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

Abstract

We measured the concentration of CD34⁺ cells in peripheral blood (PB) ½ h prior to and ½, 1, 3, 6, and 12 h following hematopoietic stem cell (HSC) infusion in 34 breast cancer patients treated with high-dose chemotherapy (HDC). The decrease in these concentrations over time enabled us to determine the clearance kinetics of CD34⁺ cells from PB. The absolute number of CD34⁺ cells in PB generally peaked at ½ h after infusion, then rapidly declined from 1 to 3 h post infusion and continued to fall until 12 h post transplant, but more slowly. In univariate analysis, CD34⁺cells/kg infused, CFU-GM/kg infused, the CD34⁺ count at ½ h, and the 12-h clearance of CD34⁺ cells from PB were predictors of hematologic recovery, as were each of the two phases of clearance when the slope was divided into rapid and slow phases (from ½ to 3 and from 3 to 12 h post transplant, respectively). We then stratified our population by the number of CD34⁺ cells/kg infused. In group 1, patients received ⩽7.5 × 10⁶ CD34⁺ cells/kg; in group 2, >7.5 × 10⁶ 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 in 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 in patients receiving lower doses of CD34⁺ cells. When the cell dose injected is over a threshold, PB clearance correlations with hematologic recovery are masked.