Parallel quantification of the sjTREC and the 13 DJbTRECs, together with CD3c gene (used as a housekeeping gene) was performed for each sample using LightCyclerTM technology (Roche Diagnostics) with a technique adapted from [29] . Intrathymic precursor T-cell proliferation was evaluated through calculation of the sj/bTREC ratio as described [23] .