EP0666907A1

EP0666907A1 - CULTURE CELLS OF $i(QUILLAJA SP.)

Info

Publication number: EP0666907A1
Application number: EP94901055A
Authority: EP
Inventors: Kristian Dalsgard; Max Henry
Original assignee: SEED CAPITAL INVESTMENTS(SCI) BV
Current assignee: SEED CAPITAL INVESTMENTS(SCI) BV
Priority date: 1992-10-30
Filing date: 1993-10-29
Publication date: 1995-08-16

Abstract

The present invention relates to cultured cells of Quillaja sp. for the preparation of active substances from Quillaja sp.,, such as saponins. The cells may either originate from a callus tissue culture or from a suspension cell culture. Preferred Quillaja sp. are species selected from the group consisting of Quillaja saponaria Molina, Quillaja smegmadermos, Quillaja brasiliensis. The invention further relates to active substances extracted from cultured cells of Quillaja sp. and to preparations comprising these active substances, or a non-dialysable or a dialysable fraction thereof, to methods of preparing the active substances and to various agents, comprising the dialysable and/or the non-dialysable fraction of an extract of cultured cells of Quillaja sp. and having various properties.

Description

Cultured cells of Quillaja sp.

The present invention relates to cultured cells of Quillaja sp.. a method for preparing active substances from Quillaja sp.. various products comprising the active sub¬ stances, a method for preparing Immune-Stimulating COMplexes (ISCOM's) from the active substances and vaccins and adju¬ vants comprising the ISCOM's, the adjuvant ISCOM-matrix (Lδvgren, K. thesis, ISBN 91-576-3202-2), the adjuvant Quil A (Dalsgaard, K. , Arch. ges. Virusforsch. 44, 243-254

(1974), the adjuvant QS 21 (Jia-Yan Wu, J. Immunology 148, 1519-1525 (1992) , and other saponin adjuvants.

Immune-stimulating complexes (so-called ISCOM's) are negatively charged pentagonal dodecahedra that form sponta- neously on mixing cholesterol and the saponins of Quillaja sp.. During their formation proteins and other lipids can be incorporated. ISCOM's have been found to strongly enhance immune responses and are therefore used as an immunological adjuvant and carrier/delivery system in e.g. vaccins. Quil A, QS 21, and other saponin adjuvants are products derived from the natural bark having immunological adjuvant activity in a variety of vaccines.

For the production of ISCOM's there is a growing need for inter alia Quil A. Quil A is a mixture of the active substances (saponins) originating from the bark of the Quillaja sp. tree growing mainly in Chile. The natural sources of Quillaja bark are limited. In fact, old trees are already rare today and yet about 1000 tons of bark per year are exported from Chile. Because the increasing demand for active substances (saponins) for various purposes a shortage of material is to be expected in the future.

It is therefore highly desirable to find other ways of isolating Quil A and other active substances of Quillaja (saponins) for the preparation of ISCOM's, as adjuvants, and for various other applications.

It has now been found that cells, tissues or organs of the Quillaja sp. plant body can be cultured in vitro in a liquid or on a solid medium. The invention thus provides cultured cells of Quillaja sp. for the preparation of active substances from Quillaja sp. The cultured cells may originate from a callus cell culture, wherein tissues or organs are grown on a solid medium. The term "callus" refers to an amorphous lump of cells having lost their organ-forming capacity, and which lump is formed when a fragment of the plant body is tissue cultured on a solid medium. The so obtained callus shows an external form resembling the agglutination tissue of the plant body. The cultured cells may also originate from a suspension cell culture. The term "suspension" cell culture refers herein to a fine flocky dispersion of the cells formed when pieces of callus are further inoculated and cultured in a liquid medium under aerobic conditions. According to the invention various kinds of Quillaja plants can be used for tissue or suspension culture, for example Quillaja saponaria Molina, Quillaja smeα adermos, Quillaja brasiliensis and the like.

