GLYCOPROTEIN E1 OF HOG-CHOLERA VIRUS EXPRESSED IN INSECT CELLS PROTECTS SWINE FROM HOG-CHOLERA

The processing and protective capacity of El, an envelope glycoprotein of hog cholera virus (HCV), were investigated after expression of dif ferent versions of the protein in insect cells by using a baculovirus vector. Recombinant virus BacE1[+] expressed E1, including its C-termi nal transmembrane region (TMR), and generated a protein which was simi lar in size (51 to 54 kDa) to the size of E1 expressed in swine kidney cells infected with HCV. The protein was not secreted from the insect cells, and like wild-type E1, it remained sensitive to endo-beta-N-ac etyl-D-glucosaminidase H (endo H). This indicates that El with a TMR a ccumulates in the endoplasmic reticulum or cis-Golgi region of the cel l. In contrast, recombinant virus BacE1[-], which expressed El without a C-terminal TMR, generated a protein that was secreted from the cell s. The fraction of this protein that was found to be cell associated h ad a slightly lower molecular mass (49 to 52 kDa) than wild-type El an d remained endo H sensitive. The high-mannose units of the secreted pr otein were trimmed during transport through the exocytotic pathway to endo H-resistant glycans, resulting in a protein with a lower molecula r mass (46 to 48 kDa). Secreted El accumulated in the medium to about 30 mug/10(6) cells. This amount was about 3-fold higher than that of c ell-associated El in BacE1[-] and 10-fold higher than that of cell-ass ociated E1 in BacE1[+]-infected Sf21 cells. Intramuscular vaccination of pigs with immunoaffinity-purified El in a double water-oil emulsion elicited high titers of neutralizing antibodies between 2 and 4 weeks after vaccination at the lowest dose tested (20 mug). The vaccinated pigs were completely protected against intranasal challenge with 100 5 0% lethal doses of HCV strain Brescia, indicating that El expressed in insect cells is an excellent candidate for development of a new, safe , and effective HCV subunit vaccine.