Purification method for alpha interferon
BACKGROUND OF THE INVENTION 
     The present invention relates to a method of purifying interferon alpha. More particularly, the present invention relates to a method employing hydrophobic electrolyte solutions throughout the purification scheme so as to preserve native isospecies composition of interferon alpha. 
     Interferons are proteins with distinctive biological properties, the most remarkable of which is the capability of rendering living cells resistant to viral infection. Interferons are produced by cells in response to certain inducers such as a virus, a mitogen or a double stranded RNA. Currently, three major types of human interferons are known, each differentiated according to the initial producer cell and the inducer applied. They are interferons alpha (leukocyte), beta (fibroblast) and gamma (immune). Within the alpha and beta types, there are multiple subspecies coded by separate interferon genes. Interferon gamma, however, is a product of a single gene; but as a result of a postranslational modification, it exists in various forms. 
     Human interferon alpha is the most complex family of interferons. The heterogeneity of isospecies of highly purified preparations is well established and is revealed by many chromatographic media, as well as SDS-PAGE or isoelectric focusing. The amino acid composition of different interferon alpha isospecies shows significant similarities, and some of them can be considered identical. However, biological activity of the isospecies is quite different and varies with the cells used for assay. It seems that different isospecies are addressed to different types of cells. In other words, the bioresponse to interferons may be critically dependent upon the presence of different isospecies in the appropriate ratio. 
     In order to obtain full therapeutic effect of interferon alpha, it is important to preserve all isospecies during the purification procedure. 
     There are many methods for interferon alpha purification, using combinations of classical chromatography techniques, monoclonal antibodies, high performance liquid chromatography, etc., in a unique sequence of steps. By using different techniques, different degrees of purity and different compositions of isospecies are achieved. 
     The classical purification method of interferon alpha described by Cantell (Methods in Enzymology 78:499-505, 1981) employs relatively harsh conditions. This method uses differential acid-ethanol precipitation within a narrow pH range, a difficult step to control, largely because of nonaqueous conditions (high concentration of ethanol) and low temperature requirements. A large variation of interferon isospecies can result from batch-to-batch. Another purification method is described by Chadha et al (U.S. Pat. No. 4,485,038) which preferentially recovers the pH labile form of interferon alpha. A drawback, however, is that the mild conditions of the purification allow possible viral contaminations, and in addition some isospecies are eliminated from the final preparation. 
     There are several more purification procedures which apply harsh conditions for the recovery of interferon causing inactivation of some of interferon alpha isospecies. 
     As the pool of leukocytes for production of interferons increases, so also does the possible contamination with exogenous microorganisms. Contamination of the leukocytes with viruses which may derive from apparently healthy individuals who donate blood is of great concern. Infections with hepatitis A, B or non-A and non-B are good examples. However, cells can also be contaminated by other DNA and RNA viruses known to infect man. These serious contaminants include, among others, the viruses responsible for chronic infections such as cytomegalo and Epstein Barr viruses, members of the herpes virus family. 
     More recently, retroviruses of the Lentivirinae subfamily (Human Immuno-deficiency Virus [HIV] [International Committee on the Toxonomy of Viruses. Science 232:697, 1981], previously known as LAV-I/HTLV-III) present a serious problem source of contamination. Although the U.S. Food and Drug Administration regulations require that leukocytes must come from blood which is negative for hepatitis B surface antigen and HTLV-III antibody, these precautions may not be sufficient. There are cases where viremia occurs without the presence of antibodies. 
     Furthermore, Montagnier et al (Science 232:343, 1986) recently have found a new AIDS virus with an antigenic structure so different from the prototype that &#34;classical&#34; antigens did not react with antibodies to the new virus, and antibodies against the &#34;classical&#34; strain of the HIV viruses did not recognize the antigens of the new isolate. In other words, some of the viruses from the retrovirus family may escape detection at screening. Thus, they may contaminate batches of starting leukocytes. 
     Since viremia cannot be assessed routinely by blood banks, there will always be a risk factor when the natural product derived from donated blood is used, unless the purification contains steps which are known to eliminate viruses. 
     The most effective way to eliminate viral contamination from interferon batches is the destruction of the virus and its nucleic acid. In the Cantell preparation, the goal is obtained by low pH treatment in the presence of ethyl alcohol. Unfortunately, such treatment has a negative impact on the composition of interferon isospecies in the final preparation. 
