Viral Liposome Particle

By attempting to purify influenza virus as much as possible, its undesirable side effects have been reduced but at the same time its antigenic effect also has been reduced.

It is an object of the present invention to increase the antigenicity of an influenza virus preparation. Another object is to reduce the toxicity of the influenza virus. Another object is to provide a simpler and more economical process for purifying influenza virus and isolating antigenic subunits. A further object is to provide a particle wherein the outer membrane of influenza virus is attached to a liposome. Still another object is to provide a liposome having an intact whole influenza virus inside. Yet another object is to provide a method for preparing such particles. These and other objects of the present invention will be apparent from the following description.

The outer membrane of influenza virus A or B is attached to a liposome by (1) reaction with a mixture of a phospholipid such as dioleoylphostidylcholine and a positively charged amino-containing surfactant such as stearylamine or (2) reaction with a positively charged amino-containing surfactant such as stearylamine followed by reaction with a phospholipid such as dioleoylphosphotidylcholine. In addition by the first technique some virus is entrapped inside some of the liposomes, usually one virus per liposome.

The present invention relates to influenza vaccine and, more particularly, to a subunit influenza vaccine wherein the outer membrane of the influenza virus is attached to a liposome. One technique, in addition, allows whole virus to be entrapped inside the liposome. A liposome is a continuous lipid surface, either unilamellar or multilamellar, enclosing a three-dimensional space.

It has been found according to the present invention that the outer membrane of the influenza virus can be removed from the rest of the influenza virus particle and reattached to the outer surface of a liposome containing phospholipid and an amino-containing surfactant which has a positive charge. The viral spikes of the influenza virus remain intact in this process. The resulting particle, a liposome having fused thereto the outer membrane of the influenza virus with intact spikes, has been named a spikoliposome.

The liposome is prepared from either a natural or synthetic phosphocholine-containing lipid having either two fatty acid chains of from 12 to 20 carbon atoms, or one fatty acid chain of from 12 to 20 carbon atoms and a second chain of at least 8 carbon atoms. In general, synthetic lipids are preferred as they have fewer impurities. The synthetic lipid may be a phosphatidylcholine containing two fatty acid side chains from 12 to 20 carbon atoms. Some suitable synthetic lipids are, for example:

dimyristoylphosphatidylcholine,

dioleoylphosphatidylcholine,

dipalmitoylphosphatidylcholine, and

distearoylphosphatidylcholine,

while some suitable natural lipids are, for example:

phosphatidylcholine, and

sphingomyelin.

The positively charged amino-containing surfactant may be a fatty acid amine of from 12 to 20 carbon atoms such as, for example, cetylamine and stearylamine, or a salt of an amino-containing surfactant such as, for example,

cetyl benzyldimethyl ammonium chloride,

N-hexadecylpyridinium chloride,

hexadecyltrimethyl ammonium bromide, and cetyltrimethyl ammonium bromide.

In preparing the spikoliposome virus particle of the present invention, the positively charged amino-containing surfactant and the phospholipid are dried together. The influenza virus in aqueous medium (water or low molarity buffer, pH 6.8-7.4), is then added under liposome forming conditions, such as agitation, e.g., bath sonication for from about 2 to about 8 minutes, to form positively charged liposomes to which the outer membrane of the virus is fused. The resulting particle is a spikoliposome, that is, a liposome having fused thereto the outer membrane of influenza virus with the spikes intact. In the same preparation there also exists liposomes having no spikes fused thereto but which contain usually one entrapped intact influenza virus per liposome.

In a second technique the virus is reacted directly with the positively charged surfactant. This, as an aqueous (water only) suspension, is then added to the dry phospholipid and the preparation agitated, e.g., by bath sonication for from about 2 to about 8 minutes, to form positively charged liposomes to which the outer membrane of the virus is fused. The resulting particle is a spikoliposome, that is, a liposome having fused thereto the outer membrane of influenza virus with the spikes intact.

The preparation containing both types of particles may be administered as an influenza vaccine but, if desired, the particles may be separated by centrifugation and column chromatography, and administered individually as an influenza vaccine.

