To assess whether the lower frequency of GFP+ cells after Lenti LTR-GFP infection in HSP compared to the TCR culture could be attributed to distinct integration efficiencies in the two culture systems, we analyzed by Alu-PCR proviral copy numbers of Lenti LTR-GFP-infected CD4+ T cells at days 0, 3, 5, and 7 after culturing under HSP or TCR conditions in the presence or absence of the HIV integrase inhibitor RAL. This evidence concerns the gene CD4 and hereditary spastic paraplegia.