The conventional medium-compositions for tissue cultures mentioned in the literature, for example, the media called White's medium (White P.R. Growth 2:53 (1943)), Hel¬ ler's Medium (Heller R. These Sc. Nat. Paris (1953)), Muras- hige and Skoog's medium (Murashige T. and Skoog F. Physiol. Plant. JL5:473 (1962)), Linsmaier and Skoog's medium (Lin- smaier E.M. and Skoog F. Physiol. Plant. 18., 100 (1965)), and Gamborg, Miller and Ojima's medium (Gamborg O.L. , Miller R.A. and Ojima K. , Exp. Cell. Res. 5_0, 151 (1968)), can be used in the present invention. These known media consist of inorganic substances and other trace elements which have hitherto been used in the media for the water-culture method for plants, such as saccharide, auxins (growth-promoting substance) , cytokinins, vitamins and amino acids. In parti¬ cular, the following are used in these media: inorganic salts selected from potassium chloride, calcium chloride, potassium nitrate, calcium nitrate, sodium nitrate, ammonium nitrate, sodium nitrate, magnesium sulfate, potassium phosp¬ hate, sodium sulfate, magnesium nitrate, ammonium nitrate, sodium sulfate, magnesium sulfate, potassium phosphate, sodium phosphate, ferric chloride, ferric sulfate, NA₂-EDTA (NA₂-ethylenediamine tetra-acetic acid) , manganese sulfate, zinc sulfate, boric acid, potassium iodide, copper sulfate, sodium molybdats, aluminium chloride, cobalt chloride, and the like, saccharide selected from sucrose, glucose, fructo¬ se, mannose, and the like, auxins such as 2,4-dichlorophe- noxyacetic acid, α-napthaleneacetic acid, indol-3-acetic acid, cytokinins such as kinetin, benzylaminopurine, zeati- ne, 2-isopentenyladenine and the like, vitamins such as thiamin hydrochloride, pyridoxin hydrochloride, nicotinic acid, myo-inositol, biotin, and a ino acids such as glycin. Table 1 shows examples of conventional medium compositions for tissue-culturing.

Table 1

Constituents White•s Murashige & Linsmaler (mg./l) medium Skoog's & Skoog's medium medium

KC1 65

440 1900

6,2 370

1650 170

27,84 37,34 22,3 8,6 0,83 0,025

In order to tissue-culture Quillaja sp. according to the present invention, the plant body of Quillaja sp. plant, fragments of leaf, stem, root, flower, seed or other organs or tissues of the plant are washed, surface-sterilized, placed on the sterile agar medium for tissue-culture which is contained in a tube or flask plugged with cotton wool, cellulose or plastic cap and has one of the compositions as described in the above Table 1, and are incubated at 25- 30°C.

Said fragments or organs or tissues swell and white, yellowish-white or greenish-yellow callus is derived in 2-6 weeks. Such callus can be gradually purified by means of repeating the similar solid medium-culturing, that is, by inoculating fresh solid medium by turns with small pieces of callus formed in the previous solid medium-culturing. The callus thus reformed and refined on the solid medium by subculture in then inoculated into a liquid medium having one of the compositions as described in Table 1, and cultured on a shaker at temperature of 25-30°C for 2-3 weeks in order to obtain a suspension cell culture. The inoculum is e.g. about 3 g (by fresh weight) of callus to 100 ml of liquid medium, and the callus propagates in the culture liquid in the state of a flocky suspension, that is, as "Quillaja cells". These Quillaja cells are further subcultu- red by repeating the similar shake-culture in liquid medium, that is, by inoculating fresh liquid medium by turns with a portion of the previous suspension cultured containing Quillaja cells. The suspension culture obtained in the shake-culture is, after scale-up, inoculated into a liquid medium set in a bioreactor made of pyrex or stainless steel, and cultured with aeration while being agitated gently. The quantity of inoculum is one tenth of the quantity of whole medium, and intensive agitation is unfavorable because the membranes of Quillaja cells are broken thereby. The amount of air to aerate is 0.2-30 liters/liter of medium/minute and the culturing period is 2-3 weeks, i.e. the same as that of the above shake-culture. The yield of dried weight of these Quillaja cells is 30-35 percent of sugar consumed in the suspension culture and amounts to 6.9 g per liter of the medium. It will take 2-6 weeks for agar medium culture and 2-3 weeks for each liquid shake-culture and aeration-liquid bioreactor culture, totalling to 6-12 weeks, to obtain a suspension containing Quillaja cells as raw material for the preparation of active substances from which saponins for the formation of ISCOM's might be isolated. However, when the suspension culture is once obtained in the aeration-culture in the bioreactor, a semi-continuous process may be adopted, wherein one portion of the culture is taken out to leave the other portion thereof in the bioreactor and fresh sterile medium is supplemented to the remaining portion so as to carry on the culturing of Quillaja cells.

