Process for the purification of virus vaccine
United States Patent l l Zaremha et al.  
 I PROCESS FOR THE PURIFICATION OF VIRUS VACCINE [75] Inventors: Edmund Anthony Zaremba; Francis Robert Cano. both of Spring Valley. NY  
 (73] Assigneei American Cyanamid Company,  
 Stamford Conn.  
 I22} Filed: Oct. 3]. i973 I1] 1 Appl No.: L564 [45] Apr. 1, 1975 Raynnud et ill 424/89 Apostolov r. 424/89 Primary Iirumz&#39;ner$um Rosen Attorney, Agent or Firm.luck W. Richards I57} ABSTRACT An improved process for removing non-viral protein and lipid impurities from an impure. egg grown virus preparation. in particular. influenza virus vaccine by selective removal of these impurities using a magnesium salt of sulfuric acid.  
 3 Claims, 1 Drawing Figure PATENTEDAPR 11975 3,  
 L HARVEST ALLA/VTO/C FLU/D k&#39; (LOW SPEED CENTR/FUGAT/O/V} CLAR/FY //2 (Low SPEED CENTR/FUGA T/O/V) CENTR/FUGE /3 (HIGH SPEED CENTR/FUGA r/0/v) CONCE/V TRA rE //4 (30x CONCENTRATE) PREC/P/TA 7&#39;5 mom/mus PROTEIN ADJUST pH ALKALINE (HOLD 4%) CLAR/FY (Low SPEED CENTR/FUGAT/O/V) ADJUST pH ALKAL/IVE (HOLD 4C) cum/FY 0 I M/LL/PORE FILTER 2 CONCENTRA TE (UL TRAP/L TRA T/O/V) DIAL YS/S I 22 COME/NE .STRAl/VS AND D/LUTE T0 Fl/VAL CONCENTRA T/O/V PROCESS FOR THE PURIFICATION OF VIRUS VACCINE BACKGROUND OF THE INVENTION The present invention is concerned with an improvement in the purification of embryonated egg-grown infectious agents. particularly influenza virus vaccine.  
  lntluenza virus vaccines containing representative serologic types have been produced commercially for many years. Conventional manufacturing procedures consist of cultivating the various virus strains in the chorioallantoie cavity of fertile hen&#39;s eggs and subsequent high speed contrifugation of the harvested allantoic fluids. Centrifugation serves to concentrate the virus and achieves some degree of purification by eliminating soluble substances and low molecular weight contaminants in the supernatant. Unfortunately. vaccines prepared in this manner still contain large amounts of impurities which can produce fever. malaise or chills in recipients. The chick embryo origin of influenza vaccines contraindicatcs their use in persons allergic to chicken or egg protein.  
  The art of influenza vaccine production is replete with attempts to develop ancillary procedures to further reduce undesirable rcactogenic substances. Following is a list of references for some of the known techniques that have been employed to purify influenza virus preparations: M. Lapidus. 1969. Applied Microbiology. Vol. 17. pages 504-506; J. L. Gerin and N. G. Anderson. 1969. Nature. Vol. 221. pages 1255-1256. British Pat. Specification No. 17.976/67; British Pat. Specification No. 8.232/67; French Pat. No. 84.337. US. Pat. No. 3.368.867; F. D. Brandon. et al.. 1967. Journal of Immunology. Vol. 98. pages 800-805; K. Apostolov and B. Fishman. 1967. Nature. Vol. 215. pages 1287-1288; C. B. Reimer. et al.. 1967. Journal of Virology. Vol. 1. pages 1207-1216; D. S. Pepper. 1967. Journal of General Virology, Vol. 1. pages 49-55; U.S. Pat. No. 3.316.153. U.S. Pat. No. 3.197.374; H. Mizutani. 1963. Nature Vol. 198. pages 109-1 N. Veeraraghavan and T. Sreevalsan. 1961. World Health Organization Bulletin. Vol. 24. pages 695-702; W. J. Hausler and E. C. Dick. 1960. Journal of Infectious Diseases. Vol. 107. pages 189-194; and Wallis. Honima and Melnick. Applied Microbiology. Vol. 23. pages 740-744 I972).  
