Addition of nucleases directly to cell culture to facilitate digestion and clearance of host cell nucleic acids
The present invention provides an efficient process for culturing viruses in the presence of an endonuclease and for producing vaccines, typically from live attenuated viruses, under conditions to reduce the presence of host cell DNA and eliminate the need for a post-harvest DNA digestion step.
1. A method for production of a flavivirus, comprising the steps of:
a) infecting a culture of cells in a cell culture medium with the flavivirus; and
b) incubating the cells in cell culture medium containing endonuclease for up to 15 days,
wherein the endonuclease is added to the cell culture medium at any time from initial infection of the cells to prior to harvesting the cells and wherein the cells are adherent to a microcarrier.
2. The method of claim 1 , wherein the endonuclease is added at the time of initial infection.
3. The method of claim 1 , wherein the endonuclease is added from 0.5 to 15 days prior to harvesting the cells.
4. The method of claim 3 , wherein the endonuclease is added 7, 8, 9, 10, 11, 12, 13, or 15 days prior to harvesting the cells.
5. The method of claim 1 , wherein the endonuclease may have DNA specificity, RNA specificity, or both.
6. The method of claim 5 , wherein the endonuclease is a broad spectrum endonuclease derived from the bacterium Serratia marcescens.
7. The method of claim 1 , wherein the cell culture medium comprises endonuclease at an initial concentration of 2.5 to 80 U per mL of medium.
8. The method of claim 7 , wherein the cell culture medium comprises endonuclease at an initial concentration of 2.5 to 20 U per mL.
9. The method of claim 8 , wherein the cell culture medium comprises endonuclease at an initial concentration of 5 U per mL.
10. The method of claim 1 , wherein the culture of cells are mammalian cells.
11. The method of claim 1 , wherein the microcarrier is selected from microcarriers made of dextran, collagen, polystyrene, polyacrylamide, gelatin, glass, cellulose, polyethylene or plastic.
12. The method of claim 1 , wherein the cell is a Vero cell.
13. The method of claim 1 , wherein the flavivirus is a dengue virus, a live attenuated dengue virus, or a live attenuated chimeric flavivirus.
14. The method of claim 13 , wherein the dengue virus, live attenuated dengue virus, or live attenuated chimeric flavivirus is a DEN1, DEN2, DEN3, or DEN4 virus.
15. The method of claim 13 , wherein the flavivirus is a live attenuated chimeric flavivirus comprising the DEN2 prM and E genes on a DEN4 backbone.
16. The method of claim 15 , wherein the flavivirus is rDEN2/4Δ30.
17. The method of claim 13 , wherein the flavivirus is a live attenuated dengue virus selected from the group consisting of rDEN1Δ30, rDEN3Δ30/31, and rDEN4Δ30.
18. The method of claim 1 , wherein trypsin is not added to the cell culture medium of step (b).
19. The method of claim 1 , wherein the microcarrier is a dextran-based sphere with diethylaminoethyl functionality.
20. The method of claim 1 further comprising:
a) harvesting infectious virus by collecting virus-containing supernatant obtained from centrifugation and/or filtration of the cell culture; and
b) preparing a vaccine by subjecting the virus-containing supernatant to at least one processing step selected from the group consisting of chromatography, filtration, centrifugation, precipitation, concentrating, freezing, freeze-drying, and stabilizing by addition of a stabilizing agent.