Cells were diluted in freezing medium (90% fetal bovine serum, 10% dimethyl sulfoxide) to concentrations ranging from 0.5 to 400 cells/μl to be spiked into 100 μl of fresh HIV-1-negative EDTA-treated whole blood samples (Core Lab, NorthShore University HealthSystems, Evanston, IL) to create a standard curve of copy numbers 5–4000