HIV particles were produced by co-transfection of HEK 293T cells with an expression vector for a CCR5-tropic (ADA) HIV-1 envelope [45] kind gift of Dr. M. Alizon, together with a pNL4.3-Env 2 -Luc containing either a parental or recombinant RRE sequence or DdNK. Forty-eight hours post transfection, supernatants were filtered trough a 0.45 mM filter and p24 levels were determined using the HIV-1 p24 enzyme-linked immunoabsorbent assay kit (PerkinElmer Life Sciences, MA, USA).