     Concerning the above, the present invention focuses on: 
     (a) elimination of exogenous Sendai virus (the interferon alpha inducer), as well as other endogenous viruses; and 
     (b) preservation of a natural composition of interferon alpha isospecies in the final preparation. 
     SUMMARY OF THE INVENTION 
     By the present invention, a high recovery of native interferon alpha isospecies is obtained by subjecting a crude interferon alpha solution to a three-step chromatography sequence under highly dissociating conditions. This three-step chromatography sequence comprises: (a) loading a crude interferon alpha solution to chromatography on a glass sorbent and eluting the adsorbed interferon alpha with a hydrophobic electrolyte solution; (b) subjecting the eluted interferon alpha to molecular sieving chromatograhy and collecting the fraction corresponding to the molecular weight ranging from about 10,000 to about 40,000; and (c) loading the collected fraction of step (b) to Zn++ chelate chromatography column and thereafter collecting the non-adsorbed material. 
     In the present invention, the chromatography steps are all carried out under highly dissociating conditions so as to avoid interferon complexation and thereby to preserve the native isospecies composition. The highly dissociating conditions are achieved by using hydrophobic electrolyte solutions buffered to a pH ranging from about 6 to about 9. The hydrophobic electrolyte solutions of the present invention are selected either separately or in combination from the following categories: (1) tetra alkyl ammonium salts such as tetra methyl ammonium chloride or tetra ethyl ammonium chloride at concentration ranges of 0.1 to 1.0M; (2) alkylamines such as methylamine, dimethylamine, trimethylamine, tetramethylamine, ethylamine, etc., at concentration ranges of 0.1M to 1.0M; and (3) by a mixture of suitable co-solvents which individually are either polar or apolar, as for example, the combination of ethylene glycol or propylene glycol at concentration ranges of 0.5M to 5M with a suitable strong electrolyte salt such as NaCl, KCl, or NH 4  Cl at concentration ranges of 0.2M to 2.0M. 
     In the first step, a crude interferon alpha solution is loaded onto a chromatography column packed with a glass sorbent. For instance, controlled pore glass, silica gel or silicic acid may be used as the glass sorbent material. Depending upon the volume of interferon to be processed, the controlled pore glass or silicic acid can either be packed in a column or used in a simple batch-type operation. The interferon alpha is selectively adsorbed to the glass sorbent and the bulk of contaminating proteins will remain in solution and pass through the column. Thereafter, the glass sorbent is washed with a hydrophobic electrolyte solution to desorb the interferon alpha from the glass sorbent. 
     In the second step, the eluted interferon alpha is passed through molecular sieving chromatography having a molecular weight resolution capacity ranging from about 10,000 to about 100,000 or more. Examples of such molecular sieving chromatography include SEPHACRYL: S-200, S-300; ULTRA-GEL: AcA 54, AcA 44; SUPEROSE: 6, 12; BIOGEL: P-60, P-100, P-150; CELLUFINE: GS-100, GS-200, GS-700, GSL-2000. Again, this step is performed under high dissociation conditions using a hydrophobic electrolyte solution. The interferon alpha is collected in the fractions corresponding to molecular weight ranging from about 10,000 to about 40,000. 
     In a third step, the collected fractions containing interferon alpha are loaded onto a Zn++ chelate resin chromatography column. The resin carriers for the metal chelate include, for example, polysaccharides, cross-linked polyolefin derivatives or vinyl polymer having hydroxy groups having terminal chelating residues for binding Zn++. (See, e.g., Hochuli, U.S. Pat. No. 4,551,271; Hosoi et al., U.S. Pat. No. 4,541,952; and references cited therein.) Any remaining contaminating proteins will adsorb to the Zn++ chelate resin while the interferon alpha passes through unabsorbed to the Zn++ chelate resin. 
     By using this three-step purification method, a highly pure interferon alpha solution is achieved; moreover, the resulting purified interferon alpha solution preserves the native isospecies composition of interferon alpha. 
