ADCC). The neutralization
epitope of LAT-27 is a linear amino acid sequence from residue 191 to 196 (
Leu-Pro-
His-Ser-Asn-Leu) of the HTLV-1 envelope gp46
protein. Here, we found that the LAT-27
epitope is well conserved among HTLV-1 clinical isolates prevalent in Okinawa. The hu-LAT-27 treatment inhibited syncytium formation by these clinical HTLV-1 isolates. Although an amino acid substitution at residue 192 in the LAT-27
epitope from
proline to
serine was found in a few HTLV-1 isolates, hu-LAT-27 could still react with a synthetic
peptide carrying this amino acid substitution. These findings demonstrate the wide spectrum of hu-LAT-27 reactivity, suggesting that hu-LAT-27 may be a candidate drug for prophylactic passive immunization against HTLV-1
infection.