Quantitative CD34 analysis may be used to guide peripheral blood stem cell harvests

The duration of neutropenia and thrombocytopenia after high-dose chemotherapy has improved since the introduction of myeloid growth factors and peripheral blood progenitor cells (PBPC), yet there remains a subset of patients who have delayed hematopoietic recovery. Currently, there are no established, reliable parameters which may be used to guide stem cell harvests. We investigated the utility of measuring harvested CD34 positive cell populations by how cytometry. From March 1990 to July 1993, 30 women with advanced breast cancer underwent therapy with high-dose cyclephosphamide and thiotepa and stem cell rescue. Patients received either cyclophosphamide (CY) mobilized PBPC or CY/G-CSF mobilized PBPC. The number of harvested CD34⁺ cells and CFU-GM (colony forming units-granulocyte macrophage) were quantitated for each stem cell product. There are complete CD34 data for 21 patients and complete CFU-GM data for 20 patients. There was a significantly delayed neutrophil recovery in those patients reinfused with <0.75 x 10⁶ CD34⁺ cells/kg body weight (median days 22) compared with patients reinfused with >0.75 x 10⁶/kg (median days 12, P = 0.0004); a similar trend was seen with platelet recovery (median 135 days vs 18 days, respectively, P = 0.002). With neutrophil recovery, there was no improvement in time to engraftment with a larger number of reinfused CD34⁺ cells, but there was a trend towards shortened platelet recovery when the number of reinfused CD34⁺ cells exceeded 2.0 x 10⁶/kg (median 15 days) compared with CD34⁺ <2.0 x 10⁶/kg (median 75 days, P = 0.05). Those patients who had <0.75 x 10⁶ CD34⁺ cells had longer hospitalizations (P = 0.007) and greater platelet transfusion requirements (P = 0.02). There was a significant positive correlation between CD34 and CFU-GM (r = 0.69, P<0.001, β₁ = 0.148). The number of reinfused CD34⁺ cells correlates with hematopoietic recovery and may be used to guide the harvesting of peripheral blood stem cells. Further experience and reliability of the CD34 assay must be obtained, however, before universal recommendations can be made.