     In another aspect of the present invention, the viral inducer, Sendai virus, and other contaminating viruses are inactivated by mixing viral induced crude or partially purified interferon alpha solutions with a nonionic detergent, and/or eliminated by membrane filtration. Generally, the non-ionic detergent is added to interferon solution to effect a concentration ranging from about 0.01% to about 1.0% (v/v). Typical examples of suitable non-ionic detergents are polyglycol esters and polyglycol ethers with aliphatic or arylphatic acids and alcohols. Examples of these are alkyl polyoxyethylene ethers, alkyl phenyl polyoxyethylene ethers, e.g., TRITON X-100; acylpolyoxyethylene esters; acylpolyoxyethylene sorbitane esters, e.g., TWEEN 20, TWEEN 80; and alkyl phenol ethylene oxides, e.g., NONIDENT P-40. 
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The invention is described hereinafter in terms of preferred embodiments which represent the best mode known to the Applicants at the time of this application. 
     I. INDUCTION 
     One of the most important factors for the proper induction is cell preparation. There are several methods of removing erythrocytes from the buffy coats in order to facilitate production of leukocyte interferon: an ammonium chloride lyse of erythrocytes, a sedimentation in starch, and the Ficoll-Hypaque technique. 
     It is generally known that induction of interferons depends upon the kind of cells used for the antigen stimulation. Since each method mentioned above enriches a different population of white blood cells, the preparation of cells is considered to be a critical factor in the expression of a unique set of individual interferon isospecies. 
     The ammonium chloride method, as a routine procedure for the preparation of white blood cells from buffy coats, is relatively reproducible and economical. Although, this method may damage polymorphonuclear cells. 
     The conditions for the induction are basically the same as for the traditional production of Cantell et al, Methods in Enzymology 78:29-38 (1981), herein incorporated by reference. Briefly, human white blood cells are grown in a 10-liter suspension culture at a concentration of 10,000,000 cells/ml using a 20-liter plastic container with continuous stirring at 37° C. Two hours before Sendai virus (200 hemagglutining units/ml) is added to the mixture, the cells are treated with primer (150 IU of IFN-Alpha per ml). Induction is carried for 16 hours. After incubation, the crude interferon is obtained by removal of cells and cellular debris by centrifugation. 
     Many other methods of producing crude interferon alpha exist. For example, Chada et al, U.S. Pat. No. 4,485,038 at columns 4 and 5, describe a particularly useful method of interferon alpha production. 
     II. PURIFICATION PROCEDURE 
     Silicic Acid Adsorption: 
     Clarified supernatant of crude human interferon alpha is cooled to 4° C. prior to purification. To practice this step as a batch operation, the cooled interferon is then gently mixed with a slurry of silica gel (preferentially silicic acid) or controlled pore glass (CPG) previously activated with 20 mM sodium phosphate buffer pH 7.4. The ratio of silicic acid to the original volume of induction culture is in the range 1:10-1:50, preferably 1:30. Continuous low speed stirring is recommended during the 1.5-hour adsorption at a temperature of 4° C. Following adsorption, the gel is transferred to a glass column and washed with 20 mM phosphate buffer pH 7.4 until the adsorption of eluate at 280 nm reaches the background level. 
     Elution of interferon is accomplished with a buffer containing 100 mM TRIS-HC1, 0.5M NaCl, 0.5M tetramethylammonium chloride (TMAC), 10% propylene glycol pH 8.0. The composition of the elution buffer has been optimized to obtain highly dissociating conditions which reduce possible complex formation and facilitate a higher yield of interferon alpha isospecies. With this step, the interferon is concentrated about five times and 93% of the protein has been removed. 
     Virus Inactivation/Ultrafiltration/Concentration: 
     Eluate containing interferon alpha activity is mixed with non-ionic detergent TRITON X-100 (a product of Rohm and Haas Co.) to a final concentration of 0.1% TRITON X-100. In this step, TRITON X-100 can be substituted with other non-ionic detergents such as TWEEN 20 (a product of ICI Americas, Inc.) or NONIDET P-40 (a product of Shell Oil Company). Continuous stirring of the mixture is recommended for 30 minutes at 4° C. to accomplish destruction of the virus. Following incubation, the mixture is transferred to a MILLIPORE cassette or equivalent provided with a membrane of a pore size to preclude passage of material having a molecular weight in excess of about 100,000. The ultrafiltrate, consisting of material of molecular weight less than 100,000, is collected and further concentrated on another ultrafiltration system provided with a membrane of a pore size to preclude passage of material having molecular weight in excess of about 10,000. The concentration procedure is continued until appropriate or desired volume is achieved. This step eliminates substantially all viruses which might resist treatment with non-ionic detergents. The concentrate, consisting of materials of molecular weight greater than 10,000 and less than 100,000, is collected and submitted to the second chromatographic step of purification. 
