To generate MSCV retroviruses, HEK293FT cells (Invitrogen) were transfected with 2 µg of viral DNA and 1 µg of gal/pol and VSV-G accessory plasmids in 6 well plates using GenJet transfection reagent (Signagen Labs). Virus-containing media was collected 72 hr later, filtered through 0.45 µm filter and applied to L929 cells with 8 µg/ml polybrene. Cells were selected and maintained in 10 µg/ml puromycin.