  U.S. Pat. No. 3.632.745 discloses the purification of influenza viruses by dialysing a suspension of the virus against water containing bivalent metallic cations (e.g.. magnesium) at a concentration of from about 0.003 to about 0.12M until the virus forms a precipitate and then separating the fractions containing the virus. The anion accompanying the cations may be sulphate. However. the U.S. Pat. No. 3.632.745 is only concerned with precipitation of the virus by dialysis while the method of the present invention involves direct precipitation of non-viral contaminants. Moreover. in the U.S. Pat. No. 3.632.745 only a bivalent metallic cation concentration of from 0.003 to about 0.012M is disclosed as operable whereas in the practice of the method of the present invention a concentration of magnesium cation of from about 0.1 to about 0.4M is considered as operable. Other differences exist between the disclosure in the U.S. Pat. No. 3.632.745 and the present invention. Limited experience indicates. however. that a preferred minimum concentration of magnesium would be 0.15 to 0.2M. Lower amounts of magnesium would precipitate very little non-viral material.  
  U.S. Pat. Nos. 3.485.718 and 3.547.779 both disclose the use of barium sulfate in the purification of influenza virus. The two methods ofthese patents precipitate the virus. whereas the magnesium salt does not. US. Pat. No. 3.478.145 discloses the use of calcium phosphate in the purification ofinfluenza virus. None of the above mentioned patents or publications employ magnesium sulphate in the purification of influenza viruses as set forth herein.  
 SUMMARY OF THE INVENTION The invention resides in an improvement in removing proteinaceous and lipid materials from an impure. egg grown virus preparation. in the purification of virus vaccines. wherein the improvement consists of treating a phosphate buffered viral suspension with about 0.1 to about 0.4 molar solution of magnesium sulfate. preferably 0.15 to 0.2 molar. at a pH of 8.0 to 9.0. at about 4C. for about 16-72 hours preferably 16-18 hours. followed by removal of the salt precipitated protein impurities through centrifugation. The virus preparation is preferably influenza vaccine. Limited experience has been had with other magnesium salts. e.g.. magnesium chloride shows promise. but its use requires further work. Limited experience also indicates that ammonium sulfate also precipitates non-viral materials. However. comparative experiments would have to be done to compare effectiveness of the magnesium sulfate with the other salts. In the process of the present invention. the virus is not precipitated whereas non-viral materials are under the stated conditions. The present methods requires the presence of magnesium and phosphate salts in the virus milieu. The critical step in this purification process is the adjustment of pH to the alkaline side.  
  Although many procedures have been devised to purify influenza virus. most are unsuitable for commercial manufacturing of influenza vaccine. To be useful. any such procedure must be capable of accommodating large volumes of virus material within a short period of time. Moreover. the procedure should not entail the need for expensive or special equipment and should preferably not result in excessive virus loss.  
  The present invention represents an important improvcment in conventional procedures used for manufacturing influenza because it results in reduction of potentially reactogenic substances in the finished product. The procedure can be rapidly applied to multi-liter quantities of influenza virus.  
 &#39; Stanley. W. M. The preparation and properties of influenza virus vaccines concentrated and purified by differential centrifugation. .1. Exp. Med. 81: 193-217 (19451.  
  According to the invention. any strain of any virus capable of culture in embryonated eggs can serve as starting material. However. since the primary thrust of this invention is concerned with influenza vaccine. the balance of this disclosure will be specifically directed to it.  
  The virus (for example. B/Massachusctts/3/66); X-37A (a hybrid virus containing the hemagglutinin and neuraminidase antigens of A/Eng/42/72 or X-38A (a hybrid virus containing equi/hemagglutinin and the A/Eng/42/72) is inoculated into the allantoic cavity of fertile hens eggs and the fluid therefrom is harvested under aseptic conditions after a suitable incubation time. (jross particles are removed from the pooled viruscontaining fluids by low speed ccntrifuga&#39; tion. The virus is removed from the allantoic fluid by high speed ccntrifugation and the sediment is reconstituted to one-thirtieth original fluid volume in the dcsircd buffer. usually sodium phosphate or a mixture of sodium phosphate and sodium citrate. containing a low concentration of formaldehyde.  
