Decrease in Thy-1 expression on peripheral CD34 positive cells induced by G-CSF mobilization. The Tohoku Children Leukemia Study Group

Expression of adhesion molecules on CD34(+) cells in peripheral blood of non-hodgkin's lymphoma patients mobilized with different growth factors

Adhesion molecules on CD34(+) cells were implicated in the process of peripheral blood stem cell (PBSC) mobilization and homing. We studied the mobilization of CD34(+)Thy1(+) cells, CD34(+) very late-acting antigen (VLA)4(+) cells, and CD34(+)L-selectin(+) cells in non-Hodgkin's lymphoma patients mobilized with cyclophosphamide plus G-CSF, GM-CSF, or GM-CSF followed by G-CSF. The mean percentage of CD34(+) cells in the bone marrow (BM) expressing Thy1 was 23.6% +/- 11% and 17.8% +/- 8% in the PB before mobilization, and was markedly decreased to 4.5% +/- 3.3% in the apheresis collections. Similarly, the mean percentage of CD34(+) cells expressing L-selectin was 35.8% +/- 4.3% in the BM, 21.6% +/- 4.1% in the PB before mobilization and was markedly decreased to 9.1% +/- 2.5% in the apheresis collections. Patients in the three arms of the study had a similar pattern of CD34(+)Thy1(+) and CD34(+)L-selectin(+) cell mobilization. Also, a similar pattern of coexpression of CD34(+)Thy1(+) and CD34(+)L-selectin(+) cells was observed when the patients were regrouped as "good mobilizers" (> or =2 x 10(6) CD34(+)CD45(dim) cells/kg, in four collections) and "poor mobilizers" (<0.4 x 10(6) CD34(+)CD45(dim) cells/kg, in two collections). The mean percentage of CD34(+) cells expressing VLA-4 in the BM and PB was relatively high (73.4% +/- 12% and 65.4% +/- 6.6%, respectively) and dropped considerably in the PBSC collections to 43.5% +/- 7.1% with a similar pattern observed for patients in arms A, B, and C. However, when the patients were regrouped as "good mobilizers" and "poor mobilizers," a higher percentage of CD34(+) cells expressing VLA-4 was observed in the PBSC of the pooled "good mobilizers" (50.5% +/- 9% versus 36.3% +/- 6.4%; p = 0.01). We conclude that release of CD34(+) cells to the PB involves a general downregulation of Thy1, L-selectin and VLA-4 on CD34(+) cells, irrespective of the growth factor used for mobilization. However, good mobilizers had a relatively higher percentage of CD34(+) cells expressing the VLA-4 antigen.

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 (> or = 0.5 x 10(9)/l) and platelet (> or = 20 x 10(9)/l or > or = 100 x 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 (> or = 0.5 x 10(9)/l) and platelet engraftment (> or = 20 x 10(9)/l and > or = 100 x 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.