Successful Customization of Peripheral Blood Stem Cell Harvest Volume and Cell Concentration during Apheresis.
Authors: Watts Michael J. , Ings Stuart J. , Balsa Carmen , Penn Caroline , Leverett David , Linch David C. 
Published: October 2019

Abstract
The high white cell counts associated with peripheral blood stem cell (PBSC) harvests make these products particularly prone to cellular damage during storage in the liquid phase. We recently described unexpectedly high thaw clonogenic losses of PBSC stored overnight at 4 deg C prior to cryopreservation. This was associated with high harvest white cell counts and delayed engraftment in a cohort of patients receiving autologous transplantation procedures (Watts et al 2003 Blood 102:113 abstract 127). We showed in this study that pre-diluting the cells in autologous plasma to a WBC of 100x10^9/L preserved clonogenic yields during liquid storage and post freeze-thaw and suggested an upper WBC threshold of 200x10^9/L for liquid storage. In many patients however, to achieve this count or below would require further dilution of the cells. Conversely, where cells are to be frozen immediately, it is advantageous to collect a low PBSC harvest volume to fully utilize cryostorage space and to achieve this without centrifugation. The present study demonstrates that the collection of either a low white count or low volume PBSC harvest can be controlled successfully using the GAMBRO BCT Spectra AutoPBSC apheresis machine (version 6.1) and avoids the need for any further laboratory manipulations. This machine allows the adjustment of the amount of autologous plasma used to rinse each cycle of PBSC cells into the collection bag and is referred to as the “plasma chase volume”. The plasma chase volume was set to maximum (20ml/cycle) for healthy donor harvests for shipping, and to minimum (4ml/cycle) where the cells were for immediate cryopreservation. A total of 114 harvests from 99 mobilised healthy donors were collected using the maximum plasma chase volume whereas 527 autograft harvests from 365 mobilised patients were collected using the lowest plasma chase setting. The median (range) WBC and volume of the 114 healthy donor harvests was 100 (28–174)x10^9/L and 473 (54–871) ml respectively. The median (range) WBC and volume of the 527 “small volume” harvests for cryopreservation was 254 (51–495)x10^9/L and 66 (20–180) ml respectively. To determine whether the maximal plasma chase setting affected the progenitor dose collected, we compared the first day harvest of the 99 mobilised healthy donors obtained with the Spectra autoPBSC with that from 114 healthy donors collected on the standard manual Spectra (n=63) and CS3000 (n=51) apheresis machines. The median (range) CD34+ cell yield was 361 (34–1,380), 291 (21–1,356) and 259 (37–738)x10^6 respectively. The first day median (range) CD34+ cell yield x10^6 of the 365 mobilised patients where small volume autograft harvests were collected on the Spectra AutoPBSC was 202 (0–7,569) compared to 195 (0–5,054) using the manual Spectra (n=142) and 152 (0–4,830) x10^6 using the CS3000 machine (n=813). Our policy is to dilute any harvest for storage/shipping with a nucleated cell count greater than 200x10^9/L with autologous plasma, but none of the donor harvests exceeded this threshold and no laboratory manipulation was required. In the case of the autograft harvests for immediate cryopreservation, 502/527(95%) of the collections were 100ml or less. In conclusion, this study demonstrates for the first time that the cell count and volume of the PBSC harvest required can be customized at apheresis, that this is not detrimental to progenitor yields and results in a product that is optimal for storage/shipping without laboratory intervention.