Cell culture HEK 293T, and CD4 + CCR5 + 293T cells were grown in Dulbecco's modified Eagle's medium supplemented with 10% foetal calf serum, penicillin, and streptomycin (from Invitrogen, CA, USA), and maintained at 37uC with 10% CO 2 . MT4 cells were maintained in RPMI 1640 medium supplemented with 10% foetal calf serum and antibiotics at 37uC with 5% CO 2 .