Serum-free culture medium for drosphila insect cells

The invention provides serum-free media for the culture of drosophila insect cells. The serum-free media of the invention comprise a basal medium to which is added yeast hydrolysate, and albumin or dextran. In another embodiment of the invention, albumin hydrolysate is added to the basal medium, in addition to the aforementioned compounds.

FIELD OF THE INVENTION 
The present invention relates to the field of media for the culture of 
cells. More particularly the present invention relates to media for the 
culture of insect cells. 
BACKGROUND OF THE INVENTION 
Beyond a basal nutrient mixture of salts, sugars, amino acids, and 
vitamins, cells in vitro have also been found to require for proliferation 
a supplement of poorly defined biological fluids or extracts. Because of 
availability and ease of storage, the most commonly used supplement is 
serum. 
The use of serum in cell culture media, however, has several disadvantages. 
Serum is comparatively expensive. Since serum is not a defined component, 
different lots of serum may vary in the concentration of compounds present 
and thus result in unpredictable culture growth. Serum may also be 
contaminated with viruses or mycoplasmas. The protein in serum may 
complicate the purification of cell products from the culture medium. 
In efforts to overcome the disadvantages of serum containing medium, 
researchers have attempted to provide serum-free media by substituting 
defined or better characterized components for serum. Unfortunately, the 
complexity of serum and the differing growth requirements of different 
types of cells has made it difficult to provide such media. For reviews on 
serum-free media for insect cell culture see Mitsuhashi (1982) "Continuous 
Cultures of Insect Cell Lines in Media Free of Sera" Appl. Ent Zool. 17: 
575-581; and Goodwin, "Growth of insect cells in serum-free media" in 
Techniques in the Life Sciences, Setting Up and Maintenance of Tissue and 
Cell Cultures, Elsevier Scientific Publishers Ireland, Ltd., (1985) pp. 
C109/1-C109/28. Lazar et al. (1987) Dev. Biol. Stand. 96: 315-323 
(Abstract) reports a serum-free medium for the culture of Aedes aegypti 
cells that contains bovine serum albumin. 
The fruit fly Drosophila melanogaster has for many years been the subject 
of intensive genetic analysis and various media have been developed for 
the culture of Drosophila cells. Inlow et al. (1989) J. Tissue Culture 
Methods 12: 13-16 discloses a serum-free medium for culture of Drosophila 
cells that contains yeast hydrolysate and a lipid emulsion. For media 
containing serum, see Shields et al. (1975) J. Embryol. exp. Morph. 33: 
159-175; Lengyel et al. "Methods with Insect Cells in Suspension Culture 
II. Drosophila melanogaster" in Methods in Cell Biol. volume 10, pp. 
195-208, (1975); Shields and Sang (1977) Drosophila Information Service, 
volume 52, page 161; Cross and Sang (1978) J. Embryol. exp. Morph. 45: 
161-172; Sang (1981) "Drosophila Cells and Cell Lines" in Advances in Cell 
Culture volume 1, pp 125-182; and Ueda and Miyake (1987) In Vitro Cellular 
& Developmental Biology 23: 707-711. 
There have been a few reports of serum-free media containing dextran or 
.beta.-cyclodextrin, however, the reported media are for the culture of 
mammalian cells. Pietrzkowski et al (1988) Folia Histochemica et 
Cytobiologica 26: 123-132 report a serum-free medium for the culture of 
chick embryo cell containing dextran. Pietrzkowski and Korohoda (1988) 
Folia Histochemica et Cytobiologica 26: 143-154 report a serum-free medium 
containing dextran for the culture of chick embryo fibroblasts. Ohmori 
(1988) Journal of Immunological Methods 112: 227-233 reports a serum-free 
medium which is able to support primary antibody responses by cultured 
murine lymphocytes. This medium is based on a basal medium supplemented 
with .beta.-cyclodextrin, insulin, transferrin, albumin, low density 
lipoprotein, putrescine and alanine. 
