Evaluation of Naked Proviral DNA as a Vaccine for Ovine Lentivirus Infection

Abstract

Ovine lentivirus (OvLV) infection is widespread in sheep of the United States and Israel and is responsible for substantial economic losses. The primary goal of this project was to evaluate naked proviral DNA as a vaccine to induce protective immunity in sheep in endemic areas. Contrary to expectations, inoculation of sheep with proviral DNA derived from the full length OvLV molecular clone pkv72 did not result in detectable OvLV infection, but infectious virus was recovered from transfected ovine cells. Kv72 virus produced by these cells infected sheep and induced antibody responses, and was used as a viral challenge in subsequent experiments. To improve in vivo transfection efficiency and compare the viral LTR with other romoters, expression of reporter genes was studied in sheep transfected in vivo by injection of cationic liposome-DNA complexes; one formulation produced gene expression in a sheep for 4 months following a single intravenous injection. Since the pol-deleted OvLV construct was not stable in vivo, twelve lambs were injected with plasmids containing the Kv72 gag region (pCMVgag) or env region (pCMVenv), or saline. Prior to challenge, no detectable anti-OvLV immune responses were detected. Following homologous challenge with OvLV. Although the naked DNA approach to vaccination holds promise for control of ovine lentivirus-induced disease, further work needs to be done to develop more effective methods of transfecting sheep with DNA.