Feasibility of Day 4 G-CSF Mobilized Peripheral Blood Stem Collection from HLA-Matched Sibling Donors

Background: Guidelines from the NMDP and ASBMT recommend allogeneic donor mobilization with 4-5 days of G-CSF followed by peripheral blood stem cell (PBSC) collection beginning the 5^th day.  While our institutional standard has been 5-day mobilization and collection, given observations that some autologous transplant patients are adequately mobilized by day 4, and due to concern that a subset of allogeneic donors may be maximally mobilized earlier than day 5, we performed a feasibility study evaluating day 4 collection of allogeneic PBSC.

Methods: Beginning 7/1/2013, HLA-matched sibling donors were collected on day 4 after G-CSF if the peripheral blood (PB) CD34 count was ≥0.04x10⁶/ml.  Collected PBSC were held overnight at 4⁰C until transplant.  Donors with day 4 PB CD34 counts of ≤0.04x10⁶/ml were collected on day 5, and those with inadequate CD34 cells/kg recipient weight in the PBSC product underwent repeat collection over two days. 

Results: 38 patients with matched-sibling donors were eligible for inclusion in the study, with a median follow-up of 217 days (range 45-458).  Of 38 donors evaluated, 22 (57.9%) had a PB CD34 count ≥0.04x10⁶/ml on day 4.  Eighteen of the 22 (81.8%) were adequately collected on day 4; 3 required 2-day PBSC collections on days 4 and 5.  One donor with an adequate PB CD34 count was collected on day 5 due to line issues.  Of the 16 donors with a PB CD34 count <0.04x10⁶/ml, 7 underwent single day collection on day 5, and 9 required two-day collections.  Of all donors eligible for inclusion, 18 (47.4%) were adequately collected on day 4, 8 (21.1%) were collected on day 5, and 31.6% required two-day collections.  There was no significant difference in the median time to ANC and platelet engraftment based on day of PBSC collection.

Conclusions: In our pilot study of HLA-matched sibling donors undergoing G-CSF mobilized PBSC collection, we found that 47.4% of donors were adequately mobilized to allow for a single PBSC collection on day 4.  Using a PB CD34 cell threshold of ≥0.04x10⁶/ml on day 4 identified donors with high likelihood of adequate PBSC collection (81.8%).  Our preliminary data suggest day 4 may be the optimal day of collection for a population of healthy donors, reducing donor G-CSF exposure leading to enhanced safety for donor and recipient, and expected cost savings.  Ongoing analyses include financial and resource utilization review, detailed comparison of day 4 versus 5 PBSC product composition, and matched cohort analysis of day 4 versus 5 collection and correlation with transplant outcomes.