     Molecular Sieving: 
     The concentrated material, consisting of proteins of molecular weight between 10,000 to 100,000, is loaded onto a column (12 cm×180 cm) with SEPHACRYL S-200 (Pharmacia) or any other sieving beads having resolution capacity ranging from about 10,000 to about 100,000 or greater molecular weight. Molecular sieving is performed at 4° C. under dissociating conditions using 10 mM phosphate buffer, 0.5M NaCl, and 10% propylene glycol pH 7.4. Most of the proteins are cleared from complexes and eluted relative to their molecular size. Fractions corresponding to the molecular weight, ranging from 40,000 to 10,000, are combined and directly applied to a Zn++ chelate column. 
     Zinc Chelate Chromatography: 
     The combined material from molecular sieving column, containing a major portion of interferon activity, is applied on a column having a chelating matrix. The metal chelate carrier used in the invention is Zn++ chelate agarose (SEPHAROSE 6B, a product of Pharmacia) prepared according to Porath et al, Nature 258:598 (1975). Following loading, the column is washed with 10 mM phosphate buffer containing 0.5M NaCl pH 7.4 and operated at a temperature of about 4° C. 
     Buffer Exchange/Concentration: 
     The non-adsorbed material containing a major portion (about 90%) of interferon alpha activity is simultaneously concentrated and buffer is exchanged to 20 mM phosphate buffer pH 7.4 using an ultrafiltration system provided with a membrane of a pore size to preclude passage of protein greater than 10,000 molecular weight. 
     The ultrafiltration procedure is continued until complete exchange of buffer (approximately 1000 fold) is obtained and the concentration of interferon is between 100,000 IU to 1,000,000 IU, preferably 500,000 IU. Following the concentration on 10,000 molecular weight membrane, human serum albumin is added as a stabilizing agent for interferon alpha at a concentration of 1 mg to 10 mg per ml, preferably 5 mg. 
     The final product is sterilized by filtration through any 0.22 um filter, usually GELMAN Products. Prior to sterilization, the filters are primed with 0.5% human serum albumin to avoid losses of interferon alpha activity. 
     The interferon titer is established on human amnion cells (WISH) and bovine kidney cells (MDBK) and adjusted to internal interferon alpha standard. Calibration of the internal interferon alpha standard has been performed against the international interferon alpha standard GA 23-092-530 obtained from the NIH of Bethesda, MD. The interferon is adjusted to the desired concentration, pipeted into vials and freeze dried. 
     In order that the invention may be more clearly understood, preferred embodiments will be further described in terms of the following examples, which should not be construed to limit the scope of this invention, but are offered as exemplary support. 
    
    
     EXAMPLE 1 
     Ten (10) liters of crude interferon alpha was used for adsorption on silicic acid. The protein concentration and interferon activity was 2 mg/ml and 10,000 IU/m1, respectively. Batch-wise type of adsorption was performed in this example. The ratio of silicic acid to crude interferon was 1:30. Prior to the adsorption, silicic acid (Sigma 300SLR) was washed five times with 20 mM phosphate buffer pH 7.4 to remove all fine particles of gel. The silicic acid was autoclaved and used under sterile conditions. Following a 1.5-hour adsorption at 4° C. with continuous stirring, the gel was placed into a 5 cm×12 cm glass column and washed with 20 mM phosphate buffer until optical density (measured at 280 nm) returned to the background level. The interferon bound to silicic acid was eluted with 2500 ml of 0.1M TRIS-HCl containing 0.5M TMAC, 0.5M NaCl, and 10% propylene glycol pH 8.0 at 4° C. Eighty percent (80%) recovery of interferon activity was obtained by this step with the purification factor about 10 fold. 
