CD4 and HIV-1 infection: Possible reasons for this could be: the low CD4 T-cell counts of these patients when ART was initiated resulting in protracted immunosuppression and/or clonal dysfunction; a need for longer duration of ART before immunotherapeutic intervention, thus allowing greater immune recovery; the permanent depletion of HIV-1-specific CD4 T-cells by direct HIV-1 infection; and/or the timing of IL-2 therapy with immunisation which may have important consequences for induction or suppression of induced responses.