Semiquantitative HIV-1 Gag DNA PCR analysis of cell aliquots during the purification course. Cells (1 × 10⁴) from each purification step were PCR-amplified with the universal SK38 and SK39 Gag primers, and the signal intensity was compared with standards containing 1 × 10⁴, 1 × 10³, 1 × 10², 10, 1, and 0 ACH2 (A3.01 cell line containing one proviral copy of the HIV-1 genome) cells (lanes 1 through 6). Lane 7, negative control; lane 8, apheresis sample; lane 9, after CD34⁺ cell enrichment; lane 10, after HSCS; lane 11, negative control; lane 12, mock transduction; lane 13, LIF transduction; lane 14, SCF transduction; lane M, molecular weight marker (in basepairs). The arrow indicates the position of the 115-bp gag gene PCR product.