We herein demonstrated that IFNa-based therapy leads to major lymphocytopenia in naïve T-cell compartments, in particular in the RTE subset. Several mechanisms could be implicated in the establishment of such a lymphocytopenia [41] . Among these, enhanced apoptosis [42, 43] , cell sequestration in lymphoid or non-lymphoid organs [12, 21, 22] and regulation of peripheral T-cell homeostasis [20] . In our study, no major change in cell survival (Bcl-2 expression) or T-cell activation (CD25 and CD69 expression) was observed during the follow-up period (data not shown). Moreover, we did not observe any significant modification in Ki-67 expression in any T-cell subset during the first month of therapy (data not shown and Figure 3 ). Finally, IFNa-induced T-cell homing, although rapid and massive, is only a transient process [22] suggesting that this mechanism marginally contributes to the observed long lasting lymphocytopenia.