To this end, the safety and tolerability of CCR5-ZFN modified CD4 T cells is currently being tested in two ongoing human clinical trials (NCT00842634, NCT01044654; Clinicaltrials.gov) and preliminary results presented at the 2011 Conference on Retroviruses and Opportunistic Infections (CROI) suggest that infusion of ZFN-modified CD4 T cells into patients currently on ART is safe, and these gene modified cells appear to initially expand and persist at a stable level over time. This evidence concerns the gene CD4 and Opportunistic infection.