Fig. 4

Temperature and time elapsed prior to testing affect MDSC quantitation. Whole blood samples from 2 healthy and 5 HCC subjects were collected in K₂EDTA tubes and kept at room temperature (red box plots) or at 4 °C (blue box plots) before testing. Antibody labeling was conducted as soon as possible after blood collection, and % change in absolute numbers of total MDSC (a) and M-MDSC (b) were calculated between these baseline data and those obtained 4, 8, or 24 h after blood collection. Paired t tests were used to determine whether differences were statistically significant. At 4 h compared to baseline, mean percent change in MDSC levels for samples maintained at 4 °C versus room temperature (RT) were 9% vs − 15% change (p = 0.02) for total MDSC and 8% vs − 24% change (p = 0.009) for M-MDSC. At 8 h, mean percent changes for the 4 °C and RT samples were − 2% vs − 16% change (p = 0.06) for total MDSC and − 5% vs − 36% change (p = 0.006) for M-MDSC. Mean differences between the two conditions by 24 h were − 17% vs − 26% change (p = 0.3) for total MDSC and − 44% vs − 57% change (p = 0.4) for M-MDSC. Percent changes in MDSC counts by 24 h were lower than at 4 h (total MDSC p = 0.04 and M-MDSC p = 0.01) for samples maintained at 4 °C