Detection of DNA in single cells using an automated cell deposition unit and PCR

A highly effective single-cell PCR method using a fluorescence-activated cell sorting (FACS)-based automated cell deposition unit (ACDU) that sorts single cells directly into PCR tubes was developed. To evaluate the sensitivity of this method, single ACH-2 cells (containing one HIV-1 genome per cell) were sorted, and 220 out of 228 samples (96.5%) were HIV DNA-positive by PCR. Furthermore, the number of samples accidentally containing more than one cell was determined by sorting single cells from a mixture of human cytomegalovirus (HCMV)-infected fibroblasts and ACH-2 cells. Multiplex nested PCR (nPCR) was then performed, detecting HCMV and HIV DNA simultaneously. From 66 sorted cells, 2 (3%) were double-positive for HIV and HCMV, 31 (47%) for HCMV alone, 30 (45.5%) for HIV alone and 3 (4.5%) were PCR-negative. The ACDU was then programmed to sort defined numbers of cells into PCR tubes. This is similar to classic dilution assays in that it allows the determination of the percentage of cells that was positive for a specific DNA. The accuracy of multiple cell deposition by the ACDU was evaluated by determining the percentage of HIV-positive cells in defined mixtures of ACH-2 and uninfected H9 cells. Infection rates determined by the ACDU correlated well with the rates expected from the given dilutions.