Gessain A, Barin F, Vernant J C, Gout O, Maurs L, Calender A, De The G

Gessain A, Barin F, Vernant J C, Gout O, Maurs L, Calender A, De The G. protein was inhibited by human sera with different neutralizing specificities. We thus identified two amino acid changes, I173V and A187T, that play an important role in the antigenicity of neutralizable epitopes located in this region of the surface envelope glycoprotein. Human T-cell leukemia virus type 1 (HTLV-1) is the etiologic agent of adult T-cell AZD-0284 leukemia and a chronic neurological disease, tropical spastic paraparesis or HTLV-1-associated myelopathy (14, 19, 29, 31, 39). The virus infects 10 to 20 million persons worldwide, 4% of whom will develop one of these diseases. In common with that of other retroviruses, the entry of HTLV-1 into the target cell is mediated by the viral envelope glycoproteins. These are two noncovalently linked subunits, a 46-kDa surface glycoprotein (SU) which is responsible CSF2RB for attachment of the virus to a cell surface receptor and a 21-kDa transmembrane glycoprotein (TM) which fuses the viral envelope to the target cell membrane, allowing penetration of the viral core into the cytoplasm. Several regions involved in viral entry have been identified on the HTLV-1 envelope glycoproteins by the use of neutralizing antibodies or peptides that inhibit fusion (1, 2, 10, 17, 30, 38) and by functional analysis (7, 8, 32). HTLV-1 is distributed worldwide but exhibits relatively little sequence variation. HTLV-1 strains from Japan, Africa, the West Indies, and the Americas and belonging to the cosmopolitan clade have at least 95% sequence similarity. AZD-0284 More distantly related strains displaying 8% nucleotide sequence variation have been found in remote populations from the Solomon Islands, Papua New Guinea, and Australia (15). HTLV-1 infection has been successfully transmitted to rats, rabbits, and monkeys in the laboratory (25, 27, 37). This infection can be prevented by passive immunization with immunoglobulins purified from HTLV-1-infected patients (21, 26, 33) or by vaccination with various versions of HTLV-1 envelope proteins (3, 12, 18, 22, 27, 36). These observations suggest that genetically engineered HTLV-1 envelope proteins or synthetic peptide-based subunits could be used in a vaccine against HTLV-1. However, protective humoral and cellular immune responses elicited by vaccine components could be foiled by the existence of different antigenic forms of HTLV-1 proteins. In this respect, incomplete cross-reactivity between some cosmopolitan and Melanesian strains of HTLV-1 has been reported (4). More recently, we AZD-0284 showed that sera from some patients infected with cosmopolitan HTLV-1 strains with only a few amino acid changes in their envelope glycoproteins displayed different neutralization patterns (5). These patterns could be classified into three categories that fit well with groups of viruses each harboring the same residues in the major immunodominant and neutralizable domain (amino acids [aa] 175 to 199) of SU. Since within each group, different amino acids could be substituted at other positions, the residues involved in the observed differences have yet to be identified. To identify the amino acid changes involved in the antigenic specificity of neutralizable epitopes, we constructed expression vectors coding for the envelope proteins of two HTLV-1 isolates (2060 and 2072) which induced human antibodies with different neutralization patterns. The serum of the patient infected with virus 2060 completely neutralized cosmopolitan HTLV-1 of the three groups mentioned above, whereas the serum of the virus 2072-infected patient had a higher neutralization potential against the autologous virus than against cosmopolitan viruses of the other two groups. The amino acid sequences of the envelope glycoproteins of viruses 2060 and 2072 differed at four positions located in surface gp46. Vectors coding for chimeric or point-mutated envelope proteins were derived from 2060 and 2072 HTLV-1 genes. Their ability to induced syncytium formation after transfection in COS-LTRHIV-LacZ cells was assessed, as was the inhibition of syncytium formation by sera from HTLV-1-infected patients. MATERIALS AND METHODS Sera. Human sera used for syncytium inhibition were provided by J. C. Vernant (La Meynard Hospital, Fort-de-France, Martinique), J. F. Moreau and J. L. Sarthou (Institut Pasteur de Guyane, Cayenne, Cayenne, French Guiana), S. Sainte-Foie and C. Hajjar (Centre Hospitalier Intercommunal de Basse-Terre/Sainte-Claude, Basse-Terre, Guadeloupe), and M. C. Georges-Courbot (CIRMF, Franceville, Gabon). All sera were heated for 30 min at 56C before use. The presence of HTLV-1 antibodies in these sera was assessed with a commercially available Western blot diagnostic kit.