This technique demonstrates an efficient way to prepare replication-defective retroviral stocks encoding a human oncogene, and subsequently used for induction of myeloproliferative disease in the mouse model.
Our lab studies human myeloproliferative diseases induced by such oncogenes as Bcr-Abl or growth factor receptor-derived oncogenes (ZNF198-FGFR1, Bcr-PDGFRα, etc.). We are able to model and study a human-like disease in our mouse model, by transplanting bone marrow cells previously infected with a retrovirus expressing the oncogene of interest. Replication-defective retrovirus encoding a human oncogene and a marker (GFP, RFP, antibiotic resistance gene, etc.) is produced by a transient transfection protocol using 293T cells, a human renal epithelial cell line transformed by the adenovirus E1A gene product. 293 cells have the unusual property of being highly transfectable by calcium phosphate (CaPO4), with up to 50-80% transfection efficiency readily attainable. Here, we co-transfect 293 cells with a retroviral vector expressing the oncogene of interest and a plasmid that expresses the gag-pol-env packaging functions, such as the single-genome packaging constructs kat or pCL, in this case the EcoPak plasmid. The initial transfection is further improved by use of chloroquine. Stocks of ecotropic virus, collected as culture supernatant 48 hrs. post-transfection, can be stored at -80°C and used for infection of cell-lines in view of transformation and in vitro studies, or primary cells such as mouse bone marrow cells, that can then be used for transplant in our mouse model.
Four critical points will assure the success of a good viral stock:
Some check-points: If desired, once harvested, the 293 cells can be used to make protein lysates for immunoblotting to check the expression of proteins encoded by the retroviral vector (e.g., the TK). We also use a LacZ encoding control plasmid in separate plate at the time of transfection (no packaging vector needed) to check for transfection efficinecy by beta-gal assay when we collect the supernatant of the other plates. Note: this will test the cells and reagents, but not the quality of the plasmids used for virus making.
Before using any virus, the titer needs to be determined. This is critical in order to match titers of different virus stocks in the same experiment, and to ensure efficient transduction of hematopoietic stem cells.
Material Name | Tipo | Company | Catalogue Number | Comment |
---|---|---|---|---|
293T cells | cell-line | Split 1:3 to 1:4 every 3 days, otherwise they will tend to clump with replating and will not transfect as well. | ||
293T cell medium | DMEM/hi-glu + 10 % FBS + 1% Pen/Strep + 1% L-Glutamine (1% NEAA, optional). We obtain our tissue culture slutions from CellGro. | |||
coding DNA plasmid | Twice purified by CsCl. MSCV backbone, encoding oncogene and marker of choice (Neo, GFP, etc.) | |||
EcoPak | also called pMCV-Ecopac: ecotropic packaging plasmid, encoding gag-pol-env | |||
2x HBS | For 500 ml: 8.0 g NaCl + 0.37 g KCl + 106.5 mg Na2HPO4 (anhydrous; 201.1 mg if 7xH2O) + 1.0 g dextrose (D-glucose) + 5.0 g HEPES powder. Dissolve in 450 ml dH2O (milli-Q), adjust pH to 7.05 with NaOH, then complete to 500 ml with dH2O. Sterile filter thru 0.45 µ filter. Store at room temperature, with the cap on tight. | |||
2M CaCl2 | Sigma | |||
miliQ H2O | sterile-filtered | |||
Chloroquine | 1000x stock is 25 mM in PBS- (w/o Ca2+/Mg2+), stored at -20C. Add fresh to the medium when needed. | |||
6 cm plates | for tissue culture | |||
Incubator | for tissue culture. Set at 37C, 10% CO2. | |||
10 cc sterile syringes | Sterile. One per virus type. | |||
18G needles | single use, one per virus type. | |||
45 um syringe filters | ||||
5 ml plastic tubes | Sterile, to mix transfection solution, for up to 2 plates at a time (2 ml). We use Falcon tubes. | |||
50 ml conical tubes | ||||
cryovials | 2 and 4 ml, for virus aliquots. |
All reagents used in the transfection must be sterile-filtered (CaCl2, 2x HBS, miliQ H2O) and kept sterile.