     TRITON x-100 (2.5 ml) was added into 2500 ml of elute from silicic acid, achieving the final concentration 0.1%. 
     Following a half hour incubation with continuous stirring of the mixture at 4° C., the material was filtered through a membrane of 100,000 molecular weight cut off using MILLIPORE cassette system. The ultrafiltrate was then concentrated to 500 ml on an AMICON membrane with 10,000 molecular weight cut off. At this step, about 90% of interferon alpha activity was recovered and additional 10 fold purification was achieved. 
     Material obtained from the previous step was loaded on a 12 cm×180 cm SEPHACRYL S-200 column previously equilibrated with 10 mM phosphate buffer containing 0.5M NaCl and 10% propylene glycol pH 7.4 and eluted with the same buffer. A constant flow rate of 240 ml/hour was achieved using 1.5 psi pressure. Under these highly dissociating conditions, most of the proteins are cleared from complexes and eluted relative to their molecular size. Fractions corresponding to a molecular weight ranging from 10,000 to 40,000 daltons were collected. In this step, an additional 3 fold increases in purification was achieved. 
     Three (3) liters of material containing the highest interferon alpha activity were pooled from the S-200 column and directly applied to a Zn++ chelate column previously equilibrated with 10 mM phosphate buffer and 0.5M NaCl pH 7.4. After loading, the gel was washed with starting buffer until optical density (measured at 280 nm) returned to background level (about 300 ml). The non-absorbed material, combined with the wash fraction (total interferon alpha activity about 90%), was applied to the buffer exchange ultrafiltration procedure (see below). The remaining 10% of interferon alpha activity was recovered from Zn++ chelate with 0.1M acetate buffer and 0.5M NaCl pH 4.5. This fraction can be used for the further purification of pH labile interferon alpha. Two (2) fold to 4 fold purification is achieved at this step. 
     A total volume of 3300 ml obtained from passage through the Zn++ chelate was applied to an AMICON ultrafiltration system provided with membrane of a pore size 10K molecular weight cut off. The buffer was exchanged with 20mM phosphate pH 7.4 until a 1000 fold exchange ratio was achieved. Simultaneously, the final product was concentrated to the volume of 500 ml. Not only no loss of interferon activity was observed during this step of purification, rather activation was observed. 
     Following the buffer exchange and concentration, human serum albumin was added to the final product at a concentration of 5 mg/ml. The interferon preparation was sterilized by filtration through a 0.22 um GELMAN filter. 
     TABLE 1 summarizes the interferon alpha recovery consistent with each step of the purification sequence, determined on MDBK cells. 
     
                       TABLE 1                                                     
______________________________________                                    
RECOVERY OF INTERFERON ALPHA ACCORDING                                    
TO PRESENT INVENTION                                                      
                 Total Interferon                                         
                 Alpha Activity                                           
                               Percent                                    
Material         (IU)          Recovery                                   
______________________________________                                    
Crude Preparation                                                         
                   1 × 10.sup.8                                     
                               100                                        
Silicic Acid Adsorption                                                   
                 7.8 × 10.sup.7                                     
                               78                                         
100K Ultrafiltrate/                                                       
                 7.3 × 10.sup.7                                     
                               73                                         
10K Concentrate                                                           
SEPHACRYL S-200 Pool                                                      
                 6.8 × 10.sup.7                                     
                               68                                         
Zn++ Chelate (non-adsorbed)                                               
                 6.3 × 10.sup.7                                     
                               63                                         
10K Concentrate  6.5 × 10.sup.7                                     
                               65                                         
______________________________________                                    
 
    
     Specific activity of final preparation measured on MDBK cells is to 1×10E7. 
     EXAMPLE 2 
     A 500 ml batch of crude interferon alpha containing 10,000 IU per ml (measured on MDBK cells) was used for batch-wise absorption with 15 ml of silicic acid equilibrated with 20 mM phosphate buffer pH 7.4. During 1.5-hour adsorption at 4° C., the mixture was continuously agitated with a Stir Pack stirrer. The gel was then placed into a glass column (0.9 cm×25 cm) and washed with 100 ml of 20 mM phosphate buffer pH 7.4. The interferon bound to silicic acid (90%) was recovered by washing the column with 100 mM TRIS-HCl containing 0.5M TMAC, 0.5M NaCl, and 10% propylene glycol pH 8.0. This highly dissociating buffer is particularly suited for the efficient recovery of the full composition of interferon alpha isospecies. The remaining 10% of interferon alpha activity was detected in the non-adsorbed fraction to silicic acid. This value is apparently due to the presence of residual Sendai virus. 
