The CD34+90+ cell dose does not predict early engraftment of autologous blood stem cells as well as the total CD34+ cell dose.

CD90 or Thy-1 is an antigen co-expressed with CD34 + on putative immature hematopoietic stem cells. Peak mobilization of CD34 + 90 + cells into the blood occurs a few days earlier than peak mobilization of total CD34 + cells. Because it is not known which cell type best correlates with engraftment, the optimal timing of apheresis remains unclear. The purpose of the study was to determine if the CD34 + 90 + cell dose predicts engraftment of autologous blood stem cells independent of the total CD34 + cell dose/kg, the dose of other CD34 + cell subsets (CD34 + 33 - , CD34 + 38 - , CD34 + 41 + ), or various clinical factors. Data were analyzed on 125 consecutive patients ranging in age from 19 to 66 years (median 46) who underwent autologous blood stem cell transplantation (ABSCT) for breast cancer (54), lymphoma (59), or other malignancies (12). By univariate analysis, neutrophil (≥0.5 × 10 9 /l) and platelet (≥20 × 10 9 /l or ≥100 × 10 9 /l) engraftment correlated better with the total CD34 + cell dose than with the CD34 + 90 + cell subset. Using Cox proportional hazards models, factors independently associated with both neutrophil engraftment (≥0.5 × 10 9 /l) and platelet engraftment (≥20 × 10 9 /l and ≥100 × 10 9 /l) were higher total CD34 + dose/kg and high-dose regimen (melphalan-containing slower than other regimens). In conclusion, the total CD34 + dose/kg was a better predictor of hematopoietic engraftment following ABSCT than the dose of any CD34 + subset, including CD34 + 90 + cells. Apheresis should continue to be timed according to peak CD34 + levels.