Comparison of PB CD34+ vs Hematopoietic Progenitor Cell Counts as Predictors of Successful PBPC Collections in Healthy Donors and Patients.

Monitorisation of PB haematopoietic cell count has been used as a reliable predictor of peripheral blood progenitor cell (PBPC) yields in healthy donors and patients following 5 day G-CSF mobilization. Routinely this evaluationn is performed by CD34+ cell count using flow cytometry and more recently by haematopoietic progenitor cell (HPC) count in a hematologic cell analyser. The aim of the present ongoing study is the comparison of PB CD34+ cell counts vs HPC in predicting the apheresis yield both for adult healthy donors and patients. From January to the end of July 2007, 21 healthy donors and 30 patients with hematologic malignancies (NHL=16, MM=11, HD=3) underwent G-CSF mobilization. On the 5^th day of mobilization WBC and HPC counts were assessed by the Sysmex XE-2100 analyser in EDTA PB samples. CD34+ cell enumeration was performed in the same samples by standard flow cytometric assay. The healthy donors showed a good PB mobilization with a median of 82 CD34+cells/μl (range 23–193) and 161 HPC/μl (22–548). The majority of donors collected in one apheresis sufficient cells for the allogeneic transplant (>4x10⁶ CD34+/kg bw receptor). The total amount of cells collected per kg bw donor was 8.2x10⁶ CD34+/kg and 21.7 x10⁶ HPC/Kg. Our data showed that HPC counts were significantly higher than CD34+ counts (2.0 fold for PB and 2.6 fold for PBPC). In relation to the patient group they showed a wide variation of PB CD34+ cells/μl (median 9, range 2–177) as well as HPC/μl (median 42, range 0–376). Patients underwent 1 to 3 apheresis to achieve >2x10⁶ CD34+/kg. The total amount of cells collected was 2.1x10⁶ CD34+/kg (range 0.2 – 13.6) and 5.0 x10⁶HPC/kg (range 0.3 – 50.1). As shown for healthy donors, patient HPC counts were significantly higher than CD34+ counts (4.6 fold for PB and 2.4 fold for PBPC). Our results showed that for both groups of individuals PB HPC counts correlated with CD34+ cell counts and these numbers predicted the PBPC yield. Thus, we set a threshold on 5^th day PB counts of >10 CD34+ cells/μl or >20 HPC/μl and analysed the PBPC collections. The majority of donors (17/21) presented in the PB >10 CD34+ cells/μl and >20 HPC/μl, whereas in the patient group the majority (18/31) had >20 PB HPC/μl and only 13/31 showed >10 PBCD34+ cells/μl. With PB counts above the threshold levels both donors and patients achieved the minimum requirement for hematopoietic transplant. Patients with PB counts of <10 CD34+ cells/μl or < 20 HPC/μl had a low probability of collecting > 2x10⁶ CD34+ cells/kg in a total of 3 apheresis. The threshold on PB counts of >10 CD34+ cells/μl or >20 HPC/μl established in the current study is similar to those reported by other groups. In summary, HPC counts can be used to decide the timing of PBPC collection, as it takes only a few minutes to be executed. At the present time HPC counts can not replace CD34+ cell enumeration, as it is not yet determined the HPC dose equivalent to the current established CD34+ cell dose necessary for transplantation. Furthermore, it remains to be determine the role of the HPC content of the graft may be important in the haematopoietic recovery of patients.