     EXAMPLE 3 
     A 500 ml batch of crude interferon alpha containing 10,000 IU per ml (measured on MDBK cells) was used for batch-wise absorption with 15 ml of silicic acid equilibrated with 20 mM phosphate buffer pH 7.4. During 1.5-hour adsorption at 4° C., the mixture was continuously agitated with a Stir Pack stirrer. The gel was then placed into a glass column (0.9 cm×25 cm) and washed with 100 ml of 20 mM phosphate buffer pH 7.4 
     Interferon activity was first recovered from silicic acid with 100 mM TRIS-HCl pH 8.0 (20% of activity) and then with 100 mM TRIS-HCl containing 0.5M TMAC, 0.5M NaCl and 10% propylene glycol pH 8.0 (70% of activity). The remaining 10% of interferon activity was detected in the non-absorbed fraction to silicic acid. This value is apparently due to the presence of residual Sendai virus. 
     EXAMPLE 4 
     The carrier for the metal chelate chromatography is prepared according to the method of Porath et al (Nature 258;598, 1975; J. Chromatography 90;87, 1974). 
     A mixture of 860 g suction-dried SEPHAROSE 6B, 860 ml of diglicidyl ether, 860 ml 0.6N NaOH and 1.72 g sodium borohydride was shaken for eight hours at 25° C. In order to stop the coupling reaction, the gel was suction-dried and washed with 20 L of deionized water on sintered glass filter. The gel, resuspended in 2 L of 1M NaCl, was again washed with 6 L of water and then with 2 L of 2M Na 2  CO 3 . Following epoxy activation procedure as described by Porath et al, the gel was suspended in 572 ml of 2M NaCO 3  containing 116 g of iminodiacetic acid and heated with continous stirring for 24 hours at 65° C. The reagents were washed from the gel with 30 L of deionized water followed by a wash with 4 L of 0.05M EDTA in 0.5M NaCl pH 7.0 and again 30 L of deionized water. 
     The gel was placed in a glass column and converted to the zinc chelate form by equilibrating with zinc chloride (3 mg/ml adjusted to pH 6.0). The effluent was monitored until the pH value returned to 6.0 and the Zn++ ion detected as evidenced by the appearance of a white precipitant following the addition of 2M NaCO 3  to an aliquot of effluent. The gel was then washed with 0.25M sodium acetate pH 5.0 and equilibrated with 20 mM phosphate buffer containing 0.5M NaCl pH 7.4. After each use, the gel was stripped with EDTA and regenerated as described above. 
     EXAMPLE 5 
     Twenty-five (25) milliliters of interferon recovered from silicic acid was taken for ultrafiltration on XM AMICON membranes with 100K and 300K molecular weight cut off. The solution was filtered to a concentrated volume 0.5 ml. Then the concentrate was washed three times with 0.5 ml of 20 mM phosphate buffer pH 7.4. An aliquot of total 26 mls of ultrafiltrate was tested for interferon alpha recovery. 
     A parallel experiment was performed with 25 mls of interferon alpha recovered from silicic acid, treated with TRITON x-100 at final concentration 0.1% for one-half hour at 4° C. as per EXAMPLE 1. Results are summarized in TABLE 2. 
