Vaccination against retroviruses is a challenge because of their ability to stably integrate into the host genome, undergo long-term latency in a proportion of infected cells and thereby escape immune response. Since clearance of the virus is almost impossible once infection is established, the primary goal is to achieve sterilizing immunity. Besides efficacy, safety is the major issue since vaccination has been associated with increased infection or reversion to pathogenicity. In this review, we discuss the different issues that we faced during the development of an efficient vaccine against bovine leukemia virus (BLV). We summarize the historical failures of inactivated vaccines, the efficacy and safety of a live-attenuated vaccine and the economical constraints of further industrial development.

Bovine leukemia virus (BLV) is an important cattle pathogen that causes major economic losses worldwide, especially in dairy farms. The use of animal models provides valuable insight into the pathogenesis of viral infections. Experimental infections of sheep have been conducted using blood from BLV-infected cattle, infectious BLV molecular clones or tumor-derived cells. The Fetal Lamb Kidney cell line, persistently infected with BLV (FLK-BLV), is one of the most commonly used long-term culture available for the permanent production of virus. FLK-BLV cells or the viral particles obtained from the cell-free culture supernatant could be used as a source of provirus or virus to experimentally infect sheep. In this report, we aimed to determine the minimum amount of FLK-BLV cells or cell-free supernatant containing BLV needed to produce infection in sheep. We also evaluated the amount of antibodies obtained from a naturally-infected cow required to neutralize this infection. We observed that both sheep experimentally inoculated with 5000 FLK-BLV cells became infected, as well as one of the sheep receiving 500 FLK-BLV cells. None of the animals inoculated with 50 FLK-BLV cells showed evidence of infection. The cell-free FLK-BLV supernatant proved to be infective in sheep up to a 1:1000 dilution. Specific BLV antibodies showed neutralizing activity as none of the sheep became infected. Conversely, the animals receiving a BLV-negative serum showed signs of BLV infection. These results contribute to the optimization of a sheep bioassay which could be useful to further characterize BLV infection. (C) 2019 Asociacion Argentina de Microbiologia. Published by Elsevier Espana, S.L.U.

The development of effective adjuvant systems remains a critical challenge in veterinary vaccine design, particularly for infectious diseases causing significant economic losses in dairy cattle. This study evaluated the immunological profile induced by a mixture of recombinant antigens, formulated with cationic liposomes containing different combinations of gemini lipopeptide AG2‐C16, bovine‐specific CpG oligodeoxynucleotide, and S. cerevisiae mannans, in dairy heifers. Thirty‐five dairy heifers aged 8–10 months were randomly assigned to seven groups and immunized with recombinant Staphylococcus aureus antigens (α‐toxin, β‐toxin, clumping factor A, and fibronectin‐binding protein A) formulated with different adjuvant combinations. Animals received two primary doses 21 days apart, followed by a booster dose 8 months later. Humoral immune responses were assessed through ELISA measuring specific immunoglobulin G (IgG), IgG1, and IgG2 levels, while cytokine production was evaluated via whole‐blood assays. Results demonstrate that liposomal formulations combining AG2‐C16, CpG‐ODN, and mannans induce a significant immune response, in heifers, with IFN‐γ production. These findings provide valuable insights for the development of new vaccine strategies in cattle.