A Higher Number of CD34+ Cells Collected during Mobilization Is Independently Associated with Successful Engraftment in Autologous Stem Cell Transplant Patients

We performed a retrospective analysis on patients who underwent PBSC collection and subsequent ASCT at our institution to assess whether efficiency of PBSC mobilization is predictive of engraftment failure.

Methods: We identified 369 patients who underwent PBSC collection between 01/01/2006-8/31/2012 for a first ASCT. We collected data on age, sex, use of lenalidomide or thalidomide (“Imid”) prior to mobilization, mobilization regimen, # of collections for final cell dose, # of CD34+ cells infused, and the presence of a positive blood culture within 30 days of ASCT.  Quintiles were created for the # of CD34+ cells collected.  The primary outcome was engraftment failure defined as not achieving an absolute neutrophil count (ANC) >1000/mL or a platelet count >50,000/mL (no platelet transfusion in </= 7 days) by day 30 post-ASCT. Secondary outcomes were time to ANC and platelet engraftment.  We performed a multivariate logistic regression analysis to assess the association of collected CD34+ cells and engraftment failure while adjusting for the other variables. For time to event analyses we used Cox proportional hazard models.

Results: Median patient age was 58 and 56% were male.  Patient-reported race was: Black (38%), White (17%), and “Other” (45%).  Indications for ASCT were Multiple Myeloma (45%), Non-Hodgkin Lymphoma (41%), Acute Leukemia (9%), Hodgkin Lymphoma (3%), Amyloidosis (1%), and Germ Cell Tumors (1%).  The median # of CD34+ cells collected was 7.7x10 ^6/kg (range 2.26-120 x10 ^6/kg) and median # of CD34+ cells infused was 5.3x10 ^6/kg (2.3-45x10 ^6/kg). Median # of collections for transplant dose was 2 (range 1-8).  CD34 cells collected were divided into quintiles (cut points: 6.04, 7.57, 9.86 and 17.7x10 ^6/kg). We found that a higher # of collected CD34+ cells during mobilization was associated with less engraftment failure (p=0.0067):  every increase in quintile was associated with a 40% decrease in the risk of engraftment failure (OR 0.60, 95%CI 0.41-0.87).  Even when adjusted for cell dose infused, a higher # of collected CD34+ cells was associated with decreased time to platelet engraftment (HR1.15, CI 1.00-1.32, p=0.052), but not ANC engraftment (HR 1.07, p=0.35). Positive blood cultures within 30 days of ASCT were associated with engraftment failure (p=0.0035), while race, sex, # of collections for the transplanted dose and mobilization regimen did not appear to affect engraftment.  We also observed that prior Imid use demonstrated a trend toward less engraftment failure (OR 0.41, 95%CI 0.17-1.01; p=0.052). 

Although a moderate correlation was observed between the variables CD34 cells collected and CD34 cells infused, a sensitivity analysis by omitting either variable did not identify a significantly different estimates.