The active substances prepared from the cultured cells of Quillaja sp. are mainly saponins. Saponins are a type of glycosides widely distributed¹ in plants. Saponins consist of a sapogenin which constitutes the aglucon moiety of the molecule, and several sugars. The sapogenin is in this case a triterpene and the sugar moiety may consist of rhamnose, fucose, arabinose, xylose, galactose, glucose, glucuronic acid, and possibly other minor sugars. The invention further relates to a method for preparing active substances from Quillaja sp. comprising the steps of: a) culturing cells from Quillaja sp. in vitro: and b) preparing a cell culture extract comprising the active substances.

It has been found that the extract of Quillaja sp. cell culture comprising active substances can be separated into two fractions, one being a non-dialysable fraction and the other one being a dialysable fraction. The term "dialy¬ sable" as used herein refers to compounds removed from a dialysis sack after dialysing a crude extract of a Quillaja sp. cell culture against saline for about 24 hours. The term "non-dialysable" as used herein refers to compounds retained in a dialysis sack after dialysing a crude extract of a

Quillaja sp. cell culture against saline for about 24 hours. Both the dialysable and the non-dialysable fraction show interesting properties. The compounds of the dialysable fraction are first of all capable of inducing foam in aque- ous solutions. This is demonstrated by the fact that the dialysate is foaming readily when shaken. Furthermore the active substances of the dialysable fraction can act as emulsifiers for producing oil-in-water emulsions showing similar properties as the compounds of the "Tween" series. For example, experiments showed that 9 ml of dialysate and 1 ml of mineral or biodegradable oil, such as squalane, forms a stable emulsion when shaken vigorously or treated by ultrasonification. The dialysable fractions are also capable of binding ammonia. The dialysable fraction from the active substances obtained from the cultured cells of Quillaja sp. therefore have properties which can be utilized for similar technical purposes as extracts of the natural bark. Examples of said technical purposes are their use as emulsifiers in food and beverages and in photographic film emulsions. They are also useful as additives in the treatment of waste water and slurries because the dialysable active fraction breaks down surface crusts and reduces ammonia- and odor formation in waste water plants, slurry tanks for liquid manure in pig production stables, slurry containers and the like, thus facilitating microbial and/or enzymatic breakdown and redu¬ cing odor of industrial-, household-, farm- and animal waste. They may also be used as an additive to animal feeds to reduce odor of their excrements, and to increase the utilization of feed. Their foaming ability renders them useful as additives in beverages, such as soft drinks, or as a foam producing agent in fire extinguishers. They may also be used as detergents in e.g. shampoos and the like.

The non-dialysable and possibly some of the dialysa¬ ble fraction contains the active substances that are useful as ISCOM-forming and adjuvant agents. The substances are non-dialysable because they have a strong intrinsic charac- teristic of forming micelles. These micelles have the capa¬ city to complex with cholesterol and other lipids leading to ISCOM formation. But these properties also means that the retained substances are hemolytic to red blood cells such as SRBC (sheep red blood cells) . This hemolytic property can be used for their assay in the cell culture extracts.

The matrix of immune-stimulating complexes of the invention is preferrably constructed by: a) preparing a non-dialysable fraction from an extract of cultured cells of Quillaja sp. : b) adding at least one lipid and at least one detergent to the non-dialysable fraction; c) allowing the ISCOM's or ISCOM-matrix to form; and d) removing the detergent.

The ISCOM's thus prepared are very well suited to be used in various vaccins as immunological adjuvants.

The cultured cells of the pre'sent invention are advantageous in many respects for preparing active substan¬ ces of Quillaja sp..

For example, the natural source for the immuno- logical and ISCOM-forming substances is a highly variable material, the individual components of which are difficult to separate. The cultured cells of the invention are a much more reliable way of producing the active substances. Anot- her advantage is that the culture cell extracts can be validated under good manufacturing principles. The cultured cell products are free from many of the e.g. coloured sub¬ stance in the natural extract from the plant. The resulting product is much more homogeneous.