  In the improvement of this invention, nonvirus protein and lipids are removed by treatment of the buffcred, virus containing suspension with about 0.! to about 0.4M (most preferably about 0.2) molar magnesium sulfate at a pH of about 8.0 to about 9.0 (prefera bly about 8.5 l. at about 4C. for about l6] 8 hours.  
  The resultant suspension is clarified by low speed centrifugation. the pH of the supernatant is adjusted to about 8.0 to about 90 (preferably about 8.5) and allowed to stand for between If) to l8 hours at about 4C. Additional clarification can be obtained by a second treatment with additional salt and/or pH adjustment to about pH 8.5. This suspension is again clarified by low speed eentrifugation and the supernatant fluid passed through a milliporc prc-filter pad. The filtrate is ultrafiltered to concentrate the virus and diafiltercd to remove the magnesium salt and low molecular weight impurities. The concentrate is sterilized by ethylene oxide and diluted to final concentration.  
  Strains may be combined by combining just prior to final dilution.  
 BRIEF DESCRIPTION OF THE DRAWING The FIGURE is a flowsheet illustrating the steps to be carried out in the method ofthe present invention using magnesium sulfate to precipitate non-virus protein.  
 DETAILED DESCRIPTION OF THE INVENTION The following will serve to further illustrate the improved process of this invention.  
  Referring to the FIGURE. after the embryonated eggs have been injected with the influenza virus and incubated. the allantoic fluid is harvested in harvesting step II. In step II. only the extra embryonic fluid is harvested. and not the yolk and membranes Monovalent pools of harvested all-antoic fluid are collected in such sire as to be conveniently handled and processed. After harvesting step 1 l, the allantoic fluid is then clarified in clarifying step I2 by low speed centrifugation. After clarification step 12. the clarified monovalcnt allantoic fluid is subjected to high speed centrifugation in centrifugation step 13 to bring down the sediment virus. In concentration step 14. the sedimented virus is then resuspended in a sterile sodium phosphate-sodium citrate buffer solution and the resulting suspension triturated and subsequently centrifuged. The supernatant fluid is saved and the solids discarded after additional elution and centrifugation. The collected supernatant suspension is then diluted with formalin in distilled water so as to provide a virus concentration of 30X [30 fold] over that present in the original harvested allantoic fluid. After the 30X concentration step 14. a high proportion of the remaining non-viral proteinaceous and lipid materials are removed from the 30X concentration suspension in precipitation step 15 by the addition of magnesium sulfate until preferably a 0.2 molar concentration of magnesium sulfate is reached. After the magnesium sulfate addition. the pH of the concentrate is adjusted to the alkaline side. preferably to about 8.5. in step 16. with sodium hydroxide and the concentrate held at about 4C. for about 16 to [8 hours or overnight. After holding. the concentrate is then subjected to low speed ccntrifugation in clarification step 17 and the supernatant collected. After step 17. steps 15 and 16 may optionally be repeated. In step 18. the pH of the collected supernatant is readjusted to the alkaline side. preferably to about pH 8.5. and held again at about 4C. for l6 to 18 hours or overnight. After holding, the supernatant is subjected to low speed centrifugation in clarification step 19 and the supernatant filtered through a millipore prefiltcr in filtering step 20. The filtrate or concentrate is then passed through an Amicon ultra-filter in concentration step 2] to further concentrate it. After concentration, the concentrate is diafiltered in dialysis step 22 with aqueous citratephosphate buffer to remove the magnesium sulfate. In step 23. the strains are combined. diluted to final concentration and sterile filtered.  
 EXAMPLE Eleven day embryonated eggs are drilled in the air sac end and through this opening is injected 0.2 ml. of a dilution of influenza virus previously titrated and calculated to produce maximum virus growth in 48 hours. The injected eggs are held at 34C. at a relative humidity of -75% for 48 hours. At the end of the incuba tion period. the eggs are candled and those containing dead embryos are discarded. The living eggs are chilled at 4C. for IS to 20 hours. The extra embryonic fluids are recovered. Yolk and membranes are not harvested. Monovalent pools of fluid are prepared in such size as to be conveniently handled and processed. During any lag in the processing cycle. the pooled fluids are held at approximately 4C. with I:l0.000 concentration of thimerosal as preservative. After harvest the infected fluids are clarified by low speed ccntrifugation.  
