CD4 and AIDS: The association between occurrence of first non AIDS-defining severe events (NADE) and time-dependent measures of immune restoration was assessed by 4 Cox models with different definitions of restoration, CD4+ cell counts (CD4), CD4/CD8 ratio, both CD4 and CD4/CD8 ratio, or a composite variable (CD4< 500/mm3, CD4 > 500/mm3 and CD4/CD8 ratio < 1, CD4 > 500/mm3 and CD4/CD8 ratio > 1).