We thus estimated thymic output through quantification of the sj/bTREC ratio in all groups of patients ( Figure 3B ). The sj/ bTREC ratio estimates the extent of thymocyte proliferation between TCRB rearrangement and the excision of the T-cell receptor delta (TCRD) locus [23] . This parameter directly reflects the extent of thymic production and, contrarily to sjTREC values, is independent from peripheral RTE proliferation or survival capacity [28] . The sj/bTREC ratio was already low in HIVinfected patients (p,0.005 as compared to healthy control donors; Figure 3B bottom left panel) and did not evolve further under IFNa therapy in co-infected patients ( Figure 3B , bottom right panel). In contrast, acutely HCV-infected patients demonstrated higher than normal sj/bTREC ratio at baseline (p,0.05 as compared to aged matched healthy controls), showed a significant reduction in sj/bTREC ratio at M1 (p = 0.014) and M2 (p = 0.001; Figure 3B , top panel). Finally, a similar decline in the sj/bTREC ratio was observed during IFNa therapy in chronically HCV-infected patients (p,0.02 at M1, M2 and M3; Figure 3B , central panel).