A serum-free medium for large-scale culture of insect (Spodoptera 
frugiperda) cells was reported in Maiorella et al., (1988) Biotechnology 
6: 1406-1410. In addition to a basal medium, the medium contained yeast 
extract, cod liver oil polyunsaturated fatty acid methyl esters, 
cholesterol and Tween. Murhammer and Goochee (1988) Biotechnology 6: 
1411-1418 discloses a medium for the culture of Spodoptera frugiperda that 
contains serum. 
It is an object of the invention to provide serum-free media for the 
culture of insect cells. It is also object of the invention to provide 
serum-free media for the culture of insect cells transformed to produce 
recombinant products that increase product yield. It is yet another object 
of the invention to provide serum-free media for the culture of Drosophila 
cells. 
SUMMARY OF THE INVENTION 
The present invention provides serum-free media for the culture of insect 
cells. The invention is more particularly pointed out in the appended 
claims and is described in its preferred embodiments in the following 
description.

DETAILED DESCRIPTION OF THE INVENTION 
The serum-free media of the invention are useful for the culture of insect 
cells. The media of the invention have been found to be useful in the 
culture of Drosophila cells, and should have utility in the culture of a 
wide variety of insect cells. Cells may be grown in batch and continuous 
culture with the serum-free media of the invention. Drosophila cells grown 
in the media of the invention reach higher cell density and show increased 
recombinant product secretion when compared to Drosophila cells grown in a 
serum-containing medium. The media of the invention have a low protein 
content which is advantageous for culturing cells for the production of 
recombinant proteins. The low protein content of the media reduces the 
amount of unwanted proteins that have to be separated from the protein 
product during purification of the protein product. Additionally, the 
media may be made at a much lower cost than media containing serum. 
The cell culture media are prepared by adding supplements to a basal medium 
designed for insect cell culture. The media are prepared accordance with 
standard procedures for preparing cell culture media. 
A preferred basal medium for use in the serum-free media of the invention 
is described in Example 1. Other suitable basal media include Grace's 
(Gibco, Grand Island, N.Y.) and Schneider's (Gibco) 
Supplements are then added to the basal medium. Yeast hydrolysate is added 
in the amount of from about 1 to about 10 grams per liter. Dextran or 
albumin are added in the amount of from about 0.1 to about 5 grams per 
liter. Albumin for use in the media is preferably bovine serum albumin, 
however, albumin from other species is also suitable. Dextran for use in 
the media is preferably dextran having a molecular weight of about 500,000 
such as Dextran T-500. In one embodiment of the invention, lactalbumin 
hydrolysate is added in the amount of from about 0.2 to about 5 grams per 
liter, preferably in the amount of about 5 grams per liter. 
The pH range of the media is preferably in the range of from about 6.3 to 
about 6.7. The osmolarity is preferably in the range of from about 320 to 
about 360 milliosmoles. 
The basal medium may be stored as a powder at 4.degree. C. for one year. 
The complete medium (basal medium with added supplements) in a liquid form 
may be stored at 4.degree. C. for six months. 
Preferred embodiments of the invention are described in the following 
Examples. 
EXAMPLE 1 
______________________________________ 
BASAL MEDIA COMPONENTS SERUM-FREE MEDIA 
Components Grams/Liter 
______________________________________ 
MgSO4 7H2O 4.40 
Potassium Glutamate 
7.88 
Sodium Glutamate 6.53 
NaH2PO4 H2O (monobasic) 
0.78 
Glucose 10.0 
Oxaloacetic Acid 0.25 
Bis-Tris 1.05 
L-aspartic acid 0.30 
L-threonine 0.50 
L-serine 0.35 
L-asparagine 0.30 
L-glutamine 0.60 
L-proline 0.40 
Glycine 0.50 
L-alanine 1.50 
L-valine 0.40 
L-methionine 0.25 
L-isoleucine 0.25 
L-leucine 0.40 
L-tyrosine 0.25 
L-phenylalanine 0.25 
B-alanine 0.25 
L-histidine 0.55 
L-tryptophan 0.10 
L-arginine 0.50 
L-lysine HCL 0.85 
L-cysteine HCL 0.20 
Choline chloride 0.05 
CaCl2 2H2O 1.00 
KHCO3 0.50 
1M NaOH as needed 
______________________________________ 
Preparation of Basal Medium: 
The components in the basal medium are mixed and ball-mill ground to 
formulate a homogeneous powder. The powdered medium is then dispensed into 
100 L packets and stored at 4.degree. C. for up to one year. 
For a final volume of 100 L: 
Ninety liters of deionized-distilled water is measured into an appropriate 
mixing vessel. A 100 L packet of ball-mill ground powdered medium. (as 
described above) is added. The pH of the medium is adjusted to 6.6 using 
10N NaOH. The volume of the medium is brought to 100 L by the addition of 
water. The medium may then be sterilized by membrane filtration using a 
0.2 micron cellulose acetate filter. 
