Quantitation of white cell subpopulations by polymerase chain reaction using frozen whole-blood samples. Viral Activation Transfusion Study.

BACKGROUND

Previous methods for processing whole blood (WB) for nucleic acid analyses of white cells (WBCs) required fresh blood samples. A simple protocol that involves the freezing of WB for quantitative polymerase chain reaction (PCR) analyses was evaluated.

STUDY DESIGN AND METHODS

Controlled studies were conducted in which paired fresh and frozen WB preparations were analyzed. The integrity of WBCs in the frozen WB samples was first assessed by flow cytometry using CD45 fluorescence, and calibration beads to quantitate recovery of WBC subsets. PCR of an HLA-DQ-A sequence was used to quantitate residual WBCs in a double-filtered red cell (RBC) component spiked with serial dilutions of WBCs, as well as in 51 filtered RBCs and 19 filtered platelet concentrates. Y-chromosome-specific PCR was used to quantitate male WBCs in five female WB samples spiked with serial dilutions of male WBCs and in serially collected frozen WB samples from four females transfused with male blood components.

RESULTS

By flow cytometry, all major WBC subpopulations in frozen-thawed WB were quantitatively recovered and immunologically intact, although they were nonviable. HLA-DQ-A PCR quantitation of a dilution series from 8 to 16,700 per mL of WBCs spiked into double-filtered RBCs showed linear correlation of the results with both fresh and frozen preparations of the expected WBC concentrations (r2 = 0.98, p<0.0001 for both), without significant difference between observed and expected values (p>0.05). Y-chromosome-specific PCR results in female WB samples spiked with male WBCs were not significantly different in fresh and frozen preparations over a 3 log10 range of male cells. The results of WBC survival studies on frozen WB samples were consistent with previous observations in fresh blood samples.

CONCLUSION

Direct freezing of WB enables subsequent recovery of WBCs for quantitative PCR analyses, with results comparable to those of fresh preparations.This protocol should facilitate wider implementation of nucleic acid-based analyses for quality control of WBC-reduced components, as well as for prospective clinical studies of microchimerism in transfusion and transplant recipients.