Merit of Initiating Peripheral Blood Stem Cell (PBSC) Collections at Low Level of Circulating CD34+ Cells.

Most patients or donors undergoing leukapheresis (LP) for autologous or allogeneic PBSC transplantation requires multiple collections to achieve a sufficient CD34+ cell dose. LP is usually initiated when peripheral blood (PB) CD34+ reached a certain level, such as 20/μl. The aim of this retrospective analysis is to summarize our institutional experience of initiating LP at a low PB CD34+ cell level of 5/μl and investigate the merit of the practice. All patients or donors underwent LP (using Cobe Spectra or Baxter Amicus) processing 3 times the blood volume. A total of 170 LP procedures (118 autologous and 52 allogeneic) was performed in 74 adult patients or donors (> 40 kg) between Jan 2004 and May 2005. Autologous patients were mobilized with chemotherapy and G-CSF while allogeneic donors with G-CSF alone. A “good” LP product is defined as one having ≥ 1 x 10⁶ CD34+ cells/kg so that a minimum dose of 3 x 10⁶/kg can be achieved in 3 collections. Our result showed that each PBSC product contained 6.07 x 10⁸ WBC/kg (median, range: 0.13–17.5) and 1.59 x 10⁶ CD34+ cells/kg (0.14–24.9). Total CD34+ cells in PBSC products were correlated to PB CD34+ cell counts (r = 0.79, data not shown). As shown in Table 1, initiating LP at higher levels of PB CD34+ cell increased the proportion of good LP. Nevertheless, 76% of collections initiated at > 5 CD34+ cells/μl achieved good LP criterion. It is possible that the level of PB CD34+ cells was still increasing in many patients or donors after initiation of LP at the low level. However, some patients /donors still achieved minimim CD34+ cell dose when second LP day (Day 2) PB CD34+ cell level was lower than that of first LP day (Day 1) (Table 2). These patients /donors would likely NOT have been collected if higher levels of PB CD34+ cells were used as guideline for start of LP. Eleven patients /donors whose Day 2 CD34+ cell count was below that of Day 1 achieved minimum CD34+ cell dose when LP was initiated at < 20/μl. When LP was initiated at < 10/μl, four individuals achieved minimum dose. All 4 were autologous patients mobilized with chemotherapy and G-CSF (3 AML and 1 NHL). In conclusion, our results showed that initiating LP at low PB CD34+ cells can be helpful to some individuals. The guideline may be especially useful in those patients that can only be mobilized marginally.