Protective vaccination against bovine leukaemia virus infection by means of cell-derived vaccine C. Altaner*:~, J. Ban*, V. Altanerova* and V. Janik t Tests were performed to determine whether live mammalian cells producing env gene glycoproteins and main structural protein p24 of bovine leukaemia virus (BLV), heterologous to bovine species, could serve as an immunogen in cattle to prevent induction of bovine leukaemia. Ovine virus-non-producing clonal cells NP-2 were used as the immunogen. The NP-2 cells synthes&ed only the env gene products - glycoprotein gp51 and gp30 and main structural protein p24 of BLV. The NP-2 cells, inoculated into rats, induced an antibody response directed against envelope glycoproteins of BLV. The antibodies neutralized the infectivity of BL V as determined by the VSV/BL V pseudotype neutralization test. Similar results were obtained by vaccination of cattle with these cells. A dose of <<, 2 x 106 live cells inoculated subcutaneously induced an antibody response in cattle, while a high dose of killed cells was ineffective. The antibodies in cattle were directed against env products of BLV. A group of 92 cows was vaccinated and followed up for 4 years. The antibody levels fluctuated slightly during the 4-year observation period, generally decreasing with time, but revaccination always increased the antibody titre. No transfer of seropositivity was observed to seronegative animals which were kept in contact with vaccinated ones. In a separate experiment a group of young heifers, after repeated vaccination, were challenged with a high dose of infectious virus and/or virus-producing cells. The response to BLV infection was followed by syncytial induction assay after co-cultivation of white blood cells with indicator cells CC81. While the unvaccinated control animals, 2 months after virus challenge, were.found to be infected, all vaccinated and challenged animals were protected during a 1-year observation period. From the data obtained it can be concluded that vaccination with live heterologous cells producing env gene products and p24 of BL V can protect cattle against BL V-induced leukaemia. Keywords: Bovine leukaemiavirus; vaccine;cell-derived INTRODUCTION Bovine leukaemia virus (BLV), an exogenous retrovirus, is the causative agent of enzootic leukaemia in cattle (for reviews, see Altaner x, Ghysdael et al. 2 and Burney et al.3). BLV infection in cattle leads to leukosis, which is characterized by persistent lymphocytosis, occurrence of antibodies directed against structural viral proteins, and the appearance of lymphoid tumours, after a long induction period, in some infected animals. The antibody response to virus antigens is induced early after infection, but despite the presence of viral antibodies, the disease is progressive and the infection can spread to other animals by contact. The incidence of BLV-induced leukaemia in cattle can be substantially reduced by strict eradication of infected animals, or better, of whole herds *Department of Molecular Virology, Cancer Research Institute, Slovak Academy of Sciences, ul. csl. armady 21, 812 32 Bratislava, Czechoslovakia. tState Veterinary Center, 693 01 Hustopece, Czechoslovakia. ~:To whom correspondence should be addressed. (Received 17 April 1991; revised 25 June 1991; accepted 10 July 1991) where infected animals have been found. Nevertheless, vaccination against BLV would probably help in efforts to control horizontal transmission. Bovine leukaemia virus is distantly related to the human T-lymphotropic viruses (HTLV-I and II) 4. Several properties of these viruses have been found to be very similar, for example, their biological and patho- logical behaviour, the virus genome organization, and the regulation of virus protein expression by products of transactivation genes present in their genomes. Many types of experiments with human retroviruses are difficult or sometimes impossible for ethical reasons. These problems are more pronounced in studies to investigate the pathogenic effects of these viruses and their mechanisms of action in vivo, and in attempts to develop a protective vaccine. Therefore the anti-BLV vaccine can be regarded as an experimentally feasible prototype of retroviral vaccine, especially for the family of trans- activating retroviruses. Several approaches to the development of anti-BLV vaccine have been reported. The use of inactivated virus preparations or virus envelope glycoproteins as immuno- gens in cattle has been found to be effective5-7. Most 0264-410X/91/120889-07 ~ 1991 Butterworth-HeinemannLtd Vaccine, Vol. 9, December 1991 889