VIROLOGY 169,27-33 (1989) Antigenic Variants of Bovine Leukemia Virus (BLV) Are Defined by Amino Acid Substitutions in the NH2 Part of the Envelope Glycoprotein gp51 DANIEL PORTETELLE,*,’ DOMINIQUE COUEZ,t CLAUDINE BRUCK,t RICHARD KEl-FMANN,* MARC MAMMERICKX,+ MARTIN VAN DER MAATENJ ROBERT BRASSEUR,” AND ARSiNE BURNY*? *Faculty of Agronomy, 5800 Gembloux, Belgium; tDepartment of Molecular Biology, University of Brussels, 1640 Rhode-Saint-Gen&e, Belgium; #National institute for Veterinary Research, 1180 Uccle, Belgium; 5U.S. Department of Agriculture, National Animal Diseases Laboratory, P. 0. Box 70, Ames, Iowa 500 10; and “Laboratory of Macromolecules at Interfaces, Faculty of Sciences, University of Brussels, Campus Plaine, 1050 Bruxelles, Belgium Received June 15, 1988; accepted September 30, 1988 Previous studies with monoclonal antibodies of the antigenic structure of bovine leukemia virus (BLV) envelope glyco- protein (gp51) have identified three epitopes (F, G, H) directly involved in the infectivity of BLV. F, G, and H lost their reactivity with the respective monoclonal antibodies after treatment with a reducing agent, indicating that these epi- topes were conformational. Sequence comparisons between BLV mutants and differential reactivities of urokinase or proteinase K gp51 fragments with monoclonal antibodies indicated that the NH, moiety of the env protein harbored the three architectural determinants F, G, and H. ELISA tests demonstrated that anti-F, -G, and-H monoclonal antibod- ies were maximally reactive toward intact virions whereas they showed much poorer affinities for their respective epitopes when presented on a purified protein. Accordingly, an efficient vaccine against BLV infection will include at least the identified gp51 region presented in its native architectural configuration. o 1999Academic press, I~C. INTRODUCTION Bovine leukemia virus, the etiological agent of bovine leukemia lymphoma, is a transactivating retrovirus dis- tantly related to human T lymphotropic virus-l (HTLV- 1) and -2 (HTLV-2) (Rice et a/., 1984, 1985; Sagata et a/,, 1985). The virus induces lymphoid tumors in rumi- nants especially in sheep (Burny et al., 1980, 1987). All experimentally infected sheep develop a neoplastic disease within 6 months to 7 years postinfection, the length of the latency period being essentially linked to the virus load at infection (Mammerickx et al., 1988). In contrast, only a small percentage of BLV-positive cattle die in the tumor phase during the observation period of their economical lifespan. Goats are very resistant. Only 2 out of 24 animals infected developed tumors within an observation period of almost 10 years. Preliminary observations also indicated that BLV can initiate the development of a wasting syndrome in rab- bits (Burny et a/., 1985). These conclusions were re- cently confirmed and extended (M. Onuma, personal communication; C. Altaner, personal communication). Age of the recipient at infection seems to play a major role in the onset of the immunodeficiency syndrome; the younger the recipient, the higher the frequency of appearance of the syndrome. Moreover, the intriguing link between HTLV-1 infection and development in ’ To whom requests for reprints should be addressed aged humans of tropical spastic paraparesis, and more generally of HTLV-1 -associated myelopathies (HAM), focuses attention on the broad spectrum of disorders in which transactivating retroviruses seem to play a role (Jacobson et al., 1988). BLV and HTLV-1 are obviously transmitted as cell- associated agents (Burny et al., 1987), a peculiarity of potential relevance when considering vaccination pro- tocols. Prevention of virus-associated diseases via vac- cination has at least two prerequisites, namely (1) it must be demonstrated that spread of cell-associated viruses can be efficiently controlled through immune defense mechanisms and (2) it is of importance that variations among existing virus strains be of limited ex- tent. In this paper we present the sequence of the enve- lope gene coding for the external glycoprotein (gp51) of four BLV variants isolated in Europe and the United States. Taking advantage of the battery of mouse monoclonal antibodies (Bruck et a/., 1982a,b, 1984b) we used the sequence data to locate the dominant an- tigenic region of gp51 in the NH2 part of the molecule. When presented in its native conformation, that region is reacted against by monoclonal antibodies able to block syncytia induction and to inhibit infection by VSV (BLV) pseudotypes. We believe that an efficient vaccine against BLV infection will include the identified gp51 region presented in its native architectural configura- tion. 27 0042-6822189 $3.00 CopyrIght 0 1999 by Academic Press, Inc. All rights of reproduction in any form resewed.