The main objective of this research project was to determine if native and/or modified forms of Classical Swine Fever Virus (CSFV) proteins present in the surface of the virion were able to induce a rapid and protective immune response against CSFV.

To accomplish the proposed objective, Dr Manuel V. Borca and colleagues at the USDA Agricultural Research Service's Plum Island Animal Disease Center took two approaches:

1. They assessed the capability of each CSFV envelope protein (E0, E1 and E2) for eliciting a protective immune response against the disease, and
2. They introduced modifications into CSFV envelope proteins to increase their capability to induce an effective early protection against the virus.

All three proteins (E0, E1, and E2) were produced using a baculovirus/insect cell system to obtain high protein yields. Proteins were purified, tested for purity, combined with adjuvant (Sigma), and used to immunise pigs weighing between 30 and 40 lbs. Animals were inoculated intramuscularly (IM), receiving boosters at 28, 42 and 56 days post-primo inoculation. All pigs were challenged intra-nasally (IN) one week after the last boost.

Using this immunisation scheme, only those animals that were immunised with E0 or E2 elicited high antibody titres and survived the challenge. E1 protein did not elicit a detectable antibody response nor did it elicit a protective immunity in pigs against CSFV. All animals succumbed to challenge.

To understand further the protective efficacy of E0 and E2 proteins, the researchers inoculated groups of four-week-old swine with one or two doses of each protein. These animals were then exposed to CSFV IN at 21 days after single or last inoculation. All the animals survived the infection, suggesting that lesser doses are sufficient to induce protection. Similarly, animals receiving three doses of the proteins and challenged one week after last inoculation were protected against CSFV, suggesting that strong response can be induced shortly after three inoculations of both proteins.

After the protective efficacy of wild-type E0 and E2 proteins was established, the Plum Island team introduced modifications to these proteins aimed to enhance the immune response against CSFV. E0 and E2 proteins were fused to flagellin; or to single chain anti-class II antibody sequences. Production and purification of modified proteins had to be adjusted from original procedures to obtain high yields of modified proteins. Proteins were then used to assess their capability to induce an antibody response in pigs.

Unexpectedly, inoculation of these proteins into swine did not elicit a measurable antibody response suggesting that as formulated E0 and E2 will not induce an efficient immune response in pigs against CSFV. Work will continue to address this problem.

October 2013