Cell lines

Rag2^−/−Ebf1^+/+Pax5^+/+, Rag2^−/−Ebf1^+/−Pax5^+/+ and Rag2^−/−Ebf1^+/−Pax5^+/− pro-B cells are cultured as previous described⁴⁰.

The wild-type D345 cell line was generously provided by David G. Schatz of Yale University. These cells were maintained in RPMI1640 (Gibco) supplemented with 10% foetal bovine serum (FBS, Gemini) and a 1× penicillin–streptomycin solution (Gibco).

293T human embryonic kidney cells used for lentiviral expression was purchased from ATCC (cat. no. CRL-3216) and cultured in Dulbecco’s modified Eagle medium (Gibco) with 10% FBS (Gemini) and 1× penicillin–streptomycin solution (Gibco).

The Platinum-E (Plat-E) cell line used for retroviral expression was purchased from Cell Biolabs (cat. no. RV-101) and cultured in Dulbecco’s modified Eagle medium (Gibco) with 10% FBS (Gemini), 1× penicillin–streptomycin solution (Gibco), 10 mM HEPES and 0.3 μg ml⁻¹ l-glutamine. All cells were cultured at 37 °C in a humidified atmosphere with 5% CO₂.