     
                                           TABLE 2                                 
__________________________________________________________________________
             Total Interferon Units (IU)                                  
                               IFN                                        
             Starting          Recovery in                                
Material                                                                  
       Type of                                                            
             Material Ultrafiltrate                                       
                               Ultrafiltrate                              
Tested Membrane                                                           
             MDBK WISH                                                    
                      MDBK WISH                                           
                               MDBK WISH                                  
__________________________________________________________________________
IFN Alpha                                                                 
       XM 100K                                                            
             31,622                                                       
                  1,995                                                   
                       6,309                                              
                             316                                          
                                20%  16%                                  
Desorbed                                                                  
       XM 300K                                                            
             31,622                                                       
                  1,995                                                   
                      10,000                                              
                           2,511                                          
                                45% 125%                                  
From Silicic                                                              
Acid                                                                      
IFN Alpha                                                                 
       XM 100K                                                            
             19,952                                                       
                  1,584                                                   
                      31,622                                              
                           5,011                                          
                               158% 316%                                  
Desorbed                                                                  
       XM 300K                                                            
             19,952                                                       
                  1,584                                                   
                      19,952                                              
                           2,511                                          
                               100% 158%                                  
From Silicic                                                              
Acid +                                                                    
TRITON                                                                    
X-100                                                                     
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     Results of ultrafiltration indicate full recovery of interferon alpha activity in material filtered in the presence of TRITON X-100 on both membranes. The drop in titer after TRITON X-100 treatment is apparently due to the presence of an excessive concentration of residual Sendai virus in starting material. 
     EXAMPLE 6 
     Twenty-five (25) milliliters of interferon recovered from silicic acid were taken for ultrafiltration on the AMICON membranes (YM and XM) with 100K molecular weight cut off. 
     The solution was filtered to a concentrate volume of 0.5 ml, then the concentrate was washed three times with 0.5 ml of 20 mM phosphate buffer pH 7.4. An aliquot of the total of 26 mls of ultrafiltrate was tested for interferon alpha activity. A parallel experiment was performed with 25 mls of interferon alpha recovered from silicic acid treated with TRITON X-100 at final concentration of 0.1%, for one-half hour at 4° C. as per EXAMPLE 1. Results are shown in TABLE 3. 
     
                                           TABLE 3                                 
__________________________________________________________________________
             Total Interferon Units (IU)                                  
                               IFN                                        
             Starting          Recovery in                                
Material                                                                  
       Type of                                                            
             Material Ultrafiltrate                                       
                               Ultrafiltrate                              
Tested Membrane                                                           
             MDBK WISH                                                    
                      MDBK WISH                                           
                               MDBK WISH                                  
__________________________________________________________________________
IFN Alpha                                                                 
       YM    31,622                                                       
                  1,995                                                   
                      12,589                                              
                           1,258                                          
                                40%  63%                                  
Desorbed                                                                  
       XM    31,622                                                       
                  1,995                                                   
                       6,309                                              
                             316                                          
                                20%  16%                                  
From Silicic                                                              
Acid                                                                      
IFN Alpha                                                                 
       YM    19,952                                                       
                  1,584                                                   
                      19,952                                              
                           1,584                                          
                               100% 100%                                  
Desorbed                                                                  
       XM    19,952                                                       
                  1,584                                                   
                      31,622                                              
                           5,011                                          
                               158% 316%                                  
From Silicic                                                              
Acid +                                                                    
TRITON                                                                    
X-100                                                                     
__________________________________________________________________________
 
    
     Results of ultrafiltration indicate full recovery of interferon alpha activity in material filtered in the presence of TRITON X-100 on both membranes. The drop in titer after TRITON X-100 treatment is apparently due to the presence of an excessive concentration of residual Sendai virus in starting material. 
     EXAMPLE 7 
     Ten (10) milliliters of crude interferon alpha were taken for the concentration/ultrafiltration on an XM AMICON membrane of 100K molecular weight cut off. The solution was filtered to a concentrate volume of 0.5 ml, then the concentrate was washed three times with 0.5 ml of 20 mM phosphate buffer pH 7.4. An aliquot of a total of 11 ml of ultrafiltrate was tested for the recovery of interferon alpha activity. 
     A parallel experiment was run with 10 ml of crude interferon alpha treated for one-half hour with 0.1% TRITON X-100. TABLE 4 summarizes the results. 
     
                                           TABLE 4                                 
__________________________________________________________________________
           Total Interferon Units (IU)                                    
                             IFN                                          
           Starting          Recovery in                                  
           Material Ultrafiltrate                                         
                             Ultrafiltrate                                
Material Tested                                                           
           MDBK WISH                                                      
                    MDBK WISH                                             
                             MDBK WISH                                    
__________________________________________________________________________
Crude IFN-Alpha                                                           
           31,620                                                         
                10,000                                                    
                    10,000                                                
                          3,162                                           
                              33%  33%                                    
Crude IFN-Alpha +                                                         
           10,000                                                         
                10,000                                                    
                    10,000                                                
                         10,000                                           
                             100% 100%                                    
0.1% TRITON X-100                                                         
__________________________________________________________________________
 
    
     TRITON X-100 increases recovery of interferon alpha from ultrafiltration on XM 100 AMICON membrane. 