The cell cultures, especially the suspension cultu¬ res, can be subcloned to establish cell lines which will produce individual substances rather than a group of related substances, which is the case in the natural plant. In the examples it will be demonstrated that one of the obtained suspension culture cells produce a much more restricted saponine pattern in HPTLC than the callus culture from which it is derived, which itself is already more restricted than natural extracts. The cultured cells for preparing active substances will be cheaper when scaled up because the fermentation of plant suspension cell culture is straight forward and the medium is inexpensive in large volumes. Furthermore the active substances will be much easier to purify and validate than substances from the natural plant, because all parame¬ ters governing the production and purification can be moni- tered in a reliable way.

The present invention will be further illustrated by means of the following examples that are in no way intended to limit the scope of the invention.

EXAMPLE 1

Preparation of cultured cells

The internode explants of stems of Ouilaja saponaria Molina where surface sterilised with first aqueous ethanol

I

70°B (1 mm.)and NaOCl 20^βCh with a drop of Teepol per liter for 20 minutes (exactly twice 10 in.), rinsed 3 times with sterile distilled water and put on a solid modified Muras- hige and Skoog's basal medium (M. and S. Physiol. Plant. 1962 JL5, 473) usually used for plant cell cultures. The modifications concern carbohydrates: saccharose is replaced by glucose (same concentration), Kl: 0.75 mg/1 instead of 0.83, vitamins: thiamine.HCl 1 mg/1, nicotinic acid 0.1 mg/1, pyridoxin.HCl 0.1 without glycin and pH 5.7. This medium was previously used with success for tissue culturing Saponaria officinalis and Gypsophilla paniculata. To this basal medium were added two phytohormones: one auxin selec- ted from 2,4 D (2,4-dichlorophenoxyacetic) , NAA (naphtalene- acetic acid) or IBA (indolbutyric acid) in three concentra¬ tions: 10^"5 M, 10^"6 M or 10^'7 M; and one cytokinin selected from kinetine (K) or benzylaminopurine (BAP or BA) . Then 54 mediums were prepared and 5 explants were put on each type of medium in test-tubes of 25 cm length and 2.5 cm width (diameter) . These tubes were put in a culture room at 25°C and a 12 hour photoperiod of classical white neons.

After 3 to 6 weeks primary calluses appeared and were subcultured on the same fresh medium. The callus cultu- res obtained on each medium are considered as one original cell line. The frequency of the subculture of each cell line depended upon the growth rate of the cell and varied from one month to three months. The cell lines not subcultured after three months (the growth rate being too slow) were discarded. Six months after obtention of the callus lines (the shortest time necessary to consider the cell line as stable as possible) callus biomass of the main cell lines were tested to estimate the saponin content and first cell suspension were established from each callus cell line to improve the growth rate and then the biomass production. One of the suspension cell lines, named NAA 10^"5 M/K10^'6 M, was detected to be an ISCOM saponin producing cell line.

Some of the choices in these conditions of obtention of these cell lines are the fruit of own experience of the inventors. For example, internodes are used directly instead of other parts of the stem (nodes and¹ leaves) because it was found by Japanese scientists in using Panax ginseng (Kubo et al, J. Nat. Prod. 1980, 43., 278) and in using Bupleurum falcatum (Tani et al, J. Chromatogr. 1986, 360. 407) and by the inventors in using Gypsophila paniculata (Henry et al, Phytochemistry 1991, 3i), 1819) that the saponin biosynthesis occurred in the phloem part of the stem in the plants that were studied. It is therefore considered the best to put the biosynthetic part of the plant in culture to obtain the production of the compound in vitro. It seems to be evident but it is not shared' by many persons skilled in the art because it is thought that the plant cells could become totipotent in vitro. Theoretically each cell of each part of a plant producing one secondary compound would be able to proliferate while keeping its biosynthetic property, but until now this has not been possible for a number of plant species, because the very precise molecular biological mechanisms bringing about the cell proliferation in plants are as yet poorly understood. It is possible that one of the definite tissues in the plant able to proliferate to give cell cultures seems to be the cambium. On the other hand the cambium might be the tissue that gives rise to the phloem tissue in the whole plant and in vitro cultures.

EXAMPLE 2 Extraction procedure

To avoid any possible breakdown of substances, both callus and suspension cell culture solids were lyophilized after harvesting. The lyophilized solids were kept in the freezer at -20°C until use.

