Increasing Post-Processing Total Nucleated Cell (TNC) Recovery in Cord Blood Banking: Hespan Addition in cGMP Environment

Purpose. Evaluate the effects of HESPAN (HES) addition on indices of cord blood unit (CBU) potency, stability and safety after automated volume reduction (reduction of erythrocyte bulk and plasma volume) using the AXP AutoXpress^TM (AXP) processing system.

Background and Methods. TNC recovery varies significantly and unpredictably after volume reduction during CBU processing. However, prompt engraftment of CBU allotransplants correlates with their TNC including hematopoietic stem/progenitor cells (HPC). As a result, TNC is important in selecting CBU for transplantation: for example, 75% of the National Cord Blood Program (NCBP) CBUs shipped during the period 2010-2013 had TNC >120 x 10⁷. Therefore, minimizing TNC losses during processing improves the chances that a CBU will be useful for clinical transplantation.

The first method to increase post-processing TNC recovery was the addition of HES to the centrifugal method for CB volume reduction [Rubinstein et al, PNAS (USA), 92:10119-10122, 1995]. Volume reduction consists of concentrating the buffy-coat (containing leukocytes and HPC) by centrifugal stratification and removal of bulk red cells and platelet-containing plasma. NCBP processed manually over 30,000 CBUs using HES during the period 1995-2006. In 2006, the AXP, a closed, automated and FDA-approved processing method, without HES, was implemented. AXP was designed to enhance the MNC and CD34+ cell recoveries but not those of granulocytes. This resulted in lower post- processing TNC counts. Additionally, CBUs with larger volume and TNC content have somewhat higher TNC losses during automated processing. Using the AXP method, NCBP’s HEMACORD^® obtained FDA License approval on November 10, 2011. However, since TNC (not MNC or CD34+ count) remains the most commonly used indicator of CBU potency and engraftment ability, we describe here implementation of HES in AXP processing to augment TNC recovery, by adding HES to the CBU to a 1-2% final concentration.

Results.The results of manual CBU processing showed that HES addition improves yield, without changes in cell viability after cryopreservation, freezing at -196°C and thawing, after 20 years (from NCBP continuing stability study). HES addition also preserved CFU numbers and CD34+ cell counts after thawing.

1. Comparison of TNC recoveries without and with HES addition in the same CBU: A total of 25 CBUs were initially processed with the AXP platform without HES, as per routine procedure, and the TNC recoveries were calculated. Each CBU was then reconstituted after its initial processing into a new AXP bag set. HES was added aseptically to the reconstituted product and each CBU was processed in the same conditions as first time (same AXP device, centrifuge, etc.). The TNC recoveries after the second volume reduction process (AXP with HES) were ~20% higher on average than after the first (AXP without HES).

2. Comparison of TNC recoveries in different cohorts of CBUs: Thirty clinical-grade CBUs, with volumes 80-156 mL and TNC counts 111-290 x 10⁷, were processed with HES in the AXP system and the results were compared with those of AXP-processed CBUs without HES over an earlier six month period. TNC and CD45+ cell recoveries improved by 16 - 20% maintaining mean post-processing hematocrit at 30.6% (SD ± 2). CD34+ and CD45+ cell viabilities were unchanged: 99% (SD ± 0.7) and 96% (SD ± 2.7), respectively, while their mean recoveries were 95% (SD ± 18) and 94% (SD ± 6). In addition, the same consistent post-processing volume was obtained (mean 20.8 mL, SD ± 0.1). CFU - CD34+ correlation (R²) after processing with HES was 0.788 (not different than what was observed in the CBUs without HES). Six CBUs AXP-processed with HES, were thawed and tested, with very minor losses in cell count and viability, similar to results of thawed AXP-processed CBU without HES. Finally, HES addition did not result in microbial contamination in any of these AXP-processed CBUs.

Conclusion. Adding HES to CBUs before automated AXP processing increased substantially the TNC and CD45+ recoveries without loss of viability, while the CD34+ recoveries remained basically unchanged, with a mean of 95%. The post-processing hematocrit was consistent and low. AXP-automated CB processing with HES addition can be performed in the GMP environment, results in higher post-processing TNC and therefore, increases the CB bank’s ability to store larger CBUs that are most useful to patients.