     EXAMPLE 8 
     Influence of TRITON X-100 on the interferon titer has been tested. Assay was performed on MDBK and WISH cell lines with the following samples: 
     (1) 10 ml of interferon alpha desorbed from silicic acid; 
     (2) 10 ml of interferon alpha desorbed from silicic acid +TRITON X-100 (0.1% final concentration); and 
     (3) 10 ml of silicic acid elution buffer+TRITON X-100 (0.1% final concentration). 
     Following one-half hour incubation at 4° C., all samples were assayed for interferon activity. Results are presented in TABLE 5. 
     
                       TABLE 5                                                     
______________________________________                                    
INFLUENCE OF TRITON X-100 ON INTERFERON TITER                             
                   Interferon Titer (IU/ml)                               
Material Tested      (MDBK)    (WISH)                                     
______________________________________                                    
1.  Interferon Alpha Desorbed                                             
                         100,000   100,000                                
    from Silicic Acid                                                     
2.  Interferon Alpha Desorbed                                             
                         100,000   100,000                                
    From Silicic Acid +                                                   
    TRITON X-100                                                          
3.  Silicic Acid Elution Buffer +                                         
                             0         0                                  
    TRITON X-100                                                          
______________________________________                                    
 
    
     EXAMPLE 9 
     A hemagglutination test for the presence of Sendai virus hemagglutinin was performed on crude interferon alpha and interferon eluted from silicic acid. The influence of TRITON X-100 on a release of hemagglutinin has been determined in a parallel experiment according to standard procedure. 
     Samples (10 ml) were tested for the presence of hemagglutinin and then treated with TRITON X-100 (0.1% final concentration) for one-half hour at 4° C. Following incubation, samples were filtered through an XM 100K AMICON membrane and assayed again for hemagglutination activity. Results are presented in TABLE 6. 
     
                       TABLE 6                                                     
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INFLUENCE OF TRITON X-100 ON RELEASE OF                                   
HEMAGGLUTININ FROM SENDAI VIRUS                                           
               Hemagglutination Titer U/ml                                
Material         Starting 100K UF  100K Conc.                             
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Crude Interferon 64       0        128                                    
Interferon Alpha Eluted                                                   
                 0        0         0                                     
From Silicic Acid                                                         
Crude Interferon +                                                        
                 128      0        256                                    
TRITON X-100                                                              
Interferon Alpha Eluted From                                              
                 6        0         24                                    
Silicic Acid + TRITON X-100                                               
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     Elevation of hemagglutinin level in samples treated with TRITON X-100 indicates disruption of virus particles and release of free hemagglutinin. 
     EXAMPLE 10 
     The influence of TRITON X-100 on multiplication of residual Sendai virus in eluate from silicic acid has been determined. The assay was performed at Wadley Institutes and uses embryonated chicken eggs (10 days old). An appropriate aliquot of a 100 ml sample was tested for the presence of an infectious virus. Then the sample was treated with TRITON X-100 (0.1% final concentration) for one-half hour at 4° C. Following incubation, the sample was filtered through an XM 100K AMICON membrane and assayed again for the presence of infectious Senai virus. The results are presented in TABLE 7. 
     
                       TABLE 7                                                     
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INFLUENCE OF TRITON X-100 ON                                              
MULTIPLICATION OF SENDAI VIRUS                                            
                  Presence of                                             
Material          Infectious Sendai Virus                                 
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Interferon Alpha Desorbed                                                 
                  Positive                                                
From Silicic Acid                                                         
Interferon Alpha Desorbed                                                 
                  Negative                                                
From Silicic Acid +                                                       
TRITON X-100                                                              
100K Ultrafiltrate                                                        
                  Negative                                                
100K Concentrate  Negative                                                
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     While the methods of this invention have been described in terms of preferred embodiments, it will be apparent to those of skill in the art that various changes can be made in the methods disclosed without departing from the scope of the invention, which is defined by the following claims.