EXAMPLE 2 
Medium MR-D1 contains the basal medium of Example 1 supplemented with 5 
grams per liter TC lactalbumin hydrolysate (Difco, Detroit, Mich.), 1 gram 
per liter TC yeastolate (Difco, Detroit, Mich.) and 1 gram per liter 
bovine serum albumin (Amour, Kankakee, Ill.). The medium is prepared as 
follows: 
For a final volume of 100 liters 
1. Measure 90 liters of deionized-distilled water into an appropriate 
mixing vessel. 
2. Add one 100 L packet of ball-mill ground powdered media (from Example 
1). 
3. Add 500 grams of TC lactalbumin hydrolysate, mix until dissolved. 
4. Add 100 grams of TC yeastolate, mix until dissolved. 
5. Add 100 grams of bovine serum albumin, mix until dissolved. 
6. Adjust pH to 6.6 using 10N NaOH. 
7. Add water to bring final volume to 100 liters and mix thoroughly. 
8. Filter sterilize using a 0.2 micron cellulose acetate filter. 
9. Check osmolarity and record. 
10. Store at 4.degree. C. for up to six months. 
EXAMPLE 3 
Medium MR-D2 contains the basal medium of Example 1 supplemented with 5 
grams per liter TC yeastolate (Difco, Detroit, Mich.) and 1 gram per liter 
bovine serum albumin (Amour, Kankakee, Ill.). The medium is prepared as 
follows: 
For a final volume of 100 L 
1. Measure 90 liters of deionized-distilled water into an appropriate 
mixing vessel. 
2. Add 100 L packet of ball-mill ground powdered media (from Example 1). 
3. Add 500 grams of TC yeastolate, mix until dissolve. 
4. Add 100 grams of bovine serum albumin, mix until dissolved. 
5. Adjust pH to 6.6 using 10N NaOH. 
6. Add water to bring final volume to 100 liters and mix thoroughly. 
7. Filter sterilize using a 0.2 micron cellulose acetate filter. 
8. Check osmolarity and record. 
9. Store at 4.degree. C. for up to six months. 
EXAMPLE 4 
Medium MR-D3 contains the basal medium of Example 1 supplemented with 5 
grams per liter TC yeastolate (Difco, Detroit, Mich.) and 1 gram per liter 
of Dextran T-500 (Pharmacia, Piscataway, N.J.). The medium is prepared as 
follows: 
For a final volume of 100 L 
1. Measure 90 liters of deionized-distilled water into an appropriate 
mixing vessel. 
2. Add one 100 L packet of ball-mill ground powder media (from Example 1). 
3. Add 500 grams of TC yeastolate, mix until dissolved. 
4. Add 100 grams of Dextran T-500, mix until dissolved. 
5. Adjust pH to 6.6 using 10N NaOH. 
6. Add water to bring final volume to 100 liters and mix thoroughly. 
7. Filter sterilize using a 0.2 micron cellulose acetate filter. 
8. Check osmolarity and record. 
9. Store at 4.degree. C. for up to six months. 
EXAMPLE 5 
Comparison of Growth of Drosophila (ACC086) cells in M3+5%FBS, MR-D1, or 
MR-D2, and the production of qp120 in these media 
Drosophila cells (cell line ACC086) (2.times.10.sup.6 cells per milliliter) 
that had been transfected to express human immunodeficiency virus-1 
protein gp120 were cultured in M3 medium with 5% fetal bovine serum (FBS); 
MR-D1, the medium of Example 2; or MR-D2, the medium of Example 3. M3 
medium is the medium described in Example 1 with 1 gram per liter 
Yeastolate (Difco, Detroit, Mich.) added. Each of the media also contained 
300 .mu.g/ml hygromycin B (HB), an antibiotic. Cells were cultured for 14 
days and the number of cells and amount of gp120 were determined at 
intervals. 