To make an extract these solids were weighed out and 10 times as much as water was added. This suspension was homogenized firstly by "Ultraturrax" and subsequently by ultrasonic disintegration (MSE) 3 x 30 min. at maximum power. After stirring for 30 min. at room temperature the mixture was centrifuged at 5000 g for 30 min. The superna¬ tant was isolated and stored at -20°C until further analy¬ sis.

EXAMPLE 3 HPTLC

0,4 microliter of callus extracts of the cell lines was applied as a band by use of a Deaga applicator to HPTLC plates, Merck Kieselgel 60 10 x 10 cm. The plates were developed in a Camag horizontal developing chamber by the solvent 200 mg CaCl₂ . 2 H₂0 dissolved in 10 ml water + 40 ml methanol + 40 ml chloroform.

The plates -were left to saturate with vapour from 10 ml of solvents in the central chamber for 3 minutes after which the plates were developed for 25 min. by 2 ml of solvent in the reservoir. The plates were dried in a fume hood for 5 min. , sprayed by a mixture of concentrated sulp¬ huric acid in methanol 1:1, and heated in an oven for 10 min. at 120°C. The separated bands were recorded densitome- trically using a 256 grey scale scanner and the Apple Macin¬ tosh software ScanAnalysis.

Almost all callus and suspension culture extracts showed the presence of two major bands. These bands corres¬ pond in their migration rate to similar bands present in extracts of the natural bark of Quillaja sp. imported from South-America. Similar to the natural compounds these two bands pass a dialysis membrane and/or ultrafiltration mem¬ branes with cut off levels higher than 10000, indicating that they do not form micelles. Figure 1 shows the results for one of the callus cell cultures ("Lc") . "A" represents point of application, "1" and "2" represent the two major bands found in the HPTLC and "F" stands for front of the solvent.

After dialysis against 1 liter of saline for 24 hours the non-dialysable fraction retained in the dialysis sack is subjected to HPTLC. The results are shown in Figure 2. "3" and "4" represent the two major bands found in the HPTLC.

EXAMPLE 4

Hemolytic assay

Serial two-fold dilutions of plant cell culture extracts are made in 0,85% NaCl. To 1.5 ml of these diluti¬ ons are added 0.5 ml of a sheep red blood cell suspension (washed and standardized to an O.D. value of 28 at 510 nm) . After end over end mixing for 10 minutes the samples are centrifuged at 2000 x G for 5 minutes. The supernatants are measured spectrophotometrically at 510 nm, and the values are used as a measure for hemolysis (hemoglobin release) .

The results¹ are shown in Figure 4. The positive suspension culture extract "L" herein also called "Ls" shows a substantially higher hemoglobin release than the low- producer suspension cell culture extract "K" and than the non-producer suspension cell culture "M" herein also called "Ms".

21 extracts of callus cultures (A' to P Table 2) grown at different conditions have been tested in the same assay and show varying content of hemolytic substances: higher the longer the dashed line at the respective letter. The callus culture L in Table 2 is the basis of suspension culture L herein also called "Ls".

Table 2

Hemolysis index

Callus culture extracts

Quillaja saponaria Molina

If making arbitrary interpolations in the hemolysis curves using an absorbance at 0.5 as end point, the following values are obtained:

_κ so .

L 20

M 7.0

N 7.0 O 20

0• 40

P 3.4

EXAMPLE 5 ISCOM forming capacity

One ml of extract "Ls" (suspension cell culture L) is dialysed against 1 liter of saline for 24 hours. To the non-dialysable fraction of the extract 10 microliters of lipid mix are added (cholesterol and phosphatidylcholine each in a concentration of 20 mg/ml in a 20% aqueous soluti¬ on of the detergent MEGA 10) . The mixture is turned end over end for a minimum of 1 hour to let the reaction take place. It is then dialysed again against 1 liter of saline to remove the detergent. The content of the dialysis sack is now inspected for ISCOM matrix structures in the electron microscope (EM) by negative staining with 2% uranyl acetate on carbon coated grids. Figure 3 shows an EM photograph showing that ISCOM's have been formed.