The following examples illustrate the present invention without, however, limiting the same thereto.

Dioleoylphosphatidylcholine (20 mg in 0.8 ml chloroform) and stearylamine (3 mg dry powder dissolved in 1-2 ml dry chloroform) are mixed together for 3-5 minutes in a 25 ml round bottom or pear-shaped flask and then dried down in vacuo at 37.degree. C. Immediately after drying, dry nitrogen gas is blown into the flask and 3.5 ml of the influenza virus preparation is added slowly. The virus preparation previously has been dialyzed aseptically in 1/4" cellulose dialysis tubing for 18 hours at 2.degree.-4.degree. C. against three charges of 1 liter each of 0.063 M sodium phosphate buffer (pH 7.0) and contains approximately 560 CCA/ml. Nitrogen gas is continuously bubbled through the solution which is placed in the center of a small (13.5 cm.times.13.5 cm) ultrasonic cleaner bath (Cole-Parmer) filled 6 cm-8 cm deep with water which contains 1 ml of Triton X-100 as detergent. The cleaner bath operates at 50-55 KHz and is maintained at 20.degree.-22.degree. C. by addition of ice. The solution is sonicated, with occasional swirling of the contents, for 7 minutes. After sonication the contents of the flask are transferred to a 6 ml serum bottle and capped with a rubber stopper. The sonicated material is stored at 2.degree.-4.degree. C. The preparation is stable for at least five months.

Stearylamine (3 mg) plus ethanol (0.4 ml) are heated to 55.degree.-60.degree. C. for 1-2 minutes until the stearylamine is completely soluble. Then deionized water (2.6 ml) which has been heated to 55.degree.-60.degree. C. is slowly added with swirling. At this stage the solution may be opalescent, but there is no precipitate. Pure dry nitrogen gas is bubbled through the solution for 10 minutes until the solution is cooled to 28.degree.-34.degree. C. Then 0.9 ml of influenza virus which has been dialyzed as in Example 1 and containing approximately 2200 CCA/ml is slowly added at room temperature and nitrogen gas bubbled through for a further 4 minutes. No obvious precipitate is present. Next, the virus-stearylamine preparation is slowly added to a dried down preparation of dioleoylphosphatidylcholine (20 mg) in a 25 ml round bottom or pear-shaped glass flask. While continuously bubbling nitrogen gas through, the preparation is sonicated for 7 minutes in a Cole-Parmer ultrasonic cleaner bath at 50-55 KHz. The temperature of the cleaner bath is maintained at 20.degree.-22.degree. C. by the addition of ice. During sonication the contents of the flask are occasionally swirled. After sonication the contents of the flask are transferred to a 6 ml serum bottle, capped with a rubber stopper, and stored at 2.degree.-4.degree. C. where the preparation is stable for at least three months. The final concentration of virus is approximately 560 CCA/ml.

The spikoliposome preparation of Example 2 is compared with aqueous influenza vaccine, dialyzed aqueous influenza vaccine, each containing New Jersey type A influenza virus and a vaccine consisting of the spikoliposome preparation of Example 2 without virus. Each is administered to a group of guinea pigs, 8 animals per test, at a virus concentration of 100 CCA units per dose, and the geometric mean hemagglutination-inhibition titer is calculated on day of injection as well as 21 and 42 days following injection. The following results are obtained.

Spikoliposome preparations prepared according to Example 2 using type A Victoria and type B Hong Kong influenza virus and various lipids are administered to a group of 8 mice and the arithmetic mean hemagglutination inhibition titer calculated 42 days following injection with the following results. An aqueous influenza vaccine without spikoliposomes is used as control.

Spikoliposome preparations produced in accordance with Examples 1 and 2 using A/Victoria and B/Hong Kong influenza virus and whole formalin killed aqueous influenza vaccines made with the same two viruses but without spikoliposomes are administered to a group of 8 mice and the geometric mean hemagglutination inhibition antibody titer is determined 30 days following injection. The following results are obtained.