The importance of CD34+/CD33- cells in platelet engraftment after intensive therapy for cancer patients given peripheral blood stem cell rescue

The study was designed to determine whether the number of CD34(+)/CD33(-) cells given at autologous peripheral blood stem cell (PBSC) rescue after intensive therapy for cancer was a better predictor of platelet engraftment than the total number of CD34(+) cells infused. Comparison between the total number of CD34(+) cells/kg infused with the number of CD34(+)/CD33(-) cells/kg infused showed that, generally, 2x10(6) total CD34(+) cells contained 1.38 x 10(6) CD34(+)/CD33(-) cells. There was poor correlation between the number of CD34(+)/CD33(-) and CD34(+)/CD33(-) cells in the graft (r = 0.332). Engraftment times for platelets and neutrophils were evaluated in 68 patients. There was no significant difference between the times for platelets to reach >25 x 10(9)/l or neutrophils to reach >0.5 x 10(9)/l among patients who received > or < 2 x 10(6) total CD34(+) cells or > or < 1.38 x 10(6) CD34(+)/CD33(-) cells although the latter was consistently the better predictor. Platelet recovery to > 50 x 10(9)/l and > 100 x 10(9)/l was delayed significantly in patients who received < 1.38 x 10(6) CD34(+)/CD33(-)/kg infused (P < 0.02 and P < 0.05, respectively). The number of CD34(+)/CD33(-) cells/kg infused was a stronger predictor of platelet recovery than the total number of CD34(+) cells infused (P < 0.05 for platelets > 50 or > 100 x 10(9)/l). Although platelet recovery was delayed significantly in patients who had < 4 x 10(4) granulocyte-macrophage colony-forming units (CFU-GM)/kg infused, the time delay between receipt of PBSCs and availability of the colony counts limits the use of this assay to patients who do not require stem cells to be given immediately. Our data suggest that the number of CD34(+)/CD33(-) cells given at PBSC rescue provide information about the quality of the graft necessary for long-term platelet engraftment, However, since the percentage of CD34(+)/CD33(-) cells shows considerable inter-patient variation, measurement of this cell population may be important in patients who experience poor stem cell mobilization or when a target dose of 2 x 10(6) total CD34(+) cells/kg is not achieved.