Biological Variables Affecting CD34+ Peripheral Cells Collection Efficiency Using the Spectra Optia Continuous Mononuclear Cell Collection System: Hematocrit as Determinant for CD34+ Collection Efficency.

Hematopoietic stem cell transplantation (HSCT), either autologous or allogenic, is a treatment strategy widely used in the onco-hematology field and less often for other diseases1. The most employed source of stem cell is peripheral blood stem cell (PBSC) identified as circulating CD34+ cells and collected by leukapheresis (LP) following mobilization process using granulocyte-colony stimulating factor (G-CSF) alone or in association with chemotherapy and/or plerixafor, the latter in case of poor-mobilizer patients.

The PBSC harvest needs dedicated platform for being properly performed: in our institution the Spectra Optia apheresis system (Terumo BCT) is routinely employed with a continuous mononuclear cells collection (cMNC) system. Spectra Optia (Terumo BCT) is designed to optimize PBSC harvest through automated buffy coat interface identification and management, low volume tubing set, low extracorporeal volumes and support of cMNC processing system3. In the dual-step mononuclear cells collection (MNC) system an intermediate chamber is used to collect white blood cells while returning the majority of platelets to the subject. Then optical sensors detect red blood cells (RBC) overflow and leucocytes are intermittently flushed in the collection bag. The cMNC system differs from the former dual-step system by eliminating the intermediate collection chamber used and thus allowing continuous collection of leucocytes from the buffy coat. This approach appears to be less time consuming, more manageable, and more efficient in returning platelet and RBC to the subject4.

One of the main benchmarks of LP quality is the collection efficiency (CE) defined as the ratio between total CD34+ cells yield in apheresis and total CD34+ cells in the processed blood volume (PBV).

Obtaining the highest possible CE for every LP procedure is critical as long as several studies have shown the importance of targeted CD34+ cells yield in order to assure a safe and rapid haematological recovery after the high dose chemotherapy regimens used in HSCT6. Therefore the objective is to reach the target PBSC yield in the safest and quickest way possible: an high CE allows to reduce the PBV and the procedure length.

The CE values are affected by different factors among which blood sample's physical properties. Such factors have been widely studied in MNC protocol7, but less studies concern the cMNC protocol8. In 147 consecutive apheresis procedures performed both on patients and healthy donors with Spectra Optia (Terumo BCT) with cMNC system, Kondo et colleagues found a moderate positive correlation between CD34+ CE and hematocrit (Ht) and only a very week correlation with white blood cells (WBC) and platelet counts. We would like to confirm these data in a setting of subjects with a predominance of patients over healthy donors, thus evaluating the influence of clinical and biochemical factors on CE for autologous and allogenic hematopoietic stem cell production. Finally we would like to assess a possible pre-LP Ht threshold associated with a sufficient (> 60%) CD34+ CE.