There are many diseases of livestock for which we do not yet have effective vaccines. This is partly due to the challenges of novel antigen discovery and suitable delivery. Recently, viral vectors have risen to prominence as candidates for vaccine delivery to generate cellular and humoral immune responses. Of these viral candidates, lentiviruses are attractive as they have the ability to elicit sustained antigen expression in non-dividing antigen presenting cells1. Here, we describe the development and characterisation of vaccine vectors derived from ovine lentivirus.
Vectors were produced by transient transfection of 293T cells with plasmids that encode the various viral components. The vectors produced contain either an eGFP reporter cassette to facilitate measurement of infectivity by flow cytometry or epitope-tagged proteins and antigens from selected ruminant pathogens to assess the quality of immune responses elicited by the viral vector.
To increase the safety profile of the vector, viral enhancers in the 3’-long terminal repeat (LTR) were removed to produce self-inactivating vectors, decreasing the probability of the generation of replication-competent virus2. Furthermore, point mutations were introduced into the integrase protein to minimise the possibility of insertional mutagenesis3.
Ovine lentivirus vectors are able to infect a wide range of cell types from different species with similar efficiency to the well characterised murine leukaemia virus (MLV) vector. In addition, these vectors infect ovine dendritic cells cultured in vitro. Further experiments showed that self-inactivating vectors with non-active LTRs retain the ability to express transgenes in vitro. Moreover, when integration deficient lentiviral vectors (IDLV) infect dividing cells expression is transient. However, when the IDLV infect non-dividing cells, expression is maintained for over 3 weeks.
We have created a novel, self-inactivating, integration deficient ovine lentiviral vector which retains the ability to express transgenes in vitro. Functional analysis of these lentiviral vaccines is currently underway.