  On the following day. the monovalent fluids are processed through a centrifuge with a minimum rotor G force of 48.000 and at a flow rate designed for optimum virus clean-out. During the centrifugation. the bowl and reservoir are refrigerated. At the end of the run. the containers are washed with 0.] molar sodium phosphate buffer. pH 7. containing l:4.000 solution of formalin U.S.P. and l:l0,000 thimerosal. Within 24 hours after ccntrifugation. the sedimcnted virus is resuspended in l/o0 volume of sterile buffer solution which contains 0.l molar sodium phosphate and 0.4 molar sodium citrate with 1:4.000 solution of formalin. U.S.P. and l:l0,000 thimerosal. This suspension is triturated and held at 25C. for two hours. Subsequently. it is centrifuged in a bucket-type centrifuge at 2.000 r.p.m. for 20 minutes. The supernatant is saved and the pellet. which contains insoluble non-viral material. is discarded following an additional elution and centrifugation step. The supernatant suspension is then diluted with 1 volume of sterile 1:4.000 solution of formalin U.S.P. in distilled water yielding a volume equivalent to one-thirtieth the original volume of harvest. This dilution will reduce the sodium phosphate buffer to 0.05 molar. and the sodium citrate to 0.2 molar level.  
  In addition to the above initial virus purification step by ultraccntrifugation. a processing stage of the influenza virus vaccine concentrate is utilized to remove a high proportion of the remaining nonviral egg protein and lipids. Crystalline MgSO. is added with constant stirring to the 30X concentrate (virus in the allantoic fluid is concentrated 30 fold) until a 0.2M concentration of MgSO is reached. The pH is then adjusted to 8.5 with NaOH and the concentrate is held at 4C. for 16-18 hours. The concentrate is then low speed centrifuged and the supernatant collected. The supernatant is readjusted to pH 8.5 with NaOH and held at 4C. for -18 hours. After another low speed centrifugation the supernatant is filtered through a Millipore prefilter. The concentrate is then processed by passage thru an Amicon ultra-filter. After concentration. this material is diafiltered with a volume of 0085M citrate and 0.05M phosphate buffer equivalent to a minimum of five times the volume of the concentrate to remove the MgSO The monovalent concentrates are treated with liquid ethylene oxide by the following procedure: The concentrates are held at 4C. after processing. To the concentrate is added liquid ethylene oxide that has been cooled to 4C. or lower. The ethylene oxide is added to a concentration of0.5&#39;% by volume with constant agitation. The treated concentrates are held at 25C. for 24 hours with occasional agitation by hand. After treatment. the ethylene oxide is removed from the monovalent concentrate within 48 hours, by exposure to reduced pressure. There should be less than 0.5 mg./ml. of residual ethylene oxide in the concentrate. After treatment with ethylene oxide. samples are removed from the monovalent concentrates for CCA titration, sterility and identity tests. The final vaccine consists of sufficient monovalent concentrates diluted to provide the CCA (chicken cell agglutination test a measure of viral activity or potency) titers specified in the formula issued by the Bureau ofBiologics. The diluent for final vaccine consists of sufficient sterile distilled water and sodium phosphate plus sodium citrate to adjust the final salt concentrations to 0.05 molar sodium phosphate buffer and 0.085 molar (+0.0l5) sodium citrate. Samples are removed from the bulk vaccine for po tency. sterility. safety. infectivity tests and analytical determinations. When all tests are satisfactory. the vaccine is filled into final containers.  
 We claim:  
  1. In a process for removing non-viral proteinaceous and lipid materials from an impure, egg grown virus preparation, the improvement which consists of treating the phosphate buffered viral suspension with about 0.l to about 0.4 molar solution of magnesium sulfate at a pH of about 8.0 to about 9.0 at about 4C. for about l672 hours: and removing the salt precipitated protein impurities by low-speed centrifugation.  
  2. A process according to claim 1. wherein the egg grown virus preparation is influenza vaccine.  
  3. A process according to claim 2, wherein the salt solution is about 0.2 molar magnesium sulfate and the pH of the suspension is about pH 8.5.  
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