An increase in the levels of naive T cells after the administration of HAART is an indicator of the quality of immune reconstitution. We investigated whether levels of naive CD4 T cells (CD4(+)/CD45RA(+)) and of recent thymic emigrants (RTEs; CD4(+)/CD45RA(+)/CD31(+)) achieved in chronically treated HIV-infected patients could predict the length of time patients could interrupt antiretroviral treatment before their CD4 counts reached values < or =350 cells/mm(3) or HIV-1 RNA levels increased to > or =100,000 copies/ml (Tibet cohort). Serial measurements revealed that the level of naive CD4 T cells among patients was extremely variable (5-95%), but the values for each patient remained stable throughout the study. We then focused on those patients who showed percentages of naive CD4 T cells above 60% or below 30%. The levels of naive T cells, RTEs, mononuclear cells containing T cell receptor excision circles (TRECs), and the strength of CD4 helper responses to HIV p24 antigen during treatment failed to predict the duration of treatment interruptions. In contrast, the median survival time of patients with a CD4 nadir > or =350 cells/mm(3) was 2-fold higher than that of patients with a CD4 nadir <350. However, the probability of restarting therapy in these two groups of patients was independent of the levels of naive T cells, RTEs, or TRECs.