EXAMPLE 6

Adjuvant assay in guinea pigs

From the densitometric analysis of the HPTLC plates of the non-dialysable fraction of the extracts it was esti¬ mated that the loyphilized callus culture "Lc" contained about 1% of hemolytic/ISCOM matrix forming substances. The lyophilized suspension cell culture "Ls" contained about 0.5%. The "Lc" suspension cell culture was produced from the "Lc" callus culture, and since both contained substantial amounts (about the same as in the natural bark) of hemolytic and ISCOM forming saponins, the extracts of these two forms of cultures were tested for immunological adjuvant activity. A suspension cell culture extract "Ms" not producing these substances was included as a negative control. The adjuvant Quil A, extracted from the natural bark served as a positive control.

A total of 30 guinea pigs have been used for each substance tested. Three independent experiments have been made with ovalbumin as antigen, and 3 independent experi¬ ments with inactivated porcine parvovirus (PPV) as antigen. 5 guinea pigs were included in each individual group. Five groups have been tested all with antigen either ovalbumin or PPV. Group l: Saline control

Group 2: + Quil A, 50 micrograms, positive control.

Group 3: + callus extract "Lc", 50 micrograms.

Group 4: + suspension extract "Ls", 50 micrograms.

Group 5: + suspension extract "Ms", 50 micrograms, negative control.

The results are shown in the figure 5. Both extracts "Lc" and "Ls" irrespective of whether obtained from callus- or suspension plant cell culture (after dialysis) had the same adjuvant activity in guinea pigs as Quil A from the natural plant. The extract "Mc" negative for hemolytic saponins was also negative for adjuvant activity.

The present invention provides cultured cells of Quillaja sp. and a method for preparing active substances therefrom, which active substances may be used for various purposes such as ISCOM formation and as emulsifiers, deter¬ gents, foaming agents and the like.

Claims

1. Cultured cells of Quillaja sp. for the preparati- on of active substances from Quillaja sp.

2. Cultured cells as claimed in claim 1, characteri¬ zed in that the active substances are saponins.

3. Cultured cells as claimed in claim 1 or 2, characterized in that the cells originate from a callus tissue culture.

4. Cultured cells as claimed in claim 1 or 2, characterized in that the cells originate from a suspension cell culture.

5. Cultured cells as claimed in any one of the claims 1-4, characterized in that the Quillaja sp. is a species selected from the group consisting of Quillaja saponaria Molina, Quillaja smegmadermos. Quillaja brasilien- sis.

6. Active substances extracted from cultured cells of Quillaja sp..

7. Preparation comprising active substances extrac¬ ted from cultured cells of Quillaja sp..

8. Preparation as claimed in claim 7, characterized in that the preparation comprises a non-dialysable fraction of the active substances of Quillaja sp..

9. Preparation as claimed in claim 7, characterized in that the preparation comprises a dialysable fraction of the active substances of Quillaja sp..

10. Method for preparing active substances from Quillaja sp. comprising the steps of:

I a) culturing cells from Quillaja sp. in vitro: and b) preparing an extract of the cultured cells comprising the active substances.

11. Method as claimed in claim 10, characterized in that the cell extract is dialysed to obtain a dialysable and a non-dialysable fraction.

12. Foaming agent, comprising the dialysable and/or the non-dialysable fraction of an extract of cultured cells of Quillaja sp..

13. Emulsifying agent, comprising the dialysable and/or the non-dialysable fraction of an extract of cultured cells of Quillaja sp..

14. Ammonia binding agent, comprising the dialysable and/or the non-dialysable fraction of an extract of cultured cells of Quillaja sp..

15. Method for preparing Immune-Stimulating COM- plexes (ISCOM's) or Immune-Stimulating COMplexes-matrix comprising the steps of: a) preparing a non-dialysable and/or dialysable fraction from an extract of cultured cells of Quillaja sp. ; b) adding at least one lipid and at least one detergent to the non-dialysable fraction; c) allowing the ISCOM's or Immune-Stimulating COMplexes-matrix to form; and d) removing the detergent.

16. Immune-stimulating complexes, prepared by the method as claimed in claim 15.

17. Immune-Stimulating COMplexes-matrix, prepared by the method as claimed in claim 15.

18. Immunological adjuvant, comprising immune- stimulating complexes prepared by the method as claimed in claim 15.

19. Immunological adjuvant, comprising immune- stimulating complex-matrix, prepared by the method as clai¬ med in claim 15.

20. Immunological adjuvant, comprising the dialysa¬ ble and/or the non-dialysable fraction of extracts of cultu¬ red cells of Quillaja sp..