Clearance kinetics of CD34(+) cells from peripheral blood: an independent predictor of hematologic recovery after high-dose chemotherapy and hematopoietic stem cell transplantation

We measured the concentration of CD34(+) cells in peripheral blood (PB) 1/2 h prior to and 1/2, 1, 3, 6, and 12 h following hematopoietic stem cell (H SC) infusion in 34 breast cancer patients treated with high-dose chemothera py (HDC), The decrease in these concentrations over time enabled us to dete rmine the clearance kinetics of CD34(+) cells from PB. The absolute number of CD34(+) cells in PB generally peaked at 1/2 h after infusion, then rapid ly declined from 1 to 3 h post infusion and continued to fall until 12 h po st transplant, but more slowly. In univariate analysis, CD34(+) cells/kg in fused, CFU-GM/kg infused, the CD34(+) count at Bh, and the 12-h clearance o f CD34(+) cells from PB were predictors of hematologic recovery, as were ea ch of the two phases of clearance when the slope was divided into rapid and slow phases (from 1/2 to 3 and from 3 to 12 h post transplant, respectivel y). We then stratified our population by the number of CD34(+) cells/kg inf used. In group 1, patients received less than or equal to 7.5 x 10(6) CD34( +) cells/kg; in group 2, >7.5 x 10(6) CD34(+) cells/kg, After adjusting for CD34(+) cells injected, age, and purged or unpurged graft in multivariate analysis, the 12 h clearance remained a predictor of hematologic recovery i n group 1. In addition, the second phase of clearance (from 3 to 12 h after infusion) was an even better predictor than the 12 h clearance. In group 2 , however, no statistically significant correlation was observed, even with the number of HSC injected. Results suggest that rapidity of clearance of CD34(+) cells from PB is an independent indicator of hematologic recovery i n patients receiving lower doses of CD34(+) cells. When the cell dose injec ted is over a threshold, PB clearance correlations with hematologic recover y are masked.