Comparison of CD4+ and CD8+ T-cell subpopulations enumerated with cryopreserved PBMC stored at −70°C versus PBMC stored in liquid nitrogen before shipment on dry ice

T-cell subpopulationNo. of samplesMedian difference (%) between −70°C and liquid nitrogen storage (1st; 3rd quartile)P valuea
CD4+ CD38+ HLADR+160.0 (−1.0; 0.5)0.78
CD4+ CD45RA+ CD9516−1.0 (−2.0; 0.5)0.13
CD8+ CD38+ HLADR+160.0 (0.0; 1.0)0.25
  • a Wilcoxon matched-pair signed-rank test. This test, applied to the sample size of 16, had statistical power to detect differences of 2.3%, 1%, and 2.7% in the percentages of CD4+ CD38+ HLADR+, CD4+ CD45RA+ CD95, and CD8+ CD38+ HLADR+, respectively.