Bone Marrow Harvest Volume and CD34+ Cell Count in Pediatric Sibling Donors: A Single Centre Retrospective Analysis
Authors: Alanazi Awatif , Nadeem Amir , Siddiqui Khawar , Ayas Mouhab , Ahmari Ali Abdallah , Ghemlas Ibrahim A. , Aljefri Abdullah , Alsaedi Hawazen S. , Al-Seraihy Amal 
Published: November 2019

INTRODUCTION:
Allogeneic hematopoietic stem cell transplantation (HSCT) is the only treatment modality offering cure or long-term survival for many hematologic malignancies, and non-malignant diseases in children. HLA-matched siblings are considered the best donors because of reduced risks of transplant-related complications and better clinical outcome. According to the National Marrow Donor Program Guidelines, the maximum amount of bone marrow harvest is limited to 20ml/kg donor's body weight. The aim of this retrospective study was to assess the optimal bone marrow harvest volume in pediatric donors needed to obtain the desired CD34+ cell count.
METHODS:
We reviewed medical charts of 553 pediatric (age at harvest <18 years) sibling donors who were harvested for bone marrow from Jan 2007 to Dec 2017 at our institution for pediatric (age at infusion < 14 years) transplant naïve recipients in order to examine the volume harvested per donor's weight, the percentage of harvests that reached the minimum desired CD34+ cell count of ≥3.0X10^6 per Kg of recipient weight, harvest related hospitalization days and side effects related to the procedure and the impact of granulocyte-colony stimulating factor (GCSF) priming on CD34 count of harvested bone marrow.
RESULTS:
288 out of 553 donors were male. 155 (28%) were below 5 years of age at harvest, 189 (34.2%) were between 5-10 and remaining 209 (37.8%) were 10 years and above, with a median of 8.4 years (range: 0.2-17.9). Primary indication for transplant among 131 (23.7%) of our pediatric recipients were Malignant Disorders, Non-Malignant Disorders in 214 (38.7%) and Primary Immunodeficiency and Histiocytic Disorders in 208 (37.6%). GCSF priming was carried out in 219 (39.6%) donors. The minimum desired CD34+ cell count of ≥3.0X10^6 per Kg of recipient weight was reached in 517 (93.5%) harvests.
Post infusion Absolute Neutrophil Counts (ANC) recovery within Day+28 was recorded among 472 (85.4%) of the transplant naïve recipients, while in 72 (13%) cases ANC never recovered and in remaining 9 (1.6%) time to recovery was beyond Day+28. ANC recovery within Day+28 was significantly associated with CD34+ cell dose of ≥3.0X10^6 per Kg of recipient weight (n=441, 93.4% vs. 31, 6.6%; P-Value<0.001). Median CD34+ cells (X10^6) collected per Kg of donor weight were significantly higher among donors younger than 5 years of age when compared to those 10 and beyond (P-Value <0.001) with a median harvested volume of 13.7, 12.0 and 8.3 mL/Kg (P-Value<0.001, Table 1). On the same note, median CD34+ cells collected per donor weight were significantly higher among donors primed with GCSF in contrast to those who did not (6.02 X10^6 vs. 3.1 X10^6, P-value <0.001).
54 (9.8%) of our donors required PRBC transfusion; among whom 34 (63%) were below 5 years of age at harvest, 15 (27.8%) 5-10 years and remaining 5 (9.3%) were 10 and above (P-Value<0.001). 2 (0.5%) donors were hospitalized for four days, 12 (3.2%) for three, 201 (54.3%) for two and 155 (42%) for one day only. No significant side effects were noted among our donor population.
CONCLUSION:
Our study confirmed that CD34 cell count were significantly higher among younger donors. The use of Higher CD34 cell dose is significantly associated with engraftment. Priming with G-CSF had significant impact on CD34+ cell count. These large data confirm the suggestion that the volume of bone marrow harvested can be decreased among younger donors without significantly changing the overall CD34 cell count.

Disclosures
No relevant conflicts of interest to declare.