As shown in Table 1, after seven days, cells grown in M3+5% FBS had a 
density of 1.6.times.10.sup.7 and the gp120 concentration was 956 ng/ml. 
Cells grown in MR-D1 medium and MR-D2 media had densities of 
1.7.times.10.sup.7 and 1.8.times.10.sup.7, respectively, and gp120 
concentrations of 916 ng/ml and 912 ng/ml, respectively. However, after 14 
days of culture, cell density and gp120 production in MR-D1 and MR-D2 
media were significantly higher than in M3+5% FBS medium. In MR-D1 medium, 
cell density was 3.0.times.10.sup.7 and the gp120 concentration was 1,962 
ng/ml. In MR-D2 medium, cell density was 2.7.times.10.sup.7 and the 
concentration of gp120 was 2,750 ng/ml. In contrast the density of cells 
grown in M3+5% FBS medium was 2.1.times.10.sup.7 and the concentration of 
gp120 was 1,207 ng/ml. 
TABLE 1 
__________________________________________________________________________ 
M3 + 5% FBS MR-D1 MR-D2 
+300 ug/ml HB +300 ug/ml HB 
+300 ug/ml HB 
CELL # . . . GP120 
CELL # . . . GP120 
CELL # . . . GP120 
__________________________________________________________________________ 
7D 1.6e7 . . . 956 nG/ml 
1.7e7 . . . 916 nG/ml 
1.8e7 . . . 912 nG/ml 
14D 2.1e7 . . . 1,207 nGml 
3.0e7 . . . 1,962 nG/ml 
2.7e7 . . . 2,750 nG/ml 
__________________________________________________________________________ 
EXAMPLE 6 
Long Term Study Comparing the Growth Of Drosophila Cells (Cell Line ACC086) 
And Production Of gp120 In Either MR-D2 or MR-D3 Media 
Drosophila cells (2.times.10.sup.6 cells per milliliter) that had been 
transfected to express human immunodeficiency virus-1 protein gp120 (cell 
line ACC086) were cultured in a 250 ml SP flask containing 120 ml of 
either MD-R2, the medium of Example 3; or MD-R3, the medium of Example 4. 
Cells were passaged at 7 day intervals, and were cultured through 41 
passages. 
After 25 passages, in MR-D2 medium there were approximately 
23.times.10.sup.6 cells. In MR-D3 medium there were approximately 
19.times.10.sup.6 cells per milliliter. After 26 passages, gp120 
production was about 550 ng/ml in MR-D2 and 700 ng/ml in MR-D3. After 30 
passages there were approximately 20.times.10.sup.6 cells per milliliter 
in MR-D2 and approximately 21.times.10.sup.6 cells per milliliter in 
MR-D3. After 33 passages there were approximately 20.times.10.sup.6 cells 
per milliliter in both MR-D2 and MR-D3 media, and gp120 production was 
about 750 ng/ml in MR-D3 and 650 ng/ml in MR-D3. 
After 35 passages there were approximately 19.times.10.sup.6 cells per 
milliliter in MR-D2 medium, and approximately 21.times.10.sup.6 cells per 
milliliter in MR-D3 medium. gp120 production was about 550 ng/ml in MR-D2 
medium, and about 500 ng/ml in MR-D3 medium. After 39 passages there were 
approximately 20.times.10.sup.6 cells per milliliter in MR-D2 cells, and 
approximately 19.times.10.sup.6 cells per milliliter in MR-D3 medium. 
gp120 production was about 375 ng/ml in MR-D2 medium and about 525 ng/ml 
in MR-D3 medium. After 40 passages, there were approximately 
21.times.10.sup.6 cells per milliliter in MR-D2 medium, and approximately 
19.times.10.sup.6 cells per milliliter in MR-D3 medium. gp120 production 
was about 300 ng/ml in MR-D2 medium and about 425 ng/ml in MR-D3 medium. 
Over an extended period of time, cell growth in these serum-free media was 
consistent, although recombinant gp120 product production decreased 
slightly.